Hygroscopic aerosols linked to forest decline

Hygroscopic aerosols — particles in the air that attract water — could be causing forest decline around the world, according to experiments performed in Germany. Researchers believe that aerosol accumulation on trees enables thin bridges of liquid to form between the leaf interior and the leaf surface, causing the plants to dry out much more rapidly.

“In the atmosphere, aerosols act as cloud condensation nuclei,” says Juergen Burkhardt of the University of Bonn, Germany. “Deposited aerosols on leaf surfaces act almost the same way but attract water from inside the plant.”

Plants have developed sophisticated mechanisms for taking up carbon dioxide from the air for photosynthesis without losing too much water but, as the scientists note, it’s a delicate balance. And one that appears to be upset by rising levels of airborne particles.

“Global aerosol concentrations have roughly doubled compared with natural conditions, and the concentration increase over the continents is even higher,” says Burkhardt. “Our results show that aerosols deposited on leaves interfere with this delicate balance, pointing to a direct mechanism by which air pollution can reduce the drought tolerance of plants.”

Burkhardt and colleagues grew three species of tree — Scots pine, silver fir and common oak — for two years in two greenhouses, one ventilated with ambient air and the other fed with air filtered to remove 99% of aerosols. Seedlings grown under filtered conditions had superior drought tolerance to those raised in ambient air, the team found.

Source: Hygroscopic aerosols linked to forest decline – Brinkwire, 2018-09-25

Diverse forests are stronger against drought

Diversity is strength, even among forests. In a paper published in Nature, researchers led by University of Utah biologist William Anderegg report that forests with trees that employ a high diversity of traits related to water use suffer less of an impact from drought. The results, which expand on previous work that looked at individual tree species’ resilience based on hydraulic traits, lead to new research directions on forest resilience and inform forest managers working to rebuild forests after logging or wildfire.

Surprisingly, says Anderegg, a forest’s hydraulic diversity is the predominant predictor of how well it can handle a drought.

“We expected that hydraulic traits should matter,” he says, “but we were surprised that other traits that a lot of the scientific community have focused on weren’t very explanatory or predictive at all.”

Source: Diverse forests are stronger against drought – University of Utah, 2018-09-19