Estimation of the transpiration rate for a tree is generally based on sap flow measurements within the hydro-active stem xylem. In this study, radial variation of sap flow velocity（Js） was investigated at five depth...Estimation of the transpiration rate for a tree is generally based on sap flow measurements within the hydro-active stem xylem. In this study, radial variation of sap flow velocity（Js） was investigated at five depths of the xylem（1, 2, 3, 5 and 8 cm under the cambium） in three mature Xinjiang poplar（Populus alba L. var. pyramidalis） trees grown at the Gansu Minqin National Studies Station for Desert Steppe Ecosystem from May to October 2011. Thermal dissipation probes of various lengths manufactured according to the Granier＇s design were installed into each tree for simultaneous observation of the radial patterns of Js through the xylem. The radial patterns were found to fit the four-parameter GaussAmp equation. The peak Js was about 27.02±0.95 kg/（dm2？d） at approximately 3 to 5 cm deep from the cambium of the three trees,and the lowest Js appeared at 1 cm deep in most of the time. Approximately 50% of the total sap flow in Xinjiang poplar occurred within one-third of the xylem from its outer radius, whereas 90% of the total sap flow occurred within two-fifth of the xylem. In addition, the innermost point of the xylem（at 8-cm depth）, which appeared as the penultimate sap flow in most cases during the study period, was hydro-active with Js,8 of 7.55±3.83 kg/（dm2？d）. The radial pattern of Js was found to be steeper in midday than in other time of the day, and steeper diurnal fluctuations were recorded in June, July and August（the mid-growing season）. Maximum differences between the lowest Js（Js,1 or Js,8） and the highest Js（Js,3 or Js,5） from May through October were 12.41, 17.35, 16.30, 18.52, 12.60 and 16.04 g/（cm2？h）, respectively. The time-dependent changes of Js along the radial profile（except at 1-cm depth） were strongly related to the reference evapotranspiration（ET0）. Due to significant radial variability of Js, the mean daily sap flow at the whole-tree level could be over-estimated by up to 29.69% when only a single probe at depth of 2 cm was used. However, the accuracy of the estimation of sap flow in Xinjiang poplar could be significantly improved using a correction coefficient of 0.885.展开更多
Populus euphratica trees are the sole natural perennial riparian woodlands native to the river oases in the lower reaches of Heihe River Basin in northwestern China.This study investigated characteristics of the stem ...Populus euphratica trees are the sole natural perennial riparian woodlands native to the river oases in the lower reaches of Heihe River Basin in northwestern China.This study investigated characteristics of the stem sap flux of Populus euphratica and its rela-tionship to environmental factors using the thermal dissipation probe(TDP) method.The results showed that(1) daily variation of sap flow of P.euphratica on clear days exhibited an obvious unimodal curve;sap flow rates in June,July,August,and September were 13.39,12.07,12.69,and 5.10 L/d,respectively;(2) the average transpiration of the Populus euphratica from June through September amounted to 1,309.84 L;(3) stem sap flow can be affected by a number of environmental factors that,in terms of the influential degree,can be arranged in the descending order of air temperature,soil moisture,relative humidity,total solar radiation,soil temperature,and wind velocity.展开更多
理解新疆杨(Populus alba var.pyramidalis)耗水特征对制定沙地人工林科学用水灌溉策略以及林场经营建设具有重要意义。采用包裹式树干茎流仪测定新疆杨液流,并对毛乌素沙地的环境因子进行长期监测。结果表明:新疆杨晴天液流速率最大,...理解新疆杨(Populus alba var.pyramidalis)耗水特征对制定沙地人工林科学用水灌溉策略以及林场经营建设具有重要意义。采用包裹式树干茎流仪测定新疆杨液流,并对毛乌素沙地的环境因子进行长期监测。结果表明:新疆杨晴天液流速率最大,阴天次之,雨天最小,日液流累计量分别为16.38、12.56、2.22 L,晴天和阴天的液流速率接近。5、6、7、8、9、10月的日平均液流量分别为12.12、14.07、14.08、11.60、8.73、3.92 L,5—8月是新疆杨主要的耗水期,累计耗水量为1722.53 L。新疆杨液流与净辐射、饱和水汽压差、气温、太阳辐射、土壤热通量、土壤温度显著正相关,相关系数分别为0.656、0.641、0.634、0.625、0.605、0.467;与土壤湿度、空气相对湿度、降水量显著负相关,相关系数分别为-0.340、-0.233、-0.178;与风速相关性不显著。净辐射对于新疆杨液流的影响最大。展开更多
基金supported by the National Natural Science Foundation of China (31070628)Field support for this research was provided by Gansu Minqin National Studies Station for Desert Steppe Ecosystem
文摘Estimation of the transpiration rate for a tree is generally based on sap flow measurements within the hydro-active stem xylem. In this study, radial variation of sap flow velocity（Js） was investigated at five depths of the xylem（1, 2, 3, 5 and 8 cm under the cambium） in three mature Xinjiang poplar（Populus alba L. var. pyramidalis） trees grown at the Gansu Minqin National Studies Station for Desert Steppe Ecosystem from May to October 2011. Thermal dissipation probes of various lengths manufactured according to the Granier＇s design were installed into each tree for simultaneous observation of the radial patterns of Js through the xylem. The radial patterns were found to fit the four-parameter GaussAmp equation. The peak Js was about 27.02±0.95 kg/（dm2？d） at approximately 3 to 5 cm deep from the cambium of the three trees,and the lowest Js appeared at 1 cm deep in most of the time. Approximately 50% of the total sap flow in Xinjiang poplar occurred within one-third of the xylem from its outer radius, whereas 90% of the total sap flow occurred within two-fifth of the xylem. In addition, the innermost point of the xylem（at 8-cm depth）, which appeared as the penultimate sap flow in most cases during the study period, was hydro-active with Js,8 of 7.55±3.83 kg/（dm2？d）. The radial pattern of Js was found to be steeper in midday than in other time of the day, and steeper diurnal fluctuations were recorded in June, July and August（the mid-growing season）. Maximum differences between the lowest Js（Js,1 or Js,8） and the highest Js（Js,3 or Js,5） from May through October were 12.41, 17.35, 16.30, 18.52, 12.60 and 16.04 g/（cm2？h）, respectively. The time-dependent changes of Js along the radial profile（except at 1-cm depth） were strongly related to the reference evapotranspiration（ET0）. Due to significant radial variability of Js, the mean daily sap flow at the whole-tree level could be over-estimated by up to 29.69% when only a single probe at depth of 2 cm was used. However, the accuracy of the estimation of sap flow in Xinjiang poplar could be significantly improved using a correction coefficient of 0.885.
基金funded by the State Basic Research Planning Development Engineering-project (2009CB421303-2)the National Natural Science Foundation of China (40501012)the Knowledge Innovation Program from the Chinese Academy of Sciences (KZCX2-XB2-04)
文摘Populus euphratica trees are the sole natural perennial riparian woodlands native to the river oases in the lower reaches of Heihe River Basin in northwestern China.This study investigated characteristics of the stem sap flux of Populus euphratica and its rela-tionship to environmental factors using the thermal dissipation probe(TDP) method.The results showed that(1) daily variation of sap flow of P.euphratica on clear days exhibited an obvious unimodal curve;sap flow rates in June,July,August,and September were 13.39,12.07,12.69,and 5.10 L/d,respectively;(2) the average transpiration of the Populus euphratica from June through September amounted to 1,309.84 L;(3) stem sap flow can be affected by a number of environmental factors that,in terms of the influential degree,can be arranged in the descending order of air temperature,soil moisture,relative humidity,total solar radiation,soil temperature,and wind velocity.
