Grass to legume facilitation in saline-sodic steppes: influence of vegetation seasonality and root symbionts

Abstract

Aim: Identify key factors driving legume seedlings performance in saline-sodic soils. Methods: Five plots were established in paired sub-humid steppes with saline-sodic soils dominated by Distichlis spicata or Panicum coloratum. In each plot, Lotus tenuis was sown in autumn and individual plants were collected close to nurse plants (dominant species), and in open areas, at the end of the cold and warm seasons. Carbon and nutrient acquisition (through C and O isotopic composition and N and P content measurements) and plant symbiotic functioning (through N fixation by rhizobia and mycorrhizal colonization measurements) were determined. Results: Biomass of legume grown close to a nurse plant was always higher than in open areas. This increase was higher close to P. coloratum and to D. spicata in the cold and warm seasons, respectively. In both cases, L. tenuis improved its nutrient acquisition and symbiosis functioning. N-acquisition and rhizobia efficiency increased in the most facilitated L. tenuis plants in the cold season while P-acquisition was greater in the warm season. Conclusions: Grass-to-legume facilitation in sub-humid steppes with saline-sodic soils was detected in cold and warm seasons, differing between steppes in relationship with the vegetation growing rate and the establishment and functioning of legume-rhizobia-mycorrhiza symbioses.