藏北高原高寒草甸光能利用效率对增温增水的响应

Effect of Experimental Warming and Increased Precipitation on Light Use Efficiency of An Alpine Meadow in the Northern Tibetan Plateau

量化植被光能利用效率对增温增水的响应是全球碳循环研究的重要组成部分。为了探讨藏北高原高寒草甸光能利用效率对气候变暖和降水增多的响应,2014年6月在藏北高原高寒草甸布设了1个增温增水实验平台,采用了完整的两因子(增温和增水)实验设计,每个因子设置3个处理水平(不处理、低幅度和高幅度处理),共9个处理组合。设置40 cm和80 cm的开顶式生长箱实现两个幅度的实验增温(分别增加了0.34℃和1.11℃的日最低空气温度),低幅度和高幅度增水处理分别增加了15%和30%的降水。基于中分辨率成像光谱仪的植被光能利用效率算法,利用观测的饱和水汽压差和日最低空气温度模拟了2014—2016年生长季节(6—9月)植被的光能利用效率。结果表明,增温对日最低空气温度(F=39.10,P=0.000)、饱和水汽压差(F=47.45,P=0.000)和光能利用效率(F=4.20,P=0.032)都有显著影响,而增水对饱和水汽压差(F=5.72,P=0.012)有显著影响。增温引起的光能利用效率的变化与增温幅度表现为二次曲线关系,与增温引起的饱和水汽压差的变化量表现为负相关关系。增水处理对光能利用效率无显著影响,且增水引起的光能利用效率的变化与增水引起的饱和水汽压差的变化量呈负相关关系。因此,降水增多可能对藏北高原高寒草甸的光能利用效率无显著影响,而光能利用效率随着增温幅度的变化而变化。

Quantifying the response of light use efficiency to experimental warming and increased precipitation is a key component of global carbon cycling. A field warming and increased precipitation experiment was conducted in an alpine meadow in the Northern Tibetan Plateau since June, 2014. The field experiment was based on a complete factorial design with nine treatments and each factor had three levels （zero, low- and high-level）. Two heights （40 cm and 80 cm） of open top chambers （OTC） were installed to obtain the two magnitudes of warming, and the low- and high-level warming treatments increased daily minimum air temperature by 0.34 ℃ and 1.11 ℃, respectively. Two diameters （approximately 44 cm and 62 cm） of precipitation collection funnels with rubber tubing （2 cm inner diameter） were installed to obtain the two magnitudes （15% and 30%） of increased precipitation. Observed vapor pressure deficit and daily minimum air temperature was used to simulate light use efficiency during the growing season in2014-2016. The light use efficiency algorithm used in this study was based on the Moderate Resolution Imaging Spectroradiometer light use efficiency model. Experimental warming had significant effects on daily minimum air temperature （F=39.10, P=0.000）, vapor pressure deficit （F=47.45, P=0.000） and light use efficiency （F=4.20, P=0.032）. In contrast, increased precipitation had significant effect on vapor pressure deficit （F=5.72, P=0.012）. The effect of warming on light use efficiency showed a quadratic relationship with warming magnitude, and a negative linear relationship with the effect of warming on vapor pressure deficit. Increased precipitation had no obvious effect on light use efficiency. The effect of increased precipitation on light use efficiency showed a negative linear relationship with the effect of increased precipitation on vapor pressure deficit. Therefore, increased precipitation likely has no obvious effect on light use efficiency, whereas warming effect on light use efficiency varies with warming magnitudes in alpine meadows in the Northern Tibetan Plateau.