Elevated [CO2] enhances soil respiration and AMF abundance in a semiarid peanut agroecosystem

Rising atmospheric carbon dioxide [CO₂] is a main climate change driver, and soil respiration is the most relevant contributor to ecosystem respiration. However, the soil microbiome and respiration responses of semiarid agroecosystems under elevated [CO₂] (eCO₂) conditions must be better understood. In particular, peanut agroecosystems host rhizobia and arbuscular mycorrhizal fungi (AMF) associations. Here, we sought to address the following questions: a) Does eCO₂ conditions (650 µmol CO₂ m⁻² s⁻¹, +250 µmol CO₂ m⁻² s⁻¹, aCO₂, control) alter soil chemical properties, soil microbial community size and composition, soil respiration, and β-Glucosidase activity? b) Are these responses influenced by transient water deficit periods? We conducted this study in a typical West Texas semiarid region (no well-watered treatment and drought was not an experimental factor) during two consecutive growing seasons (May-Oct). We induced the atmospheric CO₂ enrichment using field-installed Canopy Evapotranspiration and Assimilation (CETA) systems. Our results showed no consistent significant changes in soil moisture, C: N ratio, total soil microbial EL-FAME abundance, or β-Glucosidase activity. However, we found that eCO₂ increased soil temperature (+1 °C), AMF abundance (EL-FAME marker, +49%), and soil respiration (+82%). Our findings suggest that in future semiarid climates, peanut agroecosystems may experience: 1) increased soil metabolic activity as a result of increased autotrophic respiration; 2) increased AMF, which could further facilitate plant nutrient and water uptake; and 3) minimal change in the total size of the microbial community and C cycling enzyme activity during the growing season. In this manuscript, we demonstrated that soil respiration and temperature could be indicators of ecosystem productivity and climate feedback. Furthermore, soil organic carbon and AMF were good indicators of poor nutrient soil ecosystem transitional health across well-watered and water-deficit cycles. This study will increase our understanding of how these changes will affect soil ecology and climate feedback and will provide new insight into the peanut agroecosystem carbon source/sink functioning and productivity in future climates.