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1.
The aim of this study was to determine the effects of increasing concentrations of salt solutions (including 0.12, 2, 6, and 10 dS m−1) on the growth of berseem clover (Trifolium alexandrinum L.) and related soil microbial activity, biomass and enzyme activities. Results showed that the dry weights of root and shoot decreased with an increase in the concentrations of salt solutions. Soil salinization depressed the microbiological activities including soil respiration and enzyme activities. Substrate-induced respiration was consistently lower in salinized soils, whereas microbial biomass C did not vary among salinity levels. Higher metabolic quotients (qCO2) and unaffected microbial biomass C at high EC values may indicate that salinity is a stressful factor, inducing either a shift in the microbial community with less catabolic activity or reduced efficiency of substrate utilization. Acid phosphatase and alkaline phosphatase activities decreased with increasing soil salinity. We found significant, positive correlations between the activities of phosphatase enzymes and plant's root mass, suggesting that any decrease in the activities of the two enzymes could be attributed to the reduced root biomass under saline conditions.  相似文献   

2.
The effects of arbuscular mycorrhizal (AM) fungus, Glomus intraradices, on growth and copper (Cu) tolerance of white clover (Trifolium repens) were investigated in soils with different Cu amounts. The AM inoculation increased plant biomass and the total or bound Cu concentrations in shoots and roots but decreased the total Cu in soils and the exchangeable Cu in shoots, roots and soils at all Cu levels. Mycorrhizal plants had higher levels of root phosphorus and shoot zinc (Zn) at lower Cu levels and more nitrogen and Zn in roots and potassium, calcium and magnesium in shoots and roots at all Cu addition levels. Additionally, AM inoculation enhanced urease, acid phosphatase and catalase activities in rhizosphere soils and mycorrhizal roots showed higher levels of peroxidase, catalase, proline and soluble sugar at all Cu addition levels. These results indicate that mycorrhizal white clover is potentially suitable for Cu phytoremediation based on greenhouse studies.  相似文献   

3.
A pot experiment was conducted to investigate the mobilization of sparingly soluble inorganic andorganic sources of phosphorus (P) by red clover (Trghlium pmtense L.) whose roots were colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and in association with the phosphate-solubilizing (PS) bacterium Bacillus megaterium ACCC10010. Phosphate-solubilizing bacteria and rock phosphate hada synergistic effect on the colonization of plant roots by the AM fungus. There was a positive interaction between the PS bacterium and the AM fungus in mobilization of rock phosphate, leading to improved plant P nutrition. In dual inoculation with the AM fungus and the PS bacterium, the main contribution to plant P nutrition was made by the AM fungus. Application of P to the low P soil increased phosphatase activityin the rhizosphere. Alkaline phosphatase activity was significantly promoted by inoculation with either the PS bacterium or the AM fungus.  相似文献   

4.
ABSTRACT

Arbuscular mycorrhizal (AM) fungi can improve plant phosphorus (P) uptake; however, information about how AM fungi affect rhizosphere organic acid and microbial activity to alleviate citrus low P stress is limited. Here, a pot experiment was conducted to evaluate the effect of AM fungi (Rhizophagus intraradices, Ri) inoculation on rhizosphere organic acid content, microbial biomass (MB) and enzyme activity of trifoliate orange (Poncirus trifoliata L. Raf.) seedlings grown under three low P conditions. The results showed that mycorrhizal seedlings all recorded higher P concentrations, plant biomass and better root morphology with more lateral and fine roots, but lower root mass ratios, irrespective of P conditions. Mycorrhizal P absorption contribution did not differ significantly among three P conditions. Mycorrhizal seedling rhizosphere soil exhibited lower organic acid content, soil organic P content and ratio of MB-carbon (C)/MB-P, but higher MB and enzyme activity. Additionally, the main organic acids showed a negative relationship with mycorrhizal colonization rate and hyphal length; however, phosphatase and phytase activity had a significantly positive relationship with MB. Therefore, the results suggest that AM fungi inoculation may help citrus to efficiently utilize organic P source by improving microbial activity under low available P conditions.  相似文献   

5.
本试验通过两室分根装置种植玉米,利用网袋法研究接种Glomus mosseae和Glomus etunicatum两种AM真菌对玉米秸秆降解的影响。试验分别在玉米移栽后第20 d、30 d、40 d、50 d和60 d时取样,通过测定接种AM真菌后玉米秸秆中碳、氮释放,土壤中3种常见酶活性、微生物量碳、微生物量氮及土壤呼吸的动态变化,探讨AM真菌降解玉米秸秆可能的作用机制。研究结果表明:经60 d的培养后,与未接种根室相比,接种G.mosseae和G.etunicatum真菌的菌根室玉米秸秆降解量提高了20.75%和20.97%;另外,接种G.mosseae和G.etunicatum加快了玉米秸秆碳素释放,降低了氮素释放,致使碳氮比降低25.45%和26.17%,有利于秸秆进一步降解。在本试验条件下,接种AF真菌的菌根室中土壤酸性磷素酶、蛋白酶和过氧化氢酶活性均有显著提高,并增加了微生物量碳、氮和土壤呼吸作用,形成了明显有别于根际的微生物区系。这一系列影响都反映出AM真菌能够直接或间接作用于玉米秸秆的降解过程,是导致玉米秸秆降解加快的重要原因。  相似文献   

6.
A pot experiment was conducted to investigate the mobilization of sparingly soluble inorganic and organic sources of phosphorus (P) by red clover (Trifolium pratense L.) whose roots were colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and in association with the phosphate-solubilizing (PS) bacterium Bacillus megaterium ACCC10010. Phosphate-solubilizing bacteria and rock phosphate had a synergistic effect on the colonization of plant roots by the AM fungus. There was a positive interaction between the PS bacterium and the AM fungus in mobilization of rock phosphate, leading to improved plant P nutrition. In dual inoculation with the AM fungus and the PS bacterium, the main contribution to plant P nutrition was made by the AM fungus. Application of P to the low P soil increased phosphatase activity in the rhizosphere. Alkaline phosphatase activity was significantly promoted by inoculation with either the PS bacterium or the AM fungus.  相似文献   

7.
丛枝菌根对芘污染土壤修复及植物吸收的影响   总被引：4，自引：0，他引：4  
采用温室盆栽试验方法,研究了两种丛枝菌根真菌Glomus mosseae和 Glomus etunicatum对三叶草(Trifolium subterraneum L.)和辣椒（Capsicum annuum L.）修复芘污染土壤的影响。供试土样中芘初始浓度为0 ~ 75.18 mg/kg。结果表明,接种AMF可促进供试植物对土壤中芘的吸收,并且显著提高三叶草根的芘含量、根系富集系数、根和茎叶的芘积累量,但对辣椒根和茎叶芘含量、根系富集系数的影响不显著,这主要与植物的菌根侵染率和“菌根依赖度”不同有关。接种AMF土壤中芘的削减率高于普通植物修复,但植物吸收积累对修复的贡献率小于0.2%;因此推测,AM作用下良好的根际环境对土壤微生物数量和活性的提高、进而对土壤中芘降解的促进可能是菌根修复的主要机理。  相似文献   

8.
Earthworms and arbuscular mycorrhizal fungi (AMF) are known to independently affect soil microbial and biochemical properties, in particular soil microbial biomass (SMB) and enzymes. However, less information is available about their interactive effects, particularly in soils contaminated with heavy metals such as cadmium (Cd). The amount of soil microbial biomass C (MBC), the rate of soil respiration (SRR) and the activities of urease and alkaline phosphatase (ALP) were measured in a calcareous soil artificially spiked with Cd (10 and 20 mg Cd kg−1), inoculated with earthworm (Lumbricus rubellus L.), and AMF (Glomus intraradices and Glomus mosseae species) under maize (Zea mays L.) crop for 60 days. Results showed that the quantity of MBC, SRR and enzyme activities decreased with increasing Cd levels as a result of the elevated exchangeable Cd concentration. Earthworm addition increased soil exchangeable Cd levels, while AMF and their interaction with earthworms had no influence on this fraction of Cd. Earthworm activity resulted in no change in soil MBC, while inoculation with both AMF species significantly enhanced soil MBC contents. However, the presence of earthworms lowered soil MBC when inoculated with G. mosseae fungi, showing an interaction between the two organisms. Soil enzyme activities and SRR values tended to increase considerably with the inoculation of both earthworms and AMF. Nevertheless, earthworm activity did not affect ALP activity when inoculated with G. mosseae fungi, while the presence of earthworm enhanced urease activity only with G. intraradices species. The increases in enzyme activities and SRR were better ascribed to changes in soil organic carbon (OC), MBC and dissolved organic carbon (DOC) contents. In summary, results demonstrated that the influence of earthworms alone on Cd availability is more important than that of AMF in Cd-polluted soils; and that the interaction effects between these organisms on soil microorganism are much more important than on Cd availability. Thus, the presence of both earthworms and AMF could alleviate Cd effects on soil microbial life.  相似文献   

9.
The major objectives of this study were to determine the influence of grazing on the soil microbial biomass and activity in semiarid grassland and shrubland areas and to quantify the canopy effect (the differences in soil microbial biomass and activities between soils under plant canopies and soils in the open between plants). We also quantified changes in microbial biomass and activity during seasonal transition from dry to moist conditions. Chronosequences of sites withdrawn from grazing for 0, 11, and 16 years were sampled in a grassland (Bouteloua spp.) area and a shrubland (Atriplex canescens) area on and near the Sevilleta National Wildlife Reguge in central New Mexico, USA. Samples were obtained from beneath the canopies of plants (Yucca glauca in the grassland and A. canescens in the shrubland) and from open soils; they were collected three times during the spring and summer of a single growing season. Organic C, soil microbial biomass C, and basal respiration rates (collectively called the soil C triangle) were measured. We also calculated the microbial: organic C ratio and the metabolic quotient (ratio of respiration to microbial C) as measures of soil organic C stability and turnover. Although we had hypothesized that individual values of the soil C triangle would increase and that the ratios would decrease with time since grazing, differences in microbial parameters between sites located along the chronosequences were generally not significant. Grazing did not have a consistion effect on organic C, microbial C, and basal respiration in our chronosequences. The microbial: organic C ratio and the metabolic quotient generally increased with time since grazing on the shrubland chronosequence. The microbial: organic C ratio decreased with time since grazing and the metabolic quotient increased with time since grazing on the grassland chronosequence. The canopy effect was observed at all sites in nearly all parameters including organic C, microbial C, basal respiration, the microbial: organic C ratio, and the metabolic quotient which were predominantly higher in soils under the canopies of plants than in the open at all sites. Microbial biomass and activity did not increase during the experiment, even though the availability of moisture increased dramatically. The canopy effects were approximately equal on the shrubland and grassland sites. The microbial: organic C ratios and the metabolic quotients were generally higher in the shrubland soils than in the grassland soils.  相似文献   

10.
The ratios of soil carbon (C) to nitrogen (N) and C to phosphorus (P) are much higher in Chinese temperate forest soils than in other forest soils, implying that N and P might limit microbial growth and activities. The objective of this study was to assess stoichiometric responses of microbial biomass, enzyme activities, and respiration to N and P additions. We conducted a nutrient (N, P, and N + P) addition experiment in two temperate soils under Korean pine (Pinus koraiensis) plantation and natural broadleaf forest in Northeast China and measured the microbial biomass C, N, P; the activities of β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG), and acid and alkaline phosphomonoesterase (AP); and the microbial respiration in the two soils. Nitrogen addition increased microbial biomass N and decreased microbial biomass C-to-N ratio and microbial respiration in the two soils. Nitrogen addition decreased NAG activity to microbial biomass N ratio, P addition decreased AP activity to microbial biomass P ratio, and N, P, and N + P additions all increased BG activity to microbial biomass C ratio. These results suggest that microbial stoichiometry is not strictly homeostatic in response to nutrient additions, especially for N addition. The responses of enzyme activities to nutrient additions support the resource allocation theory. The N addition induced a decline in microbial respiration, implying that atmospheric N deposition may reduce microbial respiration, and consequently increase soil C sequestration in the temperate region.  相似文献   

11.
The effectiveness of reforestation programs on degraded soils in the Mediterranean region is frequently limited by a low soil availability and a poor plant uptake and assimilation of nutrients. While organic amendments can improve the nutrient supply, inoculation with mycorrhizal fungi can enhance plant nutrient uptake. A pot experiment was conducted in 2004 to study the influence of inoculation with an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) or with a mixture of three AM fungi (G. intraradices, G. deserticola Trappe, Bloss. & Menge, and G. mosseae (Nicol & Gerd.) Gerd. & Trappe) and of an addition of composted sewage sludge or Aspergillus niger–treated dry‐olive‐cake residue on plant growth, nutrient uptake, mycorrhizal colonization, and nitrate reductase (NR) activity in shoot and roots of Juniperus oxycedrus L. Six months after planting, the inoculation of the seedlings with G. intraradices or a mixture of three AM fungi was the most effective treatment for stimulating growth of J. oxycedrus. There were no differences between the two mycorrhizal treatments. All treatments increased plant growth and foliar N and P contents compared to the control plants. Mycorrhizal inoculation and organic amendments, particularly fermented dry olive cake, increased significantly the NR activity in roots.  相似文献   

12.
A 60-day pot experiment was carried out using di-(2-ethylhexyl) phthalate (DEHP) as a typical organic pollutant phthalic ester and cowpea (Vigna sinensis) as the host plant to determine the effect of arbuscular mycorrhizal inoculation on plant growth and degradation of DEHP in two contaminated soils, a yellow-brown soil and a red soil. The air-dried soils were uniformly sprayed with different concentrations of DEHP, inoculated or left uninoculated with an arbuscular mycorrhizal (AM) fungus, and planted with cowpea seeds. After 60 days the positive impact of AM inoculation on the growth of cowpea was more pronounced in the red soil than in the yellow-brown soil, with significantly higher (P < 0.01) mycorrhizal colonization rate, shoot dry weight and total P content in shoot tissues for the red soil. Both in the yellow-brown and red soils, AM inoculation significantly (P < 0.01) reduced shoot DEHP content, implying that AM inoculation could inhibit the uptake and translocation of DEHP from roots to the aboveground parts. However, with AM inoculation no positive contribution to the degradation of DEHP was found.  相似文献   

13.
Application of biochar to soil to achieve any number of goals should also consider unintended effects upon soil biology, including symbioses such as arbuscular mycorrhizas. We conducted an experiment to examine the interaction of biochar addition and arbuscular mycorrhizal (AM) fungus inoculation upon growth and phosphorus (P) uptake by Allium porrum L. and relate these responses to physicochemical properties of the biochars. A. porrum seedlings were grown with and without Glomus intraradices Schenck & Smith, and either without biochar or in the presence of one of 12 different biochars created by pyrolysis of three biomass feedstocks. Fast pyrolysis biochars greatly reduced colonization of roots by the AM fungus. Among biochars produced by a given pyrolysis method, higher surface areas were accompanied by higher AM fungus colonization. These findings are pertinent in selecting biochars for application to agricultural soils for such purposes as inactivation of pathogenic bacteria while being mindful of potential impacts upon the AM symbiosis.  相似文献   

14.
The addition of plant residues and the appropriate management of arbuscular mycorrhizal (AM) symbioses have been tested in an acidic soil, an Andisol from Southern Chile, to ascertain whether these agro-technologies help plants to withstand potential mineral deficiency and the toxicities inherent to the low pH conditions. Firstly, the effects of legume (lupine) and non-legume (wheat) crop residues on some key root-soil interface activities (including AM development), on mineral acquisition by the plants, and on the yield of wheat growing in the test Andisol were investigated in a pot experiment under greenhouse conditions. Both lupine and wheat residues were added at a rate equivalent to 300 g m-2 to the natural soil. These organic amendments increased soil pH (wheat more than lupine), P availability and AM development (lupine more than wheat), plant performance and mineral acquisition (wheat more than lupine). Because of an increase in mycorrhizal activity, which appeared to be involved in the effect of the added crop (particularly lupine) residues, the role of the AM symbiosis was further investigated in a tailored inoculation assay, using a selected AM fungus (Glomus etunicatum), in interaction with lupine and wheat residues. A significant effect of AM inoculation on the reduction of Zn and Cu, and Mn and Al acquisition was demonstrated, which could be of interest in acid soils with regard to potential toxicity problems.  相似文献   

15.
Plants can mediate interactions between aboveground herbivores and belowground decomposers as both groups depend on plant-provided organic carbon. Most vascular plants also form symbiosis with arbuscular mycorrhizal fungi (AMF), which compete for plant carbon too. Our aim was to reveal how defoliation (trimming of plant leaves twice to 6 cm above the soil surface) and mycorrhizal infection (inoculation of the fungus Glomus claroideum BEG31), in nutrient poor and fertilized conditions, affect plant growth and resource allocation. We also tested how these effects can influence the abundance of microbial-feeding animals and nitrogen availability in the soil. We established a 12-wk microcosm study of Plantago lanceolata plants growing in autoclaved soil, into which we constructed a simplified microfood-web including saprotrophic bacteria and fungi and their nematode feeders. We found that fertilization, defoliation and inoculation of the mycorrhizal fungus all decreased P. lanceolata root growth and that fertilization increased leaf production. Plant inflorescence growth was decreased by defoliation and increased by fertilization and AMF inoculation. These results suggest a negative influence of the treatments on P. lanceolata belowground biomass allocation. Of the soil organisms, AMF root colonization decreased with fertilization and increased with defoliation. Fertilization decreased numbers of bacterial-feeding nematodes, probably because fertilized plants produced less root mass. On the other hand, bacterial feeders were more abundant when associated with defoliated than non-defoliated plants despite defoliated plants having less root mass. The AMF inoculation per se increased the abundance of fungal feeders, but the reduced and increased root AM colonization rates of fertilized and defoliated plants, respectively, were not reflected in the numbers of fungal feeders. We found no evidence of plant-mediated effects of the AM fungus on bacterial feeders, and against our prediction, soil inorganic nitrogen concentrations were not positively associated with the concomitant abundances of microbial-feeding animals. Altogether, our results suggest that (1) while defoliation, fertilization and AMF inoculation all affect plant resource allocation, (2) they do not greatly interact with each other. Moreover, it appears that (3) while changes in plant resource allocation due to fertilization and defoliation can influence numbers of bacterial feeders in the soil, (4) these effects may not significantly alter mineral N concentrations in the soil.  相似文献   

16.
The aim of this experiment was to evaluate the impact of colonization with arbuscular mycorrhizal (AM) fungus Glomus constrictum on the biomass production, flower quality, chlorophyll content, macronutrients and heavy metals content of marigold (Tagetes erecta L.) planted under uncontaminated soil and watered with various rates of sewage water. Sewage water utilization significantly decreased biomass production, characters of flower, nutrient concentration and rates of mycorrhizal colonization of mycorrhizal (M) and non-mycorrhizal (NM) marigold as compared to control untreated plants especially at the higher rates, but the reduction rate was proportionally higher in non-AM treatments. Mycorrhizal plants had significantly greater yield, relative chlorophyll content, leaf area, flower quality and element (P, N, K and Mg) content compared to non-inoculated marigold plants irrigated with or without sewage water. Furthermore, AM inoculation had highly decreased heavy metal (Zn, Co, Mn, Cu) content in tissues as compared to equivalent non-inoculated plants grown under sewage water application. Growing marigold with AM inoculum can reduce toxicity of heavy metals and enhance biomass production and P uptake. The results support the view that AM have a protective function for the host plant, hence playing a potential function in soil polluted immobilization processes, and thus are of assessing the potential of phytoremediation of heavy metals in sewage water contaminated soil.  相似文献   

17.
The conversion of secondary forests to larch plantations in Northeast China has resulted in a significant decline in soil available nitrogen (N) and phosphorus (P), and thus affects plant productivity and ecosystem functioning. Microbes play a key role in the recycling of soil nutrients; in turn, the availability of soil N and P can constrain microbial activity. However, there is little information on the relationships between available soil N and P and the microbial biomass and activity in larch plantation soil. We studied the responses of soil microbial respiration, microbial biomass and activity to N and P additions in a 120-day laboratory incubation experiment and assessed soil microbial properties in larch plantation soil by comparing them with the soil of an adjacent secondary forest. We found that the N-containing treatments (N and N + P) increased the concentrations of soil microbial biomass N and soluble organic N, whereas the same treatments did not affect microbial respiration and the activities of β-glucosidase, N-acetyl-β-glucosaminidase and acid phosphatase in the larch plantation. In addition, the concentration of microbial biomass P decreased with N addition in larch plantation soil. In contrast, N and N + P additions decreased microbial respiration, and N addition also decreased the activity of N-acetyl-β-glucosaminidase in the secondary forest soil. The P treatment did not affect microbial respiration in either larch plantation or secondary forest soils, while this treatment increased the activities of β-glucosidase and acid phosphatase in the secondary forest soil. These results suggested that microbial respiration was not limited by available P in either secondary forest or larch plantation soils, but microbial activity may have a greater P demand in secondary forest soil than in larch plantation soil. Overall, there was no evidence, at least in the present experiment, supporting the possibility that microbes suffered from N or P deficiency in larch plantation soil.  相似文献   

18.
The effect of the dual inoculation with arbuscular mycorrhizal (AM) and saprophytic fungi and a combination of wheat straw and sewage sludge residues were studied by determining their effect on dry weight of tomato and on chemical and biochemical properties of soil. Incubation of organic residue (sewage sludge combined with wheat straw) with saprophytic fungi and plant inoculation with mycorrhizal fungi was essential to study plant growth promotion. Soil application of organic residues increased the dry weight of tomato inoculated with Rhizophagus irregularis. The greatest shoot dry mass was obtained when the organic residues were incubated with Trichoderma harzianum and applied to AM plants. However, the greatest percentage of root length colonized with AM in the presence of the organic residues was obtained with inoculation with Coriolopsis rigida. The relative chlorophyll was greatest in mycorrhizal plants regardless of the presence of either saprophytic fungus. The presence of the saprophytic fungi increased soil pH as the incubation time increased. Soil nitrogen and phosphorus contents and acid phosphatase were stimulated by the addition of organic residues, and contents of N and P. Total N and P content in soil increased when the organic residue was incubated with saprobe fungi, but this effect decreased as the incubation period of the residue with saprobe fungi increased. The same trend was observed for soil β‐glucosidase and fluorescein diacetate activities. The application of organic residues in the presence of AM and saprophytic fungi seems to be an interesting option as a biofertilizer to improve plant growth and biochemical parameters of soils.  相似文献   

19.
《Applied soil ecology》2003,22(2):139-148
A glasshouse pot experiment investigated the uptake by arbuscular mycorrhizal (AM) fungi associated with red clover of three organic sources of P added to a sterilized calcareous soil of low P availability. Each pot was separated into a central compartment for plant growth and two outer compartments for external mycelium using 30-μm nylon mesh to restrict the roots but allow hyphal penetration. Plants in the central compartments were inoculated with the AM fungus Glomus versiforme and uninoculated controls were included. Plants were harvested on three occasions: 5, 7 and 10 weeks after sowing. Application of each of the three organic P sources (lecithin, RNA and sodium phytate) or inorganic P (KH2PO4) at 50 mg P kg−1 to the outer compartments of mycorrhizal and uninoculated pots increased the yield, P concentration and total P uptake of red clover compared with pots to which no P was applied, with no differences among P sources in non-mycorrhizal plants but differences observed in mycorrhizal plants both 7 and 10 weeks after sowing suggesting differences in availability of the four P sources to AM mycelium. The contribution of external mycelium to plant uptake of applied P increased with time. The three organic P sources made smaller contributions to plant P nutrition than KH2PO4 at the first and second harvests. At the third harvest, the contribution from KH2PO4 was 23%, while those from lecithin, RNA and sodium phytate were 23, 17 and 31%, respectively. This suggests that with the mediation of AM fungi, soil organic P sources can make a contribution to host plant P nutrition comparable to that of soluble orthophosphate.  相似文献   

20.
In a controlled potted experiment, citrus (Poncirus trifoliata) seedlings were inoculated with three species of arbuscular mycorrhizal (AM) fungi, Glomus mosseae, G. versiforme or G. diaphanum. Two soil-water levels (ample water, −0.10 MPa; drought stress, −0.44 MPa) were applied to the pots 4 months after transplantation. Eighty days after water treatments, the soils and the citrus seedlings were well colonized by the three AM fungi. Mycorrhizal fungus inoculation improved plant biomass regardless of soil-water status but decreased the concentrations of hot water-extractable and hydrolyzable carbohydrates of soils. Mycorrhizal soils exhibited higher Bradford-reactive soil protein concentrations than non-mycorrhizal soils. Mycorrhizas enhanced >2 mm, 1–2 mm and >0.25 mm water-stable aggregate fractions but reduced 0.25–0.5 mm water-stable aggregates. Peroxidase activity was higher in AM than in non-AM soils whether drought stressed or not, whereas catalase activity was lower in AM than non-AM soils. Drought stress and AM fungus inoculation did not affect polyphenol oxidase activity of soils. A positive correlation between the Bradford-reactive soil protein concentrations, soil hyphal length densities, and water-stable aggregates (only >2 mm, 1–2 mm and >0.25 mm) suggests beneficial effects of the AM symbiosis on soil structure. It concluded that AM fungus colonization enhanced plant growth under drought stress indirectly through affecting the soil moisture retention via glomalin's effect on soil water-stable aggregates, although direct mineral nutritional effects could not be excluded.  相似文献   

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