Adaptation of Soil Viruses to Salinity Stress: Insights Into Genome Size Expansion and Functional Diversification.

Viruses are important components of soil biodiversity and ecosystem functions. However, their response to soil salinity stress, including ecological patterns and functional potential, remains poorly understood. Here, metagenomic data from 84 saline soil samples were retrieved from public databases and analysed. Viral sequences were extracted from metagenomes, and auxiliary metabolic genes (AMGs) were identified. 83.34% of the vOTUs had no detectable gene-sharing links with the RefSeq Viral database, highlighting the unexplored diversity of saline soil viromes. In soils with higher salinity, viral genomes exhibited larger genome sizes and increased GC content. The diversity of temperate viruses (3.16-7.32) was significantly higher than that of lytic viruses (2.49-6.99). Although the diversity of temperate viruses decreased with increasing salinity, no significant trend was observed for lytic viruses. Viral abundance correlated positively with host abundance, consistent with the 'piggyback-the-winner' ecological coupling hypothesis. Functional potentials varied with salinity, and structural analysis showed changes in atomic interactions in key proteins (NhaA, ACAT) across salinity gradients. Significantly positive correlations were found between viral diversity and functional potential related to salt tolerance, carbon fixation, organic phosphorus mineralisation and nitrogen metabolism. These results suggest viral traits correlate with salinity gradients and provide insights into viral responses in saline soils.