Abstract
<jats:p>Abstract. The activity of vegetation and soil microbiota are key drivers of soil respiration and thereby exert a strong control of an ecosystem’s net carbon balance. Plant productivity and soil microbial activity are among others dependent on phosphorus (P) availability; however, P fertilization experiments show ambiguous responses in soil respiration and underlying mechanism are difficult to identify. In the Eucalyptus Free Air CO2 enrichment experiment (EucFACE), which is situated in a mature, P-limited Eucalyptus tereticornis woodland, P fertilization decreased soil respiration, but it is unclear to what extent plant-microbe interactions, specifically plant C allocation to fine root growth, root exudation and microbial activity, contributed to this response. Here we used the terrestrial biosphere model QUINCY-JSM, which comprises an implementation of a root exudation flux dynamically dependent on plant nutrient status, as well as an explicit representation of soil microbial controls on soil organic matter decomposition to investigate how plant-microbe interactions may control the soil respiration response to P fertilization in EucFACE. Simulations suggest that reduced root exudation and increased microbial carbon-use efficiency are major drivers of reduced soil respiration under P addition. Model results further suggest microbial P demand, soil P availability and treatment duration as mediating factors in this response. The model further shows that P addition only marginally influenced the response in soil respiration to CO2 fertilization. Our results indicate soil microbial responses to reduced root exudation and microbial P demands as major drivers, highlighting the need for additional measurements in plant belowground allocation and microbial community traits to improve our understanding of the nutrient-dependence of soil respiration.</jats:p>