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1 Most rain forest tree species form vesicular-arbuscular mycorrhizas (VAM). Only a few species from several unrelated plant families form ectomycorrhizas (EM) in the tropics, although those that do are often locally abundant as colonizing species or forest dominants. 2 Both VAM and EM improve the uptake of mineral nutrients, especially immobile ones such as phosphorus, with their extensive, well-distributed mycelia. In addition, the mycorrhizal fungi of orchids and some EM fungi may directly recycle nutrients from litter by decomposing it. VAM fungi are unlikely to do so. 3 Mycorrhizal fungi almost completely close tropical mineral cycles by their efficient uptake of mineral nutrients from the soil, their advantageous position for scavenging mineral nutrients from dying roots, and their possible interspecific transfer of mineral nutrients. 4 VAM have been shown to improve the growth and survival of several tropical plants; only two indigenous rain forest tree species have been tested for response to EM, both of which showed improved growth. Species are facultatively or obligately dependent on VAM or EM for mineral nutrient uptake and growth, or are non-mycorrhizal. 5 Different dependencies on V AM or EM are adaptations to different soil fertilities and probabilities of mycorrhizal infection: EM species are favoured by seasonal dryness, inhibited nitrification, and extremely low mineral retention by soils such as white sands; facultatively mycotrophic species are favoured by high soil fertility; non-mycorrhizal species are favoured by slow rates of mycorrhiza formation by competing dependent species. Most mature-forest tree species are obligately mycotrophic. 6 Changes in soil fertility or in the probability of mycorrhizal infection can influence succession by favouring species with different dependencies on mycorrhizas. The probability of infection in rain forest soil can change markedly because these soils do not contain large numbers of spores. 7 EM species often dominate low-diversity tropical forests on poor soils because they have specifie, highly-beneficial fungal associates. VAM hosts predominate in forests with moderate turnover rates on soils of intermediate fertility; their dependence on the same few mycorrhizal fungus species for mineral nutrient uptake limits their ability to competitively exclude one another, and thereby contributes to high within-habitat species diversity.

This article is from Microbes and Environments , volume 29 . Abstract Arbuscular mycorrhizal (AM) fungi function as extended roots and take an active part in plant acquisition of nutrients and also soil pollutants, such as heavy metals. The objective of this study was to establish a method to observe the localization of cadmium (Cd) Kα at subcellular levels using X-ray fluorescence (XRF) imaging with a synchrotron irradiation microbeam in resin-embedded sections of mycorrhizas. To evaluate the methodology, distributions of Cd in high-pressure-frozen Lotus japonicus—Rhizophagus irregularis mycorrhizal roots were compared between two treatments; Cd was exposed either to the roots or to the extraradical hyphae. Results showed that, in the latter treatment, Cd was restricted to fungal structures, whereas in the former, Cd was detected in cell walls of the two organisms. Plunge-frozen extraradical mycelium of Gigaspora margarita exposed to Cd showed high signals of Cd in the cell walls and vacuoles, and low in the cytoplasm. With selective staining and elemental mapping by electron-dispersive X-ray spectrometry (EDS), a positive correlation between distributions of Cd and P was revealed in the vacuole, which suggested polyP as a counter ion of Cd. These results indicated that there was no Cd relocation in rapidly frozen resin-embedded materials, therefore supporting the usefulness of this methodology.

Book chapter

Book chapter

Jointly organised by the CSIRO Division of Forestry and Murdoch University and the Research Institute of Forestry, Chinese Academy of Forestry. Sponsored by the Crawford Fund

http://uf.catalog.fcla.edu/uf.jsp?st=UF022236690&ix=pm&I=0&V=D&pm=1

ARBUSCULAR MYCORRHIZAL PHYSIOLOG

ARBUSCULAR MYCORRHIZAL PHYSIOLOG

In order to investigate the effect of arbuscular mycorrhizas and phosphorus levels on photosynthetic capacity and enzyme activity in peppermint under different water conditions, an experiment was conducted during the 2017–2018 growing seasons. The experimental treatments comprised water deficiency at three levels (a1: irrigation after 70 mm evaporation from pan of Class A, a2: irrigation after 110 mm evaporation from pan of Class A, and a3: irrigation after 150 mm evaporation from pan of Class A), phosphorus fertilizer at three levels (without phosphorus fertilization, 25% recommended phosphorus amount, and 50% recommended phosphorus amount), and different mycorrhiza species (nonmycorrhizal inoculation, Rhizophagus intraradices , Funneliformis mosseae , Glomus hoi , and mixture of all three species). Results showed that water stress significantly reduced chlorophyll a , chlorophyll b , total chlorophyll, and essential oil yield, but increased the stomatal resistance of peppermint. The essential oil yield of peppermint was significantly reduced by severe water deficit (a3). However, inoculation with R. intraradices , G. hoi , and a mixture of all three species under severe water deficit, increased the essential oil percentage of peppermint by 21%, 21%, and 31.5%, respectively. Application of 50% recommended phosphorus fertilizer increased the yield of essential oil by 18.9%. In addition, menthol increased by 24.1% (highest) under a3 irrigation, using 25% of the optimal dosage of phosphate fertilizer and nonmycorrhizal inoculation. The maximum catalase and peroxidase activity was obtained in the treatment of G. hoi mycorrhizal fertilizer, after application of 25% recommended dose of phosphorus fertilizer and a2 and a3 irrigation.

In order to investigate the effect of arbuscular mycorrhizas and phosphorus levels on photosynthetic capacity and enzyme activity in peppermint under different water conditions, an experiment was conducted during the 2017–2018 growing seasons. The experimental treatments comprised water deficiency at three levels (a1: irrigation after 70 mm evaporation from pan of Class A, a2: irrigation after 110 mm evaporation from pan of Class A, and a3: irrigation after 150 mm evaporation from pan of Class A), phosphorus fertilizer at three levels (without phosphorus fertilization, 25% recommended phosphorus amount, and 50% recommended phosphorus amount), and different mycorrhiza species (nonmycorrhizal inoculation, Rhizophagus intraradices , Funneliformis mosseae , Glomus hoi , and mixture of all three species). Results showed that water stress significantly reduced chlorophyll a , chlorophyll b , total chlorophyll, and essential oil yield, but increased the stomatal resistance of peppermint. The essential oil yield of peppermint was significantly reduced by severe water deficit (a3). However, inoculation with R. intraradices , G. hoi , and a mixture of all three species under severe water deficit, increased the essential oil percentage of peppermint by 21%, 21%, and 31.5%, respectively. Application of 50% recommended phosphorus fertilizer increased the yield of essential oil by 18.9%. In addition, menthol increased by 24.1% (highest) under a3 irrigation, using 25% of the optimal dosage of phosphate fertilizer and nonmycorrhizal inoculation. The maximum catalase and peroxidase activity was obtained in the treatment of G. hoi mycorrhizal fertilizer, after application of 25% recommended dose of phosphorus fertilizer and a2 and a3 irrigation.

In order to investigate the effect of arbuscular mycorrhizas and phosphorus levels on photosynthetic capacity and enzyme activity in peppermint under different water conditions, an experiment was conducted during the 2017–2018 growing seasons. The experimental treatments comprised water deficiency at three levels (a1: irrigation after 70 mm evaporation from pan of Class A, a2: irrigation after 110 mm evaporation from pan of Class A, and a3: irrigation after 150 mm evaporation from pan of Class A), phosphorus fertilizer at three levels (without phosphorus fertilization, 25% recommended phosphorus amount, and 50% recommended phosphorus amount), and different mycorrhiza species (nonmycorrhizal inoculation, Rhizophagus intraradices , Funneliformis mosseae , Glomus hoi , and mixture of all three species). Results showed that water stress significantly reduced chlorophyll a , chlorophyll b , total chlorophyll, and essential oil yield, but increased the stomatal resistance of peppermint. The essential oil yield of peppermint was significantly reduced by severe water deficit (a3). However, inoculation with R. intraradices , G. hoi , and a mixture of all three species under severe water deficit, increased the essential oil percentage of peppermint by 21%, 21%, and 31.5%, respectively. Application of 50% recommended phosphorus fertilizer increased the yield of essential oil by 18.9%. In addition, menthol increased by 24.1% (highest) under a3 irrigation, using 25% of the optimal dosage of phosphate fertilizer and nonmycorrhizal inoculation. The maximum catalase and peroxidase activity was obtained in the treatment of G. hoi mycorrhizal fertilizer, after application of 25% recommended dose of phosphorus fertilizer and a2 and a3 irrigation.

Book chapter