The oxygen evolution, thermal dissipation, and photochemical energy storage of three hybrid poplar clones, namely the triploid clone B342, the diploid clone B11 [(Populus alba×P. glandulosa)×(P.tomentosa...The oxygen evolution, thermal dissipation, and photochemical energy storage of three hybrid poplar clones, namely the triploid clone B342, the diploid clone B11 [(Populus alba×P. glandulosa)×(P.tomentosa×P.bolleana)], and the triploid clone B346 [(P.tomentosa×P. bolleana)×(P. alba×P.glandulosa)], under light stress were studied using photoacoustics. The oxygen evolution signal and photochemical energy storage varied negatively with the pretreatment_PFD (photon flux density), whereas the thermal signal varied positively with the pretreatment_PFD. Photochemical energy storage was reallocated to PSⅡ more than to PSⅠ, while the photochemical energy storage in PSⅠ was more stable than that in PSⅡ when subjected to light stress. The inhibitors streptomycin (SM), dithiothreitol (DTT) and sodium fluoride (NaF) could all affect the oxygen evolution signal. Clones B11 and B342 were more resistant to light stress than clone B346.展开更多
The wood basic density, cellulose content and fiber form were investigated for all sample trees at breast height (1.3 m) in seven poplar clones, and at 0 (butt), 5.6, 9.6, 13.6, 17.6, 19.6 and 21.6 m for clone Nanlin-...The wood basic density, cellulose content and fiber form were investigated for all sample trees at breast height (1.3 m) in seven poplar clones, and at 0 (butt), 5.6, 9.6, 13.6, 17.6, 19.6 and 21.6 m for clone Nanlin-95 and Nanlin-895, respectively, for providing information on variation patterns of wood density, fiber characteristics and holocellulose content within trees and among clones. The results showed that significant variations about wood density, cellulose content, fiber diameter and the ratio of fiber length to diameter existed among poplar clones examined. Variance analysis indicated that there were significant differences in wood basic density, fiber length, fiber diameter and cellulose content among the growth rings, which had an increasing tendency along the direction from pith to bark. The significant differences also existed in wood basic density, fiber length and fiber diameter at different tree height. The mean wood basic density had a general increase trend with increasing height of trees and the lowest was found at the base, while fiber length and fiber diameter had a general decline pattern with increasing height of trees and the biggest value was observed at the height of 5.6 m. Regression analysis indicated that the relationship between examined wood properties and growth ring number (cambial age), and the relationship between examined wood properties and tree height can be described by polynomial functions.展开更多
With four poplar clones, namely 84-323 (Populus deltoides cv. ?4-323?, 84-324 (Populus deltoides cv. ?4-324?, 79-35 (Populus ?euramericana cv. ?9-35?, and I-69 (Populus deltoides cv. 慙ux?I-69/55) as a control, resear...With four poplar clones, namely 84-323 (Populus deltoides cv. ?4-323?, 84-324 (Populus deltoides cv. ?4-324?, 79-35 (Populus ?euramericana cv. ?9-35?, and I-69 (Populus deltoides cv. 慙ux?I-69/55) as a control, researches on cold, drought and salt resistance of the clones were conducted. Electrolyte permeability under a series of low temperatures, relative water loss rate of detached leaves with time series and survival rate and growth performance in salt soil were measured. The results showed that 84-323, 84-324 and 79-35 were resistant to cold as same as I-69 (CK) and more resistant to drought and salinity than I-69 (CK).展开更多
Aims Poplars grownin North Chinamay experience water-deficient periods in their life cycle.The aim of the present paper was to quantify the response of three clones to different watering regimes and to determine which...Aims Poplars grownin North Chinamay experience water-deficient periods in their life cycle.The aim of the present paper was to quantify the response of three clones to different watering regimes and to determine whichcloneamongthe three is the best adapted to drought conditions.Methods Three hybrid poplar clones(clone DN-34,R-247 and OP-367)were used in the present experiment.The seedlings of the three clones were grown under four watering regimes:control(well watered,100%field water capacity(FC))and three drought treatments(drought stress I,50%FC;drought stress II,40%FC;drought stress III,30%FC).Changes in morphological,physical and biochemical indicators of the three hybrid poplar clones were investigated.Important Findings Drought treatment(50%,40%and 30%FC)decreased net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(gs),shoot height,total biomass and chlorophyll(Chl)content in all the three clones and it increased activities of antioxidant enzymes and free proline content.The highest values of the above-mentioned morphological and physiological parameters were recorded in clone OP-367 under 30%FC,followed by clone DN-34 and R-247.Relative leaf water content(RWC)and stem diameter(sd)markedly declined in clone R-247 and DN-34 under drought stress I,II and III,whereas RWC and sd declined in clone OP-367 only under drought stress II and III.Clone OP-367 had more RWC and sd than DN-34 and R-247.Only the 30%FC induced an increase in the root-to-shoot ratio(rs)and water use efficiency(WUE)in all the three clones.OP-367 was the most efficient clone in water absorption and use,for plants of the clone had the highest values of rs and WUE.Our data demonstrate that among the three clones,OP-367 was better able to maintain photosynthesis and growth and lower the damage caused by drought.展开更多
Both of straight and inclining poplar clone 107 tree were selected for studying materials in this paper.The optimal pulping conditions was established by orthogonal experimental design both for normal wood and tension...Both of straight and inclining poplar clone 107 tree were selected for studying materials in this paper.The optimal pulping conditions was established by orthogonal experimental design both for normal wood and tension wood,and the quality of pulping and paper-making between normal wood and tension wood was compared with each other. Finally,potential application for improving paper quality of tension wood through increasing beating revolutions was discussed.The result showed that the optimal cooking condition for normal wood was alkali concentration 15%,the highest temperature 164℃,time at highest temperature 75 min,and for tension wood it was alkali concentration 13%,the highest temperature 160℃,time at highest temperature 40 min.Path coefficient of effect of alkali concentration both on pulp yield and kappa value was significant at different levels.By comparison between average result of normal wood and tension wood in quality of pulping and paper-making,it was found that tension wood had higher pulping yield and lower kappa value than normal wood. Furthermore,for all mechanical properties of paper, normal wood hold higher value than tension wood, and even near two times than tension wood,such as burst index and tensile index.However,difference of tear index was quite narrow.Result of one way ANOVA showed that difference of burst index and tear index between normal wood and tension wood was significant at the 0.001 level,of tear index was significant at the 0.05 level.Based on observation of cross surface of paper,it was assumed that contribution of gelatinous layer to rigidity of single fiber had hampered collapse and compression of fiber during paper formation,which is essential for exerting combination between fibers in paper.So, mechanical properties of tension wood paper were decreased accordingly.However,owing to high cellulose content of gelatinous layer,tension wood was easier to pulping than normal wood.Mechanical properties of tension wood paper could be improved by increasing beating revolutions,the final value even close to normal wood paper.But,the increasing effect had a limit.展开更多
The microfibril angle of seven poplar clones was determined by using X-ray diffraction technique. Microfibril angle, wood basic density, fiber length, fiber width and cellulose content were assessed for every growth r...The microfibril angle of seven poplar clones was determined by using X-ray diffraction technique. Microfibril angle, wood basic density, fiber length, fiber width and cellulose content were assessed for every growth ring at breast height for all sample trees. Significant variation in microfibril angle was observed among growth rings. Mean microfibril angle (MFA) at breast height varied from 7.8?to 28?between growth rings with cambial age and showed a consistent pith-to-bark trend of decline an-gles. Analysis of variance also indicated that there were significant differences in wood basic density, fiber length, fiber width and cellulose content between the growth rings, which had an increasing tendency from pith to bark. Correlations between MFA and examined wood properties were predominantly large and significant negative (?0.01), and the coefficients were -0.660 for cellulose content, -0.586 for fiber length, -0.516 for fiber width and -0.450 for wood basic density, respectively. Regression analysis with linear and curve estimation indicated that a quadratic function showed the largest R2 and the least standard error for describing the relationships between microfibril angle and measured wood properties, and the correlation coefficients were over -0.45 (n=125). The results from this study suggested that microfibril angle would be a good characteristic for improvement in the future breeding program of poplars.展开更多
To improve the productivity of poplar planta- tions, a field experiment of split-plot design with four tree spacings and three poplar clones was established, and four soil enzyme activities and microbial biomass were ...To improve the productivity of poplar planta- tions, a field experiment of split-plot design with four tree spacings and three poplar clones was established, and four soil enzyme activities and microbial biomass were monitored in the trial. Soil enzyme activities, in most cases, were significantly higher in topsoil （0-10 cm） than in lower horizons （10-20 cm）. Soil cellulase, catalase and protease activities during the growing season were higher than during the non-growing season, while invertase activity followed the opposite trend. Soil invertase, cellulase and catalase activities varied by poplar clone but soil protease activity did not. Cellulase and protease activities in the plantation at 5 × 5 m spacing were significantly higher than in the other spacings. The highest catalase activity was recorded at 6 × 6 m spacing. At the same planting density, invertase activity was greater in square spacings than in rectangular spacings. Soil microbial biomass was also significantly affected by seedling spacing and poplar clone. The mean soil MBC was significantly lower in topsoil than in the lower horizon, while MBN showed the opposite pattern. Significantly positive correlations were observed among soil cellulase, protease and catalase activities （p 〈0.01）, whereas soil invertase activity was negatively and significantly correlated with cellulase, protease and catalase activities （p 〈 0.01）. Soil microbial biomass and enzyme activities were not correlated except for a significantly negative correlation between soil MBC and catalase activities. Variations in soil enzyme activity and microbial biomass in different poplar plantations suggest that genotype and planting spacing should be considered when modeling soil nutrient dynamics and managing for long-term site productivity.展开更多
Poplar leaf defoliator, Clostera fulgurita （Walker） larvae were reared on three Populus deltoides clones （PL1, PL5 and PL7） in the laboratory. The nutritional indices were computed for working out the relationship...Poplar leaf defoliator, Clostera fulgurita （Walker） larvae were reared on three Populus deltoides clones （PL1, PL5 and PL7） in the laboratory. The nutritional indices were computed for working out the relationship between food consumption and growth rate of 3rd, 4th and 5th instar larvae on three clones. The result showed that the consumption index （CI）, approximate digestibility （AD）, growth rate （GR）, relative growth rate （RGR） and efficiency of conversion of ingested food （ECI） decreased with the increase in the age of the larvae. Efficiency of conversion of digested food （ECD） increased with increase in age of the larvae. GR and RGR varied significantly, indicating that larval development was enhanced on PL1 as compared to PL5 ＆ PL7. The values of AD, ECI and ECD were not affected by the different clones. Feeding and growth indices could be useful to define a defoliation prediction model.展开更多
Based on the results of more than ten year’s scientific research and practice, some key techniques for cultivating poplar veneer glued wood were summarized systematically. The results were as follows: (1)Selecting ap...Based on the results of more than ten year’s scientific research and practice, some key techniques for cultivating poplar veneer glued wood were summarized systematically. The results were as follows: (1)Selecting appropriate poplar clones for various cultivation zones according to their growth rate and wood quality. (2)Choosing good sites being suitable for poplar clone growing (at least SI≥18?m). (3)Adopting reasonable planting density which can produce more timbers to meet the need of plywood(the tree spacing should be more than 5?m×5?m). (4)Using correct planting methods for different soil conditions, however, large seedling with 2 year old root and 1 year old stem (seedling height>4?m)were advocated. (5)Taking effective measures to tend the stand, the most effective measure was interplanting with crops. (6)Pruning was neccessary to produce non node timber, but pruning method, pruning intensity and pruning season should be controlled properly. If the 6 measures mentioned above were carried out, the poplar forests with a high yield and high quality could be ensured. In order to provied some theoretical basis for cultivating poplar veneer glued wood, 4 optimum cultivation patterns were also established using the method of two dimensions system.展开更多
It is an effective way to save and take full advantage of limited water resource in China by breeding and applying water-saving cultivars of plant. Relative studies showed that water use efficiencies （WUE） of poplar...It is an effective way to save and take full advantage of limited water resource in China by breeding and applying water-saving cultivars of plant. Relative studies showed that water use efficiencies （WUE） of poplar were obviously different among clones, but its physiological mechanism was not very clear. Therefore, an experiment was conducted in field to probe it through surveying WUE of different age leaves, diurnal dynamics of leaf WUE of 4 clones with the portable photosynthesis system of LI-6400, and the experimental clones were XMH4 （Populus deltoides×P.nigra）, MH8 （P.trichocarpa×P.deltoides）、XMH12 （P.deltoides×P.nigra）、DMH3 （P. trichocarpa× P.nigra）. The results indicated that: 1) WUE was remarkably different between clones, and the WUE of XMH12 and DMH3 was higher than that of XMH4 and MH8. 2) In general, the leaves distributing at middle part of stem had higher WUE than those locating at two ends of stem. This reflected that WUE changed from low to high, then to low with leaf aging. 3) Diurnal dynamics of WUE generally declined from morning to evening. 4)The main physiological factors to influenc WUE were stomatal aperture, intercellular CO2 concentration, and activity of photosynthestic system. And the ecological factors included PAR intensity, temperature, air humidity,etc. It was clear that the regulation of stomatal aperture was central to the water use efficiency. Light, temperature, humidity and carbon dioxide concentration will all act in some way either directly or indirectly on the stomatal aperture, together with internal circadian rhythms, leaf water status and xylem borne signals.展开更多
文摘The oxygen evolution, thermal dissipation, and photochemical energy storage of three hybrid poplar clones, namely the triploid clone B342, the diploid clone B11 [(Populus alba×P. glandulosa)×(P.tomentosa×P.bolleana)], and the triploid clone B346 [(P.tomentosa×P. bolleana)×(P. alba×P.glandulosa)], under light stress were studied using photoacoustics. The oxygen evolution signal and photochemical energy storage varied negatively with the pretreatment_PFD (photon flux density), whereas the thermal signal varied positively with the pretreatment_PFD. Photochemical energy storage was reallocated to PSⅡ more than to PSⅠ, while the photochemical energy storage in PSⅠ was more stable than that in PSⅡ when subjected to light stress. The inhibitors streptomycin (SM), dithiothreitol (DTT) and sodium fluoride (NaF) could all affect the oxygen evolution signal. Clones B11 and B342 were more resistant to light stress than clone B346.
基金This study was supported by National Natural Science Foundation of China, (No. 30070616).
文摘The wood basic density, cellulose content and fiber form were investigated for all sample trees at breast height (1.3 m) in seven poplar clones, and at 0 (butt), 5.6, 9.6, 13.6, 17.6, 19.6 and 21.6 m for clone Nanlin-95 and Nanlin-895, respectively, for providing information on variation patterns of wood density, fiber characteristics and holocellulose content within trees and among clones. The results showed that significant variations about wood density, cellulose content, fiber diameter and the ratio of fiber length to diameter existed among poplar clones examined. Variance analysis indicated that there were significant differences in wood basic density, fiber length, fiber diameter and cellulose content among the growth rings, which had an increasing tendency along the direction from pith to bark. The significant differences also existed in wood basic density, fiber length and fiber diameter at different tree height. The mean wood basic density had a general increase trend with increasing height of trees and the lowest was found at the base, while fiber length and fiber diameter had a general decline pattern with increasing height of trees and the biggest value was observed at the height of 5.6 m. Regression analysis indicated that the relationship between examined wood properties and growth ring number (cambial age), and the relationship between examined wood properties and tree height can be described by polynomial functions.
文摘With four poplar clones, namely 84-323 (Populus deltoides cv. ?4-323?, 84-324 (Populus deltoides cv. ?4-324?, 79-35 (Populus ?euramericana cv. ?9-35?, and I-69 (Populus deltoides cv. 慙ux?I-69/55) as a control, researches on cold, drought and salt resistance of the clones were conducted. Electrolyte permeability under a series of low temperatures, relative water loss rate of detached leaves with time series and survival rate and growth performance in salt soil were measured. The results showed that 84-323, 84-324 and 79-35 were resistant to cold as same as I-69 (CK) and more resistant to drought and salinity than I-69 (CK).
基金State Forestry Administration of China(20030407).
文摘Aims Poplars grownin North Chinamay experience water-deficient periods in their life cycle.The aim of the present paper was to quantify the response of three clones to different watering regimes and to determine whichcloneamongthe three is the best adapted to drought conditions.Methods Three hybrid poplar clones(clone DN-34,R-247 and OP-367)were used in the present experiment.The seedlings of the three clones were grown under four watering regimes:control(well watered,100%field water capacity(FC))and three drought treatments(drought stress I,50%FC;drought stress II,40%FC;drought stress III,30%FC).Changes in morphological,physical and biochemical indicators of the three hybrid poplar clones were investigated.Important Findings Drought treatment(50%,40%and 30%FC)decreased net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(gs),shoot height,total biomass and chlorophyll(Chl)content in all the three clones and it increased activities of antioxidant enzymes and free proline content.The highest values of the above-mentioned morphological and physiological parameters were recorded in clone OP-367 under 30%FC,followed by clone DN-34 and R-247.Relative leaf water content(RWC)and stem diameter(sd)markedly declined in clone R-247 and DN-34 under drought stress I,II and III,whereas RWC and sd declined in clone OP-367 only under drought stress II and III.Clone OP-367 had more RWC and sd than DN-34 and R-247.Only the 30%FC induced an increase in the root-to-shoot ratio(rs)and water use efficiency(WUE)in all the three clones.OP-367 was the most efficient clone in water absorption and use,for plants of the clone had the highest values of rs and WUE.Our data demonstrate that among the three clones,OP-367 was better able to maintain photosynthesis and growth and lower the damage caused by drought.
文摘Both of straight and inclining poplar clone 107 tree were selected for studying materials in this paper.The optimal pulping conditions was established by orthogonal experimental design both for normal wood and tension wood,and the quality of pulping and paper-making between normal wood and tension wood was compared with each other. Finally,potential application for improving paper quality of tension wood through increasing beating revolutions was discussed.The result showed that the optimal cooking condition for normal wood was alkali concentration 15%,the highest temperature 164℃,time at highest temperature 75 min,and for tension wood it was alkali concentration 13%,the highest temperature 160℃,time at highest temperature 40 min.Path coefficient of effect of alkali concentration both on pulp yield and kappa value was significant at different levels.By comparison between average result of normal wood and tension wood in quality of pulping and paper-making,it was found that tension wood had higher pulping yield and lower kappa value than normal wood. Furthermore,for all mechanical properties of paper, normal wood hold higher value than tension wood, and even near two times than tension wood,such as burst index and tensile index.However,difference of tear index was quite narrow.Result of one way ANOVA showed that difference of burst index and tear index between normal wood and tension wood was significant at the 0.001 level,of tear index was significant at the 0.05 level.Based on observation of cross surface of paper,it was assumed that contribution of gelatinous layer to rigidity of single fiber had hampered collapse and compression of fiber during paper formation,which is essential for exerting combination between fibers in paper.So, mechanical properties of tension wood paper were decreased accordingly.However,owing to high cellulose content of gelatinous layer,tension wood was easier to pulping than normal wood.Mechanical properties of tension wood paper could be improved by increasing beating revolutions,the final value even close to normal wood paper.But,the increasing effect had a limit.
基金This research was supported by National Natural Science Foundation of China (Grant No. 30070616).
文摘The microfibril angle of seven poplar clones was determined by using X-ray diffraction technique. Microfibril angle, wood basic density, fiber length, fiber width and cellulose content were assessed for every growth ring at breast height for all sample trees. Significant variation in microfibril angle was observed among growth rings. Mean microfibril angle (MFA) at breast height varied from 7.8?to 28?between growth rings with cambial age and showed a consistent pith-to-bark trend of decline an-gles. Analysis of variance also indicated that there were significant differences in wood basic density, fiber length, fiber width and cellulose content between the growth rings, which had an increasing tendency from pith to bark. Correlations between MFA and examined wood properties were predominantly large and significant negative (?0.01), and the coefficients were -0.660 for cellulose content, -0.586 for fiber length, -0.516 for fiber width and -0.450 for wood basic density, respectively. Regression analysis with linear and curve estimation indicated that a quadratic function showed the largest R2 and the least standard error for describing the relationships between microfibril angle and measured wood properties, and the correlation coefficients were over -0.45 (n=125). The results from this study suggested that microfibril angle would be a good characteristic for improvement in the future breeding program of poplars.
基金funded by the National Key Technology R&D Program(2015BAD09B0203)the National Basic Research Program of China(973 Program,2012CB416904)by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘To improve the productivity of poplar planta- tions, a field experiment of split-plot design with four tree spacings and three poplar clones was established, and four soil enzyme activities and microbial biomass were monitored in the trial. Soil enzyme activities, in most cases, were significantly higher in topsoil （0-10 cm） than in lower horizons （10-20 cm）. Soil cellulase, catalase and protease activities during the growing season were higher than during the non-growing season, while invertase activity followed the opposite trend. Soil invertase, cellulase and catalase activities varied by poplar clone but soil protease activity did not. Cellulase and protease activities in the plantation at 5 × 5 m spacing were significantly higher than in the other spacings. The highest catalase activity was recorded at 6 × 6 m spacing. At the same planting density, invertase activity was greater in square spacings than in rectangular spacings. Soil microbial biomass was also significantly affected by seedling spacing and poplar clone. The mean soil MBC was significantly lower in topsoil than in the lower horizon, while MBN showed the opposite pattern. Significantly positive correlations were observed among soil cellulase, protease and catalase activities （p 〈0.01）, whereas soil invertase activity was negatively and significantly correlated with cellulase, protease and catalase activities （p 〈 0.01）. Soil microbial biomass and enzyme activities were not correlated except for a significantly negative correlation between soil MBC and catalase activities. Variations in soil enzyme activity and microbial biomass in different poplar plantations suggest that genotype and planting spacing should be considered when modeling soil nutrient dynamics and managing for long-term site productivity.
文摘Poplar leaf defoliator, Clostera fulgurita （Walker） larvae were reared on three Populus deltoides clones （PL1, PL5 and PL7） in the laboratory. The nutritional indices were computed for working out the relationship between food consumption and growth rate of 3rd, 4th and 5th instar larvae on three clones. The result showed that the consumption index （CI）, approximate digestibility （AD）, growth rate （GR）, relative growth rate （RGR） and efficiency of conversion of ingested food （ECI） decreased with the increase in the age of the larvae. Efficiency of conversion of digested food （ECD） increased with increase in age of the larvae. GR and RGR varied significantly, indicating that larval development was enhanced on PL1 as compared to PL5 ＆ PL7. The values of AD, ECI and ECD were not affected by the different clones. Feeding and growth indices could be useful to define a defoliation prediction model.
文摘Based on the results of more than ten year’s scientific research and practice, some key techniques for cultivating poplar veneer glued wood were summarized systematically. The results were as follows: (1)Selecting appropriate poplar clones for various cultivation zones according to their growth rate and wood quality. (2)Choosing good sites being suitable for poplar clone growing (at least SI≥18?m). (3)Adopting reasonable planting density which can produce more timbers to meet the need of plywood(the tree spacing should be more than 5?m×5?m). (4)Using correct planting methods for different soil conditions, however, large seedling with 2 year old root and 1 year old stem (seedling height>4?m)were advocated. (5)Taking effective measures to tend the stand, the most effective measure was interplanting with crops. (6)Pruning was neccessary to produce non node timber, but pruning method, pruning intensity and pruning season should be controlled properly. If the 6 measures mentioned above were carried out, the poplar forests with a high yield and high quality could be ensured. In order to provied some theoretical basis for cultivating poplar veneer glued wood, 4 optimum cultivation patterns were also established using the method of two dimensions system.
文摘It is an effective way to save and take full advantage of limited water resource in China by breeding and applying water-saving cultivars of plant. Relative studies showed that water use efficiencies （WUE） of poplar were obviously different among clones, but its physiological mechanism was not very clear. Therefore, an experiment was conducted in field to probe it through surveying WUE of different age leaves, diurnal dynamics of leaf WUE of 4 clones with the portable photosynthesis system of LI-6400, and the experimental clones were XMH4 （Populus deltoides×P.nigra）, MH8 （P.trichocarpa×P.deltoides）、XMH12 （P.deltoides×P.nigra）、DMH3 （P. trichocarpa× P.nigra）. The results indicated that: 1) WUE was remarkably different between clones, and the WUE of XMH12 and DMH3 was higher than that of XMH4 and MH8. 2) In general, the leaves distributing at middle part of stem had higher WUE than those locating at two ends of stem. This reflected that WUE changed from low to high, then to low with leaf aging. 3) Diurnal dynamics of WUE generally declined from morning to evening. 4)The main physiological factors to influenc WUE were stomatal aperture, intercellular CO2 concentration, and activity of photosynthestic system. And the ecological factors included PAR intensity, temperature, air humidity,etc. It was clear that the regulation of stomatal aperture was central to the water use efficiency. Light, temperature, humidity and carbon dioxide concentration will all act in some way either directly or indirectly on the stomatal aperture, together with internal circadian rhythms, leaf water status and xylem borne signals.
