Mesquite-associated soil and phyllosphere microbial communities differ across land use types in drylands

Plant-associated microbiomes play prominent roles in maintaining plant health and productivity. Here, we characterized the soil and phyllosphere microbiomes associated with mesquite trees in grazing and urban areas compared to natural areas in the arid Southwestern USA. Our results showed that grazing areas were associated with higher phyllosphere fungal richness, while urban areas had higher phyllosphere richness for both fungi and bacteria/archaea, and additionally, urban soils had lower fungal richness. Specifically, grazing areas were characterized by larger proportions of nitrogen-fixing bacteria in the soil and fungal plant pathogens in the phyllosphere, while urban areas presented higher proportions of fungal plant pathogens in both the soil and phyllosphere as well as nitrifying and denitrifying bacteria in the phyllosphere, but a lower proportion of cellulolytic bacteria in the soil. Furthermore, in urban areas more phyllosphere microorganisms were sourced from the soil. Collectively, these results suggest that plant-associated microbiomes change significantly across land use types, and these patterns are different between above- and below-ground parts of plants, and between bacteria/archaea and fungi. These changes in plant-associated microbiomes across land use types might have important implications for nutrient cycling, plant health, and ecosystem restoration.

植物相关微生物组（plant-associated microbiomes）在维持植物健康与生产力方面发挥着关键作用。本研究针对美国西南部干旱地区放牧与城市生境中的牧豆树关联土壤及叶围微生物组（phyllosphere microbiomes）展开表征分析，并以该区域的天然生境作为对照。研究结果显示，放牧生境的叶围真菌物种丰富度更高；城市生境的叶围真菌与细菌/古菌（bacteria/archaea）物种丰富度均处于较高水平，且城市土壤的真菌物种丰富度相对更低。具体而言，放牧生境的土壤中固氮细菌（nitrogen-fixing bacteria）占比更高，叶围则富集植物病原真菌；城市生境的土壤与叶围中植物病原真菌占比均更高，叶围同时存在更高占比的硝化细菌（nitrifying bacteria）与反硝化细菌（denitrifying bacteria），但土壤中的纤维素分解细菌（cellulolytic bacteria）占比更低。此外，城市生境的叶围微生物更多源自土壤。综合来看，本研究结果表明，植物相关微生物组的组成会随土地利用类型发生显著改变，且这种变化模式在植物地上、地下部分之间，以及细菌/古菌与真菌之间均存在差异。土地利用类型驱动的植物相关微生物组变化，可能对养分循环、植物健康及生态系统修复具有重要意义。