Arbuscular mycorrhizal fungi and plant symbiosis under stress conditions: ecological implications of drought, flooding and salinity

GARCÍA ILEANA VANESA; MENDOZA RODOLFO ERNESTO

Applied Mycology

CAB International

Lugar: Wallingford, United Kingdom; Año: 2009; p. 17 - 37

The present chapter describes some of the principal effects and mechanisms involved in AM fungi and plant symbiosis under stress conditions such as drought, flooding and salinity. The formation and function of AM symbiosis in a particular ecosystem appear to be driven by climate, soil water content, nutrient supply and oxygen availability in soil, and the plant photosynthetic capacity. The distribution of certain AM fungal species has been related to soil pH, P level, total carbon and nitrogen, salinity, vegetation, hydrologic condition of the soil, landscape position or temperature. AM fungi are advantageous for plants during certain times of the plant phenological cycle, while at the same time suggesting that flooding and soil moisture will often outweigh plant phenological effects on the dynamics of AM colonization. Knowledge of the seasonal dynamic of colonization is necessary to quantify the functioning and ecological significance of AM fungi. Periods during which mycorrhizal colonization is high are those when the fungus is most likely to influence plant nutrient status and exert a demand for carbon from the plant. In grasslands habitats, the distinct seasonalities of AM fungal species suggest a temporal partitioning of plant resources; by specializing on cool or warm season plants, fungi would minimize interspecific competition for roots. Mycorrhizal beneficial effects go beyond the individual and determine vegetation responses at the community and ecosystem levels. AM fungi are particularly beneficial to their hosts in harsh environments. They tend to form fan-shaped mycelia that extend beyond the root into the surrounding soil, thereby improving the exploratory ability of the roots and increasing the acquisition of ions that are slow to diffuse through soil. It is likely that the contribution of the AM symbiosis to plant drought tolerance results from a combination of physical, nutritional, physiological and cellular effects. Mycorrhizal soil had significantly more water stable aggregates, and this fact affects the soil moisture retention characteristic and soil structure. AM plants are known to tolerate salinity better than non mycorrhizal plants. This may was ascribed to increased uptake of nutrients with low mobility, such as P, Zn and Cu and improved water relations, which may lead to increased growth and subsequent dilution of toxic ion effects. Mycorrhizal colonization may also increase the tolerance to water excess in soil. Once the plant is established, AM symbiosis may also have an ameliorating effect on plant performance under flooding. This effect seems to be carried through an improvement of the plant nutrient status by increasing N or P acquisition in flooded plants. Nowadays exists a real need for further studies on the dynamics of AM fungal colonization and plant nutrient uptake in stress natural environments. There is a variety of information of changes in fertility, salinity and moisture content in soil on AM fungi and plant symbiosis in controlled conditions, but more field research is needed to understand more about the ecological implication of the symbiotic associations that help plants to cope stressful environment.