盐分不均匀分布对紫花苜蓿生长和离子特征的影响

【目的】土壤盐分浓度在空间上呈不均匀分布,研究不均匀盐胁迫对紫花苜蓿生长、水分吸收、光合作用以及根叶部位K~+和Na~+的影响,探讨紫花苜蓿适应根部不均匀盐胁迫的生理机制,为紫花苜蓿耐盐品种培育及改良盐碱地紫花苜蓿种植技术提供理论依据。【方法】通过水培法,将紫花苜蓿幼苗的根均匀分成两部分置于分根装置中,给予两侧根部相同或不同浓度的NaCl处理,设置对照(0/0)、低盐胁迫根部分别为0 mmol·L~(-1)NaCl(0/400)和100 mmol·L~(-1)NaCl(100/300)的不均匀盐胁迫处理和均匀的200 mmol·L~(-1)NaCl胁迫处理(200/200),处理7 d后取样分析。【结果】不均匀盐胁迫与均匀盐胁迫均抑制了紫花苜蓿生长,导致水分吸收减少、叶片Na~+浓度增加和叶片K~+浓度减少。然而,0/400处理紫花苜蓿地上部分鲜重、水分吸收分别比200/200处理提高了24.3%和44.2%,其叶片Na~+浓度比200/200处理降低了53.6%、叶片K~+浓度与200/200处理无显著差异。0/400处理0侧根部水分吸收比对照提高12.3%、Na~+浓度是对照的10.5倍、K~+浓度与对照无显著差异。100/300处理紫花苜蓿地上部分鲜重、整株水分吸收、叶片K~+浓度均与200/200处理无显著差异。100/300处理叶片Na~+浓度比200/200处理提高了31.0%。100/300处理100侧根部水分吸收比对照降低了33.9%、Na~+浓度是对照的39.5倍、K~+浓度比对照降低了31.3%。0/400、100/300与200/200的蒸腾速率、气孔导度和胞间二氧化碳浓度无显著差异且均显著低于对照,而0/400的净光合速率与200/200无显著差异,均显著高于对照,100/300的净光合速率与对照无显著差异。【结论】紫花苜蓿根部平均盐分浓度为200 mmol·L~(-1)NaCl时,一侧根部NaCl浓度等于或高于其半致死浓度,另一侧根部NaCl浓度为0 mmol·L~(-1)时,不均匀盐胁迫缓解了根部高浓度盐胁迫对紫花苜蓿生长的抑制,当低盐胁迫根部NaCl浓度为100 mmol·L~(-1)时,不均匀盐胁迫不能够缓解根部高浓度盐胁迫对紫花苜蓿生长的抑制。

Effects of Heterogeneous Root Zone Salinity on Plant Growth and Ion Characteristic in Alfalfa

【Objective】Soil salinity is spatially heterogeneous. The effects of heterogeneous salinity on the growth, water uptake, photosynthetic parameter, K⁺ and Na⁺ concentration in leaf and root of alfalfa plants were determined to improve understanding of non-uniform salt stress tolerance mechanisms of alfalfa, so as to provide theoretical evidence for breeding the new alfalfa varieties tolerant to salt, and to improve alfalfa plant in salinity areas. 【Method】 Plant growth, water uptake, tissue ionic concentrations were studied in alfalfa plants grown hydroponically for 7 days using a split-root system, with uniform 0 and 200 mmol·L^-1 NaCl or heterogeneous 0/400 and 100/300 mmol·L^-1 NaCl. 【Result】 Neither uniform salinity or heterogeneous salinity inhibited alfalfa growth, decreased water uptake, increased leaf Na⁺ concentration and decreased leaf K⁺ concentration. Compared with uniform 200 mmol·L^-1 NaCl, 0/400 treatment significantly increased the alfalfa shoot fresh weight and whole plant water uptake. Shoot fresh weight and whole plant water uptake under 0/400 treatment were 24.3% and 44.2%, respectively, higher than 200/200 treatment. The leaf Na⁺ concentration in 0/400 treatment was 53.6% lower than in 200/200 treatment, and the leaf K⁺ concentration was similar with 200/200 treatment . But water uptake in non-salinity root was 12.3% higher and Na⁺ concentration in non-salinity root of 0/400 treatment was 10.5-fold higher than control, whereas K⁺ concentration in non-salinity root of 0/400 treatment was similar with control. There were no significantly differences of shoot fresh, water uptake and leaf K⁺ concentration between 100/300 and 200/200 treatment, but leaf Na⁺ concentration in 100/300 treatment were 31.0% higher than in 200/200 treatment. Water uptake were 33.9% lower, K⁺ concentration was 31.3% lower, and Na⁺ concentration were 39.5-fold in low-salinity root of 100/300 treatment, compared with control. Transpiration rate, stomatal conductance and intercellular CO₂ concentration of 0/400, 100/300 and 200/200 treatment were similar with each other and significantly lower than control, however, net photosynthetic of 0/400 and 200/200 were significantly higher than control, and net photosynthetic of 100/300 were similar with control.【Conclusion】When root average salinity was 200 mmol·L^-1 NaCl, the NaCl concentration of high salinity root were equal or greater than half lethal concentration, heterogeneous salinity can improve alfalfa plant growth when low salinity root under 0 mmol·L^-1 NaCl, but heterogeneous salinity can not improve alfalfa plant growth when low salinity root under 100 mmol·L^-1 NaCl.