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Specialists or generalists? Nitrogen fixing bacterial communities of invasive acacias in Australia

Birnbaum, C., Bissett, A., Thrall, P.H. and Leishman, M.R. (2013) Specialists or generalists? Nitrogen fixing bacterial communities of invasive acacias in Australia. In: 5th joint conference of New Zealand Ecological Society and Ecological Society of Australia, 24 - 29 November, Auckland, New Zealand.


Although some Australian acacias are amongst the most notable invaders world-wide, information on the relative role of soil biota, particularly beneficial microbial communities such as rhizobia, in their invasion success remains elusive. We examined the nitrogen fixing bacteria (henceforth NFB, focus on rhizobia) in native and introduced populations across New South Wales, Victoria, South Australia and Western Australia of four weedy Acacia spp. and a sister-taxa Paraserianthes lophantha using 454 sequencing to identify the NFB community composition and diversity in the rhizophere and nodules. We hypothesized that if these acacias are specialists, they will associate with similar NFB subsets in their nodules across the continent and are likely to be constrained in the introduced populations if compatible microorganisms are absent from the rhizosphere. However, if these acacias are generalists, they will successfully form relationships with novel NFB in the introduced range populations and are unlikely to be constrained by the absence of suitable soil mutualists. Results showed that overall the rhizosphere NFB communities were different across the continent (south-east vs south-west), while similar across the ranges (native vs introduced) in the nodules of the host species. The most dominant rhizobial taxa in the rhizosphere and nodules were slow-growing Bradyrhizobium. These results suggest that acacias are specialists that predominantly associate with Bradyrhizobium in their nodules across native and introduced populations. However, this does not translate into an invasion constraint since Bradyrhizobium is common in the soils across the south-eastern and south-western populations of these acacias.

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