Chen Lixin, Zhang Zhiqiang, Zeppel Melanie, Liu Caifeng, Guo Junting, Zhu Jinzhao, Zhang Xuepei, Zhang Jianjun, Zha Tonggang
Key Laboratory Soil and Water Conservation and Desertification Combating, Ministry of Education, College of Soil and Water Conservation, Beijing Forestry University, Qinghua East Road 35#, Haidian District, Beijing, 100083, People's Republic of China,
Int J Biometeorol. 2014 Sep;58(7):1569-81. doi: 10.1007/s00484-013-0761-9. Epub 2014 Feb 8.
Responses of transpiration (Ec) to rain pulses are presented for two semiarid tree species in a stand of Pinus tabulaeformis and Robinia pseudoacacia. Our objectives are to investigate (1) the environmental control over the stand transpiration after rainfall by analyzing the effect of vapor pressure deficit (VPD), soil water condition, and rainfall on the post-rainfall Ec development and recovery rate, and (2) the species responses to rain pulses and implications on vegetation coverage under a changing rainfall regime. Results showed that the sensitivity of canopy conductance (Gc) to VPD varied under different incident radiation and soil water conditions, and the two species exhibited the same hydraulic control (-dG c/dlnVPD to Gcref ratio) over transpiration. Strengthened physiological control and low sapwood area of the stand contributed to low Ec. VPD after rainfall significantly influenced the magnitude and time series of post-rainfall stand Ec. The fluctuation of post-rainfall VPD in comparison with the pre-rainfall influenced the Ec recovery. Further, the stand Ec was significantly related to monthly rainfall, but the recovery was independent of the rainfall event size. Ec enhanced with cumulative soil moisture change (ΔVWC) within each dry-wet cycle, yet still was limited in large rainfall months. The two species had different response patterns of post-rainfall Ec recovery. Ec recovery of P. tabulaeformis was influenced by the pre- and post-rainfall VPD differences and the duration of rainless interval. R. pseudoacacia showed a larger immediate post-rainfall Ec increase than P. tabulaeformis did. We, therefore, concluded that concentrated rainfall events do not trigger significant increase of transpiration unless large events penetrate the deep soil and the species differences of Ec in response to pulses of rain may shape the composition of semiarid woodlands under future rainfall regimes.
本文呈现了油松和刺槐混交林中两种半干旱树种蒸腾作用（Ec）对降雨脉冲的响应。我们的目标是：（1）通过分析水汽压差（VPD）、土壤水分状况和降雨对降雨后Ec发展及恢复速率的影响，研究降雨后林分蒸腾作用的环境控制；（2）研究树种对降雨脉冲的响应以及在降雨格局变化下对植被覆盖的影响。结果表明，在不同的入射辐射和土壤水分条件下，冠层导度（Gc）对VPD的敏感性不同，且两种树种在蒸腾作用上表现出相同的水力控制（-dGc/dlnVPD与Gcref的比值）。林分强化的生理控制和较低的边材面积导致了较低的Ec。降雨后的VPD显著影响降雨后林分Ec的大小和时间序列。降雨后VPD与降雨前相比的波动影响了Ec的恢复。此外，林分Ec与月降雨量显著相关，但恢复情况与降雨事件大小无关。在每个干湿循环中，Ec随土壤水分累积变化（ΔVWC）而增强，但在降雨量大的月份仍受到限制。两种树种降雨后Ec恢复的响应模式不同。油松的Ec恢复受降雨前后VPD差异和无雨间隔持续时间的影响。刺槐降雨后Ec的立即增加幅度比油松大。因此，我们得出结论，除非大降雨事件渗入深层土壤，否则集中降雨事件不会引发蒸腾作用的显著增加，并且Ec对降雨脉冲响应的物种差异可能会在未来降雨格局下塑造半干旱林地的组成。
