祁连山北坡亚高山草地退耕还林草混合植被对土壤碳氮磷的影响

土壤有机碳、氮素和磷素是生态系统中极其重要的生态因子,土地利用变化将会引起土壤中碳、氮、磷等元素含量的变化。以祁连山北坡亚高山草地区域内三种利用方式（自由放牧天然草地、开垦20年的燕麦（Avena nuda）耕地、退耕8年的还林草混合植被）的土壤为研究对象,通过采集0~30 cm的土壤,分析土壤的理化性质得到土壤碳、氮、磷的含量,再将其转换为土壤碳、氮、磷储量,分析三种利用方式下土壤碳、氮、磷储量的差异以及影响土壤碳、氮、磷生态化学计量比的因子,旨在探讨退耕还林草工程对该地区土壤养分的影响。结果表明,3个样地的土壤碳、氮、磷储量差异显著（P〈0.05）,天然草地的有机碳、全氮储量（72.17、6.80 t·hm-2）显著高于退耕还林草地的（66.75、4.96 t·hm-2）和燕麦耕地的（36.61、3.61 t·hm-2）。这是因为,其一,比较而言天然草地受干扰小。其二,对于退耕还林草地和燕麦耕地来说,由于刈割获取地上部分,可能使得从土壤中获取的有机碳和氮素大于归还的。全磷储量则表现为燕麦耕地的（2.51 t·hm-2）显著高于天然草地的（2.17 t·hm-2）和退耕还林草地的（1.96 t·hm-2）。这是因为燕麦耕地中化肥的施用使得磷元素富集起来,所以其储量较高。与天然草地相比,耕种20年的燕麦地0-30 cm的有机碳和全氮储量分别低了35.56、3.19 t·hm-2,年平均减少速率分别为1.78、0.16 t·hm-2·a-1。与燕麦耕地相比,退耕8年的还林草地土壤有机碳和全氮储量显著升高了30.14、1.35 t·hm-2,年平均增加速率分别为3.77、0.17 t·hm-2·a-1。退耕8年的还林草地轻组有机碳比例（10.93%）显著高于天然草地（9.72%）和燕麦耕地（8.61%）。土壤含水量、容重和微生物量碳氮是影响土壤碳、氮、磷生态化学计量的重要因子。总结认为,退耕还林草混合植被对土壤碳、氮、磷库具有重要?

Effect of converting cultivated land to forest-grassland on soil carbon,nitrogen and phosphoras in sub-alpine grassland region of north slope of Qilian Mountains

Soil organic carbon, nitrogen and phosphorus are extremely important ecosystems ecological factors, land use change will cause variation in soil organic carbon, nitrogen, phosphorus and other elements content. Measurement of soil organic carbon, total nitrogen and total Phosphoras storage on three land types sites, including natural grassland for grazing, oats cultivated land for 20 years and converting cultivated land to forest-grassland for 8 years, were carried out to detect the effect of converting cultivated land to forest-grassland on soil carbon nitrogen and phosphoras pools in sub-alpine grassland region of North slope of Qilian Mountains. The results showed that there was a significant impact among three different sites on soil carbon nitrogen and phosphoras storage （P〈0.05）. The organic carbon, total nitrogen storage of natural grassland（72.17、6.80 t·hm-2）were significantly higher than that of converting cultivated land to forest-grassland（66.75、4.96 t·hm-2）and oats cultivated land（36.61、3.61 t·hm-2）. This was because, first of all, the disturbance of natural grassland was less than that of converting cultivated land to forest-grassland and oats cultivated land. The second, for converting cultivated land to forest-grassland and oats cultivated land, because of the mowing of plants may lead to take more nutrients away from the soil than the return. The total phosphorus storage of the oats cultivated land （2.51 t·hm-2） was significantly higher than that of the natural grassland （2.17 t·hm-2） and the converting cultivated land to forest-grassland （1.96 t·hm-2）. This was because that fertilizer had been put into the oats cultivated land, so the total phosphorus storage was highest. Compared to natural grassland, at the depth of 0 to 30 cm, the organic carbon and total nitrogen storage of oat cultivated land fell 35.56, 3.19 t·hm-2, the average annual reduction rate was 1.78, 0.16 t·hm-2·a-1; Compared to oats cultivated land, converting cultivated land to forest-g