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Decomposition temperature sensitivity of biochars with different stabilities affected by organic carbon fractions and soil microbes

Chen, Guanhong, Wang, Xiaojie, Zhang, Renduo
Soil & tillage research 2019 v.186 pp. 322-332
Oryza sativa, alkanes, ambient temperature, biochar, carbon sequestration, corrosion, enzyme activity, microbial communities, organic carbon, soil, soil carbon, soil microorganisms
The soil carbon (C) sequestration potential of biochar is affected by their intrinsic temperature sensitivities. The objective of this study was to quantify temperature sensitivities of decomposed biochars affected by organic C fractions and soil microbes. The hypotheses to be tested included that increasingly condensation and corrosion in biochar should increase biochar temperature sensitivity and that soil microbes should affect biochar temperature sensitivity. Rice (Oryza sativa L.) straw-derived biochars were pyrolyzed at 300, 500, and 800 °C to represent lowly, intermediately, and highly condensed biochars (denoted as LBC, MBC, and HBC), respectively. Bulk, dissolved, and chemically corroded biochars were incubated with and without soil microbial inoculation, respectively, under ambient temperatures from 5 to 45 °C for 119 d. The temperature sensitivity of biochar was characterized using the Q10 value (i.e., the proportional increase in respiration per 10 °C rise). Results showed that Q10 values of the biochars increased from 2.13 to 3.13 with increasing condensation, attributable to transformation of easily-degraded alkanes with intermediate chain lengths (C10-C24) in LBC to oxygen-containing aromatic hydrocarbon and ester in MBC and HBC. With accumulation of silica-occluding C, the decomposition of corroded biochars showed the highest Q10 values (2.47 to 3.90). The Q10 values of biochars decreased over time and became stable in range of 1.25 - 1.66 because of greater decrease in labile C and microbial enzyme activity at higher temperature. Additionally, as microbial community evolved to degrade recalcitrant C with increasing temperature, relatively low decomposition rate at higher temperature led to decreasing Q10 values of biochars. Therefore, temperature sensitivities of decomposed biochars were determined by the C structures and decreased with time by changes in soil microbial properties, showing the C sequestration potential of biochar application under warming.