氮添加对紫花苜蓿根区土壤养分及土壤微生物量的影响

采用人工氮添加研究了紫花苜蓿根区土壤养分及微生物量对不同氮添加水平[CK；低氮LN，10 g/（m²·a）；中氮MN，20 g/（m²·a）；高氮HN，30 g/（m²·a）]的响应。结果表明:氮添加对紫花苜蓿根区土壤养分及微生物量的影响表现为正的增加效应，对根区土壤全氮含量无明显影响（P > 0.05）；土壤养分及微生物量随氮素的添加呈先增加后降低趋势，均表现为MN > HN > LN > CK，以中水平的氮添加对紫花苜蓿根区土壤微生物量增加效应最为明显；除了土壤全氮以外，不同水平的氮添加处理下土壤养分和微生物量均与CK达到差异显著水平（P < 0.05）；紫花苜蓿根区土壤微生物量对氮添加的敏感性高于土壤养分，其中土壤活性有机碳是不同水平氮添加处理后紫花苜蓿根区土壤养分变化的敏感指标。Pearson相关性分析表明，土壤微生物量和土壤养分与土壤含水量之间具有较强的正相关，二者与土壤pH有较强的负相关，表明了氮添加处理下紫花苜蓿根区土壤理化因子、养分和微生物量等地下生态系统各指标之间的统一性及相互作用和影响。

Effects of Nitrogen Addition on the Soil Nutrient and Microbial Biomass in Root Zone of Medicagosativa

By using a manual nitrogen addition method, the responses of the soil nutrient and microbial biomass in root zone of of Medicagosativa to different nitrogen addition levels such as CK, LN [10 g/(m²·a)], MN [20 g/(m²·a)], HN [30 g/(m²·a)] were examined. The results indicated that the nitrogen addition stimulated the soil nutrient and microbial biomass in root zone, but no significant effect of nitrogen addition on soil total nitrogen in the root zone was observed(P > 0.05). The soil nutrient and microbial biomass in root of Medicagosativa first increased and then decreased with nitrogen additions which showed the order of MN > HN > LN > CK. In all treatments, the soil nutrient and microbial biomass in root zone of Medicagosativa except the soil total nitrogen were significant higher than CK (P < 0.05). The sensibility to nitrogen addition of soil microbial biomass in the root zone of Medicagosativa was higher than that of soil nutrient, and soil active organic carbon was the sensitive indicator to change of soil nutrient in the root zone of Medicagosativa of all treatments. Pearson correlation analysis showed that soil microbial biomass and nutrient had a significant positive correlation with soil moisture and negative correlation with soil pH which illustrated the uniformity of underground ecosystem such as soil physical and chemical factors, nutrient and microbial biomass or other various indicators.