N & P Availability and Selection Pressures Towards Small Angiosperm Genome Sizes

Angiosperm genome sizes range an astonishing 2,400 fold between species. We investigate the hypothesis that this large range in genome size has ecological consequences for plants, arising because DNA is highly demanding in terms of Nitrogen (N) and Phosphorus (P). We correlate N availability with genome size (C-values database), conducted our analysis using phylogenetic independent contrasts superimposed onto a 17-gene tree comprising 345 species of angiosperms. We observed that for plants with a 1C-value >5 pg there was a significant positive relationship between soil N and C-value. We further analyzed how N and P inputs influence plant biomass and genome size at the long-term ecological experiment Park Grass continuous hay experiment in SE England. Plots with both N and P input are significantly higher in biomass-weighted mean genome sizes than control plots and plots where only N or P have been added. The biomass of plants with large genomes also decreased under nutrient limitation, associated with an increase in abundance of plants with small genomes. These results are consistent with the hypothesized effect of macronutrient limitation on large genomes. We propose that the overall trend towards genome downsizing following polyploidy arises because of selection pressures caused by limiting N and/or P.