NaCl胁迫对不同白榆品系生物量及光合作用的影响

Effect of salt stress on the biomass and photosynthetic characteristics of Ulmus pumila L. strains

以3种一年生白榆品系(Y65、Y1、Y34)为试验材料,通过测定5种浓度NaCl处理(0、50、85、120、155 mmol/L)下其生物量、叶绿素含量及光合参数等指标的变化,探讨3个白榆品系的耐盐性差异及其光合参数的表征。结果表明:与对照相比,白榆品系生物量及叶绿素含量随NaCl胁迫增强逐渐降低,高NaCl胁迫(>85 mmol/L)会显著抑制生物量的累积及破坏叶绿素的合成。低NaCl胁迫(≤85 mmol/L)下,3个品系的光合机制以气孔限制为主,通过提高其气孔限制值而降低蒸腾作用,以提高水分利用效率(WUE)而适应盐分胁迫;而高NaCl胁迫(>85 mmol/L)下,则以非气孔限制为主,通过降低WUE而减少根系对地下水分与盐离子的吸收,以此来维持自身生长。3个白榆品系中,使非气孔限制转变为Pn下降主因的NaCl胁迫浓度不同,Y65、Y1的转折点为85 mmol/L,而Y34的转折点为50 mmol/L。结论:3个供试白榆品系中Y65的综合耐盐性较高,是盐碱地种植白榆品系的优先选择。

Salt stress is one of the major environmental factors affecting plants; it causes many changes in plant metabolism, such as changes in the content and composition of chlorophyll and reduction in the capacity and efficiency of photosynthesis. Salt stress also inhibits biomass accumulation. Therefore, plant biomass, photosynthesis, and chlorophyll content are often used as indicators of salt stress injury in plants. Ulmus pumila L. is a widely distributed and important fast-growing hardwood timber species that has good tolerance to drought, cold, salt, and wind. It is the most important timber species in China＇s Northern regions, saline-alkali areas, and desert, where it is used for afforestation, and to provide shelter forest and greenery.Consequently, it is considered to be a promising plant for cultivation in saline land. In response to salt stress, plants have evolved diverse mechanisms that can mitigate the effects of stress and lead to improved plant tolerance. In this study, 1-year-old potted seedlings of Ulmus pumila L. strains （Y65, Y1, and Y34） were used to examine their changes in chlorophyll content, photosynthetic characteristics, and biomass accumulation under different concentrations of NaCl （CK, 50 mmol/L, 85 mmol/L, 120 mmol/L, and 155 mmol/L）. The results showed that the content of chlorophyll and biomass of three the Ulmus pumila L. strains were significantly inhibited under higher-concentration salt stress, whereas no obvious changes were observed for the biomass accumulation of Y65 under lower concentrations of NaCl. Under low salinity stress （NaCl ≤85 mmol/L）, the values for leaf photosynthetic rate （Pn）, stomatal conductance （Gs）, and intercellular CO2 concentration （Ci） were decreased, whereas stomatal limitation （Ls） was increased. Stomatal inhibition （or stomatal restriction） was the main cause of the reduction in Pn of Ulmus pumila L. strains. Although no stomatal restriction occurred in the 120 mmol/L and 155 mmol/L NaCl treatments, the values for Pn and Ls were decreased, whereas Ci was increased. Under low-salinity stress （NaCl ≤85 mmol/L）, the increase in Ls resulted in a decrease in transpiration rate （Tr） and an increase in water use efficiency （WUE） that could reduce the leaf water loss, which alleviated the imbalance between water supply and demand and improved the salt-tolerance of Ulmus pumila L. strains. Under high-salinity stress （NaCl 〉 85 mmol/L）, the absorption capacity of roots was decreased, and both leaf Ls and WUE decreased, which resulted in a more severe water imbalance. Correlation analysis indicated that the biomass of Ulmus pumila L. strains was highly significantly positively related to total chlorophyll, chlorophyll a, Pn, Gs, and significantly positively related to Tr. Furthermore, WUE was significantly positively related to Ls. Collectively, our results indicated that the salt resistance of Y65 was better than that of Y1 and Y34. We accordingly recommend that Y65 is the preferred Ulmus pumila L. strains for afforestation in saline areas, which could provide a scientific basis for further research on the salinity tolerance mechanism.