Soil fungi remain active during drought
Our climate is getting warmer and many regions of the world will experience increasing heatwaves and drought periods. Drought poses a significant challenge globally, impacting both natural and agricultural ecosystems. While the effects of water stress on plants are well-documented, its influence on soils and associated microbial communities remains less understood, despite being one of the most common environmental stresses experienced by soil microorganisms.
We have both done extensive research on investigating effects of drought in the field and under laboratory conditions, but studying microbial activity in dry soil is notoriously difficult without changing water content or adding an additional substrate. Only recently, Alberto together with some colleagues, have developed a quite elegant way to trace the activity of microbes in soils using 18O vapor exchange labelling, which finally allows us to study microbial activity, and growth under conditions as realistic as possible. This method allows now to quantify community-level growth also during drought periods. In our recent study, we verified and expanded this method by using deuterium tracing into microbial lipids. With this modification we can now investigate three processes concomitantly: soil microbial community physiological activity, microbial group-specific growth patterns, and the production rates of triglycerides, which are an important class of storage compounds.
We applied this development on the unique experimental setup of the ClimGrass project in the Austrian Alps, led by a multidisciplinary team of scientists. This experiment provides a rare opportunity, as it simulates future climate scenarios through combined warming, elevated CO2, and drought treatments. The project’s design allows for high-resolution investigation of microbial responses in real-world conditions, bridging a critical gap between controlled laboratory studies and field ecology.

We quantified microbial growth and storage compound synthesis with an unprecedented level of detail. This approach enabled us to disentangle bacterial and fungal responses to drought, their growth strategies, and their contributions to soil carbon cycling.

and b) Gram-negative bacterial markers and c) fungal markers, as well as d) the ratio
of fungal to bacterial growth rates at peak drought and recovery (‘Drought’ and
‘Recovery’).
The results were really surprising. Bacterial growth halved during drought, while fungi displayed remarkable resistance (Fig. 2), maintaining stable growth rates and significantly increasing their investment in storage triglycerides (Fig. 3)— which points out that fungi can benefit from this strategy to endure stressful conditions.

specific NLFA during ‘Drought’ and ‘Recovery’ periods. b) Ratio of fungal specific
newly produced NLFA to newly produced PLFA (expressed as percentage), indicating
that fungi increase the relative investment in NLFAs during drought. This
ratio allows to account for a potential underestimation of mass-specific NLFA
production rates caused by potential necromass-NLFA accumulation.
Our findings underscore the adaptive resilience of soil fungi and their potential to mediate carbon cycling under future climate scenarios. It also highlights that to shed light on mechanisms of soil microbial responses to environmental stress conditions we need to investigate parameters beyond cell replication and including taxa-specific strategies.
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