Assessment of N2 fixation by understorey acacias in recurrently burnt eucalypt forests of subtropical Australia using 15N isotope dilution techniques

2000 ◽  
Vol 30 (1) ◽  
pp. 112-121 ◽  
Author(s):  
Danilo F Guinto ◽  
Zhihong Xu ◽  
Alan PN House ◽  
Paul G Saffigna
Keyword(s):  
Isotope Dilution ◽  
Forest Sites ◽  
Whole Plant ◽  
Sclerophyll Forest ◽  
Burnt Soil ◽  
Reference Plants ◽  
N Enrichment ◽  
Eucalypt Forests ◽  
N Natural Abundance ◽  
Subtropical Australia

The N2 fixation by understorey acacias in repeatedly burnt dry and wet sclerophyll forest sites in subtropical Australia was assessed using 15N isotope dilution techniques. In the first study, aboveground parts of established acacias and nonlegume reference plants at the two sites were collected from plots subjected to varying fire frequencies for measurements of 15N natural abundance (<$Q150E00000010446D80BFFEFF88A45505A9A1C8282ADCC6210090483DA6ED4F658F80>15N). The <$Q150E00000010446D80BFFEFF88A45505A9A1C8282ADCC6210090483DA6ED4F658F80>15N values of acacias and nonlegumes were similar, and substantial variation in these <$Q150E00000010446D80BFFEFF88A45505A9A1C8282ADCC6210090483DA6ED4F658F80>15N values precluded any evaluation of N2 fixation. In the second study, 15N enrichment method was used to examine N2 fixation of acacia seedlings grown for 5 months in glasshouse pots of top 10-cm soils collected from the fire plots at the two sites. In Acacia leiocalyx (Domin) Pedley at the dry site, whole plant percent N derived from the atmosphere (%Ndfa) was 25% in unburnt soil, 66% in periodically burnt soil, and 42% in annually burnt soil (referenceAlphitonia excelsa (Cunn. ex Fenzl) Reisseck ex Benth.), compared with 33, 69, and 66%, respectively (reference Corymbia variegata (Hook.) K.D. Hill & L.A.S. Johnson). In Acacia oshanesii F. Muell. & Maiden at the wet site, whole plant %Ndfa was 9% in unburnt soil, 41% in quadrennially burnt soil, and 50% in biennially burnt soil (reference Dodonaea triquetra Andr.), compared with -4, 26, and 55%, respectively (reference Eucalyptus pilularis Sm.).

scholarly journals A comparison of bushfire fuel hazard assessors and assessment methods in dry sclerophyll forest near Sydney, Australia

2012 ◽  
Vol 21 (6) ◽  
pp. 755 ◽  
Author(s):  
Penny J. Watson ◽  
Sandra H. Penman ◽  
Ross A. Bradstock
Keyword(s):  
Hazard Assessment ◽  
Assessment Method ◽  
Assessment Methods ◽  
Urban Fringe ◽  
The Other ◽  
Fuel Load ◽  
Forest Sites ◽  
Sclerophyll Forest ◽  
Hazard Assessments ◽  
Sydney Australia

Over the last decade, fire managers in Australia have embraced the concept of ‘fuel hazard’, and guides for its assessment have been produced. The reliability of these new metrics, however, remains to be determined. This study compared fuel hazard ratings generated by five assessment teams using two Australian hazard assessment methods, in two dry sclerophyll forest sites on Sydney’s urban fringe. Attributes that underpin hazard scores, such as cover and height of various fuel layers, were also assessed. We found significant differences between teams on most variables, including hazard scores. These differences were more apparent when fuel hazard assessments focussed on individual fuel layers than when teams’ assessments were summarised into an overall fuel hazard score. Ratings of surface (litter) fuel hazard were higher when one assessment method was used than when assessors employed the other; however, ratings of elevated (shrub) and bark fuel hazard were relatively consistent across assessment methods. Fuel load estimates based on the two hazard assessment methods differed considerably, with differences between teams also significant. Inconsistency in scoring fuel hazard may lead to discrepancies in a range of management applications, which in turn may affect firefighting safety and effectiveness.

Détermination de l'identité isotopique de l'azote fixé par le Frankia associé au genre Alnus

1988 ◽  
Vol 66 (7) ◽  
pp. 1241-1247 ◽  
Author(s):  
A. M. Domenach ◽  
F. Kurdali ◽  
C. Danière ◽  
R. Bardin
Keyword(s):  
Nitrogen Fixation ◽  
Symbiotic Nitrogen Fixation ◽  
Alnus Glutinosa ◽  
Natural Ecosystem ◽  
Free Medium ◽  
Fixed Nitrogen ◽  
Aerial Parts ◽  
Reference Plant ◽  
N Enrichment ◽  
N Natural Abundance

To use the 15N natural abundance method to evaluate the symbiotic nitrogen fixation by actinorhizal trees, it is necessary to determine the isotopic identity of assimilated nitrogen from two sources: the soil and the air. This study reports an isotopic value of fixed nitrogen by two alder species (Alnus incana (L.) Moench and Alnus glutinosa (L.) Gaertn. growing on nitrogen-free medium in greenhouse experiments. The δ15N value of the aerial parts was −2. This value was stable with time and did not depend on the Frankia strains used. This value could be used to estimate the nitrogen fixation in the natural ecosystem. Other parameters such as the mobilization of nitrogen reserves and the choice of the reference plant must be investigated to apply this method. The nodules of these two alder species were enriched in 15N relative to the rest of the plant but there was no relationship between symbiotic effectiveness of Frankia strains and 15N enrichment of nodules. On the other hand, for naturally growing trees, an enrichment in 15N was found primarily in the vesicles of nodules that are the sites of nitrogen fixation.

Evaluation of reference plants by labelling with 35S in the estimation of N2 fixation by 15N isotope dilution

1992 ◽  
Vol 145 (2) ◽  
pp. 177-185 ◽  
Author(s):  
S. D. Hamilton ◽  
P. M. Chalk ◽  
C. J. Smith ◽  
P. Hopmans
Keyword(s):  
Isotope Dilution ◽  
N2 Fixation ◽  
15N Isotope Dilution ◽  
15N Isotope ◽  
Reference Plants

scholarly journals Soil methane oxidation in both dry and wet temperate eucalypt forests shows a near-identical relationship with soil air-filled porosity

2017 ◽  
Vol 14 (2) ◽  
pp. 467-479 ◽  
Author(s):  
Benedikt J. Fest ◽  
Nina Hinko-Najera ◽  
Tim Wardlaw ◽  
David W. T. Griffith ◽  
Stephen J. Livesley ◽  
...  
Keyword(s):  
Climate Change ◽  
Soil Moisture ◽  
Climate Change Scenarios ◽  
Soil Air ◽  
Eucalypt Forest ◽  
Soil Atmosphere ◽  
Forest Sites ◽  
Ch4 Uptake ◽  
Eucalypt Forests ◽  
The Impact

Abstract. Well-drained, aerated soils are important sinks for atmospheric methane (CH4) via the process of CH4 oxidation by methane-oxidising bacteria (MOB). This terrestrial CH4 sink may contribute towards climate change mitigation, but the impact of changing soil moisture and temperature regimes on CH4 uptake is not well understood in all ecosystems. Soils in temperate forest ecosystems are the greatest terrestrial CH4 sink globally. Under predicted climate change scenarios, temperate eucalypt forests in south-eastern Australia are predicted to experience rapid and extreme changes in rainfall patterns, temperatures and wild fires. To investigate the influence of environmental drivers on seasonal and inter-annual variation of soil–atmosphere CH4 exchange, we measured soil–atmosphere CH4 exchange at high-temporal resolution (<  2 h) in a dry temperate eucalypt forest in Victoria (Wombat State Forest, precipitation 870 mm yr−1) and in a wet temperature eucalypt forest in Tasmania (Warra Long-Term Ecological Research site, 1700 mm yr−1). Both forest soil systems were continuous CH4 sinks of −1.79 kg CH4 ha−1 yr−1 in Victoria and −3.83 kg CH4 ha−1 yr−1 in Tasmania. Soil CH4 uptake showed substantial temporal variation and was strongly controlled by soil moisture at both forest sites. Soil CH4 uptake increased when soil moisture decreased and this relationship explained up to 90 % of the temporal variability. Furthermore, the relationship between soil moisture and soil CH4 flux was near-identical at both forest sites when soil moisture was expressed as soil air-filled porosity (AFP). Soil temperature only had a minor influence on soil CH4 uptake. Soil nitrogen concentrations were generally low and fluctuations in nitrogen availability did not influence soil CH4 uptake at either forest site. Our data suggest that soil MOB activity in the two forests was similar and that differences in soil CH4 exchange between the two forests were related to differences in soil moisture and thereby soil gas diffusivity. The differences between forest sites and the variation in soil CH4 exchange over time could be explained by soil AFP as an indicator of soil moisture status.

Impact of high-severity fire in a Tasmanian dry eucalypt forest

2016 ◽  
Vol 64 (3) ◽  
pp. 193 ◽  
Author(s):  
Lynda D. Prior ◽  
Grant J. Williamson ◽  
David M. J. S. Bowman
Keyword(s):  
Plant Mortality ◽  
Dry Forests ◽  
Obligate Seeder ◽  
High Severity ◽  
Fuel Loads ◽  
Eucalypt Forest ◽  
Whole Plant ◽  
Eucalypt Forests ◽  
Wet Forests

Dry eucalypt forests are believed to be highly fire tolerant, but their response to fire is not well quantified. We measured the effect of high-severity fires in dry eucalypt forest in the Tasmanian Midlands, the driest region on the island. We compared stand structures and fuel loads in long-unburnt (>15 years since fire) and recently burnt (<5 years since fire) sites that had been completely defoliated. Even in unburnt plots, 37% of eucalypt stems and 56% of acacia stems ≥5 cm in diameter were dead, possibly because of antecedent drought. The density of live eucalypt stems was 37% lower overall in burnt than in unburnt plots, compared with 78% lower for acacias. Whole-plant mortality caused by fire was estimated at 25% for eucalypt trees and 33% for acacias. Fire stimulated establishment of both eucalypt and acacia seedlings, although some seedlings and saplings were present in long-unburnt plots. The present study confirmed that eucalypts in dry forests are more tolerant of fire than the obligate seeder eucalypts in wet forests. However, there were few live mature stems remaining in some burnt plots, suggesting that dry eucalypt forests could be vulnerable to increasingly frequent, severe fires.

Fire alters soil labile stoichiometry and litter nutrients in Australian eucalypt forests

2017 ◽  
Vol 26 (9) ◽  
pp. 783 ◽  
Author(s):  
Orpheus M. Butler ◽  
Tom Lewis ◽  
Chengrong Chen
Keyword(s):  
Fire History ◽  
Fire Regime ◽  
Fire Effects ◽  
Soil System ◽  
Soil C ◽  
Burned Areas ◽  
Plant Soil ◽  
Forest Sites ◽  
Soil Stoichiometry ◽  
Eucalypt Forests

Ecological stoichiometry may be used to investigate the impacts of fire regime, as fire regime can influence the cycling and balance of elements within forest ecosystems. We investigated the effects of fire history on soil and litter stoichiometry in four forest sites in Queensland, Australia. Soil and litter in recently burned areas were compared with those in areas with no recent fire. Effects of burning on concentrations and ratios of multiple pools of carbon (C), nitrogen (N) and phosphorus (P) in soil varied between sites, indicating that site and fire regime characteristics regulate these responses. Labile pools of soil C, N and P were more responsive to burning than total pools, and labile soil C:P and N:P ratios tended to be lower in recently burned areas, consistent with our expectations. These changes suggest that the disparate volatilisation temperatures of these elements influence post-fire soil stoichiometry, and that P cycling may be enhanced in some post-fire environments. Fire-induced changes to litter chemistry were not consistent with soil effects, although litter was generally nutrient-enriched in recently burned areas. Our results reveal the potential for fire to alter elemental balances and thus modify C and nutrient cycling in the plant–soil system.

scholarly journals Growth and Metabolism of Tomato Seedlings Grown with Roots Warm during the Day and Cold at Night, or Vice Versa

HortScience ◽  
1995 ◽  
Vol 30 (4) ◽  
pp. 785C-785
Author(s):  
Yong-Zhan Ma ◽  
Martin P.N. Gent
Keyword(s):  
Plant Size ◽  
Mineral Elements ◽  
Plant Tissues ◽  
Root Temperature ◽  
Relative Growth ◽  
Tomato Seedlings ◽  
Whole Plant ◽  
The Media ◽  
N Enrichment ◽  
Stems And Leaves

Do root temperatures warm during the day and cool during the night benefit plant growth? Tomato (Lycopersicon esculentum Mill.) seedlings were grown at a constant 20C air temperature but with varied root temperature, either 28/12C or 12/28C day/night for 8 days. Eight seedlings were grown in troughs in continuously flowing nutrient solution containing 200 μM \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{14}\mathrm{NO}_{3}^{-}\) \end{document} excess amounts of other mineral elements. The flow rate was 0.6 liters/day per trough on the first day, when plants weighed 20 mg, and increased with plant size. After 8 days, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{15}\mathrm{NO}_{3}^{-}\) \end{document} was provided for 12 h when roots were warm, and eight plants were harvested at the end of labeling or 12 h later. During the treatments, weight per plant increased more in leaves, 3.5 to 44 mg, than roots, 4.3 to 19 mg, and least for stem, 12 to 30 mg. The whole-plant relative growth rate did not differ among treatments, 0.17 to 0.19/day, but was less than for plants grown at a constant 20C root temperature, 0.22/day. Uptake of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{14}\mathrm{NO}_{3}^{-}\) \end{document} from the media and exudation from the stem of decapitated plants were greater when roots were warm than when roots were cold, regardless of light. After labeling for 12 h at the warm root temperature, 15N enrichment in plant tissues was greater with roots warm during the day, 0.20, 0.15, and 0.16, than in those with roots warm during the night, 0.16, 0.11, and 0.10, for roots, stems, and leaves, respectively. Enrichment with roots warm during the day was 22%, 33%, and 62% greater, for roots, stems, and leaves, respectively, than with roots warm during the night. However, uptake of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} at night by roots that were warm during the night was sufficient so that plants grown at out-of-phase root temperature grew as fast as plants grown at in-phase root temperature. Research supported in part by grant 93-37100-9101 from the NRI Competitive Grants Program/USDA.

Use of remnant forest habitat by birds during winter in subtropical Australia: patterns and processes

1997 ◽  
Vol 3 (3) ◽  
pp. 262 ◽  
Author(s):  
Carla P. Catterall ◽  
Mark B. Kingston ◽  
Kate Park
Keyword(s):  
Structural Integrity ◽  
Interference Competition ◽  
Physical Structure ◽  
Native Forest ◽  
Ecological Processes ◽  
Noisy Miner ◽  
Habitat Differences ◽  
Eucalypt Forests ◽  
Remnant Forest ◽  
Subtropical Australia

The south-east Queensland region of subtropical Australia supports a high diversity of landbird species, many of which are migrants which visit lowland areas during winter. However, lowland habitats have been impacted by clearing and fragmentation of native forest types within the past 170 years. This paper considers the implications of loss and fragmentation of lowland eucalypt forests for birds in winter, by comparing the proportionate density of twelve selected species across 49 different cases representing a variety of structural habitat differences. There was little fragmentation effect on forest-dependant winter immigrant species down to about 10 ha. The smallest remnants had reduced proportionate abundances of forest-dependent species together with elevated abundances of two other species: Noisy Miner and Australian Magpie. Similar shifts in species composition occurred in association with a variety of types of change in native eucalypt forest, all involving alteration to physical structure incorporating reduction of foliage cover (at forest edges, in areas without understorey, in regenerating forest, on slopes and ridges, and after fires). We consider the ecological processes that might underlie these patterns, and suggest that: (1) habitat selection, possibly mediated and/or reinforced by interference competition from Noisy Miners, is a key process in the study system in winter; (2) habitat loss, rather than fragmentation, is likely to be the main cause of regional declines in forest-dependent winter migrants; and (3) the management of habitat for winter migrant birds within lowland eucalypt forests of this region should focus on maintaining and improving: (a) the overall percentage of lowland area covered by native forest, and (b) factors associated with the structural integrity (canopy and understorey cover, fire frequency, retention of complete microtopographic gradients) of remnant forest areas irrespective of their size, at least down to about 10 ha.

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