Understanding how the transpiration of this vegetation type responds to environmental stress is important for determining the wa-ter-balance dynamics of the riparian ecosystem threatened by groundwater depletion. Tran...Understanding how the transpiration of this vegetation type responds to environmental stress is important for determining the wa-ter-balance dynamics of the riparian ecosystem threatened by groundwater depletion. Transpiration and sap flow were measured using the heat-pulse technique. The results were then projected up to the stand level to investigate the stand’s water-use in relation to climate forcing in the desert riparian forest in an extreme arid region. This study took place from April through October 2003 and from May through October 2004. The experimental site was selected in the Populus euphratica Forest Reserve (101o10' E, 41o59' N) in Ejina county, in the lower Heihe River basin, China. The sapwood area was used as a scalar to extrapolate the stand-water consumption from the whole trees’ water consumption measured by the heat-pulse velocity recorder (HPVR). Scale transferring from a series of individual trees to a stand was done according to the existing natural variations between trees under given environmental conditions. The application of the biometric parameters available from individual tree and stand levels was proved suitable for this purpose. A significant correlation between the sapwood area and tree diameter at breast height (DBH) was found. The prediction model is well fitted by the power model. On the basis of the prediction model, the sapwood area can be cal-culated by DBH. The sap-flow density can then be used to extrapolate the stand-water use by means of a series of mathematical models.展开更多
Evidence exists of nighttime transpiration and its potential impact on plant/water relations for species in a diversity of ecosystems. However, relevant data related to typical desert riparian forest species remains l...Evidence exists of nighttime transpiration and its potential impact on plant/water relations for species in a diversity of ecosystems. However, relevant data related to typical desert riparian forest species remains limited Accordingly, we measured sap flow velocity of Populus euphratica using the heat ratio method between 2012 and2014. Nocturnal stem sap flow was separated into nighttime and stem refilling using the ‘‘forecasted refilling''method. Nighttime transpiration was observed for each phenophase. The highest value was during the full foliation period but lowest during leaf expansion and defoliation periods. The contribution of nighttime transpiration to daytime transpiration was an average of 15% but this was comparatively higher during the defoliation period. Relationships between nighttime transpiration, vapor pressure deficits, and air temperatures were more closely associated than with wind speed in all phenophases. Moreover, we found that nighttime transpiration linearly correlated to vapour pressure deficit during the first and the full foliation periods, but nighttime transpiration showed exponential correlations to air temperatures during the same phenophases. Additionally, environmental drivers of transpiration were significantly different between nighttime and daytime(P \ 0.05). Driving forces behind nighttime transpiration were characterized by many factors, and integrated impacts between these multiple environmental factors were complex. Future studies should focus on these integrated impacts on nighttime transpiration, and the physiological mechanisms of nighttime transpiration should be investigated, given that this could also influence its occurrence and magnitude during different phenophases.展开更多
Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night.This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China.O...Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night.This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China.Our primary goal was to reveal and understand the nature of nighttime sap flow and its functional significance.Methods Granier’s thermal dissipation method was used to determine the nighttime sap flux of A.mangium.Gas exchange system was used to estimate nighttime leaf transpiration and stomatal conductance of studied trees.Important Findings Nighttimesap flowwas substantial and showed seasonal variation similar to the patterns of daytime sap flowin A.mangium.Mean nighttime sap flow was higher in the less precipitation year of 2004(1122.4 mm)than in the more precipitation year of 2005(1342.5 mm)since more daytime transpiration and low soil water availability in the relatively dry 2004 can be the cause of more nighttime sap flow.Although vapor pressure deficit and air temperature were significantly correlated with nighttime sap flow,they could only explain a small fraction of the variance in nighttime sap flow.The total accumulated water loss(E_(L))by transpiration of canopy leaves was only;2.6–8.5%of the total nighttime sap flow(E_(t))during the nights of July 17–18 and 18–19,2006.Therefore,it is likely that the nighttime sap flow was mainly used for refillingwater in the trunk.The stem diameter at breast height,basal area and sapwood area explained much more variance of nighttime water recharge than environmental factors and other tree form features,such as tree height,stem length below the branch,and canopy size.The contribution of nighttime water recharge to the total transpiration ranged from 14.7 to 30.3%depending on different DBH class and was considerably higher in the dry season compared to the wet season.展开更多
基金supported by the National Natural Science Foundation of China (40725001 40501012)+1 种基金drought mete-orological scientific research fund projects (IAM200707)the Knowledge Innovation Program from the Chinese Academy of Sciences (KZCX2-XB2-04)
文摘Understanding how the transpiration of this vegetation type responds to environmental stress is important for determining the wa-ter-balance dynamics of the riparian ecosystem threatened by groundwater depletion. Transpiration and sap flow were measured using the heat-pulse technique. The results were then projected up to the stand level to investigate the stand’s water-use in relation to climate forcing in the desert riparian forest in an extreme arid region. This study took place from April through October 2003 and from May through October 2004. The experimental site was selected in the Populus euphratica Forest Reserve (101o10' E, 41o59' N) in Ejina county, in the lower Heihe River basin, China. The sapwood area was used as a scalar to extrapolate the stand-water consumption from the whole trees’ water consumption measured by the heat-pulse velocity recorder (HPVR). Scale transferring from a series of individual trees to a stand was done according to the existing natural variations between trees under given environmental conditions. The application of the biometric parameters available from individual tree and stand levels was proved suitable for this purpose. A significant correlation between the sapwood area and tree diameter at breast height (DBH) was found. The prediction model is well fitted by the power model. On the basis of the prediction model, the sapwood area can be cal-culated by DBH. The sap-flow density can then be used to extrapolate the stand-water use by means of a series of mathematical models.
基金financially supported by the Key Research Program of Frontier Sciences CAS(QYZDJ-SSWDQC031)Key Project of the Chinese Academy of Sciences(KZZDEW-04-05)+1 种基金the National Natural Science Foundation of China(91025024)the ‘‘Western Light’’ project of the Chinese Academy of Science
文摘Evidence exists of nighttime transpiration and its potential impact on plant/water relations for species in a diversity of ecosystems. However, relevant data related to typical desert riparian forest species remains limited Accordingly, we measured sap flow velocity of Populus euphratica using the heat ratio method between 2012 and2014. Nocturnal stem sap flow was separated into nighttime and stem refilling using the ‘‘forecasted refilling''method. Nighttime transpiration was observed for each phenophase. The highest value was during the full foliation period but lowest during leaf expansion and defoliation periods. The contribution of nighttime transpiration to daytime transpiration was an average of 15% but this was comparatively higher during the defoliation period. Relationships between nighttime transpiration, vapor pressure deficits, and air temperatures were more closely associated than with wind speed in all phenophases. Moreover, we found that nighttime transpiration linearly correlated to vapour pressure deficit during the first and the full foliation periods, but nighttime transpiration showed exponential correlations to air temperatures during the same phenophases. Additionally, environmental drivers of transpiration were significantly different between nighttime and daytime(P \ 0.05). Driving forces behind nighttime transpiration were characterized by many factors, and integrated impacts between these multiple environmental factors were complex. Future studies should focus on these integrated impacts on nighttime transpiration, and the physiological mechanisms of nighttime transpiration should be investigated, given that this could also influence its occurrence and magnitude during different phenophases.
基金National Natural Science Foundation of China(30871998,41030638)the Provincial Natural Science Foundation of Guangdong(031265,07006917)the Knowledge Innovative Program of Chinese Academy of Sciences(KSCX2-SW-133).
文摘Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night.This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China.Our primary goal was to reveal and understand the nature of nighttime sap flow and its functional significance.Methods Granier’s thermal dissipation method was used to determine the nighttime sap flux of A.mangium.Gas exchange system was used to estimate nighttime leaf transpiration and stomatal conductance of studied trees.Important Findings Nighttimesap flowwas substantial and showed seasonal variation similar to the patterns of daytime sap flowin A.mangium.Mean nighttime sap flow was higher in the less precipitation year of 2004(1122.4 mm)than in the more precipitation year of 2005(1342.5 mm)since more daytime transpiration and low soil water availability in the relatively dry 2004 can be the cause of more nighttime sap flow.Although vapor pressure deficit and air temperature were significantly correlated with nighttime sap flow,they could only explain a small fraction of the variance in nighttime sap flow.The total accumulated water loss(E_(L))by transpiration of canopy leaves was only;2.6–8.5%of the total nighttime sap flow(E_(t))during the nights of July 17–18 and 18–19,2006.Therefore,it is likely that the nighttime sap flow was mainly used for refillingwater in the trunk.The stem diameter at breast height,basal area and sapwood area explained much more variance of nighttime water recharge than environmental factors and other tree form features,such as tree height,stem length below the branch,and canopy size.The contribution of nighttime water recharge to the total transpiration ranged from 14.7 to 30.3%depending on different DBH class and was considerably higher in the dry season compared to the wet season.
