陕北黄土区陡坡地人工植被的土壤水分生态环境

通过定点土壤水分测定与对比分析，研究了陕北黄土区35～45°陡坡地人工植被的土壤水分亏缺状况、年际、年内动态变化规律、干燥化特征及其补偿恢复特征。结果表明：陡坡地多年生人工植被的土壤水分亏缺极为严重，贫水年0～10m土层贮水量仅相当于田间持水量的26．2％～42．0％，丰水年贮水量也仅占田间持水量的27．0％～43．3％；亏缺次序为：柠条〉刺槐〉苜蓿〉侧柏〉杨树〉油松〉荒坡〉杏〉枣〉农地。年际间同一植被土壤水分含量的变化主要发生在200cm以上土层内，变异程度随土壤深度的增加而减弱。同一生长季，各种植被0～120cm土层含水量的变异系数都较大，但植被间差异较小；120cm以下土层，变异系数较小，但植被间差异较大。陡坡地多年生植被均有永久干层存在，但深层土壤干燥化强度因植物种类和生长年限而存在明显的差异。雨季土壤水分的补偿和恢复深度为1．0～1．4m，但不同植被的土壤贮水增量和补偿度有较大差异。同一植被丰水年的雨水补偿深度比干旱年可增加60cm以上，5m土层贮水增量增加3倍以上。在自然降雨条件下，陡坡地多年生人工植被的土壤贮水亏缺状况不能得到改善，土壤干化现象也不可能有所缓解。

Influence of litter layer on ecological environment in northeastern leymus chinensis grassland of China

In this paper, we adopted simulation method to discuss influences of litter layer on plants habitat in grassland. Results indicated that ground surface evaporation, soil moisture, surface temperature, soil pH, soil bulk density and soil porosity were all strongly related to the litter quantity. Potassium （K） and organic materials in the soil covered by litter layer were higher than those in the soil uncovered by litter layer. With 100 g.ln-z increase of litter, the percentage of organic materials increased by 17.9%, nitrogen （N） increased by 7.6%, phosphor （P） increased by 26.4%, and K increased by 3.8%. With the litter accumulation amounting up to 600 g-m-2, the percentage of organic materials increased by 1.8 times, N increased by 81.5%, P increased by 1.8 times and K increased by 26.4%. According to the expected coefficient method of optimization, a mathematical model was established about the optimal accumulation quantity of litter.