The effect of soil pH on persistence of seeds of grassland species in soil

Soil pH is one of the main factors determining grassland plant community composition. However, its effects on seed persistence are not well understood, and it is not clear whether soil pH influences seed persistence, either directly or indirectly through microbial pathogens. This study examined the soil seed bank along a natural pH gradient from acidic to calcareous grassland in the Peak District National Park, UK. In addition, a seed burial experiment was performed using three species and including a fungicide treatment. Seeds of a calcicole species (Scabiosa columbaria), a calcifuge (Hypericum pulchrum) and a third species growing over a wide range of soil pH (Campanula rotundifolia) were buried, and seed germination, viability and damage (both physical and fungal) were recorded. Increasing soil pH was correlated with decreased total and grass seed abundance in the seed bank, and with a decline in the probability that H. pulchrum seeds persisted, mainly due to physical damage. In soils with pH higher than 5.6, fungicide increased seed persistence of all three species. Viability of intact, undamaged seeds and germination were not affected by soil pH. Decreasing soil pH was correlated with an increased proportion of persistent seeds. Results suggest that acid soils are associated with increased seed persistence, the size and longevity of grassland seed banks decrease as soil pH increases, and that pH influences seed persistence by an indirect effect mediated by microbial pathogens, while germination is not influenced by pH.