Optimising the legume symbiosis in stressful and competitive environments within southern Australia—some contemporary thoughts

In the managed agricultural ecosystems of southern Australia, if an edaphic environment is not stressful to root-nodule bacteria (hereafter rhizobia), it is likely to become a competitive environment for nodulation (although not always detrimentally so) soon after the introduction of an inoculated legume. We suggest that stressful environments limit rhizobial communities to less than 100 cells g⁻¹ soil at some time during the season. This overview puts forward the hypothesis that in perturbed ecosystems (i.e. those that are intensively managed) such as in the 25 million ha of the southern Australian grain and grazing belts, the rhizobial community is still substantially immature in an evolutionary sense. The rhizobial community is representative of only a few species, primarily those of Mediterranean origin that were accidentally introduced, or have been fostered by legume development programs, or remnants of the populations associated with native legumes. We consider there is little inter-specific competition for substrates because of this relative immaturity, but suggest that intra-specific competition for nodulation is commonplace wherever abiotic stress is absent. We nominate two primary abiotic stresses that are permanently present that have limited rhizobial colonization or legume nodulation for some species in southern Australia and four secondary (temporary) abiotic stresses. We believe that selection of adapted symbioses, or where warranted adapted elite rhizobial strains or legume host genotypes, can overcome these stress factors. We emphasise that where several abiotic stress factors are present they may act synergistically, but that this net effect is still likely to be symbiosis-specific. We acknowledge that genetic transformation in situ is providing new strain variability with which we must contend. We also put forward the suggestion that opportunities exist for the managed introduction of selected genotypes of agricultural legumes that effectively interact with rhizobial communities to achieve optimal N-fixation. In doing so, we give more precise definition to the widely used terms ‘exclusive’, ‘selective’ and ‘promiscuous’ nodulation.     

三种豆科植物种子萌发特性的研究

通过温度、光照、浸种时间及发芽床对3种豆科植物种子萌发影响的研究.结果表明:绿豆种子萌发温度以15～25℃为最佳;阴暗条件比光照条件下萌发速度更快;浸种6～10 d可极显著地提高发芽数;发芽床以纸上和纸间为最佳.大豆种子萌发温度以20℃为最佳;阴暗条件比光照条件下萌发速度更快;浸种6 d可显著地提高发芽数;发芽床以黄壤土为最佳.豇豆种子萌发温度以15℃为最佳;浸种2～3 d可显著地提高发芽数,阴暗条件比光照条件下萌发速度更快,发芽床以黄壤土为最佳.     

Rooting systems of oilseed and pulse crops. II: Vertical distribution patterns across the soil profile

Root distribution patterns in the soil profile are the important determinant of the ability of a crop to acquire water and nutrients for growth. This study was to determine the root distribution patterns of selected oilseeds and pulses that are widely adapted in semiarid northern Great Plains. We hypothesized that root distribution patterns differed between oilseed, pulse, and cereal crops, and that the magnitude of the difference was influenced by water availability. A field experiment was conducted in 2006 and 2007 near Swift Current (50°15′N, 107°44′W), Saskatchewan, Canada. Three oilseeds [canola (Brassica napus L.), flax (Linum usitatissimum L.), mustard (Brassica juncea L.)], three pulses [chickpea (Cicer arietinum L.), field pea (Pisum sativum L.), lentil (Lens culinaris)], and spring wheat (Triticum aestivum L.) were hand-planted in lysimeters of 15 cm in diameter and 100 cm in length which were pushed into soil with a hydraulic system. Crops were evaluated under low- (natural rainfall) and high- (rainfall + irrigation) water conditions. Vertical distribution of root systems was determined at the late-flowering stage. A large portion (>90%) of crop roots was mainly distributed in the 0-60 cm soil profile and the largest amount of crop rooting took place in the top 20 cm soil increment. Pulses had larger diameter roots across the entire soil profile than oilseeds and wheat. Canola had 28% greater root length and 110% more root tips in the top 10 cm soil and 101% larger root surface area in the 40 cm soil under high-water than under low-water conditions. In 2007, drier weather stimulated greater root growth for oilseeds in the 20-40 cm soil and for wheat in the 0-20 cm soil, but reduced root growth of pulses in the 0-50 cm soil profile. In semiarid environments, water availability did not affect the vertical distribution patterns of crop roots with a few exceptions. Pulses are excellent “digging” crops with a strong “tillage” function to the soil due to their larger diameter roots, whereas canola is more suitable to the environment with high availability of soil water that promotes canola root development.     

Yield development of winter wheat over 50 years of FYM,N, P and K fertilizer application on black earth soil in the Czech Republic

The black earths of Central Europe are an important soils for crop production but sustainability of crop production on such soils has not been examined. In the present paper, yield of winter wheat over 50 years of FYM, N, P and K fertilizer application (12 treatments altogether) was analyzed in the Ivanovice Crop Rotation Experiment (ICRE), established in 1955 on a degraded black earth soil (chernozem).     

豆科牧草种子萌发特性与其抗旱性差异的研究

试验采用PEG模拟干旱测定了3种豆科牧草(5个品种)种子的相对发芽率和胚根/胚芽比值,并在温室条件下采用盆栽控水研究了这3种牧草在水分胁迫下叶片相对含水量和质膜透性的变化规律。结果显示:种子萌发期抗旱性强的牧草其分枝期抗旱性亦强,抗旱能力依次为游客>德福>百脉根>胡亚>瑞文德。试验证明,利用生理生化方法和种子萌发实验进行牧草品种间抗旱性鉴定是可行的。     

郑州市园林豆科植物多样性调查与应用分析

豆科植物因为具有良好的观赏性和较强的固氮性而被广泛地应用于城市园林和废弃地植被景观恢复中。通过样地调查法对郑州市选定的26个样地进行调查,统计记录其种类、数量、频率、生长状况及常见的病虫害等。分析其多样性特征和在园林中的应用形式,提出合理的建议,使豆科植物在郑州市园林中的应用得到推广。     

Biostatic effect of fumigation and pesticide drenches on an endomycorrhizal-Rhizobium-legume tripartite association under field conditions

The effects of formaldehyde fumigation and pesticide drenching with Bavistin, Cuman, Copperthom, Sulfex, Furadon, and Termix at recommended rates on vesicular-arbuscular mycorrhizal (VAM) colonisation and Rhizobium sp. nodules were assessed regularly for a period of 90 days in the legumes Cajanus cajan, Dolichos biflorus, Vigna mungo, and V. unguiculata under field conditions. The fumigant and the pesticides initially reduced VAM fungal colonisation and the number of spores in all plants. Following the initial decrease there was a slow recovery, but by 90 days after emergence, root colonisation was either parallel to or still lower than the control, and the number of spores was still well below control levels for all species except C. cajan, which had more VAM spores than the control in all treatments except fumigation and Furadon. Although the number of nodules did not differ from control levels at 30 days after emergence, differences were evident during the later stages of plant growth for all species except V. unguiculata. The effect of pesticides on VAM fungi and root nodulation varied with the associated host plant species. Plant tissue P and VAM colonisation were significantly correlated in all host plants. The pesticide treatments had no marked effect on plant growth, but accumulations of nutrients in pesticide-treated plants were lower than those in untreated plants. Growth and nutrient status of the legumes varied with VAM fungal colonisation.     

Influence of management practices on soil organic matter,microbial biomass and cotton yield in Alabama's “Old Rotation”

The Old Rotation cotton experiment was designed to aid farm managers in implementing rotation schemes that not only increase yield, but also improve soil quality. Six different crop rotation treatments were imposed since 1896. Rotations were: IA, cotton (Gossypium hirsutum L.) grown every year without a winter legume and without N fertilization; IB, cotton grown every year with a winter legume and without N fertilization; IC, cotton grown every year without a winter legume and with 134 kg N as NH₄NO₃ ha^-1 year^-1; IIA, 2-year cotton-corn (Zea mays L.) rotation with a winter legume and without N fertilization; IIB, 2-year cotton-corn rotation with a winter legume and with 134 kg N ha^-1 year^-1 as NH₄NO₃; and III, 3-year cotton-corn- alternating soybean [Glycine max (L.) Merr.] or rye (Secale cereale L.) rotation with a winter legume and with 134 g N as NH₄NO₃ ha^-1 year^-1. Crimson clover (Trifolium incarnatum L.) was the winter legume cover crop. The 2-year cotton-corn rotation with a winter legume and with 134 kg N ha^-1 year^-1 (IIB) and the 3-year cotton-corn soybean/rye rotation with a winter legume and with 134 kg N ha^-1 year^-1 (III) had higher amounts of soil organic matter, soil microbial biomass C and crop yield than the other four treatments. The cotton grown every year without a winter legume or N fertilizer (IA) had a lower amount of soil organic matter, soil microbial biomass C and N and cotton seed yield than all other rotations. In 1988 and 1992 cotton seed and legume yield were correlated in positive, curvilinear relationships with soil organic matter (r ² ranged from 0.72 to 0.87). In most months, soil microbial biomass C and N was lower in the cotton grown every year without winter legumes or fertilizer (IA) than the other five rotations. In 1994, microbial biomass C and the C_mic:C_org ratio correlated in positive, curvilinear relationships with seed cotton yield (r ²=0.87 and 0.98, respectively). After 99 years of management the Old Rotation cotton experiment indicates that winter legumes increase amounts of both C and N in soil, which ultimately contribute to higher cotton yields. Microbial biomass C and the C_mic:C_org ratio are poor predictors of annual crop yield but may be an accurate indicator of soil health and a good predictor of long-term crop yield.     

Structural differences in the rhizosphere communities of legumes are not equally reflected in community-level physiological profiles

The relationship of structural diversity and differences in the functional potentials of rhizosphere communities of alfalfa, common bean and clover was investigated in microcosms. PCR-SSCP (single strand conformation polymorphism) analysis of 16S rRNA genes revealed significant differences in the composition of the leguminous rhizosphere communities at the shoot stage of plants grown in the same soil. Sequencing of dominant SSCP-bands indicated the presence of plant specific organisms. The partial rRNA gene sequences were related to members of the α- and γ-Proteobacteria, Bacteroidetes and Actinobacteria. Besides the plant species, the soil also affected the structural diversity in rhizospheres. The dominant bacterial populations of alfalfa grown in soils with different agricultural histories were assigned to different taxonomic groups. Addressing the functional potentials, community-level physiological profiles (CLPP) were generated using BIOLOG GN^®. The three leguminous rhizosphere communities could be differentiated by principle component analysis, though the overall analysis indicated that the metabolic potential of all rhizosphere samples was similar. The functional variation examined in rhizospheres of alfalfa was minor in response to the soil origin and was found not to be significant different at different growth stages. The results indicate that similar functional potentials may be provided by structurally different bacterial communities.     

Influence of sulphur supply on glucose and ATP concentrations of inoculated broad beans (Vicia faba minor L.)

In the present study, the influence of S supply on S concentrations, N₂ fixation, available amounts of glucose and adenylates of Vicia faba minor L. were weekly investigated, starting 6 weeks after sowing. Glucose was determined photometrically in shoots, roots and nodules and in ATP, ADP and AMP by bioluminescence in roots, mitochondria and bacteroids. Sulphur deficiency resulted in significantly lower S concentrations of shoots, roots and nodules, in a reduced N₂ fixation as well as in significantly lower amounts of glucose in shoots and nodules. In roots and bacteroids, S deficiency resulted in lower ATP concentrations, while the influence of S supply on ADP and AMP was less pronounced. With optimum S supply, the available amounts of glucose and ATP were strongly influenced by flower formation and seed development. Dedicated to Prof. Dr. Dr. h.c. W. Werner on the occasion of his 75th birthday.