Salinization influences the biodiversity-ecosystem functioning relationship more strongly at high salinity

Salinization threatens ecosystem stability by altering microbial diversity and function, yet how salinity influences biodiversity-ecosystem functioning (BEF) relationships remains unclear. In this study, we constructed artificial microbial communities (5-40 strains) with varying salt tolerance and phylogeny, culturing them across a salinity gradient (0.9%-20%). We found that low-to-moderate salinity (0.9%-7%) minimally affected BEF relationships, but high salinity (15%-20%) amplified biodiversity loss impacts, with ecosystem yield declining sharply at low richness (R ² = 0.573, p < 0.001). Hypersaline conditions shifted community composition toward halophiles (e.g., Halomonas dominance at 20% salinity) and inhibited metabolic functions, such as glycosyl hydrolase activity. Mechanistically, selection effects predominated at 15% salinity (contributing 63.1%-72.0% to net biodiversity effects), whereas complementarity effects were diminished. These findings underscore the vital role of biodiversity in mitigating hypersaline stress and highlight the necessity for targeted strategies to enhance ecosystem resilience against global salinization.