Diversity Of Legumes Research Articles

Diversidade de Leguminosae em uma área de savana do estado de Roraima, Brasil

Leguminosae é considerada a família mais diversa nas savanas de Roraima, que são as maiores áreas de savana da Amazônia brasileira. Este trabalho tem como objetivos fornecer uma listagem florística e analisar os padrões de distribuição geográfica dos táxons de Leguminosae encontrados em uma área de savana em Boa Vista, Roraima (02º52´07´´N; 60º43´03´´W). Foram registrados 80 táxons distribuídos em 38 gêneros. Seis táxons são novos registros para a flora de Roraima. Os gêneros que apresentaram o maior número de espécies foram Aeschynomene e Chamaecrista, cada um com sete espécies. Leguminosae-Papilionoideae foi a subfamília mais diversa em número de gêneros (24) e de táxons infragenéricos (53). A análise da distribuição geográfica revelou a predominância de táxons com padrão neotropical. A área estudada representa um sítio diverso em táxons de Leguminosae, pois concentra cerca de 87% da diversidade citada para a família nas savanas de Roraima.

Legume–grass species influence plant productivity and soil nitrogen during grassland succession in the eastern Tibet Plateau

In recent years, numerous studies have evaluated the effect of plant function diversity on ecosystem functions such as productivity and soil nutrient status. We performed a redundancy analysis (RDA) to examine the relationship between plant functional diversity, productivity and soil nitrogen in a chronosequence of abandoned fields in sub-alpine meadow in the eastern part of the Tibet Plateau, China. We found that along the secondary succession sequence, legume richness and aboveground biomass significantly increased and both were positively correlated with total species richness (S) and aboveground biomass (T-bio). This pattern suggests that legume richness increases community productivity. In addition, we found that total aboveground biomass, legume and grass richness were positively correlated with soil microbial nitrogen (MBN), the ratio of microbial nitrogen to soil total nitrogen (MBN/TN) and the ratio of soil organic carbon and soil total nitrogen (C/N), whereas they were negatively correlated with soil total nitrogen (TN), organic carbon (C org), and microbial carbon (MBC). Contrary to our predictions grasses such as Stipa grandis, Scirpus tripueter, Koeleria cristata were more closely associated with MBN, MBN/TN than legumes such as Oxytropis ochrocephala, Thermopsis lanceolate and Astragalus polycladus. The late-successional grass Kobresio humilis had a stronger positive correlation with NH 4-N as compared to the legumes and NO 3-N was not associated with any legume species. This suggests that the grasses and legumes have a synergetic positive influence on the ecosystem properties, especially nitrogen. Therefore, in this N-limited, plant community diversity of both legumes and grasses has a strong influence on ecosystem changes during succession.

The Impact of Ecology and Biogeography on Legume Diversity, Endemism, and Phylogeny in the Caribbean Region: A New Direction in Historical Biogeography

The legume family is so well represented in the Caribbean that if a preserve was needed somewhere on earth to harbor all of the primary lineages in this family, the flora of just Cuba would suffice. Molecular phylogenetic, biogeographic, and evolutionary rates analysis all suggest that legume diversity and endemism in the Caribbean are mostly of recent origin and are likely a function of the abundance of seasonally dry tropical forests (SDTFs) throughout the neotropics. Legumes have a strong ecological affinity for SDTFs, and the Caribbean basin is well covered by this forest type. Rate-variable molecular clock analysis suggests that the majority of worldwide island lineages of legumes have ages of much less than 30 Ma. Singular historical events invoking land bridges or mobile continental plates are thus not needed to explain Caribbean legume diversity and endemism. The Greater Antilles are large islands located close to the American continent. They are therefore expected to fairly represent the diverse continental lineages of legumes. Yet, they are distant enough to be dispersal limited. As such, island lineages can speciate and diversify over evolutionary time unimpeded by high rates of immigration from the mainland. Vicariance and other standard phylogenetic methods of historical biogeography are likely to be replaced by those of ecological and island biogeography. This is because model selection approaches derived from the neutral concept of isolation by distance will be able to quantify patterns of alpha and beta diversity and detect niche assembly and phylogenetic niche conservatism within and among metacommunities that are hypothesized to constrain phylogeny.

Visitor diversity and pollinator specialization in Mediterranean legumes

We describe the spectrum of visitors of seven Mediterranean legumes and identify the potential pollinators by observing insects’ behavior on flowers. The diversity of each population's insect assemblage (flower visitors and potential pollinators) is calculated in order to estimate to which degree pollination systems are specialized. The importance value (PI) for main taxa of potential pollinators is computed considering both insect fidelity and relative abundance. Different values of importance and dominance characterize pollinator assemblages, revealing various degrees of plant–pollinator specificity despite common papilionaceous floral traits. Visitors’ and pollinators’ diversity was negatively correlated with fruiting success, while there was a positive relation between maximum pollinator importance value and fruit set, suggesting the tendency towards a positive relationship between pollinator specificity and reproductive success.

Evaluation of perennial pasture legumes and herbs to identify species with high herbage production and persistence in mixed farming zones in southern Australia

Ninety-one perennial legumes and herbs (entries) from 47 species in 21 genera were evaluated at sites in New South Wales, South Australia and Western Australia over 3 years from 2002 to 2005 to identify plants with superior herbage production, persistence and the potential to reduce ground water recharge. Evaluation was undertaken in three nurseries (general, waterlogged soil and acid soil). Medicago sativa L. subsp. sativa (lucerne) cv. Sceptre was the best performing species across all sites. In the general and acid soil nurseries, Cichorium intybus L. (chicory) cv. Grasslands Puna was the only species comparable with Sceptre lucerne in terms of persistence and herbage production. Trifolium fragiferum L. cv. Palestine and Lotus corniculatus L. SA833 were the best performing species on heavy clay soils prone to waterlogging. Three Dorycnium hirsutum (L.) Ser. accessions persisted well on acid soils, but were slow to establish. Short-lived perennial forage legumes, such as Onobrychis viciifolia Scop. cv. Othello, and three Hedysarum coronarium L. entries, including cv. Grasslands Aokou, had high herbage production in the first 2 years and may be suitable for short-term pastures in phased pasture-crop farming systems. T. uniflorum L. and M. sativa subsp. caerulea SA38052 were highly persistent and could play a role as companion species in mixtures or ground cover species for undulating landscapes. Cullen australasicum (Schltdl.) G.W. Grimes SA4966 and Lotononis bainesii Baker cv. Miles had poor establishment, but were persistent. Chicory, T. fragiferum and L. corniculatus were identified as species, other than lucerne, with the most immediate potential for further selection to increase the diversity of perennial legumes and herbs adapted to southern Australian environments.

The genetic diversity of rhizobia associated withDalea purpureaVent. in fragmented grasslands of west-central Minnesota

The increase in human population and the spread of agriculture over the past 150 years have transformed the landscape in west-central Minnesota into a mosaic of agricultural fields and urban land, leaving only remnants of the once dominant prairie ecosystem. Limited natural habitat in this fragmented landscape threatens the diversity and abundance of native legumes and could impact the size and function of associated belowground microbial populations. In this study, BOXA1R PCR and 16S rRNA gene sequence analyses were used to assess the genetic diversity of rhizobia associated with Dalea purpurea (Vent.) in nine prairie remnants ranging in size from 0.04 to 3.5 ha. The variation in soil properties was also determined. While 53 different genotypes of rhizobia were identified, four of these accounted for 84% of the 1029 rhizobia characterized using BOXA1R PCR. Representatives from three of the four dominant genotypes had a 16S rRNA gene sequence similar to that of Rhizobium gallicum, with two of these genotypes recovered at all sites. The fourth genotype was similar to that of Rhizobium etli and occurred with frequency at only two sites. Rhizobium genotype richness and site area were positively correlated. The implications of these results are discussed.

Legume flowers bear fruit

After the grasses, the legume family (which includes peas, beans, and soya) is the plant group of greatest importance to mankind. The legume family is a source of products and services from tropical timber to atmospheric nitrogen fixation. As the botanist E. J. H. Corner (1) put it, “From arctic circle to tropics, desert to pergola, bacteria to plough, field to mouth, and legend to science, Leguminosae invest our lives.” The family is huge, with ≈20,000 species. Legume diversity is so great (and much of it hidden away in relatively unexplored tropical rain forest) that it has been difficult to gain an overview. Recently, a landmark study has covered the whole family (2). The result, a bird's-eye view of the legumes, is a chronicle of how the legumes have played out 60 million years of dazzling “evolutionary jazz,” riffing and improvising on the basic themes provided by the characteristic leguminous leaf, flower, and fruit. Despite the family's vastness, it is not (by angiosperm standards) particularly old. Current estimates suggest that the family underwent a diversity explosion ≈50–60 million years ago, during which most of the major legume clades arose (3, 4). One of the reasons for the early and continued diversification of legumes may be coevolution with pollinating bees (Hymenoptera, superfamily Apoidea), which are by far the most common pollinators of the legumes and appear to be extremely effective at the job. Bees recognize complex shapes readily, and so the pronounced bilateral symmetry (zygomorphy) of many legume flowers, which leads to complex flower outlines and intricate floral mechanisms, may promote exclusive flower visitation of some species by specific pollinators (5). The important study by Feng et al. (6), in this issue of PNAS, now elucidates the molecular architecture underlying the development of zygomorphy in legume flowers and so provides an important tool for understanding the diversification of the family.

Evolutionary genetics and biogeographic structure of Rhizobium gallicum sensu lato, a widely distributed bacterial symbiont of diverse legumes

We used phylogenetic and population genetics approaches to evaluate the importance of the evolutionary forces on shaping the genetic structure of Rhizobium gallicum and related species. We analysed 54 strains from several populations distributed in the Northern Hemisphere, using nucleotide sequences of three 'core' chromosomal genes (rrs, glnII and atpD) and two 'auxiliary' symbiotic genes (nifH and nodB) to elucidate the biogeographic history of the species and symbiotic ecotypes (biovarieties) within species. The analyses revealed that strains classified as Rhizobium mongolense and Rhizobium yanglingense belong to the chromosomal evolutionary lineage of R. gallicum and harbour symbiotic genes corresponding to a new biovar; we propose their reclassification as R. gallicum bv. orientale. The comparison of the chromosomal and symbiotic genes revealed evidence of lateral transfer of symbiotic information within and across species. Genetic differentiation analyses based on the chromosomal protein-coding genes revealed a biogeographic pattern with three main populations, whereas the 16S rDNA sequences did not resolve that biogeographic pattern. Both the phylogenetic and population genetic analyses showed evidence of recombination at the rrs locus. We discuss our results in the light of the contrasting views of bacterial species expressed by microbial taxonomist and evolutionary biologists.

Leguminosas del norte del estado de Nuevo León, México

Se estudió la diversidad de especies de leguminosas en el norte del estado de Nuevo León, contabilizando 98 taxa en total. Se registraron 38 géneros, 94 especies y 26 taxa infraespecíficos de este grupo de plantas; la familia Fabaceae comprende 18 géneros y 42 especies, Mimosaceae 10 y 30 y Caesalpiniaceae 10 y 22 respectivamente. Los géneros con mayor número de especies son Acacia (12), Dalea (10), Mimosa (6), Senna (5);Caesalpinia(4) y Bauhinia (4). Del total de 98 taxa, las leguminosas arbustivas y herbáceas son las más abundantes en la zona, representando 47% (46 especies) y 46% (45 especies) respectivamente, las arbóreas representan 7% (7). La mayor cantidad de taxa se registró en el matorral subinerme (52), matorral submontano (48) y bosque de encino-pino (44), mientras que los mezquitales albergan el menor número de especies (23).

Bradyrhizobium canariense sp. nov., an acid-tolerant endosymbiont that nodulates endemic genistoid legumes (Papilionoideae: Genisteae) from the Canary Islands, along with Bradyrhizobium japonicum bv. genistearum, Bradyrhizobium genospecies alpha and Bradyrhizobium genospecies beta

Highly diverse Bradyrhizobium strains nodulate genistoid legumes (brooms) in the Canary Islands, Morocco, Spain and the Americas. Phylogenetic analyses of ITS, atpD, glnII and recA sequences revealed that these isolates represent at least four distinct evolutionary lineages within the genus, namely Bradyrhizobium japonicum and three unnamed genospecies. DNA-DNA hybridization experiments confirmed that one of the latter represents a new taxonomic species for which the name Bradyrhizobium canariense is proposed. B. canariense populations experience homologous recombination at housekeeping loci, but are sexually isolated from sympatric B. japonicum bv. genistearum strains in soils of the Canary Islands. B. canariense strains are highly acid-tolerant, nodulate diverse legumes in the tribes Genisteae and Loteae, but not Glycine species, whereas acid-sensitive B. japonicum soybean isolates such as USDA 6(T) and USDA 110 do not nodulate genistoid legumes. Based on host-range experiments and phylogenetic analyses of symbiotic nifH and nodC sequences, the biovarieties genistearum and glycinearum for the genistoid legume and soybean isolates, respectively, were proposed. B. canariense bv. genistearum strains display an overlapped host range with B. japonicum bv. genistearum isolates, both sharing monophyletic nifH and nodC alleles, possibly due to the lateral transfer of a conjugative chromosomal symbiotic island across species. B. canariense is the sister species of B. japonicum, as inferred from a maximum-likelihood Bradyrhizobium species phylogeny estimated from congruent glnII+recA sequence partitions, which resolves eight species clades. In addition to the currently described species, this phylogeny uncovered the novel Bradyrhizobium genospecies alpha and beta and the photosynthetic strains as independent evolutionary lineages. The type strain for B. canariense is BTA-1(T) (=ATCC BAA-1002(T)=LMG 22265(T)=CFNE 1008(T)).

Counting Species: Making Choices

Imagine that you are charged with going into an ecosystem and assessing its biodiversity. But there's a catch you can only study one plant family. Which should you choose? The legumes, say researchers at the Royal Botanical Gardens in Kew, London. A preliminary assessment of plant diversity and distribution, put together by Kew graduate student Neil Brummitt, suggests that legume diversity most closely mirrors total plant diver? sity. Legumes occur in many dif? ferent habitats in significant numbers, says Kew's science coordinator, plant taxonomist Eimear Nic Lughadha. If you are allowed to count two families, however, grasses and orchids give the best result. They're a comple? mentary pair, explains Lughadha. Orchids are diverse in tropical forests, grasses in open areas. Conservation biologists need such shortcuts. The strategic plan for the Convention on Biological Diversity (CBD) contains a commitment to substantially reduce the rate of biodiversity loss by 2010. Yet for most ecosystems we do not even know what is there, let alone what is being lost and how fast. Monitoring a few represe tative groups such as legumes m ght reveal general trends. To gauge whether the rate of bio? diversi y loss is changing requires data from at least three points in time: the first two to describe the

Structure and diversity among rhizobial strains, populations and communities–a review

Published studies of rhizobial populations, communities and other strain collections were analysed to identify trends in strain richness, strain dominance and genetic diversity within and between locations. For individual populations and communities, strain richness indices were calculated by dividing the number of strain types identified by the number of isolates recovered. Where possible, strain dominance (the proportion of rhizobial isolates represented by each strain type) was also calculated. Analysis of the genetic diversity of populations, communities and rhizobial strain collections originating from diverse legume hosts and locations, was confined to studies using multilocus enzyme electrophoresis (MLEE) so that diversity could be compared on the basis of published H values. Strain richness indices were highly variable (0.02–0.94) and were influenced by both the discriminatory power of the strain typing method and the type and number of legume species used to recover rhizobia from soil. The strain richness of populations recovered either directly from soil, or from the nodules of trap hosts inoculated with the same soil, was similar. Because the arithmetic relationship between the number of strain types and number of isolates varies between different populations and communities, strain richness curves are proposed as the most appropriate method for reporting rhizobial structural diversity. Comparison of over 50 rhizobial populations and communities from published studies showed that strain dominance patterns in nodules were often similar. Typically, a single strain type occupies more than 30% of nodules with the majority of strain types being recovered at low frequency (∼75% of published populations and communities). Rhizobial populations and communities characterised by MLEE varied in their genetic diversity, with H values ranging from 0.06 to 0.78. In several studies, most of the genetic diversity within a site could be recovered from the nodules of a single plant. When hierarchical analyses were performed on populations within and between sites, the genetic diversity within sites was similar to the genetic diversity between sites. Similarly, the genetic diversity of strain collections originating from multiple hosts and locations was no more diverse than some individual populations and communities. Strain richness and genetic diversity measures were not always correlated for rhizobial populations. Populations with low strain richness were sometimes genetically diverse, and the relationship between the diversity measures varied for different legume species at the same location. We suggest that both strain richness and genetic diversity measures are required to fully describe rhizobial population and community diversity.

RRNA and nifD phylogeny of Bradyrhizobium from sites across the Pacific Basin

Many undomesticated legumes harbor nodule bacteria related to the soybean symbiont Bradyrhizobium elkanii, but little is known about their phylogenetic relationships or geographic distribution. Sequences of ribosomal genes (16S rRNA and partial 23S rRNA) and the nitrogenase α-subunit gene ( nifD) were analyzed in 22 isolates of this group sampled from diverse legumes in Korea, Japan, the USA, Mexico, Costa Rica and Panama. Some strains from Asia and North America shared identical sequences for both ribosomal genes. However, pairs of strains with closely related nifD sequences were almost never found in different regions. The major exceptions involved North American isolates B. elkanii USDA 76 and USDA 94, which had nifD sequences highly similar to certain Korean strains. However, 16S rRNA sequences of USDA 76 and USDA 94 were closely related to Central American rather than Asian bradyrhizobia, implying that these strains are genetic mosaics combining sequences from distinct ancestral areas. Several other conflicts between rRNA and nifD tree topologies indicated that the genealogical histories of these loci have been influenced by recurrent lateral gene transfer events.

Simulation of growth and development of diverse legume species in APSIM

This paper describes the physiological basis and validation of a generic legume model as it applies to 4 species: chickpea (Cicer arietinum L.), mungbean (Vigna radiata (L.) Wilczek), peanut (Arachis hypogaeaL.), and lucerne (Medicago sativa L.). For each species, the key physiological parameters were derived from the literature and our own experimentation. The model was tested on an independent set of experiments, predominantly from the tropics and subtropics of Australia, varying in cultivar, sowing date, water regime (irrigated or dryland), row spacing, and plant population density. The model is an attempt to simulate crop growth and development with satisfactory comprehensiveness, without the necessity of defining a large number of parameters. A generic approach was adopted in recognition of the common underlying physiology and simulation approaches for many legume species. Simulation of grain yield explained 77, 81, and 70% of the variance (RMSD = 31, 98, and 46 g/m2) for mungbean (n = 40, observed mean = 123 g/m2), peanut (n = 30, 421 g/m2), and chickpea (n = 31, 196 g/m2), respectively. Biomass at maturity was simulated less accurately, explaining 64, 76, and 71% of the variance (RMSD = 134, 236, and 125 g/m2) for mungbean, peanut, and chickpea, respectively. RMSD for biomass in lucerne (n = 24) was 85 g/m2 with an R2 of 0.55. Simulation accuracy is similar to that achieved by single-crop models and suggests that the generic approach offers promise for simulating diverse legume species without loss of accuracy or physiological rigour.

Identifying Tertiary Radiations of Fabaceae in the Greater Antilles: Alternatives to Cladistic Vicariance Analysis

The fossil record shows that the legume family was abundant and taxonomically diverse in Early Tertiary tropical deciduous forests of North America. Today, woody members of this family are almost nonexistent in temperate deciduous forests. This former North American legume diversity now lies in the Tropics, including the Greater Antilles. To show the Antillean refugia, we detail a phylogenetic and biogeographic analysis of two legume groups, the Ormocarpum and Robinia clades, which have either a Tertiary fossil record in North America or a sister clade with such a fossil record. A combined analysis of molecular and nonmolecular data is used for the cladistic vicariance approaches, while an exhaustively sampled data set of nrDNA ITS/5.8S sequences is used for the molecular biogeographic analysis. Results from component, three‐area‐statements, and Brooks parsimony analysis are equivocal in suggesting an influence of Tertiary history on the distribution of the woody genera Pictetia (Ormocarpum clade) and Poitea (Robinia clade), two of the most speciose endemic legume radiations in the Greater Antilles. Alternatively, nucleotide diversity, evolutionary rates, and coalescent analyses of molecular phylogenies all suggest a Tertiary diversification of Pictetia and Poitea. The results are corroborated by a regression analysis that implicates both age of island biota and island area in accurately predicting numbers of endemic legume taxa. These findings, combined with the legume fossil record, suggest that both Pictetia and Poitea stem from Tertiary North American boreotropical groups. J. A. Wolfe’s hypothesis that the Greater Antilles harbor boreotropical relicts is supported.

Identification of high-affinity binding sites for the hepta-beta-glucoside elicitor in membranes of the model legumes Medicago truncatula and Lotus japonicus.

Previous studies have led to the identification and characterization of specific, high-affinity binding sites for a hepta-beta-glucoside elicitor in soybean. A survey of plant species for elicitor-binding activity reveals that among the plants tested, the hepta-beta-glucoside elicitor is only recognized by plants belonging to the legume family. We have characterized in detail the glucan elicitor-binding site in the model legume Medicago truncatula Gaertn., and partially characterized the site in Lotus japonicus. These sites have characteristics that are very similar to the one in soybean, with dissociation constants of 4.7 and 8.9 nM respectively. The elicitor-binding sites from both plants are stable during solubilization with non-ionic alkylglycoside detergents. However, differences are observed in the abundance of the binding sites and their selectivity towards structurally related analogues of the hepta-beta-glucoside elicitor. Our results suggest that similar, but perhaps not identical, binding sites for the hepta-beta-glucoside elicitor exist in diverse legumes, but not in plants outside of the legume family.

Soil dwelling macro-invertebrates in intensively grazed dairy pastures in Pennsylvania, New York and Vermont

This study estimates the relative contributions of environment and farm management strategies in influencing soil faunal assemblages and attempts to identify the species with potential to affect sustainability of intensive grazing management systems in the north-eastern USA. It arises because of the change from confinement feeding of dairy cattle, consequent upon concerns about negative environmental effects, the rising costs for machinery and housing, and reduced profit margins, together with the absence of data from which the consequences of such change on the soil fauna may be predicted. Macro-invertebrates were sampled in soil from seventy-eight grazed pastures on twenty-one dairy farms in Pennsylvania, USA, in the spring of 1994. On five of these farms, macro-invertebrates were sampled (four pastures per farm) in the spring, summer and autumn seasons of 1994, 1995 and 1996. In 1997, macro-invertebrates were sampled in soil during spring, summer and autumn from (four pastures per farm) on three farms in New York, and during spring and summer on three farms in Vermont. Species richness ranged from two to twelve species (mean 6·4) per pasture site in Pennsylvania and five to eighteen species (mean 10·7) in New York and Vermont. The communities were dominated at most sites by earthworms. Earthworms were correlated with soil basal and substrate-induced respiration/carbon ratio, and soil moisture, but were negatively correlated with cows per hectare and herbage biomass in Pennsylvania. Sitona larvae were recorded at nineteen of the twenty-one farms during the spring of 1994 across Pennsylvania and occurred at populations >5 m−2 in 68% of the sampled pastures. Sitona larvae were less abundant in New York and Vermont. Elaterid larvae comprised a complex of seven species of which Aeolus melillus (Say) and Melanotus communis (Gyllenhal) comprised 35% and 39%, respectively, of the elaterids collected in Pennsylvania. Agriotes mancus (Say) and Ctenicera destructor (Brown) comprised 41% and 26%, respectively, of four species collected in New York and Vermont. Scarabaeid larvae, comprising a complex of eight species, were detected at only 27% of the seventy-eight pastures sampled in spring 1994 in Pennsylvania. Five species were collected in ten of the twelve New York pastures and four species in nine of the twelve Vermont pastures. Populations of scarabaeid larvae averaged <25 m−2 in all three states, except in three Pennsylvania pastures in spring 1994. Detrended canonical correspondence analysis (DCCA) showed pasture standing biomass, legume diversity, pre-winter stubble height, white clover pasture content, and soil phosphorus levels influenced numbers of invertebrate species more than climatic factors, such as temperature, rainfall, altitude, latitude and seasonal water table. DCCA also showed most pastures to be close to the average of environmental factors. The extremely low density of herbivorous macro-invertebrates in soil and the absence of pest outbreaks may indicate a stable soil ecosystem.

Nitrogen fixation in legume and non-legume trees

Nitrogen-fixing root nodules are found in 10 plant families containing trees and shrubs associated with rhizobia or Frankia. The nodulation status and nodule characteristics have been extensively studied for herbaceous legumes, while for many legume trees species these characters are unknown. Hardwood timber production represents the major economic use of both leguminous and actinorhizal trees, although other roles in providing shelter, land conservation, land reclamation and as medicinal plants are important. Their success relies not only on their ability to fix N 2 symbiotically, but also on a range of other adaptations including flooding and drought tolerance, mycorrhizal formation, cluster root production and herbivore defences. Future research to detail nodulation status, nitrogen fixation rates, physiological adaptations and genetic diversity in both legumes and actinorhizal trees will provide fundamental knowledge to further conservation and utilisation of these plants.

Distribution, abundance and symbiotic effectiveness of Rhizobium leguminosarum bv. trifolii from alkaline pasture soils in South Australia

The current dissatisfaction with low productivity of annual medic (Medicago spp.) pastures has highlighted the need to seek alternative legumes to provide efficient N2 fixation in low rainfall, alkaline soil environments of southern Australia. Clover species adapted to these environments will have limited N2 fixation if effective rhizobia are not present in sufficient quantities. A survey of 61 sites was conducted across South Australia to determine the size, distribution and effectiveness of Rhizobium leguminosarum bv. trifolii (clover rhizobia) populations resident in these low rainfall, alkaline soil environments. Clover rhizobia were detected at 56 of the sites, with a median density of 230–920 rhizobia/g soil. Most rhizobial populations were poor in their capacity to fix nitrogen. Rhizobial populations from fields provided 11–89% and 10–85% of the shoot biomass of commercial reference strains when inoculated onto host legumes T. purpureum (purple clover) and T. resupinatum (persian clover), respectively. Rhizobial population size was correlated negatively to pH and the percentage of CaCO3 in the soil, and was significantly increased in the rhizospheres of naturalised clover, found at 17 sites. Management options for rhizobial populations to improve legume diversity and productivity are discussed in terms of rhizobial population dynamics and likely soil constraints to successful rhizobial colonisation.

Modelling the effects of temperature on the rates of seedling emergence and leaf appearance in legume cover crops

Simple models of the growth and development of legume cover crops in different environments may aid the selection of species and genotypes most suitable for particular farming systems. The effects of temperature and photoperiod on the daily rate of seedling emergence (1/t50%) and the rate of leaf appearance (leaves d⊃−1&amp;/sup;) were quantified for 12 diverse legume cover crop species. Six tropical or subtropical species were grown in 12 combinations of mean temperature (16.8, 21.8 and 26.8 °C) and photoperiod (11.5, 12.5, 13.5 and 14.5 h d⊃−1&amp;/sup;). Another six genotypes of temperate species were grown in nine combinations of mean temperature (16.8, 21.8 and 26.8 °C) and photoperiod (12.5, 13.5 and 14.5 h d⊃−1&amp;/sup;). Durations from sowing to 50% seedling emergence (t50%) were recorded and the number of leaves on the main stem counted during early vegetative growth. Photoperiod did not affect either 1/t50% or leaves d⊃−1&amp;/sup;. However, the effects of temperature, photoperiod response group (short-day or long-day response), genotype or species and their interactions were all significant. An optimal temperature between 21.8 and 26.8 °C for leaves d⊃−1&amp;/sup; was identified for Vicia sativa, Vicia dasycarpa and Lupinus mutabilis. Below the optimum temperature, 1/t50% and leaves d⊃−1&amp;/sup; were positive linear functions of temperature for all legume species except Vicia dasycarpa. Estimates of base temperature (Tb) and thermal time (θ) for 1/t50% and leaves d−1 were obtained for each legume cover crop from these functions. Common values of Tb were found within each photoperiod response group: 9 °C and 1 °C for 1/t50%, and 10 °C and −2 °C for leaves d⊃−1&amp;/sup; for short-day and long-day species respectively. Differences among species were represented by variant estimates of θ. The practical consequences of the combined effects of these values of Tb and θ for selecting legume cover crops for particular farming systems are discussed.