Poster: Plant Pathogen/Symbiont Interactions

Abs # 759: The adventitious nodulation of the endemic tree legume acacia koa gray: a report of a unique phenomenon within a hawaiian montane forest ecosystem and the implication of a possible mechanism of adaptation associated with mutualism and opportunity.

Presenter:	Leary, James JK, leary@hawaii.edu
Authors	Leary, James JK (A) (B)  Borthakur, Dulal  (A) (B)
Affiliations:	(A): Department of Molecular Biosciences and Biosystems Engineering (B): University of Hawaii at Manoa

The Acacia genus is globally represented with over 1200 members. Acacia koa Gray (koa) is a dominant canopy species endemic to the Hawaiian archipelago. As one of only 14 endemic legumes, koa is an essential contributor to the nitrogen cycle of these forest ecosystems. Koa develops symbiotic relationships with the rhizospheric proteobacterium, Bradyrhizobium spp. , which are consummated with the development of root nodules typically confined to the terrestrial rhizosphere. However, within the natural habitat, koa has also demonstrated a unique capacity to develop adventitious nodulating root systems within the compartmentalized decay zones of the tree crown. The compartmentalized zones have a highly developed organic layer derived mainly from the decomposed heartwood and can harbor a complex epiphytic community. In many cases where adventitious nodulation has been observed, few to no nodules were found within the terrestrial rhizosphere. Adventitious nodules are frequently observed to be well developed and productive. The capacity for koa to adventitiously nodulate demonstrates its salutary participation within a mutualistic environment that serves not only the bacterial microsymbionts, but potentially other members of the epiphytic community through nutrient cycle subsistence at the microcosmal level. The initiation of host adventitious root systems may also be portrayed as an opportunistic adaptation by the host koa to competitively resequester nutritional resources made available through natural processes of decomposition. Comparative studies of biotic and abiotic parameters between neighboring adventitious and terrestrial rhizospheres will be presented to provide basic knowledge for explaining this unique biological event.