Mapping and predictive variations of soil bacterial richness across France

Although numerous studies have demonstrated the key role of bacterial diversity in soil functions and ecosystem services, little is known about the variations and determinants of such diversity on a nationwide scale. The overall objectives of this study were i) to describe the bacterial taxonomic richness variations across France, ii) to identify the ecological processes (i.e. selection by the environment and dispersal limitation) influencing this distribution, and iii) to develop a statistical predictive model of soil bacterial richness. We used the French Soil Quality Monitoring Network (RMQS), which covers all of France with 2,173 sites. The soil bacterial richness (i.e. OTU number) was determined by pyrosequencing 16S rRNA genes and related to the soil characteristics, climatic conditions, geomorphology, land use and space. Mapping of bacterial richness revealed a heterogeneous spatial distribution, structured into patches of about 111km, where the main drivers were the soil physico-chemical properties (18% of explained variance), the spatial descriptors (5.25%, 1.89% and 1.02% for the fine, medium and coarse scales, respectively), and the land use (1.4%). Based on these drivers, a predictive model was developed, which allows a good prediction of the bacterial richness (R2adj of 0.56) and provides a reference value for a given pedoclimatic condition.

尽管已有诸多研究证实了细菌多样性在土壤功能与生态系统服务中的核心作用，但目前学界对全国尺度下该多样性的变异规律及其驱动因子仍知之甚少。本研究的总体目标为：一是厘清法国全境土壤细菌分类丰富度的空间变异特征；二是明确影响该分布格局的生态过程（即环境筛选与扩散限制）；三是构建土壤细菌丰富度的统计预测模型。本研究依托法国土壤质量监测网络（French Soil Quality Monitoring Network, RMQS），该网络在法国全境共设置2173个采样点位。研究通过焦磷酸测序16S rRNA基因测定土壤细菌丰富度（即操作分类单元数，Operational Taxonomic Unit, OTU），并将其与土壤理化性质、气候条件、地貌特征、土地利用方式及空间位置进行关联分析。细菌丰富度的空间分布制图结果显示，其呈现异质性空间分布格局，形成约111km的斑块结构；主要驱动因子包括土壤理化性质（解释方差占比18%）、空间特征变量（精细尺度、中尺度、粗尺度分别占5.25%、1.89%与1.02%）以及土地利用方式（1.4%）。基于上述驱动因子，本研究构建了预测模型，该模型可对土壤细菌丰富度实现良好预测（调整决定系数R²_adj为0.56），并可为特定土壤气候条件下的细菌丰富度提供参考阈值。