Biochar superior than straw in enhancing soil carbon sequestration via altering organic matter stability and carbon...

Organic amendments can effectively improve soil organic matter (SOM) contents while mitigating Cd bioavailability. However, the interplay between soil carbon functional microbe and SOM stability response to straw and its biochar amendment in Cd contaminated soil remains poorly understood. Therefore, to reveal the interaction of SOM stability moieties with soil carbon cycle genes under Cd pressure, the effects of straw and its biochar on SOM stabilities in aggregates and soil carbon cycle related genes were evaluated. Fourier transform infrared (FTIR) and two-dimensional correlation FTIR spectroscopy were employed to appraise the stability of SOM within aggregates. Results showed that biochar reduced while straw promoted soil DTPA-Cd content by 9.4 %-21.9 % and 21.9 %-25.0 %, respectively. Straw return improved the relative abundance of aliphatic carbon and polysaccharides carbon but biochar mainly elevates the proportion of aromatic carbon, especially in 0.25-0.053 mm aggregates. The ratio of aromatic carbon to aliphatic carbon in biochar-amended soil was higher than that in control and straw-amended soil, indicating biochar outperforms straw in enhancing SOM stability. Biochar and straw application promoted the abundance of carbon degradation genes by 2.8 %-5.4 % but reduced the abundance of carbon sequestration genes by 1.1 %-4.6 %. Biochar enhanced the carbon degradation genes related to aromatics (xynA, alkB, aceB, and vdh) and chitin (chbG and cpbD) degradation while straw improved the genes participating in cellulose (endoglucanase, bglB, and bglX) and hemicellulose (xynB, abfA, and xylA) degradation. Mantel test showed that the alterations of soil carbon cycle are closely related to DTPA-Cd contents and SOM stability. Overall, biochar holds considerable potential than straw in enhancing soil carbon sequestration potential in Cd-contaminated soil.