Nitrogen and phosphorus fertilization consistently favor pathogenic over mutualistic fungi in grassland soils

Ylva Lekberg,Jonathan W Leff,Lorinda S Bullington,Noah Fierer,Elizabeth T Borer,Peter G Kennedy,Eric W Seabloom,Carlos A Arnillas,Jeremiah A Henning,Angela D Luis

doi:10.1038/s41467-021-23605-y

Abstract

Ecosystems across the globe receive elevated inputs of nutrients, but the consequences of this for soil fungal guilds that mediate key ecosystem functions remain unclear. We find that nitrogen and phosphorus addition to 25 grasslands distributed across four continents promotes the relative abundance of fungal pathogens, suppresses mutualists, but does not affect saprotrophs. Structural equation models suggest that responses are often indirect and primarily mediated by nutrient-induced shifts in plant communities. Nutrient addition also reduces co-occurrences within and among fungal guilds, which could have important consequences for belowground interactions. Focusing only on plots that received no nutrient addition, soil properties influence pathogen abundance globally, whereas plant community characteristics influence mutualists, and climate influence saprotrophs. We show consistent, guild-level responses that enhance our ability to predict shifts in soil function related to anthropogenic eutrophication, which can have longer-term consequences for plant communities.

Highlights

Ecosystems across the globe receive elevated inputs of nutrients, but the consequences of this for soil fungal guilds that mediate key ecosystem functions remain unclear
We predicted that arbuscular mycorrhizal fungi (AMF) would be suppressed by P and respond less consistently to N, whereas pathogens would be promoted by N and possibly be suppressed by P
To identify the underlying mechanisms, we used structural equation modeling (SEM) to determine if guild responses were directly driven by N and P, or indirectly mediated by plant community responses

Summary

Results and discussion

Guild responses to N and P additions. Independent and combined N and P addition promoted fungal pathogens as we observed an average increase of 140% in N + P plots relative to control plots in relative pathogen abundances. Compared with pathogens and mutualists, nutrient addition did not alter the relative abundance of fungal saprotrophs (Fig. 1 and Supplementary Fig. 1), concordant with an earlier study conducted along a soil fertility gradient[42]. This lack of response was evident despite an increase in productivity and may be because litter biomass, and substrate inputs, did not increase with N or P addition (Supplementary Table 1). Even though we found directional responses to N and P addition by putative pathogens and AMF across sites, among-site variability and pre-treatment soil conditions explained more variability than the N and P effects or the differences among plant communities at the time of sampling. De-aggregating bulk fungal responses and examining differences among fungal guilds will help us better predict soil function and responses to future perturbations

Limitations

Methods

Code availability