Microbial Stress-Tolerance and Resource-Acquisition Traits in Irrigated and Rainfed Soils of East Kazakhstan: An Exploratory Long-Read Metagenomic Study

Irrigation relieves water limitation in dryland soils and may shift soil microbes from stress tolerance towards resource acquisition. Field tests are scarce and often confound irrigation with site. In this exploratory study, we compared twelve long-read nanopore metagenomes from six spatially matched pairs of irrigated and rainfed fields in the East Kazakhstan Region, with one composite sample per field, and tested irrigation within pairs. With six pairs, the design can detect only large effects. Sequencing was shallow (0.16–2.19 Gb per soil) and read accuracy modest (median Q17). We detected no large or consistent community-wide shift: site explained 50–52% of compositional variance and irrigation 8–10%, close to the 8% expected by chance. A reference-free comparison agreed; equal-depth Aitchison tests hint at a weak log-ratio shift. Trait-level signals were consistent in direction but failed multiple-testing correction. The desiccation-tolerant genus Rubrobacter was 2- to 40-fold less abundant in the irrigated field of five of six pairs, and polysaccharide-degradation genes were 26% more abundant under irrigation, whereas compatible-solute genes did not differ. Most reads (64–80%) could not be placed against reference genomes. These results identify Rubrobacter depletion and greater polysaccharide-degradation potential as hypotheses to test in larger, crop-balanced studies with measured soil properties.