Agroforestry, which is the integration of trees into monoculture cropland, can alter soil properties and nutrient cycling. Temperate agroforestry practices have been shown to affect soil microbial communities as indicated by changes in enzyme activities, substrate-induced respiration, and microbial biomass. Research exploring soil microbial communities in temperate agroforestry with the help of molecular tools which allow for the quantification of microbial taxa and selected genes is scarce. Here, we quantified 13 taxonomic groups of microorganisms and nine genes involved in N cycling (N2 fixation, nitrification, and denitrification) in soils of three paired temperate agroforestry and conventional monoculture croplands using real-time PCR. The agroforestry croplands were poplar-based alley-cropping systems in which samples were collected in the tree rows as well as within the crop rows at three distances from the tree rows. The abundance of Acidobacteria, Actinobacteria, Alpha- and Gammaproteobacteria, Firmicutes, and Verrucomicrobia increased in the vicinity of poplar trees, which may be accounted for by the presence of persistent poplar roots as well as by the input of tree litter. The strongest population increase was observed for Basidiomycota, which was likely related to high soil moisture, the accumulation of tree litter, and the absence of tillage in the tree rows. Soil microorganisms carrying denitrification genes were more abundant in the tree rows than in the crop rows and monoculture systems, suggesting a greater potential for nitrate removal through denitrification, which may reduce nitrate leaching. Since microbial communities are involved in critical soil processes, we expect that the combination of real-time PCR with soil process measurements will greatly enhance insights into the microbial control of important soil functions in agroforestry systems.

中文翻译：

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温带农林农田中的杨树行促进土壤中的细菌，真菌和反硝化基因。

农林业是将树木整合到单一种植农田中，可以改变土壤特性和养分循环。酶活性，底物诱导的呼吸作用和微生物生物量的变化表明，温带农林业实践会影响土壤微生物群落。在分子工具的帮助下，对温带农林中土壤微生物群落进行探索的研究很少，该工具可以对微生物分类群和选定的基因进行量化。在这里，我们使用实时荧光定量PCR定量分析了三对温带农林和常规单作耕地土壤中N循环（N2固定，硝化和反硝化）的13个微生物分类群和9个基因。农林业农田是基于杨树的胡同种植系统，在该系统中，在树行中以及在距树行三段距离的作物行中收集了样本。在杨树附近增加了酸性细菌，放线菌，α和γ变形杆菌，Firmicutes和Verrucomicrobia的丰度，这可能是由于存在持久的杨树根以及输入树木凋落物造成的。观察到的担子菌种群增长最强，这可能与土壤湿度高，树木凋落物的积累以及树木行耕作的缺乏有关。与农作物行和单一栽培系统相比，树行中携带反硝化基因的土壤微生物更为丰富，这表明通过反硝化去除硝酸盐的潜力更大，这可以减少硝酸盐的浸出。由于微生物群落参与了关键的土壤过程，因此我们期望将实时PCR与土壤过程测量相结合将大大增强对农林业系统中重要土壤功能的微生物控制的认识。