Rapid evolution in managed grasslands: different land-use regimes are associated with contrasting phenotypes in Plantago lanceolata

Land-use intensification is a major driver of biodiversity declines, and it is known to decrease species numbers and alter community composition of managed grasslands. An open question is whether similar impacts occur within species, i.e. whether grassland management affects also the genetic diversity of plant populations and alters their genetic composition, possibly reflecting adaptation to land use. To address these questions, we sampled 61 populations of the common grassland herb that covered a broad range of land use intensities in the German Biodiversity Exploratories, and we grew their offspring in a common environment to quantify variation in plant size, architecture, reproduction, and leaf economy. All measured traits harboured substantial heritable variation, and six out of nine traits showed population differentiation. Interestingly, several traits were significantly correlated with land use intensity, but with opposing trends for mowing versus grazing: Increased mowing intensity was associated with larger plant size and lower specific leaf area (SLA), which may reflect evolutionary responses to increased light competition and a lesser need for resource conservation in highly productive meadows. In contrast, increased grazing intensity tended to be associated with smaller plant size and higher SLA, a phenotype syndrome known from grazing lawns. Moreover, we found that land-use intensification also affected genetic diversity, again with opposing effects for mowing versus grazing: while increased mowing was associated with decreased levels of intrapopulation phenotypic variation, the opposite was true for increased grazing intensity. In summary, land use intensification has not only already caused rapid evolutionary changes in these grassland populations, it also affects their future evolutionary potential.