根系隔离和氮添加对湿性常绿阔叶林土壤碳氮组分的影响

Effect of root isolation and nitrogen addition on soil carbon and nitrogen component in a moist evergreen broad-leaved forest

持续增加的氮（N）沉降改变了森林生态系统土壤的养分状况和光合产物的分配,从而影响了根系分泌物质和量以及根凋落物分解过程.为揭示根系在土壤碳（C）、N组分响应N沉降增加中的作用,于2013年4月起在瓦屋山湿性常绿阔叶林中开展N添加试验,N添加1年后利用壕沟法在各样地设置根系隔离子样方.N添加和根系隔离分别处理3.5年和2.5年后,取土样分析各处理腐殖土壤层（A层）和矿质土壤表层（B层）的C、N组分.结果表明：根系隔离显著降低了A层土壤的总有机C和总N含量（P〈0.05）;N添加显著提高了A、B土壤层硝态N含量而降低了土壤pH值,且土壤pH值与土壤硝态N之间呈极显著的负相关关系（P〈0.05）;N添加与根系隔离交互效应不显著.本研究表明根系对湿性常绿阔叶林土壤C、N储存有重要影响,而N沉降可提高土壤N可利用性并导致土壤酸化.

Increasing nitrogen（N） deposition changes soil nutrient status and photosynthate distribution, thereby affecting the quality and quantity of root exudate and root litter decomposition. The effect of roots on soil carbon（C） and N component response to increasing N deposition was investigated by performing an N addition experiment since April 2013 in a moist evergreen broad-leaved forest of Wawu Mountain. One year later, sub-plots of root isolation were established using the trench method. After 3.5 years of N addition and 2.5 years of root isolation, the fractions of soil C and N in humus horizon（layer A） and upper mineral soil（layer B） were measured. The results showed that root isolation significantly decreased the total organic C and total N concentrations in layer A（P〈0.05）. Nitrogen addition increased soil NO_3^--N and decreased soil pH in layers A and B. A significant negative correlation was noted between pH and NO_3^--N（P〈0.05）. However, N addition and root isolation had no interactive effect. This study indicates that roots play an important role in C and N storage of moist evergreen broadleaved forest soil. Nitrogen deposition can increase soil NO_3^--N and decrease soil p H value.