Tina L. Bell

Temperature-dependent release of volatile organic compounds of eucalypts by direct analysis in real time (DART) mass spectrometry

A method is described for the rapid identification of biogenic, volatile organic compounds (VOCs) emitted by plants, including the analysis of the temperature dependence of those emissions. Direct analysis in real time (DART) enabled ionization of VOCs from stem and leaf of several eucalyptus species including E. cinerea, E. citriodora, E. nicholii and E. sideroxylon. Plant tissues were placed directly in the gap between the DART ionization source skimmer and the capillary inlet of the time-of-flight (TOF) mass spectrometer. Temperature-dependent emission of VOCs was achieved by adjusting the temperature of the helium gas into the DART ionization source at 50, 100, 200 and 300 degrees C, which enabled direct evaporation of compounds, up to the onset of pyrolysis of plant fibres (i.e. cellulose and lignin). Accurate mass measurements facilitated by TOF mass spectrometry provided elemental compositions for the VOCs. A wide range of compounds was detected from simple organic compounds (i.e. methanol and acetone) to a series of monoterpenes (i.e. pinene, camphene, cymene, eucalyptol) common to many plant species, as well as several less abundant sesquiterpenes and flavonoids (i.e. naringenin, spathulenol, eucalyptin) with antioxidant and antimicrobial properties. The leaf and stem tissues for all four eucalypt species showed similar compounds. The relative abundances of methanol and ethanol were greater in stem wood than in leaf tissue suggesting that DART could be used to investigate the tissue-specific transport and emissions of VOCs.

Application of the ecosystem mimic concept to the species-rich Banksia woodlands of Western Australia.

This article describes the structure and functioning of a natural Banksia woodland at Moora, Western Australia. Species are first grouped in terms of growth form, root morphology, phenology and nutrient acquisition strategy. Above- and belowground standing biomass of a woodland is measured and its net annual primary production per unit rainfall compared with that of adjacent crops and plantings of the tree tagasaste. Information on seasonal water use and nutrient cycling in the dominant tree species Banksia prionotes is used to highlight the pivotal role of deep rooted summer growing trees in the maintenance of sustainability of the system. The article then addresses how one might select species mixtures as functionally effective analogues of the woodland. Assuming the mimic system replaces cleared virgin woodland not previously subject to runoff of water and nutrients from agriculture, a selection procedure would incorporate native flora representing (a) summer-growing deep- rooted and winter-growing shallow-rooted trees and shrubs, (b) herbaceous ground cover species, (c) fire resistant and fire sensitive species, and (d) a range of complementary nutrient uptake strategies. Assuming the mimic is designed to rehabilitate agricultural land experiencing rising water tables and nitrate pollution of ground water, incorporation of fast growing deep rooted exotic trees or herbaceous perennials is recommended alongside conventional annual crops or pastures, with appropriate nutrient stripping through removal of biomass. Difficulties in this context are scale of planting required and current lack of profitable incentives for planting and maintenance of perennials.

Carbon loads, forms and sequestration potential within ash deposits produced by wildfire: new insights from the 2009 ‘Black Saturday’ fires, Australia

Forest fires release substantial amounts of carbon (C). Much of it is emitted to the atmosphere, but some is deposited within ash on the ground. Little is known about amount and types of C deposited in ash. Here, we quantify total C, and total inorganic, water-soluble and particulate organic fractions deposited in ash during the catastrophic 2009 ‘Black Saturday’ wildfires in Australia. These fires coincided with the highest air temperatures and lowest humidity ever recorded in the local area, which, combined with high fuel loads of mostly long unburnt eucalypt forests, generated extreme burning conditions. In three mixed-species eucalypt forest sites sampled, the canopy, understorey and litter fuels were almost completely consumed, resulting in substantial ash deposition (mean, 81.9 t ha−1), with 5.9 t ha−1 of C being transferred from vegetation to the forest floor. In five temperate rainforest sites sampled, the canopy was not burnt and ash deposition was lower (mean, 48.3 t ha−1) than in the mixed-species eucalypt forest, but overall their higher C content resulted in higher C deposition (8.1 t ha−1). In all cases, most C contained in ash was organic and its pyrogenic nature infers increased resistance to degradation. Pyrogenic C is viewed by many as an important C sink, which could contribute to long-term C sequestration when incorporated into soils or sediments. Our results highlight the potential importance of the pyrogenic C pool in freshly deposited ash and, therefore, the necessity of a systematic and detailed analysis of ash deposition and C forms in ash to improve our understanding of C fluxes by forest fires.

Attack on all fronts: functional relationships between aerial and root parasitic plants and their woody hosts and consequences for ecosystems

This review discusses how understanding of functional relationships between parasitic plants and their woody hosts have benefited from a range of approaches to their study. Gross comparisons of nutrient content between infected and uninfected hosts, or parts of hosts, have been widely used to infer basic differences or similarities between hosts and parasites. Coupling of nutrient information with additional evidence of key processes such as transpiration, respiration and photosynthesis has helped elucidate host-parasite relationships and, in some cases, the anatomical nature of their connection and even the physiology of plants in general. For example, detailed analysis of xylem sap from hosts and parasites has increased our understanding of the spatial and temporal movement of solutes within plants. Tracer experiments using natural abundance or enriched application of stable isotopes ((15)N, (13)C, (18)O) have helped us to understand the extent and form of heterotrophy, including the effect of the parasite on growth and functioning of the host (and its converse) as well as environmental effects on the parasite. Nutritional studies of woody hosts and parasites have provided clues to the distribution of parasitic plants and their roles in ecosystems. This review also provides assessment of several corollaries to the host-parasite association.

Fungi and fire in Australian ecosystems: a review of current knowledge, management implications and future directions

Fungi are essential components of all ecosystems in roles including symbiotic partners, decomposers and nutrient cyclers and as a source of food for vertebrates and invertebrates. Fire changes the environment in which fungi live by affecting soil structure, nutrient availability, organic and inorganic substrates and other biotic components with which fungi interact, particularly mycophagous animals. We review the literature on fire and fungi in Australia, collating studies that include sites with different time since fire or different fire regimes. The studies used a variety of methods for survey and identification of fungi and focussed on different groups of fungi, with an emphasis on fruit-bodies of epigeal macrofungi and a lack of studies on microfungi in soil or plant tissues. There was a lack of replication of fire treatment effects in some studies. Nevertheless, most studies reported some consequence of fire on the fungal community. Studies on fire and fungi were concentrated in eucalypt forest in south-west and south-eastern Australia, and were lacking for ecosystems such as grasslands and tropical savannahs. The effects of fire on fungi are highly variable and depend on factors such as soil and vegetation type and variation in fire intensity and history, including the length of time between fires. There is a post-fire flush of fruit-bodies of pyrophilous macrofungi, but there are also fungi that prefer long unburnt vegetation. The few studies that tested the effect of fire regimes in relation to the intervals between burns did not yield consistent results. The functional roles of fungi in ecosystems and the interactions of fire with these functions are explained and discussed. Responses of fungi to fire are reviewed for each fungal trophic group, and also in relation to interactions between fungi and vertebrates and invertebrates. Recommendations are made to include monitoring of fungi in large-scale fire management research programs and to integrate the use of morphological and molecular methods of identification. Preliminary results suggest that fire mosaics promote heterogeneity in the fungal community. Management of substrates could assist in preserving fungal diversity in the absence of specific information on fungi.

Nitrogen uptake by Eucalyptus regnans and Acacia spp. – preferences, resource overlap and energetic costs

In southeastern Australia, the overstory species Eucalyptus regnans F. Muell. commonly grows with either of the two leguminous understory trees, Acacia melanoxylon (R. Br. Ex Ait. f.) or Acacia dealbata (Link.). Our objective was to elucidate interactions between the dominant eucalypt and its companion acacias for nitrogen (N) sources. Use of stable N isotopes as tracers revealed that ammonium was the preferred soil N source for all species, nevertheless, total N uptake varied greatly among species. Studies with double-labeled ((13)C/(15)N) glutamine indicated the uptake of this form of organic N in small amounts by both E. regnans and the Acacia spp. These and other data imply that, in contrast to boreal forests, organic N is not a significant component of N nutrition in mountain ash forests. Field and laboratory studies provided evidence that N(2)-fixation capacity of acacias varies with stand development, with N-fixing species playing an important role in N nutrition during the early but not the mature stages of forest growth. An index of N-uptake efficiency - the amount of oxygen consumed per unit N taken up - was compared across four N sources and three species. Nitrate uptake was the least efficient form of N acquisition, especially compared with ammonium uptake which was up to 30-fold less costly. Efficiency of glutamine uptake was intermediate between that of ammonium and nitrate. Differences in uptake efficiency among N forms were most pronounced for the Acacia spp. and least for E. regnans. We conclude that an overlap in requirements among sympatric Acacia spp. and E. regnans for specific soil N sources can be bypassed because of changes in biochemical strategies of Acacia spp. triggered by increasing soil N concentrations during stand development. Further studies might elucidate whether this is a common feature of complex forest ecosystems, or a specialty of the interaction between eucalypts and acacias.

Productivity and water relations of burnt and long-unburnt semi-arid shrubland in Western Australia

This study provides a comparison between vegetation of relatively recent and long-unburnt shrubland in terms of structural and functional groups, annual net primary productivity and water relations. Adjacent areas of vegetation long-unburnt or burnt 5 years previously were compared within a remnant block of Acacia–Allocasuarina–Melaleuca arid shrubland at Kalannie, south west Western Australia. Species were classified according to growth and life form, fire response, phenology and rooting morphology and densities, mean plant above-ground dry weights and shoot:root dry mass ratios of each assessed. Species compositions, seedling densities and absence of recruitment in the long-unburnt area suggested marked dependence on fire in maintenance of biodiversity. Comparisons of above-ground standing dry biomass and annual net primary productivity of total (above-ground plus below-ground) dry matter showed the 4.09 kg m−2 biomass of long-unburnt vegetation to be increasing at 0.52 kg m−2 year−1 versus 0.45 and 0.18 kg m−2 year−1 for vegetation of the burnt area. Water relations of soils indicated consistently wetter profiles in burnt than long-unburnt areas and no deep drainage during the year of study. Lower water stress of key species in burnt than long-unburnt areas were indicated by less negative pre-dawn water potentials and higher stomatal conductance during the year of study and more negative carbon-isotope composition (δ13C) in wood laid down over the past 5 years. Budgets for water use were estimated for both sites and compared with annual net primary productivities. Data suggested much greater transpiration loss per unit dry matter gain by the rapidly growing plants at the burnt site (437 ml H2O g−1 DM) than by the plants of the long-unburnt community (92 ml H2O g−1 DM). Results are discussed in relation to composition and functioning of other Western Australian ecosystems. It is clear that time since fire affects productivity and water-use of vegetation of semi-arid shrublands and is therefore an important consideration for management and protection of remnant vegetation.

Ecophysiology of ectomycorrhizal fungi associated with Pinus spp. in low rainfall areas of Western Australia

As a potential means of monitoring functional properties of plantations of Pinus pinaster and Pinus radiata established as part of land rehabilitation in the wheatbelt of Western Australia, we examined aspects of the ecophysiology of ectomycorrhizal fungi associated with tree roots. A single species of ectomycorrhizal fungi, Rhizopogon roseolus, dominated the mycorrhizal flora. Sporocarps of Rhizopogon roseolus appeared with the onset of winter rains in May, increased in number and total biomass to peak in September, and decreased to negligible levels at the beginning of the summer drought in December. A greater number of sporocarps, and consequently a greater biomass of sporocarp tissue, was associated with roots of P. radiata than P. pinaster. A similar seasonal pattern of mycorrhizal root infection was determined by counts of individual ectomycorrhizal root tips from bimonthly collection of soil core samples. At the low rainfall (380 mm annually) site, greater numbers of live root tips were more strongly correlated with soil moisture than organic matter content of soil. In contrast, in wetter areas closer to Perth (800 mm annually), highest numbers of active root tips and greatest amounts of organic matter were both within 0–10 cm depths. Results suggest an overriding importance of soil moisture rather than nutrient status of the soil as the key determinant of spatial and temporal distribution of the fungus. Results from a range of assays determining enzyme activity of soil (protease, phosphomonoesterase, cellulase, L-asparaginase, L-glutaminase and β-glucosidase) surrounding mycorrhizal roots indicated seasonal patterns to be similar to those described for reproductive activity of mycorrhizal fungi. Factors responsible for patterns of seasonal activity and distribution of ectomycorrhizal roots are discussed in terms of managing systems in order to maximise tree growth and form while effectively restoring soil water balance.

Intra-specific variation in carbohydrate reserves and sprouting ability in Eucalyptus obliqua seedlings

Seedlings of 13 provenances of Eucalyptus obliqua L’Her. grown under favourable moisture and nutrient conditions in a glasshouse for 9 months showed significant differences in seedling height, lignotuber size and carbohydrate reserve pools in roots and lignotubers. Lignotuber size was strongly and inversely correlated with mean annual rainfall of the source provenance, and larger E. obliqua lignotubers had higher concentrations and pools of carbohydrate reserves than smaller lignotubers. When seedling stems were clipped just above the lignotuber to simulate grazing or damage by fire, clipped seedlings showed significantly different responses to disturbance; seedlings with large carbohydrate reserve pools produced more sprouts of greater dry weight than seedlings with small carbohydrate reserve pools. The sprouting ability of lignotubers was related to carbohydrate reserves, such that plants with larger reserves in the lignotubers and roots supported production of a greater number of sprouts of greater total biomass than plants with smaller reserves. These results suggest that the sprouting mechanism provided by lignotubers is more important for seedling survival in areas of lower rainfall.

Role of plant functional traits in determining vegetation composition of abandoned grazing land in north-eastern Victoria, Australia

Abstract Question: In the Northern Hemisphere, species with dispersal limitations are typically absent from secondary forests. In Australia, little is known about dispersal mechanisms and other traits that drive species composition within post-agricultural, secondary forest. We asked whether mode of seed dispersal, nutrient uptake strategy, fire response, and life form in extant vegetation differ according to land-use history. We also asked whether functional traits of Australian species that confer tolerance to grazing and re-colonisation potential differ from those in the Northern Hemisphere. Location: Delatite Peninsula, NE Victoria, Australia. Methods: The vegetation of primary and secondary forests was surveyed using a paired-plot design. Eight traits were measured for all species recorded. ANOSIM tests and Non-metric Multi-dimensional Scaling were used to test differences in the abundance of plant attributes between land-use types. Results: Land-use history had a significant effect on vegetation composition. Specific leaf area (SLA) proved to be the best predictor of response to land-use change. Primary forest species were typically myrmecochorous phanerophytes with low SLA. In the secondary forest, species were typically therophytes with epizoochorous dispersal and high SLA. Conclusions: The attributes of species in secondary forests provide tolerance to grazing suggesting that disturbance caused by past grazing activity determined the composition of these forests. Myrmecochores were rare in secondary forests, suggesting that species had failed to re-colonise due to dispersal limitations. Functional traits that resulted in species loss through disturbance and prevented re-colonisation were different to those in the Northern Hemisphere and were attributable to the sclerophyllous nature of the primary forest. Nomenclature: Ross & Walsh (2003).