根瘤菌结瘤基因的表达调控研究概况

根瘤菌结瘤基因的表达调控在根瘤菌与植物的共生结瘤过程中起着十分重要的作用。随着研究的深入,发现根瘤菌的结瘤过程不仅与根瘤菌结瘤基因表达调控有关,而且与寄主植物的信号分子如黄酮类物质有关。根瘤菌结瘤基因的表达调控有一个复杂的过程,本文将简要地介绍这方面的研究成果。     

Nitrogen requirements associated with improved conservation tillage for corn production

Abstract

Excessive soil erosion and use of nitrogen fertilizer are costly to the Atlantic Coastal Plain corn (zea mays L., ’Funks G 4507') producer and both may serve to create environmental hazards. An in‐row chisel (36 cm deep) tillage method was compared with the standard 5 cm fluted coulter method for planting corn in premature wheat (Triticim aestivum L.) residues grown on an Orangeburg sandy loam (Typic Paleudult). Five orthogonal N levels ranging up to 440 kg of N/ha were used to determine an economic N optimum for each tillage method.

The in‐row chisel tillage method provides a possible yield advantage in the Atlantic Coastal Plain because of observed restricting soil layers within the normal corn rooting zone. The estimated profit‐maximizing quantities of N fertilizer were 262 and 295 kg of N/ha (234 and 263 1b of N/acre) for the fluted coulter and in‐row tillage procedures, respectively. Corn grain yields associated with these inputs were 9.6 × 10³ and 12.6 × 10³ kg/ha (153 and 200 bu/acre), respectively. The yield increase associated with in‐row chiseling through a 2.5 metric ton mulched surface is attributed to potentially improved rooting and more efficient water storage and use.     

Influence of Dual Inoculation of AM Fungi and Rhizobium on Growth Indices,Production Economics,and Nutrient Use Efficiencies in Garden Pea (Pisum sativum L.)

Field experimentation was conducted at Palampur, India during 2011–2012 in an acid Alfisol to quantify the influence of integrated use of arbuscular mycorrhizal fungi (AMF), Rhizobium and inorganic nitrogen (N) and phosphorus (P) on growth, productivity, profitability, and nutrient use efficiencies in garden pea (Pisum sativum L.). The experiment was laid out in randomized block design (RBD) replicated thrice comprising 13 treatments involving AMF (Glomus mosseae), Rhizobium (R. leguminosarum), and inorganic N and P fertilizers. The results revealed that dual inoculation of pea seed with AMF and Rhizobium enhanced the plant height, leaf area index, and dry matter accumulation significantly by 19.4 and 13.1, 10.7 and 10.7, and 16.6 and 16.7%, respectively at 60 and 120 days after sowing (DAS). Similarly, dual inoculation exhibited significant respective increases of 9.5 and 14.6% in absolute and crop growth rates over generalized recommended NP potassium (K) dose (GRD) during 60–120 DAS. The dual inoculation led to significant respective increases of 1.0 and 2.2, 1.06 and 1.74, 0.21 and 1.5, and 1.05 and 1.60 folds in partial factor productivity, crop recovery efficiency, physiological efficiency, and % recovery of applied N and P, respectively over GRD. The magnitude of increase in pea productivity, net returns, and boron to carbon (B:C) ratio following dual inoculation was to the tune of 20, 54.4, and 104.1%, respectively over GRD. Dual inoculation also exhibited significant increases of 19.4 and 53.1% in production and monetary efficiencies of pea over GRD. Overall, dual inoculation of AMF and Rhizobium with 75% soil-test-based N and P dose in pea has great potential in enhancing pea productivity, profitability, and nutrient use efficiency besides saving about 25% fertilizer N and P without impairing pea productivity in Himalayan acid Alfisol.     

根瘤菌在污染土壤修复中的地位和作用

根瘤菌是一种在环境中广泛存在,常与豆科植物共生结瘤固氮的细菌类群,在农、林、牧业的可持续发展中具有重要作用。近年来研究发现,除了人们熟知的固氮功能,根瘤菌还参与环境中重金属、有机物等污染土壤的修复,在生态环境修复、维持土地生产力以及节能减排方面发挥了重要的作用,尤其是根瘤菌与豆科植物联合修复污染环境效果更为显著。本文综合介绍了根瘤菌在重金属、有机物等污染土壤及滨海盐渍土壤修复中的地位、作用及潜在价值,以期为改善生态环境提供一些可参考的方法和依据。     

Lentil (Lens culinaris L.) growth promoting rhizobacteria and their effect on nodulation in coinoculation with rhizobia

Lentil is cultivated in Chilean Mediterranean drylands, in areas with soils that are nutrient depleted and eroded. Inoculation of lentil with rhizobia in co-inoculation with growth promoting rhizobacteria would allow higher biomass and an opportunity for early nodulation and increased nitrogen fixation. The objective of this research was to select rhizosferic bacteria (PGPR) from lentils and to evaluate their effect on lentil nodulation in co-inoculation with rhizobia. Sixty three lentil rhizobacteria isolates where obtained from nine soils in the mediterranean area. These were fingerprinted through BOX-PCR reducing the number to 57 distinct strains. The strains were evaluated for ACCdeaminase activity, IAA production and compatibility with rhizobia. Seventeen strains showed ACC-deaminase activity, all of them synthesized IAA and 38 were compatible with the rhizobia. Ten selected strains were identified as Pseudomonas spp. through 16S rRNA sequencing. The strains were inoculated in lentil seedlings growing on seed germination pouches, to evaluate nodule formation. The strain LY50a increased early nodulation in 85% in comparison to the control inoculated with rhizobia (AG-84) only. In conclusion, bacteria from the rhizosphere from Mediterranean soils of Chile can be used as nodulation promoters in lentils.     

Inoculant effects on alfalfa nodulation

Abstract

Alfalfa (Medicago sativa L.) does not grow as well as it used to in areas of Canada and northwestern United States. Affected plants have nitrogen (N)‐deficiency symptoms, few or no nodules, and respond to N fertilizer. For lack of a good explanation, such plants are called “sick”;.

Six commercial inoculant products were tested with alfalfa grown on cores of eight soils in which alfalfa establishment and stand duration have been problems, to determine if inoculant quality influenced development of any sick‐alfalfa symptoms. Percentages of nodulated plants ranged from 35 to 82 after 5 to 8 weeks’ growth, and corresponded closely with estimated rhizobia numbers in the products. Dry forage yields were not closely related to percentage nodulation, however, because of residual soil N levels that supported seedling growth. Inoculant products containing inadequate numbers of rhizobia to promptly and effectively nodulate plants resulted in poor nodulation that may lead to establishment failure or sparse, weak stands.

Contribution from the Central Oregon Exp. Stn. and Dep. of Microbiology, Oregon Agric. Exp. Stn. Journal Article No. 4910.     

EFFECTS OF pH ON GROWTH AND NODULATION OF TWO FORAGE LEGUMES

A study was conducted to compare the responses to acid pH of Medicago sativa and Lotus glaber, two forage legumes with different environmental requirements, either supplied with inorganic nitrogen (N) or inoculated with different strains of their nodule bacteria. Medicago sativa showed, in both treatments, a significant reduction in total dry weight at pH below 6.0. In contrast, Lotus glaber grew equally well at all the pHs assayed in the presence of adequate N. Under inoculated conditions, in the absence of N supply, plant growth was dependent on the bacterial strain used. When the ability of each strain to multiply in culture medium was examined, it was observed that Sinorhizobium meliloti strains showed a pH-sensitive response that inhibited growth at pH 4.0, whereas Mesorhizobium loti strains showed normal growth at this pH. These results suggest that for the effectiveness of Mesorhizobium loti–Lotus glaber symbiosis in acid soils the major factor to be considered is the tolerance of the bacterial strain to acid conditions, while the limiting factors for the Sinorhizobium meliloti–Medicago sativa symbiosis are the sensitivity to low pH of both the plant and its bacteria.     

Low root zone temperature effects on bean (Phaseolus vulgaris L.) plants inoculated with Rhizobium leguminosarum bv. phaseoli pre-incubated with methyl jasmonate and/or genistein

Abstract

Methyl jasmonate (MeJA) has recently been shown to act as a plant-to-bacteria signal. We tested the hypothesis that pre-induction of Rhizobium leguminosarum bv. phaseoli cells with genistein and/or MeJA would at least partially overcome the negative effects of low root zone temperature (RZT) on bean nodulation, nitrogen fixation and plant growth. Otebo bean plants were grown at constant air temperature (25^oC) and two RZT regimes (25 and 17^oC) and inoculated with R. leguminosarum bv. phaseoli pre-induced with MeJA and/or genistein. Our results indicate that low RZT inhibited nodulation, nitrogen fixation and plant growth. The plants growing at low RZT began fixing nitrogen seven days later compared to those at higher RZT. The low RZT plants had fewer nodules, lower nodule weight, less N fixation, slower plant growth, fewer leaves, smaller leaf area, and less dry matter accumulation comared to plants at a higher RZT. Rhzobium leguminosarum bv. phaseoli cells induced with genistein and/or MeJA enhanced bean nodulation, nitrogen fixation and growth at both optimum and suboptimum RZTs. The results of this study indicate that MeJA improves bean nitrogen fixation and growth at both optimum and suboptimum RZTs, and can be used alone or in combination with genistein to partially overcome the low RZT induced inhibitory effects on nodulation and nitrogen fixation.     

Mycorrhiza‐soil fertility effects on regrowth,nodulation and Nitrogenase activity of siratro (Macroptilium atropurpureum (DC) Urb.)

Siratro (Macroptilium atropurpureum (DC) Urb.) is a vigorous perennial forage legume with good potential for improving pastures in the extensive neotropical regions of the world. It is well adapted to a wide range of soil and climatic conditions. The objective of these studies was to determine effects of Glomus fasciculatum colonization, rigorous defoliation, and soil fertility treatments to a Psammentic Paleustalf (Eufaula) soil on growth, regrowth, nodulation, and nitrogenase activity (C₂H₂ red.) of Siratro inoculated with Rhizobium leguminosarum Frank. Top growth increased significantly with soil K and P amendment and with mycorrhiza colonization. Nodulation and nitrogenase activity were correlated with highly significant increases from G. fasciculatum, P treatments and K additions to 300 mg K kg^‐1 soil. Growth and peduncles of nonclipped plants increased about 4 fold from 90 to 225 day age with mature seed yield increasing about 10 fold; nodule mass and nitrogenase activity levels approximately doubled. Regrowth response of plants defoliated at 45 day intervals, following their initial 90 day age, was somewhat constant between clippings for magnitude of regrowth 12.3–13.8g, development in number of peduncles 4.0–6.8, seed yield 1.4–2.6g, nodulation 2.9–3.7g, and nitrogenase activity 73.9–95.8μ mol C₂H₄g^‐1 nodule. Multiple regression for nitrogenase = 0.55 g top wt. + 0.63 g nodule wt. + 1.91 day age ‐ 0.07 peduncle no., R² = 0.85 and C.V. = 14.3%. Favorable tripartite symbiosis with both effective Rhizobium and endophyte mycorrhiza were essential for high levels of symbiotic nitrogen fixation.     

复合型PGPR和苜蓿对新垦地土壤培肥效果研究

研究了利用根际有益微生物和豆科植物相结合培肥新垦地土壤的效果。试验采用裂区设计法研究了重庆北碚新垦坡耕地中性土壤上种植紫花苜蓿并接种根瘤菌和其他根际有益微生物(PGPR)(如联合固氮菌、解磷菌和解钾菌等)对土壤养分的影响。结果显示:接种根瘤菌+其他PGPR的处理对土壤有机质、全氮、全磷、全钾、有效磷和速效钾的提高均达到显著水平,较只接种根瘤菌的处理分别提高33.5%、22.7%、3.8%、11.5%、11.4%和22.3%,较不接种根瘤菌和PGPR的处理分别高42.2%、58.8%、8%、12.6%、37.2%和40.2%,接种根瘤菌+其他PGPR的效果优于只接种根瘤菌和不接种的。同时,上述处理对豆科植物苜蓿植株瘤重、株高、根鲜重、地上部鲜重以及植株全氮含量的提高均达到显著水平,比只接种根瘤菌的处理分别高44.5%、33.2%、77.3%、76.7%和17.7%。将苜蓿和相应的PGPR两者联合使用有更好的土壤改良效果,加速了新垦地贫瘠土壤的培肥过程。