LB 6-55 - Nutrients and climate shape plant community structure based upon genome size

Background/Question/Methods:

Genome size (GS) varies 2400-fold across angiosperms. Given that nucleic acids are some of the most nitrogen- (N) and phosphorus- (P) demanding molecules of cells, it has been hypothesised that differences in GS may alter cellular N and P demands and that nutrient limitations should disproportionately favour plants with smaller GS. Previous research has found that species with larger GS become more productive under conditions with high N and/or P fertilisation, but such findings are not ubiquitous. We tested whether NP enrichment disproportionately favours plants with larger GS and whether such patterns are dependent upon climatic conditions and/or vary amongst plant groups. First, we combined GS with plant annual coverage data from 25 fertiliser trials that are part of the Nutrient Network (https://nutnet.org/). Next, we analysed plot-level data by calculating a metric of average community-weighted genome size (cwGS) and estimated changes in cwGS from pre-treatment conditions using log response ratios. Linear mixed models were fitted to compare change in cwGS under different nutrient conditions and under varying climatic conditions. Lastly, to examine species level responses, change in percentage cover for each plant group was fitted against GS and nutrient treatment in a phylogenetic context using brms.

Results/Conclusions:

Across sites, plot cwGS generally increased under NP enrichment (F_1,689 = 11.38, p = 0.0008), but this increase was climate dependent, becoming less pronounced with increasing temperature (F_3,675 = 2.78, p = 0.04) and precipitation (F_3,675 = 3.12, p = 0.03). These results indicate that the strength of GS-nutrient interactions in influencing growth may be influenced by the extent to which other environmental factors also limit plant growth. At the species level, only grasses with larger genomes showed greater increases in coverage under NP enrichment (μ = 2.45, CI = 1.00, 3.90) while legumes with larger genomes showed greater increases in coverage under P enrichment (μ = 1.30, CI = 0.01, 2.58), further suggesting that GS-nutrient interactions may depend upon what factor limits plant growth. Cumulatively, our results support previous findings that nutrient enrichment can shift community compositions towards species with larger GS but that different plant groups may respond differently to nutrient enrichments and climatic variables. Because GS can fundamentally alter grassland community structure responses to nutrient enrichment, GS should be a useful functional character to include in models for predicting individual species and wider community responses to changes in nutrient availability in complex and varied natural systems.