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1.
We performed a controlled experiment with rice seedlings (Oryza sativa L.) growing in Petri dishes on homogeneous nutrient agar containing a simple rhizosphere food web consisting of a diverse bacterial community and a common soil protozoa, Acanthamoeba castellanii, as bacterial grazer. Presence of amoebae increased bacterial activity and significantly changed the community composition and spatial distribution of bacteria in the rhizosphere. In particular, Betaproteobacteria did benefit from protozoan grazing. We hypothesize that the changes in bacterial community composition affected the root architecture of rice plants. These effects on root architecture affect a fundamental aspect of plant productivity. Root systems in presence of protozoa were characterized by high numbers of elongated (L-type) laterals, those laterals that are a prerequisite for the construction of branched root systems. This was in sharp contrast to root system development in absence of protozoa, where high numbers of lateral root primordia and short (S-type) laterals occurred which did not grow out of the rhizosphere region of the axile root. As a consequence of nutrient release from grazed bacteria and changes in root architecture, the nitrogen content of rice shoots increased by 45% in presence of protozoa. Our study illustrates that interactions over three trophic levels, i.e. between plants, bacteria and protozoa significantly modify root architecture and nutrient uptake by plants. 相似文献
2.
Soil salinity is a major factor relating microbial communities to environmental stress in the microbial selection process as stress can reduce bacterial diversity. In the San Joaquin Valley (SJV) of California, the problem of increasing salinity and consequently, decreasing crop productivity, due to reuse of saline drainage water are major concerns. An experiment was conducted in a closed, recirculating volumetric lysimeter system (VLS) consisting of 24 experimental plant growth units to determine the interactive effects of salinity, boron and pH on rhizosphere and non-rhizosphere microbial composition of cucumber (Cucumis sativus L. cv. Seminis Turbo hybrid). Plants in the VLS were irrigated from individual reservoirs containing a modified half-strength Hoagland's nutrient solution combined with salinity, boron (B), and pH treatments. The results indicated that salinity and pH were the most influential factors affecting the growth of plants and the effect of boron on the plant was more severe under slightly acidic conditions. Total bacterial DNA was extracted from rhizosphere and non-rhizosphere samples, and a 236-bp DNA fragment in the V3 region of the small subunit ribosomal RNA genes of eubacteria was amplified. The 16S rRNA and the products were subjected to denaturing gradient gel electrophoresis (DGGE) and sequencing. Analyses of bacterial diversity showed that the effects of salinity, boron, and pH were more severe on the rhizosphere bacterial population during the first week of growing cucumber, with decreasing impacts with plant growth. However, there was no salinity-B-pH interaction effects on plant biomass, but the effects were seen in the number of heterotrophic bacteria in the rhizosphere and on species richness and diversity during week seven of the study. These suggest that the effects of salinity-B-pH interactions may influence microorganisms first before plants and may pose long term effects on soil quality. 相似文献
3.
Anat Lerner Ezekiel Baudoin Yvan Moenne-Loccoz Edouard Jurkevitch 《Soil biology & biochemistry》2006,38(6):1212-1218
Nucleic acid-based techniques allow the exploration of microbial communities in the environments such as the rhizosphere. Azospirillumbrasilense, a plant growth promoting rhizobacterium (PGPR), causes morphological changes in the plant root system. These changes in root physiology may indirectly affect the microbial diversity of the rhizosphere. In this study, the changes in the rhizobacterial structure following A. brasilense inoculation of maize (Zea mays) plants was examined by PCR-denaturating gradient gel electrophoresis (DGGE) and automated ribosomal intergenic spacer analysis (ARISA), using two universal primers sets for the 16S rRNA gene, and an intergenic 16S-23S rDNA primer set, respectively. Similar results were obtained when using either ARISA or DGGE performed with these different primer sets, and analyzed by different statistical methods: no prominent effect of A. brasilense inoculation was observed on the bacterial communities of plant roots grown in two different soils and in different growth systems. In contrast, plant age caused significant shifts in the bacterial populations. 相似文献
4.
Kristin Krome Katja Rosenberg Michael Bonkowski Stefan Scheu 《Soil biology & biochemistry》2009,41(9):1866-1873
Plant roots are densely colonized by bacteria which form the basis of the rhizosphere bacterial food web with protozoa as most effective predators. We established a well defined laboratory system with Arabidopsis thaliana as model plant allowing to investigate in detail the effect of rhizosphere interactions on plant performance. We used this system to analyse separate and combined effects of natural rhizobacteria and the protozoa Acanthamoeba castellanii on plants.Protozoa and bacteria increased plant growth with the effect of protozoa markedly exceeding that of bacteria only. Arabidopsis immediately responded to the presence of protozoa by increasing carbon but not nitrogen uptake. Later protozoa enhanced plant uptake of nitrogen from organic material and prolonged vegetative growth of Arabidopsis resulting in strongly increased seed production. It is concluded that the immediate plant response was based on changes in rhizosphere signalling inducing increased plant carbon fixation rather than on protozoa-mediated increase in nitrogen availability. The subsequently increased plant nitrogen uptake presumably originated from nitrogen fixed in bacterial biomass made available by protozoan grazing, i.e. the microbial loop in soil. The results suggest that Arabidopsis prepared for the upcoming mobilization of nitrogen by increasing carbon fixation and root carbon allocation which paid-off later by increased nutrient capture and strongly increased plant reproduction. 相似文献
5.
Mette Vestergård 《Pedobiologia》2004,48(3):257-265
Nematodes from rhizosphere soil of barley grown at three fertiliser treatments (control (0), NK and NPK) were studied in a field experiment. Sampling was done twice, during vegetative growth and flowering, respectively, to determine how fertiliser effects on nematode assemblages depended on plant growth phase. At the growth stage the proportion of fungal feeding nematodes (dominated by Aphelenchoides spp. and Aphelenchus sp.) was highest in NK. During flowering, the abundance and proportion of fungal feeders in the 0 and NPK plots had increased and reached a level similar to the NK plot. Overall densities of bacterial feeders (mainly Cephalobidae and Rhabditidae) were similar, but opportunistic bacterial feeders constituted a higher proportion in the fertilised plots compared to the unfertilised. Ectoparasitic plant feeders (Tylenchorhynchus sp.) were more numerous in NK and NPK than in the control at both sampling dates. Endoparasite (Pratylenchus spp.) numbers were lower in the NPK plot at the growth stage. Numbers of Tylenchidae increased between samplings. The classification of Tylenchidae as epidermal cell and root hair feeders as opposed to hyphal feeders is discussed. Results thus indicate that: (i) bacterial and especially fungal feeding nematodes are stimulated by unbalanced fertilisation; (ii) ectoparasitic plant feeders are stimulated by N-fertilisation, while migratory endoparasites are inhibited at high and balanced fertilisation; (iii) nutrient effects diminish after plants reach the flowering stage. 相似文献
6.
Rice plants (Oryza sativa L.) were grown in microcosms containing soil with a diverse bacterial community (control) and inoculated either with an axenic arbuscular mycorrhizal fungus (Glomus intraradices) or an axenic inoculum of protozoan grazers of bacteria (Acanthamoeba castellanii), or both, in a factorial design.Amoebae and mycorrhiza affected the root architecture of rice in opposite directions, with mycorrhiza reducing and protozoa increasing early root growth. Rice biomass did not increase in presence of mycorrhiza (×1.08), but strongly increased in presence of Acanthamoebae (×1.29). The positive effects of amoebae were always reduced when plants were also infected with mycorrhiza. Microbial biomass increased (×1.4) and microbial growth was less limited by phosphorus in presence of mycorrhiza. However, plant phosphorus uptake did not increase, rather, plant concentrations of carbon and nutrients decreased in presence of mycorrhiza, suggesting a sequestration of resources during the establishment of a mycorrhizal network. Amoebae strongly interacted with, and partly compensated for, the effects of mycorrhiza, demonstrating that interactions between AM fungi and the microbial food web in the rhizosphere significantly feed back on early plant performance. 相似文献
7.
The influence of inoculation of olive trees with arbuscular mycorrhizal (AM) fungi, Glomus (G) intraradices, on microbial communities and sugar concentrations, were examined in rhizosphere of olive trees (Olea europaea L.). Analyses of phospholipid and neutral lipid fatty acids (PLFA and NLFA, respectively) were then used to detect changes in microbial community structure in response to inoculation of plantlets with G. intraradices.Microscopic observations studies revealed that the extraradical mycelium of the fungus showed formation of branched absorbing structures (BAS) in rhizosphere of olive tree. Root colonization with the AM fungi G. intraradices induced significant changes in the bacterial community structure of olive tree rhizosphere compared to non-mycorrhizal plants. The largest proportional increase was found for the fatty acid 10Me18:0, which indicated an increase in the number of actinomycetes in mycorrhizal rhizosphere soil, whereas the PLFAs i15:0, a15:0, i16:0, 16:1ω7 and cy17:0 which were used as indicators of bacteria decreased in mycorrhizal treatment compared to non-mycorrhizal control treatment. A highest concentration of glucose and trehalose and a lowest concentration of fructose, galactose, sucrose, raffinose and mannitol were detected in mycorrhizal rhizosphere soil. This mycorrhizal effect on rhizosphere communities may be a consequence of changes in characteristics in the environment close to mycorrhizal roots. 相似文献
8.
《Applied soil ecology》2005,28(3):191-201
Annual plant species differ in their rhizosphere microbial community composition. However, rhizosphere communities are often investigated under controlled conditions, and it is unclear if perennial plants growing in the field also have rhizosphere communities that are specific to a particular plant species. The aim of our study was to determine the bacterial community composition of three species of Banksia (B. attenuata R. Brown, B. ilicifolia R. Brown and B. menziesii R. Brown) growing in close proximity in a native woodland in Western Australia and to relate community structure to function. All three species are small trees that produce cluster roots in the field following winter rains. Cluster roots and rhizosphere soil were sampled in early spring (August 2001) and again four weeks later (September 2001). Many new cluster roots were formed in the period between the August and the September sampling. Rhizosphere soil pH, percent soil moisture and C and N content did not differ significantly among species or sampling times. However, the bacterial community composition on the cluster roots and in the rhizosphere soil, studied by denaturing gradient gel electrophoresis (DGGE), differed among the three species, with cluster root age class (young or mature to senescing) and also between sampling times. These changes in community composition were accompanied by changes in the activity of some of the enzymes studied. The activities of β-glucosidase and protease increased over time. The three species differed in asparaginase activity, but not in the activity of acid and alkaline phosphatase in the rhizosphere. These results suggest a relationship between the changes in composition and function of bacterial communities. 相似文献
9.
The interaction between the salt marsh plant Spartina patens, arbuscular mycorrhizal fungi (AMF) and bacteria in salt marsh sediment was examined in a long-term arbuscular mycorrhizas (AM) suppression study by applying the systemic fungicide benomyl to field-collected sediment cores with and without S. patens plants. Microbial populations were sampled four times corresponding to major plant phenological stages (dormancy, vegetative growth, reproduction, and senescence) previously linked to changes in microbial populations under field conditions. Benomyl-treatment of soil cores significantly suppressed AM colonization on S. patens, keeping values relatively consistent throughout the growing season (11.5%) whereas plants in non-treated cores experienced seasonal increases and declines in AM colonization (26.6% during vegetative growth to 11.5% during dormancy). Soil physicochemical parameters were not affected by benomyl application. In unvegetated cores, no benomyl- or seasonal effects were displayed by cell numbers and specific biomass of DAPI-stained organisms, members of the domain bacteria and here especially members of the α-, β-, γ- and δ-subdivisions of proteobacteria that were the most abundant bacterial groups. In vegetated cores, the microbial community as well as specific bacterial populations were at least twice as large in terms of number and biomass than in samples from unvegetated cores with significant seasonal changes for DAPI-stained cells, for members of the domain bacteria and for members of the α- and γ-subdivisions of proteobacteria. In benomyl-treated cores, the population of γ-subdivision of proteobacteria was significantly smaller than in non-treated cores, and a positive association was found between this bacterial group and root length colonized by AM suggesting that AM-suppression can affect populations of specific soil bacterial populations in salt marsh sediment. Benomyl-treatment had no effect on the diversity of N-fixing bacteria as evidenced by PCR-RFLP analysis, but seasonal changes were noted in vegetated cores with populations during active plant growth substantially different from populations during dormancy and senescence. 相似文献
10.
The interactions between soil P availability and mycorrhizal fungi could potentially impact the activity of soil microorganisms and enzymes involved in nutrient turnover and cycling, and subsequent plant growth. However, much remains to be known of the possible interactions among phosphorus availability and mycorrhizal fungi in the rhizosphere of berseem clover (Trifolium alexandrinum L.) grown in calcareous soils deficient in available P. The primary purpose of this study was to look at the interaction between P availability and an arbuscular mycorrhizal (AM) fungus (Glomus intraradices) on the growth of berseem clover and on soil microbial activity associated with plant growth. Berseem clover was grown in P unfertilized soil (−P) and P fertilized soil (+P), inoculated (+M) and non-inoculated (−M) with the mycorrhizal fungus for 70 days under greenhouse conditions. We found an increased biomass production of shoot and root for AM fungus-inoculated berseem relative to uninoculated berseem grown at low P levels. AM fungus inoculation led to an improvement of P and N uptake. Soil respiration (SR) responded positively to P addition, but negatively to AM fungus inoculation, suggesting that P limitation may be responsible for stimulating effects on microbial activity by P fertilization. Results showed decreases in microbial respiration and biomass C in mycorrhizal treatments, implying that reduced availability of C may account for the suppressive effects of AM fungus inoculation on microbial activity. However, both AM fungus inoculation and P fertilization affected neither substrate-induced respiration (SIR) nor microbial metabolic quotients (qCO2). So, both P and C availability may concurrently limit the microbial activity in these calcareous P-fixing soils. On the contrary, the activities of alkaline phosphatase (ALP) and acid phosphatase (ACP) enzymes responded negatively to P addition, but positively to AM fungus inoculation, indicating that AM fungus may only contribute to plant P nutrition without a significant contribution from the total microbial activity in the rhizosphere. Therefore, the contrasting effects of P and AM fungus on the soil microbial activity and biomass C and enzymes may have a positive or negative feedback to C dynamics and decomposition, and subsequently to nutrient cycling in these calcareous soils. In conclusion, soil microbial activity depended on the addition of P and/or the presence of AM fungus, which could affect either P or C availability. 相似文献
11.
Annelies S. de Ridder-Duine George A. Kowalchuk Paulien J.A. Klein Gunnewiek Wiecher Smant Johannes A. van Veen Wietse de Boer 《Soil biology & biochemistry》2005,37(2):349-357
The relative importance of specific plant properties versus soil characteristics in shaping the bacterial community structure of the rhizosphere is a topic of considerable debate. Here, we report the results of a study on the bacterial composition of the rhizosphere of the wild plant Carex arenaria (sand sedge) growing at 10 natural sites in The Netherlands. The soil properties of the sandy soils at these sites were highly disparate, most notably in pH, chloride and organic matter content. Rhizosphere and bulk soil bacterial communities were examined by culture-independent means, namely, 16S rDNA-directed PCR-DGGE profiling. Large differences were observed between the bacterial communities of the different sites for both bulk and rhizosphere soil. Cluster analysis of bacterial profiles revealed that the rhizosphere community of each site was generally more closely related to the bulk soil community of that site rather than to rhizosphere communities of other sites. Hence, bacterial community structure within the rhizosphere of C. arenaria appeared to be determined to a large extent by the bulk soil community composition. This conclusion was supported by a reciprocal planting experiment, where C. arenaria shoots of different sites yielded highly similar rhizosphere communities when planted in the same soil. 相似文献
12.
Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments. 相似文献
13.
Arbuscular mycorrhizal (AM) fungi have been shown to induce the biocontrol of soilborne diseases, to change the composition of root exudates and to modify the bacterial community structure of the rhizosphere, leading to the formation of the mycorrhizosphere. Tomato plants were grown in a compartmentalized soil system and were either submitted to direct mycorrhizal colonization or to enrichment of the soil with exudates collected from mycorrhizal tomato plants, with the corresponding negative controls. Three weeks after planting, the plants were inoculated or not with the soilborne pathogen Phytophthora nicotianae growing through a membrane from an adjacent infected compartment. At harvest, a PCR-Denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments amplified from the total DNA extracted from each plant rhizosphere was performed. Root colonization with the AM fungi Glomus intraradices or Glomus mosseae induced significant changes in the bacterial community structure of tomato rhizosphere, compared to non-mycorrhizal plants, while enrichment with root exudates collected from mycorrhizal or non-mycorrhizal plants had no effect. Our results support that the effect of AM fungi on rhizosphere bacteria would not be mediated by compounds present in root exudates of mycorrhizal plants but rather by physical or chemical factors associated with the mycelium, volatiles and/or root surface bound substrates. Moreover, infection of mycorrhizal or non-mycorrhizal plants with P. nicotianae did not significantly affect the bacterial community structure suggesting that rhizosphere bacteria would be less sensitive to the pathogen invasion than to mycorrhizal colonization. Of 96 unique sequences detected in the tomato rhizosphere, eight were specific to mycorrhizal fungi, including two Pseudomonas, a Bacillus simplex, an Herbaspirilium and an Acidobacterium. One Verrucomicrobium was common to rhizospheres of mycorrhizal plants and of plants watered with mycorrhizal root exudates. 相似文献
14.
15.
Olga S. Correa Marcela S. Montecchia María F. Berti María C. Fernández Ferrari Norma L. Pucheu Norma L. Kerber Augusto F. García 《Applied soil ecology》2009,41(2):185-194
The increase in soybean productivity has contributed to a greater use of agrochemicals, which cause major problems, such as soil and water pollution and reduction of biodiversity, and have a negative impact on non-target species. The development of microbial biocontrol agents for soybean diseases can help to reduce pesticide abuse. Bacillus amyloliquefaciens BNM122 is a potential microbial biocontrol agent able to control the damping-off caused by Rhizoctonia solani when inoculated in soybean seeds, both in a plant growth chamber and in a greenhouse. In this study, we report the effect of soybean seed treatments with strain BNM122 or with two fungicides (thiram and carbendazim) on the structure and function of the bacterial community that colonizes the soybean rhizosphere. Also, soybean root nodulation by Bradyrhizobium japonicum, mycorrhization by arbuscular mycorrhizal fungi and plant growth were evaluated. We used the r- and K-strategist concept to evaluate the ecophysiological structure of the culturable bacterial community, community-level physiological profiles (CLPP) in Biolog? EcoPlates to study bacterial functionality, and the patterns of 16S RNA genes amplified by PCR and separated by denaturing gradient gel electrophoresis (PCR–DGGE) to assess the genetic structure of the bacterial community. Neither the ecophysiological structure nor the physiological profiles of the soybean rhizosphere bacterial community showed important changes after seed inoculation with strain BNM122. On the contrary, seed treatment with fungicides increased the proportions of r-strategists and altered the metabolic profiles of the rhizosphere culturable bacterial community. The genetic structure of the rhizosphere bacterial community did not show perceptible changes between treated and non-treated seeds. Regarding the bacterial and fungal symbioses, seed treatments did not affect soybean nodulation, whereas soybean mycorrhization significantly decreased (P < 0.05) in plants obtained from seeds treated with strain BNM122 or with the fungicides. However, a higher negative effect was observed in plants which seeds were treated with the fungicides. Plant growth was not affected by seed treatments.It can be concluded that soybean seed treatment with B. amyloliquefaciens BNM122 had a lesser effect on soil microbial community than that with the fungicides, and that these differences may be attributed to the less environmental persistence and toxic effects of the strain, which deserve further studies in order to develop commercial formulations. 相似文献
16.
When plants establish in novel environments, they can modify soil microbial community structure and functional properties in ways that enhance their own success. Although soil microbial communities are influenced by abiotic environmental variability, rhizosphere microbial communities may also be affected by plant activities such as nutrient uptake during the growing season. We predicted that during the growing season, plant N uptake would explain much of the variation in rhizosphere microbial community assembly and functional traits. We grew the invasive C3 grass Bromus tectorum and three commonly co-occurring native C3 grasses in a controlled greenhouse environment, and examined rhizosphere bacterial community structural and functional characteristics at three different plant growth stages. We found that soil N availability and plant tissue N levels strongly correlated with shifts in rhizosphere bacterial community structure. It also appeared that the rapid drawdown of soil nutrients in the rhizosphere during the plant growing season triggered a selection event whereby only those microbes able to tolerate the changing nutrient conditions were able to persist. Plant N uptake rates inversely corresponded to microbial biomass N levels during periods of peak plant growth. Mechanisms which enable plants to influence rhizosphere bacterial community structure and function are likely to affect their competitive ability and fitness. Our study suggests that plants can alter their rhizosphere microbiomes through influencing nutrient availability. The ways in which plants establish their rhizosphere bacterial communities may now be viewed as a selection trait related to intrinsic plant species nutrient demands. 相似文献
17.
The progenitor of maize is Balsas teosinte (Zea mays subsp. parviglumis) which grows as a wild plant in the valley of the Balsas river in Mexico. Domestication, primarily targeting above-ground traits, has led to substantial changes in the plant's morphology and modern maize cultivars poorly resemble their wild ancestor. We examined the hypotheses that Balsas teosinte (accession PI 384071) has a) a different root system architecture and b) a structurally and functionally different rhizosphere microbial community than domesticated cultivars sweet corn (Zea mays subsp. mays accession PI 494083) and popping corn (Zea mays subsp. mays accession PI 542713). In a greenhouse experiment, five plants from each corn variety were grown in individual pots containing a Maury silt loam – perlite (2:1) mixture and grown to the V8 growth stage at which rhizosphere bacterial and fungal community structure was assessed using terminal restriction fragment length polymorphism and fatty acid methyl ester analysis. Functional characteristics of the rhizosphere were assayed by examining the potential activity of seven extracellular enzymes involved in carbon, nitrogen and phosphorus cycling. Root system architecture was characterized by root scans of sand grown plants at the V5 growth stage. Compared to the control the sweet corn rhizosphere had different bacterial and fungal community structure, decreased fungal diversity and increased bacterial abundance. Teosinte caused a significant change in the rhizosphere bacterial and fungal community structure and increased bacterial abundance, but no significant decrease in bacterial or fungal diversity where the former was found to be significantly greater than in the sweet corn rhizosphere. Popping corn did not trigger significant changes in the bacterial or fungal diversity and bacterial abundance in the soil. The individual popping corn plants changed the bacterial and fungal communities in different directions and the overall effect on community structure was significant, but small. Of the enzymes analyzed, potential N-acetylglucosaminidase (NAG) activity was found to contributed most to the differentiation of teosinte rhizosphere samples from the other corn varieties. The teosinte root system had proportionally more very fine (diameter < 0.03 mm) roots than popping corn and sweet corn and it developed the highest root to shoot dry weight ratio, followed by popping corn. Sweet corn had significantly lower average root diameter than popping corn and teosinte and grew proportionally the least below-ground dry mass. The results allude to functional and structural differences in the rhizosphere microbial communities of the corn varieties that, with additional research, could lead to useful discoveries on how corn domestication has altered rhizosphere processes and how plant genotype influences nutrient cycling. 相似文献
18.
Interactions between the arbuscular mycorrhizal (AM) fungus Glomus intraradices and bacteria from the genus Paenibacillus (P. macerans and P. polymyxa) were examined in a greenhouse pot experiment with Cucumis sativus with and without organic matter amendment (wheat bran). P. polymyxa markedly suppressed AM fungus root colonization irrespective of wheat bran amendment, whereas P. macerans only suppressed AM fungus root colonization in combination with wheat bran amendment. Dual inoculation with P. macerans and G. intraradices in combination with wheat bran amendment also caused severe plant growth suppression. Inoculation with G. intraradices was associated with increased levels of dehydrogenase activity and available P in the growth substrate suggesting that mycorrhiza formation accelerated the decomposition of organic matter resulting in mobilization of phosphorus. Inoculation with both Paenibacillus species increased all measured microbial fatty acid biomarkers in the cucumber rhizosphere, except for the AM fungus biomarker 16:1ω5, which was reduced, though not significantly. Similarly, inoculation with G. intraradices increased all measured microbial fatty acid biomarkers in the cucumber rhizosphere, except for the Gram-positive bacteria biomarker 15:0 anteiso, which was overall decreased by G. intraradices inoculation. In combination with wheat bran amendment G. intraradices inoculation caused a 39% reduction in the amount of 15:0 anteiso in the treatment with P. polymyxa, suggesting that G. intraradices suppressed P. polymyxa in this treatment. In conclusion, plant growth promoting species of Paenibacillus may have suppressive effects of AM fungi and plant growth, especially in combination with organic matter amendment. The use of an inert plant growth media in the present study allowed us to study rhizosphere microbial interactions in a relative simple substrate with limited interference from other soil biota. However, the results obtained in the present work mainly show potential interactions and should not be directly extrapolated to a soil situation. 相似文献
19.
The effect of Bacillus thuringiensis (B.t.) inoculation on plant growth and on the intra- and extraradical mycorrhizal development of lettuce roots colonized by Glomus mosseae or Glomus intraradices was examined in an inert, soil-less substrate. Histochemical determination of succinate dehydrogenase (SDH) and alkaline phosphatase (ALP) activities which indicate active fungal metabolism was carried out at two phosphorus (P) levels. The presence of B.t. increased extra- and intraradical colonization [measured as frequency (%F), intensity (%I) and percentage of arbuscules (%A)] for both arbuscular mycorrhizal fungi (AMF) rather than plant growth or nutrition regardless P level. Under the lowest level of P fertilization, B.t. enhanced to a similar extent the extra- and intraradical development of both endophytes, but the proportion of fungal tissue showing SDH or ALP was increased in G. intraradices-colonized plants. [SDH: 458% (M) and 512% (A); ALP: 358% (M) and 300% (A)]. P supply decreased G. intraradices colonization to a higher extent than G. mosseae. Nevertheless, the totality of G. intraradices structures developed in P-amended medium showed intraradical o extraradical activity, while in G. mosseae-colonized roots, SDH and ALP activities highly decreased relative to fungal tissue determined by TB staining as affected by P. Our results show that bacterial inoculation compensates the negative effect of P on the intraradical fungal growth and vitality. P amendment reduced in a higher extent G. intraradices infection intensity (non-vital and vital staining) and G. mosseae activity (ALP staining). Thus, big differences in the proportion of SDH-active infection showing ALP activity in mycelium developed by each endophyte were noted at the highest P level. Physiological plant parameters such as photosynthetic activity did not explain specific changes on each arbuscular-mycorrhizal fungus as affected by P or B.t. inoculation. The increased extraradical mycelium development and metabolic fungal activity as a result of B.t. inoculation positively affected N and P plant content and photosynthetic rate in G. intraradices-colonized plants under the lowest P conditions. In general, the increased metabolically active fungal biomass in co-inoculated plants was irrespective of P level and was not related to the P plant uptake from the inert soil-less substrate. These results show the bacterial effect increasing the physiological and metabolic status of AM endophytes, which not only confirms but also extends previous findings on arbuscular mycorrhizae-bacteria interactions. The present study emphasizes the ecological and practical importance of rhizosphere free-living bacteria as mycorrhizae-helper microorganisms. 相似文献
20.
Recycling of olive mill wastewaters (OMW) into agricultural soils is a controversial issue since benefits to soil fertility should counterbalance potential short-term toxicity effects. We investigated the short-term effects of OMW on the soil-plant system, regarding the diversity, structure and root colonization capacity of arbuscular mycorrhizal (AM) fungi and the respective growth response of Vicia faba L, commonly used as green manure in olive-tree plantations. A compartmentalized pot system was used that allowed the establishment of an AM fungal community in one compartment (feeder) and the application of three OMW dose levels in an adjacent second compartment (receiver). At 0, 10, and 30 days after OMW treatment (DAT), V. faba pre-germinated seeds were seeded in the receiver compartment. At harvest, shoot and root dry weights, AM fungal root colonization, soil hyphal length and P availability were recorded in the receiver compartment. In addition, OMW effects on AM fungal diversity in plant roots were studied by DGGE. A transient effect of OMW application was observed; plant growth and AM fungal colonization were initially inhibited, whereas soil hyphal length was stimulated, but in most cases differences were absent when seeding was performed 30 DAT. Similarly, changes induced in the structure of the root AM fungal community were of transient nature. Cloning and sequencing of all the major DGGE bands showed that roots were colonized by Glomus spp. The transient effects of OMW on the structure and function of AM fungi could be attributed to OMW-derived phytoxicity to V. faba plants or to an indirect effect via alteration of soil nutritional status. The high OMW dose significantly increased soil P availability in the presence of AM fungi, suggesting efficient involvement of AM fungi in organic-P minerilization. Overall our results indicate that soil application of OMW would cause transient changes in the AM fungal colonization of V. faba plants, which, would not impair their long-term plant growth promoting ability. 相似文献