Dryland (arid and semiarid) ecosystems are extensive, home to a third of the human population, and a major contributor to terrestrial net primary productivity and associated biogeochemical cycles. Many dryland systems are undergoing woody plant encroachment, which can substantially alter landscape‐scale soil nutrient dynamics via long‐recognized “islands of fertility” mechanisms. To effectively constrain soil biogeochemistry responses to woody plant encroachment, predictions are needed for microbial biomass and especially microbial activity in addition to existing predictions for soil nutrients—referred to collectively hereafter as “collective soil functioning.” Here we evaluated whether collective soil functioning could be predicted from a suite of metrics including plant cover, precipitation, soil physiochemical characteristics, and topographic variables across complex landscapes undergoing woody plant encroachment by mesquite (Prosopis velutina). Plant cover alone predicted nearly half of the variability (R² = 48.5%) in collective soil functioning and had a significant effect on each component of this index (soil nutrients, microbial biomass, and microbial activity). Prediction strength for collective soil functioning increased to 55.4%, and the error term decreased by 13.4% when precipitation, soil physiochemical characteristics, and topographic metrics were also included in models (plant and environment model). Besides the expected effects of plant cover, other significant predictors of collective soil functioning included state factors such as topography, precipitation, and parent material along with soil age and bulk density. These results illustrate that mesquites influence many components of soil functionality but the strength of this effect depends on which component is analyzed and which environmental variables are considered.

中文翻译：

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木本植物侵占在复杂景观中预测土壤集体功能的动因

旱地（干旱和半干旱）生态系统十分广泛，人口占三分之一，是陆地净初级生产力和相关生物地球化学循环的主要贡献者。许多旱地系统都在遭受木本植物的侵害，这可以通过长期公认的“增肥岛”机制来大大改变景观尺度上的土壤养分动态。为了有效地限制土壤对木本植物入侵的生物地球化学反应，除了对土壤养分的现有预测外，还需要对微生物生物量尤其是微生物活性进行预测（以下统称为“集体土壤功能”）。在这里，我们评估了是否可以通过一系列指标（包括植物覆盖率，降水，土壤理化特性，螺旋藻（Prosopis velutina）。仅植物覆盖率就预测了近一半的变异性（R ² = 48.5％）在集体土壤功能中发挥作用，并且对该指数的每个组成部分（土壤养分，微生物生物量和微生物活性）都有显着影响。在模型（植物和环境模型）中还包括降水，土壤理化特性和地形指标的情况下，集体土壤功能的预测强度提高到55.4％，误差项降低了13.4％。除了对植物覆盖的预期影响外，集体土壤功能的其他重要预测指标还包括状态因素，如地形，降水和母体材料，以及土壤年龄和容重。这些结果说明了豆科灌木林会影响土壤功能的许多组成部分，但这种作用的强度取决于所分析的组成部分和所考虑的环境变量。