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Variation in canopy conductance of Cunninghamia lanceolata forest and its response to environmental factors after an extreme rainfall event |
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| Authors: | Wanqiu Xing You Cheng Lilin Yang Weiguang Wang |
| Institution: | 1. The National Key Laboratory of Water Disaster Prevention, Hohai University, Nanjing, China;2. The National Key Laboratory of Water Disaster Prevention, Hohai University, Nanjing, China
College of Hydrology and Water Resources, Hohai University, Nanjing, China;3. College of Hydrology and Water Resources, Hohai University, Nanjing, China Project Planning Department, Shandong Survey and Design Institute of Water Conservancy Co., LTD, Ji'nan, China;4. The National Key Laboratory of Water Disaster Prevention, Hohai University, Nanjing, China College of Hydrology and Water Resources, Hohai University, Nanjing, China Key Laboratory of Water Big Data Technology of Ministry of Water Resources, Hohai University, Nanjing, China |
| Abstract: | Canopy conductance (gc) is a crucial parameter in simulating evapotranspiration and modulating water exchange, but its variation mechanism has regional uncertainties and complex environmental co-controls. In addition, the effect of extreme rainfall on gc cannot be ignored under the changing climate. Here, we investigated the variation and environmental controls on gc and the effect of extreme rainfall events in a Cunninghamia lanceolata forest across the subtropical area of Southern China. In July 2020, an extreme rainstorm hit the source area of the Xin'an River, with the cumulative rainfall on July 7 and 8 reaching 216.6 mm. The thermal diffusion probe method was used to measure the density of sap flow, and the environmental factors such as air temperature (Ta), net solar radiation (Rn) and soil water content (SWC) were monitored during the growing seasons of 2020 and 2021. Ultimately, gc obtained by the Penman-Monteith equation was adopted since the result from the Köstner equation was overestimated. gc showed a unimodal curve on the diurnal scale, and this characteristic was more obvious after the extreme rainfall. Daily gc appeared a fluctuating pattern with a maximum in summer. gc was simultaneously affected by Ta, Rn, water vapour pressure difference (VPD), SWC, among which Ta was the most significant driving factor at both the diurnal and daily timescales. The regulation of Ta, VPD and SWC on gc had obvious thresholds, and the most definite response mode was VPD (2020: 1.25 kPa; 2021: 0.95 kPa). SWC and Ta were the dominant factors after the rainfall period, and the promotion effect of VPD on post-rainy days turned to inhibition effect on typical sunny days. These findings will further reveal the water exchange mechanism between atmosphere and vegetation and impacts of environmental factors in subtropical coniferous forests, especially after the extreme rainfall events. |
| Keywords: | canopy conductance environmental factors extreme rainfall sap flow subtropical evergreen coniferous forest |