Temperature sensitivity of microbial respiration of soils amended with pine and oak litters is affected by tree growing CO2

The temperature sensitivity (Q(10)) of heterotrophic soil respiration (RH) of forests affects terrestrial carbon (C) dynamics under climate change. However, the effects of changed chemistry of tree leaf litter (referred to as litter hereafter) under elevated atmospheric CO2 concentrations ([CO2]) on the Q(10) of RH has not been explored. To fill the knowledge gap, the Q(10) of RH was investigated through incubation experiments at three temperature levels using litters of pine (Pinus densiflora Siebold & Zucc.) and oak (Quercus variabilis Blume) that were produced under ambient ([CO2](a)) and elevated ([CO2](e)) [CO2]. Regardless of [CO2] conditions, pine litter had higher lignin but lower nonstructural carbohydrate (NSC), calcium (Ca), and manganese (Mn) concentrations than oak, suggesting that pine litter has inherently poor chemistry. [CO2]e increased the ratios of lignin-to-nitrogen (lignin/N; by 58 and 122% for pine and oak, respectively) and C-to-N (C/N; by 47 and 125%, respectively) of litter through decreasing litter N concentration. For soils amended with [CO2](a)-litter, Q(10) was greater for pine (1.54) than oak (1.39) litters in agreement with the kinetic theory on the substrate quality-Q(10) relationship. However, amending [CO2](e)-litter decreased Q(10) for pine (1.44) but marginally increased Q(10) for oak (1.44). The decreased Q(10) for pine by [CO2](e) could be attributed to the inherently poor litter chemistry (e.g., high lignin, and low NSC, Ca, and Mn concentrations). Our study shows that the changed litter chemistry by [CO2](e) modifies Q(10) of R-H of litter-amended soils.