Plant viral richness correlates with both host richness and biomass at different scales in Mediterranean, temperate, and tropical grasslands

In this study, we address a major gap in ecology: while the drivers of species diversity are well explored for many organisms, parasitic microorganisms—particularly viruses—remain understudied. Using standardized metagenomic surveys of global grasslands, we examine how plant community features shape virus richness across scales. We find that virus occurrence is stochastic at fine scales but becomes predictable at 100 m², where it closely tracks host plant richness and biomass, with weaker links to environmental factors. Importantly, plant cover heterogeneity proves more influential than simple species counts. Our results reveal two core mechanisms: niche diversification through host richness and metapopulation persistence, driven by host abundance and connectivity. These insights underscore the value of multi-scale, transmission-informed approaches to understanding viral community dynamics.