Drought stress alters the function of rainforest soil

Prolonged drought has a significant impact on the extent to which rainforest soils can emit and consume biogenic volatile organic compounds (VOCs). This was the finding of an international research team, including scientists from University of Freiburg and Max Planck Institute for Chemistry in Mainz, Germany, who studied the effects of drought and rewetting on soil VOC fluxes. The associated measurement campaign was conducted from September 2019 to January 2020 at the U.S. research facility of the Biosphere 2. It was part of the project B2WALD (Biosphere 2 Water Atmosphere and Life Dynamics). B2WALD is led by Prof. Dr. Christiane Werner, Professor of Ecosystem Physiology at the University of Freiburg, and Dr. Laura Meredith, Director of the Biosphere 2 Research Center and Assistant Professor at the School of Natural Resources and the Environment at the University of Arizona in the US. The soil VOC fluxes measurements were conducted by scientists from the Max Planck Institute for Chemistry, led by VOC group leader Prof. Dr. Jonathan Williams. The latest results were recently published in the journal Nature Communications.

Behaviour of soil microbes is crucial

“The data evaluated suggests that prolonged drought stress progressively reduces the capacity of the soil to consume atmospheric VOCs and, at same time, the soil starts to be a source of VOCs. We were able to identify a soil moisture content of 19 percent as a critical threshold below which this shift in soil behaviour occurs,” says the first author Dr. Giovanni Pugliese. Position-specific ¹³C-pyruvate labelling experiments in the experimental rainforest attribute the effects to the activity of soil microbes, which, under drought conditions, produce decisively more atmospheric VOCs than they consume.

In response to soil rewetting after a prolonged drought period, the emission of some VOCs actually intensify. “Our measurements 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”, Pugliese adds.

Climate impacts: Observation of soil VOC fluxes enable more reliable future predictions

The measurement campaign in the experimental rainforest, which lasted several months, collected data around the clock under carefully controlled environmental conditions. The analysis of the data was able to show clear interactions between drought-impacted environmental factors and soil VOC fluxes. Particularly with regard to climate impacts such as heat and drought, it illustrates the relevance of understanding these relationships. According to Williams: “We now know that drought stress can profoundly affect the behaviour of VOC fluxes to and from soil. 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.” 

• Original publication: Giovanni Pugliese, Johannes Ingrisch, Laura K. Meredith, Eva Y. Pfannenstill, Thomas Klüpfel, Kathiravan Meeran, Joseph Byron, Gemma Purser, Juliana Gil-Loaiza, Joost van Haren, Katerina Dontsova, Jürgen Kreuzwieser, S. Nemiah Ladd, Christiane Werner, Jonathan Williams. Effects of drought and recovery on soil volatile organic compound fluxes in an experimental rainforest. In: Nature Communications | (2023)14: 5064. DOI: https://doi.org/10.1038/s41467-023-40661-8

• Dr. Giovanni Pugliese was part of Prof. Dr. Christiane Werner's team at the Faculty of Environment and Natural Resources at the University of Freiburg. Currently, he is a postdoctoral researcher at the Max Planck Institute for Chemistry in Prof. Dr. Jonathan Williams’ research group. His research activity focuses on the measurement of soil volatile organic compound (VOC) fluxes at the Amazon rainforest measurement station ATTO. Websites: www.mpic.de/person/123640/4586221 und www.mpic.de/4586680/biosphere.

• The measurement campaign was financed by funds from the ERC Consolidator Grant, which Prof. Dr. Christiane Werner received from the European Research Council in 2015 to implement the ERC project VOCO2. The B2WALD project is a building block of VOCO2.

		The measurements of VOC fluxes in soil were carried out in the experimental rainforest of Biosphere 2. Photo: Laura Meredith
		Outside view of the experimental rainforest of the Biosphere 2 in Oracle, Arizona. Photo: Laura Meredith

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