Increased contribution of microbial necromass to soil organic carbon in solar farms on the Tibetan Plateau

Solar farms have been rapidly expanding on the Qinghai-Tibetan Plateau. However, the effects of photovoltaic arrays on the contribution of microbial necromass carbon (MNC) to soil organic carbon (SOC), along with the underlying mechanisms, remain unclear. To address this, we collected soil samples from the top 20 cm in under-panel, inter-panel and control plots at five solar farms constructed between 2012 and 2014 in the dry Yarlung Tsangpo and Lhasa River valleys on the Qinghai-Tibetan Plateau. We determined SOC, fungal and bacterial necromass and relevant soil properties. We found that the concentration of MNC in the under-panel plots (3.93 +/- 0.79 mg g-1) was significantly higher compared to the control plots (2.28 +/- 0.79 mg g-1) across all five solar farms. The proportion of MNC to SOC in the under-panel plots (34.7 +/- 2.4%) was also significantly higher than that in the control plots (27.5 +/- 1.4%). Specifically, the contribution of fungal necromass to SOC in the under-panel plots (26.4 +/- 2.2%) was significantly larger than that in the control plots (19.7 +/- 1.6%), while the increase in the bacterial necromass proportion was insignificant. Partial least squares structural equation modeling (PLS-SEM) indicated a significant and positive effect of increased soil moisture in the under-panel plots on the proportion of fungal necromass to SOC. These results highlight that beyond their economic benefits, solar farms in the arid regions on the Qinghai-Tibetan Plateau can enhance soil C sequestration by improving soil moisture and promoting microbial necromass accumulation.