高寒草甸生态系统表层土壤水分时间稳定性研究

选取西藏高原北部那曲地区一处典型的高寒草甸生态系统为研究对象,用TDR 300测量样地中2个样带共82个测点表层0~7.5 cm的土壤含水率,在2015年生长季中共测量14次。基于所测数据分析了土壤含水率的时空变异性和时间稳定性。结果表明,2015年生长季2个样带表层平均土壤含水率为26.0%,在空间上表现为弱变异性,在时间上表现为中等变异性,土壤含水率较高时,土壤水分的变异性也较高;82个测点土壤含水率的空间模式在7月份—8月初相似性较弱,在8月中旬—9月初相似性较强;土壤含水率的相对差分平均值在-11.5%~8.5%之间,相对差分标准差的平均值为8.6%,二者表现为开口向上的二次曲线关系,说明土壤含水率接近样地平均值的测点具有较高的时间稳定性,而在较干和较湿的测点,土壤含水率的时间稳定性相对较弱;时间稳定性指数、平均绝对偏差、均方根误差和最小相对差分标准差平衡法4种方法均能准确地判定土壤含水率时间稳定性最佳代表测点,利用最佳代表测点估算样带平均土壤含水率均具有较高的精度,相比较而言,最小相对差分标准差平衡法精度更高。

Temporal Stability of Surface Soil Moisture in Alpine Meadow Ecosystem on Northern Tibetan Plateau

Surface (0~7.5cm) soil water content (SWC) was measured at 82 locations in a typical alpine meadow ecosystem on the northern Tibetan Plateau by using time domain reflectometry for 14 times during the 2015 growing season to evaluate spatial variability and temporal stability of surface SWC. Results showed that the mean SWC of the two transects during the 2015 growing season was 26.0%. SWC had a weak variability in space and a moderate variability in time. The variability of SWC was increased with the increase of SWC. The spatial pattern of SWC at the 82 measuring locations had a weak similarity during July and early August and a strong similarity from middle August to early September. The mean relative difference (MRD) of SWC was from -11.5% to 8.5% and the mean standard deviation of relative difference (SDRD) was 8.6%. MRD was correlated with SDRD in a concave curve relationship. Index of temporal stability, mean absolute bias error, root mean square error and minimum-SDRD constant methods could all identify the best representative location and the accuracy of mean SWC estimation of the representative location was high. Comparatively, the minimum-SDRD constant method had a higher accuracy. This study can provide data supplement and method innovation for SWC study in alpine meadow ecosystems.