Haustorial development and growth benefit to seedlings of the root hemiparasitic tree Nuytsia floribunda (Labill.) R.Br. in association with various hosts

Abstract

Dry matter gains and haustorial production of pot-cultured seedlings of Nuytsia floribunda were assessed after a 12 month period of association singly with each of a range of potential woody host species. One species, Adenanthos cygnorum, of similar size to most parasitized hosts, served as measure of response of Nuytsia in a non-benefiting situation. Rated on this basis, all 23 parasitized hosts elicited greater mean dry weights of Nuytsia than when on Adenanthos, and seven of these instances were highly significant. Numbers and weights of penetrating and presumably functional haustoria formed on a host were broadly correlated with growth benefit to Nuytsia, but there were notable instances of unusually poor or great benefit from a host relative to the complement of haustoria involved. Experiments in which haustoria-bearing associations of Nuytsia partnered with nodulated Acacia hosts (Acacia acuminata and A. cyclops) were fed 15N2 showed significant transfer of 15N to the parasite, but failed to determine whether the label had been acquired through haustoria or directly by Nuytsia roots following turnover of nodule and root residues of the host in the rooting medium. A parallel study using the unusual non-protein amino acid, djenkolic acid, as a marker of benefit from the djenkolic acid-containing host A. cyclops, showed appearance and progressive build-up of the compound in foliage of Nuytsia over a 6 month period after partnering the species in pot culture. Presence of the compound at final harvest in xylem sap of both partners but not in soil solution of the cultures strongly indicated xylem transfer via haustoria as the principal avenue for N benefit to the parasite. Results are discussed in relation to a recent evaluation of haustorial structure and functioning of N. floribunda. (C) 2000 Annals of Botany Company.