Understorey Legumes Research Articles

Overstorey-understorey interactions reveal trade-offs for achieving competing land-use goals in jarrah forest restored after bauxite mining: Initial prescription and targets affect restoration success over 32 years

Quantitative ‘completion criteria’ agreed between mining companies and regulatory authorities are typically used to assess restoration outcomes. Completion criteria provide the basis for determining whether mining companies have fully met their obligations for site restoration. Relationships among potentially conflicting criteria, particularly around site productivity (e.g., timber production), the return of biodiversity, long-term ecosystem trajectories and other ecosystem services remain poorly understood during the development of mine restoration.For the jarrah forest of southwest Australia, we manipulated site productivity in post bauxite mine restoration by establishing four initial Eucalyptus marginata (jarrah) tree stocking rates in factorial combination with seeding a range of large N2-fixing understorey legume species. We measured jarrah growth rates over the 32-year duration of the experiment, soil-N concentrations at 3 and 32 years-of-age and understorey plant species richness and cover at 15 and 32 years-of-age.Stand basal area over bark (BA) increased with increasing tree stocking rates. However, there was a significant negative effect of increasing stand BA on understorey plant cover and species richness. These negative effects were still significant 32 years after the commencement of the experiment.Seeding large understorey legumes increased total soil-N. However, this did not increase tree growth. Rather, seeding large legumes reduced tree survival and diameter at breast height, and reduced understorey species richness, even though the applied seed mix in the large legume treatment contained 14 more species compared with the control.Our data highlight trade-offs between individual aspects of restoration success, such as tree stocking rates and understorey species richness. Further these results suggest reducing site productivity, by the judicious use of large understorey legumes and establishing low tree stocking rates, may facilitate the return of diverse vegetation communities. Finally, it is important to recognise that when restoration success is viewed through the lens of one-dimensional metrics such as completion criteria, restoration may function as a ‘zero-sum game’ in which a gain for one outcome (e.g., N2-fixation) may result in a loss to one or more other outcomes (e.g., tree growth and species richness).

Plantation understorey legume functional groups enhance soil organic carbon sequestration by promoting species richness

AbstractDespite evidence showing that plant diversity or tree mixtures increase carbon storage in experimental grasslands or mixed forests, the effects of understorey plant communities on changes in soil organic carbon (SOC) storage in planted forests remain unclear, especially for monoculture plantations. Therefore, based on field observations in monoculture plantations on the Loess Plateau in China, we investigated the direct effects of understorey species richness (USR) and plantation age on SOC storage, and identified the indirect effects of understorey legume species richness (ULSR) and soil moisture (SM) mediated by USR. Results indicated that plantation age and USR significantly increased SOC sequestration with almost equal effects. The changes in the relationship between USR and SOC storage varied along the water availability gradient, from significantly positive (in plots with SM ≤11.14%) to insignificant (in plots with SM >11.14%). We observed that ULSR could increase SOC sequestration by promoting USR, while SM had negative and positive effects on ULSR and USR, respectively. Our findings can provide insights into plantation management in semiarid regions: Thinning mature plantations and introducing understorey legumes can increase SOC sequestration and maintain water resource sustainability.

Biological nitrogen fixation by two Acacia species and associated root-nodule bacteria in a suburban Australian forest subjected to prescribed burning

Prescribed burning is a forest management practice which can lead to nitrogen (N)-limited conditions. This study aimed to explore whether biological N2 fixation (BNF) remained the main source of N acquisition for two understorey Acacia species in a Eucalyptus-dominated suburban forest of subtropical Australia, 3 to 6 years after prescribed burning. Root-nodule bacteria associated with these acacias were also characterised to unravel the differences in rhizobial communities between sites and species. Two sites, burned 3 and 6 years before sample collection, were selected within a dry subtropical forest of south-east Queensland, Australia. Leaves were collected from individuals of Acacia disparrima and A. leiocalyx at each site to determine leaf total carbon (C) and N content, C and N isotope composition (δ13C and δ15N) and the percentage of N derived from atmospheric N2. Nodules were harvested from both acacia species at each site to isolate root nodule bacteria. Bacterial isolates were processed for 16S rDNA gene sequencing. Generally, no differences were found in plant physiological variables between the two acacia species. Six years after the fire, both species still depended upon BNF for their N supply, with a higher dependence in winter than in summer. Fire, although of low intensity, was likely to have created a N-limited environment which induced the reliance of legumes on BNF. Root nodule bacteria were dominated by non-rhizobial endophytes, mainly from the Firmicutes phylum. No difference in nodule bacterial diversity was found between sites. The relative abundance of rhizobial genera varied amongst plant species and sites, with a shift in dominance from Bradyrhizobium to Rhizobium species between sites 1 and 2. Our results show that even 6 years after burning, ecosystem remained under N stress and BNF was still the main mechanism for N acquisition by the understorey legumes.

Enduring effects of large legumes and phosphorus fertiliser on jarrah forest restoration 15 years after bauxite mining

Restoring nutrients lost in the mining process and re-establishing nutrient-cycling are often key goals of mine restoration. One common strategy to facilitate these goals is to seed fast-growing legumes combined with one application of P-fertiliser to maximise legume growth and increase soil-N. However, the longer term effects of this strategy have received little attention. Here we report the results of a 15-year-old experiment that was established to test the effects of fertiliser-P application and seeding large understorey legumes, both singly and in combination, on jarrah forest restoration after bauxite mining.Fifteen years after the establishment of this experiment, the majority of the seeded legumes had senesced, with total legume cover having declined significantly compared with results of the same experiment at 5-years-of-age. Yet, despite the legumes having senesced there were still negative effects of both large legumes and P-fertiliser on species richness and abundance of non-leguminous understorey species. These negative effects may be mediated by the persistent effects of legume competition that was evident at 5 years and the accumulation of significant quantities of leaf litter and fine woody debris in the large legume × P-addition treatments. Compared with the 0 kg P ha−1 treatment, application of 20 kg P ha−1 significantly increased jarrah tree growth, but there was no additional benefit of 80 kg P ha−1. These data suggest that moderation of P-fertiliser and large understorey legumes could maximise understorey cover, tree growth and understorey species richness, and therefore simultaneously address multiple key restoration goals.

Genetic compatibility among morphotypes of Vigna lanceolata and implications for breeding improved cultivars

As well as being part of the wider gene pool of cultivated species such as mungbean and cowpea, Vigna lanceolata Benth. is of agronomic interest as a potentially useful species in its own right. It is widely adapted across northern Australia from the coast to inland desert regions, and possesses attributes that make it potentially suited as a ley, cover crop or pasture legume in seasonally arid tropical environments. The species comprises several morphotypes that variously differ in their broad geographic distribution, life cycle, habit, edaphic adaptation and/or amphicarpy. In order to assess the potential for breeding improved cultivars, eight representative accessions were hybridised in a complete diallel cross and the viability and fertility of the resultant hybrid progeny evaluated. Of the 56 parental combinations in the diallel, 33 resulted in healthy F1 hybrid plants, and of these, nine were at least partly self-fertile. Six of these combinations were the reciprocal crosses between three of the perennial, tuberous-rooted, amphicarpic morphotypes. Another two were the reciprocal crosses between the two annual morphotypes. The patterns of relatedness among accessions indicated by the cross-pollination studies were broadly supported by DArT molecular marker analyses, and suggested that there has been some genetic differentiation within the V. lanceolata complex. Although the process of speciation remains far from complete, the levels of genetic compatibility between some morphotypes would be inadequate to enable a breeding program to draw easily on the full range of genetic diversity within V. lanceolata. Two plausible breeding options are suggested. The first is the development of perennial, tuberous-rooted, amphicarpic ideotypes suited perhaps as pasture or understorey legumes, drawing on selected accessions from the three perennial morphotypes, where there was sufficient genetic compatibility and which collectively have wide geographical spread. The second is an annual, freely seeding, fibrous-rooted, amphicarpic ideotype suited perhaps for use as a self-regenerating ley legume, drawing on selected accessions from the two annual morphotypes.

Phosphorus fertilisation and large legume species affect jarrah forest restoration after bauxite mining

Re-establishing nutrient-cycling is often a key goal of mine-site restoration. This goal can be achieved by applying fertilisers (particularly P) in combination with seeding N-fixing legumes. However, the effect of this strategy on other key restoration goals such as the establishment and growth of non-leguminous species has received little attention. We investigated the effects of P-application rates either singly, or in combination with seeding seven large understorey legume species, on jarrah forest restoration after bauxite mining. Five years after P application and seeding, legume species richness, density and cover were higher in the legume-seeded treatment. However, the increased establishment of legumes did not lead to increased soil N. Increasing P-application rates from 0 to 80kgPha−1 did not affect legume species richness, but significantly reduced legume density and increased legume cover: cover was maximal (∼50%) where 80kgPha−1 had been applied with large legume seeds. Increasing P-application had no effect on species richness of non-legume species, but increased the density of weeds and native ephemerals. Cover of non-legume species decreased with increasing P-application rates and was lower in plots where large legumes had been seeded compared with non-seeded plots. There was a significant legume×P interaction on weed and ephemeral density: at 80kgPha−1 the decline in density of these groups was greatest where legumes were seeded. In addition, the decline in cover for non-legume species with increasing P was greatest when legumes were seeded. Applying 20kgPha−1 significantly increased tree growth compared with tree growth in unfertilised plots, but growth was not increased further at 80kgha−1 and tree growth was not affected by seeding large legumes. Taken together, these data indicate that 80kgha−1 P-fertiliser in combination with (seeding) large legumes maximised vegetation cover at five years but could be suboptimal for re-establishing a jarrah forest community that, like unmined forest, contains a diverse community of slow-growing re-sprouter species. The species richness and cover of non-legume understorey species, especially the resprouters, was highest in plots that received either 0 or 20kgha−1 P and where large legumes had not been seeded. Therefore, our findings suggest that moderation of P-fertiliser and legumes could be the best strategy to fulfil the multiple restoration goals of establishing vegetation cover, while at the same time maximising tree growth and species richness of restored forest.

Ecophysiological and foliar nitrogen concentration responses of understorey Acacia spp. and Eucalyptus sp. to prescribed burning.

Eucalyptus spp. is a dominant tree genus in Australia and most Eucalyptus spp. are canopy dominant species. In Australian natural forests, Eucalyptus spp. commonly are associated with understorey legumes which play a crucial role for ecological restoration owing to their nitrogen (N) fixing ability for replenishing the soil N lost after frequent prescribed burning. This study aimed to explore to what extent physiological responses of these species differ 7 and 12years after last fire. Two most common understorey Acacia spp., Acacia leiocalyx and A. disparrima, as well as one non-leguminous Eucalyptus resinifera, were studied due to their dominance in the forest. Both A. leiocalyx and A. disparrima showed higher carbon (C) assimilation capacity, maximum photosynthetic capacity, and moderate foliar C/N ratio compared with E. resinifera. A. leiocalyx showed various advantages compared to A. disparrima such as higher photosynthetic capacity, adaptation to wider light range and higher foliar total N (TNmass). A. leiocalyx also relied on N2-fixing ability for longer time compared to A. disparrima. The results suggested that the two Acacia spp. were more beneficial to C and N cycles for the post burning ecosystem than the non-N2-fixing species E. resinifera. A. leiocalyx had greater contribution to complementing soil N cycle long after burning compared to A. disparrima.

Appraisal of 15N enrichment and 15N natural abundance methods for estimating N2 fixation by understorey Acacia leiocalyx and A. disparimma in a native forest of subtropical Australia

Purpose It is anticipated that global climate change will increase the frequency of wildfires in native forests of eastern Australia. Understorey legumes such as Acacia species play an important role in maintaining ecosystem nitrogen (N) balance through biological N fixation (BNF). This is particularly important in Australian native forests with soils of low nutrient status and frequent disturbance of the nutrient cycles by fires. This study aimed to examine 15N enrichment and 15N natural abundance techniques in terms of their utilisation for evaluation of N2 fixation of understorey acacias and determine the relationship between species ecophysiological traits and N2 fixation.

Impact of global climate change and fire on the occurrence and function of understorey legumes in forest ecosystems

IntroductionThe objective of this review was to provide a better understanding of how global climate change and fire influence the occurrence of understorey legumes and thereby biological nitrogen (N) fixation rates in forest ecosystems. Legumes are interesting models since they represent an interface between the soil, plant, and microbial compartments, and are directly linked to nutrient cycles through their ability to fix N. As such, they are likely to be affected by environmental changes.Result and discussionBiological N fixation has been shown to increase under enriched CO2 conditions, but is constrained by the availability of phosphorus and water. Climate change can also influence the species composition of legumes and their symbionts through warming, altered rainfall patterns, or changes in soil physicochemistry, which could modify the effectiveness of the symbiosis. Additionally, global climate change may increase the occurrence and intensity of forest wildfires thereby further influencing the distribution of legumes. The establishment of leguminous species is generally favored by fire, as is N2 fixation. This fixed N could therefore replenish the N lost through volatilization during the fire. However, fire may also generate shifts in the associated microbial community which could affect the outcome of the symbiosis.ConclusionUnderstorey legumes are important functional species, and even when they cannot reasonably be expected to reestablish the nutrient balance in forest soils, they may be used as indicators to monitor nutrient fluxes and the response of forest ecosystems to changing environmental conditions. This would be helpful to accurately model ecosystem N budgets, and since N is often a limiting factor to plant growth and a major constraint on C storage in ecosystems, would allow us to assess more precisely the potential of these forests for C sequestration.

Innovative maize-legume intercropping results in above-and below-ground competitive advantages for understorey legumes

Innovative maize-legume intercropping results in above-and below-ground competitive advantages for understorey legumes

Radiation Capture and Use as Affected by Morphologically Contrasting Maize/Pea in Sole and Intercropping

Field experiments were conducted at the Field Unit of the School of Plant Sciences in Reading, UK, during the 2000 and 2001 growing seasons to compare the radiation capture and use efficiency of morphologically and physiologically contrasting maize/pea intercrops with sole crops. The maize cultivars comprised Nancis with erect and Sophy with floppy leaves whilst the peas consisted of Maro, a conventional leaved, and Princess, a semi-leafless cultivar. Radiation capture by the sole and intercrops was measured using a Sunflek Ceptometer (Delta T Devices), with a sensor length of 80 cm. Measurements were taken at four equidistant positions in each plot, 1 m away from the edges of the plot. Before the maize grew above the peas, measurements were taken at the top of the canopy and below. When the canopies were distinct, three measurements were taken, above the canopy, above peas and below the canopy from 9.30 a.m. to 1.00 p.m. at weekly intervals. In both seasons the intercrops and sole pea crops intercepted more radiation compared to the sole maize crops. Towards the end of the season the intercrops and sole maize had similar interception. Intercropping both maize cultivars in 2000 with the conventional pea had the greatest interception in 2001. Radiation use efficiency (RUE) was measured by taking the respective changes in above ground dry weight and dividing by the respective changes in cumulative absorbed photosynthetic active radiation (PAR). The RUE were highest at mid-season for both intercrops and sole crops in both seasons. Comparisons were also made using cumulative radiation use efficiencies (CRUE), representing the RUE from emergence to any time. Sole pea had the lowest CRUE in both seasons. The sole maize in 2000 had highest CRUE. However, in 2001 intercrops had similar CRUE to sole maize, suggesting an increase in RUE of peas in intercrops. Nancis had consistently higher CRUE in both seasons compared to Sophy. The results emphasize that radiation capture and use efficiency in sole and intercrops are greatly affected by morphological characteristics of the component crops. In choosing cropping partners for intercropping special attention should be given to selecting cereal crops with erect leaves as against those with droopy leaves. The under-storey legume crop should also have erect or semi erect leaves so as to capture radiation filtering through the cereal canopy in order to maximize the capture and use of photosynthetically active radiation for increased and stable yields.West African Journal of Applied Ecology Vol. 13 2008: pp. 55-66

Tansley Review No. 95: 15N natural abundance in soil–plant systems

The following citations were erroneously omitted from the ‘References’: Groffman PM, Zak DR, Christensen S, Mosier A, Tiedje JM. 1993. Early spring nitrogen dynamics in a temperate forest landscape. Ecology74: 1579–1585. Handley LL, Brendel O, Scrimgeour CM, Schmidt S, Raven JA, Turnbull MH, Stewart GR. 1996. The 15N natural abundance patterns of field‐collected fungi from three kinds of ecosystems. Rapid Communications in Mass Spectrometry10: 974–978. Handley LL, Daft MJ, Wilson J, Scrimgeour CM, Ingleby K, Sattar, MA. 1993. Effects of the ecto‐ and VA‐mycorrhizal fungi Hydnagium carneum and Glomus clarum on the δ15N and δ13C values of Eucalyptus globulus and Ricinus communis. Plant, Cell and Environment16: 375–382. Handley LL, Odee D, Scrimgeour CM. 1994.δ15N and δ13C patterns in savanna vegetation: dependence on water availability and disturbance. Functional Ecology8: 306–314. Handley LL, Raven JH. 1992. The use of natural abundance of nitrogen isotopes in plant physiology and ecology: commissioned review. Plant, Cell and Environment15: 965–985. Handley LL, Scrimgeour CM. 1997. Terrestrial plant ecology and 15N natural abundance: the present limits to interpretation for uncultivated systems with original data from a Scottish old field. Advances in Ecological Research27: 133–212. Hansen AP, Pate JS. 1987. Evaluation of the 15N natural abundance method and xylem sap analysis for assessing N2 fixation of understorey legumes in jarrah (Eucalyptus marginata Donn ex Sm.) forest in S.W. Australia. Journal of Experimental Botany38: 1446–1458. New Phytologist apologizes unreservedly to all authors of the above papers for this error.

Field estimation of N 2 fixation by Acacia spp. using 15N isotope dilution and labelling with 35S

Biological N 2 fixation by understorey legumes Acacia melanoxylon and Acacia mucronata in a mixed eucalypt forest was estimated by both natural 15N abundance and 15N-enriched isotope dilution methods over a period of 27 months following a prescribed fire. A native grass, Poa sieberiana, and opportunistic non-fixing species were used as reference plants. The natural 15N abundance, method was considered to provide accurate estimates of N 2 fixation because of uniformity in natural 15N enrichment and high δ 15N values in soil and reference plants. Estimates of N 2 abundance method. Estimates of N 2 fixed by A. melanoxylon and A. mucronata increased from 2.0 and 1.4 mg per plant after 1 year to 26 mg per plant and 57 mg per plant after 27 months, respectively. Accretion of N to the forest ecosystem from N 2 fixation by these Acacia species was low (5 and 116 g ha −1 after 27 months) due to low plant densities following prescribed fire. Labelled S ( 35S) was applied to the plots at sowing with labelled N (N/S=10/1). Legumes accumulated significantly less dry matter and total S compared with the reference plants, although total N uptake was similar. Reference plants accumulated more labelled S and generally more labelled N than the legumes, and ratios of labelled to unlabelled S for all species were higher than ratios of labelled to unlabelled N derived from soil sources. Equal ratios of labelled to unlabelled S between legumes and reference plants did not correspond with equal ratios of soil-derived labelled to unlabelled N. These results therefore cast doubt on the validity of the concept of labelling with 35S to assess the accuracy of reference plants to estimate the isotopic composition of soil-derived legume N.

Nodule Production and Nitrogen Fixation (Acetylene Reduction) by an Understorey Legume (Bossiaea Laidlawiana) in Eucalyptus Forest

Nodule production and rates of acetylene reduction by the understorey legume Bossiaea laidlawiana were estimated in Eucalyptus diversicolor (karri) forest stands in south-western Australia in relation to plant age, time of day and season, and phosphorus supply. Highest numbers and masses of nodules, and highest rates of acetylene reduction were observed in the spring and early summer months when soil temperature was rising and soil moisture was adequate for functioning of fine roots (...)

Twig and foliar nutrient concentrations in relation to nitrogen and phosphorus supply in a eucalypt (Eucalyptus diversicolor F. Muell.) and an understorey legume (Bossiaea laidlawiana Tovey and Morris)

The sensitivity of tissue nutrient concentrations to changes in plant age and the supply of P and N was compared between leaves and associated twigs in two forest species. In a young regrowth stand, tissues were sampled on three occasions from the mid-crown position of karri (Eucalyptus diversicolor F. Muell.) and Bossiaea laidlawiana Tovey and Morris, a major understorey legume. Leaves and twigs were also sampled from young plants of B. laidlawiana growing in a mature eucalypt stand to which P treatments had been applied.

Potential inputs of nitrogen by seeder legumes to the jarrah forest ecosystem

Summary With an increase in density of seed-regenerated legumes on the jarrah forest floor, induced by an appropriate burning treatment, combined with moderate thinning of the forest to increase available soil moisture, it was estimated that the symbiotic activity of understorey legume species could account for up to 10 kg of fixed nitrogen per hectare per year over a 6 year growth period. Acacia pulchella was the most active legume in the ability to capture atmospheric nitrogen. The contributions of nitrogen from Acacia alata, A. extensa and Bossiaea aquifolium under possible ameliorated field conditions, were estimated to be less than half that of A. pulchella but still a significant input to the ecosystem. The additional nitrogen fixed by understorey stands of seeder legumes, promoted by appropriate burning and thinning treatments, could be sufficient to increase the growth of jarrah by 10 to 25 per cent.

Acetylene reduction byDaviesia mimosoides under Eucalyptus

Daviesia mimosoides is a common understorey legume in Eucalyptus forests of the Brindabella Range in southeastern Australia, capable of fixing atmospheric nitrogen. Rates of N fixation were measured by the acetylene-reduction technique over a growing season in the field. Pot trials under controlled conditions were also carried out to elucidate effects of soil moisture, temperature, and light.