Using amino‐nitrogen pools and fluxes to identify contributions of understoryAcaciaspp. to overstoryEucalyptus regnansand stand nitrogen uptake in temperate Australia

Abstract

Summary• Amino acid concentration and composition in xylem and phloem sap and in plant tissues are good markers of plant performance and general plant nitrogen (N)-supply. Here, we tested if amino acid pools in Eucalyptus regnans, growing in southeastern Australia were increased by understory acacias in 70-yr-old stands, and if xylem N-transport of temperate Acacia spp. differs from their tropical counterparts.• We analysed amino-N concentrations and composition in foliage, xylem and phloem. In a novel approach we coupled amino-N concentrations of xylem with long-term sap flow measurements to calculate total stand N-transport.• Xylem N-transport of E. regnans is largely based on amino compounds of the glutamate group (more than 90%). By contrast, Acacia spp. transport mainly aspartate group amino acids in xylem (up to 80%). Amino compound diversity and concentration in tissues and xylem and phloem sap were universally greater in acacias compared to eucalypts. Acacias investigated here can be classified as 'amide transporters'.• We conclude that N-status and growth potential of aging E. regnans forest is not enhanced by a contribution of N from understory acacias, and that xylem N-transport in temperate Acacia spp. differs from acacias located in the tropics.

Determinants of maximum tree height inEucalyptusspecies along a rainfall gradient in Victoria, Australia

“…Great stature is also favored by the relatively rich, fine-grained soils that E. regnans occupies in southern portions of the Great Dividing Range and its various subdivisions; the relatively high levels of P and major cations in these soils presumably reflect bedrock weathering and soil rejuvenation associated with orogeny (see Vitousek et al 2003). Soils associated with E. regnans are typically rich in N, with high rates of N mineralization and high rates of N 2 fixation by associated Acacia immediately following disturbance by fire (Wang et al 2008, Pfautsch et al 2009, Tng et al 2012, presumably facilitated by relatively high levels of soil P (Vitousek et al 2010). The combination of relatively high soil fertility (Appendix: Figs.…”

The priming molecule β‐aminobutyric acid is naturally present in plants and is induced by stress

“…Until now, the consensus has been that plants themselves do not, or only exceptionally, synthesize BABA. In fact, the few positive studies present in the literature are either lacking detailed experimental descriptions (Gamliel & Katan, 1992;Pfautsch et al, 2009) or report surprisingly high levels of BABA in plants, suggesting possible confusion with GABA (Barrado et al, 2009).…”

The challenge of tree height in Eucalyptus regnans: when xylem tapering overcomes hydraulic resistance

“…Eucalyptus regnans (mountain ash) is the tallest hardwood in the world (Boland et al, 2006). Tree heights of 100 m have been reported from several sites in south-eastern mainland Australia and in Tasmania (Hickey et al, 2000;Mifsud, 2002), where nonlimited water supply and high soil nitrogen (N) concentrations favour such development (Adams & Attiwill, 1986;Attiwill & May, 2001;Pfautsch et al, 2009). Surprisingly little is known about the hydraulic architecture of mature E. regnans or tall angiosperms in general.…”