Soil organic matter quality in agrivoltaic systems: contrasting responses of SOM pools and microbial carbon utilization

Introduction Agrivoltaic (APV) systems can modify soil microclimate, but their short-term Q9 effects on soil organic matter (SOM) and microbial functioning remain incompletely understood. Methods We assessed SOM fractions and microbial activity in permanent grassland and raspberry shrubland under and outside APV over two years (2024–2025), sampling two soil depths. Three replicate plots represented each vegetation × APV combination. Thermogravimetric SOM fractions and oxidizable carbon were evaluated alongside dehydrogenase activity, basal respiration, substrate-induced respiration (SIR), and microbial functional diversity (MFD). Results Responses varied among vegetation types, APV conditions, depths, years, and measured variables. SIR responses showed significant interactions among all four factors, indicating context-dependent patterns rather than a uniform APV effect. Changes in oxidizable carbon and thermogravimetric SOM fractions were selective, while MFD showed lower-order effects but no four-way interaction. Exploratory PCA showed that associations among microbial indicators and SOM fractions varied across vegetation–APV combinations and soil depths. Discussion The results reveal treatment- and year-dependent differences already within this short observation period. They support the hypothesis that microbial indicators and SOM fractions may respond differently to APV conditions, a possibility that requires testing through longer-term monitoring.