Static tests under cyclic loading were carried out on Populus alba var. pyramidalis to determine its characteristic curves of restoring forces. The results show that P alba var. pyramidalis had good elastic performanc...Static tests under cyclic loading were carried out on Populus alba var. pyramidalis to determine its characteristic curves of restoring forces. The results show that P alba var. pyramidalis had good elastic performance. There was degradation of strength and stiffness under cyclic loading and unloading, where characteristic curves of restoring forces ofP. alba var. pyrarnidalis assumed a ＂flat and contrary S-shape＂ form. Simultaneously, P alba vat. pyramidalis showed typical characteristics of brittle destruction under large high peak loading and unloading. Furthermore, dynamic tests were carried out under wind loads to obtain dynamic displacement curves and dynamic strain curves. P alba var. pyramidalis reflected its stochastic dynamic performance in building up its resistance to the stochastic wind loads and its dynamically hysteretic properties. The dynamic response of this species was random and fuzzy under stochastic wind loads. This study has theoretical significance and reference value to research on the static characteristics and wind-induced dynamic performance of forests.展开更多
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
本文研究两组同龄新疆杨(Populus alba L.var.pyramidalis)(一组土壤含盐量较低,树木长势良好,另一组土壤盐分高,树木长势差)对盐分离子的吸收选择性系数和从根至边材,从边材至叶的运输选择性系数,结合盐分离子在树体各部位的分布状况,...本文研究两组同龄新疆杨(Populus alba L.var.pyramidalis)(一组土壤含盐量较低,树木长势良好,另一组土壤盐分高,树木长势差)对盐分离子的吸收选择性系数和从根至边材,从边材至叶的运输选择性系数,结合盐分离子在树体各部位的分布状况,探讨新疆杨对长期盐胁迫的生理反应。主要结论为:盐胁迫下新疆杨通过选择性吸收K+,抑制过多Na+进入根系,新疆杨对盐分离子的运输选择性主要体现在根向边材的运输中,新疆杨根系对Na+具有较强的截留作用,对Cl-和SO42-也有一定截留作用。展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 30872071)
文摘Static tests under cyclic loading were carried out on Populus alba var. pyramidalis to determine its characteristic curves of restoring forces. The results show that P alba var. pyramidalis had good elastic performance. There was degradation of strength and stiffness under cyclic loading and unloading, where characteristic curves of restoring forces ofP. alba var. pyrarnidalis assumed a ＂flat and contrary S-shape＂ form. Simultaneously, P alba vat. pyramidalis showed typical characteristics of brittle destruction under large high peak loading and unloading. Furthermore, dynamic tests were carried out under wind loads to obtain dynamic displacement curves and dynamic strain curves. P alba var. pyramidalis reflected its stochastic dynamic performance in building up its resistance to the stochastic wind loads and its dynamically hysteretic properties. The dynamic response of this species was random and fuzzy under stochastic wind loads. This study has theoretical significance and reference value to research on the static characteristics and wind-induced dynamic performance of forests.
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.
文摘杨树受损伤后能诱导一些基因的表达,其编码的蛋白质可能在杨树的防卫反应中起一定作用。用PCR方法从新疆杨叶片中克隆出一个损伤诱导型Kun itz胰蛋白酶抑制剂基因PaTI1。序列分析表明:此基因不含内含子,其翻译起点上游具有‘TATA’和‘CCAAT’等转录控制元件,包含的阅读框架能编码一个长为213个氨基酸的多肽。此多肽与克隆自美洲山杨的PtTI2和PtTI1氨基酸序列同源性最高,分别为95%和80%,其N端存在一长度为27个氨基酸的信号肽。将此基因以融合蛋白的形式在大肠杆菌中进行表达,纯化后的融合蛋白对胰蛋白酶的活性有抑制作用,每8.5μg融合蛋白可完全抑制1μg牛胰蛋白酶的活性。W estern b lot分析表明融合蛋白与PtTI2特异的抗体之间有明显的血清学反应。
文摘本文研究两组同龄新疆杨(Populus alba L.var.pyramidalis)(一组土壤含盐量较低,树木长势良好,另一组土壤盐分高,树木长势差)对盐分离子的吸收选择性系数和从根至边材,从边材至叶的运输选择性系数,结合盐分离子在树体各部位的分布状况,探讨新疆杨对长期盐胁迫的生理反应。主要结论为:盐胁迫下新疆杨通过选择性吸收K+,抑制过多Na+进入根系,新疆杨对盐分离子的运输选择性主要体现在根向边材的运输中,新疆杨根系对Na+具有较强的截留作用,对Cl-和SO42-也有一定截留作用。
