Sodium chloride facilitates the secretohalophyte Atriplex canescens adaptation to drought stress

Atriplex canescens is a C₄ shrub with excellent adaptation to saline and arid environments. Our previous study showed that the secretion of excessive Na⁺ into leaf salt bladders is a primary strategy in salt tolerance of A. canescens and external 100 mM NaCl can substantially stimulate its growth. To investigate whether NaCl could facilitate Atriplex canescens response to drought stress, five-week-old seedlings were subjected to drought stress (30% of field water capacity) in the presence or absence of additional 100 mM NaCl. The results showed that, under drought stress, the addition of NaCl could substantially improve the growth of A. canescens by increasing leaf relative water content, enhancing photosynthetic activity and inducing a significant declined leaf osmotic potential (Ψs). The addition of NaCl significantly increased Na⁺ concentration in leaf salt bladders and the Na⁺ contribution to leaf Ψs, while had no adverse effects on K⁺ accumulation in leaf laminae. Therefore, the large accumulation of Na⁺ in salt bladders for enhancing osmotic adjustment (OA) ability is a vital strategy in A. canescens responding to drought stress. In addition, the concentration of free proline, bataine and soluble sugars exhibited a significant increase in the presence of NaCl under drought stress, and the betaine contribution to leaf Ψs was significantly increased by additional NaCl compared with that under drought treatment alone, suggesting that compatible solutes are also involved in OA in addition to functioning as protectants to alleviate water deficit injury.