（2）胡杨枝条导水率损失50%对应木质部水势P50=-1.06 MPa，表明胡杨木质部抗干旱栓塞能力低。各观测点胡杨枝条平均导水率损失百分比数（PLC）均高于60 %，各观测点之间无显著差异，表明受高蒸腾压力的区域环境影响，胡杨枝条木质部普遍存在较高程度的栓塞，水力安全处在高风险的状态；
（3）观测点S1（地下水埋深0-2.75 m）7月Kl与Ks较6月显著提高，表明地下水升高枝条导水能力增大；观测点S2（地下水埋深3.7-4.8 m）、观测点S3（地下水埋深>6 m）Ks、Kl各月间没有显著差异，但最大值均出现在生长旺盛7-8月，表明近河道浅地下水条件下胡杨枝条导水功能受地下水季节波动影响明显，而远离河道深地下水条件下主要受植物生长物候的影响； （4）随着地下水水位降低，枝条比导率（Ks）、叶比导率（Kl）显著增大，表明深地下水条件下枝条导水效率显著高于浅地下水条件，并且高Kl表明需要由枝条给其末端叶片供水所需的压力梯度小。气孔导度（gs）与Kl、Ks呈弱相关性，且深地下水条件下gs显著高于浅地下水条件，表明在高蒸腾水分需求下水力结构可塑性调整维持水分平衡作用较气孔调节显著。WUE与Kl、Ks呈显著负相关，深地下水条件下Pn显著增大，表明水力结构调整促进叶片光合，并以消耗更多的水为代价。|
|其他摘要||Woody plants in arid areas are subject to environment stress imposed by soil drought, higher transpiration rate (Tr) and higher leaf-to-air vapor pressure deficit (VpdL) which inevitably have great effects on the plant-water relations. On the one hand, woody plants have developed corresponding hydraulic architecture during the long-time adaption. On the other hand, the plasticity of hydraulic architecture can positively response to the short-term environmental fluctuations. Therefore, the hydraulic architecture and function can reflect the hydraulic strategy for plants in a given habitat, which provides significant insights into their adaptations to environmental changes in the scope of ecology and botany.
Populus euphratica is the constructive tree species occupying the arid desert riparian forest along the Tarim River. As a result of the hydro-geomorphical interaction, groundwater depth in riparian zones increases with the distance to active channel, which forms varying water habitats for P. euphratica populations with different distances from the active channel. However, the hydraulic strategy that how P. euphratica adapt to the variation of groundwater depth is not well understood. In this study, P.euhratica populations at 3 sites with varying groundwater depth were selected for characterizing the hydraulic function and the leaf gas exchanges, as well as their seasonal dynamics. Furthermore, the relationships between hydraulic function and leaf gas exchanges were explored in the growing season. The aim was to improve the understanding of the hydraulic strategy of desert riparian plants in adaption to the water habitat in desert riparian zones. The main results are shown as follows.
(1) The maximum hydraulic conductivity(Kmax), real hydraulic conductivity(Kini), xylem-specific hydraulic conductivity(Ks) and leaf-specific hydraulic conductivity(Kl) were significantly higher at deep groundwater site than those at shallow groundwater depth, while the Huber value(Hv) reversed, suggested that the increases in hydraulic conductivity of the shoots and water supply efficiency of the surported leaves with the decline of groundwater level. The increased Kl was driven by Ks rather than Hv.
(2) The measured P50 of shoot was -1.06 MPa, which showed the highly hydraulic vulnerable xylem of P. euphratica. Meanwhile, the averaged percentage loss of hydraulic conductivity (PLC) was higher than 60% for all sites, and there was not significant difference between sites, suggested the prevailing of a high cavitation in plant vessel under the great transpiration demand in the study area. These suggested the real hydraulic function operated under high risk of hydraulic dysfunction.
(3) At study site S1(groundwater depth range 0-2.75 m), the xylem-specific hydraulic conductivity(Ks) and leaf-specific hydraulic conductivity(Kl) significantly increased in July than those in June. It meant a rise of hydraulic capacity. There was no significant difference in Ks and Kl at study site S2(groundwater depth range 3.7-4.8 m) and S3(groundwater depth being more than 6 m), but their maximum values were observed in July or August. These suggested the seasonal variation of shoot hydraulic function was more subject to groundwater dynamics for the shallow groundwater site close to channel, whereas to plant growth phenology for the deep groundwater site.
(4) Ks and Kl both significantly increased with the decline of groundwater depth，which suggested the increase of shoot hydraulic conductivity at deep groundwater site，and the higher Kl meant the less shoot water potential needed to support a given water demand；The somatal conductivity(gs) had a weak correlation with Ks and Kl, and gs at deep groundwater site was higher than that at shallow groundwater site. These suggested the prevailing control of plants-water balance by the regulation of hydraulic architecture rather than stomatal behavior. Water use efficiency(WUE) was significantly negative correlation with Ks and Kl, and the net photosynthetic rate at deep groundwater site was higher than that at shallow groundwater site, suggested the regulation of hydraulic architecture promoted the leaf photosynthesis at the cost of much more water.|
蒋少伟. 胡杨水力结构与功能对地下水埋深变化的响应[D]. 北京. 中国科学院大学,2016.