Rhizobium spp. strains improve the physiological attributes of Mimosa tenuiflora (Willd.) Poiret seedlings under different water contents

Abstract

Rhizobium spp. inoculation is a strategy to promote plant growth and enhance drought tolerance, particularly in semiarid environments. This study evaluated the morphological and physiological responses of Mimosa tenuiflora (Willd.) seedlings inoculated with Rhizobium spp. under different water contents. Seeds were collected from 12 naturally growing mother trees (Patos, Paraíba, Brazil). No specific genotype or cultivar was used. A completely randomized experiment was conducted in a 5 × 2 factorial design with four replicates, comprising five treatments (inoculation with three Rhizobium spp. strains: CA19PT, RO19PT, and MK17PT; nitrogen fertilization; and a non-inoculated control) under two water-content levels (40% and 80% of pot capacity). M. tenuiflora seedlings were grown in 3 dm³ pots for 90 days, after which growth, biomass production, nodulation, relative water content (RWC), and gas exchange parameters were evaluated. The results demonstrated that physiological variables were influenced by the treatments and water availability, whereas growth variables were affected only by water availability. Among the evaluated treatments, inoculation with strain CA19PT showed physiological responses comparable to those observed under nitrogen fertilization. Even under low water availability (40% pc, seedlings maintained adequate hydration levels, with an increase in root biomass. Inoculation with selected Rhizobium isolates, particularly CA19PT, improved the physiological performance of M. tenuiflora seedlings under contrasting water-content conditions. Physiological responses observed in seedlings inoculated with CA19PT were comparable to those obtained with nitrogen fertilization. Additionally, seedlings grown under higher water content (80% pc exhibit better overall growth, whereas reducing water content to 40% pcstimulates root growth.