Relative humidity(RH)plays a pivotal role in regulating plant transpiration by modulating stomatal conductance().Accurate modeling under varying RH conditions is essential for predicting plant water use and gas exchan...Relative humidity(RH)plays a pivotal role in regulating plant transpiration by modulating stomatal conductance().Accurate modeling under varying RH conditions is essential for predicting plant water use and gas exchange,with important implications for both agricultural management and bionic applications.In this study,field experiments were conducted to measure in plants exposed to moderate-and high-RH environments.The results demonstrated that is greater and transpiration rates are lower in high-RH environments than in moderate-RH environments.The response functions of stomatal conductance to environmental factors were further developed via a boundary line technique.These functions elucidate how stomatal conductance is correlated with environmental conditions.Specifically,stomatal conductance reaches saturation at a photosynthetically active radiation(PAR)of approximately 300 and 500μmol·m^(−2)·s^(−1) in both high-and moderate-RH environments.Furthermore,the vapor pressure deficit(VPD)threshold triggering stomatal closure was shifted by ambient RH,occurring at approximately 1000 Pa under high RH and 2000 Pa under moderate RH.This RH-dependent adjustment highlights the indirect yet critical role of RH in modulating stomatal sensitivity to atmospheric dryness.On the basis of the established response functions,stomatal conductance models tailored for high-and moderate-RH environments were constructed by extending the Jarvis empirical framework.These models offer improved predictive capacity for simulating plant physiological responses under diverse humidity conditions and provide new insights into the stomatal regulation of plants in natural field settings.展开更多
Stomatal behavior is a central topic of plant ecophysiological research under global environmental change. However, the physiological mechanism controlling the response of stomata to vapor pressure deficit （VPD） or ...Stomatal behavior is a central topic of plant ecophysiological research under global environmental change. However, the physiological mechanism controlling the response of stomata to vapor pressure deficit （VPD） or relative humidity （RH） has been inadequately understood till now. In this study, responses of stomatal conduc- tance （gs） to VPD in two species of trees （Fraxinus chinensis Roxb., Populus alba L. var. pyramidalis Bge.）in three different climate zones （Jinan with typical warm humid/semi-humid climate, Urumqi with temperate continental arid climate and Turpan with extreme arid desert climate） were measured. Levels of two phytohormones （abscisic acid, ABA; indole-3-acetic acid, IAA） in the leaves of the two tree species at these three sites were also measured by high performance liquid chromatography. The results showed that the responses of gs to an increasing VPD in these two tree species at the three sites had peak curves which could be fitted with a Log Normal Model （gs=a.exp（-O.5（In（DIc）lb）2）. The VPD/RH values corresponding to the maximum g, can be calculated using the fitting models for the two tree species in the three sites. We found that the calculated g, -VPD correlated nega- tively with relative air humidity in the three sites during the plant growth period （April to October 2010）, which showed the values of g,-max-VPD were related to the climate conditions. The prevailing empirical stomatal model （Leuning model） and optimal stomatal behavior model could not properly simulate our measured data. The water use efficiency in the two tree species did not show obvious differences under three very different climatic conditions, but the highest gs, photosynthetic and transpiration rates occurred in P. alba var. of Turpan. The sensitivity in re- sponse of g~ to VPD in leaves of the two trees showed positive correlations with the concentration of ABA, which implied that ABA level could be used as an indicator of the sensitivity of stomatal response to VPD. Our results confirmed that the prediction of the response of gs to VPD might be incomplete in the two current popular models. Therefore, an improved g, model which is able to integrate the results is needed. Also, the stomatal response mechanism of single peak curves of g~ to VPD should be considered.展开更多
Tropospheric ozone(O_(3))is a harmful air pollutant negatively impacting forest health,causing O_(3)-specific visible foliar injury(O_(3)VFI).Ozone monitoring in forests has usually implemented by passive samplers,alt...Tropospheric ozone(O_(3))is a harmful air pollutant negatively impacting forest health,causing O_(3)-specific visible foliar injury(O_(3)VFI).Ozone monitoring in forests has usually implemented by passive samplers,although they cannot detect the diurnal peak when a significant part of stomatal O_(3)uptake occurs.This results into uncertainties for the calculation of stomatal O_(3)uptake.This study compares the stomatal-flux-based POD1(phytotoxic ozone dose above a threshold of 1 nmol m^(-2)s^(-1))for forest trees/shrubs estimated from data collected by either passive samplers or active O_(3)monitors to evaluate O_(3)damage to plants in terms of O_(3)VFI in the Southern Alps.The study was conducted over two years(2018-2019)in a mountainous Alpine area(Valle Stura,Italy).An integrative monitoring station for active O_(3)monitoring,as well as passive O_(3)monitors,were installed in an open field area(OFD).The O_(3)VFI was investigated in woody species in the light exposed sampling Site(LESS—Betula pendula,Fagus sylvatica,Larix decidua,Populus tremula,Salix caprea,Rubus sp.and Vaccinium myrtillus)in late summer according to the international co-operative programme on assessment and monitoring of air pollution effects on forests(ICP Forests)manual.The results confirmed that Fagus sylvatica and Rubus sp.are O_(3)-sensitive species showing relatively high POD1(>20 mmol m-2),while Larix decidua is O_(3)-tolerant.We derived flux-based critical levels(CL)corresponding to the presence of O_(3)VFI(5,25,and 50%of symptomatic plants along the LESS)from flux-effect relationships for forest protection against O_(3)VFI.The results support the hypothesis that passive samplers cannot detect episodic high stomatal O₃fluxes(>1 nmol m^(-2)s^(-1)).According to the active monitoring,the CL for O_(3)VFI occurrence was estimated to be 17.1 mmol m-2 POD1 for 25%presence and 34.3 mmol m-2 POD1 for 50%presence of symptomatic plants,while passive samplers underestimated POD1 values for CL calculations by 17%on average,with underestimation increasing at higher CL thresholds.The findings demonstrate that active monitoring refines CLs towards a proper quantitative assessment of O_(3)impact,particularly in capturing peak flux events that are crucial for evaluating plant damage and emphasizes the importance of active O₃monitoring for reliable forest health assessments.展开更多
The maximum carboxylation rate of Rubisco(Vcmax)and maximum rate of electron transport(Jmax)for the biochemical photosynthetic model,and the slope(m)of the Ball-Berry stomatal conductance model influence gas exchange ...The maximum carboxylation rate of Rubisco(Vcmax)and maximum rate of electron transport(Jmax)for the biochemical photosynthetic model,and the slope(m)of the Ball-Berry stomatal conductance model influence gas exchange estimates between plants and the atmosphere.However,there is limited data on the variation of these three parameters for annual crops under different environmental conditions.Gas exchange measurements of light and CO2 response curves on leaves of winter wheat and spring wheat were conducted during the wheat growing season under different environmental conditions.There were no significant differences for Vcmax,Jmax or m between the two wheat types.The seasonal variation of Vcmax,Jmax and m for spring wheat was not pronounced,except a rapid decrease for Vcmax and Jmax at the end of growing season.Vcmax and Jmax show no significant changes during soil drying until light saturated stomatal conductance(gssat)was smaller than 0.15 mol m^–2 s^–1.Meanwhile,there was a significant difference in m during two different water supply conditions separated by gssat at 0.15 mol m^–2 s^–1.Furthermore,the misestimation of Vcmax and Jmax had great impacts on the net photosynthesis rate simulation,whereas,the underestimation of m resulted in underestimated stomatal conductance and transpiration rate and an overestimation of water use efficiency.Our work demonstrates that the impact of severe environmental conditions and specific growing stages on the variation of key model parameters should be taken into account for simulating gas exchange between plants and the atmosphere.Meanwhile,modification of m and Vcmax(and Jmax)successively based on water stress severity might be adopted to simulate gas exchange between plants and the atmosphere under drought.展开更多
Cupressus sempervirens is a relevant species in the Mediterranean for its cultural,economic and landscape value.This species is threatened by Seiridium cardinale,the causal agent of the cypress canker disease(CCD).The...Cupressus sempervirens is a relevant species in the Mediterranean for its cultural,economic and landscape value.This species is threatened by Seiridium cardinale,the causal agent of the cypress canker disease(CCD).The effects of biotic stressors on O_(3)risk assessment are unknown and a comprehensive O_(3)risk assessment in C.sempervirens is missing.To fill these gaps,two clones of C.sempervirens,one resistant(Clone R)and one susceptible to CCD(Clone S),were subjected to three levels of O_(3)(Ambient Air-AA;1.5×AA;2.0×AA)for two consecutive years in an O_(3)-free-air controlled exposure facility and artificially inoculated with S.cardinale.Both the exposure-(AOT40)and flux-based(PODy)indices were tested.We found that PODy performed better than AOT40 to assess O_(3)effects on biomass and the critical level for a 4%biomass loss was 2.51 mmol/m^(2)POD2.However,significant O_(3)dose-response relationships were not found for the inoculated cypresses because the combination of middle level O_(3)(1.5×AA)and inoculation stimulated a biomass growth in Clone S as hormetic response.Moreover,we found a different inter-clonal response to both stressors with a statistically significant reduction of total and belowground biomass following O_(3),and lower root biomass in Clone S than in Clone R following pathogen infection.In summary,Clone R was more resistant to O_(3),and inoculation altered O_(3)risk via an hormetic effect on biomass.These results warrant further studies on how biotic stressors affect O_(3)responses and risk assessment.展开更多
基金supported by the Fundamental Research Funds for the Central Universities(WK2090000046).
文摘Relative humidity(RH)plays a pivotal role in regulating plant transpiration by modulating stomatal conductance().Accurate modeling under varying RH conditions is essential for predicting plant water use and gas exchange,with important implications for both agricultural management and bionic applications.In this study,field experiments were conducted to measure in plants exposed to moderate-and high-RH environments.The results demonstrated that is greater and transpiration rates are lower in high-RH environments than in moderate-RH environments.The response functions of stomatal conductance to environmental factors were further developed via a boundary line technique.These functions elucidate how stomatal conductance is correlated with environmental conditions.Specifically,stomatal conductance reaches saturation at a photosynthetically active radiation(PAR)of approximately 300 and 500μmol·m^(−2)·s^(−1) in both high-and moderate-RH environments.Furthermore,the vapor pressure deficit(VPD)threshold triggering stomatal closure was shifted by ambient RH,occurring at approximately 1000 Pa under high RH and 2000 Pa under moderate RH.This RH-dependent adjustment highlights the indirect yet critical role of RH in modulating stomatal sensitivity to atmospheric dryness.On the basis of the established response functions,stomatal conductance models tailored for high-and moderate-RH environments were constructed by extending the Jarvis empirical framework.These models offer improved predictive capacity for simulating plant physiological responses under diverse humidity conditions and provide new insights into the stomatal regulation of plants in natural field settings.
基金supported partly by the National Natural Science Foundation of China (30270146)
文摘Stomatal behavior is a central topic of plant ecophysiological research under global environmental change. However, the physiological mechanism controlling the response of stomata to vapor pressure deficit （VPD） or relative humidity （RH） has been inadequately understood till now. In this study, responses of stomatal conduc- tance （gs） to VPD in two species of trees （Fraxinus chinensis Roxb., Populus alba L. var. pyramidalis Bge.）in three different climate zones （Jinan with typical warm humid/semi-humid climate, Urumqi with temperate continental arid climate and Turpan with extreme arid desert climate） were measured. Levels of two phytohormones （abscisic acid, ABA; indole-3-acetic acid, IAA） in the leaves of the two tree species at these three sites were also measured by high performance liquid chromatography. The results showed that the responses of gs to an increasing VPD in these two tree species at the three sites had peak curves which could be fitted with a Log Normal Model （gs=a.exp（-O.5（In（DIc）lb）2）. The VPD/RH values corresponding to the maximum g, can be calculated using the fitting models for the two tree species in the three sites. We found that the calculated g, -VPD correlated nega- tively with relative air humidity in the three sites during the plant growth period （April to October 2010）, which showed the values of g,-max-VPD were related to the climate conditions. The prevailing empirical stomatal model （Leuning model） and optimal stomatal behavior model could not properly simulate our measured data. The water use efficiency in the two tree species did not show obvious differences under three very different climatic conditions, but the highest gs, photosynthetic and transpiration rates occurred in P. alba var. of Turpan. The sensitivity in re- sponse of g~ to VPD in leaves of the two trees showed positive correlations with the concentration of ABA, which implied that ABA level could be used as an indicator of the sensitivity of stomatal response to VPD. Our results confirmed that the prediction of the response of gs to VPD might be incomplete in the two current popular models. Therefore, an improved g, model which is able to integrate the results is needed. Also, the stomatal response mechanism of single peak curves of g~ to VPD should be considered.
基金supported by the INTERREG ALCOTRA project MITIMPACT,PNRR for Mission 4(Component 2,Notice 3264/2021,IR0000032)-ITINERIS-Italian Integrated Environmental Research Infrastructure System CUP B53C22002150006Project funded under the National Recovery and Resilience Plan(NRRP),Mission 4 Component 2 Investment 1.4-Call for tender No.3138 of December 16,2021,rectified by Decree n.3175 of December 18,2021 of Italian Ministry of University and Research funded by the European Union-NextGenerationEU,Award Number:Project code CN_00000033,Concession Decree No.1034 of June 17,2022 adopted by the Italian Ministry of University and Research,CUP,H43C22000530001 Project title“National Biodiversity Future Center-NBFC”(Spoke 3 and 5)AP and IP were supported by the FOR-CLIMSOC Programme,Project ID PN23090101,financed by the Ministry of Research,Innovation,and Digitization in Romania.
文摘Tropospheric ozone(O_(3))is a harmful air pollutant negatively impacting forest health,causing O_(3)-specific visible foliar injury(O_(3)VFI).Ozone monitoring in forests has usually implemented by passive samplers,although they cannot detect the diurnal peak when a significant part of stomatal O_(3)uptake occurs.This results into uncertainties for the calculation of stomatal O_(3)uptake.This study compares the stomatal-flux-based POD1(phytotoxic ozone dose above a threshold of 1 nmol m^(-2)s^(-1))for forest trees/shrubs estimated from data collected by either passive samplers or active O_(3)monitors to evaluate O_(3)damage to plants in terms of O_(3)VFI in the Southern Alps.The study was conducted over two years(2018-2019)in a mountainous Alpine area(Valle Stura,Italy).An integrative monitoring station for active O_(3)monitoring,as well as passive O_(3)monitors,were installed in an open field area(OFD).The O_(3)VFI was investigated in woody species in the light exposed sampling Site(LESS—Betula pendula,Fagus sylvatica,Larix decidua,Populus tremula,Salix caprea,Rubus sp.and Vaccinium myrtillus)in late summer according to the international co-operative programme on assessment and monitoring of air pollution effects on forests(ICP Forests)manual.The results confirmed that Fagus sylvatica and Rubus sp.are O_(3)-sensitive species showing relatively high POD1(>20 mmol m-2),while Larix decidua is O_(3)-tolerant.We derived flux-based critical levels(CL)corresponding to the presence of O_(3)VFI(5,25,and 50%of symptomatic plants along the LESS)from flux-effect relationships for forest protection against O_(3)VFI.The results support the hypothesis that passive samplers cannot detect episodic high stomatal O₃fluxes(>1 nmol m^(-2)s^(-1)).According to the active monitoring,the CL for O_(3)VFI occurrence was estimated to be 17.1 mmol m-2 POD1 for 25%presence and 34.3 mmol m-2 POD1 for 50%presence of symptomatic plants,while passive samplers underestimated POD1 values for CL calculations by 17%on average,with underestimation increasing at higher CL thresholds.The findings demonstrate that active monitoring refines CLs towards a proper quantitative assessment of O_(3)impact,particularly in capturing peak flux events that are crucial for evaluating plant damage and emphasizes the importance of active O₃monitoring for reliable forest health assessments.
基金This research was jointly supported by the National Natural Science Foundation of China(41375019,41730645,and 41275118)the China Special Fund for Meteorological Research in the Public Interest(Major projects)(GYHY201506001-2).
文摘The maximum carboxylation rate of Rubisco(Vcmax)and maximum rate of electron transport(Jmax)for the biochemical photosynthetic model,and the slope(m)of the Ball-Berry stomatal conductance model influence gas exchange estimates between plants and the atmosphere.However,there is limited data on the variation of these three parameters for annual crops under different environmental conditions.Gas exchange measurements of light and CO2 response curves on leaves of winter wheat and spring wheat were conducted during the wheat growing season under different environmental conditions.There were no significant differences for Vcmax,Jmax or m between the two wheat types.The seasonal variation of Vcmax,Jmax and m for spring wheat was not pronounced,except a rapid decrease for Vcmax and Jmax at the end of growing season.Vcmax and Jmax show no significant changes during soil drying until light saturated stomatal conductance(gssat)was smaller than 0.15 mol m^–2 s^–1.Meanwhile,there was a significant difference in m during two different water supply conditions separated by gssat at 0.15 mol m^–2 s^–1.Furthermore,the misestimation of Vcmax and Jmax had great impacts on the net photosynthesis rate simulation,whereas,the underestimation of m resulted in underestimated stomatal conductance and transpiration rate and an overestimation of water use efficiency.Our work demonstrates that the impact of severe environmental conditions and specific growing stages on the variation of key model parameters should be taken into account for simulating gas exchange between plants and the atmosphere.Meanwhile,modification of m and Vcmax(and Jmax)successively based on water stress severity might be adopted to simulate gas exchange between plants and the atmosphere under drought.
基金supported by the Italian Integrated Environmental Research Infrastructures Systems(ITINERIS)(Nos.IR0000032 and CUP B53C22002150006).
文摘Cupressus sempervirens is a relevant species in the Mediterranean for its cultural,economic and landscape value.This species is threatened by Seiridium cardinale,the causal agent of the cypress canker disease(CCD).The effects of biotic stressors on O_(3)risk assessment are unknown and a comprehensive O_(3)risk assessment in C.sempervirens is missing.To fill these gaps,two clones of C.sempervirens,one resistant(Clone R)and one susceptible to CCD(Clone S),were subjected to three levels of O_(3)(Ambient Air-AA;1.5×AA;2.0×AA)for two consecutive years in an O_(3)-free-air controlled exposure facility and artificially inoculated with S.cardinale.Both the exposure-(AOT40)and flux-based(PODy)indices were tested.We found that PODy performed better than AOT40 to assess O_(3)effects on biomass and the critical level for a 4%biomass loss was 2.51 mmol/m^(2)POD2.However,significant O_(3)dose-response relationships were not found for the inoculated cypresses because the combination of middle level O_(3)(1.5×AA)and inoculation stimulated a biomass growth in Clone S as hormetic response.Moreover,we found a different inter-clonal response to both stressors with a statistically significant reduction of total and belowground biomass following O_(3),and lower root biomass in Clone S than in Clone R following pathogen infection.In summary,Clone R was more resistant to O_(3),and inoculation altered O_(3)risk via an hormetic effect on biomass.These results warrant further studies on how biotic stressors affect O_(3)responses and risk assessment.
