Annals of Botany 77: 389–397, 1996 Nitrogen and Phosphorus Nutrition in Mycorrhizal Epacridaceae of South-west Australia TINA L. BELL and JOHN S. PATE Department of Botany, Uniersity of Western Australia, Nedlands WA 6907, Australia Received: 2 February 1995 Accepted: 31 July 1995 Downloaded from https://academic.oup.com/aob/article/77/4/389/2587438 by guest on 27 September 2021 Xylem transport of nitrogen and phosphorus was examined in mature mycorrhizal plants of 41 species in 15 genera of Epacridaceae in native habitat in south-west Australia. Glutamine was the principal nitrogenous solute of xylem of all but four species. In the latter species, arginine or asparagine predominated. Nitrate and ammonium comprised minor fractions of xylem (tracheal) sap N, except in two species in which nitrate contributed over half of the N. Ratios of total-N:phosphate-P in xylem sap varied widely (mean 67³18, range 0±2–495) between species and habitats. Plants of Croninia kingiana (syn. Leucopogon kingeanus) from the one habitat showed higher levels of N and P in xylem early than late in the mycorrhizal season, but there was no consistent evidence of higher N and P levels from upper than deeper parts of their root systems. Study of juvenile populations of four species of epacrids indicated that substantial fractions of the yearly increment of N, P and dry matter was accumulated during the three summer months when infected mycorrhizal hair roots were absent. Glasshouse culture of mycorrhizal plants of Epacridaceae in habitat soil "$ "& enriched with decomposed and leached double ( C, N)-labelled dry matter of wheat showed substantial labelling "& "$ "& "& of shoots with N but not with C. Plants fed similarly treated N-labelled root residues of maize acquired N but "$ failed to generate ¦ C values different from those of control plants. Possible avenues of mycorrhizal and non- mycorrhizal nutrition of Epacridaceae are discussed. # 1996 Annals of Botany Company Key words: Epacridaceae, nitrogen, phosphorus, amino acids, mycorrhizal nutrition, xylem transport, amino acids, south-west Australia. both nitrogenous ions were transported to and assimilated INTRODUCTION by seedling shoots, although it was impossible to determine In view of the close taxonomic relationships of Epacridaceae the extents to which fungus and host roots had been and Ericaceae (Watson, 1964; Powell, 1983), their frequent involved in uptake, transfer and partial assimilation of the association with acidic nutrient-poor habitats and their ammonium and nitrate. common development of specialized hair roots harbouring This paper extends the use of root xylem sap analyses to ericoid-type mycorrhizas (Pearson and Read, 1975; Harley provide information on the export of nitrogenous solutes and Smith, 1983; Reed, 1987; Hutton, Dixon and and phosphate from roots of mycorrhizal plants of 41 Sivasithamparam, 1994), one might reasonably conclude species of 15 genera of Epacridaceae sampled across a wide that benefits through mycorrhizal nutrition might be closely range of native habitats in south-west Australia. A detailed similar for members of the two families. Mycorrhiza of a study of sap composition within a single species is described number of Northern Hemisphere Ericaceae have been for an autumn-winter-spring cycle of hair root production suggested to function principally by providing their hosts and infection, and the information obtained related to with nitrogen derived from direct uptake of amino acids or measurements of increments in total N and P of young following enzymatic breakdown of otherwise intractable plants of four species during and after a seasonal cycle of forms of soil organic nitrogen such as peptides or mycorrhizal symbiosis at the same study site. A glasshouse proteinaceous materials (e.g. Bajwa, Abuarghub and Read, study is described in which possible acquisition of carbon to 1985; Bajwa and Read, 1986; Read, Leake and Langdale, host epacrid through mycorrhizal breakdown of organic 1989; Leake and Read, 1990). In a number of studies (e.g. matter is examined in juvenile plants supplied with organic Stribley and Read, 1976, 1980; Read, 1978) measurable matter derived from decomposed and leached plant material "$ "& benefit from presence of mycorrhiza in terms of growth and labelled with C and N. increased N uptake has been observed. Equivalent in- formation on Epacridaceae is simply not available although the recent report of Bell, Pate and Dixon (1994) on response MATERIALS AND METHODS of mycorrhizal seedlings of four south-west Australian Collection and analysis of xylem sap epacrids to added nutrient supplements under glasshouse conditions has indicated primary limitation by nitrogen Xylem sap was collected from roots of a range of south-west rather than phosphorus. Analyses of root bleeding (xylem) Australian epacrids growing in native habitats ranging from "& "& sap of NH%NO$-orNH% NO$-treated plants showed that kwongan sandplain, dunal heath, swamp, Banksia wood- 0305-7364}96}040389­09 $18.00}0 # 1996 Annals of Botany Company 390 Bell and Pate—Nitrogen and Phosphorus Nutrition in Epacridaceae land, and jarrah (Eucalyptus marginata Donn ex Smith) and length per plant and percentage of hair root infected at karri (E. diersicolor F. Muell.) forests. For each species at times of sampling for each species. least three adult plants were utilized for sap collection. In certain cases plants of the same species were sampled from two or more widely separated habitats. Sampling was Glasshouse study of utilization by mycorrhizal plants of "$ "& conducted in autumn, winter and spring of 1993 or 1994 and C- and N-labelled plant organic matter all plants from which sap was collected showed well infected Two sources of labelled plant residues were used in the hair roots. Sap collection involved displacement of xylem "$ study, one comprising finely ground material of double ( C, (tracheal) fluid by mild vacuum from freshly excavated "& N)-labelled wheat, Triticum aestium L., the other root 10–20 cm segments of root using the apparatus and "& techniques described by Pate et al. (1994). In three cases material of sand-cultured N-labelled maize, Zea mays L. roots were of insufficient diameter for sap collection so (C% species), decomposing in situ after removal of shoot material. Prior to feeding, samples of each labelled material lower regions of the stem were sampled. Downloaded from https://academic.oup.com/aob/article/77/4/389/2587438 by guest on 27 September 2021 Detailed study of xylem composition through a single were mixed into habitat soil and allowed to decompose for season was undertaken on an adult population of Croninia a 6 month period under conditions of frequent leaching with kingiana (F. Muell.) J. Powell [syn. Leucopogon kingeanus deionized water to remove mineralized N. (F. Muell.) C. A. Gardner] growing in deep infertile sand in Juvenile plants of Leucopogon striatus R. Br., L. open Banksia woodland on private property near Gingin conostephioides, Astroloma xerophyllum and Croninia (31m08« S, 115m35« E). At each of four sampling periods kingiana and the non-epacrid species Banksia attenuata R. during the mycorrhizal season (May, Jul., Sep. and Nov. Br. (Proteaceae) and Acacia pulchella R. Br. (Mimosaceae) 1993) five to seven plants were progressively excavated to utilized for the feeding study were harvested in Jul.–Aug. the full extent of their root systems (1±5–2±0 m depth) and 1992 or 1993 from natural habitats at approximately 3–10 lateral roots on upper, mid and lowest parts of each root months of age, using the intact root core (15 cm height, system harvested for sap collection. The water table at the 7±2 cm diameter) procedure described by Bell et al. (1994) to study site was at 1±8 m depth in winter retreating to 2±4mby preserve as carefully as possible their complements of hair the end of summer. Specific amino compounds, ammonium, roots or other specialized root structures. After 2 months of nitrate and phosphate were identified and measured in sap acclimitization in the glasshouse, plants and their intact root samples using the HPLC-based assays detailed by Bell et al. cores were transferred to larger pots (22 cm height, 10±7cm (1994). diameter) and each core surrounded by habitat soil into which a labelled residue had been incorporated. Plants were grown for a further 10 month period during which they were watered regularly with deionized water but received no Seasonal studies of increases in total plant N and P nutrient supplements. Shoots of all plants were harvested Populations of juvenile plants of four species of together with those of control plants of all species grown Epacridaceae [Astroloma xerophyllum (DC.) Sond., under the same conditions but without labelled residues. Andersonia gracilis DC., Leucopogon conostephioides DC. Harvested plants were examined for presence of infected and Croninia kingiana] recruiting after a hot wild fire (May hair roots (Epacridaceae), cluster roots (Proteaceae) and 1991) at the Gingin site (see above) were successively nodules (Mimosaceae) in the original soil and in those parts sampled over 1 year at a sequence of harvest times to enable of the root systems which had penetrated into outer regions increments in plant dry matter N and P to be assessed of the pot where the labelled residues were located. Dried, finely ground shoot material of all species and treatments between the following times; (a) the commencement of the "$ "& was analysed for C and N by high resolution mass annual cycle of hair root formation (end of Mar. 1992), (b) "$ spectrometry [see Pate et al., 1990 ( C) and Unkovich, Pate the senescence of hair roots at the end of the subsequent "& season of mycorrhizal activity (end of Dec. 1992), and (c) and Sanford, 1993 ( N)]. the end of the ensuing non-mycorrhizal season (end of Mar. 1993). During the non-mycorrhizal season [interval between (b) and (c)] roots were almost devoid of hair roots and the RESULTS few hair roots which were present showed negligible Xylem sap composition of selected epacrids from south- infection.