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Seedling development under nutrient-deficient conditions was investigated for five bradysporous members of the Proteaceae to test the hypothesis that large seed size and high embryo nutritional quality reflect the outcome of selection favouring propagules suited for establishment in infertile soils characteristic of those natural environments dominated by members of the Proteaceae. Seeds of Protea lorifolia. Protea cynaroides, Leucadendron laureolum. Hakea sericea and Banksia laricina were germinated and grown on nutrient-deficient sand for 200 days. Every forty days ten seedlings of each species were harvested to determine growth, allocation patterns and nutrient use. Seedling parts were dried, weighed and analysed for N, P, K, Ca and Mg. Seedlings of all Proteaceae species were able to survive prolonged periods of nutrient scarcity irrespective of seed size. Rapid germination of Proteaceae seeds does not appear to be a significant means of increasing seedling fitness. Seed mass was positively correlated with seedling size. No correlation between relative growth rates and seed size was found. Seeds of members of the Proteaceae show selective storage of specific nutrients (N and P) such that seed chemical composition is unbalanced for optimum seedling growth. These elements complement the rich sources of cations Ca.Mg and K found in soils air post-tire environments when maximal recruitment of proteoid species occurs. [ABSTRACT FROM AUTHOR]

When freshly cut segments of naturally decorticated steles of horizontal roots of the Australian grass tree (Xanthorrhea preissii ) are subjected to gentle suction, bubbles of gas sometimes appear, as well as liquid, in capillaries attached to the aspirated ends of the steles, We tested the hypothesis that this gas comes from vessels embolized in the intact xylem stream, and that the gas volume extruded is therefore an effective measure of the extent of this embolism. To do this, twin samples were taken from individual roots of X. preissii in the field, one was fast-frozen intact for subsequent estimation of vessel embolisms in the cryo-scanning electron microscope (CSEM), the other 15-cm segment rapidly assessed for volume of gas aspirated into a standard micropipette tube. The two measures mutually confirmed one another by showing a strong positive correlation between numbers of embolized vessels and extracted gas volume. Similar gas volumes were obtained from replicate root segments excised directly from a root when the ends of the segment were frozen before excision, and aspiration conducted after subsequent thawing of the ends under water. The pattern of changes in embolisms during unstressed conditions in early summer, shown by both CSEM and aspiration, indicated almost no embolisms before dawn, followed by a rapid rise to a peak in mid morning, than a progressive loss of embolisms in late afternoon. It was also shown that the amount of embolism did not change with time after excision of the roots up to at least 30 min. A comparison of changes in leaf transpiration with gas volumes in steles during a 24-h cycle at peak transpiration stress in mid summer showed rapid rates of transpiration in early morning and law afternoon, with an intervening period of low water loss during the rest of the day. Numbers of embolisms rose to an carly morning peak, followed by apparent repair of these before noon. There was a second spate of embolisms in late afternoon, followed by complete refilling of all xylem with liquid by an hour or so after dusk .All vessels then remained fully recharged until the following dawn. We believe that aspiration is a direct and reliable technique, which offers a simple, inexpensive means of assessing the relative extent of embolism of vessels in xylem, and a means to test earlier findings by the other direct method of the CSEM. In a broad context, the technique should provide new opportunities for evaluating water relations of the xylem of whole plants. [ABSTRACT FROM AUTHOR]

A comparison is made of the phenologies of infructescence, follicle and seed growth development of two species of Banksia with particular reference to nutrient provision of dissimilarly sized seeds and associated mechanical defence costs. Follicles and seeds of B. attenuata developed sequentially while the smaller seeded B. laricina, exhibited an almost synchronous pattern of development. Seed nitrogen loading, assayed by temporal changes in amino pool sizes in different parts of the seed, was confined to a relatively short period (± 3 months) prior to infructescence desiccation in both species. Prolonged infructescence development in the larger seeded B. attenuata cannot therefore be interpreted simply as a mechanism for extending time available for mobilization of scarce nutrients within the plant, but may be a result of selective pressures related to the development of large woody structures around the seeds which provide mechanical defence against predators. Both Banksia spp. make relatively large investments of carbon, but not of nitrogen, in defence structures (up to 5.5 g per seed in B. attenuata) which in plants with low photosynthetic rates could have associated penalties in terms of N required for photosynthetic enzymes. Sequential development of follicle and then seed assumes significance, since nitrogen used in photosynthesis to provide carbon to the follicle can subsequently be mobilized from the leaf and redeployed in seed protein synthesis. The often held view that larger seeds require longer maturation periods is not universal as, in the Banksia spp. examined, defence costs and photosynthetic capacity might play a more dominant role in determining seed developmental patterns. [ABSTRACT FROM AUTHOR]

Samples of recently produced shoot material collected in winter/spring from common plant species of mulga vegetation in eastern and Western Australia were assayed for 13C and 15N natural abundance. 13C analyses showed only three of the 88 test species to exhibit C4 metabolism and only one of seven succulent species to be in CAM mode. Non-succulent winter ephemeral C3 species showed significantly lower mean δ13C values (– 28·0‰) than corresponding C3-type herbaceous perennials, woody shrubs or trees (– 26·9, – 25·7 and – 26·2‰, respectively), suggesting lower water stress and poorer water use efficiency in carbon acquisition by the former than latter groups of taxa. Corresponding values for δ15N of the above growth and life forms lay within the range 7·5–15·5‰. δ15N of soil NH4+ (mean 19·6‰) at a soft mulga site in Western Australia was considerably higher than that of NO3– (4·3‰). Shoot dry matter of Acacia spp. exhibited mean δ15N values (9·10 ± 0·6‰) identical to those of 37 companion non-N2-fixing woody shrubs and trees (9·06 ± 0·5‰). These data, with no evidence of nodulation, suggested little or no input of fixed N2 by the legumes in question. However, two acacias and two papilionoid legumes from a dune of wind-blown, heavily leached sand bordering a lake in mulga in Western Australia recorded δ15N values in the range 2·0–3·0‰ versus 6·4–10·7‰ for associated non-N2-fixing taxa. These differences in δ15N, and prolific nodulation of the legumes, indicated symbiotic inputs of fixed N in this unusual situation.... [ABSTRACT FROM AUTHOR]

Infestation of Acacia acuminata by the xylem-tapping mistletoe Amyema preissii invariably results in inhibition of growth, defoliation and eventual death of host branch parts distal to the mistletoe. Branch sectional areas proximal (P) and distal (D) to mistletoes are used to classify stages of parasitism, with P:D area ratios of 5--6 invariably associated with distal branch senescence. As monopolization of the branch proceeds, mistletoe leaf area increases in parallel with declining host foliage area, and the specific hydraulic conductivity of distal host wood declines sharply relative to that of proximal wood. Mineral composition and concentrations of nitrogenous solutes in xylem sap are at no stage appreciably different from those of proximal wood. After the demise of the distal branch parts, the transectional area of the host branch stump increases linearly with increasing mistletoe leaf area, the branch area supporting a unit of mistletoe leaf area always being about 3 times greater than that supporting a unit of host foliage area on unparasitized branches. This differential, compounded with high transpiration rates and selective uptake of host xylem solutes by the haustorium, fosters substantial mineral enrichment of the mistletoe relative to its host. The study provides a background for future investigation of possible cellular mechanisms continuously driving structural and functional changes in favour of the mistletoe. [ABSTRACT FROM AUTHOR]

The amino acid compositions of the root xylem saps of Olax phyllanthi and a range of its common hosts were examined in native coastal heath in Western Australia and in pot cultures of Olax reliant on single hosts. When hosts specializing in the xylem transport of one major solute (asparagine, glutamine, histidine, arginine or proline) were exploited, the endophytic tissue of haustoria and the xylem sap of Olax showed much lower proportions of this than of other solutes, suggesting pronounced metabolic transformation prior to xylem loading by the parasite. However, the xylem sap of Olax did partly reflect the compositions of its hosts; for example, djenkolic acid and pipecolic acid were present when Olax was parasitic on species of Acacia, and levels of citrulline and aspartic acid were higher than normal when it exploited hosts transporting large amounts of these compounds. Back-flow of S-ethenyl cysteine, a novel amino acid specific to Olax, was observed to another root hemiparasite (Exocarpos sparteus) in native habitat and to certain non-parasitic hosts in water-stressed pot cultures. Haustoria exhibited high levels of glutamine synthetase but showed appreciable in vivo nitrate reductase activity only when on hosts with high xylem levels of nitrate. [ABSTRACT FROM AUTHOR]

Studies of the variation in δ15N values for plants from a fire-prone Banksia woodland in South West Australia showed that pioneer herbaceous, non-mycorrhizal species which were active in nitrate reduction and storage, had the highest values (1.81‰). A detailed study of one such species Ptilotus polystachus demonstrated a close correspondence between the δ15N values of soil nitrate, xylem nitrate and leaf total nitrogen, suggesting an exclusive reliance on nitrate ions as nitrogen source. These pioneer species also showed a preponderance of the chloroplastic isoform of glutamine synthetase while woody species generally had higher activity associated with the cytosolic isoform. The group comprising monocotyledonous hemicryptophytes and geophytes contained species with slightly positive δ15N values and moderately active in nitrate reduction and storage. Nitrogen-fixing species had the lowest δ15N values (-0.36‰), irrespective of their apparent utilisation of nitrate. However, woody resprouter species which had low levels of nitrate reduction and storage had δ15N values which fell within the range of values obtained for the miscellaneous assemblage of N2 fixing species. Consequently, 15N abundance values failed to distinguish N2 fixing from non-fixing woody species, and therefore, could not be used in the ecosystem to determine the dependence of putative nitrogen fixing species on N2 fixation. The study demonstrated complex patterns of nitrogen ultilization in the ecosystem in which exploitation of different nitrogen resources related to plant the form and the physiological attributes of nitrogen assimilation by component species. [ABSTRACT FROM AUTHOR]

A range of approaches was used to investigate how species within a fire-prone Banksia woodland in South West Australia exploited inorganic soil nitrogen sources and how this changes through the development of the fire chrono-sequence. Nitrate and ammonium were present in soil solution throughout the chronosequence but nitrate predominated in recently burnt sites. Mean shoot nitrate reductase activities were high for all species in recently burnt sites and showed little increase when nitrate was supplied via the transpiration stream. Nitrate reductase of shoots of most species was low at sites not burnt for several years, but following transpirational induction with nitrate, developed activities similar to those at recently burnt sites. The principal amino compounds transported in the xylem were species specific, including asparagine, glutamine and citrulline-dominated species, and changed little in relative composition across the chronosequence. Species most active in leaf nitrate reduction transported the largest amounts of nitrate in their xylem sap and proportional amounts of nitrate in xylem tended to be greatest in recently burnt sites. Most of the species examined appeared to be shoot rather than root nitrate assimilators, but marked differences were recorded in potential of leafy shoots of different species to reduce nitrate. As a general rule, shallow-rooted herbaceous, non-mycorrhizal or VAM-positive species had the highest capacity to reduce nitrate, whereas woody species with ericoid mycorrhizae or combined vesicular arbuscular/ectomycorrhizal associations exhibited little capacity to reduce nitrate in roots or shoots. It seems likely that this latter group utilize ammonium or even organic forms of nitrogen rather than nitrate. Some putative nitrogen-fixing species were active in reducing and transporting nitrate, others were virtually inactive in these respects. [ABSTRACT FROM AUTHOR]

The acetylene reduction assay was used to follow seasonal changes in nitrogen fixation activity in a white clover-perennial ryegrass Icy in Northern Ireland. The annual estimate for fixation by the ley was 268 kg ha-1 (239 lb/acre) nitrogen virtually all of which was fixed during March to October. Nitrogen fixation was curtailed drastically after the Iey was cut but recovered as new foliage expanded on the clover. Glasshouse experiments described the effects of temperature, shading and defoliation on nitrogen fixation by white clover, and indicated that these factors might be important in modifying symbiosis under field conditions. [ABSTRACT FROM AUTHOR]

There are conflicting reports in the literature of the possible rote of the ureides, allantoin and. allantoic acid, in the nitrogen economy of Arachis species. Therefore, xylem sap composition in food peanut (Arachis hypogaea L.), and two forage peanuts (A. pintoi L. and A. glabrata Benth.) has been studied in detail. Xylem saps were collected from peanuts grown under different nutritional regimes and environmental conditions in the glasshouse and field in Australia, Malaysia and indonesia, and the N-containing solutes analysed. The relative amounts and concentrations of ureides in these peanut exudates were compared with those of soybean (Glycine max [L.] Merr.) - a species known to export ureides in its xylem stream as the major product of N2 fixation. Xylem concentrations of ureides in soybean were high in N2-fixing plants (2.9 to 3.7 μmol ml-1), representing 60 to 88% of xylem solute nitrogen, but it contributed only 9% (0.7 μmol ml-1) if plants were unnodulated and supplied nitrate. In all species of peanut, concentrations of ureides measured in xylem sap were generally inch smaller (0.02 to 0.37 μmol ml-1; 1-7% of xylem nitrogen) and were unaffected by peanut species or cultivar, rhizobial strain, plant size, growth rate, or stage of development, and were not related to N2, fixation (less than 0.1% of currently fixed nitrogen exported as ureides) or the assimilation, of nitrate. Apparently high levels of ureides in sap from some field-grown plants were shown to he due to in reference with the ureide colorimetric assay by some contaminating compound rather than represent increased ureides per se. [ABSTRACT FROM AUTHOR]

Nitrate was found to be the predominant form of available nitrogen in mulga soils. Nitrate reductase activities on a fresh mass basis of a range of plants from eastern (Queensland) mulga ecosystems 2 weeks after partial relief from drought were uniformly low for both herbaceous species (165 &plumn; 25 pkat g-1) and woody perennials (77 ± 14 pkat g-1). Supply of nitrate for 24 h to cut transpiring shoots of woody species or application of nitrate solution to the rooting zone of herbaceous species promoted little further increase in mean shoot nitrate reductase activities. Most species exhibited high tissue nitrate concentrations during water stress and soluble organic N profiles were in many cases dominated by the osmoprotective compounds, proline or glycine betaine. Species with low levels of proline or glycine betaine showed high foliar concentrations of other compatible osmotica such as polyols or sugars. Effects of relieving water stress on nitrate reductase activity, proline, glycine betaine and nitrate levels were followed over 3 d of irrigation. Available soil nitrate rose 10-fold immediately and, following rapid restoration of leaf water status of the eight study species, a 4-fold increase occurred in mean tissue concentrations of nitrate, proline and glycine betaine over the 3 d period. Similar changes in soil nitrate, nitrate reductase activity, proline and tissue nitrate were observed in the some ecosystem following a natural rainfall event and in western (S.W. Australia) mulga following irrigation. It is concluded that, although nitrate nitrogen is present at high concentrations and is the predominant inorganic nitrogen sources in soils of the mulga biogeographic region, its assimilation by perennial and ephemeral vegetation is limited primarily by water availability. A scheme is presented depicting interrelated physiological and biochemical events in typical mulga species following a rain event and subsequent drying out of the habitat. [ABSTRACT FROM AUTHOR]

The presence of host plants was found to be a key determinant of soil infectivity for endophytes of epacrids growing in south-west Australian jarrah forest carrying a sparse epacrid understorey. A comparable Banksia woodland with higher density of epacrids showed more uniform levels of infective endophytes, presumably because of closer overlap of host-supported patches of endophyte. Disturbed sites in jarrah forest, in which topsoil had been recently returned following bauxite mining, initially showed extremely low endophyte infectivity, probably due to disruption of the hyphal network, absence of host plants and/or increased competition from soil micro-organisms antagonistic to the endophytes. As the system stabilized and epacrids recruited and grew, inoculum potential of the soil re-established and by 12 yr it equalled that of adjacent undisturbed native forest. At disturbed sites with sparsely distributed adult members of the Epacridaceae, endophyte inoculum proved to be adequate only directly adjacent to the epacrids and declined steeply to negligible levels at only 40 cm radially distant from a host plant. The significance of live epacrid root systems on survival of endophyte inoculum in Banksia woodland was examined following removal of shoots of adult plants of the endemic epacrid, Leucopogon conostephioides DC. Coincident with demise of roots of the detopped plants, endophyte inoculum potential of closely adjacent soil declined by 50 % during the growing season. However, the effect was short lived and infectivity rose the following year to equal that of undisturbed adjacent woodland as mycelial matrices supported by neighbouring epacrids invaded the depleted study areas. [ABSTRACT FROM AUTHOR]

The nature and location of infective inocula of ericoid endophytes were examined in habitat soil sampled dry during midsummer from different depths down the rooting profile of an Epacridaceae-rich mediterranean-type ecosystem in south-western Australia. Efficacy of soil inocula was tested using aseptically germinated seedlings of Lysinema ciliatum R. Br. grown in a glasshouse. Hair roots, the principal structures colonized by endophytes, constituted c. 70 % of the total length of root systems formed under glasshouse culture. Colonization of these hair roots by endophytes was greatest (17 %) when seedlings had been inoculated with habitat soil from the upper 24 cm zone and declined to less than 1 % following inoculation with soil obtained from a depth of 36 cm and beyond. By contrast, sampling of a naturally growing epacrid (Leucopogon conostephioides D.C.) at the same study site during the wet midwinter growing season showed uniformly high (31-43 %) infection of hair roots down to maximum rooting depth at 70 cm. The infectivity of sieved soil fractions from bulk habitat soil was considerably greater (mean of 17 % hair root infection) for glasshouse-cultured Lysinema ciliatum inoculated with the 251-305 μm particle size fraction than for that inoculated with coarser (306-5000 μm) and finer (39-250 μm) sieve fractions (0-6% infection). Dilution of bulk soil with sterilized soil indicated maximum infection at 1: 16 dilution, declining to negligible infectivity at a dilution of 1 : 100. The data support the hypothesis that inoculum persists through summer principally in relatively coarse fractions of organic matter near the soil surface. With the onset of autumn rains, downward mycelial growth emanating from this upper zone rapidly recolonizes the soil profile and eventually promotes extensive colonization of hair roots produced that season by the epacrid root system. [ABSTRACT FROM AUTHOR]

The influence of factors associated with fire on seed germination ofAustralian native species is generally well documented, but examplesinvolving the use of smoke as a fire analogue for ecological research remain limited. The role of season of treatment in the efficacy of smoke as a promotive germination agent was investigated over two growing seasons using natural soil stored seedbanks in Banksia woodland near Perth, Western Australia. Smoke was applied to unburnt sites in the autumn, winter and spring of 1994. Germinant emergence and seedling survival of 37 species representing 18 families was monitored in both unburnt sites and in adjacent, recently burnt sites until the second spring after treatment (October 1995). Recruitment from seed was found to be profoundly affected by the season in which dormancy breaking treatment had been applied. The promotive effect extended beyond the initial year of application. For the majority of the species investigated, application of smoke to unburnt sites in autumn promoted a significantly greater germination response than treatment in winter orspring. In only three cases (introduced annuals, the Fabaceae and Hibbertia amplexicaulis) did autumn smoke treatment not yield better germination than in summer-burnt counterparts. However, in almost half of the cases examined, proportions of seedlings surviving past their first summer after emergence in burnt areas were consistently greaterthan those in smoked or untreated sites. Most notably, no seedlings emerging during the spring of the first year of study survived into the following summer. Implications of the results with respect to future seed bank research and management of native vegetation are discussed. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we present an integrated account of the diurnal variation in the stable isotopes of water (δ D and δ 18 O) and dry matter (δ 15 N, δ 13 C, and δ 18 O) in the long-distance transport fluids (xylem sap and phloem sap), leaves, pod walls, and seeds of Lupinus angustifolius under field conditions in Western Australia. The δ D and δ 18 O of leaf water showed a pronounced diurnal variation, ranging from early morning minima near 0‰ for both δ D and δ 18 O to early afternoon maxima of 62 and 23‰, respectively. Xylem sap water showed no diurnal variation in isotopic composition and had mean values of -13·2 and -2·3‰ for δ D and δ 18 O. Phloem sap water collected from pod tips was intermediate in isotopic composition between xylem sap and leaf water and exhibited only a moderate diurnal fluctuation. Isotopic compositions of pod wall and seed water were intermediate between those of phloem and xylem sap water. A model of average leaf water enrichment in the steady state (Craig & Gordon, pp. 9–130 in Proceedings of a Conference on Stable Isotopes in Oceanographic Studies and Palaeotemperatures , Lischi and Figli, Pisa, Italy, 1965; Dongmann et al ., Radiation and Environmental Biophysics 11, 41–52, 1974; Farquhar & Lloyd, pp. 47–70 in Stable Isotopes and Plant Carbon–Water Relations , Academic Press, San Diego, CA, USA, 1993) agreed closely with observed leaf water enrichment in the morning and early afternoon, but poorly during the night. A modified model taking into account non-steady-state effects (Farquhar and Cernusak, unpublished) gave better predictions of observed leaf water enrichments over a full diurnal cycle. The δ 15 N, δ 13 C, and δ 18 O of dry matter varied appreciably among... [ABSTRACT FROM AUTHOR]

Abstract A variety of native Western Australian legumes produced root clusters in sand culture confirming field and published observations. In general, these legumes grew equally well when supplied with organic or inorganic sources of phosphorus. The nitrogen content of shoots and roots varied little among treatments for all species, however, phosphorus content was always greater in plants supplied with inositol-P. The plasticity of root growth in response to localized placement of organic and inorganic sources of phosphorus was demonstrated using a simple ‘split root’ technique. Total root dry weight was, on average, more than doubled in P-amended sand when compared with non-amended sand. Root clusters tended to be produced in areas of relatively high phosphorus concentration and nodules in areas of low phosphorus concentration. Levels of phosphorus in lateral roots grown in P-amended sand were significantly different from lateral roots grown in the corresponding non-amended sand. Growth increases averaging 70% for white sand to over 100% for yellow sand indicated a large degree of ‘plasticity’ in roots under conditions of heterogeneous supply of phosphorus. Spatially exclusive development of organs for the acquisition of nutrients is discussed in relation to requirements for carbon in organ production and maintenance. [ABSTRACT FROM AUTHOR]