放牧对退化草地近地面辐射的影响

随着环境变化，草原地表状态也会改变，尤其是近地面能量收支过程变化更明显。为深入理解半干旱草原地表辐射能量平衡过程对放牧的响应特征，利用内蒙古正镶白旗典型退化草原2020年生长季（6—10月）的辐射通量观测资料，对比分析了禁牧、放牧草地太阳总辐射、地表反射辐射、大气长波辐射、地表长波辐射、净辐射以及地表反照率的日变化和生长季变化规律的差异。结果表明：在生长季，太阳总辐射随着时间推进逐月递减；禁牧区的地表反射辐射总体小于放牧区；各月大气长波辐射日变化幅度很小，处于130—370 W·m^-2；禁牧、放牧条件下地表长波辐射存在明显的季节变化规律，但是二者之间的差异甚微。内蒙古典型退化草原生长季近地面辐射通量有显著单峰型日变化特征。禁牧、放牧草地地表反照率都呈现“U”型日变化规律。生长季放牧草地的反照率明显高于禁牧草地。在禁牧区，辐射分量（地表反射辐射、大气长波辐射）和植被指数（归一化差异植被指数）对净辐射的影响是正向极显著的；而地表反照率和另一辐射分量（地表长波辐射）对净辐射有显著的负向作用。在放牧区，地表反射辐射和大气长波辐射对净辐射有极显著的正向作用；而地表反照率和地表长波辐射对净辐射的作用则是负向显著的。植被状况是影响内蒙古典型退化草原近地表辐射能量收支过程的首要因子。

Effects of grazing on near surface radiation in degraded steppe in Inner Mongolia， China

With the change of environment， the surface states of grassland has also changed， especially the near surface energy budget process changed more obvious. In order to comprehend the response of surface radiation energy balance processes to prohibited grazing and grazing in semi-arid grasslands， this paper analyzes the radiation flux observation data of typical degraded grasslands in Zhengxiangbai Banner of Inner Mongolia during the growing season （June-October） in 2020. The differences of diurnal and seasonal variation of total solar radiation， surface upward shortwave radiation， downward longwave radiation， surface upward longwave radiation， net radiation and albedo and their responses to meteorological factors， soil moisture， and vegetation conditions were studied in comparison between the prohibited grazing and grazing steppes. The indicated that the total solar radiation decreases month by month as time advances during the growing season. The surface upward shortwave radiation in the prohibited grazing area is generally smaller than that in the grazing area. The daily variation of the downward longwave radiation in each month is small， ranging from 130 to 370 W·m^-2. There is an obvious seasonal variation pattern of the surface upward longwave radiation under the prohibited grazing and grazing condition， but the little difference between them. The near surface radiation fluxes in the typical degraded grassland in Inner Mongolia has a significant unimodal diurnal variation during the growing season. The albedo of the both pastures showed a "U" shaped daily variation pattern. The Albedo of grazing pasture in the growing season was significantly higher than one of prohibited grazing pasture. The Piecewise Structural Equation Modeling analysis revealed that the radiation components （surface upward shortwave radiation， downward longwave radiation） and the vegetation index （normalized difference vegetation index） had a positive and highly significant effect on the net radiation； while Albedo and another radiation component （surface upward longwave radiation） had a significant negative effect on the net radiation in the prohibited grazing area. In the grazing area， the surface upward shortwave radiation and the downward longwave radiation had a highly significant positive effect on the net radiation； while Albedo and the surface upward longwave radiation had a negatively significant effect on the net radiation. Therefore， in the study， the vegetation status was the strongest factor affecting the near surface radiative energy balance process in typical degraded grasslands in Inner Mongolia under different grazing prohibition conditions.