Vesicular-arbuscular mycorrhizal fungi can affect the water balance of both amply watered and droughted host plants. This review summarizes these effects and possible causal mechanisms. Also discussed are host drought resistance and the influence of soil drying on the fungi.

Water relations, drought and vesicular-arbuscular mycorrhizal symbiosis

Publisher Summary The chapter presents a discussion on plant growth-regulating (PGR) substances in the rhizosphere, with emphasis on microbial production and functions. The chapter discusses the rhizosphere as a site of plant-microbe interactions; plant growth-regulating substances and their sources; biochemistry of microbial production of PGRs; production of PGRs by rhizosphere microorganisms; metabolism of PGRs in soil; and ecological significance of PGRs produced in the rhizosphere. The chapter provides a better understanding of the mechanisms of actions of microbially derived PGRs and their interactions with plants. Moreover, development of hormone-deficient plant mutants can provide opportunities to clearly define the role of microbially produced PGRs in plan-microbe interactions. An understanding of these aspects can aid in the utilization of microbial PGRs for the betterment and benefit of sustainable agriculture.

Plant growth-regulating substances in the rhizosphere: microbial production and functions

Taxonomy and phylogeny of the glomales, S. Rosendahl et al biodiversity and characterization of arbuscular mycorrhizal fungi at the molecular level, D. van Tuinen et al characterization of arbuscular mycorrhizal fungi by immunochemical methods, A. Hahn et al European bank of glomales - an essential tool for the efficient international and interdisciplinary collaboration, J.C. Dodd et al physiological characteristics of the host plant promoting an undisturbed functioning of the mycorrhizal symbiosis, C. Azcon-Aguilar and B. Bago recognition and infection process, basis for host specificity of arbuscular mycorrhizal fungi, M. Giovannetti et al ultrastructural analysis reveals the complex interactions between root cells and arbuscular mycorrhizal fungi, P. Bonfante impact of mycorrhizal colonization on root architecture, root longevity and the formation of growth regulators, D. Atkinson et al biogeochemical cycling and arbuscular mycorrhizas in the sustainability of plant-soil systems, P. Jeffries and J.M. Barea arbuscular mycorrhizas and agrosystem stability, G.J. Bethlenfalvay and H. Schuepp hyphal phosphorous transport - a keystone to mycorrhizal enhancement of plant growth, I. Jakobsen et al approaches to the study of the extraradical mycelium of arbuscular mycorrhizal fungi, J.C. Dodd water relations and alleviation of drought stress in mycorrhizal plants, M. Sanchez-Diaz and M. Honrubia impact of arbuscular mycorrhizal fungi on plant uptake of heavy metals and radionuclides from soil, K. Haselwandter et al biocontrol of plant pathogens using arbuscular mycorrhizal fungi, J.E. Hooker et al management of positive interactions of arbuscular mycorrhizal fungi with essential groups of soil microorganisms, G. Puppi et al micropropagated plants, an opportunity to positively manage mycorrhizal activities, M. Vestberg and V. Estaun.

Impact of Arbuscular Mycorrhizas on Sustainable Agriculture and Natural Ecosystems

Effects of several kinds of charcoal applied to soil on citrus growth and vesiculararbuscular mycorrhizal (VAM) development were investigated. Satsuma mandarin (Citrus unshiu Marc.) trees on trifoliate orange (Poncirus trifoliata Raf.) rootstocks were transplanted to root boxes using the soil mixed with charcoal derived from rice husk, citrus juice sediment or western spruce bark. The trees were inoculated with the spores of Glomus fasciculatum (Thaxter) Gerdemann and Trappe emend. Walker and Koske. Elongation of the roots in the charcoal treatments was more vigorous than that in the charcoal-free control. The fresh weigths of the root, shoot and the whole tree increased in response to charcoal application. The intensity of VAM infection in any charcoal treatment was higher than that in the control. In particular, the percentage of the infection in the rice husk charcoal plot was 41.5 and P concentration in the leaf exceeded that of the control. In a Citrus iyo orchard, the percentage of VAM infection was 52% in the rice husk charcoal plot, the highest among plots. The intensity in the Bahia grass (Paspalum notatum Flugge.) plot was next, followed by the third highest rate found in the abandoned plot which had not been cultivated in recent years. The lowest percentage of VAM infection was in a clean-culture plot. A microscopic observation also revealed that in a charcoal-treated plot there were many sites where VAM fungi infected the root.

https://www.jstage.jst.go.jp/article/jjshs1925/63/3/63_3_529/_pdf

Effects of charcoal as a soil conditioner on citrus growth and vesicular-arbuscular mycorrhizal development

During drying, mycorrhizal plants often maintain higher stomatal conductance (g s ) than similarly-sized and -nourished non-mycorrhizal plants, but the mechanism of mycorrhizal influence remains unclear. Several hydraulic and non-hydraulic factors previously implicated in control of stomatal behavior during drought were measured, to learn which are affected when roots of cowpea (Vigna unguiculata [L.] Walp. cv. White Acre) are extensively colonized by Glomus intraradices Schenck and Smith isolate UT143. At low soil water contents (θ), mycorrhizal plants maintained higher g s , transpiration and shoot water potential (ψ) than non-mycorrhizal plants. These higher foliar water status characters were associated with lower xylem-sap abscisic acid concentrations ([ABA]) and lower ABA fluxes to leaves in mycorrhizal plants at low soil θ. Stomatal conductance was most closely correlated with xylem-sap [ABA], ABA flux to leaves and shoot ψ. Stomatal conductance was not correlated with xylem-sap concentrations of calcium or zeatin riboside equivalents, or with xylem-sap pH, nor were these xylem-sap constituents affected by mycorrhizal symbiosis. Stomata of mycorrhizal and non-mycorrhizal leaves showed similar sensitivities to ABA, whether leaves were intact or detached. It is concluded that mycorrhizal fungi probably increased the capability of root systems to scavenge water in drier soil, resulting in less strain to foliage and hence higher g s and shoot ψ at particular soil θ.

M. H. Edriss

Papers

In vitro propagation of ‘Troyer’ citrange from epicotyl segments

Influence of mycorrhizal fungi on cytokinin production in sour orange

Micro-grafting shoot-tip culture of citrus on three trifoliolate rootstocks

Increased growth responses of Citrus by several species of mycorrhizal fungi