Intracellular plant defense against pathogens is mediated by a class of disease resistance genes known as NB-LRRs or NLRs (R genes). Many of the diseases these genes protect against are more prevalent in regions of higher rainfall, which provide better growth conditions for the pathogens. As such, we expect a higher selective pressure for the maintenance and proliferation of R genes in plants adapted to wetter conditions. In this study, we enriched libraries for R genes using RenSeq from baits primarily developed from the common sunflower (Helianthus annuus) reference genome. We sequenced the R gene libraries of Silphium integrifolium Michx, a perennial relative of sunflower, from 12 prairie remnants across a rainfall gradient in the Central Plains of the United States, with both Illumina short-read (n=99) and PacBio long-read (n=10) approaches. We found a positive relationship between the mean effective annual precipitation of a plant’s source prairie remnant and the number of R genes in its genome, consistent with intensity of plant pathogen coevolution increasing with precipitation. We show that RenSeq can be applied to the study of ecological hypotheses in non-model relatives of model organisms.

Decomposition facilitates the recycling of often limiting resources, which may promote plant productivity responses to diversity, i.e. overyielding. However, the direct relationship between decomposition and overyielding remains underexplored in grassland diversity manipulations. We test whether local adaptation of microbes, i.e. home-field advantage (HFA), N-priming from plant inputs, or precipitation drive decomposition and whether decomposition generates overyielding in an established rainfall and diversity manipulation. Precipitation was a strong, independent driver of decomposition. Grass diversity stimulates decomposition, which decreased with phylogenetic dissimilarity from and densities of the ‘home’ species, providing strong evidence HFA drives decomposition through closely related neighbors, rather than conspecifics. Legumes stimulate decomposition of litter carbon, suggesting N-priming stimulates decomposition. However, decomposition and overyielding were unrelated in legume communities and positively related in grass communities. Combined this suggest diversity stimulates decomposition through multiple mechanisms, but only HFA generates overyielding through resource recycling, linking diversity with ecosystem processes directly facilitating overyielding.