Deep vertical rotary tillage mitigates salinization hazards and shifts microbial community structure in salt-affected anthropogenic-alluvial soil

Soil tillage management is one of the major agricultural countermeasures to the ever-expanding soil salinization in arid and semiarid irrigated regions worldwide. However, how tillage implementations mitigate soil salinization hazard, improve soil quality and enhance microorganism function has not yet been clearly clarified. A two-consecutive-year field plot experiment with three tillage treatments, including CT (conventional rotary tillage, depth 25 cm), VRT (vertical rotary tillage, depth 25 cm) and DVRT (deep vertical rotary tillage, depth 50 cm), were conducted to examine the tillage effect on soil salinization and microbial communities. Dynamics of soil salinity (EC1:5), bulk density (ρb), saturated hydraulic conductivity (Ks), organic carbon (OC), water-stable aggregates (WSA), and bacterial and fungal community structures were measured. The results indicated that, compared with the CT and VRT treatments, the DVRT treatment had lower EC1:5 and ρb, but higher Ks at 0–40 cm soil layers. The promoted salt leaching was mostly attributable to the improved soil porosity and permeability under the DVRT treatment. The DVRT significantly increased soil total OC and percentage of > 2 mm (WSA1) and 2–0.25 mm (WSA2) aggregates, but decreased that of 0.053–0.01 mm (WSA4) aggregates. Soil bacterial richness and diversity was negatively responsive to the DVRT, whereas fungal richness and diversity showed positive responses to the DVRT. The DVRT did not alter the dominant microbial phyla but changed their relative abundance. At the genus level, the DVRT shifted bacterial community from Vicinamibacterales and Lysobacter -dominated to Vicinamibacterales, Geminicoccus and Marmoricola -dominanted, and transformed fungal community from Mortierella and Chaetomium -dominated to Mortierella and Aspergillus -dominated. Moreover, seasonal changes also showed significant direct and interactive influences on the above edaphic properties and microbial communities. Edaphic properties including EC1:5, OC, ρb and WSA1 explained the causal connection among tillage practices and microbial richness, diversity and community structure. It was concluded that the DVRT mitigated soil salinization hazards by promoting salt leaching and improving macro-aggregates and organic carbon, and shifted soil microbial communities by evolving the microbes better adaptable to the changed microhabitats.