短期型林(竹)-草复合植被还林初期土壤碳氮动态变化

Soil Organic Carbon and Nitrogen Dynamics of Forest(Bamboo)-Grass Compound Vegetation in Initial of Conversion Cropland to Forest

对退耕地短期型光皮桦-扁穗牛鞭草和苦竹-扁穗牛鞭草复合植被还林初期（1～7年）不同年份土壤表层（0～20cm）和下层（20～40cm）土壤有机碳（Soil organic carbon．SOC）和全氮（Soil total nitrogen，TSN）含量进行了定位研究，探讨了退耕还林初期SOC和氮变化规律。研究表明：SOC和STN随恢复时间的延长呈先下降后增加趋势，光皮桦-扁穗牛鞭草和苦竹-扁穗牛鞭草表层SOC和STN分别在第6年和第4年时开始恢复，下层土均在第5年时开始回升；还林后各年之间C／N变化不大，只是在第2，3年有所升高，表现为土壤氮素有一定缺乏；还林7年后，苦竹-扁穗牛鞭草的SOC和C／N均高于光皮桦-扁穗牛鞭草，但其土壤氮素改善状况不甚明显。还林7年后土壤碳氮含量虽尚未恢复到农耕地水平，但随着退耕年限的延长，土壤碳氮素水平正在逐渐恢复，初步显示了实行退耕还林工程后土壤SOC和氮的固存效应。

Based on located research method, soil organic carbon （SOC） and soil total nitrogen （STN） contents in 0 - 20 cm （upper） and 20- 40 cm （below） soil layer of Betula lumlnifera - Hemarthria compressa and Pleioblastus amarus - Hernarthria cornpressa two vegetations were analyzed in the initial（1 - 7 year） of conversion cropland to forest. The results showed that SOC and STN contents in two layers of B. lurninlfera - H. cornpressa and P. arnarus - H. compressa two vegetations rapidly decreased in the beginning and subsequently increased with time, those in the upper layer accumulated in the sixth year and the fourth year respectively, but those in the below layer both accumulated in the fifth year. C/N ratio only increased in the second or third year but showed indistinct change in other years. After seven years＇ vegetation restoration, SOC contents and C/N ratio of 19. amarus - H. cornpressa vegetation were higher than B. luminifera - H. compressa, but the improving condition of soil nitrogen was not obvious. Following the conversion cropland to forest project, the soil carbon and nitrogen content were picking up and appearing sequestration effects despite that they didn＇t restore the level of cropland.