Alfalfa and its rhizobial symbiont are sensitive to salinity. We compared the physiological responses of alfalfa populations inoculated with a salt-tolerant rhizobium strain, exposed to five NaCl concentrations (0, 20, 40, 80, or 160 mM NaCl). Two initial cultivars, Halo (H-TS0) and Bridgeview (B-TS0), and two populations obtained after three cycles of recurrent selection for salt tolerance (H-TS3 and B-TS3) were compared. Biomass, relative water content, carbohydrates, and amino acids concentrations in leaves and nodules were measured. The higher yield of TS3-populations than initial cultivars under salt stress showed the effectiveness of our selection method to improve salinity tolerance. Higher relative root water content in TS3 populations suggests that root osmotic adjustment is one of the mechanisms of salt tolerance. Higher concentrations of sucrose, pinitol, and amino acid in leaves and nodules under salt stress contributed to the osmotic adjustment in alfalfa. Cultivars differed in their response to recurrent selection: under a 160 mM NaCl-stress, aromatic amino acids and branched-chain amino acids (BCAAs) increased in nodules of B-ST3 as compared with B-TS0, while these accumulations were not observed in H-TS3. BCAAs are known to control bacteroid development and their accumulation under severe stress could have contributed to the high nodulation of B-TS3.

Composting fruit and vegetable waste from grocery stores on farms is a challenge due to the large quantity of liquid that leaches out. This leachate needs to be characterized for its effects on plant growth and soil. It was acidic with high conductivity; the plant mineral nutrient contents derived from the leachate (in decreasing order) were K, N mainly as ammonium-N, Ca, Mg, Na, and P; the trace elements were quite low. The germination and rootlet growth of cress and corn increased with the dilution of the compost leachate. In greenhouse assays, the compost leachate exhibited phytotoxicity to corn when used at high application rates. The corn leaf area, shoot and root biomass, plant concentrations and uptake of N, P and K were similar among the 20 mM N-fertilized control and the 30–40 m³/ha leachate treatments. In a field study on sandy loam, corn yields and plant uptake of P and K were similar among the mineral fertilized control and split-application leachate treatments applied to meet the P or K requirements of corn. After harvest, the soil pH, conductivity, and total N, P, and K contents were not affected by the leachate treatments. These results demonstrate the opportunity of recycling plant nutrients from compost leachate of fruit and vegetable waste as fertilizer to meet crop nutrient requirements without phytotoxicity and trace elements threats.

Acid mine drainage (AMD) poses persistent environmental challenges despite ongoing restoration efforts, particularly through the generation of acidic and metal-rich substrates. Fungi-assisted phytoremediation has emerged as a complementary strategy to support plant establishment in these environments. This study examines culturable root-associated fungi from four plant species, Populus balsamifera (PBA), Salix discolor (SDI), Scirpus atrocinctus (SAT), and Typha latifolia (TLA), growing at an AMD-impacted site and a nearby non-impacted reference site. Culture-dependent estimates of culturable fungi were obtained from bulk soil, rhizosphere soil, and root samples using two culture media. The taxonomic composition of culturable root-associated fungi was characterized, and relationships among taxa, soil physicochemical properties, and plant mineral parameters were examined. Estimates of culturable fungi on Modified Melin-Norkrans medium increased from bulk soil to roots, indicating stronger associations with root compartments under AMD-related stress. Most of the isolates belonged to Ascomycota, with a substantial proportion identified as dark septate endophytes (DSE). Phialocephala spp. were strongly associated with SAT and TLA growing in acidic, metal-rich, and water-saturated soils typical of AMD-impacted sites, whereas Cadophora spp. were more frequently associated with plants growing under less stressful environmental conditions. Overall, these results highlight the influence of site-specific edaphic conditions on the composition of culturable root-associated fungi and their associations with plant hosts. Together, these patterns suggest that specific fungal-plant associations may contribute to fungi-assisted phytoremediation in AMD-impacted environments.