Response of Nodulation, Nitrogen Fixation to Salt Stress in a Desert Legume Alhagi Sparsifolia

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Environmental and Experimental Botany



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© 2020 Elsevier B.V. Salinity has adverse effects on the nitrogen (N) metabolism of legumes in dryland ecosystems. Although the response of biological N fixation (BNF) to salt stress has received much research attention, less is known about how N fixing plants may adjust their N acquisition strategies in response to variation in salt stress. Alhagi sparsifolia, a perennial deep-rooted legume located in both riparian and desert environments of the hyperarid Taklimakan Desert, China, is a regionally important species due to its capacity for fixing atmospheric N and increasing soil stability. We investigated how groundwater biogeochemistry was related to seasonal differences in BNF of Alhagi sparsifolia located at terminal ends of a soil salinity gradient (high salinity riparian; inland low salinity sand dunes) in the Taklimakan Desert. Additionally, to elucidate the plasticity of A. sparsifolia nitrogen fixation to variation in soil salinity, we experimentally treated Alhagi seedlings from the same parental lineage with NaCl, Na2SO4, NH4NO3, and groundwater, and evaluated N fixation potential via root nodule development. We did not find evidence that mineral nitrogen concentrations influenced the varied N2 fixation rates (indicated by foliar δ15N value) in A. sparsifolia that we observed in the field. Instead, BNF of Alhagi plants was higher in high salinity riparian areas, whereas these plants utilized groundwater N when located in low salinity inland sand dunes. In our experimental treatments, salt addition did not significantly influence the nodulation of Alhagi seedlings, suggesting that nitrate assimilation instead of BNF is suppressed by salt stress. Thus, BNF in A. sparsifolia is tolerant to salt stress, and can be adjusted in response to variation in N availability and soil salinity. Relationships between salt tolerance and biological nitrogen fixation in A. sparsifolia explains how these species can increase soil nutrient availability across differing dryland environments, and illustrates a possible strategy whereby dryland legumes enhance their adaptability to saline environments by both building symbiotic associations with Rhizobium and utilizing readily available N when salt stress is less prohibitive.


Arid; Dryland; N2 fixation; Riparian; Taklimakan desert


Botany | Plant Sciences



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