Trait-density-microsite interactions indicate plastic and non-plastic germination strategies of co-occurring desert annual plants

Abstract

Functional traits have been linked to relevant vital rates across co-occurring species, such as growth and survival. However, the relationship between plant traits and germination has been much less studied, despite that germination can be a key transition for plants. Building on evolutionary theory, we propose that variation in germination fraction across co-occurring desert annual plants may result from the interaction of post-germination plant traits, density dependence and microsite type. Our study system consisted of three summer annual species abundant in a desert in western Argentina, for which we quantified germination fractions in three microsite types: Larrea divaricata shrub, Bulnesia retama shrub, and open spaces among shrubs. Based on post-germination trait data (summarized by a principal component, PC1), the annual species can be arranged in terms of increasing stress-tolerance, from Amaranthus standleyanus, to Gomphrena martiana and Tribulus terrestris. We found an interaction between PC1 and density of conspecific seeds suggesting that the strength of plastic negative density-dependence decreased with the increase of plant stress-tolerance. Our results emphasize that both plastic and non-plastic (bet-hedging) mechanisms would contribute to shape germination dynamics across annual plants, and that plant traits can offer parsimonious explanations for such cross-species variation.