杨树人工林幼林阶段林下植被管理对土壤微生物生物量碳、氮酶活性的影响

Abstract

为了探讨林下植物物种多样性对杨树（Populus spp.）人工幼林阶段土壤微生物区系的影响，在林下设计了林下植被物种数量递增的3种处理，即清除林下植被（无林下植物）、保留单一林下植物（一种林下植物）和保留物种多样的自然林下植被（多种林下植物），于处理1年后采样分析土壤微生物生物量碳（MBC）和氮（MBN）含量、基于Biolog-ECO微平板的土壤微生物群落代谢特征以及与土壤碳、氮转化相关的胞外酶活性的差异，以期从土壤养分转化和供应的角度为科学管理人工林林下植被提供依据。结果表明，林下植被处理对8月份0-5 cm土层的土壤MBC、MBN含量以及酶活性有较大影响。与清除林下植被处理相比，保留单一林下植物处理8月份0-5 cm土层的土壤MBC、MBN含量以及β-葡萄糖苷酶、多酚氧化酶和芳基酰胺酶活性显著增加，增幅分别为27.91%、54.48%、14.74%、32.53%和6.20%，而保留物种丰富度高的自然林下植被处理林地土壤的上述指标进一步分别增加了4.88%、14.93%、9.22%、13.63%和12.86%。此外，林下植被处理还改变了土壤微生物群落代谢特征，8月份0-5 cm土层的土壤微生物Shannon指数随着林下植被物种数量的增加而显著增大。清除林下植被处理的土壤微生物主要利用的碳源包括部分糖类、氨基酸类和酯类，与清除林下植被处理相比，保留单一林下植物处理的土壤微生物提高了对上述几种碳源的利用能力，同时对糖类、氨基酸类、酯类和有机酸类碳源的利用种类范围明显扩大，而保留物种多样的自然林下植被的土壤微生物对31种碳源基本上可以全面有效利用。因此，保留林下植被，特别是提高林下植被的物种丰富度，有利于增加土壤微生物生物量，提高土壤微生物的代谢功能和分解活性，可以在一定程度上加快土壤的物质转化和养分循环功能。;Understory vegetation plays crucial roles on nutrient turnover and cycling in plantation soil by regulating soil microbial biomass and extracellular enzyme activity. Under normal condition, the understory vegetation generally contains diverse plant species in plantations. Whether increasing the species abundance of understory vegetation can change the effect of understory vegetation is still inconclusive. In this study, a diversity gradient of understory vegetation species was setup to study its effects on soil microbial biomass carbon (MBC) and nitrogen (MBN), soil microbial communities' metabolic profiles, and enzyme activities that related to soil C and N turnover in a popular plantation. Three understory treatments were designed including the understory vegetation removal, the retention of single main understory vegetation species, and the retention of natural diverse understory vegetation. The soils were sampled in June, August and October after one year treatment for the analysis of corresponding soil microbial properties. The results showed that the understory vegetation treatments had strong effects on 0-5 cm soil layer in August. Compared with understory vegetation removal, the retention of single main understory species resulted in significant increases in soil MBC and MBN contents and the activities of soil β-glucosidase, polyphenol oxidase and arylamidase by 27.91%, 54.48%, 14.74%, 32.53%, and 6.20%, respectively, in the 0-5 cm soil layer in August; moreover, the retention of natural understory vegetation showed further increases by 4.88%, 14.93%, 9.22%, 13.63%, and 12.86%, respectively, when compared with the retention of single main understory species. Understory vegetation treatments also changed soil microbial communities' metabolic profiles, soil microbial Shannon index of the 0-5 cm soil layer in August increased significantly with the increase in understory vegetation species. The main carbon sources utilized by soil microorganism with understory removal treatment were a few kinds of carbohydrates, amino acids and esters. By contrast, soil microorganisms under the retention of single main understory species treatment improved the utilization capacity of the above-mentioned carbon sources, and expanded the available carbon sources to some organic acids. At the same time, the retention of natural diverse understory vegetation enabled soil microorganisms to effectively utilize all of the 31 carbon source types. Therefore, the retention of understory vegetation, especially with high diversity, was beneficial to increase soil microbial biomass, improve soil microbial metabolism and activities, and to a certain extent accelerate the decomposition of soil organic matter and nutrient cycling.