Microbial gene activity in straw residue amendments reveals carbon sequestration mechanisms in agricultural soils

Land-use practices and their intensity along with climatic conditions alter amounts of soil organic carbon content and consequently influence soil microorganisms. However, land-use management, such as crop residue incorporation to soils has a potential to mitigate losses of soil organic carbon and thereafter promote the diversity of soil microorganisms. To gain insight of microbial functional diversity and activity under organic soil amendments, a glasshouse experiment with arable and grassland soils was performed. Straw was added as a crop residue and microbial activity in the soils was monitored using a captured metatranscriptomics technique. The overall expression of genes related to soil organic matter degradation differed between the two land-use systems. Straw addition enhanced the expression of genes involved in the degradation of organic material, particularly in arable soils. After a month of the amendment, the overall gene expression in arable soils had a similar pattern to that of the grasslands. The straw addition triggered the upregulation of a set of enzyme families catalysing the organic matter degradation in both land-uses but downregulated a higher number of enzyme families in grasslands. However, in the grasslands, the gene families involved in the biosynthesis of carbohydrates were upregulated at straw addition. These findings indicate that arable soils with a low organic carbon content have a potential to get a higher and more active microbial diversity with amendments. In soils such as grasslands the amendments trigger a carbon sequestration process from the added organic material to the soil and can significantly contribute to enhanced soil carbon sequestration.