Rhizobial mediation of Acacia adaptation to soil salinity: evidence of underlying trade‐offs and tests of expected patterns

Abstract

Summary 1.The ecological importance of host-soil symbiont associations for plant community structure and dynamics has been recently highlighted, particularly with regard to ecological and evolutionary responses along environmental gradients. 2. We used a range of native Australian shrubby legumes ( Acacia spp.) and associated root-nodule forming bacteria (rhizobia) in laboratory and glasshouse studies to investigate the ecology of Acaciarhizobial interactions with respect to soil salinity, a major environmental stressor in many parts of the world. 3. Analysis of laboratory growth data provided clear evidence of a trade-off in that growth rate of individual rhizobial isolates was reduced with increasing salt tolerance in culture. 4. A large replicated glasshouse inoculation trial using 40 strains of rhizobia and nine species of Acacia that varied in their ability to grow in saline soils found strong evidence of host specificity, but neither the average growth promotion of host plants nor the specificity of growth promotion was related to salt tolerance of the isolates. 5. In a second glasshouse experiment, we used a subset of salt-sensitive and salt-tolerant rhizobia and six Acacia species to evaluate performance and symbiotic effectiveness across different levels of soil salinity. Overall, we found no evidence of a relationship between rhizobial salt-tolerance (as measured in the laboratory) and impact on host growth performance, either in saline or nonsaline soils, and there was no evidence that salt-tolerant rhizobia perform better in more saline environments. 6. Synthesis . More salt tolerant Acacia spp. were less responsive in growth to rhizobial inoculation than salt sensitive hosts, implying that evolution towards reduced dependence on the symbiosis may facilitate adaptation to salt, raising a general question regarding the extent to which shifts in dependence on microbial symbionts underlies plant adaptation to other environmental gradients.

Phenotypic, Stress Tolerance and Plant Growth Promoting Characteristics of Rhizobial Isolates from Selected Wild Legumes of Semiarid Region, Tirupati, India

“…Decrease in growth of rhizobial isolates with increased salt concentration was also reported by Ali et al [9] and Thrall et al [25], this may be due to toxicity and also osmotic stress imposed by salinity [25] [26]. The isolates from woody legumes of Saudi Arabia showed nearly normal growth up 3% NaCl [10], rhizobia from Lotus spp.…”

Synergism and context dependency of interactions between arbuscular mycorrhizal fungi and rhizobia with a prairie legume

“…McKnight's solution is commonly used in ecological experiments with legumes (see Thrall et al 2008), and allowed us to manipulate the availability of nitrogen and phosphorus independently. To this baseline nutrient solution, we added either nitrogen (1.24 mmol NH 4 NO 3 ), phosphorus (0.73 mmol KH 2 PO 4 ), or both.…”

Improvement of tree growth in salt-affected soils under greenhouse conditions using a combination of peanut shells and microbial inoculation

“…Similar results have been obtained on Vigna radiata by Singh et al (2011), Acacia mangium and Acacia auriculoformis (Diouf et al, 2005), Acacia spp. (Thrall et al, 2008). The study further shows that microbial inoculation, peanut shells or their combination significantly improved the growth of S. senegal, V. seyal and P. juliflora plants under salinity conditions.…”

“…The role of biofertilizers such as rhizobia (Diouf et al, 2005;Thrall et al, 2008), Frankia (Diagne et al, 2013;Ngom et al, 2016), arbuscular mycorrhizal fungi (Evelin et al, 2009;Kohler et al, 2010) and plant growth-promoting rhizobacteria (Paul and Nair, 2008;Kohler et al, 2010) in plants tolerating salt stress has been well established in many studies. The bacterialmycorrhizal-legume tripartite symbiosis is currently being suggested as a possible solution to reforestation (Kohler et al, 2010 ;Diagne et al, 2013;Soliman et al, 2014;Ngom et al, 2016;Zhu et al, 2016).…”