Changes in soil physicochemical properties and bacterial communities among different soil depths after long-term straw mulching under a no-till system

Abstract. Conservation tillage has attracted increasing attention over recent decades, mainly due to its benefits in improving soil organic matter content and reducing soil erosion. Under intensive conventional tillage systems, some studies have focused on the responses of soil properties in the topsoil to straw retention. However, long-term straw mulching effects on soil physicochemical properties and bacterial communities among different soil depths under a no-till system are still obscure. One twelve-year experiment was conducted that included straw removal (CK) and straw mulching (SM) treatments. Soil samples were collected at 0–5, 5–10, 10–20, and 20–30 cm soil depths. Most soil physicochemical properties and the relative abundances of bacterial phyla were varied with soil depth. Compared with CK, SM increased soil total nitrogen and organic carbon, available phosphorus and potassium, dissolved organic carbon and nitrogen, and water content. SM increased soil bacterial abundance but reduced the Shannon diversity of the bacterial community at 0–5 cm depth. SM increased the relative abundances of Proteobacteria, Bacteroidetes, and Acidobacteria but reduced those of Actinobacteria, Chloroflexi, and Cyanobacteria. SM had different effects on the relative abundances of some C- and N-cycling genera, for instance, increasing Rhodanobacter, Rhizomicrobium, and Terracidiphilus, and reducing Anaeromyxobacter, Mycobacterium, and Syntrophobacter. A principal coordinate analysis indicated that SM largely affected soil bacterial communities at topsoil depth. Soil pH and different nitrogen and organic carbon fractions were the major drivers shaping soil bacterial community. Overall, straw mulch is highly recommended for use under a no-till system because of its benefits to soil fertility and bacterial abundance. However, inorganic nitrogen fertilizer levels may be reduced under straw mulching to maintain or increase soil bacterial Shannon diversity in future studies.