Shading gradients shape soil microbial biomass carbon and carbon stability in a horticultural agri-photovoltaic field in Germany

Agri-photovoltaic (Agri-PV) systems are increasingly implemented for combined food and renewable energy production, yet their impacts on soil carbon cycling and stabilization remain insufficiently understood. This study aimed to understand how shading in a horticultural Agri-PV field alters microbial activity, soil carbon (C) stocks and stability compared with a conventional open-field management in western Germany.The experimental fields were established in 2021 and soils (homogeneous silt loam: 5% sand, 15% clay, 80% silt) were sampled (0–30 cm) in 2025 along replicated transects across under-panel (UP) and inter-row (GAP) zones in the Agri-PV field. This Agri-PV system consisted of south-facing, fixed-tilt PV modules inclined at 20° and mounted at a maximum height of 4.30 m. An adjacent, identically managed Control open-field was sampled using the same approach. We measured gravimetric soil water content, microbial biomass C (Cmic), aggregate size distribution (8–2 mm,