The effect of drought on mycorrhizas of beech ( Fagus sylvatica L.): changes in community structure, and the content of carbohydrates and nitrogen storage bodies of the fungi

Abstract

In a water-exclusion experiment, five different ecotypes of beech (Fagus sylvatica L.; representing regions of different environmental and climatic conditions in Baden-Württemberg, Germany) were subjected to drought conditions of different severity between July and September of two consecutive years. Drought stress as characterised by the water content and the pre-dawn water potential of the leaves was related to the degree of mycorrhization, the type of ectomycorrhiza, and the physiological properties of individual fungus/plant interactions at the fine roots of different beech ecotypes. Our data show that decreased soil water availability did not significantly change either the degree of fungal colonisation of beech roots (measured by the amount of ergosterol) or the number of ectomycorrhizal types per root system. Drought did, however, have an influence on the composition of the ectomycorrhizal community, and different mycorrhizal types responded to drought differently in terms of their patterns of occurrence/abundance. While the abundance of the dominant mycorrhizal types, formed with Byssocorticium atrovirens and Lactarius subdulcis, was not affected, drought increased the abundance of mycorrhiza formed between beech and Xerocomus chrysenteron. A detailed analysis of plant and fungal carbohydrates in mycorrhizas indicated that different drought intensities led to distinguishable responses. In plants exhibiting a pre-dawn water potential of down to -1.96 MPa, drought caused the accumulation of sucrose, glucose and fructose, and of fungus-specific compounds such as mannitol and arabitol in mycorrhizal roots at the expense of, e.g. trehalose. The accumulation of sugar alcohols, which constitute compatible solutes known to counteract drought stress, was species-specific. Mycorrhizas with X. chrysenteron formed large amounts of arabitol, while those with L. subdulcis accumulated mannitol. Sustained partitioning of carbon towards the mycorrhizal fungi under drought was also reflected by an increase of nitrogen storage in the fungal vacuoles. In treatments where the pre-dawn water potential reached values of as low as -2.4 MPa, such alterations were no longer found. In such plants, the starch and soluble sugars content was generally reduced, which also resulted in a lack of increase in protective, fungus-specific sugar alcohols. In summary, the data show that, within certain limits, an increase in drought causes a shift in plant/fungus communities. The shift in the pattern of fungus-specific compounds could possibly be used as a sensitive measure of physiological stress imposed on this symbiosis.

Vegetation and Soil Environment Influence the Spatial Distribution of Root-Associated Fungi in a Mature Beech-Maple Forest

“…In June, fungal communities were significantly correlated with soil pH, soil moisture, and soil C and N at fine spatial scales, while in September, fungal communities were significantly correlated with labile P o , soil C, and C/N ratio. Soil water availability can affect mycorrhizae on beech (36,59), and this could be an important factor controlling fungi during early summer. A substantial body of evidence suggests that soil N can significantly alter and affect the distribution and community structure of ECM fungi (3,11,24,47,53).…”

The Role of Plants in the Effects of Global Change on Nutrient Availability and Stoichiometry in the Plant-Soil System

“…Coinciding with these general physiological responses, an increase of mycorrhizal symbiosis under drought is frequently observed in field studies (RuizLozano et al, 1995;Davies et al, 1996;Al-Karaki and Al-Raddad, 1997;Shi et al, 2002;Roldán et al, 2008). The enhancement of mycorrhizal symbiosis improves the capacity of plants to take up both water and nutrients (Ruiz-Lozano et al, 1995;Alvarez et al, 2009;Wu et al, 2011a).…”

Ectomycorrhizal communities in a Mediterranean forest ecosystem dominated by Quercus ilex: seasonal dynamics and response to drought in the surface organic horizon

“…As in most temperate forests, under the harsh and unpredictable Mediterranean climate, Ectomycorrhizae are crucial for nutrition of both partners and protect plants against soil parasites (Morin et al 1999), toxic compounds (Hall 2002) and drought (Jany et al 2002). Understanding and documenting species responses to current and predicted climate change scenarios are current frontiers in ecology (O'Neill et al 2008;Shi et al 2002). To our knowledge, the response of ECM fungal communities to the predicted rainfall decline in the Mediterranean basin has not been investigated.…”