Agricultural and Forest Meteorology112(2002)
67–85
Transpiration response to soil moisture in pine
and spruce trees in Sweden
Fredrik Lagergren?,Anders Lindroth
Department of Physical Geography and Ecosystem Analysis,Lund University,Box118,SE-22100Lund,Sweden
Received28September2001;received in revised form9May2002;accepted14May2002
Abstract
Variation in transpiration and conductance between individual trees of Scots pine and Norway spruce was investigated in a mixed50-year-old stand in central Sweden.Daily transpiration rates were measured by the tissue heat balance method on ?ve trees of each species during a dry,warm growing season.Daytime averages of sap?ow,climatic variables and soil water content were used to?t an empirical model of tree conductance for each tree.Conductance per unit needle area was about twice as high in pine as in spruce,while equal-sized trees transpired similarly in both species.Conductance generally decreased more steeply with increasing vapour pressure de?cit and increased faster with increasing light in pine than in spruce,although one individual spruce behaved more like the pines.Inclusion of a linear or exponential function for air temperature improved the model for pine,but of the spruces,only one tree showed a clear temperature dependency.The response to decreasing soil water content varied widely;the spruces tended to be more sensitive to drought than the pines.When the drought was at its worst,no sap?ow could be detected in some of the trees.On average,the reduction in transpiration began when ca.80%of the extractable water in the rooting zone had been depleted.
?2002Elsevier Science B.V.All rights reserved.
Keywords:Stomatal conductance;Drought;Transpiration;Pinus sylvestris;Picea abies
1.Introduction
Tree transpiration is the major pathway for both water and energy leaving the forest ecosystem.Mea-surement of transpiration provides access to the canopy conductance of the forest,a key parameter in models of water-and carbon-exchange(Collins and Avissar,1994),since the water and carbon?uxes are strongly linked by their common passage through the stomata(Morén et al.,2001).
?Corresponding author.Tel.:+46-46-222-0000;
fax:+46-46-222-4011.
E-mail addresses:https://www.doczj.com/doc/832558497.html,gergren@nateko.lu.se(https://www.doczj.com/doc/832558497.html,gergren), anders.lindroth@nateko.lu.se(A.Lindroth).
The scale at which the forest is studied answers dif-ferent questions in the context of exchanges of energy and matter(Jarvis,1995).Studies at shoot or branch level(e.g.Harley and Baldocchi,1995;Roberntz and Stockfors,1998),for instance,are particularly useful in the study of physiological processes;scaling-up to stand level from single shoots is intrinsically complex but can give?rm results(e.g.Baldocchi and Harley, 1995).Studies at tree level(e.g.Cermak et al.,1995; Granier et al.,1996)provide an average response of the mostly non-linear physiological processes,and are therefore,more useful for empirical modelling.Such studies are particularly useful for scaling-up?uxes for a certain stand or plot if a suf?cient number of trees are measured(Cermak et al.,1995),and provide
0168-1923/02/$–see front matter?2002Elsevier Science B.V.All rights reserved. PII:S0168-1923(02)00060-6
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answers about the variation within it.The ecosystem or landscape level(e.g.Tenhunen et al.,1998;Grelle et al.,1999)provides answers about net exchange and the variation between stands or regions.
The sap?ow technique(Swanson,1994)is very useful for obtaining the total water use of a single tree. Sap?ow is commonly scaled up to stand level and con-sidered as representing transpiration.A problem with this approach is that,because of the capacitance of the trunk and branches,sap?ow lags somewhat behind transpiration(Granier and Loustau,1994;K?stner et al.,1996).The lag is not constant over the course of the day,between days or between trees(Lundblad and Lindroth,2002;Phillips et al.,1997),even though in many approaches it is assumed to be constant; modelling the lag is consequently not a simple task. However,daily sap?ow totals can often be assumed to equal the sum of transpiration,although under some conditions,e.g.after a dry period followed by some rainy days,this may not be true(Waring et al.,1979; Zweifel and H?sler,2001).Another drawback of a daily time step is that the processes which affect tran-spiration are non-linear,hence,any model would be truly empirical and should be used with caution out-side the range for which it was calibrated.The daily pattern of the variables can also vary between differ-ent days;this will affect conductance,even though the mean of the variables may be unchanged.
Soil moisture is considered to be a critical parameter in many models of evaporation or surface energy par-titioning.Many models show large sensitivity to soil moisture,and general circulation models,which are used to predict future climate change,are no excep-tion(e.g.Viterbo and Beljaars,1995).Unfortunately, it is inherently dif?cult to establish?rm relationships between transpiration(or canopy conductance)and soil water content,mainly because of the large spa-tial variation in soil properties and soil moisture,but also because of transpiration’s strong dependence on other weather parameters.There are,however,several empirical studies of such relationships in which?rm relationships have been established;e.g.for Scots pine by Rutter(1967),Sturm et al.(1996)and Irvine et al. (1998),for Norway spruce by Lu et al.(1995)and Lu et al.(1996),and for mixed stands of these species by Cienciala et al.(1998).As far as the present authors are aware,variation in individual response in a mixed stand has not previously been estimated and modelled.Evaluation of individual variation can increase our understanding of the response of the entire stand. The primary aim of this study was to quantify how tree conductance,and thus,the transpiration of indi-vidual trees in a mixed pine and spruce forest,depends on soil moisture.In order to do that it was also neces-sary to quantify the in?uence of weather conditions on the conductance of individual trees under non-limiting soil water conditions.Daily data from a growing sea-son with large variation in soil water content were used to estimate and model conductance and its de-pendence on weather parameters and soil moisture.
2.Material and methods
2.1.The stand
Scots pine(Pinus sylvestris L.)and Norway spruce (Picea abies(L.)Karst)are dominant species in most of the Eurasian Taiga.Scots pine is a pioneer species that is well adapted to dry conditions.Norway spruce is a secondary species that is shade-tolerant and prefers wetter habitats that are not frequently disturbed.Mixed stands are,however,very common.The studied stand was located in the Norunda forest in central Sweden (60?5 N,17?29 E,altitude45m).The stand was ca. 50years old and was growing on a boulder-rich,sandy glacial till.The stand was naturally regenerated and was a mix of Scots pine(64%of the basal area(BA) at1.3m height),Norway spruce(33%)and deciduous trees(3%).A plot,60m×120m,was established in1997for studies of tree water relations,and the diameter of all trees on it was measured.The mean diameter was20cm,mean height was17m,BA was 29m2ha?1and there were872trees per hectare. 2.2.Sap?ow
Sap?ow was measured by the tissue heat balance method(Cermak et al.,1973;Cermak et al.,1976; Cermak et al.,1982)with a P4.1sap?ow meter(Eco-logical Measuring Systems,Bruno,Czech Republic). This is a method that has previously been proven to give reliable transpiration estimates in the studied for-est(Grelle et al.,1997;Cienciala et al.,1999)and the method was evaluated in Lundblad et al.(2001).The system used?ve electrodes inserted in parallel,and
https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–8569 supplied with a constant power of1W,to heat a seg-
ment of the stem.The temperature difference between
the heated and unheated part of the stem was measured
with a thermo battery consisting of eight sensors.
The measured temperature difference, T(K),is
correlated to sap?ow for the heated segment as
Q w=
P
c w T
?
k
c w
(kg s?1)(1)
where P(W)is the heat input,c w the speci?c heat of water(4186.8J kg?1K?1)and k(W K?1)is the coef-?cient of heat loss from the heated segment,obtained under zero-?ow conditions.Tree level sap?ow,Q,was calculated by dividing Q w by the width of the heated segment(8cm)and multiplying by the circumference under bark at the measuring point.
To record as much as possible of the variation in sap?ow,both between trees and around the circumfer-ence of a tree,with the12sap?ow channels available, the following set-up was used:the installations were made on?ve pines and?ve spruces in July1998(de-noted P1–5and S1–5).On each tree,two measuring points were installed,on the eastern and western side, respectively.On one pine and one spruce,both mea-suring points were continuously measured.Only one side of the other trees was connected on each mea-surement period.In1999,measurements were shifted from the east to the west side on16June and shifted back on5August.The two relationships,before and after the shifts,to the sap?ow in the continuously mea-sured tree of the same species,was used to calculate a mean value based on measurements of both sides,as in Lundblad et al.(2001).There was a difference in sap?ow between opposite sides,but the relationship was relatively stable(see Lundblad et al.,2001).In the present study,sap?ow measurements from16April to 27October1999were used.In2000,the systems were installed in another sample of trees,sap?ow from this year was used to validate the?nal model of the tran-spiration,this year sap?ow was measured19May to 22October.No severe visual injuries were detected when the electrodes were removed in autumn1999. For the2days during which the measured side was shifted,sap?ow was calculated as the mean fraction of the?ow a few days before and after the shift,in the trees that was not shifted.Similarly,the missing days for P1,P3,P5,S1and S4on6–9July were replaced. For S5,the heating control malfunctioned from16June to6July and from6to11August.Data from these periods were replaced by data generated from the relationship with the remainder of the pines before and after the heating failure.
2.3.Weather and soil moisture
Soil water content(θ)at0–20and0–50cm depth, was measured with the TDR-technique(Topp et al., 1980)at eight positions located in a transect through the stand.This transect was not in the same direction as the sap?ow transect,so it was not possible to link ‘local’soil moisture to the individual trees.A general formula for mineral soils was used to obtainθfrom the measurements.At each position,one pair of20cm rods and one pair of50cm rods were placed verti-cally.The signal was read manually about every tenth day during the growing season,by means of a Tek-tronix1502C cable tester(Tektronix Corp.,Beaverton, OR,USA).Additionally,θwas measured with two ThetaProbes(ML1,Delta-T Devices Inc.,Cambridge, UK),installed at10–15cm depth,which were read every minute with a Campbell CR10-datalogger and a Campbell AM32-multiplexer(Campbell Scienti?c Inc.,NE,USA).Data were stored as10min means. The dynamic information from the ThetaProbes was used to obtain interpolated daily values ofθ,based on the level of the mean of the TDR measurements. Fromθ,the relative extractable water(REW)(θREW) was calculated as
θREW=
θ?θm
θFC?θm(2) whereθm is minimumθ(0.02for0–20cm and0.05 for0–50cm depth in the present study)andθFC isθat ?eld capacity(0.30in the present study,both depths). Theθm was taken as the minimumθfound in the present study,and was in accordance with the wilting point found by Lundin et al.(1999)in an adjacent stand.TheθFC was taken as theθin the spring shortly after the groundwater table had fallen to the lower limit of the measured soil volume.
Climatic data were taken from a tower ca.500m from the site and,for missing values,from a scaf-fold tower50m from the site(instrumentation is given in Table1).The data from the tower500m away were preferred,because the instruments in the scaffold tower were below the height of the tallest trees.
https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–85 Table1
Meteorological instrumentation in the Norunda tower and the scaf-
fold tower
Quantity Instrument
Air temperature Thermocouple(in situ,Ockelbo,
Sweden)a
Hygrometer MP probe(Rotronic
Instruments Ltd.,Horley,UK)b
Relative humidity Hygrometer MP probe(Rotronic
Instruments Ltd.,Horley,UK)a,b
Global radiation Pyranometer CM-21(Kipp&Zonen,
Delft,The Netherlands)a
LI-190SZ quantum sensor(LI-COR
Inc.,Lincoln,NE,USA)b
Precipitation IS200W rain gauge(in situ,Ockelbo,
Sweden)a
Data were recorded every minute with Campbell CR10-datalogger
(Campbell Scienti?c Inc.,NE,USA)and stored as10min means.
a Norunda tower.
b Scaffold tower.
2.4.Leaf area of the sap?ow trees
The leaf area index(LAI)of the stand(L LAI2000)
was estimated three times in1999with the LAI2000
plant canopy analyser(LI-COR Inc.,Lincoln,NE).
The measurements were corrected for foliage clump-
ing by the factor1.65provided by the manufacturer,
and averaged.
The functions obtained from a detailed biomass
sampling(Morén et al.,2000)were used to?nd pro-
jected leaf area(L tree)for all individual trees in the
stand,with diameter as input.The L tree was corrected
to sum up to the level of L LAI2000,because the sam-
pled stand differed somewhat in age and the sampling
was done in a different year:
L treecor=L tree L LAI2000A
L tree(3)
where A is the area of the plot(m2).
Tree height and live crown length were measured both on the sap?ow trees and on a sample of115 pines and85spruces.The needle mass according to Marklund(1988),was calculated from diameter at breast height,height and live crown length.For pine,the north co-ordinate,according to the Swedish co-ordinate system,was also included in the input pa-rameters.A relationship between diameter and needle mass was established for pine and spruce,respectively and was applied to all trees in the plot.
Functions between needle mass and L treecor could then be?tted for pine and spruce,respectively.The functions were used to obtain the projected leaf area of the sap?ow trees from needle mass(in which tree height and live crown length were taken into account). The polynomial functions,on average,corresponded to speci?c leaf areas of7.3and4.5m2kg?1for pine and spruce,respectively which is close to the values in Morén et al.(2000).
The?nal leaf area of the sap?ow trees was used to express sap?ow per unit leaf area.The properties of the sap?ow trees are summarised in Table2.
2.5.Tree conductance
The mean daytime value of temperature(T day(?C)), vapour pressure de?cit(D day(Pa))and global radi-ation(R day(W m?2))were calculated for the period when global radiation(R)>0.Daily sums of sap?ow for each tree were calculated with no restriction in R, but were divided by the duration of R>0to obtain mean daytime transpiration per unit needle area(E day (g m?2s?1)).This was done because sap?ow may be expected to lag behind transpiration,but transpiration will only occur when R>0.For pine and spruce,re-spectively mean values of E day,weighted by the leaf area were calculated,for which the conductance also was modelled.Tree conductance(g tday)was then cal-culated according to Monteith and Unsworth(1990): g tday=
λE dayγ
ρc p D day(4) whereλis the latent heat of vaporisation of wa-ter(2465J g?1),γthe psychrometer constant (65.5Pa K?1),ρthe density of the air(1225g m?3), and c p is the speci?c heat of air(1.01J g?1K?1).The use of this simpli?ed equation for calculating conduc-tance is valid if the trees are well coupled to the at-mosphere,which can be assumed for conifers(Jarvis et al.,1976;Granier and Loustau,1994;Phillips and Oren,1998).The advantage of using a daily time step when modelling conductance is that the problem of the time-lag between sap?ow and transpiration is overcome.The disadvantage is that Eq.(4)rightfully should be used on instantaneous values,but the error
https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–8571 Table2
Dendrological properties of the pines(P1–5)and spruces(S1–5)in the present study and their distance to the centre of the nearest strip road(see Section4)
P1P2P3P4P5S1S2S3S4S5 Diameter(cm)24.521.822.319.015.824.621.620.419.616.4 Height(m)17.016.816.715.416.919.016.617.216.516.0 Crown length(m)9.08.07.98.7 6.315.314.112.413.713.1 Leaf area(m2)62.747.448.944.323.5107.196.477.183.266.1 Needle mass(kg)8.81 6.35 6.60 5.86 2.4825.221.314.916.811.8 Distance to road(m)8.4 2.07.5 2.1 6.8 2.6 1.5 3.810.7 2.8
is generally small,and thus acceptable,as described by Phillips and Oren(1998).
To estimate the effect of soil moisture on tree conductance,it is necessary to analyse the in?u-ence of weather conditions on conductance under non-limiting soil moisture conditions.Thus,the aim of the modelling described later was primarily to ob-tain a tool to‘normalise’conductances with respect to different weather parameters,i.e.not to obtain a general model of individual tree conductance.An empirical model of the calculated g tday was?tted to vapour pressure de?cit,radiation,temperature and soil moisture:
g tday=g tmax f(D day)f(R day)f(T day)f(θ)(5) The modelling approach was stepwise,?rst g tmax and f(D day)was decided by using data when the other func-tions were close to1.Then f(R day)was?tted when f(T day)and f(θ)were close to1,thereafter f(T day)when θwas not limiting,and?nally f(θ).
The period18May to15June was used to?t the functions for D day and R day;this was a period with little variation in T day(mean15.2?C;σ=2.2)and suf?cient soil moisture.The function for T day was?t-ted after the period from7July to27September had been excluded(during this period,θREW0–50cm was <0.30).Days with Penman potential evaporation(E p) (Penman,1948)less than1mm were also excluded as a small absolute measured error is likely to have a large effect when two small numbers are divided. When?tting the functions forθ,the period1June to15September was used,days with E p less than 1mm being excluded,as also days with D day above 2000Pa,because maximum D day during the period when f(D day)was?tted was1355Pa.In total,there were11,2and12days,respectively,outside the range for which the functions for D day,R day and T day were ?tted,from a total of189days for which the?nal model was applied.
3.Results
3.1.Weather
The winter and early spring of1999were wet. Precipitation from December to April was270mm, i.e.64%more than for the normal period1960–1990 (Uppsala Weather Station,30km south).The growing season began with high soil water content(θ)and with the ground water table at or close to the soil surface at many points.May,June and August had precip-itation and temperature close to the normal,while July and September were warmer than normal,by1.9 and3.2?C,respectively(Fig.1a).In July,only about one-third of the normal precipitation fell,and the?rst half of September was also very dry.This depleted the soil water,andθ0–50cm decreased to minimum values<6%on4August and15September(Fig.1b). After some rainy days at the end of June,at the end of July and at the beginning of August,θrecovered temporarily.In the middle of July,and at the turn of the month to August,there were some days with very warm and dry conditions.The mean daytime vapour pressure de?cit(D day)then had a maximum value of ca.2400Pa(Fig.1c).
3.2.Sap?ow
The decreasingθhad a high impact on the sap?ow rate.In spite of high demand,i.e.high vapour pressure de?cit and global radiation(Fig.1c)in middle of July,
https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–85
Fig.1.Environmental conditions and sap?ow for the1999season.(a)Mean daytime temperature,T day(thin line)and accumulated monthly precipitation(bold line).In April,a manual rain gauge was emptied a few times and only a total for this month is presented.(b)Soil water content at0–20cm(normal line)and0–50cm(bold line)depth.The points are means from manual reading of eight positions with TDR rods and the lines are calculated from the dynamics of continuously measured ThetaProbes.(c)Mean daytime vapour pressure de?cit, D day(bold line)and mean daytime global radiation,R day(thin line).(d)Seven-day running means of sap?ow for the pines P1(thin line), P2(normal line)and P4(bold line).(e)Seven-day running means of sap?ow for the spruces S1(thin line),S2(normal line)and S3(bold line).The presented trees were selected to represent the range in soil moisture response.
F .Lagergren,A.Lindroth /Agricultural and Forest Meteorology 112(2002)67–8573
at the beginning of August and the end of September,sap?ow decreased dramatically (Fig.1d and e ).At the beginning of July,the ?rst trees began to respond to the decreasing θ,while others maintained transpiration a few weeks longer.This individual behaviour can be demonstrated by comparing the relationship in sap?ow rates between trees at the beginning of June,when soil water content was high,with a period in Septem-ber,when soil water content was low and decreasing (Fig.2).The three selected pines did not differ
by Fig.2.Sap?ow and environmental conditions for 2days in June and 6days in September 1999(note that the x -axis is not continuous).(a)Sap?ow for the pines P1(thin line),P2(normal line)and P4(bold line).(b)Sap?ow for the spruces S1(thin line),S2(normal line)and S3(bold line).(c)Soil water content at 0–50cm.(d)Global radiation (normal line)and vapour pressure de?cit (bold line).The presented trees were selected to represent the range in soil moisture response.
more than about 20%at most in June,whereas the difference in mid-September was 15orders of mag-nitude between the tree with the highest maintained sap?ow rate,and that which was least able to tran-spire (Fig.2a ).It may also be noted that the tree with the highest sap?ow rate in June decreased most in September,while the tree with the lowest rate in June maintained its ?ow rate best.The picture was simi-lar for the spruces,but here all trees decreased their sap?ow rates to almost zero in mid-September.
74F .Lagergren,A.Lindroth /Agricultural and Forest Meteorology 112(2002)67–85
3.3.Tree conductance
The period 18May to 15June was selected to ?t the functions f (D day )and f (R day ),because soil mois-ture was high at the same time as there was a large variation in vapour pressure de?cit and global radia-tion.Tree conductance showed the characteristic be-haviour for conifers,i.e.decreasing conductance with increasing D day ,with a large scatter for low D day and increasing conductance with increasing R day (Fig.3).The pines showed a stronger response to high D day than the spruces.The g tday increased with increasing R day in a logarithmic fashion.For the pines,there was a tendency towards decreasing g tday at the high-est radiation levels,which was caused by the steep response to D day .The correlation between D day and R day was high,r 2=0.65.
As the ?rst step,the dependence on D day was con-sidered by applying boundary-line analysis (Webb,1972;Martin et al.,1997).Lines were ?tted to the
up-
Fig.3.Tree conductance,based on sap?ow per unit projected needle area,dependence on daytime vapour pressure de?cit (D day )and daytime radiation (R day )for the period 18May to 15June 1999.(a)Dependence on (D day )for pines,P1(×),P2(+),P3(?),P4( )and P5(?),the lines are ?tted through boundary-line analysis (see text).(b)Dependence on D day for spruces,S1(×),S2(+),S3(?),S4( )and S5(?).(c)The pines’dependence on R day (symbols as in (a)).(d)The spruces’dependence on R day (symbols as in (b)).
per right part of Fig.3a and b ,where no limitation due to low radiation could be expected.Although the relationships seemed linear for the pines,exponential functions of the form:g tday =g tmax exp (?aD day )
(6)
were used,where g tmax and a are ?tted parameters whose values are given in Table 3;g tmax is a hy-pothetical conductance at zero D day and saturated radiation,which varied between 5.9and 14.3mm s ?1for the pines and between 1.3and 2.6for the spruces.The parameter a was ca.0.002for the pines and 0.001for the spruces.Exponential functions were preferred,to make extrapolation possible,as this is the known common behaviour (e.g.Stewart,1988).
As the next step,the dependence on global radiation was considered.The quotient between measured con-ductance (Eq.(4))and g tmax ×f (D day )was regarded as a function of R day (Fig.4).The relationships were
https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–8575 Table3
Parameters for the conductance,g tday,functions of vapour pressure de?cit,D day,and radiation,R day(g tday=g tmax exp(?aD day)(b ln R day?c)),for the pines P1–5,the spruces S1–5and for a weighted average for respective species
P1P2P3P4P5S1S2S3S4S5Pine Spruce g tmax(mm s?1)11.0510.4314.31 5.917.12 1.55 1.31 2.35 2.60 1.7610.44 1.48
a×103 2.15 2.12 2.44 1.46 2.04 1.29 1.080.920.99 1.55 2.120.92
b0.5630.5550.5730.5820.5760.4580.4970.4570.4710.6150.5780.470 c 2.51 2.49 2.60 2.50 2.57 1.84 2.21 1.87 1.93 2.79 2.59 1.91
Fig.4.The ratio of measured conductance(g tday)to conductance modelled using vapour pressure de?cit(g tmax f(D day))plotted against global radiation;the lines are logarithmic regressions and data are from18May to15June1999.(a)Pines P1(×),P2(+),P3(?),P4 ( )and P5(?).(b)Spruces S1(×),S2(+),S3(?),S4( )and S5(?).
76F .Lagergren,A.Lindroth /Agricultural and Forest Meteorology 112(2002)67–85
best described by logarithmic functions:f (R day )=b ln R day ?c
(7)
where b and c are parameters.When the functions de-livered negative values (if b ln R day f 1(T day )=k exp (lT day ) (8) For one tree,the relationship was linear:f 2(T day )=mT day (9)The quotient showed a clear linear response to tem-perature for one of the spruces only,for the rest of the spruces,there was no relationship,i.e.f 3(T day )=1 (10) The parameter values (k ,l and m )and the function used for each tree are given in Table 4. Accordingly,it was now possible to assess the ef-fect of soil moisture on tree conductance.The quotient between measured conductance (Eq.(4))and conduc-tance modelled with radiance,vapour pressure de?cit,and temperature,showed a strong dependence on the Table 4 The function used for temperature,T day ,dependence of the conductance and the derived parameters (f 1(T day )=k exp (lT day ),f 2(T day )=mT day ,f 3(T day )=1),for the pines P1–5,the spruces S1–5and for a weighted average for respective species P1 P2P3P4P5S1S2S3S4S5Pine Spruce f (T day )111212333313k 0.1600.1700.123–0.222–––––0.171–l 0.1140.1130.130–0.095–––––0.110–m – – – 0.063 – 0.066 – – – – – – relative amount of extractable water,θREW (Fig.6).Linear functions up to a threshold value (x )were used to describe the relationships:f (θ)= θREW x ,x <θREW (11)f (θ)=1,x =θREW (12) To obtain x ,Eqs.(11)and (12)were combined to one equation (Eq.(13))which was solved by the ‘nlin procedure’in SAS statistical software (version 6.12,SAS Institute,Cary,NC): f (θ)= θREW x |x ?θREW | (x ?θREW ) +1 +|θREW ?x |(θREW ?x)+1 ×0.5(13)The threshold value (x )was derived for both θREW 0–20cm and θREW 0–50cm ;the values of x are listed in Table 5.The variation in x was large,be-tween 0.04and 0.37θREW 0–50cm for the pines and between 0.18and 0.39for the spruces. The slope and the r 2values for the relationship be-tween measured conductance and conductance mod-elled with all functions in Eq.(5),are given in Table 6.The conductance in the early spring and late autumn was dif?cult to explain by the model for some of the spruces,for which reason,the relationships restricted to the period 1May to 30September are also given.For the pines,there was little difference between the model ?tted to θREW 0–20cm or θREW 0–50cm ;it ex-plained 46–74%of the variation,and underestimated conductance by 0–14%.For the spruces,when the spring and autumn period were excluded,the model was improved by 1–6%if θREW 0–20cm was used in-stead of θREW 0–50cm ;r 2was between 0.59and 0.80,and the slope was between 0.94and 1.0when the re-stricted period and θREW 0–20cm were used. https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–8577 Fig.5.The ratio of measured conductance to conductance modelled using radiance and vapour pressure de?cit,plotted against temperature and regression lines.Data are from16April to6July and from28September to27October1999.Days with Penman potential evaporation less than1mm were excluded.(a)Pines P1(×),P2(+),P3(?),P4( )and P5(?).(b)Spruces S1(×),S2(+),S3(?),S4( )and S5(?),the line is for S1,the only spruce with a temperature dependence. Table5 The values of the parameter x derived for the pines P1–5,the spruces S1–5and for a weighted average for respective species P1P2P3P4P5S1S2S3S4S5Pine Spruce x0–200.2190.0650.2560.3280.2070.2050.3680.2670.2000.3290.2070.239 x0–500.2050.0420.2600.3710.1960.1880.3920.3030.1760.3840.1950.214 Above this value of relative extractable water(θREW),there is no restriction due to drought;below,there is a linear decrease down to zero at0θREW.The parameter was calculated forθREW at both0–20and0–50cm depth. 78F .Lagergren,A.Lindroth /Agricultural and Forest Meteorology 112(2002) 67–85 Fig.6.The ratio of measured conductance to conductance modelled using radiance,vapour pressure de?cit,and temperature,plotted against relative extractable water.The lines are the dependence for mean pine and spruce.Data are from 1June to 15September 1999.Four days with daytime vapour pressure de?cit above 2000Pa and 5days with Penman potential evaporation less than 1mm were excluded.(a)Pines P1(×),P2(+),P3(?),P4( )and P5(?).(b)Spruces S1(×),S2(+),S3(?),S4( )and S5(?). The model was used to calculate the transpiration in 1999and 2000.The modelled conductance for pine and spruce,respectively were used in Eq.(4)to calculate E day (g m ?2s ?1),and in combination with daylength (s),total needle area ( L treecor (m 2))and the area of the plot scaled to transpiration in millime-tres per day.The measured E day was scaled in the same way.In 1999,the model generally ?tted the data well;the slope and r 2for the regressions between the measured and modelled transpiration forced through origin were 0.96and 0.85,respectively for pine (θREW 0–50cm )and 0.94and 0.86for spruce (Fig.7a and b ).This is an important test,because it should reveal whether some extrapolations were made which would seriously have biased the results.In 2000,the spring and autumn were warm and dry while the summer was very wet.The soil water content was as high in the end of July as in the beginning of May;the lowest values of θwere found in the middle of June and in the end of September.There were only 7days for pine and 11days for spruce in the end of September that had θREW 0–50cm below the threshold. https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–85 79 Fig.7.Modelled daily stand level transpiration?tted to the measurements for the1999season and validated against the measurements for the2000season;measured transpiration(×)and modelled transpiration(?):(a)pine1999,(b)spruce1999,(c)pine2000and(d)spruce 2000. In general,the model explained the variation in total transpiration well(r2=0.85)but underestimated the transpiration by26%(Fig.8).This was due to an un-derestimation of the spruce transpiration by as much as38%while that of the pine was13%(Fig.7c and d). There was,however,a shift in the performance of the model from the end of July when the weather became much drier.For the period before26July,the https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–85 Table6 Slope and r2values for linear regressions,forced through origin,between measured and modelled conductance(g tday measured= slope(g tday modelled),for the pines P1–5,the spruces S1–5and for a weighted average for respective species P1P2P3P4P5S1S2S3S4S5Pine Spruce Slope0–200.9690.8550.9980.9230.9500.9610.8990.8700.5810.9660.9780.911 r20–200.640.460.690.740.630.620.560.480.230.520.680.58 Slope0–20ex0.9930.864 1.0030.9150.9630.9670.9400.9370.982 1.0050.9850.984 r20–20ex0.660.390.700.820.650.710.800.680.730.590.680.74 Slope0–500.9740.8570.9870.9020.9470.9620.9030.8460.5740.9410.9760.918 r20–500.640.440.700.740.620.580.500.450.220.530.670.52 Slope0–50ex0.9980.8660.9920.8930.960.9690.9430.9050.9870.9750.9830.993 r20–50ex0.670.360.710.810.640.660.80.620.670.580.670.68 The regressions were calculated for conductance modelled with soil water content(θ)at both0–20and0–50cm depth.The relationships restricted to the period1May to30September are also given(‘ex’in subscript). Fig.8.Measured and modelled daily stand level transpiration for the2000season.The data were divided in two sets,before(?, solid regression line)and after(×,dashed regression line)26July. For the whole season the r2and slope was0.85and0.74,respec-tively. model underestimated the total transpiration by12% but after that date it gave just64%of the measured transpiration(Fig.8). 4.Discussion The levels of g tday can be compared to studies of canopy conductance if g tday is multiplied by the estimated leaf area index,assuming the stand to be monospeci?c(LAI:3.7for pine or7.1for spruce). This scaling-up to canopy conductance showed that the conductances for monospeci?c stands of pine and spruce,respectively were similar,with slightly greater scatter for spruce.This also indicates that mean transpiration for equally sized(diameter)pines and spruces was approximately equal,although there was some individual variation,which has previously been shown for a nearby stand(Cienciala et al.,1998). For spruce,the level of the canopy conductance was ca.50%lower than in Cienciala et al.(1992),and for pine it was ca.35%lower than that for a stand of Pinus taeda(Phillips and Oren,1998).The level of g tmax for spruce was close to what has been found by Cienciala et al.(1994),where also the daytime aver-age and the same approach to modelling the response to D day were used. The spruces exhibited two distinct levels of con-ductance.Three trees had a much lower conductance than the others(Fig.3b).It has previously been re-ported that spruces belonging to the comb or brush type,according to Dengler(1992),differed almost threefold in maximum conductance in a nearby stand (Morén,1999).The branches of the brush type are more outspread and branched than those of the comb type which shoots are hanging.In the present study, however,all sap?ow trees belonged to the brush type, although some of the comb type were present in the stand.A possible explanation may be that the three trees with the lower conductance were all growing closer than3m to a strip road of about3m width used in a thinning in1990/1991(Table2).Soil compaction and root damage may have reduced their ability to ex-tract water.The effect of strip roads on water?ux has been little studied,but there are some contradictory https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–8581 studies of their in?uence on tree growth:Kardell (1978)reported a negative and Kardell and Nilsson (1986)a positive effect on growth in studies of Nor-way spruce.In the estimates of leaf area,mainly based on the needle biomass according to Marklund (1988),there is also uncertainty.If their crown density had been lowered,the lower conductance of the trees close to the strip roads could have been caused by an overestimate of the needle area.In the most advanced form of Marklund’s(1988)functions,the diameter in-crement for the last5years is included as the second most signi?cant variable after diameter.Unpublished results from the stand of the present study indicate that the spruces close to strip roads do have reduced growth.The small variation in the conductance for the pines and the other two spruces,however,indicates that this simply calculated needle mass is correlated with transpiration,because the leaf area of the trees was based on the needle mass.The needle mass could therefore be regarded as a useful tool for scaling-up sap?ow,as in Cienciala et al.(1998). The parameter a,which describes how steep is the reduction in conductance with increasing D day,was ca.0.002for the pines and0.001for the spruces. Where the same function for vapour pressure de?cit has been used in other studies,the level has gener-ally been lower.Cienciala et al.(1992,1994)reported values of0.00045and0.00070for Norway spruce. K?stner et al.(1996)reported values for Scots pine between0.00037and0.00051and Grelle et al.(1999) a value of0.00099for a mixed pine and spruce forest. Of these studies,only those by Cienciala et al.(1992, 1994)were based on daily averages;the other stud-ies used30min data.Variables such as radiation and vapour pressure de?cit have different dynamics dur-ing the course of the day,and when daily averages are used,the effect of this is smoothed out.The values of the parameters can therefore not really be compared with those of parameters based on analyses with a shorter time step. The difference in light response(Fig.4a and b) between the pines and spruces may be a consequence of different light regimes.The radiation level was measured above the stand,and treated as identical for all trees in the modelling work.The pines had a much shorter crown length(Table2),and their leaf area was distributed higher than the spruces(Morén et al.,2000).Spruce S5,which had values of the parameters a–c closer to the pines,had small open- ing in the stand on its southern side,hence might be expected to have been exposed to higher light levels. In many studies,the temperature response func- tion has been found to be non-signi?cant and has been omitted(e.g.Grelle et al.,1999;Granier et al., 2000b).In others,a bell-shaped relationship using an optimum temperature(Stewart,1988;Gash et al., 1989)has been used.In Granier et al.(2000a)a linear relationship between10and17?C was used,where the function took the value of0below the span and1 above.In the present study,an exponential or linear relationship was found for the pines,while there was only one spruce that showed a linear response(Fig.5a and b).For the spruces for which no dependence of temperature was used there was at tendency for lower conductance at the lowest temperatures(<7?C).A temperature response function without an optimum or maximum level con?icts with the theory of the physical processes involved.The reason for the ex- ponential behaviour for the pines could be that the parameter a was overestimated,i.e.the function of D day was too steep.This could be explained if none of the data points in the right side of Fig.3a reached the maximum level of the conductance for the respec- tive D day.Too low radiation might explain this,but all of those points belonged to high radiation levels (R day>350W m?2s?1).Another explanation may be that the points in question belonged to the second half of May,and that the current year’s shoots were not fully developed and the conductance therefore was lower.Pine exchanges more of its needles each year than spruce.Nevertheless,the?nal model showed no clear tendency to over-or underestimation when it was extrapolated above the range for which it was calibrated. The effect of decreasing soil water content(θ)has been an issue in several studies.In Fig.9,the results of some of them are presented together with the results from the present study.The results of the present study agree well with those of Stewart(1988),but are steeper than the?ndings by Ewers et al.(2001),Irvine et al. (1998)and Granier et al.(2000b).The most striking feature in the present study was the large variation between trees:for pine P2,there were16days below the thresholdθREW,while for S2there were as many as95days(Fig.6a and b,Table5).One explanation https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002) 67–85 Fig.9.The reduction of conductance/transpiration due to decreas-ing soil water content from a number of studies.Granier et al. (2000a,b)is a general study,Stewart(1988)is from a mixture of Scots pine and Corsican pine(Pinus nigra var.miritima(Ait.) Melv.),Irvine et al.(1998)is from Scots pine and Ewers et al. (2001)is from Pinus taeda(control treatment).The equations by Granier et al.and Stewart were converted fromθREW toθby their relationship in the present study. for this behaviour could be the highly variableθin the stand;the standard deviation was about0.15in May and0.05in July.There was a tendency for the spruces to be more affected by drought than the pines, although this was not signi?cant.For the average pine and spruce,there were63and75days,respectively with drought restriction.During the dry summer of 1994,pine and spruce transpiration was reduced by40 and67%,respectively in an adjacent stand(Cienciala et al.,1998). Soil water content was only measured down to 50cm depth although during a drought it is likely that also deeper soil layers contribute to water up-take(e.g.VanSplunder et al.,1996).The relationship between soil moisture and soil tension was not deter-mined for this particular soil,but measurements in a nearby pit(St?hli et al.,1995)shows that20%θREW corresponds to about?2500hPa.It should,however, be pointed out that the soil properties of the studied forest are very heterogeneous. In1999,the model?tted the measurements well (Fig.7a and b).Much of the deviation occurred dur-ing periods when daily total sap?ow and transpiration could not be expected to be the same(Waring et al., 1979;Zweifel and H?sler,2001).Zweifel and H?sler (2001)reported that the diurnal variation in stem ra-dius can be as much as1–2mm in Norway spruce in winter and spring,which could explain some of the very high?ow rates in the spruce trees on some days in April.The underestimate for some days in August could probably also be explained to some extent by the recharge of stored water after some rain events. Waring et al.(1979)reported that the change in water content of the sapwood could contribute to more than 1mm per day of transpiration in a Scots pine planta-tion.The scatter of the model is also large during the warmest days in the middle of July,when the model was extrapolated far outside the temperature range for which it was calibrated.The performance of the model on the2000data changed drastically when the very rainy period ended.The reason could be that the trees adapts to the high soil moisture by decreasing the sen-sitivity of the stomatal conductance to increased VPD. The diurnal pattern in the transpiration and weather showed that although the radiation ended1.5h later in the end of August than in the beginning of June,the sap?ow continued equally long(Fig.10). In Table7,the correlations between the variables used in this study are listed.In addition to the high correlation between D day and R day,it is noteworthy that T day andθREW are correlated.This behaviour is probably normal during moderately wet to dry grow-ing seasons.As the driest periods normally are left out when the parameterisation is made,so are also the warmest.For this reason,it is dif?cult to distinguish the effect of temperature,vapour pressure de?cit and soil moisture at the most extreme https://www.doczj.com/doc/832558497.html,I,which was not measured over the course of the season in the present study,is probably also correlated to tempera-ture,especially in deciduous forests. Table7 The r2values for linear regressions between the variables(vapour pressure de?cit(D day),global radiation(r day),temperature(T day) and relative extractable water at two depths(θREW))used in the model D day R day T dayθREW0–20θREW0–50 D day10.650.62?0.16?0.05 R day10.34?0.010.01 T day1?0.48?0.28 θREW0–2010.89 Negative values indicate that the relationship was negative. https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–85 83 Fig.10.Average diurnal pattern for2weeks of temperature(a),global radiation(b),vapour pressure de?cit(c)and transpiration(d)for a period in the beginning of June(solid line)and in the end of August(dotted line)of2000. 5.Conclusions The main conclusions to be drawn from this paper are that on average,the reduction of conductance does not begin until80%of the extractable amount of soil water has been depleted.We also found that the individual response to low soil water content varies greatly;spruce tended to be more affected by drought than was pine.It is also evident that the canopy conductance in Scots pine and Norway spruce trees shows slightly different responses to vapour pres-sure de?cit and radiation when they are growing in a mixed stand.Pine shows a steeper response to both variables.In spring,and when the soil water con-tent changes rapidly,there may be a poor connection between transpiration and sap?ow,also when daily averages are used. Validation of the model on data from the year af-ter the calibration showed that after a sharp shift in weather conditions,from wet and rainy to warm and dry,the model underestimated the transpiration sub-stantially. For future studies,it is important to point out that the location of strip roads should be considered when selecting trees for sap?ow measurements and when scaling-up to larger areas. Acknowledgements This research was mainly founded by the Swedish Council for Forestry and Agricultural Research.Con-tribution was also obtained from the Swedish Na-tional Energy Administration.We thank Jiri Kuèera for https://www.doczj.com/doc/832558497.html,gergren,A.Lindroth/Agricultural and Forest Meteorology112(2002)67–85 advice and technical assistance concerning the sap?ow measurements.We also thank Meelis M?lder for me-teorological data,Harry Lankreijer for valuable com-ments on the manuscript and Jeremy Flower-Ellis for careful language revision. 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Zweifel,R.,H?sler,R.,2001.Dynamics of water storage in mature subalpine Picea abies:temporal and spatial patterns of change in stem radius.Tree Physiol.21,561–569. 安全生产演讲稿 安全生产演讲稿 第一篇： 安全生产演讲稿 “百日安全无事故”——安全与梦想齐飞 我想先和大家提一个我们从小到大都会谈论的话题。－“梦想”。我想问大家梦想对我们而言意味着什么？是一辆跑车？一座豪宅？还是花不完的钱，还是至高的荣誉？有人说年轻就是无限，有梦想就有动力。年轻的我们都不曾忘记那份豪情壮志。我们努力奋斗，为的就是实现心中的梦想。 可是，你们有没有想过，在我们怀抱着梦想努力工作的时候，也许在某一天，我们会因为自己的一次麻痹失误，一次不起眼的违章作业而让自己的梦想变成幻想呢？ 在我们的工作生活中，我们最基本的需求就是安全，“安全第一，预防为主”这是我们应牢记在心的，企业是时时讲、周周学、月月喊。作为萍钢这样的大型钢铁企业，为了确保安全，工厂里所有的设备都专门编制了操作规程，针对特殊工种还特配了相关岗位说明书。除此之外，公司还在明显的位置张贴、悬挂各种类型的安全标语和安全标致，为的就是要提高我们对安全的意识。生产部还定期组织对公司进行安全隐患排查，及时发现并消除隐患，这些都是为了保证我们能够在一个确保安全的情况下生产。 在公司，老员工的安全意识向来都比较强烈，因为他们都见证了安全意识淡薄、不遵守规章制度所造成的后果。发生事故的往往都是 些年轻的新进人员，每一位员工进厂的时候都要经过公司的四级安全教育。可是有部份同志对于这样的教育全当成耳边风，对相关操作规程不学不问，对公司的安全制度和进出车间的注意事项漠不关心。总以为事故永远不会发生在自己身上，但就是这一刻的疏忽就有可能造成长久的悲痛。所以作为萍钢这个大家庭中的一份子，除了要掌握安全工作规程、技术操作规程、企业纪律章程这几件法宝，还要多有几颗心： 一、专心。学一行，专一行，爱一行。“既来之，则战之；既战之，胜之则”，不能“身在曹营心在汉”，工作的时候就应该专心工作，不要想工作以外的事情。 二、细心。不管是长年在干的，还是第一次接触的工作都来不得半点马虎，粗枝大意实在是安全生产的天敌。从小父母每到考试前都会再三叮嘱“要拿双百分，不要粗心大意”。 三、虚心。“谦虚使人进步，骄傲使人落后”， 人的生命只有一次，失去了生命，所有的梦想都成为幻影，海尔经验告诉我们，不容易就是，把容易的事情一千次，一万次地做好。安全工作时刻从零开始，未雨绸缪胜过亡羊补牢，年轻的朋友们，当我们怀抱梦想的时候，当我们满怀豪情要实现自己的理想时候，必须要时刻牢记，安全就是第一，梦想与安全并进！ “百日安全无事故”这是对于我们每一个萍钢职工的一种激励，激励着萍钢公司在未来的安全生产中一路平安，基业长青。 第二篇： 石油安全生产演讲稿 安全生产是效益，是幸福 新闻评论的格式写法 新闻评论的格式写法新闻评论的文体结构与其他新闻文体相比基本是一致的，它包括标题、导语、主体、结尾四个部分，而在具体写作新闻评论时，各个构成部分又有其独特的写法。1．引人注意的标题新闻评论的标题既可以标明论题的对象和范围，也可以直接提出评论的观点和主旨；总的要求是生动活泼、言简意赅，使标题成为引人耳目的招牌。首先，要巧用动词，强化动词在评论标题中的动态感和鲜活感。2005年11月4日《经济日报》的评论《扬起企业品牌之帆》，这篇评论的标题用动词“扬起”，既揭示出我国目前实施自主品牌的必要性，也展现了我国企业界创新品牌的信 心与决心，给人以昂扬向上的感2005年8月23日《人民日报》的评论标题是《匹夫不可夺志国难见气节》，运用了引用的否定式陈述句的标题能够直接给受众一个非常坦率的态度；疑问句式的标题使受众始终带着一种特定的悬念去思考。《文化产业呼唤”中国创造”》，其标题运用肯定式陈述句，非常鲜明地揭示了媒体所要表达的一种态度和观点；《不该误读”平民医院，’))，虽用表面否定的句式却表达了非常干脆的态度；《洋教材冲击了我们什么？》，这一个带着问号的标题首先就会给受众留下悬念：谁在用洋教材？到底怎么回事？带着种种谜团就会循文找答案了。依据评论的思想内容，善于调动不同的句式，能够造成一种特有的情感效果。评论的标题写作方法不止这些。只要能吸引受众、揭示评论的思想内容，就是好的评论标题。新闻评论标题的写作原则追求有个性、有创新，这样的评论标题才更具魅力。2．富有悬念的导语新闻评论的导语，即开头部分、 引论部分。导语的设计应始终以受众为着眼点，总的要求是：要把最能吸引受众兴趣、最能引起受众关注的事实、观点或问题放在前面。的主体由两个层次构成，一是老百姓对”平民医院” 的错误理解，二是一些地方政府主管部门对”平民医院”的误读。哪个程度更为严重呢？该评论指出：”百姓们对’平民医院’是对眼下’公立医院’就医门槛过高的无奈”，而一些地方政府主管部门也会误读”平民医院只能说明”政府服务功能的缺位”，而后者也是评论者在文中所要着重阐明的重点内容。前后两个层次之间形成一种必然的逐层递进的关系。③对比式。就是主体部分的事实材料及其所要表达的思想内容是相互对照的，通过对比的手法论述论题和观点，有力地证实某一论点的正确或谬误。2005年12月26日《人民日报》”人民论坛”发表的《在磨砺中成长》，主体部分在重点叙述洪战辉自强不息、顽强奋斗的先进事迹，评价其崇高的道德品质的同时，也对目前 放飞梦想演讲稿三篇-梦想演讲稿 无论是你，是他，还是我，当我们走进这个纷繁的世界时，心中都藏着一个美好的梦想。为了这个梦想，我们立下坚定的信念，我们有着不屈的意志和不懈的努力。以下是给大家整理的放飞梦想演讲稿三篇，喜欢的过来一起分享吧。 放飞梦想演讲稿一 我们，撇下无知迎来了属于我们的青春。青春，让我们肆无忌惮，畅然释怀，体味风那样的自由，感受云那般的自在，因为青春赋予我们的是生命的巅峰，我们无须成熟，我们不再无知，我们唯有执着。 人生是对梦想的追求，梦想是人生的指示灯，失去了这灯的作用，就会失去生活的勇气。因此，只有坚持远大的人生梦想，才不会在生活的海洋中迷失方向。托尔斯泰将人生的梦想分成一辈子的梦想，一个阶段的梦想，一年的梦想，一个月的梦想，甚至一天、一小时、一分钟的梦想。当你听到那里，同学们，你是否想到了自己的梦想？ 人生的花季是生命的春天，它美丽，却短暂。作为一名大学生就就应在这一时期，努力学习，奋发向上，找到一片属于自己的天空。青年是祖国的期望，民族的未来。每个人主宰着自己的明天。 有一位哲人说过：“梦里走了许多路，醒来还是在床上。”它形象地告诉我们一个道理：人不能躺在梦幻式的梦想中生活。是的，人不仅仅要有梦想，还要大胆幻想，但更要努力去做，在梦想中躺着等 待新的开始，如果不仅仅遥遥无期，甚至连已经拥有的也会失去。同学们，你们是否也正在梦幻的梦想中彷徨呢？ 前人说得好，“有志之人立长志，无志之人常立志”，那些无志之人的“志”，就是美梦，就是所谓的“梦想”，他们把自己的蓝图构画得再完美，再完善，也只是空中楼阁，海市蜃楼罢了。同学们，你是立长志之人，还是常立志之人呢？ 最后我想用梁启超的话来结束这天的演讲：“少年智则国智，少年富则国富，少年强则国强，少年进步则国进步，少年雄于地球，则国雄于地球。”让我们洒一路汗水，饮一路风尘，嚼一跟艰辛，让青春在红旗下继续燃烧；愿每一位青年都怀抱着自己的梦想，在人生的航程上不断乘风破浪，奋勇前进！ 放飞梦想演讲稿二尊敬的老师、亲爱的同学们： 大家上午好！ 这天我演讲的题目是《放飞梦想》。 每年的春天，万物复苏，人们都会走出家门放风筝。望着这满天的风筝，我们可曾想过：是不是我们的梦想也能够像这风筝一样放飞呢 给大家讲一个故事：一个平凡的乡村邮差，每一天都会在来回的路上拾一些石子，人们问他为什么做这样无聊的事，他说，他要建一座自己的城堡。他一天一天坚持不懈，日复一日，年复一年，当乡里的人们早已忘了这事时，一座美丽的城堡已经建成了，这就是邮差的城堡，他梦想的城堡。这就是梦想的力量。如果心中有了一个梦想而 【实用】安全生产演讲稿范文锦集十篇安全生产演讲稿篇1 尊敬的各位评委、同事们，大家好： 我是XXXX公司的员工王娟，今天我演讲的题目是“安全生产是效益，是幸福”。清晨，当第一缕阳光升起时，我们开始为生活而繁忙，劳动者挥舞臂膀，播洒汗水；傍晚，当夕阳西下，百鸟归巢，忙碌了一天的人们个个携老扶幼，漫步公园，欢声笑语，连绵不绝。好一副“兴旺发达创效益，和美天伦出幸福”的美好画卷。此时此刻，我心中不由激起了对安全生产的无限思索，企业蒸蒸日上的发展，滚滚而来的效益，家庭和谐美满的幸福，何不是平日安全生产盛开的喜悦花朵。 国家的安全是国泰，民众的安全是民安，有了安全生产，我们的企业才能象三春的桃李红红火火，有了安全生产，我们才会有幸福就象花儿一样的放歌，有了安全生产，我们的国家才能在建设有中国特色的社会主义道路上稳步前进。安全生产工作要从经济发展和社会稳定的大局出发，充分认识安全生产的重要性，切实加强安全生产工作。 然而，尽管有领导的高度重视，尽管有安全法律法规的约束，我们的一些企业仍是片面强度经济增长，效益优先，不重视安全生产，不懂安全，不讲安全，不要安全，我们的一些员工也是一味地追求高产，高效，高奖金，对安全生产工作，是说起来重要，干起来次要，忙起来可以不要，蛮打蛮干，违章操作。然而，就在这违章操作的背后，却是一幕幕惨绝人寰的场面，一份份撕心裂肺的悲痛，一笔笔巨额的经济损失。还记得，20xx年重庆开县特别重大硫化氢中毒事故，20xx多人中毒住院，243人死亡，直接损失8000万元；20xx 年大连石化特别重大爆炸事故，直接经济损失2.2亿元；20xx年动车事故，41人死亡，200多人受伤，直接损失1.9亿元；一件件安全事故，一份份血的教训，给我们的国家和企业造成的巨大的经济损失，给我们欢乐祥和的家庭带来了巨大的悲痛。 20xx年3月28日，山西省王家岭煤矿发生重大透水事故，近一百五十多名煤矿工人被困井下，而这起透水事故的起因就是相关领导好大喜功，只贪图一时的经济利益，不注意安全生产的要求，导致惨剧发生。此时此刻，试问，我们企 小学生新闻消息写法技巧 导读：消息的特点 1、短小精练：消息要短小精练，这是新闻写作的基本要求。就小记者采写新闻来说，写好短消息，便于迅速及时的报道新闻事实，同时也锻炼小记者的采写能力;就读者阅读新闻来说，它便于阅读。 2、语言生动简洁：消息的语言只有生动、简洁，才能吸引读者 3、“倒金字塔”结构：消息的写作是将最重要、最新鲜的事实写在新闻的最前面，按事实重要性程度和读者关注的程度先主后次的安排，内容越是重要的，读者越是感兴趣的'，越要往前安排，然后依次递减。这在新闻写作中称为“倒金字塔”结构。 二、消息导语的几种写作方法 1、叙述式导语的写作：就是直截了当地用客观事实说话，通过摘要或概括的方法，简明扼要地反映出新闻中最重要、最新鲜的事实，给人一个总的印象，以促其阅读全文。 2、描写式导语的写作：记者根据目击的情况，对新闻中所报道的主要事实，或者事实的某个有意义的侧面，作简练而有特色的描写，向读者提供一个形象，给人以生动具体的印象，这就是描写式导语的一般特点。一般用在开头部分，以吸引读者，增强新闻的感染力。 3、议论式导语的写作：往往采用夹叙夹议的方式，通过极有节制、极有分寸的评论，引出新闻事实。一般分为三种形式：评论式、引语式、设问句。 三、学会恰当运用新闻背景材料 背景材料在不少新闻中占据一定的位置，是新闻稿件中不可缺少的内容。交代背景应根据需要因稿而异，更要紧扣主题，还有交代背景时不宜太多，材料要写的生动活泼。 【小学生新闻消息写法技巧】 1.小学生新闻消息的写法技巧 2.新闻消息的写作方法 3.新闻通讯的写法 4.盘点新闻消息写作方法大全 5.2015年新闻时事评论的写法 6.有关将新闻稿改写为消息 7.2015新闻的写作基础知识：消息的写作 8.新闻宣传报道的格式与写法 上文是关于小学生新闻消息写法技巧，感谢您的阅读，希望对您有帮助，谢谢 为梦想插上腾飞的翅膀 如果你在生活中受到了创伤，请记住，在那片伤口的地方，长出的，是洁白的梦的翅膀。 有一只蝴蝶，曾经她有一双美丽的翅膀。在一次玩耍中，不幸被树枝刮断了一片，她重重地摔在了地上，他挣扎着，呻吟着，心中充满了绝望，她觉得自己再也不能展翅飞翔。可是当她看到风雨中蜘蛛网摇摇欲坠的时候，蜘蛛仍在不停地努力地补网。她震撼了，于是，她深信：折翼仍可轻舞。她开始了一次次的尝试，又经历了一次次的失败。终于，在一个阳光明媚的早晨，她又一次振翅飞翔，重返蓝天。 蝴蝶因为有了方向，所以她不懈努力；我们因为有了梦想，所以我们变得坚强。 梦是什么？梦是在我们的汗水和泪水的浇灌下萌发的一粒种子。的确，我们的付出，我们的汗水，泪水甚至我们的鲜血，都是为了那个纯真的梦想。 从古至今，梦想鞭策了多少仁人志士。有不顾严寒，步行百里的宋濂；有真诚待人，知识渊博的孔子；有为中华之崛起而读书的周恩来；有无私奉献，视死如归的革命战士……他们这些人因为心系天下，怀揣梦想，才在人生道路上，不畏困难，不惧挑战，一步一个脚印，走向自己的康庄大道，来让自己的梦想得以实现。 颜回在陋巷中废寝忘食，他在努力让自己的梦想不再遥不可 及。现在的我们，总以为在这个陈旧的校园里，找不到出路，不知道未来在哪里。孰不知，那个最接近天堂的地方，竟是自己心中的那条“陋巷”。每个人都希望实现人生的辉煌，每年我们都会看到高考的学子们在高考考场上演着曲折离奇的剧目。有人成功，完美的谢幕；有人却因功底不足而被重重的摔在舞台上。成功者之所以能成功，是因为他们曾在那段最艰难的岁月里，绽放出了最纯粹的记忆；在那个最疲惫的身躯下，依旧掩藏着最完美的自己。他们追随着属于自己的启明星，一路奔跑，留下了一串串足迹。最终，成为了天空中那颗最闪耀的星。 时间在一点一滴的流逝，我们在追梦的旅途上怎能够迷茫？虽然，我们在会很累，泪水可能打湿我们的脸庞，但我们应明白：若非热泪盈眶，何必年少轻狂？现在的我们，正是为梦想而发疯的时候，时间已不允许我们等待，我们要做的，就是找准目标，奋力前行。在我们的旅途中，不能没有方向，更不能没有终点。因为那样的行程，便可以称为浪费生命，虚度年华。我们决不允许这样的事发生在我们身上，为此，我们要在内心中找到那个最完美的自己，确立一个最满意的理想并为此而奋斗，一点点离开最初的模样。 青春是自由挥洒的天空，在这样的天空中，我们将为梦想插上腾飞的翅膀，让人生之路充满挑战，让自己一生无悔。 安全生产演讲稿优秀篇 安全生产演讲稿优秀篇 篇一《关爱生命安全为天》 当你拥有它时，好像不觉得它有什么了不起；当你失去它时，才会真 正觉得拥有它是多么地幸福。 它便是我们万分关注的一个永恒的话题――安全。 安全不需要太多的理由，生命已足以使之永恒。 我们不能因为产量而轻视安全，不能因为效益而忽视安全，更不能因 为工作面、工作条件稍好一些就藐视安全。 安全意识的淡化，薄弱是导致事故发生的首要原因，每一次事故的发 生，我们都后悔莫及，那么在事故发生之前，我们的隐患排除了吗？我们 的防范措施到位了吗？千里之堤溃于蚁穴，早防早治才能确保安全。 而抓安全，就必须时刻如履薄冰，如临深渊。 安全工作来不得半点马虎，只有提高警惕，居安思危，防患于未然， 努力做到紧绷安全弦，才能确保企业的长治久安。 我们要尊重生命， 就要敬畏规章， 遵守规章是责任， 是道义， 是权力， 更是义务。 只有遵守规章才能保安全，这是安全生产的经验昭示。 安全源于长期警惕，事故出于瞬间麻痹，思想上的松懈麻痹必然会导 致安全隐患的存在和违章现象的发生，哪怕一次偶然现象的发生，哪怕一 次偶然违章，就有可能一失足成千古恨。 没有了安全就丧失了和和美美的家庭，更没有企业的可持续发展，依 法遵章，所有的事故都可以避免，松懈麻痹，所有的事故都可能发生，遵 章二字，正是水之源，树之根，安全之本。 一花一世界， 一叶一菩提， 每一个人的生命都是天地之魂， 万物之灵， 生命因此而珍贵，我们要热爱生命，热爱生活，珍惜眼前的每一天；让我 们永远牢记安全责任， 警钟长鸣， 才会让安全之花扎根于我们的生活之中。 篇二《六月，让我们共同走进安全月》 刚刚送走激情、温馨的五月，六月的祝福已亭亭玉立在我们面前。 13 亿双期盼的眼光一起向"安全月"汇聚，在这个阳光铺满的季节里， 铿锵走来了"安全月"的脚步。 安全是什么？安全就是生命！安全意味着什么？对于一个人，安全意 味着健康；对于一个家庭，安全意味着和睦；对于一个企业，安全意味着 发展；对于一个国家，安全意味着强大。 没有安全，就没有一切。 安全是什么？安全就是一首歌，需要我们天天来弹唱；安全就是一首 诗，需要我们日日来吟诵；安全就是一盘棋，需要我们走一步看两步；安 全就是标准化，要求建设者严格规范的操作；安全就是有序的节奏，推进 科学化管理上水平；安全就是沸腾的生活，预示我们生机勃勃的明天；安 全就是一根七彩的丝带，连接一个又一个美好的愿望。 1、新闻要素：不可忽略5W1H。（Who、What、When、Where、Why、How） 2、新闻构成：题、文、图、表。 3、题：简要、突出、吸引人。 4、文：导语100至200字：开宗明义，人事时地物。 5、主体300至500字：深入浅出，阐扬主旨。 6、结语100字：简洁有力，强调该新闻的意 义与影响，或预告下阶段活动。7、图：视需要加入有助于读者理解的图片。 8、表：视需要加入有助于读者理解的表格。9、写作要律：具有新闻价值、正确的格式、动人的标题。简洁切要的内容、平易友善的叙述、高度可读性、篇 幅以1至2页为宜（一页尤佳）。写作技巧：清晰简洁、段落分明、使用短句、排版清爽。切忌偏离事实、交代不清、内容空洞。一篇好的新闻稿除了必须具有 新闻价值、把握主诉求与正确的格式外，行文应力求简洁切要，叙述应有事实基础，文稿标题则以简要、突出、吸引人为原则，用字要避免冷僻艰深，以提高文 稿的可读性。此外，篇幅也不宜长篇大论，一般以1至2页为原则，必要时可以加入图表，增加文稿的专业性，切忌内容空洞、语意不清、夸大不实。 倒金字塔结构是绝大多数客观报道的写作规则，被广泛运用到严肃刊物的写作 中，同时也是最为常见和最为短小的新闻写作叙事结构。内容上表现在在一篇新闻中，先是把最重要、最新鲜、最吸引人的事实放在导语中，导语中又往往是将 最精彩的内容放在最前端；而在新闻主体部分，各段内容也是依照重要性递减的 顺序来安排。犹如倒置的金字塔，上面大而重，下面小而轻。此种写作方式是目 前媒体常用的写作方式，亦即将新闻中最重要的消息写在第一段，或是以「新闻提要」的方式呈现在新闻的最前端，此种方式有助于媒体编辑下标题，亦有助于阅听人快速清楚新闻重点。基本格式（除了标题）是：先在导语中写一个 新闻事件中最有新闻价值的部分（新闻价值通俗来讲就是新闻中那些最突出，最 放飞梦想演讲稿10篇 【篇一】 我喜欢飞翔的感觉，像空气一样轻盈，像雄鹰一样自由。而几乎，每一个向往飞翔的人，都拥有一个生着一双美丽翅膀的梦想，因为，只有让梦想插上了翅膀，让它更高更高的飞翔，人生才会发出璀璨的光芒，才能成就不休和辉煌。 春秋季世，诸侯纷争，战火连天，太阳也失了光芒，大地上到处是悲哭和苍凉，血污的现实让好多人，或是不问世事终老山林，或是得过且过苟延残喘，而，孔子，正是在这样一个人性压抑的时代，依然将梦想放飞，他的梦想自由而骄傲——那就是推行礼制，宣扬仁政，还世界一个完美而合理的秩序。尽管遭遇了无数的磨难，权贵的排挤，暴力的围攻，路途的坎坷，但这些都没有使孔子屈服和放下，他的梦想，飞翔前方，高扬复高扬，让他心中充满期望，让他“知其不可而为之”，最终成就了一个“万世之师”的人生。清朝末年，又是一个痛苦和绝望的年代，帝国列强在中华大地上肆虐横行，天地变色，草木含悲，满目疮痍，屈辱和彷徨充斥着人心，而，孙中山，正是在中华民族这样生死存亡的关头，依然将梦想放飞，他梦想着驱除鞑虏恢复中华，他梦想着与所有拥有相同梦想的仁人志士一齐，救亡图存，振兴中华。正是在这样伟大梦想的鼓舞下，他身陷囹圄而不悔，黄花岗血洒而不退，直到听到辛亥革命那划破长夜的枪声，直到看到民族完全独立，东方睡狮发出震撼世界的长长怒吼。梦想是期望，是拂向寒冷大地的一缕春风，是穿过漫漫黑夜的一线光明，是荒蛮大原上的一点火种，是浩瀚沙漠中的一块绿州。有梦就有期望，梦想有多远，路就有多远。 相反，没有梦想的民族，不会长久;没有梦想的国家，不会强大;同样，没有梦想的人生，不可想象。 如果没有一向飞扬的梦想，摩西的子孙不会在流浪世界近千年，历尽世世苦难之后，终回到耶路撒冷的热土建立起富强的以色列;如果没有一向飞扬的梦想，一穷二白的炎黄后代，不会在伤痕累累疮痍处处的中华大地，独立自主艰苦奋斗，励精图治勇于改革，让这个古老的民族重焕生机，以大国的形象屹立在世界的东方。如果没有飞扬的梦想，毛泽东不会在他人生最艰难的关头依然坚守信仰永不言弃，成为中国人民的伟大领袖。 将梦想放飞吧，让梦想拥有一双美丽而矫健的翅膀，让它在人生的天空飞得更高，飞得更高。放飞的梦想之于人生，就像那无边无际的深夜里一盏刺破黑暗的明灯，它能引导出一个光明的世界。放飞的梦想之于人生，就像那广袤的大地上永不干涸的河流，它能慢慢向东汇聚，就会构成蔚蓝的海洋。 放飞的梦想能照亮我们前进的人生。冰雪覆盖的时候，它能帮我们创造出一团熊熊燃烧的烈火，温暖我们的疲惫身体;暗夜无边的时候，它能帮我们更好的领悟星光的好处，点化我们人生的迷茫;前途困顿的时候，它能帮我们开启尘封的心智之光，寻到到真正属于自己的人生航标。 放飞的梦想能温暖我们的生命。梦想是我们生命的温床和灵魂的栖息地。梦想不在，生命和灵魂便永远不能安寝。梦想让每一个如风一样轻的生命，增加了存在尊严和重量。梦想让我们的生命，在俗世中独焕斑斓，甚至让我们美丽的人性，得如幽兰一般升华。我们的生命所负载的心胸，因为梦想而变得宽如大海，阔如天空;我们的视野，因为梦想而“一览众山小”着眼处尽是天蓝云白水碧花红芳草青青。 将梦想放飞吧，让梦想挥动长长的翅膀，在人生美丽的天空自由而骄傲地飞翔，且得更高，更高…… 【篇二】 尊敬的老师、亲爱的同学： 大家好！我演讲的题目是《放飞梦想》。 安全生产、党员争先 煤矿生产，安全为天。当单位或部门新分来学员和新工人时，都要进行有关安全政策、法令、规章制度的学习、培训。上岗工作时，安监部门、各级领导又是人人讲安全，天天进行安全戴帽说安全。可是，每次事故的发生都事出有因，究其原因何在？答案是：绝大多违章人员都是没有管好自己。由于参加工作时间长了，工作环境熟悉了，讲安全听腻了，思想上逐渐产生了麻痹大意思想，尽管安全规章天天讲，也当成了耳旁风，心里有一搭无一搭。事故发生后，震动一阵子，过后又随着时间的流逝而淡化。这种“管不住自己”的毛病，无疑是酿成事故的病症所在。 要搞好安全，真正做到安全为了生产、生产必须安全，除了严格按照各项安全操作规程规定作业外，最重要的一点就是要“自己管住自己”。各科室、区队里有科长、队长、班长、青年安全监督岗员和群监员，但都不能时时处处跟着你、看着你、附在你身上，钻进你心里。你工作走神，思想溜号，有意违章，违章操作，事故往往就在这种情况下找上门来。有位在煤矿工作多年，从未发生过任何事故的老工人说过这样一句话：“我的安全经验就是自己管自己”，这句话言简意赅，值得品味再三。在工作时如果三心二意，就有可能发生事故。根据有关部门统计资料表明：百分之九十以上的事故，都是由于思想麻痹和“三违”造成的。 俗话说得好：“世界上什么药都可以买到，就是‘后悔药’买不到”。出了事故，单位受损失不说，自己轻则受皮肉之苦，重则缺胳膊少腿，甚至连生命都没有了，你的父母、妻子、儿女还要为你承担痛苦与不幸。生活是美好的，家庭是温暖的，何必为一时之错、一念之差，付出如此沉重的代价？ 作为一名党员干部，我们应当牢固树立“本质安全，珍爱生命”的理念，去营造遵章守法，治理“三违”的安全文化氛围，把安全生产的制度，变为我们自己的自觉行动。同时还要加强学习、注重提高自身的安全技术素质和安全生产能力、切实在安全生产工作中发挥出党员的先进性和模范带头作用。 党旗在飘扬，党旗在召唤。让我们在全矿蓬勃开展的“创先争优”活动中，时刻牢记这样一个道理：党员就是责任，党员就是旗帜，党员就是榜样，党员就是先锋；让我们忠诚做好人民群众的领头雁，真情当好安全发展的排头兵，为鲜红的党旗增辉添彩，为建设庇山和谐矿区、本质安全矿井、五优矿井做出积极的贡献。 放飞梦想演讲稿500字5篇 当我听了这个故事后吗，我有了非常深的感受。每个人都有自己的梦想，我的梦想就是当一名科学家，每天我都在搞科研。但是直 到有一天，我脑海了闪过一个念头，现在我还在小学阶段，以后还 要走更长的路，此时我应该好好读书。之后，我就换了一个梦想， 努力考上名牌大学，长大后好好孝顺父母，报答父母多年来的养育 之恩。我就像杨孟衡一样，虽然第一个梦想不能实现，但还能有第 二个梦想，第三、第四甚至更多。因为人的一生可以不止一个梦想。失败并不可怕，可怕的是没有梦想。有了梦想就是有了希望，有了 光芒! 梦想并不是一个梦。有志者，事竟成。只要你有努力过、坚持过，就一定会成为现实!放飞我们的梦想吧，一起加油!我的梦，中国梦! 每个人都不愿在牢笼中平庸的度过一生，而是要插上自由的翅膀飞翔。 孩提时，我们童稚的认为翅膀是一种毛绒绒的东西。能带我们飞上蓝蓝的天空，悠闲的坐在白白的云朵上。 长大后，我们固执的认为翅膀是一种载满希望的东西。能使我们乘着翅膀越过高山，跨过河流，飞向有梦的未来。 成年后，我们诚恳的认为翅膀是一种具有超能量的东西。能让我们驾驭着翅膀战胜更多的竞争对手，直至的飞上顶峰。 翅膀总是神奇的，无论是在儿时的眼中抑或是成年后的心中。 现在，我发现我有一双翅膀。一双隐形的翅膀。它指引我飞向明天，飞向未来。尽管途中会遇到很多困难，但一种毅力激励着我前进。很多人没有坚持，便在这一座山峰前坠落了，而我有我超越的 翅膀，助我度过绝望，飞越山峰。 其实每个人身上都有一双隐形的翅膀，取决于你是否发现它，运用它。 张开翅膀，放飞梦想，带你自由飞翔，到达一个任心灵翱翔的世界…… 会当凌绝顶，一览众山小。——杜甫 “我的未来不是梦，我认真的过着每一分钟”，每当我听到《我的未来不是梦》这首歌曲，我的理想不由得放飞了起来。当一名人 民教师，是我最大的理想。 高中 我现在是为初中二年级学生，再过一年多就要考高中。我的目标是灵宝一高。 从现在开始，我要分秒必争，积极乐观的完成初中教学任务，还要努力培练自己的独立自主能力，我坚信“阳光总在风雨后”经过 我长期的奋斗，我一定会成功。 大学 我的第二梦想是考上清华大学，清华大学人才济济，我在他它里可以学到很多的知识。大学能成就我的人生，在大学里，我可以实 现我的梦想，放飞我的梦想。 我时刻准备着，时刻努力着，时刻拼搏着。 教师 “教师是人类灵魂的工程师”，从小就树立了远大的梦想，当一名人民教师。为千千万万的学子传授知识。 在儿时，爷爷经常给我讲一些带有一定哲理的故事，虽然我那时听不懂故事中的哲理，但我完全可以把爷爷给我讲的故事叙述下来，爷爷听后两眼瞪圆，十分惊讶，就抚摸着我的头悄悄对我说：“不 愧为我的好孙儿，你真是当教师得料，你真是太棒了。”我的心不 由扑通扑通地跳了起来，不由的喊了起来：我是人民教师。 化工厂安全生产演讲稿范文 安全生产是安全与生产的统一，其宗旨是安全促进生产，生产必须安全。以下是小编整理的化工厂安全生产演讲稿范文，欢迎大家阅读。 化工厂安全生产演讲稿范文一： 尊敬的各位领导、同事们： 我演讲的题目是：打牢化工企业安全基础，是构建化工企业安全长效机制的根本。 首先，我认为大家能站在这里都是幸运的，为什么这么说呢?比起现在躺在医院里的人，我们是幸运的;比起灾区的人们，我们是幸运的。 安全是企业之魂，是企业生存与发展的基础。员工的人身安全得不到保障，企业就无法发展壮大;公民的人身安全得不到保障，国家就无法繁荣富强。人是以个体的形式出现在社会上的，社会上的每一个公民就如同珠子，和谐顽强的生命力将珠子串起来，形成一个不可分割的生命体。线一旦没有了生命力，珠子便滑落下来，也就不存在这个生命体了。所以我们每个人无论在社会中还是在企业中的力量是不容忽视的。 领导和同志们，作为化工行业的一员，有几起事故我本想忘记，更不愿向人们提起，但今天我要再一次提起：1984年12月3日,印度一化工厂，由于工人操作失误，异氰酸甲酯大量泄露，致使2500多人死亡，5万多人眼睛失明;2005年，中石油吉林石化分公司双苯厂发生爆炸，造成8人死亡，60人受伤，并引发松花江水污染事件;今年8月29日，广西宜州化工厂爆炸事故，造成20人遇难。几起化工事故虽然离我们越来越远，但那一幕幕惨剧仿佛就在眼前，遇难者那一具具冰冷的尸体，一张张因极度痛苦变得扭曲的脸，亲人们那一声声嚎哭，还在叩击着我们的心。领导和同志们，几起化学事故产生的原因虽然不同，但共同点却都是化工企业安全基础不牢。 基础不牢地动山摇。胡锦涛总书记在党的十七届三中全会上指出："人命关天，绝不能把人的生命当儿戏"。胡总书记的指示，充分体现了科学发展观以人为本的核心要求。可是，在现实生活中，少数化工企业，只注重生产，而忽视安全，生产不讲科学。土办法管理，老经验办事，无视标准和规范。人们常说：安规本是血染成。面对成千上万条鲜活的生命，用鲜血和泪水书写的操作规程，有的人总是熟视无睹，麻木不仁。"小型分散，少量多次勤运走"，烟花爆竹安全生产的"十一"字诀。短短的十一个字，却保证了不知道多少企业财产和工人生命的安全。美国杜邦公司是一个生产炸药的军工企业，可是杜邦老板却敢夸口说：在杜邦公司上班比在马路上散步还安全，因为杜邦有一整套保证企业安全运转的规范，即使放一只桶都要放在指定的圆圈。我们危化处在科学发展观学习讨论时，得出了这样的结论：危化企业最危险，危化企业难监管，只有安全才能生产，规范生产才能确保安全。 邓小平同志在1988年9月就提出了：科学技术是第一生产力的科学发展观思想。很多化工事故都是由于设备落后，科学技术低下造成的。实行科技兴安，大力引进新工艺，提高安全装备水平和科技含量，是我们刻不容缓的责任。提高化工设备自动化程度，优化生产工艺，创造一流信息化化工企业，打造数字化化工企业，是化工企业安全发展的唯一出路。 人才是科技进步的第一资源，是安全生产的根本基础。可是个别化工企业领导对安全工作认识不到位，管理不到位，措施不到位。致使企业管理松弛，作风涣散，不讲科学，违章蛮干。但随着人才强企战略的实施，人才在企业安全工作中的地位越来越重要，也使**安全工作插上了科技的翅膀。领导和同志们，安全没有后悔的机会，失误只会留下千古遗憾。在这里我要大声疾呼：生命诚可贵，安全大于天。 曾给他们讲看过的一篇文章，至今还记忆犹新，某火电公司在一化工工厂施工时，一位日本专家曾这样说施工人员："你们中国人的确有不怕死的可贵精神，在施工现场有不戴安全帽的现象。在日本，厂长，经理开会时安全帽都系得紧紧的。"这是对违章现象的莫大讽刺。它一针见血地言明了一些人安全意识的淡薄与无知，对自己的轻视就是对家庭和社会的犯罪。安全的警钟要常鸣，奉劝可叹的"勇士们"，收起你的蛮干和无知吧!有人说：安全生产的难点在我们自己，在我们自身的安全意识。仔细想想不无道理今天。"安全生产月"活动的展开，《安全生产法》的颁布实施，"两票三制"的严格执行。。。 这不都是为了搞好安全生产，领导和职工们用血的教训组成的努力与决心。安全的 新闻写法——消息写作 各位同仁，大家下午好！今天我很荣幸坐在这里同大家一起学习探讨有关新闻的写作技巧，但愿我讲的内容对各位有点启发。分两部分：一是消息，二是通讯。 天下文章，总体来说，都是一个写什么、怎么写的问题。写什么不仅是内容，还有一个形式问题；怎么写是技术问题。新闻是文章种类中一种特殊的文体，怎么写又有它特别的规范。是不是不自由了呢？不是，规范只是一个大笼子，在笼子里可以自由飞翔。 新闻是思想的产物，是意识形态。不是纯客观，不可有闻必录。同时，新闻不是公文，不是法律，不是判决书。读者自由地接受新闻事实，自由地作出判断。新闻以事实形成舆论，左右社会，“人言可畏”，“千夫所指，不疾而亡。”新闻写作提高表达技巧十分重要。 在这里，我先介绍一下消息的写作，这是目前适用最广泛的一种新闻写作方式。对于我们这些从事新闻报道的基层通讯员来说，也是最常用的文体，最容易发稿见报的文体。困为通讯较消息篇幅长、覆盖面大，像我们基层的乡镇、县直单位，一般很难被上级新闻单位采用。 一、什么是消息。 1、消息的定义。消息，就是用最简要和迅速的手段报道最近发生事件的一种新闻宣传文体。也就是说新闻消息就是告诉人们发生了什么，报道最近发生的事实。狭义的新闻就是指消息，它是新闻体裁的重要形式，是报纸和广播电视新闻的主角，其它新闻报道如通讯、广播稿、新闻评论等是它的发展和补充。学会消息写作便意识着掌握了打新闻写作大门的钥匙。我们初学新闻的同志在看报读报时，看到的“本报讯、本刊讯、新华社南昌讯、据**社**讯”等开头的，都称之为消息，我们常说的“豆腐块”，任何一张报纸都有若干条消息。 2、消息的特点：（一）采写发稿迅速、及时，叙事直截了当，语言简洁明快，篇幅短小；（二）消息5W+1H，whe何时、where何地、who何人、what何事、why何故、how如何；（三）在结构上，消息一般由标题、导语、主体、背景和结尾五个部分组成，有“倒金字塔结构”与“非倒金字塔结构”两大类。 3、消息的种类：(一)动态消息：也称动态新闻，这种消息迅速、及时地报道国内国际的重大事件，报道社会主义建设中的新人新事、新气象、新成就、新经验。动态消息中有不少是简讯(短讯、简明新闻)，内容更加单一，文字更加精简，常常一事一讯，几行文字。(二)综合消息：也称综合新闻，指的是综合反映带有全局性情况、动向、成就和问题的消息报道。 (三)典型消息：也称典型新闻，这是对某一部门或某一单位的典型经验或成功做法的集中报道，用以带动全局，指导一般。(四)述评消息：也称新闻述评，它除具有动态消息的一般特征外，还往往在叙述新闻事实的同时，由作者直接发出一些必要的议论，简明地表示作者的观点。记者述评、时事述评就是其中的两种。 以上四类消息，以动态消息较易写作，大家可以经常练习写一些，从实践中提高新闻写作能力。 尊敬的各位评委、各位老师： 大家上午好！今天我给大家带来的故事是《我的科技梦》。 夜深了，万籁俱静，人们都甜蜜的睡熟了。忽然，从书房里传来一阵吵闹声，把我都给吵醒了！我竖起一耳朵一听，原来是我家三台电脑在吵架呢！怎么回事，赶紧起床去瞧瞧。 看！台式电脑正得意洋洋的唱着歌呢：“我的本领高，我的体积大！上网玩游戏，办公查资料。累了看电影，烦了听听歌。主人有了我，啥都不用怕！”“别唱了别唱了！就你那点德行，有我能耐大吗？”笔记本不屑的翻了翻白眼：“看你那笨重的身体！别忘了，我可相当于主人的小秘书。主人上哪都要带着我呢！”笔记本一副自恋的样子，一旁的平板电脑早就沉不住气了。“别争了别争了！你们的本领我都有！主人最钟爱的是我才对呢！他走路、坐车的时候都用得着我呢！”平板电脑完全不理会台式和笔记本嫉妒的眼神，“记得上次，主人还带我参观了中国科技展览馆，那叫一个爽啊！”台式和笔记本显然被吸引住了，由嫉妒转为羡慕：“真的啊？那儿可能看到我国最先进的高科技啊！”“当然咯，航空火箭、人造卫星、宇宙探测器，还有磁悬浮列车，那是科技的盛典，应有尽有！”台式和笔记本电脑再也不说话了，尤其是台式电脑，委屈得眼泪都快掉下来了。这时电大叔闻讯赶来：“都别吵了，大家都是好兄弟。你们都为主人作出了贡献，不应该揪住别人的短处不放，更不能骄傲自满。大家都是中国科学的产物，科技的发展才造就了我们。何况刚才说的那些高科技产品，哪一个作用不比我们强？” 吵闹声渐渐平息，原来刚才是我的一个梦。梦醒来了，我的心里却久久不能平静。 是啊，中国高科技发展如此之快，就以电脑来说吧，听爸爸说，十年前他都还没见过电脑呢。而这只是我国科技发展的一个缩影，也是我们民族复兴的一个缩影。中华儿女们正依靠着他们的无穷智慧和不懈努力，在走向伟大复兴的路上，在实现梦想的路上，迈着坚定的步伐，留下一串串脚印。作为中国未来希望的我们，一定要脚踏实地，努力学习，向着前进的方向，努力！篇二：2015中国梦演讲稿：实干铸就科技强国梦 2015中国梦演讲稿：实干铸就科技强国梦 第一 中国梦演讲稿：实干铸就科技强国梦 实现“中国梦”是中华儿女的美好夙愿，是科技工作者的理想追求，离不开科技的驱动，离不开知识的力量。科学技术作为第一生产力，已成为当代经济发展的决定因素，也是中华民族实现“中国梦”的先决条件。“中国梦”的基本内涵包括国家富强、民族振兴、人民幸福，这三点的前提首先是“强军梦”。军强则民安，这是自鸦片战争以降170多年来中国命运跌宕起伏的深刻教训，也是中国人民在不屈不挠、艰苦奋斗中得到的经验启示。军强国富靠的是什么？靠得就是科技，只有强大的科技力量才能铸就起钢铁长城般的国防力量，只有强大的科技力量才能承载着中国经济的飞速腾飞，只有强大的科技力量才能实现中华民族真正的伟大复兴。 内江市农科院的老一辈科学家胸怀理想、淡泊名利，献身科技事业，投身国家建设，以不懈奋斗精神和卓越科技成就实现了自己的报国之志，实现了内江农科院昨日的辉煌。我院现今的广大科技工作者也追逐他们的足迹，为实现内江市农科院的再次腾飞而不断弘扬科学精神，志存高远、脚踏实地、潜心钻研，努力实现自己心中那伟大的“中国梦”。我身为内江农科院蔬菜所的科研工作者，我热爱我的工作，我的“中国梦”是通过科研育种，繁育出更多更好的甘薯蔬菜新品种，并研究出相应的高新现代化配套栽培技术，并加以推广示范，能够为农户带去丰厚的收益，为四川特别是内江地区特色保健蔬菜产业提供强有力的科技支撑作用，能产生较高的经济效益和社会效益。 身为中华民族伟大复兴“排头兵”——科技工作者的一员，我将在科研工作中志存高远、脚踏实地、潜心钻研，通过实干铸就自己心中的“中国梦”。古人云：天下大事必作于细，古 企业关于安全生产的演讲稿演讲是在公众面前就某一问题发表自己的见解的口头语言活动。今天一些演讲稿，欢迎大家围观参考，想了解更多，。 尊敬的各位领导，各位同事，各位友人。 我们联力公司在公司各级领导的指挥下，在各位员工的积极努力下，我们圆满的完成了又一个百日安全活动。成绩是可喜的，但是我们不能骄傲，我们要更加的努力学习，积极探讨，追寻安全的真谛，让我们再次的研讨一下带给我们幸福安康的安全，到底是什么? 安全是什么?安全是一种态度。我们经常讲“安全第一”。这就是我们的态度，也是我们的原则。安全是保证我们事业顺利完成的法宝，安全是我们取得效益的前提，安全对我们来说至关重要。因此我们就要事事讲安全、时时讲安全,不重视安全的后果是无法估量的、是要付出沉痛代价的。我们不能把安全第一只放在口头，只做成标语写的哪里都是，我们要实实在在的在思想里刻上安全第一，在做每件事前都要考虑安全，在工作的每时每刻不忘安全，特别是有违章违纪没有什么的思想念头出来的时候、在冒一次险不会出问题的时候，这时候想一下安全第一，我想很多事故都是可以避免的。 安全是什么?安全是一种经验。每出一个事故，都能总 结一二三条教训，日积月累，就成了我们的规章。换一种说法，血的教训换来了我们的规章制度，我们靠规章制度来保证我们的安全。事故都是违章造成的，我们要树立防事故、保安全的思想，处处想在前、安全关口前移，真正把别人的事故当作自己的防止事故的经验，人类之所以进步，就是人类善于总结、并从总结中得到进步。我们也要善于在容易出现问题的时候想一下，别人在处理这样问题是怎么做的，我这样做的后果是什么?这样我们才会不断提高自己、完善自己。 安全是什么?安全就是一切。有的同志说了，这话说得大了，安全怎么可能就是一切呢?大家都可以想到：没有安全，我们的生命有保障吗?我们的企业效益有保障吗?我们的队伍稳定有保障吗?说得实在一点，保证不了安全，我们谈什么家庭幸福?谈什么个人理想?我们把握住了安全，我们才有现在的一切，我们才有美好的明天! 追根结底，安全就是我们工厂的命根子，就是我们的每个人的命根子。我们大家要在各自的工作岗位上，干好自己的本职工作，在工作上真正树立安全第一的思想，克服种种困难，吸取别人的教训，遵章守纪、严格把关、搞好自控互控，从工作的每一分钟入手，从每个安全月入手，最终实现一个个安全百天、安全千天，实现我们的奋斗目标。另外，安全的目标也不是靠一个人、一天、一件事就能实现的，这 消息导语的写法 导语是消息的重要组成部分，是消息的开头，通常是指消息的第一个自然段。消息导语的写作，是新闻记者的基本功。美国大学新闻学院的大学生或研究生要花一年的时间专门学习导语的写作。许多人构思和写作导语的时间要占据通篇稿件的三分之一到一半。由此可见导语写作的难度和重要性。 导语最基本的要求是言简意赅，即用最简洁凝炼的语言将消息中最新鲜、最主要、最精彩、最生动、最吸引人的新闻事实表现出来。导语的写法千变万化、灵活多样。概括起来，大致可以分为下列8种。 一、概要式：即用叙述的方式来归纳概括新闻的要点。 如：新华社1949年4月22日电人民解放军百万大军，从一千余华里的战线上，冲破敌阵，横渡长江。 再如：本报讯中国科学院昆明动物研究所培育计划中的第一只白猴于5月1日降生。（1988年全国好新闻消息二等奖，原载《云南日报》1988 年6月29日一版） 再如：本报讯（记者李捷）613万考生迎来了他们一生一博的时刻-2003年非典时期的正常高考今天静静拉开帷幕。（第十四届中国新闻奖二等奖消息作品） 一、描写式：即用现场目击、白描勾勒的方式来切入。 如：新华社北京1982年7月16日电（记者郭玲春）鲜花、翠柏丛中，安放着中国共产党员金山同志的遗像。千余名群众今天默默走进首都剧场，悼念这位人民的艺术家o（第四届中国新闻奖消息一等奖作品） 再如：本报讯（记者健吾）古埃及的金字塔、法国的巴黎圣母院、缅甸的仰光大金塔、加拿大的尼亚加拉瀑布，还有列宁的墓、白求恩的故居以及日本的劈啪舞……人们不用出国，在五泉山公园文昌宫举行的《劳崇聘外国风光写生展览》上，便可欣赏到外国的名胜古迹，领略到外国的风土人情。（原载《兰州晚报》1985年10月8日四版）再如：本报讯（记者健吾）大西北一个偏僻山村的崎岖小道上，一支娶亲的人马抬着花轿，拥着新郎入场，由此引出一个凄凉的、为人们所熟悉 却又弄不清发生在何年何月的故事。这是省歌剧团为建国40周年正在排练的献礼之作——《阴山下》的序幕o（《兰州晚报》1989年3月5日四版） 三、提问式：即先提出问题，引出悬念，进而解答。 2021放飞梦想演讲稿精彩篇 梦想，如一个星星，一眨就是一个故事;梦想，似一层台阶，让我们登上智慧之峰;梦想，像一滴甘露，滋润了我的内心;梦想，若一颗神秘的种子，在我的心里慢慢地生根发芽……每个人都有自己的梦想，而且截然不同。什么?你问我的理想是什么?那就是当一名作家! 小时候，刚咿咿呀呀地学会说话，就迫不及待地想看书，在二年级时，就已经开始了读书，每当我看到好的文章，就特别羡慕文章的作者，也想写出这样的文章。于是，梦想的种子便深深地埋在了我的心里。在三年级时，就已经开始了写作文，但我在写作文方面不是很有天赋。到了四，五，六年级时，也就相当于步入了更高的阶梯了，作文也随着年级的变化而变化着。 我知道写好一篇文章要有很好的基础，而这个基础就是多看书，多积累好词好句，并且运用到实际中去。于是，我为了这个梦想一直努力着。在暑假时，我已经把四大名著之一——《西游记》，看完了;每个周末。我都会央求妈妈带我到新华书店去看书或买一些有利于我写作的书。于是，梦想的种子便悄悄地生根发芽。 大家都有可能认为这是遥不可及的事情，但是我相信，只要我肯努力，坚持不懈就一定能成为像冰心像老舍那样大名鼎鼎的作家的。从现在开始，让我们一起放飞梦想，为梦想而奋斗吧! 人生是一条崎岖的山路，有着太多太多的路口，于是便有了一个又一个梦想。人生是一条广阔的大海有着太多太多的航向，于是便有了追求的目标。不管风景变幻，不变的是我的梦想。不管昼夜更替，我心依旧飞翔。 我，平凡的男孩，却有一个不平凡的梦想——当作家。小时候，我将这个梦想隐藏，如今，我要放飞梦想。 春雨，打湿了屋檐。我冒着倾盆大雨穿梭一个又一个补习班。目的，让我的写作能力更加提高!小记者补习班，作文提高班，语文培优班。凡是跟文学有关的，我都要参加，但一点也不知疲惫和辛苦，因为这是在为梦想努力! 夏风，带来胜利的讯息。我的一遍文章在报纸上发表了。这个消息伴着夏的脚步悄悄来到我的身边。是的，我的努力没有白费!我的汗水没有白流，我第一次站在胜利的最顶端，露出灿烂的笑容。 秋夜，迎来了淡淡的哀伤。一篇有一篇报社的退稿，让我的泪一滴一滴划过。心中仿佛针刺般疼痛。我对自己感到失望。人生这片沃土上我已播下放飞梦想作文500字希望的种子，为何看不见胜利的果实?我的脚步已不想往前走。我，累了。看着桌子上写的文章，凝结了我多少汗水和心血，有谁知道?这时，我看见桌角旁写的字：无论安全生产演讲稿(完整版)
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