盐旱复合胁迫对小麦幼苗生长和水分吸收的影响

摘要

Salt and drought stress are two major limiting factors to wheat (Triticum aestivum L.) productivity.In north or northwest China,salt and drought stress often occur simultaneously owing to less rainfall and higher evaporation in winter and spring,which results in higher wheat yield loss.Recently,several studies have indicated that certain crop species exhibit lower growth inhabitation under the combined stress of salt and drought compared with salt and drought stress separately,but less information about adaptation mechanisms of these plants is available.Drought-tolerant and susceptible cultivars may possess variable morphological and metabolic adaptation processes in response to salt and drought stress that may contribute differently to their adaptation capability towards stress conditions.This study aims to investigate the combined effects of salt with drought stress (SD) on wheat seedling growth and water absorption characteristics,therefore providing a theoretical basis for wheat cultivation and management under salt and drought stress conditions.For this purpose two wheat cultivars,Yangmail6 (drought-susceptible) and Luohan7 (drought-tolerant),were used in a hydroponic experiment to investigate the effects of SD on root morphology,photosynthesis,and water absorption characteristics at the seedling stage of wheat.Sodium chloride(NaCl) and polyethylene glycol 6000 (PEG) were applied to solution to simulate salt and drought stress,respectively.Leaf gas exchange,chlorophyll fluorescence parameters,leaf water potential and root hydraulic conductivity was determined,and hormone concentrations were estimated according to the enzyme-linked immunosorbent assay method.The results showed that both salt and drought stress significantly affected the plant growth and physiological activities for both wheat cultivars.However,the combined effects of SD on plant growth and dry matter production reduction were lower than their sole effects.The root length,root surface area and root volume in SD-treated plants were higher than those in single stress treated plants although these were significantly lower when compared with the control.This indicates that SD has less negative effects on root growth than the single stress does.Similarly,chlorophyll content,chlorophyll fluorescence parameters (Fv/Fm or Fv'/Fm'),net photosynthetic rate,and stomatal conductance under SD treatment were all significantly higher than the single salt or drought stress,showing that SD caused less damage to the photosynthetic apparatus than their single application.Root hydraulic conductivity and xylem sap intensity under SD were observed to be significantly higher than those for the single stress,which resulted in higher leaf water potential and relative water content under SD than under single stress.The Na+/K+ ratio in leaves and roots under SD treatment were significantly lower than that for the single salt stress,and the abscisic acid (ABA) content in SD-treated plants was lower than that in single stresstreated plants,although those were significantly higher than those for the control,indicating that SD could reduce root ABA formation as compared to single stress.Compared with single salt and drought stress,SD not only improved the root water uptake capacity and leaf water status,but also decreased the Na+/K+ and ABA content,hence alleviating inhibition of leaf photosynthetic capacity.Overall,maintaining a higher water absorption capacity and photosynthesis were the major contributors for wheat seedlings to adapt SD.Luohan7 and Yangmai16 responded similarly to salt and SD,whereas Luohan7 showed more obvious tolerance to drought stress than Yangmai16.%为明确盐害、干旱及盐旱复合胁迫对小麦幼苗生长和水分吸收的影响,从而为盐害和干旱胁迫下栽培调控提供理论依据.以2个抗旱性不同的小麦品种(扬麦16和耐旱型洛旱7号)为材料,采用水培试验,以NaCl和PEG模拟盐旱复合胁迫,研究了盐旱复合胁迫下小麦幼苗生长、根系形态、光合特性及水分吸收特性的变化.结果表明,盐、旱及复合胁迫下小麦幼苗的生物量、叶面积、总根长与根系表面积、叶绿素荧光和净光合速率均显著下降,但是复合胁迫处理的降幅却显著低于单一胁迫.盐旱复合胁迫下根系水导速率和根系伤流液强度显著大于单一胁迫,从而提高了小麦幼苗叶片水势和相对含水量.盐胁迫下小麦幼苗Na+/K+显著大于复合胁迫,但复合胁迫下ABA含量却显著小于单一的盐害和干旱胁迫.因此,盐旱复合胁迫可以通过增强根系水分吸收及降低根叶中ABA含量以维持较高光合能力,这是盐旱复合胁迫提高小麦适应性的重要原因.洛旱7号和扬麦16对盐及盐旱复合胁迫的响应基本一致,但在干旱胁迫下洛旱7号表现出明显的耐性.