Differential Effects of Single and Combined PGPR Inoculation on Growth and Physiology of Atriplex canescens Under Saline Irrigation

Salinity stress severely constrains plant growth and ecosystem functioning in arid and semi-arid regions, and plant growth-promoting rhizobacteria (PGPR) have been increasingly applied to enhance plant salt tolerance. Hoswever, it remains unclear whether different PGPR inoculation strategies confer salt resistance through similar or distinct physiological pathways, particularly in perennial halophytes adapted to saline environments. In this study, a field experiment was conducted to evaluate the effects of single- and multi-strain PGPR inoculation on the growth performance, physiological responses, and stress regulation of Atriplex canescens under saline conditions. Plant biomass allocation, photosynthetic traits, osmotic adjustment substances, antioxidant enzyme activities, and comprehensive stress tolerance indices were systematically assessed. The results showed that PGPR inoculation significantly improved plant growth and stress tolerance; however, the magnitude and underlying mechanisms varied across inoculation strategies. Single-strain inoculation predominantly enhanced root development and antioxidant regulation, whereas multi-strain inoculation tended to promote aboveground growth and photosynthetic performance. In contrast, certain strain combinations did not produce additive benefits, suggesting potential incompatibility among microbial consortia under salt stress. Multivariate analyses further indicated that improvements in stress tolerance were more closely associated with coordinated physiological regulation than with biomass accumulation alone. Overall, our findings demonstrate that PGPR-mediated salt tolerance in A. canescens is strategy-dependent and involves distinct resource allocation and stress-defense pathways. These results highlight the importance of considering inoculation strategies and functional compatibility when applying PGPR to improve plant performance in saline ecosystems.