Influences of interyear rainfall variability and microhabitat on the germinable seed bank of annual plants in a sandy Monte Desert

We addressed the effects of growing-season rainfall of two consecutive years and of two microhabitats on seed density and floristic composition of the germinable seed bank of annual plants in a sandy desert. We hypothesised that seed composition and density is affected by the presence of vegetated patches, but that this effect varies according to rainfall. We predict an overall lower soil-seed density with higher values under shrubs after a dry growing season. We found significant effects of interyear variability and microhabitat on the germinable soil seed bank of annual plants. Twice as many germinable seeds were present in soil after the rainy summer than after the drier summer. Moreover, seed density under shrubs was 1.3 times greater than on bare ground. Although we found no statistic interaction between factors affecting the germinable soil seed density, the relative amount of germinable seeds under shrubs increased after a drier growing season. Species composition showed non-additive effects for the interaction of precedent growing-season rainfall and microhabitat, resulting in four species-assemblages. Altogether, our findings suggest that shrub patches and rainfall events of the precedent growing season may affect the abundance and identity of ephemeral and annual plant species in the germinable seed bank. (C) 2009 Elsevier Ltd. All rights reserved.