The phosphorus legacy of former agricultural land use can affect the production of germinable seeds in forest herbs

Abstract

Land-use history can have large effects on the different life stages and demography of forest plant species. Here we studied how the legacies of former land use in post-agricultural forests, and increased phosphorus (P) availability in particular, may alter the germinability and seed quantity in populations of the forest herbs Primula elatior and Geum urbanum. We collected seeds in experimental populations of P. elatior and G. urbanum established in post-agricultural and ancient forest stands 10 y ago and determined the number of seeds per fruit and germination percentage. The effect of P availability on the production of germinable seeds was tested in a pot experiment with 3 P levels. Former land use had an impact on the mean germination percentage: seed germinability tended to be higher in post-agricultural compared to ancient forest sites. For G. urbanum, the number of seeds per fruit was also higher in post-agricultural forest. Whereas P availability had no effect on G. urbanum seed quantity and germinability, the germination percentage of P. elatior seeds increased significantly with P supply. Whereas previous studies showed that former agricultural land use can have detrimental effects on particular life stages of forest herbs (e.g., reduced juvenile or adult survival), the production of germinable seeds might rather benefit from it. The environmental legacies of former land use thus affect the various life stages of a plant differently, which results in complex effects of land-use history on the demography of forest plants.