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

https://www.researchgate.net/profile/Rupam_Kapoor/publication/26881549_Arbuscular_mycorrhizal_fungi_in_alleviation_of_salt_stress_A_review/links/0c960523fd2cc5ec7f000000.pdf

Arbuscular mycorrhizal fungi in alleviation of salt stress: a review.

Publisher Summary This chapter discusses the ecological implications of mycorrhizal associations in natural ecosystems and the role of soil or environmental factors, mycorrhizal fungus characteristics or host plant properties. Mycorrhizal associations are regulated by features of the host plant and mycorrhizal fungus, as well as by soil conditions and environmental factors. Factors which can influence the occurrence and effectiveness of mycorrhizal associations include (1) root properties (2) edaphic or climatic factors (3) soil organisms, (4) soil disturbance, and (5) host-fungus compatibility. Several other complex ecological topics also discussed in the chapter include (1) mycorrhizal phenology , (2) factors responsible for varying degrees of mycorrhizal dependency in host plants, (3) the role of mycorrhizal hyphae in soil (4) nutrient competition involving mycorrhizal and non-mycorrhizal plants, and (5) mycorrhizal interactions involving pollution and other stresses, the rhizosphere, soil properties and allelopathy. Finally, the chapter also discusses the population ecology of mycorrhizal fungi and the influence of their associations on plant population ecology.

Mycorrhizas in Natural Ecosystems

Tomato and salinity

Salinity is one of the most severe environmental stress as it decreases crop production of more than 20% of irrigated land worldwide. Hence, it is important to develop salt-tolerant crops. Understanding the mechanisms that enable plant growth under saline conditions is therefore required. Acclimation of plants to salinized conditions depends upon activation of cascades of molecular networks involved in stress sensing, signal transduction, and the expression of specific stress-related genes and metabolites. The stress signal is first perceived at the membrane level by the receptors and then transduced in the cell to switch on the stress-responsive genes which mediate stress tolerance. In addition to stress-adaptative mechanisms developed by plants, arbuscular mycorrhizal fungi have been shown to improve plant tolerance to abiotic environmental factors such as salinity. In this review, we emphasize the significance of arbuscular mycorrhizal fungi alleviation of salt stress and their beneficial effects on plant growth and productivity. Although salinity can affect negatively arbuscular mycorrhizal fungi, many reports show improved growth and performance of mycorrhizal plants under salt stress conditions. These positive effects are explained by improved host plant nutrition, higher K+/Na+ ratios in plant tissues and a better osmotic adjustment by accumulation of compatible solutes such as proline, glycine betaine, or soluble sugars. Arbuscular mycorrhizal plants also improve photosynthetic- and water use efficiency under salt stress. Arbuscular mycorrhizal plants enhance the activity of antioxidant enzymes in order to cope with the reactive oxygen species generated by salinity. At the molecular level, arbuscular mycorrhizal symbiosis regulates the expression of plant genes involved in the biosynthesis of proline, of genes encoding aquaporins, and of genes encoding late embryogenesis abundant proteins, with chaperone activity. The regulation of these genes allows mycorrhizal plants to maintain a better water status in their tissues. Gene expression patterns suggest that mycorrhizal plants are less strained by salt stress than non-mycorrhizal plants. In contrast, scarce information is available on the possible regulation by the arbuscular mycorrhizal symbiosis of plant genes encoding Na+/H+ antiporters or cyclic nucleotide-gated channels. These genes encode proteins with a key role in the regulation of uptake, distribution and compartimentation of sodium and other ions within the plant, and are major determinants for the salt sensitiveness of a plant. Thus, we propose that investigating the participation of cation proton antiporters and cyclic nucleotide-gated channels on arbuscular mycorrhizal symbiosis under salinity is a promising field that should shed further light on new mechanisms involved in the enhanced tolerance of mycorrhizal plants to salt stress.

https://hal.archives-ouvertes.fr/hal-00930499/document

Salinity stress alleviation using arbuscular mycorrhizal fungi. A review

Vesicular-arbuscular (VA) mycorrhizal fungi were collected and identified from saline locations throughout southern and central California and Nevada. From this collection, 38 soil samples containing VA mycorrhizal fungi from 22 plant species were used to inoculate tomato seedlings and evaluate their growth under artificial salinization. Six samples significantly improved growth of tomato in salinized soil when compared to a salinized, nonmycorrhizal control. Growth with 14 samples in salinized soil was as good as growth of a nonmycorrhizal control in nonsalinized soil. Glomusfasciculatum consistently provided the largest growth response. Negative correlations were found between the amount of mycorrhizal colonization on tomato roots in the greenhouse and electrical conductivity, Na concentration, and osmotic potential of the saline soil samples from the field. The amount of mycorrhizal colonization on hosts in the field from which the soil samples were collected was not correlated to growth response or mycorrhizal colonization of tomato in the greenhouse.

Improved growth of tomato in salinized soil by vesicular-arbuscular mycorrhizal fungi collected from saline soils

Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg−1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m−1. Onion colonized withGlomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low (≤ 0.2 mmol kg−1 NaHCO3-extractable P) at soil saturation extract salinities from 1.1 dS m−1 to 8.8 dS m−1. When 0.8 and 1.6 mM P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments.Glomus fasciculatum (Gerdeman and Trappe) andGlomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m−1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake.

Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

The influence of temperature on the abundance, developmental sequence, morphology, and size of Phytophthora cinnamomi sexual structures was studied in a cross between isolates of A1 and A2 mating t...

E. C. Pond

Papers

Improved growth of tomato in salinized soil by vesicular-arbuscular mycorrhizal fungi collected from saline soils

Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

The Influence of Temperature and Nutrition on Formation of Sexual Structures by Phytophthora Cinnamomi

A new canker disease of avocado caused by Phytophthora heveae.