Initial temperature of seed germination as related to species occurrence along a temperature gradient

Abstract

Reproductive stages of life cycle are important for the explanation of distribution patterns of plant species at different scales, due to their extreme vulnerability to environmental conditions. Despite reported evidences that seed germination is related to habitat macroclimatic characteristics such as mean annual temperature (MAT) and precipitation, the role of this trait in controlling plant species distribution is not systematically and quantitatively evaluated yet. Using the data on seed germination along a temperature gradient for 49 species originating from contrasting climatic conditions, we test here whether initial temperature of seed germination (Tmin) is a direct correlate for predicting species distribution ranges along the temperature gradient. Our study reveals that Tmin is strongly negatively correlated with habitat temperature; among the studied species, Tmin clearly increased with decreasing MAT (r2 = 0·57, P < 0·001). Considering phylogenetic biases, co-evolution of seed traits as well as precipitation along with microclimatic factors did not affect the strength of this relationship. The results suggest that the Tmin-MAT relation can provide insights particularly into species distribution patterns, vegetation dynamics and community assembly rules along altitudinal and latitudinal gradients. We argue that including the Tmin in species distribution models may help to improve the accuracy and specificity of predictions of vegetation shifts under global change scenarios.