Contrasting Coordination Among Photosynthesis, Growth, and Storage of Two Dominant Desert Shrubs in Response to...

Carbon dynamics are essential for understanding plant drought adaptation, yet how desert shrubs coordinate photosynthesis, growth, and storage under drought remains unclear. We quantified light-saturated photosynthetic assimilation rate (A_sat), leaf absolute growth rate (AGR), and whole-plant non-structural carbohydrates (NSCs) in two dominant desert shrubs, Haloxylon ammodendron and H. persicum, across a water-stress gradient associated with groundwater depth, precipitation exclusion, and seasonal drying, using predawn leaf water potential (Ψ_PD) as an integrative index of plant water status. Furthermore, we evaluated linkages among Ψ_PD, A_sat, AGR, and NSCs. AGR declined faster than A_sat as Ψ_PD decreased, suggesting the photosynthesis-growth decoupling at the leaf level under increasing water stress. While whole-plant NSCs remained stable, organ-specific starch and soluble sugar patterns diverged between species: H. ammodendron accumulated starch in branches, whereas H. persicum increased leaf starch concentrations and decreased sugar:NSCs ratios, with opposite trends observed in the roots. Moreover, A_sat was negatively correlated with branch starch concentrations in H. ammodendron, but negatively correlated with leaf starch concentrations in H. persicum. The relationships between AGR and branch starch concentrations tended to be negative in H. ammodendron, whereas leaf and root NSCs were negatively related to AGR in H. persicum. These findings suggest that aboveground organs adopt conservative carbon utilization strategies under drought, while belowground organs shift toward acquisitive strategies, highlighting contrasting carbon use patterns that may enhance drought survival in desert shrubs.