The nitrogen (N) metabolism of legumes in dryland ecosystems is suffered from salt stress. Although the response of biological N fixation (BNF) to salt stress has received much research attention, how N fixing plants may adjust their N acquisition strategies in response to variation in salt stress remains unclear.

The nodulation and nitrogen fixation of Alhagi sparsifolia, a perennial deep-rooted legume naturally distributed in the transition zone of Taklimakan Desert and Qira oasis, showed a large variation in N₂ fixation, and nodulated Alhagi plants have been found to down-regulate nitrate reductase activity (NRA) when compared to non-nodulated individuals.

It is not clear whether the variation in N₂ fixation and NRA is a genetic trait that varies across Alhagi populations, or a plastic response of individual plants to environmental conditions.

Researchers from the Xinjiang Institute of Ecology and Geography (XIEG) of the Chinese Academy of Sciences examined the potential factors that shape the symbiotic nitrogen fixation of naturally growing Alhagi individuals at terminal ends of gradient change in the Taklimakan Desert, from high salinity riparian areas into low salinity desert sand dunes.

They found that nodulation and N₂ fixation in Alhagi plants is highly plastic in response to variation in soil chemistry (nitrate or salt concentrations), and found evidence supporting that this variation in N acquisition is not genetically based.

BNF of Alhagi plants is more salt-tolerant than mineral nitrogen assimilation is, and this trait helps legume plants better adapt and colonize diverse habitats with differing resource availability and salt concentrations.

The ecological importance of deep-rooted legumes in arid and semiarid ecosystems is receiving increasing attention due to global climate change and soil degradation worldwide.

The study improves understanding of the response of nitrogen metabolism of deep-rooted legumes to environmental factors and nitrogen utilization strategies of these plants in drylands, and provides new insight on their important role in dryland regions.

The attribute of deep-rooted legumes has an increasingly prominent role in bio-remediating areas affected by soil salinization by increasing soil productivity and improving soil structure.

Related findings were published in Environmental and Experimental Botany on Dec. 9.