Mycorrhizae, biocides, and biocontrol 3. Effects of three different fungicides on developmental stages of three AM fungi

The effects of biocide use on nontarget organisms, such as arbuscular mycorrhizal (AM) fungi, are of interest to agriculture, since inhibition of beneficial organisms may counteract benefits derived from pest and disease control. Benomyl, pentachloronitrobenzene (PCNB) and captan were tested for their effects on the germination and early hyphal growth of the AM fungiGlomus etunicatum (Becker & Gerd.),Glomus mosseae (Nicol. & Gerd.). Gerd. and Trappe andGigaspora rosea (Nicol & Schenck) in a silty-clay loam soil placed in petri plates. Application of fungicides at 20 mg active ingredient (a.i) kg^?1 soil inhibited spore germination by all three AM-fungal isolates incubated on unsterilized soil for 2 weeks. However, fungicides applied at 10 mg a.i. kg^?1 soil had variable effects on AM-fungal isolates. Fungicide effects on germination and hyphal growth of G.etunicatum were modified by soil pasteurization and CO₂ concentration in petri plates and also by placing spores below the soil surface followed by fungicide drenches. Effects of fungicides on mycorrhiza formation and sporulation of AM fungi, and the resulting host-plant response, were evaluated in the same soil in associated pea (Pisum sativum L.) plants. Fungicides applied at 20 mg a.i. kg^?1 soil did not affect the root length colonized byG. etunicatum, but both benomyl and PCNB reduced sporulation by this fungus. Benomyl and PCNB reduced the root length colonized byG. rosea at 48 and 82 days after transplanting. PCNB also reducedG. mosseae-colonized root length at 48 and 82 days, but benomyl only affected root length colonized byG. mosseae at the earlier time point. Only PCNB reduced sporulation byG. mosseae, consistent with its effect on root length colonized by this fungus. captan reduced the root length colonized by G. rosea at 48 days, but not at 82 days, and reduced colonization byG. mosseae at 82 days, but not at 48 days. Captan did not affect sporulation by any of the fungi.G. rosea spore production was highly variable, but benomyl appeared to reduce sporulation by this fungus. Overall,G. etunicatum was the most tolerant to fungicides in association with pea plants in this soil, andG. rosea the most sensitive. Benomyl and PCNB were overall more toxic to these fungi than captan. Interactions of AM fungi and fungicides were highly variable and biological responses depended on fungus-fungicide combinations and on environmental conditions.     

Mycorrhizae,biocides, and biocontrol. 4. Response of a mixed culture of arbuscular mycorrhizal fungi and host plant to three fungicides

The effects of three commonly used fungicides on the colonization and sporulation by a mixture of three arbuscular mycorrhizal (AM) fungi consisting of Glomus etunicatum (Becker & Gerd.), Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, and Gigaspora rosea (Nicol. & Schenck) in symbiosis with pea plants and the resulting response of the host-plant were examined. Benomyl, PCNB, and captan were applied as soil drenches at a rate of 20 mg active ingredient kg^-1 soil 2 weeks after transplanting pea seedlings in a silty clay-loam soil containing the mixed inocula of AM fungi (AM plants). Effects of fungicides were compared to untreated plants that were inoculated with fungi (AM control). The effect of mycorrhizal inoculation on plant growth was also examined by including nonmycorrhizal, non-fungicide-treated plants (non-AM control). Fungicides or inoculation with AM fungi had only a small effect on the final shoot weights of pea plants, but had greater effects on root length and seed yield. AM control plants had higher seed yields and lower root lengths than the corresponding non-AM plants, and the fungicide-treated AM plants had intermediate yields and root lengths. Seed N and P contents were likewise highest in AM control plants, lowest in non-AM plants, and intermediate in fungicide-treated AM plants. All three fungicides depressed the proportion (%) of root length colonized by AM fungi, but these differences did not translate to reductions in the total root length that was colonized, since roots were longer in the fungicide-treated AM plants. Pea plants apparently compensated for the reduction in AM-fungal metabolism due to fungicides by increasing root growth. Fungicides affected the population of the three fungi as determined by sporulation at the final harvest. Captan significantly reduced the number, relative abundance, and relative volume of G. rosea spores in the final population relative to the controls. The relative volume of G. etunicatum spores was greater in all the fungicide-treated soils, while G. mosseae relative volumes were only greater in the captan-treated soil. These findings show that fungicides can alter the species composition of an AM-fungal community. The results also show that AM fungi can increase seed yield without enhancing the vegetative shoot growth of host plants.     

Uptake of Arsenic by Maize Inoculated with Three Different Arbuscular Mycorrhizal Fungi

Effects of inoculation with three different arbuscular mycorrhizal (AM) fungi (Glomus etunicatum, Glomus constrictum, and Glomus mosseae) on arsenic (As) accumulation by maize were investigated by using soil spiked with As at rates of 0, 25, 50, and 100 mg kg^?1. The root colonization rates by the three fungi were significantly different (G. mosseae > G. etunicatum > G. constrictum) and decreased markedly with increasing As concentration in the soil. Inoculation with G. etunicatum or G. mosseae increased maize biomass and phosphorus (P) accumulation (G. mosseae > G. etunicatum) and reduced As accumulation in shoots (G. mosseae ≈ G. etunicatum), whereas inoculation with G. constrictum had little effect on these parameters. Inoculation with G. mosseae produced greater biomass and P uptake and less shoot As accumulation, and therefore it may be a promising approach to reduce As translocation from contaminated soils to plants.     

Mycorrhizal fungi effects on nutrient composition and yield of soybean seeds

Nutrient composition and yield of soybean [Glycine max (L.) Merr] seeds are heritable traits affected by environmental factors. This study determined the effects of arbuscular‐mycorrhizal (AM) fungi on seed protein, lipid, and phosphorus (P) composition and yield in soybean grown under a high nitrogen (N) regime. Plants were grown in pot cultures without AM fungi in P‐fertilized (+P) or unfertilized (‐P) soil, or in ‐P soil inoculated with one of the AM fungi Glomus mosseae (Nicol. & Gerd.) Gerd, and Trappe (Gm), Glomus etunicatum Becker and Gerd.(Ge), or Gigaspora rosea Nicol. and Schenck (Gr). Seed yields of+AM plants, as a group, were halfway between those of the +P and ‐P plants. Seed size was highest in Gm plants. Differences in protein concentrations between Ge and Gr and the other treatments were highly significant. Seed P and protein concentrations were not significantly correlated (p=0.162), but a highly significant (r =‐0.949) negative correlation between seed P and lipid concentrations was observed. Phosphorus concentration was highest and that of lipids lowest in +AM plants. Seed yield and nutrient composition were independent of the intensity of root colonization. The seed protein/lipid ratio was highly correlated with seed P concentration and was significantly higher for +AM plants, as a group, than for both +P and ‐P ‐AM plants. Differences in seed dry weight, size, seed/ stem ratio, P content, and protein concentration among +AM plants showed mycorrhiza‐specific host responses. These responses suggest that AM fungi can modify soybean seed development and chemical composition.     

Interaction between the soil yeast Rhodotorula mucilaginosa and the arbuscular mycorrhizal fungi Glomus mosseae and Gigaspora rosea

The effect of the soil yeast, Rhodotorula mucilaginosa LBA, on Glomus mosseae (BEG n°12) and Gigaspora rosea (BEG n°9) was studied in vitro and in greenhouse trials. Hyphal length of G. mosseae and G. rosea spores increased significantly in the presence of R. mucilaginosa. Exudates from R. mucilaginosa stimulated hyphal growth of G. mosseae and G. rosea spores. Increase in hyphal length of G. mosseae coincided with an increase in R. mucilaginosa exudates. No stimulation of G. rosea hyphal growth was detected when 0.3 and 0.5 ml per petri dish of yeast exudates was applied. Percentage root length colonization by G. mosseae in soybean (Glycine max L. Merill) and by G. rosea in red clover (Trifolium pratense L. cv. Huia) was increased only when the soil yeast was inoculated before G. mosseae or G. rosea was introduced. Beneficial effects of R. mucilaginosa on arbuscular mycorrhizal (AM) colonization were found when the soil yeast was inoculated either as a thin agar slice or as a volume of 5 and 10 ml of an aqueous solution. R. mucilaginosa exudates (20 ml per pots) applied to soil increased significantly the percentage of AM colonization of soybean and red clover.     

Response of Two Maize Inbred Lines with Contrasting Phosphorus Efficiency and Root Morphology to Mycorrhizal Colonization at Different Soil Phosphorus Supply Levels

ABSTRACT

A pot experiment investigated the response of two maize inbred lines with contrasting root morphology and phosphorus (P) efficiency to inoculation with Glomus mosseae or Glomus etunicatum compared with non-mycorrhizal controls. Soil phosphorus was supplied at rates of 10, 50, and 100 mg P kg ^?1 soil. Root length, specific root length, and specific phosphorus uptake of maize line 178 (P-efficient) were significantly higher than of line Hc (P-inefficient). Percentage of root length colonized showed the opposite trend regardless of soil P supply level. The two maize lines did not differ significantly in growth response to mycorrhizal colonization. Root colonization rate decreased with increasing soil phosphorus supply. The beneficial effect of the two AM fungi on plant growth and P uptake was greatest at low soil P level and the responses were negative at high P supply. Mycorrhizal responsiveness also decreased with increasing P supply and differed between the two mycorrhizal fungal isolates.     

Pre-inoculation with arbuscular mycorrhizal fungi suppresses root knot nematode (<Emphasis Type="Italic">Meloidogyne incognita</Emphasis>) on cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis>)

A pot experiment was conducted to evaluate the influence of pre-inoculation of cucumber plants with each of the three arbuscular mycorrhizal (AM) fungi Glomus intraradices, Glomus mosseae, and Glomus versiforme on reproduction of the root knot nematode Meloidogyne incognita. All three AM fungi tested significantly reduced the root galling index, which is the percentage of total roots forming galls. Numbers of galls per root system were significantly reduced only in the G. intraradices + M. incognita treatment. The number of eggs per root system was significantly decreased by AM fungus inoculation, no significant difference among the three AM fungal isolates. AM inoculation substantially decreased the number of females, the number of eggs g⁻¹ root and of the number of eggs per egg mass. The number of egg masses g⁻¹ root was greatly reduced by inoculation with G. mosseae or G. versiforme. By considering plant growth, nutrient uptake, and the suppression of M. incognita together, G. mosseae and G. versiforme were more effective than G. intraradices.     

Rhodotorulic acid enhances root colonization of tomato plants by arbuscular mycorrhizal (AM) fungi due to its stimulatory effect on the pre-symbiotic stages of the AM fungi

Exudates of Rhodotorula mucilaginosa, a yeast commonly found in the rhizosphere, increased hyphal length of the arbuscular mycorrhizal (AM) fungi Gigaspora rosea and Gigaspora margarita. Rhodotorulic acid (RA), a siderophore compound obtained from R. mucilaginosa exudates, increased hyphal length and branching. Thus, the increase in the number of entry points and the higher AM root colonization of tomato plants in the presence of RA can at least partially be explained by the positive effect of RA on the pre-symbiotic stages of the AM fungi.     

EXPLOITATION OF PHOSPHORUS PATCHES WITH DIFFERENT PHOSPHORUS ENRICHMENT BY THREE ARBUSCULAR MYCORRHIZAL FUNGI

The effect of three arbuscular mycorrhizal (AM) fungi on phosphorus (P) nutrient activation and acquisition by maize from spatially heterogeneous sand was investigated using dual-mesh packages enriched with different P concentrations and compared with non-mycorrhizal cotrols. As would be expected the AM fungi significantly enhanced leaf photosynthetic rate and the biomass and P concentrations in shoots and roots. All three fungi (Glomus intraradices, Glomus mosseae and Glomus etunicatum) displayed the capacity to dissolve inorganic P and promoted P nutrient availability in the packages (P patches). G. etunicatum showed the largest effect comparing with Glomus intraradices and Glomus mosseae, particularly in packages with high concentrations of P. Possible mechanisms involved include the acidification of the P patches by the AM fungi, promotion of the dissolution of the P, and more marked effects of the three fungal isolates with increasing enrichment of P in the patches. Inoculation with G. etunicatum resulted in greater acidification compared to the other two fungi. We conclude that AM fungi can promote P availability by acidifying the soil and consequently exploiting the P in nutrient patches and by facilitating the growth and development of the host plants.     

AM fungi inoculation and addition of microbially‐treated dry olive cake‐enhanced afforestation of a desertified Mediterranean site

A field experiment was carried out to compare the effectiveness of inoculation with three arbuscular mycorrhizal (AM) fungi, namely Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge) and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe, and the addition of Aspergillus niger‐treated dry olive cake (DOC) in the presence of rock phosphate, in increasing root nitrate reductase (NR) and acid phosphatase activities, mycorrhizal colonization, plant growth and nutrient uptake in Dorycnium pentaphyllum L. seedlings afforested in a semiarid degraded soil. Three months after planting, both the addition of fermented DOC and the mycorrhizal inoculation treatments had increased root NR activity significantly, particularly the inoculation with G. deserticola (by 75 per cent with respect to non‐inoculated plants), but they had no effect on root acid phosphatase. Mycorrhizal inoculation treatments with G. deserticola or G. mosseae on their own were even more effective than the addition of fermented DOC alone in improving the growth and (NPK) foliar nutrients of D. pentaphyllum plants. The combined treatment involving the application of microbially‐treated agrowastes and mycorrhizal inoculation with AM fungi, particularly with G. mosseae, can be proposed as a successful revegetation strategy for D. pentaphyllum in P‐deficient soils under semiarid Mediterranean conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of ammonium and nitrate on the growth of vesicular-arbuscular mycorrhizalErythrina poeppigiana O.I. Cook seedlings

Erythrina poeppigiana, a woody tropical plant, was inoculated with vesicular-arbuscular mycorrhizal (VAM) fungiGlomus etunicatum Becker and Gerdeman,G. mosseae Nicol. and Gerd. Gerdeman and Trappe, orG. intraradices Schenk and Smith. Growth, N uptake, and nutrition were evaluated in VAM-inoculated plants and controls fertilized with two levels (3 or 6 mM) of either NH _inf4 ^sup+ -N or NO _inf3 ^sup- -N. The response by the mycorrhizal plants to N fertilization, according to N source and/or level differed significantly from that of the control plants. In general, the growth of the mycorrhizal plants was similar to that of the non-mycorrhizal plants when N was provided as NH _inf4 ^sup+ . When the N source was NO _inf3 ^sup- the control plants grew significantly less than the VAM plants. Inoculation with VAM fungi gave yield increases of 255 and 268% forG. etunicatum-colonized plants, 201 and 164% forG. mosseae-colonized plants and 286 and 218% forG. intraradices-colonized plants fertilized with 3 and 6 mM NO _inf3 ^sup- -N, respectively. The increased growth and acquisition of nutrients by plants fertilized with NO _inf3 ^sup- -N and inoculated with VAM shows that VAM mycelium has a capacity for NO _inf3 ^sup- absorption. The results also showed thatE. poeppigiana seedlings preferred NH _inf4 ^sup+ as an N source.G. etunicatum was the most effective endophyte, not only increasing N, P, Ca, Mg, and Zn uptake in the presence of NO _inf3 ^sup- fertilizer but also P and Mg in the presence of NH _inf4 ^sup+ applications. From these results we conclude that VAM symbiosis affects N metabolism inE. poeppigiana plants and that this species can overcome limitations on the use of NO _inf3 ^sup- -N by the mediation of VAM fungi.     

Interaction between Alternaria alternata or Fusarium equiseti and Glomus mosseae and its effects on plant growth

The effect of inoculation with the saprophytic fungi Alternaria alternata or Fusarium equiseti on maize (Zea mays) and lettuce (Lactuca sativa) with or without arbuscular mycorrhizal (AM) colonization by Glomus mosseae was studied in a greenhouse trial. Plant dry weights of non-AM-inoculated maize and lettuce were unaffected by the presence of A. alternata and F. equiseti. In contrast, A. alternata and F. equiseti decreased plant dry weights and mycorrhization when inoculated to the rhizosphere before G. mosseae. The saprophytic fungi inoculated 2 weeks after G. mosseae did not affect the percentage of root length colonized by the AM endophyte, but did affect its metabolic activity assessed as succinate dehydrogenase activity. Although F. equiseti inoculated at the same time as G. mosseae did not affect mycorrhization of maize roots, its effect on AM colonization of lettuce roots was similar to that with A. alternata. In the rhizosphere of both plants, the population of saprophytic fungi decreased significantly, but was not affected by the presence of G. mosseae. Our results suggest that there may have been a direct effect of the saprophytic fungi on the mycorrhizal fungi in the extramatrical phase of the latter, and when the AM fungus was established in the root the AM fungus was less affected by the saprophytic fungi. Received: 16 January 1996     

Effects of soil compaction and arbuscular mycorrhiza on corn (Zea mays L.) nutrient uptake

Soil compaction is of great importance, due to its adverse effects on plant growth and the environment. Mechanical methods to control soil compaction may not be economically and environmentally friendly. Hence, we designed experiments to test the hypothesis that use of plant symbiotic fungi, arbuscular mycorrhiza (AM) may alleviate the stressful effects of soil compaction on corn (Zea mays L.) growth through enhancing nutrient uptake. AM continuously interact with other soil microorganisms and its original diversity may also be important in determining the ability of the fungi to cope with the stresses. Hence, the objectives were: (1) to determine the effects of soil compaction on corn nutrient uptake in unsterilized (S1) and sterilized (S2) soils, and (2) to determine if inoculation of corn with different species of AM with different origins can enhance corn nutrient uptake in a compacted soil. Using 2 kg weights, soils (from the field topsoil) of 10 kg pots were compacted at three and four levels (C1, C2, C3 and C4) (C1 = non-compacted control) in the first and second experiment, respectively. Corn (cv. 704) seeds were planted in each pot and were inoculated with different AM treatments including control (M1), Iranian Glomus mosseae (M2), Iranian G. etunicatum (M3), and Canadian G. mosseae, received from GINCO (Glomales In Vitro Collection), Canada (M4). Corn leaf nutrient uptake of N, P, K, Fe, Mn, Zn and Cu were determined. Higher levels of compaction reduced corn nutrient uptake, however different species of AM and soil sterilization significantly increased it. The highest increase in nutrient uptake was related to P (60%) and Fe (58%) due to treatment M4S2C3. Although it seems that M3 and M4 may be the most effective species on corn nutrient uptake in a compacted soil, M2 increased nutrient uptake under conditions (C3 and C4 in unsterilized soil) where the other species did not. Through increasing nutrient uptake AM can alleviate the stressful effects of soil compaction on corn growth.     

Arbuscular mycorrhizal fungi associated with wild forage plants in typical steppe of eastern Inner Mongolia

A preliminary investigation was conducted on the arbuscular mycorrhizal (AM) status of the dominant and common wild forage plants in typical steppe of eastern Inner Mongolia, a major semi-arid grassland region in China. Fifty-four wild forage plant species were collected and examined, and 27 of these were colonized by AM fungi. Some plants belonging to families that are presumed to lack mycorrhizas (Cyperaceae, Caryophyllaceae and Chenopodiaceae) were also found to be mycorrhizal. Higher proportions of arbuscular mycorrhizal plants were found in perennial (56.1%) and monocotyledonous (64.7%) forage species. However, neither percentage of root length colonized nor spore density varied significantly between the two life forms or cotyledon types. Twenty-seven species belonging to 7 genera of AM fungi were identified in total according to the morphological characteristics of the spores from field soil and trap cultures, and the results indicate that Glomus was the dominant AM genus and Glomus geosporum (Nicolson & Gerdemann) Walker and Glomus mosseae (Nicolson & Gerdemann) Gerdemann & Trappe were the dominant species in field soil and trap cultures, respectively. Glomus intraradices Schenck & Smith, Glomus etunicatum Becher & Gerdemann, Glomus claroideum Schenk & Smith emend Walker & Vestberg, Glomus clarum Nicolson & Schenck and Scutellospora callospora (Nicolson & Gerdemann) Walker & Sanders also occurred with high frequencies.     

Suppression of other soil microorganisms by mycelium of arbuscular mycorrhizal fungi in root-free soil

The influence of mycelium of two arbuscular mycorrhizal (AM) fungi, Glomus intraradices and Glomus mosseae, on other soil microorganisms, was examined in root-free soil with and without organic substrate amendment in terms of cellulose. The AM fungi were grown in symbiosis with cucumber in a compartmented growth system, which allowed AM fungal external mycelium to grow into root-free compartments. The fungicide Benomyl was applied to the root-free compartments to create an alternative non-mycorrhizal control treatment. Whole cell biomarker fatty acids were employed to quantify different groups of soil microorganisms including the two AM fungi. Abundance of most microbial groups were reduced by external mycelium of both AM fungi, though differential effects on the microbial community composition were observed between the two AM fungi as revealed from principal component analysis. Inhibition of other soil microorganisms was more pronounced in root-free soil with mycelium of G. mosseae than with mycelium of G. intraradices. In general, cellulose increased the amount of biomarker fatty acids of most groups of soil microorganisms, but cellulose did not affect the influence of AM fungi on other soil microorganisms. Benomyl suppressed growth of the external mycelium of the two AM fungi and had limited non-target effects on other microbial groups. In conclusion, our results show differential effects of external mycelium of AM fungi on other soil microbial communities, though both AM fungi included in the study overall inhibited most microbial groups as examined using whole cell biomarker fatty acids.     

Interactive effects of co-inoculation of Bradyrhizobium japonicum strains and mycorrhiza species on soybean growth and nutrient contents in plant

The main objective of this study was to investigate the effects of co-inoculation with different strains of Bradyrhizobium japonicum (i.e. Helinitro, Rizoking, and Nitragin) and arbuscular mycorrhizal fungi (AMF) species (i.e. Glomus fasciculatum, Glomus versiforme, Glomus intraradices, Glomus mosseae, and Glomus etunicatum) on soybean growth, fungal root colonization, and nutrient uptake of nitrogen (N), phosphorus (P), zinc (Zn), iron (Fe), and copper (Cu). Co-inoculation with various AMF species and rhizobia significantly (p<0.01) increased the soybean biomass production as compared to the non-inoculated controls. Furthermore, AMF colonization of roots of soybean plants increased by 79, 70.1, 67, 63, 57.5, and 50.1% in the presence of G. fasciculatum (GF), G. versiforme (GV), G. intraradices (GI), G. mosseae (GM), and G. etunicatum (GE), and Gmix (a mixed culture of fungi), respectively. Higher nutrient contents were observed in plants co-inoculated with Helinitro and GF. More insight into these results will enable optimization of the effective use of AM fungi in combination with their bacterial partners as a tool for increasing soybean yields in Iran; however, its general analytical framework could be applied to other parts of the world.     

Solubilization of Insoluble Inorganic Phosphate by Hyphal Exudates of Arbuscular Mycorrhizal Fungi

Increased phosphate (P) uptake in plants by arbuscular mycorrhizal (AM) fungi is thought to depend mainly on the extension of external hyphae into soil. On the other hand, it is known that the hyphae of some kinds of ectomycorrhizal fungi release organic acids into soil and that they dissolve the insoluble inorganic P. This study collected hyphal exudates of AM fungi within compartmentalized pot culture and clarified their ability to solubilize insoluble inorganic P. Sterilized Andisol was packed in pots that were separated into root and hyphal compartments with a nylon net of 30 μm pore size. Seedlings of Allium cepa inoculated with AM fungi, Gigaspora margarita, or Glomus etunicatum were grown. Control pots were not inoculated. Mullite ceramic tubes were buried in the soil of each compartment and soil solution was collected. The anionic fraction of the soil solution was incubated with iron phosphate (4 mg FePO₄ in 1 mL of 0.4 acetate buffer). Solubilized P was measured. The AM colonization of plants inoculated with G. margarita and G. etunicatum was 86% and 54%, respectively. Adhesion of external hyphae was observed on the surface of the mullite ceramic tubes buried in soil of the hyphal compartment. Colonization of both fungi increased shoot P uptake and growth. Soil solution collected from the hyphal compartments of both fungi solubilized more P than did that from uninoculated plants. It is suggested that hyphal exudates can contribute to increased P uptake of colonized plants.     

葫芦科蔬菜对丛枝菌根真菌依赖性的研究

在盆栽条件下试验研究了5种葫芦科(Cucurbitaceae)蔬菜对2种丛枝菌根(Arbuscular Mycorrhiza，AM)真菌的依赖性。结果表明，AM真菌Glomus mosseae(G.m)和Gigaspora rosea(Gi.r)均能有效地促进葫芦科蔬菜的生长，显著增加叶面积和植株干物质量，提高叶片的光合速率，降低气孔阻力。供试葫芦科蔬菜对菌根的依赖程度顺序为黄瓜＞西瓜＞苦瓜＞葫芦＞南瓜。5种葫芦科蔬菜对AM的依赖性与AM真菌对根系的浸染率呈正相关关系，符合直线回归方程：y=117.19+0.7468x。     

Responses of Parkia biglobosa (Jacq.) Benth, Tamarindus indica L. and Zizyphus mauritiana Lam. to arbuscular mycorrhizal fungi in a phosphorus-deficient sandy soil

Responses of three multipurpose fruit tree species, Parkia biglobosa (Jacq.) Benth, Tamarindus indica L. and Zizyphus mauritiana Lam., to inoculation with five species of arbuscular mycorrhizal fungi, Acaulospora spinosa Walker and Trappe, Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, Glomus intraradices Schenck and Smith, Glomus aggregatum Schenck and Smith emend. Koske and Glomus manihotis Howeler, Sieverding and Schenck, differed markedly with respect to functional compatibility. This was measured as root colonization, mycorrhizal dependence (MD) and phosphorus concentrations in shoots of plants. Root colonization of fruit trees by A. spinosa, G. aggregatum and G. manihotis was high and tree growth increased significantly as a consequence. G. intraradices also colonized well, but provided little growth benefit. G. mosseae colonized poorly and did not stimulate plant growth. The MD of P. biglobosa and T. indica was similar, reaching no more than 36%, while Z. mauritiana showed the highest MD values, reaching a maximum of 78%. The Z. mauritiana A. spinosa combination was the most responsive with respect to total biomass production; phosphorus (P) absorption probably contributed to this more than the absorption of sodium, potassium, magnesium or calcium. The density and length of root hairs were positively correlated with MD, suggesting that root hairs are not indicative of MD. Received: 20 January 1997     

分根装置中接种AMF对12 mm土壤水稳性团聚体的影响

采用分根装置研究了丛枝菌根真菌侵染白三叶草（Trifolium repens）后对中性紫色土12 mm土壤水稳性团聚体（WSA1-2mm）含量的影响,并运用通径分析对其主要影响因子进行了量化比较。结果表明,接种Glomus intraradices、G. mosseae和G. etunicatum的菌根室土壤有机质、球囊霉素相关土壤蛋白（GRSP）含量均有增加的趋势; 接种3种菌种都显著增加了菌根室土壤WSA1-2mm含量。通径分析结果表明,菌丝密度对WSA1-2mm含量有较大的直接效应（直接通径系数 0.678）,而GRSP对WSA1-2mm的影响系数较小,既有直接效应又有间接效应,但以直接效应为主。菌丝和GRSP对12mm 土壤水稳性团聚体作用大小的差异可能源于二者作用机制的不同。