Molecular Phytopathology and Mycotoxin Research, Faculty of Agricultural Sciences, University of Goettingen, Goettingen, Germany.
PLoS One. 2021 Feb 10;16(2):e0246919. doi: 10.1371/journal.pone.0246919. eCollection 2021.
Tree-based intercropping (agroforestry) has been advocated to reduce adverse environmental impacts of conventional arable cropping. Modern agroforestry systems in the temperate zone are alley-cropping systems that combine rows of fast-growing trees with rows of arable crops. Soil microbial communities in these systems have been investigated intensively; however, molecular studies with high taxonomical resolution are scarce.
Here, we assessed the effect of temperate agroforestry on the abundance, diversity and composition of soil bacterial communities at three paired poplar-based alley cropping and conventional monoculture cropland systems using real-time PCR and Illumina sequencing of bacterial 16S rRNA genes. Two of the three systems grew summer barley (Hordeum vulgare); one system grew maize (Zea mays) in the sampling year. To capture the spatial heterogeneity induced by the tree rows, soil samples in the agroforestry systems were collected along transects spanning from the centre of the tree rows to the centre of the agroforestry crop rows.
Tree rows of temperate agroforestry systems increased the abundance of soil bacteria while their alpha diversity remained largely unaffected. The composition of the bacterial communities in tree rows differed from those in arable land (crop rows of the agroforestry systems and conventional monoculture croplands). Several bacterial groups in soil showed strong association with either tree rows or arable land, revealing that the introduction of trees into arable land through agroforestry is accompanied by the introduction of a tree row-associated microbiome.
The presence of tree row-associated bacteria in agroforestry increases the overall microbial diversity of the system. We speculate that the increase in biodiversity is accompanied by functional diversification. Differences in plant-derived nutrients (root exudates and tree litter) and management practices (fertilization and tillage) likely account for the differences between bacterial communities of tree rows and arable land in agroforestry systems.
基于树木的间作（农林复合经营）被提倡用来减少传统耕地种植的不利环境影响。温带现代农林复合系统是一种将速生树木行与耕地作物行相结合的间作系统。这些系统中的土壤微生物群落已经得到了广泛的研究；然而，具有高分类分辨率的分子研究却很少。
在这里，我们使用实时 PCR 和 Illumina 测序细菌 16S rRNA 基因，评估了温带农林复合经营对三个白杨基间作和传统单作耕地系统中土壤细菌群落丰度、多样性和组成的影响。三个系统中的两个系统在采样年份种植夏季大麦（Hordeum vulgare）；一个系统种植玉米（Zea mays）。为了捕捉树木行引起的空间异质性，农林复合系统中的土壤样本沿从树木行中心到农林复合作物行中心的横断面进行收集。
温带农林复合系统的树木行增加了土壤细菌的丰度，而其 alpha 多样性基本保持不变。树木行中的细菌群落组成与耕地（农林复合系统的作物行和传统单作耕地）不同。土壤中的几个细菌群与树木行或耕地强烈相关，这表明通过农林复合将树木引入耕地伴随着引入一个与树木行相关的微生物组。
农林复合系统中树木行相关细菌的存在增加了系统的整体微生物多样性。我们推测生物多样性的增加伴随着功能多样化。植物衍生养分（根系分泌物和树木凋落物）和管理实践（施肥和耕作）的差异可能是农林复合系统中树木行和耕地细菌群落之间存在差异的原因。
