• Soil nutrient multifunctionality (SNMF) of saline-alkali soils between two tillage systems was investigated. • Paddy-upland rotation boosted SNMF under mild salinity. • Macroaggregates were key physical hotspots, driving 48% of SNMF. • Macroaggregates drove SNMF by nutrient retention and enhancing microbial function potentials. Coastal saline-alkali soils threaten global food security due to severe nutrient deficiencies. Although rice cultivation is a widely adopted reclamation strategy, its efficacy in enhancing soil nutrient multifunctionality (SNMF) and the underlying mechanisms remain poorly understood. This study investigated the effects of paddy-upland rotation (PU) versus upland-upland rotation (UU) on SNMF across varying salinity gradients in a 10-year reclaimed coastal field of East China. The treatments were designated as P1 and P2 for PU under mild and moderate salinity, respectively, and U1 and U2 for UU under corresponding salinity levels. Our results demonstrated that PU significantly enhanced SNMF under mild salinity (total salt content ∼ 1 g kg −1 ) compared to UU, with values of 0.83 and 0.46 for P1 and U1, respectively. In contrast, under moderate salinity (total salt content ∼ 3 g kg −1 ), SNMF did not differ significantly between PU and UU, with both P2 and U2 showing similarly low values (0.12). The superiority of PU under mild salinity was primarily driven by improved soil aggregate stability—as evidenced by the significantly higher proportion of macroaggregates, MWD, and GMD in P1 than in U1 by 11.11%, 7.06%, and 79.80%, respectively—and microbial functional potential, particularly through their synergistic interaction. Specifically, the formation of stable macroaggregates served as functional hotspots, accounting for 48.22% of the SNMF variation. However, elevated salinity disrupted aggregate structure, where no significant differences in aggregate stability indices were found between P2 and U2, suppressed macroaggregate-associated functional gene abundance, thereby offsetting the benefits of PU. Consequently, the effectiveness of PU systems in enhancing SNMF is critically dependent on maintaining low salinity, highlighting the necessity of integrated management strategies that couple salt stress alleviation with soil aggregate optimization for sustainable coastal saline-alkali farmland utilization.
Chen et al. (Fri,) studied this question.