Heathland management affects soil response to drought

1. Drought can affect ecosystem functioning by altering plant–soil interactions, posing a significant threat to vulnerable ecosystems like heathlands. In heathlands, ongoing nitrogen deposition increases the dominance of fast-growing grasses over the slow-growing shrub Calluna vulgaris. These changes above-ground can influence soil dynamics and heathlands' responses to drought. Here, we assessed whether the legacy effects of drought on heathland soils depended on mowing times as a management practice commonly used to regenerate Calluna and decrease the abundance of fast-growing grasses.
2. Using a long-term field experiment, we investigated if soil response to drought differed under Calluna and grasses, as well as under Calluna plants of different growth stages through different mowing times. We hypothesized that drought would decrease soil C and nutrient pools underneath grasses and younger Calluna plants through its impact on soil microbial communities.
3. Our results show that long-term drought decreased soil C but only underneath grasses and old Calluna, while under young Calluna, soil C increased under drought when compared to control conditions. Bacterial and fungal community composition differed between drought and control and were affected by the growth stage of Calluna but not by plant growth strategies. Furthermore, drought and Calluna growth stage-induced changes in bacterial communities directly affected total soil C and indirectly by reducing microbial C, which was positively related to total soil C.
4. Synthesis and applications. Understanding ecosystem response to drought is crucial for maintaining biodiversity and mitigating climate change feedbacks. Heathlands are threatened by high nitrogen deposition, a lack of management and an increasing frequency of drought. Our results emphasize the importance of frequent mowing (decadal) as a management practice that promotes a younger and more Calluna-dominated plant community for reducing soil C losses under future climate change-induced drought conditions. The active management of heathlands is essential not only for keeping above-ground vegetation dynamics, but also for maintaining below-ground soil nutrient and carbon pools.