暖温带森林土壤微生物量、群落结构和活性对植物地下碳源的响应

该研究以典型的亚热带—温带过渡区森林为对象，采用野外过程监测和控制试验相结合的方法，利用磷脂脂肪酸和土壤胞外酶活性分别表征土壤微生物群落结构和活性，并结合微环境因子，重点探究土壤微生物生物量、群落结构和活性对植物地下碳输入的响应特征。结果表明：在观测周期内，处理均能显著降低三组年龄段林分的土壤微生物量碳，其变化幅度在－8.72％~－5.72％之间，其中在80年的林分中降幅最大，而在160年的林分中降幅最小；微生物量氮的变化规律与相应的微生物量碳的变化规律相似，但与对照相比其差异性均未达到显著性水平；另外，经壕沟处理2~4个月后，所有林分的土壤微生物量碳和氮与对照相比出现增加的现象。处理均能对三组年龄段林分的土壤微生物群落结构产生不同程度的影响，其中40年林分的土壤微生物群落对处理的响应程度要高于另外两个年龄段的林分；与对照相比，壕沟处理样方的腐生真菌的相对丰富度均下降明显，其中在40年和80年林分中的下降幅度达到显著水平，而细菌、放线菌和丛枝菌根真菌均无明显变化；壕沟处理样方的水解酶(β-葡萄糖苷酶和N-乙酰-葡萄糖苷酶)活性均显著下降，而氧化酶(酚氧化酶和过氧化物酶)活性的变化相对较小，除80年的林分外，其余林分均不显著。此外，处理均不能显著影响土壤的含水量和温度。该研究结果为初步阐明全球气候变化背景下森林土壤微生物结构及其功能的变化特征以及更加精确预测未来森林土壤碳的变化趋势提供了科学依据。

Responses of soil microbial biomass, community structure and soil enzyme to below-ground carbon change in the warm-temperate forest ecosystem

This study focuses on the controlling mechanisms of soil microbial community structure and function to the change of below-ground carbon inputs through root-trenching experiments in a typical forest ecosystem of the subtropical and temperate transitional zone in China. By combining field investigations and manipulation experiments, phospholipid fatty acids (PLFAs) and activities of soil extracellular enzymes were studied as indicators of soil microbial community
structure and functioning. We also studied the response characteristics of soil microbial biomass, community structure and activities in below-ground carbon inputs. The results showed that soil microbial biomass carbon in root-trenching plots reduced significantly in an age sequence of Quercus aliena forest (40-year-old, 80-year-old, and >160-year-old). Integrated over the entire experimental period; the mean difference of soil microbial biomass carbon in root-trenching plots were reduced between-8.72%and-5.72%, and the highest reduction was in the 80-year-old forests, whereas the lowest decline was in the 160-year-old forests. The variation of soil microbial biomass nitrogen was similar with the chan-ges of soil microbial biomass carbon in the forest stands of similar age, but compared with the control plots, it did not decrease significantly. In addition, compared with the control plots, the soil microbial biomass carbon and nitrogen in all forest stands increased after trench for 2 to 4 m. The root-trenching can produce different effects on soil microbial commu-nity structure in all forest stands, the response of microbial communities to the change of below-ground carbon input in 40-year-old forests were higher than the other two age groups. The relative abundances of saprotrophic fungal community in root-trenching plots was declined sharply in all stands, and it reduced significantly in 80 and 160-year-old forests com-pared to control. Other communities like bacteria, actinomycete and arbuscular mycorrhizal fungi changed slightly in all forest stands;the hydrolase activities ( i. e. β-1,4-glucosidase and β-1,4-N-acetylglucosaminidase) in root-trenching plots decreased remarkably in the 40, 80 and 160-year-old stands, but the oxidase activity (i.e. phenol oxidase and per-oxidase) was not diminish in all plots except 160-year-old stands. The root-trenching treatment had no obvious influence on soil moisture and soil temperature. By addressing the response characteristics of soil microbial biomass, community structure and function on the plant root carbon input, this study sheds light on the trends of soil microbial structure and function change under the context of global climate change. This study shows the need for more accurate prediction trends of forest soil carbon in the future.