Study predicts increase in hydraulic failures in tropical regions

Hydraulic failures in tropical environments are expected to increase, according to a new study published in New phytologist. As climate conditions change and temperatures rise, plants must adapt to survive. Hydraulic failure occurs when more water is lost through transpiration than is absorbed by the roots. If left uncorrected, the xylem loses its conductivity and the plant will not survive.

“Increasing hydraulic failure rates will likely increase vegetation mortality and turnover. Over long periods of time, this will change plant composition, forcing more drought-tolerant species to become a larger proportion of forests,” said Zachary Robbins, a researcher at Los Alamos National Laboratory and corresponding author of the study.

“The long-term risk is that we lose natural reserves of terrestrial carbon at a time when we need to reduce atmospheric carbon.”

The study is the first to use the FATES-HYDRO model to assess the risk of hydraulic failure, an important piece of the puzzle that helps scientists understand the impacts of climate change. The results show that while rising temperatures in tropical climates typically lead to short-term productivity improvements, the long-term effects lead to significant increases in mortality rates.

Previous studies relied on the Penman-Monteith-Leuning model, which ignores two important variables: increased carbon dioxide and vapor pressure deficit. Robbins’ study analyzed assemblages of plant traits to determine which ones might perform well under future climate conditions. Robbins and his team used 16 Earth system models to test different traits under potential future scenarios.

Hydraulic failure is an amalgam of multiple assemblages of plant characteristics, and the ability to understand how these assemblages interact with each other to contribute to hydraulic failure is critical to understanding how to promote healthy growth.

Some plants are able to adapt by implementing strategies such as adjusting the percentage of time their stomata remain open. Through this process, plant pathway assemblages act as a “functional trait filter,” and plants that cannot survive changing conditions give way to plants that are more resistant to drought and heat.

The reduction of tropical forests due to water shortages would be felt worldwide.

“Simulations like this can help us understand future risks to natural resources and allow us to respond to or anticipate the global consequences of ecological change,” Robbins said. “Accounting for these changes in hydraulic failure rates will be critical to understanding rates of wildfires, forest dieback and natural resource security.”

The Los Alamos team is continuing its efforts with the FATES-HYDRO model to better understand plant mortality around the world and is working on extending this project to the American Southwest.