John S. Pate

The promotive effect of smoke derived from burnt native vegetation on seed germination of Western Australian plants

Exposure of dormant seed to cold smoke derived from burnt native vegetation had a positive influence on germination in one or more seed provenances in 45 out of 94 species of native Western Australian plants that are normally hard to germinate. When tested under controlled conditions some species showed earlier germination in smoke treatments than controls; in others smoke-treated seeds continued to germinate for several weeks after controls had achieved full germination. In the remainder, treated and control seeds germinated to similar time schedules. A group of 23 species which responded positively had previously been recorded as extremely difficult or impossible to germinate using conventional techniques. These included members of the genera Geleznowia (Rutaceae), Hibbertia (Dilleniaceae), Stirlingia (Proteaceae), Verticordia (Myrtaceae), Actinostrobus (Cupressaceae) and Pimelea (Thymelaeaceae). Both large- and small-seeded species were encountered amongst the positively responding taxa, which encompassed representatives of 15 families and 26 genera of dicotyledons, 5 families and 8 genera of monocotyledons and the gymnosperm Actinostrobus acuminatus. Sowing seeds on smoke-fumigated filter papers or watering with aqueous eluates of smoke elicited similar degrees of stimulation of germination, as did exposure to gaseous smoke in a readily germinating species Anigozanthos manglesii (Haemodoraceae) and the normally intractable species Lysinema ciliatum (Epacridaceae). Exposing recently burnt and unburnt natural bushland sites to smoke, smoked water or smoked dry sand elicited a significant germination response in 15 species. Over one third of the species sampled in the burnt site exhibited germination additional to that caused by the fire. Data are discussed in relation to previous germination studies on Australian and other taxa.

An appraisal of recent field measurements of symbiotic N2 fixation by annual legumes

In this paper we review both the methods for estimating N2 fixation and the quantity of N2 fixed by annual crop legumes. Available data on the N difference method for estimating N2 fixation reveal it to be unreliable. Although we advocate the use of isotope-based techniques their limitations necessitate the simultaneous collection of supporting data in the form of nodulation status, soil mineral N availability, and N yields of non-N2 fixers. To improve confidence in isotopic techniques for estimating N2 fixation differences in the form and function of plant roots are highlighted as critical areas for future research, as is a greater understanding of the total N contained in legume roots. A survey of the quantities of N2 fixed reveals the principal crop legumes to be ranked in the following descending order: soybean, lupin, field pea, faba bean, common bean, lentil, and chickpea.

Seed Ageing and Smoke: Partner Cues in the Amelioration of Seed Dormancy in Selected Australian Native Species

Seed germination of many Australian native plant species has consistently proven to be fractious. With the discovery of smoke-mediated germination, it is now possible to better understand the heterogeneity in germination patterns for a wide range of species both in situ and ex situ. In the present study, over 180 species were examined as to viability and smoke responsiveness of freshly collected seed. Soil storage and a number of commonly used seed pre-treatments were employed in combination with smoke to examine both longevity in artificially constructed seed banks, and the role of seed ageing in improved germination. Methods of smoke application for commercial use were also investigated. Viability decline over 1 year varied between 10% and 80%. Reductions of as little as 15% were found to compromise the ability of a number of species to successfully recruit in consecutive seasons. When fresh seed was used,almost 70% of species tested responded positively to smoke whether applied prior to or after sowing. Variation in success between the two methods confirmed earlier conclusions that substances contained in plant-derived smoke may be inhibitory at high concentrations for particularly sensitive species. Only 10% of species under investigation recorded optimum germination with seed ageing alone but when smoke was applied as a treatment after soil storage, 60% of species responded positively. Implications for horticulture, rehabilitation, seed bank research and habitat management are discussed.

δ13C analysis of phloem sap carbon : novel means of evaluating seasonal water stress and interpreting carbon isotope signatures of foliage and trunk wood of Eucalyptus globulus

Abstract A recently described phloem-bleeding technique was used to study seasonal changes in δ13C, sugar levels and the amino acid:sugar balance of phloem translocate of 2- to 3-year old trees of Eucalyptus globulus at a rain-fed site (Eulup) and a waste-effluent-irrigated site (Albany) in south-west Australia. δ13C of phloem sap from the Eulup site fluctuated widely between winter (−27.6‰) and peak summer stress (−20.2‰), compared with a much smaller range of −28.4 to −26.3 at Albany. Seasonal changes in sugar concentrations in sap fluctuated closely with those of phloem δ13C, with highest concentrations and least negative δ13C values at times of greatest soil water deficit. Molar ratios of amino acids to sugars in phloem sap were similar between plantations in winter through to early summer. They then remained high at the nitrogen-rich effluent-treated site, but fell dramatically once soils dried out at Eulup. Mature leaf dry matter sampled at peak yearly stress (early autumn) showed more negative δ13C values than concurrently harvested phloem sap or recently initiated shoot apex dry matter, presumably because the sampled foliage had laid down its structural carbon earlier under relatively unstressed winter/spring conditions. Differences between Albany and Eulup were much greater for δ13C of phloem and new apical dry matter than for dry matter of mature foliage. Comparisons of δ13C signatures of phloem sap carbon with those of dry matter of nascent xylem tissues showed seasonal fluctuations in δ13C of phloem translocate which were mirrored a month or so later by those for xylem carbon. δ13C analyses of trunk growth rings from Eulup and Albany showed well-defined seasonal oscillations over the first 2 or 3 years of growth until irrigation commenced at Albany. Fluctuations in δ13C at the latter site then became noticeably less pronounced than at Eulup. Future use of phloem sap δ13C and solute analyses for studying seasonal water and nutrient status of E. globulus is discussed.

Availability of organic and inorganic forms of phosphorus to lupins (Lupinus spp.)

Inositol phosphate is at least equal to KH2PO4 as a source of P for the growth of lupins in sand but a much poorer source in soil. RNA and glycerophosphate were excellent sources of P for lupin growth in a P-fixing soil. Soil and root phosphatase activity were not altered by amendment of soils with either inorganic- or organic-P. The difference in availability of differing P-sources is related to their solubility in soils rather than susceptibility to phosphatases.

Water Relations Link Carbon and Oxygen Isotope Discrimination to Phloem Sap Sugar Concentration in Eucalyptus globulus

A strong correlation was previously observed between carbon isotope discrimination (Δ13C) of phloem sap sugars and phloem sap sugar concentration in the phloem-bleeding tree Eucalyptus globulus Labill. (J. Pate, E. Shedley, D. Arthur, M. Adams [1998] Oecologia 117: 312–322). We hypothesized that correspondence between these two parameters results from covarying responses to plant water potential. We expected Δ13C to decrease with decreasing plant water potential and phloem sap sugar concentration to increase, thereby maintaining turgor within sieve tubes. The hypothesis was tested with analyses of E. globulus trees growing on opposite ends of a rainfall gradient in southwestern Australia. The Δ13C of phloem sap sugars was closely related to phloem sap sugar concentration (r = −0.90,P < 0.0001, n = 40). As predicted, daytime shoot water potential was positively related to Δ13C (r = 0.70, P< 0.0001, n = 40) and negatively related to phloem sap sugar concentration (r = −0.86,P < 0.0001, n = 40). Additional measurements showed a strong correspondence between predawn shoot water potential and phloem sap sugar concentration measured at midday (r = −0.87, P < 0.0001, n = 30). The Δ13C of phloem sap sugars collected from the stem agreed well with that predicted from instantaneous measurements of the ratio of intercellular to ambient carbon dioxide concentrations on subtending donor leaves. In accordance, instantaneous ratio of intercellular to ambient carbon dioxide concentrations correlated negatively with phloem sap sugar concentration (r = −0.91, P < 0.0001, n = 27). Oxygen isotope enrichment (Δ18O) in phloem sap sugars also varied with phloem sap sugar concentration (r = 0.91,P < 0.0001, n = 39), consistent with predictions from a theoretical model of Δ18O. We conclude that drought induces correlated variation in the concentration of phloem sap sugars and their isotopic composition in E. globulus.

The nitrogen supply from soils and insects during growth of the pitcher plants Nepenthes mirabilis, Cephalotus follicularis and Darlingtonia californica

Abstract This study investigated the nitrogen (N) acquisition from soil and insect capture during the growth of three species of pitcher plants, Nepenthes mirabilis, Cephalotus follicularis and Darlingtonia californica. 15N/14N natural abundance ratios (δ15N) of plants and pitchers of different age, non-carnivorous reference plants, and insect prey were used to estimate proportional contributions of insects to the N content of leaves and whole plants. Young Nepenthes leaves (phyllodes) carrying closed pitchers comprised major sinks for N and developed mainly from insect N captured elsewhere on the plant. Their δ15N values of up to 7.2‰ were higher than the average δ15N value of captured insects (mean δ15N value = 5.3‰). In leaves carrying old pitchers that are acting as a N source, the δ15N decreased to 3.0‰ indicating either an increasing contribution of soil N to those plant parts which in fact captured the insects or N gain from N2 fixation by microorganisms which may exist in old pitchers. The δ15N value of N in water collected from old pitchers was 1.2‰ and contained free amino acids. The fraction of insect N in young and old pitchers and their associated leaves decreased from 1.0 to 0.3 mg g−1. This fraction decreased further with the size of the investigated tiller. Nepenthes contained on average 61.5 ± 7.6% (mean ± SD, range 50–71%) insect N based on the N content of a whole tiller. In the absence of suitable non-carnivorous reference plants for Cephalotus, δ15N values were assessed across a developmental sequence from young plants lacking pitchers to large adults with up to 38 pitchers. The data indicated dependence on soil N until 4 pitchers had opened. Beyond that stage, plant size increased with the number of catching pitchers but the fraction of soil N remained high. Large Cephalotus plants were estimated to derive 26 ± 5.9% (mean ± SD of the three largest plants; range: 19–30%) of the N from insects. In Cephalotus we observed an increased δ15N value in sink versus source pitchers of about 1.2‰ on average. Source and sink pitchers of Darlingtonia had a similar δ15N value, but plant N in this species showed δ15N signals closer to that of insect N than in either Cephalotus or Nepenthes. Insect N contributed 76.4 ± 8.4% (range 57–90%) to total pitcher N content. The data suggest complex patterns of partitioning of insect and soil-derived N between source and sink regions in pitcher plants and possibly higher dependence on insect N than recorded elsewhere for Drosera species.

Ion Circulation via Phloem and Xylem Between Root and Shoot of Nodulated White Lupin

The exchange rates of mineral cations in the xylem and phloem between root and shoot of white lupin (Lupinus albus L., cv. Ultra) were measured using nodulated plants grown in a defined liquid culture medium low in Na and lacking nitrogen. Harvests were taken at 39 and 49 days after sowing and plant parts analysed for C, N, and the mineral cations K(+), Mg(++), Ca(++), and Na(+). Respiration losses of carbon by nodulated roots were assessed using Pettenkofer assemblies, and concentrations of C, N, and cations in xylem and phloem assayed by collecting root bleeding xylem sap and phloem sap of stem base during the day and night at several times throughout the study period. Flow rates of C and N between root and shoot were determined as in earlier modeling studies (Pate et al., 1979 b), using data on consumption of C by roots, increments of C and N in shoot and root dry matter and, C : N ratios in xylem and phloem sap. Using ratios of cation : C in xylem and phloem, net flow of the various ions between shoot and root were computed. The data showed substantial return of K(+) and Mg(++) from shoot to root with phloem translocate. This return flow provided roots with more K(+) or Mg(++) than was required for growth. It was estimated that 76 % or 87 % of the phloem-borne K(+) and Mg(++) respectively reentered the xylem and was thus circulated within the plant. Rates of return flow to roots and circulation within the plant were very small for Ca(++) and for Na(+) under the conditions of the experiment.

Stable isotope techniques in the study of biological processes and functioning of ecosystems.

1. Fundamentals of Stable Isotope Chemistry and Measurement T.E. Dawson, P.D. Brooks. 2. Carbon Isotope Discrimination and Plant Water-Use Efficiency: Case Scenarios for C3 Plants J.S. Pate. 3. Extraction and Analysis of Plant Water for Deuterium Isotope Measurement and Application to Field Experiments J.V. Turner, et al. 4. The Use of Stable Isotopes of Water for Determining Sources of Water for Plant Transpiration G. Walker, et al. 5. What do delta15N Signatures tell Us about Nitrogen Relations in Natural Ecosystems? G. Stewart. 6. Assessing N2 Fixation in Annual Legumes using 15N Natural Abundance M. Unkovich, J.S. Pate. 7. The Use of 15N to study Biological Nitrogen Fixation by Perennial Legumes M.B. Peoples, et al. 8. Source/Sink Interactions in Crop Plants: Application of 13CO2 and Urea-15N Techniques in Quantitative Analysis J.A. Palta. 9. Use of Enriched 15N Sources to study Soil N Transformations I.R.P. Fillery, S. Recous. 10. Stable Isotope Techniques using Enriched 15N and 13C for Studies of Soil Organic Matter Accumulation and Decomposition in Agricultural Systems A. McNeill. 11. Source Identification in Marine Ecosystems: Food Web Studies using delta13C and delta15N A.J. Smit. 12. delta13C as an Indicator of Palaeoenvironments: A Molecular Approach K. Grice. Index.

Co-occurrence of Proteaceae, laterite and related oligotrophic soils: coincidental associations or causative inter-relationships?

This communication presents the hypothesis that certain Australian lateritic and related oligotrophic soils may have been partly derived biotically from soluble iron-rich complexes generated following secretion of low-molecular weight organic acids by phosphate-absorbing specialised proteoid (cluster) roots of proteaceous plants. Subsequent precipitation of the iron is then pictured as occurring onto the oxide rinds of developing laterite after consumption of the organic components of the complexes by soil bacteria. The hypothesis is f irst examined in relation to current theories of origins of laterites and the extent of the coincidences worldwide in past and present times between Proteaceae and oligotrophic soil types of lateritic character. The paper then provides more definitive lines of evidence supporting the hypothesis, based largely on recent studies by the authors in south-western Western Australia. This relates to (a) cases of definitive association in habitats rich in Proteaceae between zones of root proliferation and ferricrete layers in lateritic soils, (b) proximity in soil profiles between ferric deposits and current and ancestral root channels, (c) the recovery of citrate-consuming bacteria from soil profiles and specifically from ferricrete rinds and horizons accumulating sesquioxide organic matter and (d) distribution of iron and phosphorus within plant and soil profile components consistent with ferricrete rinds being generated by rhizosphere-mediated interactions of plants and microbes under conditions of severely limited availability of phosphorus. The mode of functioning of proteoid root clusters is then discussed, especially in relation to exudation of organic acid anions, uptake of phosphorus and the subsequent fate of organic anions and their metal ion complexes in the system. An empirically based scheme is presented indicating flow profiles for phosphorus and iron between soil, ferricrete rinds and bacterial and plant components. We then discuss possible carbon costs to proteaceous plant partners when accessing phosphorus under the nutrient-impoverished conditions typical of heathlands and open woodlands of Mediterranean-type ecosystems of Western Australia. The paper concludes with a critical overview of the hypothesis, particularly its implications regarding possible higher plant: microbial influences shaping soil and landscape evolution in the regions involved.