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The present study aimed to investigate the effect of defoliation frequency (low and high) and water stress (excess or deficit) on biomass production, P and N nutrition, and symbiosis with native soil microorganisms on a Lotus tenuis and Schedonorus arundinaceus co-culture in a pot experiment. Combined effects of defoliation frequency and water stress affected plant accumulated shoot biomass. L. tenuis root biomass decreased in response to defoliation and water stress, while S. arundinaceus root biomass was similar between non-defoliated and defoliated plants, at all water levels. Low and high frequencies of defoliation in a waterlogged soil can be considered the most stressful scenario for L. tenuis and S. arundinaceus co-culture. Colonization of arbuscular mycorrhizal fungi in L. tenuis roots and dark septate endophytes colonization in S. arundinaceus roots were affected by both factors, whereas arbuscular mycorrhizal colonization in S. arundinaceus was affected only by water stress. Both plants tolerated defoliation and water stress due to the interaction between the translocation of nutrients and carbon compounds from roots to shoots, and P and N absorption (plus N2 fixation in L. tenuis). [ABSTRACT FROM AUTHOR]

Highlights: [•] Lotus seedlings are highly tolerant to water stress from deficit to waterlogging. [•] Lotus seedlings tolerate salinity and regulate Na+ concentration in tissue. [•] Lotus establishes early associations with AM fungi and Rhizobium. [•] Lotus seedlings acquire early imprints to respond better to future stress episodes. [Copyright &y& Elsevier]

Salinity and waterlogging interact to reduce growth for most crop and pasture species. The combination of these stresses often cause a large increase in the rate of Na+ and Cl− transport to shoots; however, the mechanisms responsible for this are largely unknown. To identify mechanisms contributing to the adverse interaction between salinity and waterlogging, we compared two Lotus species with contrasting tolerances when grown under saline (200 m M NaCl) and O2-deficient (stagnant) treatments. Measurements of radial O2 loss (ROL) under stagnant conditions indicated that more O2 reaches root tips of Lotus tenuis, compared with Lotus corniculatus. Better internal aeration would contribute to maintaining Na+ and Cl− transport processes in roots of L. tenuis exposed to stagnant-plus-NaCl treatments. L. tenuis root Na+ concentrations after stagnant-plus-NaCl treatment (200 m M) were 17% higher than L. corniculatus, with 55% of the total plant Na+ being accumulated in roots, compared with only 39% for L. corniculatus. L. tenuis accumulated more Na+ in roots, presumably in vacuoles, thereby reducing transport to the shoot (25% lower than L. corniculatus). A candidate gene for vacuole Na+ accumulation, an NHX1-like gene, was cloned from L. tenuis and identity established via sequencing and yeast complementation. Transcript levels of NHX1 in L. tenuis roots under stagnant-plus-NaCl treatment were the same as for aerated NaCl, whereas L. corniculatus roots had reduced transcript levels. Enhanced O2 transport to roots enables regulation of Na+ transport processes in L. tenuis roots, contributing to tolerance to combined salinity and waterlogging stresses. [ABSTRACT FROM AUTHOR]

Lotus tenuis (Wadst. & Kit.) is a perennial legume widely grown for pasture in the flood-prone and salt affected Pampa region of Argentina. The physiology of salt and waterlogging tolerance in L. tenuis (four cultivars) was evaluated, and compared with Lotus corniculatus (three cultivars); the most widely cultivated Lotus species. Overall, L. tenuis cultivars accumulated less Na+ and Cl−, and more K+ in shoots than L. corniculatus cultivars, when exposed to 200 mM NaCl for 28 days in aerated or in stagnant solutions. Root porosity was higher in L. tenuis cultivars due to greater aerenchyma formation. In a NaCl dose–response experiment (0–400 mM NaCl in aerated solution), L. tenuis (cv. Chaja) accumulated half as much Cl− in its shoots than L. corniculatus (cv. San Gabriel) at all external NaCl concentrations, and about 30% less shoot Na+ in treatments above 250 mM NaCl. Ion distributions in shoots were determined for plants at 200 mM NaCl. L. tenuis (cv. Chaja) again accumulated about half as much Cl− in old leaves, young leaves and stems, compared with concentrations in L. corniculatus (cv. San Gabriel). There were not, however, significant differences between the two species for Na+ concentrations in the various shoot tissues. The higher root porosity, and maintenance of lower shoot Cl− and Na+ concentrations in L. tenuis, compared with L. corniculatus, contributes to the greater tolerance to combined salt and waterlogging stress in L. tenuis. Moreover, significant variation for tolerance to combined salinity and waterlogging stress was identified within both L. tenuis and L. corniculatus. [ABSTRACT FROM AUTHOR]