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.     

Depletion of non‐exchangeable NH$ _4^+ $ at the root–soil and hyphae–soil interface of VA mycorrhizal maize (Zea mays) and parsley (Petroselinum sativum)

Mobilization of non‐exchangeable ammonium (NH ) by hyphae of the vesicular‐arbuscular mycorrhizal (VAM) fungus Glumus mosseae was studied under controlled experimental conditions. Maize (Zea mays) and parsley (Petroselinum sativum) were grown either alone or in symbiosis with Glomus mosseae in containers with separated compartments for roots and hyphal growth. In one experiment, ¹⁵NH was added to the soil to differentiate between the native non‐exchangeable NH and the non‐exchangeable NH derived from N fertilization. Non‐exchangeable NH was mobilized by plant growth. Plant dry weight and N uptake, however, were not significantly influenced by mycorrhizal colonization of the roots. The influence of root infection with mycorrhizal fungus on the mobilization of non‐exchangeable NH was negligible. In the hyphal compartment, hyphal uptake of N resulted in a decrease of NH in the soil solution and of exchangeable NH . However, the NH concentration was still too high to permit the release of non‐exchangeable NH . The results demonstrate that, in contrast to roots, hyphae of VAM fungi are not able to form a non‐exchangeable‐NH depletion zone in the adjacent soil. However, under conditions of a more substantial depletion of the exchangeable NH in the mycorrhizal sphere (e.g., with longer growth), an effect of mycorrhiza on the non‐exchangeable NH might be found.     

Protection of olive planting stocks against parasitism of root-knot nematodes by arbuscular mycorrhizal fungi

The effects were investigated, under controlled conditions, of single and joint inoculation of olive planting stocks cvs Arbequina and Picual with the arbuscular mycorrhizal fungi (AMF) Glomus intraradices , Glomus mosseae or Glomus viscosum , and the root-knot nematodes Meloidogyne incognita and Meloidogyne javanica , on plant performance and nematode infection. Establishment of the fungal symbiosis significantly increased growth of olive plants by 88·9% within a range of 11·9–214·0%, irrespective of olive cultivar, plant age and infection by M. incognita or M. javanica . In plants free from AMF, infection by Meloidogyne spp. significantly reduced the plant main stem diameter by 22·8–38·6%, irrespective of cultivar and plant age. Establishment of AMF in olive plants significantly reduced severity of root galling by 6·3–36·8% as well as reproduction of both Meloidogyne spp. by 11·8–35·7%, indicating a protective effect against parasitism by root-knot nematodes. Infection by the nematodes influenced root colonization by AMF, but the net effect depended on the AMF isolate–olive cultivar combination. It is concluded that prior inoculation of olive plants with AMF may contribute to improving the health status and vigour of cvs Arbequina and Picual planting stocks during nursery propagation.     

华南主要树木丛枝菌根真菌物种多样性调查研究

为调查华南地区丛枝菌根（arbuscular mycorrhiza,AM）真菌的物种多样性与资源分布状况,本研究对该区域红花羊蹄甲（Bauhinia blakeana）、黄梁木（Neolamarckia cadamba）、构树（Broussonetia papyrifera）、尾叶桉（Eucalyptus urophylla）和杧果（Mangifera indica）5种主要树木AM真菌侵染状况进行研究,通过形态学特征及核糖体18S rRNA基因序列分析鉴定AM真菌种类。结果表明:1）5种树木均能形成丛枝菌根,红花羊蹄甲和尾叶桉为疆南星型（Arum-type）,杧果、构树和黄梁木为重楼型（Paris-type）。红花羊蹄甲和杧果的菌根侵染率高、孢子密度大,构树、黄梁木和尾叶桉的AM真菌侵染率和孢子密度相对较低。2）鉴定出AM真菌5属8种,分别为无梗囊霉属（Acaulospora）的浅窝无梗囊霉（Acaulospora lacunosa）和刺无梗囊霉（Acaulospora spinosa）,斗管囊霉属（Funneliformis）的摩西斗管囊霉（Funneliformis mosseae）,根孢囊霉属（Rhizophagus）的根内根孢囊霉（Rhizophagus intraradices）,以及球囊霉属（Glomus）的3种Glomus spp.和硬囊霉属（Sclerocystis）1种Sclerocystis sp.。3）球囊霉属的AM真菌广泛分布在红花羊蹄甲、杧果和构树根际,刺无梗囊霉分布在杧果和尾叶桉根际,摩西斗管囊霉为优势种,分布在构树和黄梁木根际;而浅窝无梗囊霉和硬囊霉只分布在1种树根际,表明其宿主专一性相对较强。结果显示华南树木根际土壤中AM真菌物种多样性较高,同时本研究为深入研究该地区林木根际AM真菌功能多样性提供了初步科学依据。     

放牧因子与VA菌根的相互作用对鸭茅养分吸收和生长发育的影响

探讨了放牧因子与VA菌根的相互作用对鸭茅(Dactylis glomerataL.)养分吸收和生长发育的影响。菌根效应表现在不施磷肥条件下的鸭茅地上部生育与地上、地下部的磷素营养上,但对地上部生育的效应因刈割次数的增加而降低,对地上、地下部磷素营养的效应因土壤镇压而降低。菌根对鸭茅钙素营养的效应只见于不施磷肥条件下的土壤镇压处理,而在相同条件下菌根却降低了鸭茅的镁含量。说明VA菌根对鸭茅磷素营养和生长发育的效应与土壤磷营养有关,而且因地上部的过度采食和土壤镇压而降低。     

Constraints on development of fungal biomass and decomposition processes during restoration of arable sandy soils

In an earlier study we reported the apparent stabilization of a low fungal biomass in ex-arable lands during the first decades after abandonment. It was hypothesized that the lack of increase in fungal biomass was due to constraints on development of fungi with persistent hyphae such as lignocellulolytic basidiomycetes and ericoid mycorrhizal fungi. With respect to the former group, the slow increase of the pool of lignocellulose-rich organic matter was expected to be the major constraint for their development. To study this, we enriched soil samples of one arable land, of two recently abandoned arable lands, of one older abandoned arable land and of heathland with carbon substrates that differed in composition (glucose, cellulose and sawdust). In addition, we combined the effect of carbon addition on fungal biomass development in arable and recently abandoned lands with inoculation of 1% of soil from the older abandoned site and the heathland. All treatments induced a fast increase and a subsequent rapid decline in fungal biomass in the arable and ex-arable fields. Denaturing Gradient Gel Electrophoresis (DGGE) band patterns and enzyme activities did show differences between the carbon treatments but not between the recent and older abandoned field sites, indicating a similarly responding fungal community even after three decades of land abandonment and irrespective of soil inoculation. Identification of fungi by sequencing and culturing confirmed that decomposition processes were mostly dominated by opportunistic fungi in arable and ex-arable fields. In the heathland, only a very slow increase of microbial activity was observed after addition of carbon and sequencing of DGGE bands showed that ericoid mycorrhiza (ERM) fungi were responsible for carbon decomposition. We conclude that an increase of enduringly present fungal hyphae in ex-arable land may only be possible when a separate litter layer develops and/or when suitable host plants for ERM fungi become established.     

Microbiota accompanying different arbuscular mycorrhizal fungal isolates influence soil aggregation

Arbuscular mycorrhizal fungi (AMF) are key components of ecosystems through their influence on plant communities and ecosystem processes. A major source of information regarding the importance of AMF species richness on process rates are mesocosm experiments using different levels of diversity of AMF as provided by single-species cultures of AMF. Since AMF inocula are generally made available in the form of non-sterile pot culture material, it is possible that AMF symbiosis-associated microbiota are at least partially responsible for some effects hitherto directly attributed to the AMF mycelium. Here, we provide evidence that microbiota associated with single-species cultures of AMF (after long-term pot culture enrichment of 7–8 years) can strongly affect the ecosystem process of soil aggregation. This effect occurred in an AMF isolate specific manner, but in the absence of live and active AMF mycelium. We additionally documented large differences in microbiota communities associated with the different AMF inocula (using PLFA analyses), suggesting that these differences were at least partly responsible for the observed changes in soil aggregation. This result points to AMF–microbiota interactions as a largely unexplored mechanism underlying soil aggregation (and potentially other ecosystem processes). We suggest that a reinterpretation of previous experiments using greenhouse-derived AMF cultures may be necessary, and the need to consider AMF symbiosis-associated microbiota in mechanistic studies of AMF and mycorrhizae in general is emphasized.     

Grazing preferences of some collembola for endomycorrhizal fungi

The ability of five collembolan species to distinguish and graze selectively on vesicular-arbuscular mycorrhiza (VAM) has been verified. Four species preferred the food infected by VAM fungi. All collembolan species showed more of less significant preferences for one species/isolate of the VAM fungi.