The frequency and mechanisms behind drought-induced hydraulic failure in woody angiosperms from temperate to tropical biomes

• Applicant: Professor Dr. Steven Jansen
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410768178

As the flow of water through plants has utmost importance for the functioning of our biosphere and the human population, most people would be extremely surprised to learn that it is still unknown how exactly plants accomplish long-distance water transport. While there is massive evidence for water transport in plant xylem under negative pressure, it is still unknown whether hydraulic failure by air entry represents a common or rare occurrence. This project aims to investigate the frequency of drought-induced embolism in woody angiosperms and the underlying mechanisms of embolism at the bordered pit level in water conducting cells. By conducting field work at a temperate forest in Germany and a savannah and seasonal rainforest site in China for a total of 30 angiosperm species, we will test the hypothesis that a diverse range of species show a similar relative risk to hydraulic failure, despite clear differences in absolute resistance to drought-induced embolism. We expect that hydraulic failure in the field is largely limited to extreme events. Comparison of embolism resistance in stems and leaves will allow us to test the hydraulic vulnerability segmentation hypothesis, suggesting that xylem in leaves is more prone to hydraulic failure than stem xylem.Moreover, we will test the idea that embolism resistance is associated with the potential occurrence of positive root/stem pressure, and/or with seasonal changes in xylem sap lipids. While positive root/stem pressure is known in various species of temperate forests during spring, it is unclear if root/stem pressure is common in plants from the savannah and seasonal rainforest areas. Since insoluble, amphiphilic lipids were recently discovered in xylem sap of angiosperms, we hypothesize that seasonal drought determines the quantity and/or quality of these lipids, which could play a role in embolism avoidance.Finally, functional characteristics of pit membranes between water conducting cells will be investigated with respect to their porosity and air-seeding fatigue to better understand the mechanisms behind embolism. Hydraulic measurements and ultrastructural observations will be integrated in a spatially explicit model to simulate flow and embolism formation across nanoporous pit membranes.This innovative project will contribute to our understanding of the frequency and spatial distribution of drought-induced embolism in xylem tissue of woody angiosperms. The application is a joint project with Prof. Dr. Kun-Fang Cao at Guangxi University in China, with mutual benefits for both teams, including complementary expertise in plant hydraulics, training of PhD students, and research visits to both countries. This proposal could have implications for biomimetic applications, and will increase our understanding of plant water use and drought tolerance, which is especially relevant given current concerns about climate change.

• DFG Programme: Research Grants
• International Connection: China
• Partner Organisation: National Natural Science Foundation of China
• Cooperation Partner: Professor Dr. Kunfang Cao