Acceleration of straw-nitrogen mineralization under co-elevation of CO₂ and temperature is associated with microbial attributes in the rhizosphere of rice

Quantifying the straw-nitrogen (N) in soil N pools and exploring soil microbial phylogenetic diversity involved in N mineralization are important for effectively managing crop straw to optimize crop N use under climate change. This study used 15N-labeled rice straw to quantify straw-N mineralization in the rhizosphere and N uptake of rice plants in response to elevated CO2 (700 ppm) and warming (2 °C above ambient). The CO2 and temperature co-elevation resulted in 20 mg kg−1 of straw-N mineralized in the rhizosphere, 50 % greater than the ambient control. A similar trend was found for soil-N mineralization. The CO2 and temperature co-elevation significantly increased the gaseous loss of straw-derived N from the rhizosphere, and straw-N in microbial biomass fraction, soluble organic and mineral N fractions in bulk soil. It also increased microbial biomass N originated from the rhizosphere soil. Irrespective of climatic treatments, the amount of mineralized N from straw and soil was greater in the rhizosphere than bulk soil. The CO2 and temperature co-elevation increased plant N uptake by 32 % with the dominant origin of soil-N rather than straw-N. With straw amendment, elevated CO2 plus warming significantly (p < 0.05) increased the abundance of leucine aminopeptidase (pepA) gene. The abundances of pepA, urease (ureC) and chitinase (chiA) genes were lower in the rhizosphere than in the bulk soil. Elevated CO2 plus warming significantly (p < 0.05) altered urease (ureC) and leucine aminopeptidase (pepA)-relevant community compositions in both rhizosphere and bulk soils, which were in turn associated with the N mineralization. The results suggest that the climate-change-induced shift of the composition rather than gene abundances of microbial communities that are involved in ammonification contributes to faster mineralization of soil N and straw N in paddy soils.