Physiological Effects Of Na~+ On Improving The Tolerances Of Drought,High Temperature And Wind-Borne Sand Of Salt-Secreting Xerophyte Reaumuria Soongorica

Reaumuria soongorica,a salt-secreting xerophytic shrub belonging to Tamaricaceae,possesses very strong capabilities of drought resistance,cold resistance,salt tolerance,sand fixation,and sand collection.This species has become one important species for vegetation restoration and reconstruction in the arid desert regions of China,but is not yet widely used in artificial vegetation construction due to its low growth rate and weak drought resistance in the juvenile phase.Interestingly,its growth performance in the arid-rich Na⁺habitat is better than that in the corresponding arid-poor Na⁺habitat.Previous investigations showed that moderate NaCl could stimulate the growth of R.soongorica under indoor condition.However,there are few studies on physiological effects of Na⁺on growth and tolerance of drought,high temperature or wind-borne sand of salt-secreting xerophytes as yet.Therefore,the potted seedlings were treated with a range of different concentrations of 0-1.17 g·kg^-1 NaCl,and also were treated respectively at different intensities of drought,temperature and wind-borne sand under without or supplementary 0.59 g·kg^-1 NaCl,and then the parameters related to growth and anti-adversity physiology were assayed.The purpose of the study was to reveal the physiological mechanisms of Na⁺on stimulating the growth and alleviating stresses of drought,high temperature or wind-borne sand in R.soongorica,determine the optimum fertilization of Na⁺in sandy soil on R.soongorica,and solve the bottleneck problem that R.soongorica possesses slow growth and weak stress resistance in the juvenile phase.1.R.soongorica possesses a strong capability of selectivity absorbing and secreting Na⁺,enhancing with the increase of NaCl concentration in medium,while the concentration of K⁺in its tissues is maintained stability.Supplementary moderate NaCl(0.59 g·kg^-1 dry sandy soil)effectively stimulated the growth in R.soongorica,in which the plant height,root length,fresh weight,and relative growth rate were higher than that in corresponding treatment without NaCl addition after supplying NaCl for 45 days.Likewise,a significant increase in net photosynthetic rate?P_n?,stomatal conductance?G_s?or cell turgor pressure??_t?was observed in plants grown in the presence compared with the absence of supplementary moderate NaCl,respectively,whilst a significant decrease in leaf osmotic potential??_s?.2.The addition of moderate NaCl induced an obvious reduce in the leaf?_s of R.soongorica under drought,high temperature and wind-borne sand stresses,where the contribution of Na⁺to leaf?_s was very bigger than the corresponding K⁺,proline or soluble sugar;likewise,the supplementary NaCl caused a sharp increase in the Na⁺contribution to leaf?_s,while the contributions of other three solutes were decreased correspondingly.These results show that Na⁺plays a key role in the R.soongorica resisting all kind of adverse stresses by osmotic regulation,which is enhanced by supplying moderate NaCl in medium.3.A significant increase in the RWC in leaves of the supplied moderate NaCl plants exposed to severe drought?12.4%of FWC?,high temperature?50°C?or strong wind-borne sand stress(10m·s^-1)was observed,compared with the corresponding plant without supplied NaCl;meanwhile,the length,width and area of leaf cross section in NaCl-supplied plants were significantly bigger than those of the corresponding control.Additionally,the addition of NaCl helped plant to maintain a higher transpiration rate?T_r?under high temperature conditions,where a significant lower hurt degreed of leaf and young shoot correspondingly in the presence than the absence of supplementary moderate NaCl was observed under 50°C temperature.These results indicate that NaCl may sustain the leaf anatomical structure of R.soongorica by improving water status when subjected to severe drought,high temperature or wind-borne sand stress,as well as alleviate heat damage on the leaf and young shoot by enhancing transpiration rate.4.Under the wind-borne sand at a speed of 10 m·s^-1for 30 min,the leaf hurt rate and degree and cell breakage rate of leaf epidermis in the NaCl-supplied plants were significantly lower than the corresponding control,respectively,while an obvious increase in the above parameters of NaCl-supplied plants washed leaf surface secreta was observed.Therefore,the leaf surface secreta may play an important role in alleviating the abrasion damage of strong wind-borne sand on leaf of R.soongorica,and the addition of moderate NaCl could mitigate the abrasion of wind-borne sand by inducing Na⁺secretion.5.Severe drought,high temperature or wind-borne sand stress triggered a significant reduction in P_n,G_s,photosynthetic pigment content,and the maximal quantum yield of photosystem II?PSII?photochemistry?F_v/F_m?,efficiency of excitation capture by the opening of the PSII reaction center?F_v?/F_m??,actual PSII efficiency(?_{P SII})and photochemical quenching coefficient?qP?of R.soongorica,respectively,as well as an increase in the non-photochemical quenching coefficient?NPQ?;however,supplementary moderate NaCl effectively mitigated the above influences of these stresses.Based on the above results,it suppose that the better growth performance of the plant subjected to the above stresses is due to the higher photosynthetic capacity resulted from supplying moderate NaCl maintaining higher G_s,alleviating degradation of the photosynthetic pigment and improving PSII photochemistry activity.6.Under the severe drought,high temperature or wind-borne sand stress,a sharp increase in the malondialdehyde?MAD?content in leaves of R.soongorica was observed,as well as an obvious decrease in soluble protein content and the activities of superoxide dismutase?SOD?,peroxidase?POD?and catalase?CAT?.However,supplementary moderate NaCl significantly alleviated above influences of these stresses.Therefore,it supposes that the increased NaCl may effectively mitigate the deleterious influence of severe drought,high temperature or strong wind-borne sand stress on leaf soluble protein content and antioxidase activity,which contributes to maintaining a stronger ability to get rid of reactive oxygen species?ROS?in some extent,thereby reducing membrane lipid peroxidation effectively.In summary,our results systematically revealed the physiological mechanisms of moderate Na⁺stimulating growth of the salt-secreting xerophyte R.soongorica and enhancing its drought,high temperature and wind-borne sand resitances.