生草栽培对柑桔丛枝茵根形成及果实品质的影响

试验以枳砧锦橙（Citrus sinensis Osbeck．）初结果树为试材。试验设4个处理，分别为柑桔园间作百喜草（Bahia grass）（Paspalum notaturn Flugge）、白三叶草（White clover）（Trifolium repens L．）、紫花苜蓿（Alfalfa）（Medicago sativa L．）和多年生黑麦草（Perennial ryegrass）（Lolium perenne L．），以清耕为对照。单行小区，随机区组排列，3次重复。结果表明，在干旱季节，所有生草处理区都显著改善了根际土壤水分和温度状况．而百喜草和白三叶草生草区土壤丛枝菌根真菌孢子数和柑桔根系菌根侵染率显著高于清耕区和其它生草区。表明在干旱季节．百喜草和白三叶草生草栽培促进了果园土壤丛枝菌根真菌的生长和柑桔根系菌根的形成，从而促进了柑桔根系对水分和磷素营养的吸收利用。试验结果表明果园管理中宜选择菌根侵染率高的草种如百喜草、白三叶草在柑桔园进行生草栽培，促进柑桔根系菌根形成，改善植株生理代谢，提高果品质量。     

Organic acid induced release of nutrients from metal-stabilized soil organic matter – The unbutton model

Processes of soil organic matter (SOM) stabilization and the reverse, destabilization of SOM resulting in subsequent release and mobilization of nutrients from SOM, remain largely unresolved. The perception of SOM as supramolecular aggregates built of low molecular mass biomolecules is currently emerging. Polyvalent metal cations contribute to SOM tertiary structure by bridging functional groups of such molecules (Simpson et al., 2002). The strong bond to metals protects high quality organic material from being immediately accessed and decomposed. Here we propose a three-step process by which low molecular mass organic acids (LMMOAs) and hydrolytic enzymes act in series to destabilize SOM supramolecules to release organic nitrogen (N) and phosphorus (P) for local hyphal and root uptake. Complexation of the stabilizing metals by fungal-released LMMOA gives fungal-root consortia direct access to organic substrates of good quality. Because of their small sizes and carboxyl group configuration, citric and oxalic acids are the most effective LMMOAs forming stable complexes with the main SOM bridging metals Ca and Al in SOM. Citrate, forming particularly strong complexes with the trivalent cations Al and Fe, is dominant in soil solutions of low-productive highly acidic boreal forest soils where mycorrhizal associations with roots are formed predominantly by fungi with hydrophobic hyphal surfaces. In these systems mycelia participate in the formation of N-containing SOM with a significant contribution from strong Al bridges. In less acidic soils of temperate forests, including calcareous influenced soils, SOM is stabilized predominantly by Ca bridges. In such systems mycorrhizal fungi with more hydrophilic surfaces dominate, and oxalic acid, forming strong bidentate complexes with Ca, is the most common LMMOA exuded. A plant-fungus driven biotic mechanism at the supramolecular aggregate level (10³–10⁵ Da) resolves micro-spatial priming of SOM, where the destabilization step is prerequisite for subsequent release of nutrients.     

Effects of inoculation with stress-adapted arbuscular mycorrhizal fungus Glomus deserticola on growth of Solanum melogena L. and Sorghum sudanese Staph. seedlings under salinity and heavy metal stress conditions

The beneficial effects of a Glomus deserticola strain isolated from the rhizosphere of grasses (belonging to Poaceae family) growing along the industrial waste from a distillery were investigated under stress conditions. The study was conducted to assess the efficacy of the arbuscular mycorrhizal (AM) fungal ecotype in salinity and heavy metal (HM) tolerance of eggplant (Solanum melongena L.) in soils amended with various stress levels of NaCl, zinc and cadmium. Mycorrhizal (M) seedlings produced a significantly (p < 0.05) greater growth response and were more tolerant to salt and HM stresses than nonmycorrhizal (NM) seedlings in all treatments. The HM contents in the plant tissues were significantly higher in M than NM eggplants. Furthermore, when the efficacy was compared with other AM isolates in HM-polluted soils with Sudan grass (Sorghum sudanese Staph.) as a test plant, the AM ecotype responded best to these soils, as evident from the significantly greater growth response and its aggressiveness in colonizing roots in all soil types tested. These results suggest that this G. deserticola ecotype can be used as an effective tool to alleviate the adverse effects of excessive salinity and HM toxicity on plant growth. Finally, the isolate may have potential in the bioremediation of polluted soils.     

Synergistic effects of vesicular-arbuscular mycorrhizal fungi and diazotrophic bacteria on nutrition and growth of sweet potato (Ipomoea batatas)

Summary Sweet potatoes were micropropagated and then transplanted from axnic conditions to fumigated soil in pots in the greenhouse. Spores of Glomus clarum were obtained from Brachiaria decumbens or from sweet potatoes grown in soil infected with this fungus and with an enrichment culture of Acetobacter diazotrophicus. Three experiments were carried out to measure the beneficial effects of vesicular-arbuscular mycorrhizal (VAM) fungi-diazotroph interactions on growth, nutrition, and infection of sweet potato by A. diazotrophicus and other diazotrophs obtained from sweet potato roots. In two of these experiments the soils had been mixed with ¹⁵N-containing organic matter. The greatest effects of mycorrhizal inoculation were observed with co-inoculation of A. diazotrophicus and/or mixed cultures of diazotrophs containing A. diazotrophicus and Klebsiella sp. The tuber production was dependent on mycorrhization, and total N and P accumulation were increased when diazotrophs and G. clarum were applied together with VAM fungal spores. A. diazotrophicus infected aerial plant parts only when inoculated together with VAM fungi or when present within G. clarum spores. More pronounced effects on root colonization and intraradical sporulation of G. clarum were observed when A. diazotrophicus was co-inoculated. In non-fumigated soil, dual inoculation effects, however, were of lower magnitude. ¹⁵N analysis of the aerial parts and roots and tubers at the early growth stage (70 days) showed no statistical differences between treatments except for the VAM+Klebsiella sp. treatment. This indicates that the effects of A. diazotrophicus and other diazotrophs on sweet potato growth were caused by enhanced mycorrhization and, consequently, a more efficient assimilation of nutrients from the soil than by N₂ fixation. The possible interactions between these effects are discussed.     

Interaction of the vesicular-arbuscular mycorrhizae of maize with extractable soil phosphorus levels and nitrogen-potassium fertilizers

Summary A field experiment was conducted for 3 years to determine whether increasing extractable soil P levels would affect vesicular-arbuscular mycorrhizae (VAM) of maize (Zea mays L.) and the subsequent uptake of P and production of dry matter. Five levels of extractable soil P were established on an Aquic Dystrochrept soil with high and low NK fertilization. The results show that as extractable soil-P levels increase the vesicular-arbuscular mycorrhizae of maize decrease, but P concentrations in both leaf and root tissue increase. There was a significant interaction between the extractable soil-P levels and NK treatment. At the low soil-P level NK fertilization increased mycorrhizae, while at the high soil-P levels NK fertilization reduced mycorrhizae. Dry-matter production generally paralleled extractable soil-P levels from 1.0 mg P kg^–1 to a maximum at 10 mg P kg^–1 soil (by ammonium acetate, pH 4.8). The reduction in vesicular-arbuscular mycorrhizae at the highest levels of extractable soil P apparently was not critical to either P uptake or dry-matter production.Scientific contribution No. 1196 Storrs Agricultural Experiment Station     

Susceptibility and effectiveness of vesicular-arbuscular mycorrhizae in wheat cultivars under different growing conditions

Summary Wheat cultivars assumed to be non-susceptible to vesicular-arbuscular (VA) mycorrhizae became colonized, and this effect persisted under different growth conditions. Colonization of all cultivars was similar regardless of the amount of inoculum and the time interval of inoculation. Different plant growth temperatures and the support given by the culture media, inoculation with different endophytes, and inoculation with sterilized and unsterilized spores affected VA colonization levels, although the level of colonization reached in cv. Champlein was similar to that reached in cv. 7-Cerros under each condition. VA mycorrhizal colonization was also affected by different plant growth conditions. After VA reinoculation, the plant dry weight of Castan and 7-Cerros increased, but not Negrillo and Champlein cultivars. VA mycorrhizae increased the shoot dry weight of 7-Cerros only, but not of Champlein, when grown at 35/24°C, and had no effect on the dry weight of either cultivar grown at 18/12°C and 42/24°C. Inoculation with Glomus mosseae increased the dry weight of the cultivars more than inoculation with G. fasciculatum or G. agregatum. The effect on the plant dry weight was greater in plants grown in soil than in sand/vermiculite pots. Inoculation with sterilized and unsterilized spores of G. mosseae, either in soil pots or in sand/vermiculite tubes, did not increase the plant dry weight. Our results indicate that there was no close relationship between the level of root colonization and the effect on plant growth. The effects of accompanying microorganisms in the VA inoculum on VA mycorrhizal symbiosis are discussed.     

Infection of valuable broadleaf hardwood trees by Glomus mosseae: growth and mineral nutrition

In the past century, the excessive exploitation of the environment by human beings has resulted in the depletion of valuable broadleaf hardwood trees in Italian forests, creating a need for re-forestation. The aim of this research was to verify whether a vescicular-arbuscular mycorrhizal (VAM) fungus is able to colonise the root of valuable hardwood trees and to evaluate the impact of the VAM fungus on growth and macroelement nutrition of its plant hosts.Four species of valuable broadleaf hardwood trees, Prunus avium L., Fraxinus excelsior L., Acer pseudoplatanus L., and Juglans nigra L., were inoculated with Glomus mosseae, a VAM fungus, and cultivated in a greenhouse. Infection after inoculation and root colonization by the fungus, tree growth, and macro-element nutrition were evaluated two-years after inoculation. G. mosseae formed mycorrhizae on all plants. However, different morphological aspects - predominantly the formation of Arum type arbuscles in P. avium and F. excelsior - were observed. A general improvement of macro-element nutrition from species to species characterised an enhanced growth of mycorrhizal plants. Therefore, it is plausible that the association of VAMs with these broadleaf trees, could overcome the difficulties encountered in the transplanting and the slow growth typical of these tree species.Although numerous articles have reported the beneficial effects of ectomycorrhizal fungi on trees, there is a sparse literature on the association of VAM with tree species. Therefore, this study contributes to the understanding of the role of the symbiosis between valuable broadleaf trees and VAM fungi in macroelement nutrition.     

不同作物对VA菌根真菌的依赖性差异

以玉米、 小麦、 大豆、 三叶草四种作物为试材, 在低和高两个施磷水平下接种或 不接种泡囊-丛枝菌根真菌(VAMF), 研究不同作物的菌根依赖性及其影响因子。 结果表明 , 接种菌根真菌显著地促进了玉米、 大豆、 三叶草的生长, 但小麦无此效果, 菌根依 赖性的大小顺序为玉米＞大豆＞三叶草＞小麦。 菌根真菌提高作物的叶绿     

VA菌根对黄檗幼苗抗性生理指标的影响

通过盆栽接种试验,研究VA菌根对黄檗（Phellodendron amurense）1年生实生苗的抗性生理指标的影响。结果表明,VA菌根可明显提高黄檗幼苗的抗性指标。可溶性糖含量随着侵染率的增加而增大,并能促进黄檗叶片中可溶性糖向根系中转移,游离脯氨酸和MDA含量逐渐降低,呼吸酶活性和保护酶活性增强。接种Glomus diaphanum的苗木可溶性糖,游离脯氨酸、CAT活性及POD活性变化最为明显,叶片可溶性糖含量为0.5736%,叶片脯氨酸含量为16.27 μg/g,叶片CAT活性为0.3186 mg/(g?min),叶片POD活性为258.32 u/(g?min)。接种G. mosseae对黄檗苗木MDA含量、呼吸酶活性及SOD活性影响最大,叶片MDA含量为0.0119 μmol/g,叶片抗坏血酸氧化酶活性为0.2714 mg/(g?min),叶片多酚氧化酶活性为0.3487 mg/(g?min),叶片SOD活性为274.18 u/(g?FW)。     

VA 菌根真菌对酸枣实生苗抗旱性的影响

 在盆栽条件下, 研究了VA 菌根对酸枣实生苗生长和抗旱性的影响。结果表明, 在土壤相对含水量为20 %、40 %、60 %条件下, VA 菌根能显著增加酸枣实生苗的生长量(株高、叶面积、鲜样质量、干样质量等) , 降低叶片自然饱和亏和脯氨酸含量, 提高植株叶片气孔导度、蒸腾速率、光合速率, 显著增强了植株的抗旱能力。在土壤相对含水量相同状况下, 接种菌根真菌植株制造1 g 干物质的需水量低于不接种的处理, 节水效果为16. 5 %～29. 8 %。干旱条件对VA 菌根的侵染影响不大。播种时进行控水处理和在播种后40 d 开始控水两个水分试验对菌根的侵染率、植株的生长及水分状况影响差异不大。