Effects of leaf silicon on drought performance of tropical tree seedlings

Elevated leaf silicon (Si) concentrations improve drought resistance in
cultivated plants, suggesting Si might also improve the drought
performance of wild species. Tropical tree species, for instance, take up
substantial amounts of Si, and leaf Si varies markedly at local- and
regional-scales, suggesting consequences for seedling drought resistance.
Yet, whether elevated leaf Si improves seedling drought performance in
tropical forests is unknown. To manipulate leaf Si concentrations,
seedlings of seven tropical tree species were grown in Si-rich and -poor
soil, before exposing them to drought in the forest understory. Survival,
growth, and wilting were monitored. Elevated leaf Si did not improve
drought survival and growth in any of the species. In one species, drought
survival was reduced in seedlings previously grown in Si-rich soil,
contrary to our expectations. Our results suggest that elevated leaf Si
does not improve the drought resistance of wild tropical tree species.
Elevated leaf Si may even reduce drought performance, suggesting
differences in soil conditions influencing leaf Si may contribute to
soil-related variation of tropical seedling performance. Furthermore, our
results are at odds with most studies on cultivated species and show that
alleviative effects of Si in crops cannot be generalized to wild plants in
natural systems.