Divergent Responses of Microbial Diversity and Extracellular Enzymatic Activities to Straw Addition in Reclaiming Salt‐Affected Soil

Abstract

Soil salinization threatens food security and ecosystem functions, particularly in arid and semi‐arid regions. Besides degrading soil structure and nutrient availability, salinization also disrupts microbial functionality. Although irrigation and organic amendments are widely used to alleviate salinity, their combined effects on microbial diversity and nutrient metabolism remain unclear. Through a 120‐day microcosm experiment, the results demonstrated that intermittent leaching (320.0 mm) significantly reduced soil saltness by 29.3%–36.9% (p < 0.05). Although straw addition (6.5 t/ha) did not directly reduce salt content, it improved leaching efficiency by 7.6% (p > 0.05). Both straw and leaching decreased nitrate nitrogen contents (p < 0.05). Straw addition reduced microbial diversity due to the disproportionate growth of dominant taxa, and the decreased fungal diversity was partially alleviated by lower salinity under leaching. Straw addition also significantly increased the activities of β‐glucosidase and N‐acetylglucosaminidase by 94.6%–161.2% and 187.3%–210.9% (p < 0.05), respectively, while the activities of β‐cellobiosidase, leucine aminopeptidase, and alkaline phosphatase remained unaffected (p > 0.05). Ecoenzymatic vector analysis indicated vector length generally below 0.3, with straw increasing it by 44.9%–64.4%. Leaching indirectly reduced microbial carbon limitation by alleviating salinity stress (p < 0.05). The soils were primarily nitrogen‐limited (vector angles < 55°), with straw addition and leaching exerting indirect effects through fungal diversity. These findings indicate that the proposed vector length threshold of 0.61 may underestimate soil microbial carbon limitation in extreme conditions like salt‐affected soils. Given that straw addition improves salt leaching efficiency and nutrient metabolism, combining optimized irrigation with organic amendments could be an effective strategy for reclaiming salt‐affected soils.