State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling, 712100, China; CAS Center for Excellence in Quaternary Science and Global Change, Chinese Academy of Sciences, Xian, 710061, China.
Institute of Soil and Water Conservation, Chinese Academy of Sciences, Ministry of Water Resources, Yangling, 712100, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
Environ Pollut. 2020 Oct;265(Pt A):114744. doi: 10.1016/j.envpol.2020.114744. Epub 2020 May 6.
Being signaling molecules, nitric oxide (NO) and hydrogen sulfide (HS) can mediate a wide range of physiological processes caused by plant metal toxicity. Moreover, legume-rhizobium symbiosis has gained increasing attention in mitigating heavy metal stress. However, systematic regulatory mechanisms used for the exogenous application of signaling molecules to alter the resistance of legume-rhizobium symbiosis under metal stress are currently unknown. In this study, we examined the exogenous effects of sodium nitroprusside (SNP) as an NO donor additive and sodium hydrosulfide (NaHS) as a HS donor additive on the phytotoxicity and soil quality of alfalfa (Medicago sativa)-rhizobium symbiosis in lead/cadmium (Pb/Cd)-contaminated soils. Results showed that rhizobia inoculation markedly promoted alfalfa growth by increasing chlorophyll content, fresh weight, and plant height and biomass. Compared to the inoculated rhizobia treatment alone, the addition of NO and HS significantly reduced the bioaccumulation of Pb and Cd in alfalfa-rhizobium symbiosis, respectively, thus avoiding the phytotoxicity caused by the excessive presence of metals. The addition of signaling molecules also alleviated metal-induced phytotoxicity by increasing antioxidant enzyme activity and inhibiting the level of lipid peroxidation and reactive oxygen species (ROS) in legume-rhizobium symbiosis. Also, signaling molecules improved soil nutrient cycling, increased soil enzyme activities, and promoted rhizosphere bacterial community diversity. Both partial least squares path modeling (PLS-PM) and variation partitioning analysis (VPA) identified that using signaling molecules can improve plant growth by regulating major controlling variables (i.e., soil enzymes, soil nutrients, and microbial diversity/plant oxidative damage) in legume-rhizobium symbiosis. This study offers integrated insight that confirms that the exogenous application of signaling molecules can enhance the resistance of legume-rhizobium symbiosis under metal toxicity by regulating the biochemical response of the plant-soil system, thereby minimizing potential health risks.
作为信号分子，一氧化氮（NO）和硫化氢（HS）可以介导由植物金属毒性引起的广泛的生理过程。此外，豆科植物-根瘤菌共生在缓解重金属胁迫方面受到了越来越多的关注。然而，目前尚不清楚用于通过外源应用信号分子改变金属胁迫下豆科植物-根瘤菌共生体抗性的系统调节机制。在这项研究中，我们研究了作为 NO 供体添加剂的硝普酸钠（SNP）和作为 HS 供体添加剂的硫氢化钠（NaHS）对铅/镉（Pb/Cd）污染土壤中苜蓿（Medicago sativa）-根瘤菌共生体的植物毒性和土壤质量的外源效应。结果表明，根瘤菌接种通过增加叶绿素含量、鲜重和株高及生物量显著促进了苜蓿的生长。与单独接种根瘤菌的处理相比，添加 NO 和 HS 分别显著降低了苜蓿-根瘤菌共生体中 Pb 和 Cd 的生物积累，从而避免了金属过量存在引起的植物毒性。信号分子的添加还通过增加抗氧化酶活性和抑制脂类过氧化和活性氧（ROS）水平来缓解金属诱导的植物毒性在豆科植物-根瘤菌共生体中。此外，信号分子通过改善土壤养分循环、增加土壤酶活性和促进根际细菌群落多样性来提高土壤养分循环。偏最小二乘路径模型（PLS-PM）和变异分解分析（VPA）都确定，通过调节豆科植物-根瘤菌共生体中的主要控制变量（即土壤酶、土壤养分和微生物多样性/植物氧化损伤），外源应用信号分子可以改善植物生长。这项研究提供了综合的见解，证实了通过调节植物-土壤系统的生化反应，外源应用信号分子可以增强豆科植物-根瘤菌共生体对金属毒性的抗性，从而最小化潜在的健康风险。
