Cascading Effects Of N Fertilization Activate Biologically Driven Mechanisms Promoting P Availability In A Semi-Arid Grassland Ecosystem

1. Nitrogen (N) fertilization due to N deposition, N in manure from grazing livestock and direct input to soil by humans are impacting our terrestrial ecosystems globally. However, to date, our understanding of how artificial gradients of N fertilization indirectly affect phosphorus (P) availability by altering the rates and interrelationships of multiple structural and functional attributes of terrestrial ecosystems is still limited.2. Here, we conducted a 3-year field experiment to evaluate the direct and indirect effects of multiple level of N addition on a wide range of ecosystem structural and functional attributes associated with >20 plant, soil and microbial variables in a semi-arid grassland.3. We found that N fertilization can have multiple cascading effects on ecosystem structures and functions. These cascading events ultimately result in the activation of multiple biologically driven mechanisms to promote P availability (e.g. increased soil organic P mineralization, plant phosphorus resorption, enzymatic and genetic processes of phosphatase). The increasing phosphatase production and its functional gene expression, and decreasing plant and microbial biomass might imply important shifts in the carbon-use strategies of plants and microbes allocating more resources to high-C consuming enzymatic and genetic processes and less in plant and microbial biomass. Nitrogen addition decreases fungal community biomass which suggests the decoupling of key symbiotic plant-fungal relationships for nutrient acquirement.4. Overall, our study advances our understanding of how and why N fertilization simultaneously influences multiple structural and functional attributes, ultimately accelerating phosphorus cycle in terrestrial ecosystems.