Abstract
Background and aims Soil nutrient content is a major driver of primary productivity. Microbial biomass comprises a substantial soil nutrient pool, the properties of which could be shaped by plant nutrient-limitation status. We aimed to determine how plant nutrition affects soil microbial biomass nitrogen (MBN) and phosphorus (MBP), and whether such effects are linked to microbial composition. Methods To isolate the effect of plant nutrition on soil microbes, we used a split-root system with Syncarpia glomulifera Smith seedlings fertilised with either P-free Hoagland solution or a P-only solution, and quantified rhizosphere soil microbial biomass carbon (MBC), MBN, MBP, and microbial polar lipid fatty acids (PLFAs). Results Provision of N + micronutrients to S. glomulifera seedlings in basalt-derived soils led to a 19% decline in soil MBP relative to controls. This effect was not evident in comparatively P-depleted sandstone-derived soils. MBC and MBN were not affected by plant nutritional status, and neither were the abundances and composition of microbial PLFAs. Conclusion Rhizosphere microbial nutrient pools are potentially sensitive to plant nutritional status. Microbial P can be reduced when plants are P-limited. These effects are not necessarily paralleled by altered microbial composition, implicating microbial physiology as a possible driver of variation in microbial P.