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1.
The effects of soil disturbance and residue retention on the functionality of the symbiosis between medic (Medicago truncatula L.) and arbuscular mycorrhizal fungi (AMF) were assessed in a two-stage experiment simulating a crop rotation of wheat (Triticum aestivum L.) followed by medic. Plants were inoculated or not with the AMF, Glomus intraradices and Gigaspora margarita, separately or together. The contribution of the arbuscular mycorrhizal (AM) pathway for P uptake was determined using 32P-labeled soil in a small hyphal compartment accessible only to hyphae of AMF. In general AM colonization was not affected by soil disturbance or residue application and disturbance did not affect hyphal length densities (HLDs) in soil. At 4 weeks disturbance had a negative effect on growth and phosphorus (P) uptake of plants inoculated with G. margarita, but not G. intraradices. By 7 weeks disturbance reduced growth of plants inoculated with G. margarita or AMF mix and total P uptake in all inoculated plants. With the exception of plants inoculated with G. margarita in disturbed soil at 4 weeks, the AM pathway made a significant contribution to P uptake in all AM plants at both harvests. Inoculation with both AMF together eliminated the negative effects of disturbance on AM P uptake and growth, showing that a fungus insensitive to disturbance can compensate for loss of contribution of a sensitive one. Application of residue increased growth and total P uptake of plants but decreased 32P in plants inoculated with the AMF mix in disturbed soil, compared with plants receiving no residue. The AMF responded differently to disturbance and G. intraradices, which was insensitive to disturbance, compensated for lack of contribution by the sensitive G. margarita when they were inoculated together. Colonization of roots and HLDs in soil were not good predictors of the outcomes of AM symbioses on plant growth, P uptake or P delivery via the AM pathway.  相似文献   

2.
The P efficiency, crop yield, and response of maize to arbuscular mycorrhizal fungus (AMF) Glomus caledonium were tested in an experimental field with long-term (18-year) fertilizer management. The experiment included five fertilizer treatments: organic amendment (OA), half organic amendment plus half mineral fertilizer (1/2 OM), mineral fertilizer NPK, mineral fertilizer NK, and the control (without fertilization). AMF inoculation responsiveness (MIRs) of plant growth and P-uptake of maize were estimated by comparing plants grown in unsterilized soil inoculated with G. caledonium and in untreated soil containing indigenous AMF. Soil total P, available P, microbial biomass P, alkaline phosphatase activity, plant biomass, crop yield and total P-uptake of maize were all significantly increased (P < 0.05) by the application of OA, 1/2 OM, and NPK, but not by the application of NK. Specifically, the individual crop yield of maize approached zero in the NK-fertilized soils, as well as in the control soils. All maize plants were colonized by indigenous AMF, and the root colonization at harvest time was not significantly influenced by fertilization. G. caledonium inoculation increased mycorrhizal colonization significantly (P < 0.05) only with the NK treatment, and produced low but demiurgic crop yield in the control and NK-fertilized soils. Compared to the inoculation in balanced-fertilized soils, G. caledonium inoculation in either the NK-fertilized soils or the control soils had significantly greater (P < 0.05) impacts on soil alkaline phosphatase activity, stem length, plant biomass, and total P-uptake of maize, indicating that AMF inoculation was likely more efficient in extremely P-limited soils. These results also showed that balanced mineral fertilizers and organic amendments did not differ significantly in their effects on MIRs in these soils.  相似文献   

3.
The role of intact extraradical mycelium (ERM) as the most effective fungal propagule in the formation of the tripartite symbiosis between indigenous arbuscular mycorrhizal fungi (AMF), rhizobia and subterranean clover was investigated under conditions of Mn toxicity. ERM was previously developed in 8 L pots under greenhouse conditions by growing plants, which exhibited various levels of mycotrophicity and were tolerant to the levels of Mn in the soil used in the experiment (Silene gallica L, Lolium rigidum L, Ornithopus compressus L. and Rumex bucephalophorus L). Contrasting conditions of the integrity of the ERM at the planting of subterranean clover were created by soil disturbance (ERM fragmented – soil disturbed; ERM intact – soil undisturbed). Where an intact ERM was present at the time of planting, growth of subterranean clover was 2.5 times greater after 21 days and 3.9 times after 42 days relative to other forms of AMF propagule. This enhanced growth was associated with a reduction in the Mn concentration of roots due to a greater AMF colonization at 21 days after planting. The protection granted by an enhanced AMF root colonization allowed a greater root nodule development, leading to more N acquisition and plant growth. The ERM can be developed in the soil by mycotrophic plants tolerant to the stressing agent and kept intact at the seeding of the crop to be protected by adopting appropriate tillage techniques.  相似文献   

4.
The composition of arbuscular mycorrhizal fungi (AMF) communities found in agricultural systems has been found to be very different to that of forest. The implications of this, if any, for the restoration of indigenous forest on ex-agricultural land is poorly understood. This study investigated the effect that AMF communities isolated from ex-agricultural and forest soils have on the growth of an indigenous New Zealand tree species (Podocarpus cunninghamii). The forest AMF community was isolated from a remnant stand of P. cunninghamii forest and the ex-agricultural AMF from a retired grazing grassland. In addition, the study examined how the two AMF communities affected the competitiveness of P. cunninghamii when grown in competition with an invasive grass species (Agrostis capillaris), which is frequently dominant on ex-agricultural land in New Zealand. P. cunninghamii growth was significantly decreased by inoculation with ex-agricultural AMF compared to forest AMF. Furthermore, the forest AMF community was able to significantly increase P. cunninghamii root production when in competition with A. capillaris. The findings suggest that when attempting to restore indigenous forest on ex-agricultural land, inoculation of tree seedlings with appropriate forest AMF may improve their growth and survival.  相似文献   

5.
A collection of 299 isolates of rhizobia nodulating Medicago truncatula was isolated from 10 Tunisian soils and was characterized by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR/RFLP) of 16S rRNA gene. Results showed that 227 and 72 isolates were assigned, respectively, to Sinorhizobium meliloti and Sinorhizobium medicae. In 9 out of 10 soils S. meliloti was detected, whereas S. medicae was recovered from only 5 out of 10 soils. The cross-nodulation of three populations of M. truncatula grown on Bulla Regia soil, which contained naturally the two Sinorhizobium species, showed that M. truncatula population collected from Amra site was selective to S. meliloti at least in soil conditions. Forty-eight isolates of each Sinorhizobium species trapped by M. truncatula populations collected from Bulla Regia, Soliman and Rhayet sites on Bulla Regia soil were characterized by repetitive extragenic palindromic-PCR (REP-PCR) and showed a clear distinction between the two Sinorhizobium species and a higher diversity for S. meliloti.  相似文献   

6.
Many legume plants benefit from the tripartite symbiosis of arbuscular mycorrhizal fungi (AMF) and rhizobia. Beneficial effects for the plant have been assumed to rely on increased P supply through the mycorrhizas. Recently, we demonstrated that P does not regulate the establishment of the tripartite symbiosis. Flavonoids appear to play a role as early signals for both rhizobia and AMF. Four soybean lines known to express different concentrations of the isoflavones genistein, daidzein and glycitein in the seed were used to test three hypotheses: (i) The establishment of the tripartite symbiosis is not dependent of a nutrient mediated effect; (ii) There is a positive correlation between seed isoflavone concentrations of different soybean lines and the progress of the tripartite symbiosis; (iii) Specific flavonoids control the establishment of the tripartite symbiosis in that a change in flavonoid root accumulation resulting from the development of one microbial partner can stimulate colonization of soybean roots by the other. Disturbed versus undisturbed soil treatments were produced to vary the potential for indigenous AMF colonization of soybean. In contrast, the potential for Bradyrhizobium was kept identical in both soil disturbance treatments. The uptake of P and Zn and the concentration of flavonoids in mycorrhizal soybean roots at 10 d after emergence were analysed either separately of Bradyrhizobium or in context of the tripartite symbiosis. Zinc nutrition did not differ between AMF treatments which supports the first hypothesis. The concentration of daidzein was at least four times greater in the root than in the seed reaching 3958±249 μg g−1 dry across soybean lines. Coumestrol, which was absent in the seed, was synthesized to reach 2154±64 μg g−1 dry. Conversely, the concentration of genistein was approximately three times smaller in the root that in the seed (301±15 μg g−1 dry), while glycitein and formononetin were never detected. The establishment of the tripartite symbiosis was identical across soybean lines which does not support the second hypothesis. Concentrations of flavonoids were significantly greater in roots under disturbed soil, for which both symbioses were not as developed as in plants from undisturbed soil. This clearly supports the third hypothesis. This research provides the first data linking the function of different flavonoids to the establishment of the tripartite symbiosis, and suggests that these compounds are produced and released into the rhizosphere as a function of the colonization process.  相似文献   

7.
This study is the first report assessing the effect of soil inoculation on the signalling interaction of Bradyrhizobium japonicum, arbuscular mycorrhizal fungi (AMF) and soybean plants throughout the early stages of colonisation that lead to the tripartite symbiosis. In a study using soil disturbance to produce contrasting indigenous AMF treatments, the flavonoids daidzein, genistein and coumestrol were identified as possible signals for regulating the establishment of the tripartite symbiosis. However, it was unclear whether soil disturbance induced changes in flavonoid root accumulation other than through changing the potential for AMF colonization. In this study, soil treatments comprising all possible combinations of AMF and B. japonicum were established to test whether (1) modifications in root flavonoid accumulation depend on the potential for AMF colonization, and (2) synthesis and accumulation of flavonoids in the roots change over time as a function of the early plant-microbial interactions that lead to the tripartite symbiosis. The study was comprised of two phases. First, maize was grown over 3-week periods to promote the development of the AM fungus Glomus clarum. Second, the interaction between soybean, G. clarum and B. japonicum was evaluated at 6, 10, 14 and 40 days after plant emergence. Root colonization by G. clarum had a positive effect on nodulation 14 days after emergence, producing, 30% more nodules which were 40% heavier than those on roots solely inoculated with B. japonicum. The tripartite symbiosis resulted in 23% more N2 being fixed than did the simpler symbiosis between soybean and B. japonicum. The presence of both symbionts changed accumulation of flavonoids in roots. Daidzein and coumestrol increased with plant growth. However, development of the tripartite symbiosis caused a decrease in coumestrol; accumulation of daidzein, the most abundant flavonoid, was reduced in the presence of AMF.  相似文献   

8.
In Venezuela, low yields of black bean crops are attributed, in part, to the low manganese (Mn) and phosphorus (P) contents in the Quartzipsamment soils where this crop is usually sown. To test this hypothesis, black bean plants were grown in sterilized sand to simulate soil physical properties, were fertilized with increasing Mn concentrations (0.1-20 μM) and inoculated with a commercial mixture of Rhizobium leguminosarum bv phaseoli strains 127K44, 127K89, 127K105 (+Rh), in combination with arbuscular mycorrhizal fungi Scutellospora heterogama and Entrophospora colombiana (+AMF). Non-inoculated plants fertilized with 6 mM NO3 and 2 mM P served as controls. Plants were harvested at 18, 25, 33, and 40 days after emergence. At all harvests, the greatest growth and highest P and iron (Fe) leaf concentrations occurred in control plants grown in 5 μM Mn. The growth of +AMF plants was promoted at 0.1 μM Mn and inhibited at higher than 1 μM Mn. Whereas, concentrations of 5-10 μM Mn enhanced the growth and the Mn concentrations in leaves of +Rh plants 40 days after emergence. The tripartite symbiosis (+Rh+AMF) decreased growth, nodulation and leaf ureide and chlorophyll concentrations in plants grown in less than 20 μM Mn, imputed to severe ultrastructural alterations in the leaf and nodule tissues. Only +Rh+AMF plants grown in 20 μM Mn were effectively nodulated, AMF colonized and reached the flowering stage, although with diminished growth and low chlorophyll concentrations. Results confirm the high Mn requirement of +Rh plants for growth and nodulation and question the implementation of the tripartite symbiosis to improve yields in early flowering black bean varieties planted in soils deficient in Mn and P.  相似文献   

9.
《Applied soil ecology》2000,14(3):201-211
Culturing in soils from degraded ecosystems significantly influenced the effectiveness of indigenous arbuscular mycorrhizal fungi (AMF) isolated from disturbed and undisturbed soils. The AMF isolates from degraded or artificially created habitats (acid rain polluted site, power station fly ash deposits, spoil banks, pyrite deposit), were not, in most cases, more effective than those from undisturbed soils, when grown in symbiosis with maize in the disturbed soils. Significant effects of soil or substrate on plant growth were found, while the influence of the AMF inoculant was much less pronounced. The development of AMF isolates was reduced in soils with more adverse chemical properties irrespective of the isolate origin. The length of extraradical mycelium of AMF and NADH-diaphorase activity of the mycelium were good indicators of negative effects of stress factors in the soil.  相似文献   

10.
Earthworms and arbuscular mycorrhizal fungi (AMF) might interactively impact plant productivity; however, previous studies reported inconsistent results. We set up a three-factorial greenhouse experiment to study the effects of earthworms (Aporrectodea caliginosa Savigny and Lumbricus terrestris L.) and AMF (Glomus intraradices N.C. Schenck & G.S. Sm.) on the performance (productivity and shoot nutrient content) of plant species (Lolium perenne L., Trifolium pratense L. and Plantago lanceolata L.) belonging to the three functional groups grasses, legumes and herbs, respectively. Further, we investigated earthworm performance and plant root mycorrhization as affected by the treatments. Our results accentuate the importance of root derived resources for earthworm performance since earthworm weight (A. caliginosa and L. terrestris) and survival (L. terrestris) were significantly lower in microcosms containing P. lanceolata than in those containing T. pratense. However, earthworm performance was not affected by AMF, and plant root mycorrhization was not modified by earthworms. Although AMF effectively competed with T. pratense for soil N (as indicated by δ15N analysis), AMF enhanced the productivity of T. pratense considerably by improving P availability. Remarkably, we found no evidence for interactive effects of earthworms and AMF on the performance of the plant species studied. This suggests that interactions between earthworms and AMF likely are of minor importance.  相似文献   

11.
Despite a general consent about the beneficial contribution of arbuscular mycorrhizal fungi (AMF) on natural ecosystems, there is an intense debate about their role in agricultural systems. In this work, soybean (Glycine max L.) and sunflower (Helianthus annuus L.) field plots with different P availabilities were sampled across the Pampean Region of Argentina (> 150 samples from Mollisols) to characterize the relationship between available soil P and indigenous mycorrhizal colonization. A subsequent pot experiment with soybean and sunflower was carried out to evaluate the effect of P supply (0, 12, and 52 mg P kg–1) and AMF inoculation on AMF colonization and crop responsiveness to P in a Mollisol. Both crops showed high AMF colonization in the field (average: 55% for soybean and 44% for sunflower). While mycorrhizal colonization in soybean was significantly and negatively related to available soil P, no such trends were apparent in sunflower. Also, total biomass was 3.5 and 2.0 times higher in mycorrhizal than in nonmycorrhizal pot‐grown soybean under low‐ and medium‐P conditions, respectively. Sunflower, on the other hand, did not benefit from AMF symbiosis under medium and high P supply. While mycorrhization stimulated P‐uptake efficiency in soybean, the generally high P efficiency in sunflower was not associated with AMF symbiosis.  相似文献   

12.
Planting trees to stabilize metalliferous mine tailings is a widely used form of land reclamation although substantial soil amendment is invariably required, both to improve the physico-chemical status of the tailings and to ameliorate toxicity prior to planting. Here, we report a glasshouse study of the combined effects of burrowing earthworms (Pheretima guillelmi) and arbuscular mycorrhizal fungi (Glomus spp., AMF) on establishment of a naturally invasive, woody, nitrogen-fixing legume, Leucaena leucocephala, on topsoil-amended Pb/Zn mine tailings. AMF provided the most effective preliminary inoculant, improving N, P and K uptake, but earthworms had more influence improving N nutrition. In most cases, the combined effects of AMF and earthworms were additive and proved to be beneficial to plant growth, plant nutrition and for protection against uptake of toxic metals. AMF influenced metal uptake more than earthworms, but together they reduced mobility of Pb and Zn in soil by as much as 25%. Some minor but significant negative interactions were also evident; for example, earthworms enhanced soil microbial activity but inhibited the beneficial effects of AMF on N2-fixation. We argue that increased attention to ecological interactions in soil could reduce costs and improve the efficacy of restoring a vegetation cover to land impacted by contaminated spoils.  相似文献   

13.
It is suggested that the diversity of arbuscular mycorrhizal fungi (AMF) and their association with distinct plants species are crucial in the early stages of revegetation procedures since the AMF roots colonisation plays an important role improving plant establishment and growth. We carried out a study where we analyse the AMF community composition in the roots of Ephedra fragilis, Rhamnus lycioides, Pistacia lentiscus and Retama sphaerocarpa fourteen months after revegetation in a Mediterranean semiarid degraded area of southeast Spain in order to verify whether different plant species can variably promote the diversity of AM fungi in their rhizospheres after planted. We analysed a portion of approximately 795 bases pairs of the small-subunit ribosomal DNA by means of nested PCR, cloning, sequencing and phylogenetic analyses. Eight fungal sequence types belonging to Glomus group A and B and to the genus Paraglomus were identified. The different plant species had different AM fungal community composition. Thus, R. lycioides harboured the highest number of four fungal sequence types while from E. fragilis only two types could be characterized that were specific for this plant species. P. lentiscus and R. sphaerocarpa harboured each one three sequence types and two of them were shared. All AMF sequence types were found in the natural soil. These results show that one effective way of restoring degraded lands is to increase the number of plant species used, which would increase the AMF diversity in the soil and thus the below-ground, positive interactions.  相似文献   

14.
Densely branched lateral roots (DBLRs) in Sesbania cannabina are formed in response to patchily distributed phosphorus (P) in volcanic soils. Little attention has been paid to morphological and physiological responses of DBLRs. Here, we investigated the relation between plant growth and DBLR development, enzymatic activities involved in P acquisition, and the influence of arbuscular mycorrhizal fungi (AMF), which contribute to P uptake, to clarify the function of DBLRs. We investigated DBLR development induced by localized application of P fertilizer and we compared the activities of phosphoenolpyruvate carboxylase (PEPCase) and acid phosphatase (APase) between DBLRs and non‐DBLRs. Additionally, plants were grown with or without AMF to investigate the effect of AMF colonization on the numbers of DBLRs and plant P uptake, and we compared AMF colonization between DBLRs and non‐DBLR roots. Secondary to quaternary lateral DBLRs were produced after the primary lateral roots passed near P fertilizer. Pi content per DBLR increased as DBLRs developed, promoting higher shoot growth. Under P deficiency, PEPCase and APase activities increased in non‐DBLR, but were significantly lower in DBLRs in the same plants. AMF inoculation changed the root system architecture by significantly decreasing the number of DBLRs, and AMF colonization was lower in DBLRs than in non‐DBLRs. Our results indicate that DBLR formation is a P‐coacquisition strategy of S. cannabina grown in P‐deficient andosolic soil. Roots that form DBLR are clearly different from non‐DBLR roots in morphological and biochemical response and AMF symbiosis.  相似文献   

15.
Effects of arbuscular mycorrhizal fungi (AMF) on the growth, nutrient absorption, and inoculation effectiveness of AMF on pioneer plants Pharagmites japonica (C4) and Polygonum cuspidatum (C3) were evaluated by performing a pot experiment in a greenhouse at Saitama University, Japan. AMF spores were collected from the commercial product, Serakinkon. The average colonization levels of P. japonica and P. cuspidatum were 24–33% and 0.2–0.5% respectively and no colonization was found in sterilized soil treatment. AMF colonization increased the plant dry mass, phosphorus (P), and nitrogen (N) concentrations of P. japonica’s roots, stems, and leaves when AMF applied with natural and sterilized soil compared with only sterilized and natural soil. This was a significant effect for N-loss minimization from soil. Maximum value showed when P. japonica was grown with natural soil in combination with AMF whereas P. cuspidatum showed very less or a negative response to AMF colonization in all cases.  相似文献   

16.
In the present study we investigated how the community of arbuscular mycorrhizal fungi (AMF) in roots of Centrosema macrocarpum responded to different doses and sources of phosphorus (40 kg ha−1 of P as rock phosphate, 150 kg ha−1 of P as rock phosphate and 75 kg ha−1 of P as diammonium phosphate together with 75 kg ha−1 of P as rock phosphate) in a Venezuelan savanna ecosystem. We also related AMF diversity to soil parameters (total N, total P, available P, extractable K, total Ca, total Mg, total Fe, total Cu, total Zn, total Mn, glomalin-related soil protein, microbial biomass C, dehydrogenase, urease and acid phosphatase activities, water-soluble carbon and carbohydrates and aggregate stability) at different doses of P. The AM fungal small-subunit (SSU) rRNA genes were subjected to PCR, cloning, SSCP, sequencing and phylogenetic analyses. Nine fungal types were identified: six belonged to the genus Glomus and three to Acaulospora. The majority of fungal types showed high similarity to sequences of known glomalean isolates: Aca 1 to Acaulospora mellea, Aca 2 to Acaulospora rugosa, Aca 3 to Acaulospora spinosa, Glo 1 to Glomus intraradices and Glo 3 to Glomus fasciculatum. The control treatment was dominated by species belonging to the genus Acaulospora. However, when the soil was fertilised with low doses of P, the colonisation of roots increased and there was a change in the AMF diversity, the genus Glomus dominating. The AM development and the abundance of AM fungal types in roots were decreased dramatically by the fertilisation with high doses of P, without differences between the sources of P used. The available P in soil was negatively correlated with the AMF diversity. In conclusion, the application of low doses of P as rock phosphate stimulated mycorrhization and enhanced the soil quality parameters except water-soluble carbohydrates, helping to offset a loss of fertility in P-poor tropical savanna soils.  相似文献   

17.
Populations of many orchids, especially terrestrial species, have been rapidly decreasing due to mass collection by plant sellers and enthusiasts. Given the presumably negative demographic and genetic consequences, such anthropogenic activity should be taken into consideration for predicting ecological and evolutionary dynamics and for planning conservation strategies. To determine how recent human disturbance alters spatial demographic and population genetic processes, populations of the terrestrial orchid Cymbidium goeringii located in South Korea were examined to quantify the spatial distributions of individuals and genotypes with respect to three levels of disturbance: “disturbed” (four populations), “putatively disturbed” (two), and “undisturbed” (two). Undisturbed and putatively disturbed populations were found to possess significantly positive spatial clustering of individuals over a range of spatial scales. In contrast, disturbed populations exhibited little or no spatial aggregation, consistent with the selective removal of plants by collectors from higher density areas within these populations. Although overall genetic differentiation among populations was moderate and significant (FST = 0.082), levels of genetic diversity within populations were similar despite the different disturbance histories (mean He = 0.257-0.324). Spatial genetic autocorrelation analyses revealed that the undisturbed populations exhibited significant declines in kinship (Fij) with distance, that mean kinship at interplant distances of ?4-6 m was significantly greater than zero and between plants ?0.5 m apart was in the range expected for first cousins to half-sibs. In contrast, only one putatively disturbed and one disturbed population exhibited significant declines in kinship with distance. These differences between disturbed versus putatively disturbed and undisturbed populations in the spatial distribution of individuals and genetic variation likely reflect the consequences of mass collections. Since these differences (and reduced population density) have important implications for future ecological and evolutionary trajectories, conservation managers of endangered terrestrial orchids may want to analyze the spatial distribution of individuals and their genotypes to infer whether a population with few individuals represents a natural state or the likely outcome of mass collection.  相似文献   

18.
Previous greenhouse and field studies have shown arbuscular mycorrhizal (AM) plants usually have greater P uptake and growth when raised in undisturbed soil compared to soil disturbed between plantings, such as by tillage. We report here for the first time that AM fungi able to stimulate shoot P uptake in experimental comparisons to non-mycorrhizal plants differ in their ability to bring about similar responses in undisturbed soil compared to disturbed soil. This outcome indicates a difference in functional character between the two stimulation processes. Three isolates of AM fungi were tested for growth promotion of maize (Zea mays L.) in pots in a soil disturbance experiment that included non-mycorrhizal controls. All three fungi colonized roots well and promoted shoot P uptake compared to non-inoculated controls, but only Glomus mosseae was able to stimulate growth in undisturbed soil compared to disturbed soil. This effect was seen when Glomus mosseae was alone or in combination with Gigaspora margarita. However, the presence of Glomus aggregatum in combination with Glomus mosseae prevented any stimulation, presumably due to domination by Glomus aggregatum. The ability of AM fungi to be beneficial to plants in comparison to non-mycorrhizal situations likely relates to the spread of mycelium in the soil and the capacity for nutrient transfer to the root. The ability of an AM fungus to promote growth in undisturbed soil appears to be related to these features and, in addition, a capacity for persistence and retention of functional capacity of the extraradical mycelium from one plant generation to the next.  相似文献   

19.
Controls on the colonization and abundance of arbuscular mycorrhizal fungi (AMF) in ecosystems are little understood and may be related to host factors, the fungal community, and soil physio-chemical properties; and changes in these variables during soil development may affect succession between mycorrhizal groups. Here we investigated the effects of litter, litter leachates, and common soluble phenolic compounds on AMF colonization of roots. In previous studies, we observed a negative correlation between increases in black cottonwood (Populus trichocarpa) litter and AMF abundance and inoculum potential along a riparian chronosequence in northwest Montana. From this, we hypothesized that litter inputs negatively affect the native AMF community and may contribute to the shift between AMF and ectomycorrhizas. We tested the effects of cottonwood foliage and litter extract additions on the colonization of AMF of both cottonwood and Sudan grass (Sorghum sudanese) seedlings. Addition of 5% (v/v) dried cottonwood leaves completely inhibited AMF colonization of S. sudanese. AMF colonization of S. sudanese was significantly reduced by litter extract of P. trichocarpa foliage, and colonization was negatively correlated with litter extract concentrations. Additions of aqueous litter extract significantly reduced AMF colonization of cottonwood seedlings as well. The effect of the litter extract on AMF colonization of S. sudanese did not appear to be mediated by changes in soil pH or plant biomass. Available phosphorus was higher in soil receiving highest concentration of litter extract, but not at a level expected to be inhibitory to AMF colonization. Litter additions significantly increased total soil phenolics, but with a range similar to natural soils of the Nyack floodplain. We tested pure soluble phenolic compounds common to Populus for their effect on AMF colonization by native fungi from the Nyack floodplain. All tested compounds significantly reduced AMF colonization but did not affect colonization by non-AMF root-colonizing fungi. This suggests secondary compounds present in cottonwood litter can affect colonization ability of a native AMF community. The potential mechanisms of inhibition and the relevance of these findings to AMF succession within both a single host and soil are discussed.  相似文献   

20.
A pot experiment was conducted to investigate the effect of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal (AM) fungi (Glomus intraradices) on soil enzyme activities and nutrient uptake by maize, which was grown on a mixture of sterilized soil and sand. Maize plants were grown in pots inoculated or not inoculated with AMF, treated or not treated with earthworms. Wheat straw was added as a feed source for earthworms. Mycorrhizal colonization of maize was markedly increased in AM fungi inoculated pots and further increased by addition of epigeic earthworms. AM fungi and epigeic earthworms increased maize shoot and root biomass, respectively. Soil acid phosphatase activity was increased by both earthworms and mycorrhiza, while urease and cellulase activities were only affected by earthworms. Inoculation with AM fungi significantly (p?<?0.001) increased the activity of soil acid phosphatase but decreased soil available phosphorus (P) and potassium (K) concentrations at harvest. Addition of earthworms alone significantly (p?<?0.05) increased soil ammonium-N content, but decreased soil available P and K contents. AM fungi increased maize shoot weight and root P content, while earthworms improved N, P, and K contents in shoots. AM fungi and earthworm interactively increased maize shoot and root biomass through their regulation of soil enzyme activities and on the content of available soil N, P, and K.  相似文献   

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