Changes in soil organic carbon and microbial community in saline soil following different forms of straw incorporation

Straw has been commonly incorporated into soil to increase soil organic carbon (SOC) content. However, the response and mechanism of organic carbon transformation following the addition of different forms of straw to saline soil to have not been fully evaluated. Thus, in our study, chopped wheat straw, granular wheat straw and wheat straw biochar were used as exogenous organic amendments. The carbon-to-nitrogen ratio of each form of straw was adjusted to 25:1. Under the same amount of carbon input, the three forms of straw were added to saline soil for a one-year incubation experiment. The research focused on studying the changes in SOC transformation, enzyme activity, and microbial community structure. At the end of incubation, both granular and biochar straw treatments had significantly increased SOC relative to the unamended control, with extent of SOC increase greater in the biochar straw treatment. The biochar straw treatment also had significantly higher dissolved organic carbon than the other treatments at end of the incubation. The enzyme activity of beta-cellobiohyrolase (CBH) was the highest in the granular straw treatment, which was increased by 71.9% compared with the chopped straw treatment (p < 0.05). The cumulative carbon mineralization amount (Cum C) in the granular straw treatment was the highest, which was increased by 757.4% and 21.3% compared with the biochar straw and chopped straw treatments, respectively (p < 0.05). The Mantel test analysis further revealed significant correlations between soil bacterial community and SOC content in soils treated with different straw incorporation forms, as well as between fungal community and extracellular enzyme activities. We assumed that a possible reason for the high SOC mineralization amount in the granular straw treatment was changing the structure of the Bacteroidota in the bacterial phylum and Blastocladiomycota in the fungal phylum. Based on these findings, it is believed that adding biochar can increase the SOC content, but its utilization by microorganisms is limited. However, applying granular straw will not have a negative impact on its use as a microbial carbon source, thereby promoting carbon transformation. Therefore, in future research aimed at enhancing soil fertility in saline soil regions, the adoption of granular straw as an agricultural practice is recommended and should be promoted.