刺槐林魔芋健康高产的土壤微生态机制

通过对刺槐林和农田魔芋健株根区、根表及根外土壤微生物区系及养分含量比较,探索刺槐林魔芋健康高产的土壤微生态机制。结果表明:(1)刺槐林魔芋根外和根表土壤细菌数量分别较农田增加11.8%和588.9%,根区土壤真菌数量较农田显著减少74.4%。(2)刺槐林魔芋根区、根表及根外土壤中的有益优势微生物数量及其比例远高于农田魔芋,有害微生物数量远低于农田魔芋;在刺槐林魔芋根区、根表及根外土壤中,3种优势细菌为放射型根瘤菌(Rhizobium radiobacter)、苏云金芽孢杆菌(Bacillus thuringiensis)及摩氏假单胞菌(Pseudomonas mosselii),其中,根表土壤中放射型根瘤菌及苏云金芽孢杆菌数量分别为农田的25.7倍及13.0倍;2种优势真菌为黒附球菌(Epicoccum nigrum)和疣孢青霉(Penicillium verruculosum),1种优势放线菌为绿淀粉酶链霉菌(Streptomyces viridodiastaticus),其中刺槐林魔芋根表和根外土壤中黒附球菌数量分别较农田高159.2%和120.3%;大量存在于刺槐林下魔芋根外土壤中的疣孢青霉、以及根区、根表、根外土壤中的绿淀粉酶链霉菌在农田魔芋相应部位均未检出。(3)刺槐林下魔芋根外、根区土壤有机质含量分别较农田显著增加167.6%、39.6%,但速效P、K含量较农田分别显著降低85.6%~91.3%、12.4%~13.0%。研究认为,刺槐林魔芋健康高产与其根区、根表及根外土壤中特有的有益优势微生物数量多、有害微生物数量少以及土壤有机质含量高密切相关。     

Occurrence of Salt, pH, and Temperature-tolerant, Phosphate-solubilizing Bacteria in Alkaline Soils

An ecological survey was conducted to characterize 4800 bacterial strains isolated from the root-free soil, rhizosphere, and rhizoplane of Prosopis juliflora growing in alkaline soils. Of the 4800 bacteria, 857 strains were able to solubilize phosphate on plates. The incidence of phosphate-solubilizing bacteria (PSB) in the rhizoplane was highest, followed by rhizosphere and root-free soil. Eighteen bacterial strains out of 857 PSB were able to produce halo at 30°C in a plate assay in the presence of 5% salt (NaCl) and solubilize tricalcium phosphate in National Botanical Research Institute's phosphate growth medium (NBRIP) broth, in the presence of various salts, pHs, and temperatures. Among the various bacteria tested, NBRI4 and NBRI7 did not produced halo in a plate assay at 30°C in the absence of salt. Contrary to indirect measurement of phosphate solubilization by plate assay, the direct measurement of phosphate solubilization in NBRIP broth assay always resulted in reliable results. The phosphate solubilization ability of NBRI4 was higher than in the control in the presence of salts (NaCl, CaCl₂, and KCl) at 30°C. Phosphate solubilization further increased in the presence of salts at 37°C as compared with 30°C. At 37°C, CaCl₂ reduced phosphate solubilization ability of NBRI4 compared with the control. The results indicated the role of calcium salt in the phosphate solubilization ability of NBRI4. Received: 9 March 1999 / Accepted: 16 April 1999     

Comparative identification by fatty acid analysis of soil,rhizosphere, and geocarposphere bacteria of peanut (Arachis hypogaea L.)

Bacterial isolates were collected from the geocarposphere, rhizosphere, and root-free soil of field grown peanut (Arachis hypogaea L.) at three sample dates, and the isolates were identified by analysis of fatty acid methyl-esters to determine if qualitative differences exist among the bacterial microflora of these zones. Five bacterial genera were associated with isolates from soil, while pod and root isolates constituted 16 and 13 genera, respectively, indicating that bacterial diversity was higher in the rhizosphere and geocarposphere than in soil. The dominant (most frequently identified) genus across all three samples dates was Flavobacterium, for pods, Pseudomonas for roots, and Bacillus, for root-free soil. Sixteen bacterial taxa were only isolated from the geocarposphere, 7 only from the rhizosphere, and 5 only from soil. These results show that specific bacterial taxa are preferentially adapted to colonization of the geocarposphere and suggest that the soil, rhizosphere, and geocarposphere constitute three distinct ecological niches. Bacteria which colonize the geocarposphere should be examined as potential biological control agents for pod-invading fungi such as the toxigenic strains of Aspergillus flavus and A. parasiticus.     

Effects of antibiotics in soil on the population dynamics of transposon Tn5 carrying Pseudomonas fluorescens

The effects of kanamycin and streptomycin added to soil on the survival of transposon Tn5 modified Pseudomonas fluorescens strain R2f were investigated. Kanamycin in high (180 g g^-1 dry soil) or low (18 g g^-1) concentration or streptomycin in low concentration in Ede loamy sand soil had no noticeable effect on inoculant population dynamics in soil and wheat rhizosphere, whereas streptomycin in high concentration had a consistent significant stimulatory effect, in particular in the wheat rhizosphere. Streptomycin exerted its effect by selecting P. fluorescens with Tn5 insertion whilst suppressing the unmodified sensitive parent strain, as evidenced by comparing the behaviour of these two strains in separate and mixed inoculation studies.Soil textural type influenced the effect of streptomycin on the Tn5 carrying inoculant; the effect was consistently detected in rhizosphere and rhizoplane samples of wheat grown in Ede loamy sand after 7 and 14 days incubation, whereas it was only apparent after 7 days in rhizoplane or rhizosphere (and bulk soil) samples of wheat grown in two silt loam soils. Modification of soil pH by the addition of CaCO₃ or bentonite clay resulted in an enhancement of the selective effect of streptomycin by CaCO₃ and its abolishment by bentonite clay.The addition to soil of malic acid or wheat root exudate, but not of glucose, enhanced the streptomycin selective effect on the Tn5-modified P. fluorescens strain. Neither the streptomycin producer Streptomyces griseus nor two non-inhibiting mutants obtained following UV irradiation affected the dynamics of P. fluorescens (chr::Tn5) in soil and wheat rhizosphere.The effect of streptomycin in soil on inoculant Tn5 carrying bacteria depends on conditions such as soil type, the presence of (wheat) root exudates and the type of available substrate.     

Bacterial flora in the rhizosphere of sugarcane plant,Saccharum officinarum

Streptomycin-resistant bacteria were recovered from the root-free soils under sugarcane plants. Nitrosomonas species and Azotobacter chrococcum were also present in greater numbers in rhizosphere soils as compared to root-free soils up to 30 cm deep.The author is with the Department of Biosciences, P.G. Science College, Bardoli-394602, Dist. Surat, Gujarat, India.     

PYRENE EFFECTS ON RHIZOPLANE BACTERIAL COMMUNITIES

Certain plant species promote biodegradation of polycyclic aromatic hydrocarbons (PAHs), but few studies have examined the microbial populations that are associated with the rhizoplane of these plants. In this study, the bacterial composition of the rhizoplane were characterized for four plant species during in soils with different histories of exposure to PAH and in the presence or absence of a pyrene spike at 100 mg kg^?1 pyrene. Three of the plant species including Andropogon gerrardii, Panicum coloratum and Melilotus officinalis were known to stimulate PAH degradation. Wheat (Triticum aestivum) was used as a reference species. Results showed that after 90 days, approximately 45% of the pyrene spike disappeared from soil without plants. In contrast, cultivation of plants resulted in 95% disappearance of pyrene. There were no significant differences in the extent of pyrene disappearance for different plants. In all cases, 16S rRNA gene profiles of the rhizoplane were less complex in the pyrene-spiked soils, suggesting that richness and evenness of the predominant bacteria were reduced. Our results show that pyrene contamination results in significant shifts in the composition of rhizosphere bacterial communities that are still further influenced by the plant species and prior exposure history to PAH contamination.     

Host plant changes produced by the aphid Sipha flava: consequences for aphid feeding behaviour and growth

Induced plant responses may affect the behaviour and growth of the attacking herbivore insect. The aphid Sipha flava (Forbes) produces reddish spots on the infested leaf of its host plant Sorghum halepense (L.). In order to assess the consequences on the aphid of this presumptive induced plant response, we studied the feeding behaviour and growth of S. flava on previously infested and non-infested leaves of S. halepense. Considering that the reddish pigment could play a defensive role, its effect on aphid survival was determined in artificial diets. In addition, changes in the histology of the leaf and the chemical nature of the induced pigment were also studied. Aphids devoted a significantly shorter total time to non-penetration activities in infested than in non-infested leaves. Time before the first phloem ingestion tended to be shorter in infested leaves. The mean relative growth rate of S. flava nymphs was significantly higher on infested than on non-infested leaves. Survival of aphids on diet containing the reddish extract was not significantly different from that on the control diet. Infestation of S. halepense by S. flava produced a reddish coloration in the leaf, which was identified as an anthocyanin by UV-visible spectrometry. Light microscopy showed that only mesophyll cells of previously infested plants presented swelled, dispersed, and heterogeneously stained chloroplasts with a higher accumulation of starch granules, no grana arranged in stacks, and reduction in the amount of inner membranes (thylakoids), relatively to chloroplasts of non-infested leaves. Scanning electron micrographs of leaf surface revealed reduced presence of crystalline epicuticular waxes of epidermal cells in infested leaves as compared to non-infested ones. The main conclusion is that the attack of S. flava to S. halepense leaves induced plant susceptibility where aphid feeding behaviour and growth were both enhanced on previously infested leaves.     

Colonization of plant rhizosphere by actinomycetes of different genera

The survival of environmental isolates of actinomycetes introduced with the seeds of agricultural plants in the root-free soil and in the rhizosphere and rhizoplane was studied. Different strategies of colonization of the rhizosphere were revealed for the representatives of the genera Streptomyces, Micromonospora, and Streptosporangium, the organisms typical for the moderate climate rhizosphere. The plants of winter rye (Secale cereale L.) inoculated with actinomycetes were shown to have growth advantages, while the cow clover plants (Trifolium pratense L.) had no growth advantages compared to uninoculated plants. The role of the plant component in the interaction with mycelial prokaryotes is discussed.     

Colonization of plant rhizosphere by actinomycetes of different genera

The survival of environmental isolates of actinomycetes introduced with the seeds of agricultural plants in root-free soil and in the rhizosphere and rhizoplane was studied. Different strategies of colonization of the rhizosphere were revealed for the representatives of the genera Streptomyces, Micromonospora, and Streptosporangium, organisms typical for the moderate climate rhizosphere. The plants of winter rye (Secale cereale L.) inoculated with actinomycetes were shown to have growth advantages, while the cow clover plants (Trifolium pratense L.) had no growth advantages compared to uninoculated plants. The role of the plant component in the interaction with mycelial prokaryotes is discussed.     

Artificial induction of the apple replant problem byPenicillium claviforme inoculation

Inoculation of apple seedling roots withPenicillium claviforme reduced plant growth and resulted in morphological changes of roots resembling those found in seedlings growing in ‘apple replant problem’ soil (apple-sick soil). The introduced fungus persisted in the rhizosphere throughout the 30-month test period. The numbers of colony-forming units (CFU) ofPenicillium claviforme, as well as the ‘total’ number of CFU of micromycetes, were higher in the rhizoplane of the inoculated seedling in comparison with uninoculated plants. The numbers of CFU of phytotoxic micromycetes in the rhizosphere soil of inoculated seedlings were also proportionally higher. Apple tree growth was also reduced when seedlings were inoculated with the flucrescent bacteriumPseudomonas putida; however, no morphological changes were observed in the roots. Both micro-organisms introduced into the apple seedling rhizosphere caused changes in the microbial community. Inoculation withPenicillium claviforme andPseudomonas putida caused a decrease in the number of mycolytic bacteria in the rhizoplane of apple seedlings.     

Searching and Oviposition Behavior of Anagrus atomus L. (Hymenoptera: Mymaridae) on Four Host Plants of Its Host, the Green Leafhopper Empoasca decipiens Paoli (Homoptera: Cicadellidae)

Anagrus atomus L. is an important egg parasitoid of the green leafhopper Empoasca decipiens Paoli. In this study the ability of the parasitoid to locate and parasitize its host was investigated on four host plants, i.e., broad beans (Vicia faba L.), sweet pepper (Capsicum annuum L.), cucumber (Cucumis sativus L.), and French beans (Phaseolus vulgaris L.). For each plant species, the behavior of the parasitoid was observed on E. decipiens infested and noninfested plants. Searching and oviposition behavior were characterized by drumming, probing, and resting. Parasitoids spent significantly less time on non-infested than infested plants, 274.5 and 875.7 s, respectively, and no probing behavior was observed on non-infested plants. Frequency of resting behavior was significantly greater on non-infested than on infested plants. Total foraging time was significantly longer on infested than on non-infested plants, indicating that A. atomus females can efficiently discriminate between leaves with and without infestation. Parasitism of A. atomus was influenced by parasitoid density, with the highest parasitism rate (64.0%) obtained at a density of 10 A. atomus females/0.1356 m² but the number of parasitized eggs per female and the searching efficiency decreased with increasing parasitoid density.     

Microbial Growth and Carbon Use Efficiency in the Rhizosphere and Root-Free Soil

Plant-microbial interactions alter C and N balance in the rhizosphere and affect the microbial carbon use efficiency (CUE)–the fundamental characteristic of microbial metabolism. Estimation of CUE in microbial hotspots with high dynamics of activity and changes of microbial physiological state from dormancy to activity is a challenge in soil microbiology. We analyzed respiratory activity, microbial DNA content and CUE by manipulation the C and nutrients availability in the soil under Beta vulgaris. All measurements were done in root-free and rhizosphere soil under steady-state conditions and during microbial growth induced by addition of glucose. Microorganisms in the rhizosphere and root-free soil differed in their CUE dynamics due to varying time delays between respiration burst and DNA increase. Constant CUE in an exponentially-growing microbial community in rhizosphere demonstrated the balanced growth. In contrast, the CUE in the root-free soil increased more than three times at the end of exponential growth and was 1.5 times higher than in the rhizosphere. Plants alter the dynamics of microbial CUE by balancing the catabolic and anabolic processes, which were decoupled in the root-free soil. The effects of N and C availability on CUE in rhizosphere and root-free soil are discussed.     

独山子区优势草本植物根际与非根际土壤微生物功能多样性

以独山子区3种优势草本植物的根际与非根际土壤为研究对象,采用Biolog-ECO微平板法对土壤微生物功能多样性进行了研究。结果表明:3种不同植物根际与非根际土壤微生物代谢活性(AWCD)、丰富度指数Shannon(H)和均匀度指数Mc Intosh(U)均存在不同差异,且博乐蒿根际土壤微生物功能多样性均优于非根际土壤及其他两种植物;根际土壤微生物对糖类、脂类、酸类和胺类碳源物质比较敏感,非根际土壤微生物敏感于酸类、氨基酸类以及糖类碳源,根际土壤微生物对碳源的利用能力更强,且不同植物根际环境微生物碳源利用特征不同;微生物活性、丰富度指数和微生物均匀度指数与土壤pH值、SOM、AP和NO-3-N存在显著正相关(P0.05);博乐蒿根际土壤养分含量与微生物活性均较高,对环境的适应性更强,在独山子区生态环境管理与建设中可对其进行关注。     

Microbial Complexes Occurring on the Apogeotropic Roots and in the Rhizosphere of Cycad Plants

The microbial complexes of soil, the rhizosphere, and the rhizoplane of the apogeotropic (coralloid) roots of cycad plants were comparatively studied. The aseptically prepared homogenates of the surface-sterilized coralloid roots did not contain bacterial microsymbiont, indicating that in the root tissues the symbiosis is a two-component one (plant–cyanobacteria). At the same time, associated bacteria belonging to different taxonomic groups were detected in increasing amounts in the cycad rhizoplane, rhizosphere, and the surrounding soil. The bacterial communities found in the cycad rhizoplane and the surrounding soil were dominated by bacteria from the genus Bacillus. The saprotrophic bacteria and fungi colonizing the cycad rhizosphere and rhizoplane were dominated by microorganisms capable of degrading the plant cell walls. The local degradation of the cell wall was actually observed on the micrographs of the thin sections of cycad roots in the form of channels through which symbiotic cyanobacterial filaments can penetrate into the cortical parenchyma.     

Root-induced increases in soil pH and nutrient availability to field-grown cereals and legumes on acid sandy soils of Sudano-Sahelian West Africa

A field experiment with millet (Pennisetum glaucum L.), sorghum [Sorghum bicolor (L.) Moench], cowpea (Vigna unguiculata L.) and groundnut (Arachnis hypogeae L.) was conducted on severely P-deficient acid sandy soils of Niger, Mali and Burkina Faso to measure changes in pH and nutrient availability as affected by distance from the root surface and by mineral fertiliser application. Treatments included three rates of phosphorus (P) and four levels of nitrogen (N) application. Bulk, rhizosphere and rhizoplane soils were sampled at 35, 45 and 75 DAS in 1997 and at 55 and 65 DAS in 1998. Regardless of the cropping system and level of mineral fertiliser applied, soil pH consistently increased between 0.7 and two units from the bulk soil to the rhizoplane of millet. Similar pH gradients were observed in cowpea, but pH changes were much smaller in sorghum with a difference of only 0.3 units. Shifts in pH led to large increases in nutrient availability close to the roots. Compared with the bulk soil, available P in the rhizoplane was between 190 and 270% higher for P-Bray and between 360 and 600% higher for P-water. Exchangeable calcium (Ca) and magnesium (Mg) levels were also higher in the millet rhizoplane than in the bulk soil, whereas exchangeable aluminium (Al) levels decreased with increasing pH close to the root surface. The results suggest an important role of root-induced pH increases for crops to cope with acidity-induced nutrient deficiency and Al stress of soils in the Sudano-Sahelian zone of West Africa. This revised version was published online in June 2006 with corrections to the Cover Date.     

Types and properties of some bacteria isolated from hypersaline soils

Five rhizosphere soil samples from the dominant xerophytic plants, and nearby root-free soil samples were obtained from a series of hypersaline soils (5.0–10.7% NaCl) from sites near Alicante in Spain. Physico-chemical analyses were made, and the bacterial flora estimated using three different plating media. Counts from rhizosphere soil were always significantly higher than those from root-free soils. A total of 211 strains isolated were purified and identified to genus level; 12 could not be classified. The range of salt concentration allowing growth was determined for each isolate, but this did not correlate with the salt content of the soil habitat. Most isolates appeared to be typical moderate halophiles (with optimum growth between 5 and 15% salts), but about half of them grew on normal media with only 0.9% naCl, a notable difference from moderately halophilic aquatic bacteria. Extreme halophiles were rare but this may have been due to an insufficient incubation period.     

黄河三角洲不同类型盐生植物土壤真菌群落结构特征

盐生植物种类及其所具有的不同耐盐调节方式影响着根际微生物群落的结构与组成。为明确不同类型盐生植物根际与非根际土壤中真菌群落结构与组成的差异及其与土壤环境间的相互关系,该研究采集了黄河三角洲地区芦苇、盐地碱蓬、獐毛3种不同类型盐生植物0～20 cm土层的根际和非根际土壤,通过高通量测序对其真菌群落多样性和结构进行了分析,以探究真菌群落特征与土壤理化因子间的关系。结果表明：(1)3种不同类型盐生植物根际土壤真菌群落丰富度显著大于各自非根际土,且獐毛根际土壤真菌群落丰富度显著大于芦苇和盐地碱蓬的根际土。(2)距离热图分析表明,芦苇和盐地碱蓬非根际土壤真菌群落间的相似性最大。(3)土壤真菌多样性和丰富度与土壤总碳、总氮、有效磷、pH呈正相关关系,与土壤盐分含量呈负相关关系。(4)3种不同类型盐生植物的根际与非根际土壤中,球囊菌门(Glomeromycota)均为绝对优势门,盾巨孢囊霉属(Scutellospora)为优势属。(5)RDA分析表明,土壤盐分含量是影响土壤真菌群落结构的重要因子,球囊菌门丰度与土壤总氮、总碳、有效磷、有机碳、pH呈正相关关系,与盐分呈负相关关系。(6)植物土壤真菌群...     

Survival ofXanthomonas campestris pv.vesictoria in pepper seeds and roots in symptomless and dry leaves in non-host plants and in the soil

Summary A population ofXanthomonas campestris pv.vesicatoria developed as endophytes in the leaves and rhizosphere of apparently symptomless plants grown under mist but not under dry conditions. The pathogen survired for long periods on, and could be isolated from, the surface of infested dried seeds, inoculated sandy loam soil, dried leaves, and the rhizosphere of pepper and of other non-host plants. In addition, small numbers of the pathogen survived for 18 months in a field previously cropped with pepper diseased with bacterial scab. Healthy nursery or mature plants developed symptoms while growing in soil containing infested leaves, either buried or placed on the soil surface.     

Impact of flooding on soil bacterial communities associated with poplar (Populus sp.) trees

Soil bacterial communities were analyzed in different habitats (bulk soil, rhizosphere, rhizoplane) of poplar tree microcosms (Populus tremulaxP. alba) using cultivation-independent methods. The roots of poplar trees regularly experience flooded and anoxic conditions. Therefore, we also determined the effect of flooding on microbial communities in microcosm experiments. Total community DNA was extracted and bacterial 16S rRNA genes were amplified by PCR and analyzed by terminal restriction fragment length polymorphism (T-RFLP) analysis, cloning and sequencing. Clone libraries were created from all three habitats under both unflooded and flooded conditions resulting in a total of 281 sequences. Numbers of different sequences (<97% similarity) in the different habitats represented 16-55% of total bacterial species richness determined from the nonparametric richness estimator Chao1. According to the number of different terminal restriction fragments (T-RFs), all of the different habitats contained approximately 20 different operational taxonomic units (OTUs), except the flooded rhizoplane habitat whose community contained less OTUs. Results of cloning and T-RFLP analysis generally supported each other. Correspondence analysis of T-RFLP patterns showed that the bacterial communities were different in bulk soil, rhizosphere and rhizoplane and changed upon flooding. For example OTUs representing Bacillus sp. were highest in the unflooded bulk soil and rhizosphere. Sequences related to Aquaspirillum, in contrast, were predominant on the poplar roots and in the rhizosphere of flooded microcosms but were rarely found in the other habitats.     

Avian pest control in tea plantations of sub-Himalayan plains of Northeast India: Mixed-species foraging flock matters

This study reports on the biocontrol role birds play in caterpillar pest control of tea plantations of Northeast India. In this area large tracts of tea plantations have been extensively defoliated by the recent invasion of two forest-dwelling geometrid looper caterpillars, Hyposidra spp. and a lymantriid hairy caterpillar, Arctornis submarginata. This exacerbated tea herbivory by two resident pest caterpillars, Biston suppressaria and Eterusia magnifera. Currently there are no identified resident insect predators for any life stage of Hyposidra spp. and A. submarginata. Larvae of these pests drop from tea bushes using salivary thread, allowing caterpillars to escape from insect predators. The study identified 38 native insectivorous bird species in tea plantations, of which four species (Asian-pied starling, Chestnut-tailed starling, Jungle Myna, Red-vented Bulbul) could be potential control agents of looper and hairy caterpillar pests. These species had high population densities. Their cumulative abundances represented a major proportion of the total bird community during both the infested (86.44%) and non-infested phase (75.34%). They foraged in mixed-species flocks in both tea foliage and on the ground. This behavior is suited to capture foliage-living and dropped caterpillars that were flushed from tea bushes by foraging birds. Abundance and species richness of overall tea layer-foraging birds were higher in infested phase when compared to non-infested phase. The predation rate of four bird species of the foraging flock varied significantly. These results suggest that birds should be considered as important biological control agent of caterpillar pests of tea and considered in pest management plans.