Microbial scents: Soil microbial Volatile Organic Compounds (mVOCs) as biomarkers for grasslands across a land use gradient

Extensifying land use practices – i.e. decreasing management intensity – is pivotal to facilitate the transition towards sustainable agriculture in productive grasslands, as it promotes the enhancement of soil biotic communities that support important ecosystem services. To monitor these transitions effectively, improved inventories are needed to track changes in microbial communities. Microbial Volatile Organic Compounds (mVOCs) are potential biomarkers that can link soil community change to land use extensification (i.e. reducing land use intensity) and may provide important information on changes in soil processes in transitional productive grasslands. We investigated how land use extensification affects mVOC profiles in grassland soils through both abiotic and biotic factors and whether mVOCs can be linked to bacterial (16S) and fungal (ITS2) community composition. We measured mVOCs (GC-MS), microbial communities, and abiotic soil parameters (SOM, SOC, pH, bulk density, and nutrients) across eighteen grasslands with varying land use intensity. A total of 75 mVOCs were identified using the mVOC 4.0 library. Furthermore, we show that mVOC profiles and chemical classes differ across land use types – conventional, extensive, and semi-natural grasslands. Within these grasslands, only fungi showed distinct community compositions between land use intensity types, whereas there were no compositional differences of bacteria. Using Taxon Indicator Threshold Analysis (TITAN), we identified sixteen mVOC compounds that varied significantly along a land use intensification gradient. These findings suggest that mVOCs can serve as biomarkers linking changes in land use intensity and soil microbial communities, although these relationships are complex in field conditions. We identified a set of mVOCs tied to changes in land-use extensification and highlighted their potential as indicators of soil microbial community turnover. mVOCs offer a valuable tool for monitoring land use transitions, and our results emphasize their role in integrating microbial community metrics and soil health indicators into land management strategies.