Compound and simple leaf woody species of the Chilean matorral are equally affected by extreme drought

Two main leaf types are recognized among vascular plant species: compound and simple. Compound leaves are believed to be photosynthetically more productive than simple ones, by diluting mass tissue in more projected area. Conversely, simple leaves are believed to be more stress-tolerant by packing mass tissue in less projected area during stress like drought. Nevertheless, convective cooling is more efficient in compound than simple leaves, a process that could alleviate water loss in drought periods. In Central Chile, woody species with simple and compound leaves coexist. This zone is facing a mega-drought event, causing browning and tree mortality. However, how severe droughts affect photosynthetic traits on both leaf-type species have not been addressed so far. We measured photosynthetic traits in well-watered and drought conditions in three compound and three simple leaf species, and drought response ratios were obtained. We hypothesized that with no water limitation compound leaf species will show higher net photosynthesis (A(N)) than simple leaf species associated with a higher mesophyll conductance (g(m)). Opposite results are expected for simple leaf species due to their stress-tolerant physiology, showing fewer changes in their photosynthetic traits. We found that g(m) and A(N) were larger in compound leaf species in well-watered conditions. With drought, both leaf-type species were negatively affected despite foliar temperature in compound leaf species was 4 degrees C lower. Our result suggests that regardless of leaf shape the matorral species in Central Chile will be seriously affected in their A(N) due to the megadrought currently affecting this zone.

Automated summary

There are two main types of leaves in vascular plant species: compound and simple. Compound leaves have higher productivity due to their larger projected area, while simple leaves have higher stress tolerance during drought due to their ability to pack more mass tissue in a smaller projected area. However, compound leaves have more efficient convective cooling, which helps alleviate water loss in drought periods. In Central Chile, both simple and compound leaf species coexist, but the impact of severe droughts on their photosynthetic traits has not been studied. This study found that compound leaf species had higher net photosynthesis (A(N)) and mesophyll conductance (g(m)) under well-watered conditions. However, both leaf types were negatively affected by drought, despite compound leaves having lower foliar temperature. This suggests that the matorral species in Central Chile will be severely impacted in terms of A(N) by the ongoing megadrought in the region.