Germination strategies under climate change scenarios along an aridity gradient

Abstract

Abstract Aims Climate change in the eastern Mediterranean region will have a strong impact on ecosystem functioning and plant community dynamics due to a reduction in annual rainfall and increased variability. We aim to understand the role of seed banks as potential buffers against climatic uncertainty determined by climate change. Methods We examined germination strategies of 18 common species present along an aridity gradient. Data were obtained from soil seed banks germinated during nine consecutive years from arid, semi-arid, Mediterranean and mesic Mediterranean ecosystems. At the semi-arid and Mediterranean sites, rainfall manipulations simulating 30% drought and 30% rainfall increase were applied. Germination strategies were tested under optimal irrigation conditions during three consecutive germination seasons to determine overall seed germinability in each soil sample. Changes in germination strategy were examined using a novel statistical approach that considers the climatic and biotic factors that may affect seed germinability. Important Findings The results showed that dominant species controlled their germination fractions by producing seeds with a different yearly germination fraction probability. The amount of rainfall under which the seeds were produced led to two major seed types with respect to germinability: high germinability, seeds leading to transient seed banks, and low germinability, seeds leading to persistent seed banks. We conclude that differential seed production among wet and dry years of both seed types creates a stable balance along the aridity gradient, enabling the soil seed bank to serve as a stabilizing mechanism buffering against rainfall unpredictability. Additionally, we present a general model of germination strategies of dominant annual species in Mediterranean and arid ecosystems that strengthens the notion of soil seed banks as buffers against climatic uncertainty induced by climate change in the region.