韧皮部环割诱导下的花花柴衰老机制

衰老是植物器官和组织发育的最后阶段, 是一个受到严格控制的高度协调过程, 其中碳水化合物浓度对衰老的影响十分显著。花花柴(Karelinia caspia)是塔克拉玛干沙漠南缘策勒绿洲的主要植物种, 为了研究花花柴在韧皮部环割后的碳水化合物变化和叶片衰老过程, 对其进行韧皮部环割, 测量叶片光合色素含量、光合速率、可溶性糖含量、淀粉含量、脱落酸(ABA)含量和叶水势。结果表明: (1)环割能够诱导花花柴叶片的衰老, 而诱导叶片衰老的主要因素有: 叶片碳水化合物的积累、叶片ABA含量的上升, 以及叶片水分状况的恶化。(2)相比于自然衰老, 环割诱导的衰老导致许多正常的生理过程受到破坏。(3)类胡萝卜素在衰老过程中主要起光保护的作用。(4)韧皮部半环割也导致花花柴各种生理指标显著下降, 表明植物无法通过增加剩余部分韧皮部筛管的运输通量而达到维持整个韧皮部运输系统顺畅的目的。     

短期环割对塔克拉玛干沙漠南缘两种荒漠植物的生理影响

随着气候条件的改变, 人口和载畜量的日益增加, 塔克拉玛干沙漠南缘策勒绿洲主要植物种群花花柴(Karelinia caspia)和骆驼刺(Alhagi sparsifolia)正遭受日益严重的虫噬、放牧等机械损伤的影响, 干扰因子对花花柴和骆驼刺的影响日趋明显。以塔克拉玛干南缘沙漠策勒绿洲主要建群种花花柴和骆驼刺为材料, 测量了韧皮部环割处理10天后, 光合色素含量和光系统II (PSII)叶绿素荧光的变化。结果表明: (1)在韧皮部半割处理下, 花花柴、骆驼刺的光合色素含量和叶绿素荧光变化都不明显。(2)在韧皮部全割处理下, 花花柴、骆驼刺的光合色素含量和叶绿素荧光各参数变化较大, 在该处理下, 两种植物光合原初反应被抑制, PSII结构和功能遭到损害, 活性降低, 光合器官对光能的吸收、传递、转化和电子捕获等过程被抑制。(3)韧皮部全割对花花柴和骆驼刺各生理状况产生较大影响, 相比而言, 环割对花花柴的影响更为持久。对于单个植株而言, 机械损伤对花花柴的破坏损伤更为显著。(4)在环割对花花柴和骆驼刺光合速率的影响中, 存在着依赖于碳水化合物(carbohydrate-dependent)的机制。     

Sap flow characteristics and its responses to precipitation in Robinia pseudoacacia and Platycladus orientalis plantations

Aim In the loess hilly region, drought stress frequently occurs during the late spring and early summer as a result of insufficient water supply and asynchronous changes between temperature and precipitation. Our objective was to quantify the characteristics of water-consumption through transpirations and their responses to precipitation in the dominant plantations in this region. Methods Thermal dissipation probe (TDP) was used to measure the sap flow density (F_d) of Robinia pseudoacacia and Platycladus orientalis from April through October in 2009 in Ansai National Ecological Experimental Station. Environmental variables, including meteorological factors and soil water content, were simultaneously measured. Important findings The diurnal variation of F_d exhibited a single-peak curve during the growing season of R. pseudoacacia and P. orientalis. The maximum F_d was three times greater in R. pseudoacacia (0.12068 m³·m^-2·h^-1) than that in P. orientalis (0.03737 m³·m^-2·h^-1). Except in the rapid-growth season (July to August), the F_d of these two species during the post-precipitation period were significantly higher than that during the pre-precipitation period. The F_d of P. orientalis and R. pseudoacacia was well fitted with transpiration (VT), an integrated index calculated from both vapor pressure deficit (VPD) and solar radiation (R_s), using an exponential saturation function. Generally, F_d increased in response to rising VT, while these values tended to be stable when VT reached about 50 kPa (W·m^-2)^1/2. Furthermore, R. pseudoacacia showed more sensitive to precipitation (p < 0.001) than P. orientalis, according to different hydraulic conductance model coefficients (fitting parameter b) between pre- and post-precipitation periods. Therefore, R. pseudoacacia could be considered as a precipitation-sensitive species, while P. orientalisasa precipitation-insensitive species. Through analyzing the different responses of plantation species to precipitation in the loess hilly region, this study provides a scientific basis for the local plantation management from the aspect of tree water use during ecological restoration.