The Post-Transplant Response of Acacia Koa and Leucaena Leucocephala to Pre-Transplant Colonization of Their Roots by Glomus Aggregatum in the Presence or Absence of Indigenous Arbuscular Mycorrhizal Fungi.

The results of efforts to apply arbuscular mycorrhizal fungi (AMF) in the field in Hawaii and elsewhere have yielded unpredictable results. The causes of this unpredictability are not clearly known. A better understanding of the variables regulating the activities of AMF in soil is key to bridging this knowledge gap.  The aim of the current study was to determine the role played by indigenous AMF on the response of Acacia koa and Leucaena leucocephala to pre-transplant colonization of their roots by Glomus aggregatum. Populations of indigenous AMF were enriched in trap cultures, and the mixed cultures were mass cultured after concentrating them by wet sieving and decanting. Different densities of the fungi were established in soil optimized for mycorrhizal activity. Mycorrhiza-free and mycorrhizal seedlings of A. Koa and  L.Leucocephala were transplanted in the soil contained in D₆₀ Deepots (Stuewe and Sons, Tangent, OR). The Deepots were incubated in the greenhouse under sprinkler irrigation. Pinnule P content monitored as a function of time and dry matter yield determined at harvest revealed that the response of the legumes to pre-transplant colonization of their roots by G. Aggregatum was dampened or eliminated in the presence of indigenous AMF. Our results suggest that variations in indigenous AMF could potentially explain the often observed unpredictability of field response of the legumes to nursery colonization of theirs roots by AMF.