| 23 Jul 2026
Plant-microbe interactions modulate the effect of soil respiration to P fertilization in a mature Eucalyptus woodland
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.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Biogeosciences.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
