14 September 2023

Here’s how drought stress alters soil function in the rainforest


Drought progressively reduces the ability of soil to consume biogenic volatile organic compounds according to a German study. The emission intensifies after soil rewetting

by Matteo Cavallito


Prolonged drought significantly impacts the emission and consumption of biogenic volatile organic compounds in rainforests. This is supported by research by a team of scientists from the University of Freiburg and the Max Planck Institute for Chemistry in Mainz, Germany.

The investigation, conducted from September 2019 to January 2020 at the Biosphere 2 research facility at the University of Arizona, is part of the B2WALD (Biosphere 2 Water Atmosphere and Life Dynamics) project, which also involves the same U.S. university. The results were published in the journal Nature Communications.

The role of compounds

Biogenic volatile organic compounds (BVOCs) are substances emitted by plants such as nitrogen oxide, carbon monoxide, and non-methane hydrocarbons, which affect the overall carbon balance. That is, the balance between the amount of element absorbed and that released from the soil. Vegetation, as is well known, is a key factor in climate change mitigation.

In contrast, recalls the Italian National Research Council (CNR) among others, “BVOCs have a negative impact on atmospheric chemistry because they play an important role in the production of ozone and tropospheric aerosols.”

The global amount of carbon produced in this way each year is estimated to be 1.1 billion tons. That is the same order of magnitude as methane emissions. That’s why is important to understand “the synthesis mechanisms of BVOCs and ecosystem responses to climate change”. In order “to improve our overall ability to predict future emissions.”

Soil microbes are crucial

“The data evaluated suggests that prolonged drought stress progressively reduces the capacity of the soil to consume atmospheric VOCs and at the same time, the soil starts to be a source of VOCs,” Giovanni Pugliese, a researcher at the Max Planck Institute and lead author of the study, explains in a statement released by the University of Freiburg. “We were able to identify a soil moisture content of 19 percent as a critical threshold below which this shift in soil behaviour occurs,” ha adds.

The phenomenon, according to the researchers, is related to the activity of soil microbes, which, under drought conditions, produce significantly more atmospheric BVOCs than they consume.

Measurements, Pugliese continues, “have demonstrated that soil rewetting induce a rapid, albeit brief, abiotic emission peak of carbonyl compounds and a slow, but more persistent biotic emission peak of sulfur-containing compounds.”

Climate and drought: more reliable future predictions

Understanding the relationships between environmental factors related to water scarcity and emissions of volatile compounds is essential. Especially thinking about the impact of drought on rainforests. “We now know that drought stress can profoundly affect the behavior of VOC fluxes to and from soil,” explained in fact Jonathan Williams, a Max Planck Institute researcher, co-author of the study and director of the group engaged in the measurements. “Since current climate models predict that the Amazon rainforest region will suffer more frequent and prolonged droughts in future, we need to incorporate these newfound soil effects into atmospheric models to improve ecosystem response predictions, and simulations of future regional atmospheric chemistry and climate.”