Root convex hull area reflects coordinated root–shoot adaptation to salt stress in spring wheat

Abstract

Abstract Background Root architecture determines the capacity of crops for spatial exploration under stress conditions; however, existing studies on salt tolerance screening have mostly been confined to single traits such as root length or biomass, overlooking the overall spatial configuration of the root system and its intrinsic linkage with aboveground physiological functions. On this basis, the present study aimed to determine whether root convex hull area can characterize root–shoot synergistic adaptability under salt stress, and whether this synergy involves a physiological mechanism of resource conservation through cortical tissue remodeling. Methods Using a paper-based root phenotyping platform, we screened 28 spring wheat varieties originating from the arid regions of northwest China under 200 mM NaCl stress, and compared the differences between large-convex hull area and small-convex hull area varieties in root architecture, root cortical anatomy, stomatal traits, leaf water status, photosystem II efficiency, canopy temperature, and transpiration rate under salt stress. Results The results showed that large-convex hull area varieties maintained total root length, maximum depth, and convex hull area under salt stress, whereas small-convex hull area varieties exhibited significant reductions in all these parameters. Meanwhile, compared with small-convex hull area varieties, large-convex hull area varieties possessed greater cortical lacunar tissue area and cortex/stele ratio, as well as higher stomatal density, leaf relative water content, F v/ F m, and transpiration rate, but lower canopy temperature and smaller stomatal aperture. Convex hull area was positively correlated with leaf water status, photochemical efficiency, cortical lacunar area, and stomatal density, while negatively correlated with canopy temperature and stomatal aperture, indicating that root spatial maintenance, moderate cortical senescence, and stomatal regulation together constitute a functionally coordinated response module under salt stress. Conclusion In summary, convex hull area is not merely a descriptive indicator of root morphology, but rather a functional trait that reflects the synergistic integration of belowground exploration capacity and aboveground physiological resilience. This study proposes that convex hull area can serve as a candidate high-throughput phenotypic indicator for salt tolerance screening in wheat at the seedling stage; nevertheless, its predictive capacity for field yield performance still requires further validation under soil conditions, across the full growth cycle, and under interactions with multiple environmental factors.

Code and data availability

The preprint describes a paper-based root phenotyping study of 28 spring wheat varieties under salt stress, but contains no public phenotype dataset, image repository, author analysis code, or trained model deposit. Software mentioned (RootNav, RhizoVision Explorer, ImageJ, SPSS, Origin) are generic third-party tools;

No evidence-backed public reproduction asset is currently recorded.