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Growth, water relations, and stomatal development of Caragana korshinskii Kom. and Zygophyllum xanthoxylum (Bunge) Maxim. seedlings in response to water deficits

Abstract The selection and introduction of drought tolerant species is a common method of restoring degraded grasslands in arid environments. This study investigated the effects of water stress on growth, water relations, Na+ and K+ accumulation, and stomatal development in the native plant species Zygophyllum xanthoxylum (Bunge) Maxim., and an introduced species, Caragana korshinskii Kom., under three watering regimes. Moderate drought significantly reduced pre‐dawn water potential, leaf relative water content, total biomass, total leaf area, above‐ground biomass, total number of leaves and specific leaf area, but it increased the root/total weight ratio (0.23 versus 0.33) in C. korshinskii. Only severe drought significantly affected water status and growth in Z. xanthoxylum. In any given watering regime, a significantly higher total biomass was observed in Z. xanthoxylum (1.14 g) compared to C. korshinskii (0.19 g). Moderate drought significantly increased Na+ accumulation in all parts of Z. xanthoxylum, e.g., moderate drought increased leaf Na+ concentration from 1.14 to 2.03 g/100 g DW, however, there was no change in Na+ (0.11 versus 0.12) in the leaf of C. korshinskii when subjected to moderate drought. Stomatal density increased as water availability was reduced in both C. korshinskii and Z. xanthoxylum, but there was no difference in stomatal index of either species. Stomatal length and width, and pore width were significantly reduced by moderate water stress in Z. xanthoxylum, but severe drought was required to produce a significant effect in C. korshinskii. These results indicated that C. korshinskii is more responsive to water stress and exhibits strong phenotypic plasticity especially in above‐ground/below‐ground biomass allocation. In contrast, Z. xanthoxylum was more tolerant to water deficit, with a lower specific leaf area and a strong ability to maintain water status through osmotic adjustment and stomatal closure, thereby providing an effective strategy to cope with local extreme arid environments.