Differential responses of soil nutrients to edaphic properties and microbial attributes following reclamation of abandoned salinized farmland

Salinization is a global threat to the sustainability of farmland in arid areas. However, the mechanisms by which soil physicochemical and microbial properties affect soil nutrients in salinized farmlands are not completely understood. Here, the direct and indirect responses of edaphic properties (bulk density [BD], saturated hydraulic conductivity [SC], field capacity [FC], alkalinity[pH], microbial biomass carbon [MBC], and microbial biomass nitrogen [MBN]) and soil microbial properties (denitrifying genes [nirS], nitrogen-fixing genes [nifH], catalase [CAT] and urease [UR] activities, and species richness [Chao1]) to the total soil N content (TN), soil organic carbon (SOC), alkali hydrolyzable N (AN), potassium (K+), and calcium (Ca2+) ions at low-salinity (2-4 dS m-1), mid-salinity (4-8 dS m-1), high-salinity (8-15 dS m-1) sites, and non-salinity (Control, 0-2 dS m-1) farmland in arid areas of northwest China were examined. Soil UR activity (range: 703.5-956.6 U UR L-1 ) and nifH, AN, SOC, and MBN content were higher at the low-salinity than at the medium-and high-salinity sites. Furthermore, FC was indirectly affected by the soil nutrients due to their effects on nifH and CAT activities. The relative contri-bution of soil TN, SOC, and AN content on the direct responses of the microbial attributes (52-70%) was higher than that of the soil physicochemical properties (27-45%) in different reclamation types. The reclamation process on abandoned salinized farmland promoted the activity of microorganisms, further improving the soil's physical properties and nutrient status. This study has found that improving microbial metabolic activity in combined with reclamation measures will be crucial for future salinity management.