不同海拔高度高寒草甸光能利用效率的遥感模拟

利用植被光合模型模拟了藏北高原3个海拔高度(4300,4500 m和4700 m)的高寒草甸生态系统的光能利用效率.海拔4500 m的光能利用效率均值(0.47 g C/MJ)显著高于海拔4300 m(0.38 g C/MJ)和4700 m(0.35 g C/MJ),而海拔4300 m和4700 m两者间差异不显著.相关分析和多重逐步回归分析表明,影响每个海拔光能利用效率季节变化的主要因子为空气温度,相对湿度以及地表水分指数,这3个因子共同解释了99％以上的光能利用效率的季节变化,其中空气温度的贡献最大,相对湿度的贡献次之,地表水分指数的贡献最小,这说明在3个海拔的任何一个海拔高度,温度对光能利用效率季节变化的胁迫作用大于水分对光能利用效率季节变化的胁迫作用.多重逐步线性回归分析表明,生长季节均土壤含水量是决定生长季节均光能利用效率沿海拔高度分布的主导因子.单因子线性回归分析表明,地表水分指数可以定量化高寒嵩草草甸生态系统水分状况,它同时可以反应土壤水分、近地表空气湿度以及生态系统植被含水量状态.因此,在高寒嵩草草甸生态系统,用地表水分指数反应生态系统尺度水分对光能利用效率的胁迫作用是可行的.

Satellite-based modelling light use efficiency of alpine meadow along an altitudinal gradient

Light use efficiency is defined as the ratio of gross primary production or net primary production against the absorbed light energy by vegetation canopy. The quantification modeling of gross primary production or net primary production is based on the quantification modeling of light use efficiency to some extent. Therefore, quantifying light use efficiency at various spatial and temporal resolutions is significant for global carbon cycle because quantifying primary production at various spatial and temporal resolutions is one important component of quantifying global carbon cycle. Alpine meadow is one typical vegetation type on the Qinghai-Tibet Plateau. It is a typical ecosystem in both the Central Asia and the world. Meanwhile, alpine meadow plays a very important role in regiononal carbon budget in China. Hence, quantifying light use efficiency of alpine meadow ecosystem is very important for quantifying region carbon budget on Qinghai-Tibet Plateau. We modeled the light use efficiency of three alpine meadow ecosystems along an altitudinal gradient (4300-4700 m) on the Northern Tibetan Plateau by using the vegetation photosynthesis model in this study. The light use efficiency is determined by two attenuation scalars, land surface water index and air temperature in the vegetation photosynthesis model. Land surface water index can reflect the effects of land surface water content and vegetation phenology on the light use efficiency in the vegetation photosynthesis model. The mean values of the light use efficiency on altitudes of 4300 m, 4500 m and 4700 m were 0.38 g C/MJ, 0.47 g C/MJand 0.35 g C/MJ, respectively. Analysis of variance showed that the light use efficiency on altitude 4500 m was significantly higher than those on altitudes of 4300 m and 4700 m. Besides, the light use efficiency difference between altitude of 4300 m and 4700 m was not significant. Simple linear correlation analysis and multiple stepwise linear regression analysis between light use efficiency and soil temperature, soil water content, air temperature, relative humidity and land surface water index showed that the seasonal change of the light use efficiency was determined by air temperature, relative humidity and land surface water index on all studied altitudes. Air temperature, relative humidity and land surface water index together explained at least 99% of seasonal change of the light use efficiency. The standard regression coefficient of air temperature was the largest, followed by relative humidity and then by land surface water index. Therefore, the contribution ranking of each factor to the light use efficiency regression equation was air temperature > relative humidity > land surface water index on all altitudes. This indicated that the influence of temperature on seasonal change of light use efficiency was larger than water. Multiple stepwise linear regression analysis showed that growing season average soil water content was the dominant factor controlling the spatial variations of growing season average light use efficiency along the altitudinal gradient. Single linear regression analysis showed that land surface water index significantly explained seasonal changes of soil water content and relative humidity on all altitudes. Land surface water index on altitude of 4500 m and 4700 m also significantly explained seasonal changes of vapor pressure deficit. Additionally, seasonal changes of vapor pressure deficit on altitude of 4300 m was explained by land surface water index to some extent. These results indicated that land surface water index could quantify the seasonal change of environmental water content of land surface in the alpine meadow ecosystem. Thus, it is feasible to use land surface water index to infer the water attenuation scalar for the alpine meadow ecosystem on the Northern Tibetan Plateau.