Oxidases and hydrolases mediate soil organic matter accumulation in chernozem of northeastern China

An enzymatic latch on carbon store in peatlands or desert soils has been verified but has rarely been examined in a cultivated field with a high pH and a high calcium carbonate content. Soil organic matter (SOM) contents of chernozem have decreased over the last few decades in northeast China. However, the enzymatic mechanism of SOM loss in this region remains unclear. An experiment was conducted to investigate the effects of soil oxidases and hydrolases on SOM, the correlations between soil oxidases and hydrolases, and the relationships between soil microbial community and related soil enzymes with 40 soil samples from different cultivated fields in Lishu County, northeastern China. The results showed that SOM increased significantly over the pH range of 5.0–7.0, and decreased sharply in the range of 7.0–8.0. Soil oxidases (peroxidase and total oxidases) activities showed significant and negative correlations with SOM content but positive correlations with hydrolases (β-glucosidase, β-xylosidase and total hydrolases) activities. The SOM content was significantly and negatively correlated with α-glucosidase, β-glucosidase, cellobiohydrolase, β-xylosidase, and total hydrolases activities. Results of redundancy analysis indicated that all soil hydrolases activities had positive relationships with bacteria i15:0, 16:3 ω6c and 16:0. Peroxidase and total oxidases activities were positively associated with bacteria cy17:0 ω7c, 15:0 DMA, i16:0, 18:0, i17:0, 14:0, 15:0 and actinomycetes 17:0 10-methyl, 18:0 10-methyl, while phenol oxidase activity was positively associated with bacteria i17:1 ω9c, 17:1 ω8c, i14:0 and fungi 18:1 ω9c. These findings confirmed the enzymatic latch mechanism of SOM accumulation in this test chernozem, which means that oxidases relieve the inhibition of hydrolases, resulting in SOM hydrolysis by higher hydrolases activities.