Terrestrial plant methane production and emission

In this minireview, we evaluate all experimental work published on the phenomenon of aerobic methane (CH(4) ) generation in terrestrial plants and plant. Clearly, despite much uncertainty and skepticism, we conclude that the phenomenon is true. Four stimulating factors have been observed to induce aerobic plant CH(4) production, i.e. cutting injuries, increasing temperature, ultraviolet radiation and reactive oxygen species. Further, we analyze rates of measured emission of aerobically produced CH(4) in pectin and in plant tissues from different studies and argue that pectin is very far from the sole contributing precursor. In consequence, scaling up of aerobic CH(4) emission needs to take into consideration other potential sources than pectin. Due to the large uncertainties related to effects of stimulating factors, genotypic responses and type of precursors, we conclude that current attempts for upscaling aerobic CH(4) into a global budget is inadequate. Thus it is too early to draw the line under the aerobic methane emission in plants. Future work is needed for establishing the relative contribution of several proven potential CH(4) precursors in plant material.     

温度对亚热带地区常见树种叶片甲烷排放的影响

以亚热带常见树种米槠、木荷、浙江桂、罗浮栲、杉木和柑橘为对象,利用控制试验研究了温度对树木叶片甲烷(CH₄)排放的影响.结果表明: 当温度在10 ℃时,供试的6种树木中,仅木荷、柑橘和罗浮栲的叶片排放CH₄;温度高于20 ℃时,所有树木叶片均可排放CH₄.温度高于30 ℃时,叶片排放CH₄的平均排放速率(1.010 ng CH₄·g^-1DM·h^-1)是10～30 ℃时平均排放速率(0.255 ng CH₄·g^-1DM·h^-1)的3.96倍.增温对柑橘和杉木CH₄排放速率的影响显著高于其他4种树木.培养时间对叶片排放CH₄速率有显著影响,温度胁迫对树木排放CH₄的影响受植物活性的控制.在低温或高温条件下,树木干叶均不能排放CH₄.高温胁迫对树木叶片排放CH₄有重要影响,全球变暖可能增加植物的CH₄排放.     

Contrasting wetland CH4 emission responses to simulated glacial atmospheric CO2 in temperate bogs and fens

Wetlands were the largest source of atmospheric methane (CH(4) ) during the Last Glacial Maximum (LGM), but the sensitivity of this source to exceptionally low atmospheric CO(2) concentration ([CO(2) ]) at the time has not been examined experimentally. We tested the hypothesis that LGM atmospheric [CO(2) ] reduced CH(4) emissions as a consequence of decreased photosynthate allocation to the rhizosphere. We exposed minerotrophic fen and ombrotrophic bog peatland mesocosms to simulated LGM (c. 200 ppm) or ambient (c. 400 ppm) [CO(2) ] over 21 months (n = 8 per treatment) and measured gaseous CH(4) flux, pore water dissolved CH(4) and volatile fatty acid (VFA; an indicator of plant carbon supply to the rhizosphere) concentrations. Cumulative CH(4) flux from fen mesocosms was suppressed by 29% (P < 0.05) and rhizosphere pore water [CH(4) ] by c. 50% (P < 0.01) in the LGM [CO(2) ], variables that remained unaffected in bog mesocosms. VFA analysis indicated that changes in plant root exudates were not the driving mechanism behind these results. Our data suggest that the LGM [CO(2) ] suppression of wetland CH(4) emissions is contingent on trophic status. The heterogeneous response may be attributable to differences in species assemblage that influence the dominant CH(4) production pathway, rhizosphere supplemented photosynthesis and CH(4) oxidation.     

Plant succession and rhizosphere microbial communities in a recently deglaciated alpine terrain

This study describes how early and late successional plant species affect soil microorganisms in alpine ecosystems. We quantify the relative importance of plant species and soil properties as determinants of belowground microbial communities. Sixteen plant species were selected from six successional stages (4–14–20–43–75–135 years) within the foreland of the Rotmoosferner glacier, Austria, and at one (reference) site outside the foreland. The size, composition and function of the communities of microorganism in the bulk soil and the rhizosphere were characterized by ninhydrin-reactive nitrogen, phospholipid fatty acids and enzyme activities (β-glucosidase, β-xylosidase, N-acetyl-β-glucosaminidase, leucine aminopeptidase, acid phosphatase, sulphatase). The results show that the microbial data could be grouped according to early (up to 43 years) and late-colonizing plant species (75 or more years). In early succession, no plant species or soil age effect was detected on the microbial biomass, phospholipid fatty acids, or enzyme activity. The rhizosphere microbial community was similar to that in the bulk soil, which in turn was determined by the abiotic environmental conditions. In late succession, improved soil conditions probably mediated plant species effects on the belowground microbial community. The most pronounced rhizosphere effects were attributed to plant species of the 75- and 135-year-old sites. The microbial colonization (size, composition, activity) of the bulk soil predominantly followed changes in vegetation cover, plant life forms and soil organic matter. In summary, the observed successional pattern of the above- and belowground communities provides an example of the facilitation models of primary succession.     

Fluorescent pseudomonads in the rhizosphere of plants and their relation to root exudates

Fluorescent pseudomonads were present in chernozem soil not influenced by plant roots (10(3)-10(4) per g dry soil) in the rhizosphere soil of various plants (10(4)-10(5) per g soil) and on roots (10(3) to 10(7) per g fresh roots), depending on the species and age of the plant. Relative species representation of fluorescent pseudomonads changed on the roots and in the plant rhizosphere as compared with free soil. Pseudomonas fluorescens, representing 60-93% of the population of fluorescent pseudomonads predominated on the roots of all plants investigated. Somewhat different results were obtained in rhizosphere soil. Relatively higher numbers of P. fluorescens were detected in the rhizosphere soil of cucumber and maize, numbers in the rhizosphere soil of wheat were practically the same as in free soil and higher numbers of P. putida were found in the rhizosphere soil of barley. Almost all components contained in the root exudates of the plants studied, including beta-pyrazolylalanine from the root exudates of cucumbers were utilized as carbon and energy sources. Root exudates of wheat and maize were utilized by the strain P. putida K2 with an efficiency of 73-91%, depending on species and age of the plant.     

Organic acids and ethanol inhibit the oxidation of methane by mire methanotrophs

Aerobic methane (CH(4) ) oxidation reduces the emission of CH(4) from mires and is regulated by various environmental factors. Organic acids and alcohols are intermediates of the anaerobic degradation of organic matter or are released by plant roots. Methanotrophs isolated from mires utilize these compounds preferentially to CH(4) . Thus, the effect of organic acids and ethanol on CH(4) oxidation by methanotrophs of a mire was evaluated. Slurries of mire soil oxidized supplemental CH(4) down to subatmospheric concentrations. The dominant pmoA and mmoX genotypes were affiliated with sequences from Methylocystis species capable of utilization of acetate and atmospheric CH(4) . Soil slurries supplemented with acetate, propionate or ethanol had reduced CH(4) oxidation rates compared with unsupplemented or glucose-supplemented controls. Expression of Methylocystis-affiliated pmoA decreased when CH(4) consumption decreased in response to acetate and was enhanced after acetate was consumed, at which time the consumption of CH(4) reached control levels. The inhibition of methanotroph activity might have been due to either toxicity of organic compounds or their preferred utilization. CH(4) oxidation was reduced at 5 and 0.5 mM of supplemental organic compounds. Acetate concentrations may exceed 3 mM in the investigated mire. Thus, the oxidation of CH(4) might decrease in microzones where organic acids occur.     

Contribution of methanotrophic and nitrifying bacteria to CH4 and NH4+ oxidation in the rhizosphere of rice plants as determined by new methods of discrimination

Methanotrophic and nitrifying bacteria are both able to oxidize CH4 as well as NH4+. To date it is not possible to estimate the relative contribution of methanotrophs to nitrification and that of nitrifiers to CH4 oxidation and thus to assess their roles in N and C cycling in soils and sediments. This study presents new options for discrimination between the activities of methanotrophs and nitrifiers, based on the competitive inhibitor CH3F and on recovery after inhibition with C2H2. By using rice plant soil as a model system, it was possible to selectively inactivate methanotrophs in soil slurries at a CH4/CH3F/NH4+ molar ratio of 0.1:1:18. This ratio of CH3F to NH4+ did not affect ammonia oxidation, but methane oxidation was inhibited completely. By using the same model system, it could be shown that after 24 h of exposure to C2H2 (1,000 parts per million volume), methanotrophs recovered within 24 h while nitrifiers stayed inactive for at least 3 days. This gave an "assay window" of 48 h when only methanotrophs were active. Applying both assays to model microcosms planted with rice plants demonstrated a major contribution of methanotrophs to nitrification in the rhizosphere, while the contribution of nitrifiers to CH4 oxidation was insignificant.     

Ultraviolet radiation drives methane emissions from terrestrial plant pectins

Recent studies demonstrating an in situ formation of methane (CH(4)) within foliage and separate observations that soil-derived CH(4) can be released from the stems of trees have continued the debate about the role of vegetation in CH(4) emissions to the atmosphere. Here, a study of the role of ultraviolet (UV) radiation in the formation of CH(4) and other trace gases from plant pectins in vitro and from leaves of tobacco (Nicotiana tabacum) in planta is reported. Plant pectins were investigated for CH(4 )production under UV irradiation before and after de-methylesterification and with and without the singlet oxygen scavenger 1,4-diazabicyclo[2.2.2]octane (DABCO). Leaves of tobacco were also investigated under UV irradiation and following leaf infiltration with the singlet oxygen generator rose bengal or the bacterial pathogen Pseudomonas syringae. Results demonstrated production of CH(4), ethane and ethylene from pectins and from tobacco leaves following all treatments, that methyl-ester groups of pectin are a source of CH(4), and that reactive oxygen species (ROS) arising from environmental stresses have a potential role in mechanisms of CH(4) formation. Rates of CH(4 )production were lower than those previously reported for intact plants in sunlight but the results clearly show that foliage can emit CH(4) under aerobic conditions.     

Can methane suppression during digestion of woody and leafy browse compensate for energy costs of detoxification of plant secondary compounds? A test with muskoxen fed willows and birch

Digestion and metabolism of woody and leafy browse requires detoxification of plant secondary compounds that can incur an energy cost. Browse, however, inhibits methane (CH(4)) production and therefore could offset some costs of detoxification. We measured an index of heat increment of feeding (HIFi) and CH(4) production in muskoxen (Ovibos moschatus) given a single test meal (at 10 g/kg BM(0.75)) composed of hay mixed with one of three browse species (Willow: Salix alaxensis, S. pulchra; Birch: Betula nana). Detoxification cost was estimated as HIFi of browse diet-HIFi of hay diet and CH(4) compensation as CH(4) production of hay diet-CH(4) production of browse diet. CH(4) compensation was noted in 47% of 15 trials in which a detoxification cost was evident; six trials were with woody browse and one with leafy browse. Separate controls were responsible for the difference in CH(4) compensation for leafy browse vs. woody browse. Detoxification costs for twigs and leaves of B. nana were underestimated because of their low digestibility. In only one of six treatments was CH(4) compensation documented for B. nana. We conclude that energy saved by CH(4) suppression was small (<6%) compared with detoxification costs.     

宁南山区典型植物根际与非根际土壤微生物功能多样性

选择宁南山区9种典型植物的根际与非根际土壤为研究对象,采用Biolog方法对土壤微生物功能多样性进行了研究。结果表明:9种不同植物根际土壤与非根际土壤的微生物活性(AWCD)、微生物多样性指数和微生物均匀度指数均存在明显差异;除冰草外,其他各种植物的根际土壤的微生物活性AWCD、微生物多样性指数和微生物均匀度指数均比非根际土壤的高;9种典型植物根际土壤微生物主要碳源利用类型是羧酸类和氨基酸类,非根际土壤微生物主要碳源利用类型是羧酸类、胺类、氨基酸类;微生物活性、微生物多样性指数和微生物均匀度指数两两之间均达到了极显著相关,与土壤化学性质各指标之间均未达到显著相关水平。     

蚯蚓和三叉苦对亚热带人工林土壤N2O和CH4通量的短期效应

在广东鹤山大叶相思(Acacia auriculaeformis)人工林内设置外来蚯蚓西土寒宪蚓(Ocnerodrilus occidentalis)和乡土植物三叉苦(Evodia lepta)野外控制实验,用静态箱-气相色谱法对土壤N2O和CH4通量进行15 d的原位测定,研究蚯蚓和三叉苦对土壤N2O和CH4通量的影响。结果表明,三叉苦并未明显增加土壤N2O和CH4的通量,而假植物(模拟三叉苦的物理效应)则显著促进了土壤N2O的释放通量。整个实验阶段,蚯蚓效应分别使无植物对照和三叉苦处理土壤N2O通量增加了26.7%和66.3%,而在种假植物条件下,添加蚯蚓使土壤N2O通量降低了39.7%;同时,蚯蚓效应使对照处理土壤CH4吸收通量增加了10.3%,使假植物处理土壤CH4吸收通量降低了90.6%,而使三叉苦处理土壤CH4释放通量增加了301.8%。可见,蚯蚓能够促进人工林土壤N2O释放;同时促进人工林土壤从CH4“汇”向“源”转变。三叉苦的物理过程促进土壤N2O的释放,而三叉苦的生物过程抑制土壤N2O的排放。如何减缓人工林中土壤N2O和CH4的排放,必须综合考虑植物物理过程、生物过程以及蚯蚓对土壤N2O和CH4排放过程影响的独立效应和交互效应。     

Studies on soil rhizosphere: speciation and availability of Cd

ABSTRACT

The rhizosphere soils of two durum wheat (Triticum turgidum var. durum L.) cultivars Kyle and Areola grown in two selected soils of southern Saskatchewan were collected both at 2-week and 7-week plant growth stages. The cadmium availability index (CAI), determined as M NH₄CI-extractable Cd, pH and the distribution of the particulate- bound Cd species of the soils were carried out and the data were discussed in comparison with those of the corresponding bulk soil. At the 2-week growth stage, the pH of the rhizosphere soil was less than that of the corresponding bulk soil and the CAI values were higher in the rhizosphere soil, indicating that more Cd was complexed with the low-molecular-weight organic acids (LMWOAs) at the soil-root interface and was extractable by M NH₄CI. Compared with the bulk soils, the CAI values were 2–9 times higher in the soil rhizosphere of the plots fertilized with Idaho monoammonium phosphate fertilizer at 2-week growth stage, which is attributed to the combined effects of the Cd introduced into the soil rhizosphere from the fertilizer (Cd content of the fertilizer was 144 mg kg^?1) and complexation reactions of phosphate and LMWOAs with soil Cd. At 7-week plant growth stage, such differences were not observed. The increased amounts of carbonate-bound and metal-organic complex-bound Cd species of the rhizosphere soils are due to the increased amounts of carbonate, a product of plant respiration, and the LMWOAs at the soil-root interface, respectively. Simple correlation analysis of the data showed that the CAI of the rhizosphere soils of the control plots correlated at least two orders of magnitude better with the metal-organic complex-bound Cd whereas the CAI of the rhizosphere soils treated with Idaho phosphate correlated better with carbonate-bound Cd species in comparison to other species.     

植物排放N2O和CH4的研究

N2O和CH4是2种重要的温室气体,但其排放源尚未得到充分鉴别.1990年和2006年先后报道植物能排放N2O和CH4,并日益受到广泛的关注.然而,迄今为止对植物排放这2种气体的研究均是分开单独进行的.该文以8种陆生草本植物为研究对象,首次同步考察了新鲜离体植物地上部排放N2O和CH4的通量.研究结果表明:8种植物均能排放这2种气体.其中,黑麦草(Lolium perenne)、抱茎苦荬菜(Ixendium sonchifolium)和菠菜(Spinacia oleracea)的CH4通量较高,分别为165.38、52.28和21.64 ngCH4.g-1dw·h-1;抱茎苦荬菜、蒙古蒿(Artemisia mongolica)、大豆(Glycine max)和菠菜的N2O通量较高,分别为7.19、6.92、5.44和4.05 ngN2O·g-1dw.h-1.研究结果不仅为植物本身既能排放N2O又能排放CH4在植物中可能具有普遍性提供了进一步的实验依据,而且为深入研究其机理找到了几种适宜的植物种(如抱茎苦荬菜、菠菜).     

Properties of Barley Seed Chitinases and Release of Embryo-Associated Isoforms during Early Stages of Imbibition

Barley (Hordeum vulgare L.) seeds contain at least five proteins with chitinase (CH) activity. Two of these (CH1 and CH2) are found primarily in the aleurone and endosperm tissues, and the other three (CH3, CH4, and CH5) are enriched in the embryo. From the bran fraction, three of these CHs (CH1, CH2, and CH3) were purified to apparent homogeneity. These three CHs have apparent molecular masses of 27, 34, and 35 kilodaltons and isoelectric points of 9.3, 9.2, and 8.7, respectively. CH2 and CH3 have amino terminal sequences resembling a portion of the chitin-binding domain of lectins and other plant defense proteins. CH1 lacks this domain. All three CHs exhibit antifungal activity and inhibit the mycelial growth of some species of trichoderma and Fusarium in vitro. During the early period of imbibition by seeds, two of the embryo-associated CHs are selectively released into the surrounding aqueous medium.     

Plant growth promoting bacteria from Crocus sativus rhizosphere

Present study deals with the isolation of rhizobacteria and selection of plant growth promoting bacteria from Crocus sativus (Saffron) rhizosphere during its flowering period (October–November). Bacterial load was compared between rhizosphere and bulk soil by counting CFU/gm of roots and soil respectively, and was found to be ~40 times more in rhizosphere. In total 100 bacterial isolates were selected randomly from rhizosphere and bulk soil (50 each) and screened for in-vitro and in vivo plant growth promoting properties. The randomly isolated bacteria were identified by microscopy, biochemical tests and sequence homology of V1–V3 region of 16S rRNA gene. Polyphasic identification categorized Saffron rhizobacteria and bulk soil bacteria into sixteen different bacterial species with Bacillus aryabhattai (WRF5-rhizosphere; WBF3, WBF4A and WBF4B-bulk soil) common to both rhizosphere as well as bulk soil. Pseudomonas sp. in rhizosphere and Bacillus and Brevibacterium sp. in the bulk soil were the predominant genera respectively. The isolated rhizobacteria were screened for plant growth promotion activity like phosphate solubilization, siderophore and indole acetic acid production. 50 % produced siderophore and 33 % were able to solubilize phosphate whereas all the rhizobacterial isolates produced indole acetic acid. The six potential PGPR showing in vitro activities were used in pot trial to check their efficacy in vivo. These bacteria consortia demonstrated in vivo PGP activity and can be used as PGPR in Saffron as biofertilizers.This is the first report on the isolation of rhizobacteria from the Saffron rhizosphere, screening for plant growth promoting bacteria and their effect on the growth of Saffron plant.     

The rhizosphere microbiome and plant health

The diversity of microbes associated with plant roots is enormous, in the order of tens of thousands of species. This complex plant-associated microbial community, also referred to as the second genome of the plant, is crucial for plant health. Recent advances in plant-microbe interactions research revealed that plants are able to shape their rhizosphere microbiome, as evidenced by the fact that different plant species host specific microbial communities when grown on the same soil. In this review, we discuss evidence that upon pathogen or insect attack, plants are able to recruit protective microorganisms, and enhance microbial activity to suppress pathogens in the rhizosphere. A comprehensive understanding of the mechanisms that govern selection and activity of microbial communities by plant roots will provide new opportunities to increase crop production.     

Influence of foliar application of chemicals on the root exudations and rhizosphere microflora ofSorghum vulgare andCrotalaria juncea

The effect of foliar application of sodium nitrate (0.1%), disodium hydrogen phosphate (0.1%), 2,4-D (25 p.p.m.) and Dithane Z-78 (200p.p.m.) on the quantity, and quality of sugars and amino acids exuded by sorghum and sunnhemp and on the rhizosphere microflora were studied. The sodium oitrate spray adversely affected the amino acid exudation in sorghum but increased the same in sunnhemp; the disodium hydrogen phosphate and Dithane Z-78 sprays reduced amino acid exudations whereas the 2,4-D spray enhanced the same in both the plant species. The disodium hydrogen phosphate spray caused qualitative changes in sugars but enhanced the quantity only in sorghum; the 2, 4-D spray increased exudation of sugars in both plant species and the sodium nitrate and Dithane Z-78 sprays caused qualitative changes in both plant species. Increases in bacterial population by 2, 4-D spray, in actinomycetes by 2, 4-D, disodium hydrogen phosphate and sodium nitrate sprays, and in fungal population by 2, 4-D and sodium nitrate sprays were observed in sorghum rhizosphere whereas in sunnhemp 2, 4-D and sodium nitrate sprays increased the bacterial, actinomycetes and fungal populations.     

Influence of plant species on population dynamics, genotypic diversity and antibiotic production in the rhizosphere by indigenous Pseudomonas spp

The population dynamics, genotypic diversity and activity of naturally-occurring 2,4-diacetylphloroglucinol (DAPG)-producing Pseudomonas spp. was investigated for four plant species (wheat, sugar beet, potato, lily) grown in two different soils. All four plant species tested, except lily and in some cases wheat, supported relatively high rhizosphere populations (5 x 10(4) to 1 x 10(6) CFU/g root) of indigenous DAPG-producing Pseudomonas spp. during successive cultivation in both a take-all suppressive and a take-all conducive soil. Although lily supported on average the highest population densities of fluorescent Pseudomonas spp., it was the least supportive of DAPG-producing Pseudomonas spp. of all four plant species. The genotypic diversity of 492 DAPG-producing Pseudomonas isolates, assessed by Denaturing Gradient Gel Electrophoresis (DGGE) analysis of the phlD gene, revealed a total of 7 genotypes. Some of the genotypes were found only in the rhizosphere of a specific plant, whereas the predominant genotypes were found at significantly higher frequencies in the rhizosphere of three plant species (wheat, sugar beet and potato). Statistical analysis of the phlD(+) genotype frequencies showed that the diversity of the phlD(+) isolates from lily was significantly lower than the diversity of phlD(+) isolates found on wheat, sugar beet or potato. Additionally, soil type had a significant effect on both the phlD(+) population density and the phlD(+) genotype frequencies, with the take-all suppressive soil being the most supportive. HPLC analysis further showed that the plant species had a significant effect on DAPG-production by the indigenous phlD(+) population: the wheat and potato rhizospheres supported significantly higher amounts of DAPG produced per cell basis than the rhizospheres of sugar beet and lily. Collectively, the results of this study showed that the host plant species has a significant influence on the dynamics, composition and activity of specific indigenous antagonistic Pseudomonas spp.     

Plant induced alteration in the rhizosphere and the utilisation of soil heterogeneity

Plant-soil interactions result in a special rhizosphere soil chemistry, differing from that of the bulk soil found only a few mm from the root. The aim of this study was to investigate adaptation mechanisms of herbs growing in acid soils through studying their rhizosphere chemistry in a greenhouse experiment and in a field study. Ten herbs were grown in acid soil (pH 4.2 in the soil solution) in the greenhouse. The concentrations of NO₃ ^-, SO₄ ^2-, phosphates, Ca²⁺, Mg²⁺, Mn²⁺, K⁺, Na⁺, NH₄ ⁺ and pH were analysed in soil solutions obtained by centrifugation. The general pattern found was a depletion of nutrients in the rhizosphere compared with their concentrations in the bulk soil. The pH increase (up to 0.7 units) in the rhizosphere soil appeared to be caused by plant uptake of NO₃ ^- (r²=0.88). The ion concentrations in the soil solution of the rhizosphere were dependent on plant species and biomass increase. Although species with a larger biomass and higher growth rates showed a higher degree of ion depletion (except for Na⁺, SO₄ ^2-) in the rhizosphere, there were also species specific responses. A field study of five herbs at five oak forest sites in Southern Sweden (Scania) was also carried out. In addition to the soil solution concentrations, the loss on ignition (LOI) and the concentrations of 0.1 M BaCl₂ extractable K⁺, Mg²⁺, Mn²⁺, Ca²⁺, and Al ions were measured. The amount of soil solution Al was determined as free ionic (quickly reacting) Al. For all species and sites, the LOI and the concentrations of exchangeable cations were higher in the rhizosphere than in the bulk soil, apparently due to the roots preferably growing at organic-rich microsites. The concentrations of the ions as measured in the centrifuged soil solution, were either higher in the rhizosphere than in the bulk soil or were the same in both, except for NO₃ ^- and quickly reacting Al. The lower concentrations of quickly reacting Al in the rhizosphere, compared with the bulk soil could indicate the uptake of Al by the plant or the exudation of complexing substances. The pH differences were only small and mostly non-significant. Plant-soil interactions and the ability of plants to utilise heterogeneity of the soil appear to be more important for plant growth in acid soils than recognised heretofore. Rhizosphere studies provide an important means of understanding plant strategies in acid soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

定殖植物根内和根围放线菌的分离鉴定及其体外抑菌促生效应

【目的】旨在分离、筛选并鉴定体外具抑菌促生作用的定殖于植物根内和根围的放线菌,以期丰富放线菌种质资源,为研制植物病害生防菌剂提供技术依据。【方法】采用稀释涂布平板法分离盐碱地、湿地、工业污染土壤中优势植物根内及其根围中的放线菌;通过平板对峙试验筛选具有抑菌效应的菌株,进而采用Salkowski比色法、CAS平板检测法和无氮源培养法进一步检测抑菌菌株的促生作用;通过形态观测、生理生化特性检测及16SrRNA基因序列分析鉴定菌种。【结果】共分离到链霉菌属(Streptomyces)、诺卡氏菌属(Nocardia)和小单孢菌属(Micromonospora) 3属共283株定殖于植物根内和根围的放线菌,3个采样地中湿地数量最多,均为根围土根内;其中链霉菌属占总数的77%,可分为10个类群。经筛选获得7株抑菌活性和促生效应较强的菌株,其中菌株H6-1抑菌效应最大,其无菌发酵液对尖孢镰刀菌(Fusariumoxysporum)、禾谷镰刀菌(Fusariumgraminearum)、灰葡萄孢菌(Botrytis cinerea)、立枯丝核菌(Rhizoctoniasolani)、轮纹大茎点霉(Macrophomakawatsukai)和瓜类炭疽菌(Colletotrichumorbiculare)的抑制率分别为32.3%、42.6%、48%、72.2%、58.1%和60.5%;而D11-4菌株的促生作用最强,能产吲哚乙酸(22.3 mg/L)、产铁载体(晕圈直径25.2 mm)和固氮。经鉴定这7株放线菌是吸水链霉菌变种(Streptomyces angustmyceticus) H4-6、娄彻氏链霉菌(Streptomyces rochei) S2-2、浑圆链霉菌(Streptomycesglobosus)H6-1、(Streptomycesiakyrus)GD8-4、波卓链霉菌(Streptomyces bottropensis) GH8-6、(Streptomyces paradoxus) H8-2和(Streptomyces coralus) D11-4。【结论】三个生境中定殖于植物根内和根围的放线菌类群丰富且所筛选获得的7株放线菌具有生防潜力,值得进一步研发。