Divergent responses of seed banks and aboveground vegetation to drought and deluge in grasslands across an elevational gradient

Increased variability in precipitation associated with climate change creates extreme conditions of drought and deluge that can have profound effects on the abundance and composition of plant communities. Responses to these extremes likely vary across climatic gradients and depend on local plant community composition, which includes the emergent, aboveground vegetation as well as belowground seed banks. Because seed banks can both buffer the effects of environmental change and influence the future trajectories of communities, it is critical to understand seed bank responses to precipitation extremes in relation to the aboveground vegetation and how patterns vary across environmental gradients. Here we quantified the responses of aboveground and seed bank communities at five perennial grass-dominated sites across an elevational gradient to 6 years of extreme drought and deluge, by implementing experimental water exclusion and water addition treatments. Responses were stronger for drought than for deluge. Drought decreased abundance aboveground, while seed bank abundances were generally unaffected. Similarly, drought decreased richness and diversity of aboveground vegetation at intermediate elevations, without concurrent changes in seed banks. Surprisingly, the lowest and middle elevation sites showed stronger shifts in functional composition and dissimilarity in response to treatments, despite the expectation of greater buffering in seed banks in more arid environments. The relatively attenuated responses of seed bank communities to drought and deluge suggest potential for resistance and recovery, though species and functional composition may show greater responses to change particularly in more arid, lower elevation sites.