Drought considerably affects physiological and biochemical processes in trees and thus also reproduction. However, little is known about shifts in reproductive strategies in relation to changes in water availability.
We investigated cone and seed traits as well as needle and twig growth traits in pine trees along a natural precipitation gradient (290 mm–750 mm) and in a long-term irrigation experiment to understand reproductive responses to water availability. Combining multiple traits, we found that cone trait richness and divergence were positively correlated with water availability. This suggests drought-induced environmental filtering resulting in a reduced set of cone trait combinations. In contrast, seed trait diversity indices were negatively correlated with water availability, suggesting that pine trees tend to maximize seed trait dissimilarity in multiple dimensions to efficiently utilize scarce resources. Trade-offs between reproduction and vegetative growth were observed along the transect but not in the irrigation experiment, which may be a result of different drought severity between the two study regions.
Our results highlight the importance of considering a broad aridity gradient and different spatial-temporal scales when studying plant reproductive responses to precipitation change. Furthermore, the present study indicates that quantifying complementary components of trait diversity allows to interpret ecologically complex changes in trait distribution in multiple dimensions.