Response Characteristics Of Wetland Plant Species Under Saline-alkaline Stress During Their Propagation And Growth Stages

In recent decades,natural causes?e.g.,high evaporation rates?and anthropogenic activities?e.g.,poor irrigation practices?contribute to the increase of the area of saline-alkaline soil and degree of saline-alkalization in various wetlands.Saline-alkalization can lead to the decrease of wetland area and the degradation of wetland ecological function.Wetland plant species,regarded as a dominating component of wetland ecosystems,play an irreplaceable role in maintaining ecological functions of wetlands.Therefore,revealing the physiological response of a specific wetland plant species under saline-alkaline condition is of great significant for both understanding the vegetation community succession process during a saline-alkalization process and the vegetation restoration of degraded wetlands..The aim of this work was to assess the response characteristics of wetland plant species under saline-alkaline condition during their seed germination,seedling growth,asexual propagation and continued growth stages.The specific objectives were to:1)quantify the response characteristics of seed germination and seedling growth of tested plant species under five different NaCl and NaHCO₃ treatments;2)investigate the response characteristics of wetland plant species under saline-alkaline condition during their asexual propagation and continued growth stages;3)evaluate the nutrients?i.e.,nitrogen and phosphorus?uptake ability of typical wetland plants under saline-alkaline stress;4)discuss the ionic response characteristics of wetland plant species under saline-alkaline condition during their propagation and growth stages,and analyze its regulation mechanism at the ionic level;and 5)develop the pretreatment methods to improve seed germination ability of selected plant species in saline-alkaline environment.The main conclusions are as follows:?1?The saline-alkaline tolerance of 10 wetland plant species during their seed germination and growth stages differed greatly among species.Among tested species,Iris pseudacorus and Oenanthe javanica showed relatively strong ability of salt?NaCl?tolerance,while Iris sibirica showed relatively strong ability of saline-alkaline?NaHCO₃?tolerance during seed germination stage.Vetiveria zizanioides,Juncus effusus and Lythrum salicaria showed relatively strong ability of salt tolerance,while I.pseudacorus,Suaeda glauca,L.salicaria and O.javanica showed relatively strong ability of saline-alkaline tolerance during seedling growth stage.?2?The tested wetland plant species showed different responses and salt stress symptoms during their asexual reproduction and growth stages.Excessive salt?i.e.,NaCl and NaHCO₃?can inhibit the capacity of asexual reproduction and continued growth of wetland plant species,and even affected the survivability of plants.Among the tested species,Acorus tatarinowii and L.salicaria showed relatively strong ability of salt?NaCl?tolerance,while A.tatarinowii,Phragmites australis,Arundo donax and Scirpus validus showed relatively strong ability of saline-alkaline?NaHCO₃?tolerance during asexual propagation stage.NaCl stress exhibited relatively less influence on P.australis,Phyllostachys heteroclada and Pontederia cordata during their continued growth stage,while NaHCO₃ stress presneted relatively less influence on P.australis and A.donax during their continued growth stage.?3?The assimilation of nutrients into plants varied with the salinity levels,as well as the plant species.NaCl and NaHCO₃ inhibited the absorption of nitrogen and phosphorus into most plant species?e.g.,Canna indica,A.donax?However,the existing of medium saline-alkaline stress could increase the nitrogen and phosphorus absorption into some plant species?e.g.,A.tatarinowii,L.salicaria?,and the saline-alkaline tolerance ability of these species was accordingly imporved due to the absorption of substantial amount of nutrients.?4?Species-specific regulation mechanisms were observed,i.e.,controlled the entry of Na⁺?e.g.,Typha orientalis,A.tatarinowii?,compartmentalization of Na⁺?e.g.,P.australis?,and maintained a low Na⁺/K⁺ratios in different parts of plants?e.g.,P.cordata?to resist the saline-alkaline stress at the ionic level during their propagation and growth stages.Some plant species may use a variety of regulation mechanisms to improve their salt tolerance at the same time.?5?Mechanical Scarification,Hot water,1 mM Mannitol,1 mM Ethephon and Hot water+1 mM Ethephon methods can effectively promote the germination of Alternanthera philoxeroides,Hydrocotyle vulgaris and P.cordata under nonsaline conditions.While,the Hot water+1 mM Ethephon method exhibited the best promotive effect on seed germination under saline-alkaline condition.