Plant Genome Size Is Associated With Fine‐Scale Spatial Variation in Soil Depth, but Not Climatic Conditions, in the Grass <i>Festuca ovina</i>

Genome size varies among individuals within plant species and their populations. Interspecific variation in plant genome size is associated with phenology, climate, and latitude and longitude-suggesting that genome size may be linked with environmental adaptation-but the evolutionary significance of intraspecific variation in genome size remains unresolved. In particular, little is known regarding how selection under different climatic and micro-environmental conditions shapes intraspecific variation in genome size. We measured genome size within <i>Festuca ovina</i> populations collected from grassland plots exposed to 16 years of experimental drought treatment at the Buxton Climate Change Impacts Laboratory. We assessed whether genome size was associated with either drought treatment or fine-scale heterogeneity in soil depth within grassland plots. Genome size varied by up to 1.28-fold among <i>F. ovina</i> individuals, but was not associated with either drought treatment or plant phenotypes (cell size, flowering time, and biomass). Genome size was, however, negatively associated with fine-scale variation in soil depth, implying that abiotic and biotic conditions linked with soil depth impose either direct or indirect selection on genome size. We suggest that the higher nutrient availability and reduced competition associated with shallow soils enable individuals with larger genomes to persist locally within the grassland.