Extreme drought has limited effects on soil seed bank composition in desert grasslands

Question Does climate change affect vegetation and seed bank composition in desert grasslands? Location Sevilleta National Wildlife Refuge, New Mexico, USA. Methods Vegetation and seed bank species composition were recorded in black grama (Bouteloua eriopoda) and blue grama (Bouteloua gracilis) grasslands. At each site, two rainfall manipulations and ambient controls were established in 2013 (n = 10). Treatments included extreme drought (-66% rainfall reduction during the growing season) and delayed monsoon (precipitation captured during July-August and reapplied in September-October). Above-ground species composition was assessed, and composite soil samples were collected in 2017, five years after the experiment started. Seed bank was evaluated using the seedling emergence method. Results Rainfall treatments increased the above-ground vegetation and seed bank richness in the blue grama community, but not in the black grama community. Vegetation cover was reduced by both rainfall manipulations, but seed bank density increased or remained the same compared with controls. In above-ground vegetation, cover of annual and perennial forbs increased, and dominant perennial grasses decreased under drought. In the soil seed bank, species composition was similar among all treatments and was dominated by annual and perennial forbs. Conclusions The seed bank was more resistant to drought than above-ground vegetation. Because seed banks can enhance long-term community stability, their drought resistance plays an important role in maintaining ecosystem processes during and following drought in these grassland communities.