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

Journal of Ecology - Tập 96 Số 4 - Trang 746-755 - 2008
Peter H. Thrall1, James D. Bever2, J. F. Slattery1
1CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia, and
2Department of Biology, Indiana University, 1001 East Third Street, Bloomington, IN 47405-3700, USA

Tóm tắt

Summary 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. 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 Acacia–rhizobial interactions with respect to soil salinity, a major environmental stressor in many parts of the world. 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. 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. 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 non‐saline soils, and there was no evidence that salt‐tolerant rhizobia perform better in more saline environments. 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.

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Journal of Ecology

Tập 96 Số 4

746-755

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