Impact Type: Direct exposure to pollutant
Several experimental studies have been conducted to examine the effect of ozone on mycorrhizal fungi (Cairney and Meharg 1999). Although short term exposure of conifers to ozone may in some instances lead to increased colonisation by ectomycorrhizal fungi (Rantanen et al. 1994, Manninen et al. 1988), clear negative effects have been seen following longer term exposure or exposure at higher doses. The overall balance of evidence suggests a decline in response to ozone exposure (Reich et al. 1986, Meier et al. 1990, Edwards and Kelly 1992, Pirez-Soba et al. 1995). Since ozone does not penetrate the soil, Cairney and Meharg (199 9) note that the effects are most likely to be mediated via effects of ozone on the host plant, for example changes in photosynthesis and carbohydrate allocated to the plant roots (Anderson and Rygiewicz 1995, Dmaz et al. 1996).
Mycorrhizal fungi are an important part of the soil system, forming associations with plant roots to improve nutrient uptake. There are many species of mycorrhizal fungi contributing to soil biodiversity. Although at present the functional importance of this biodiversity on the roles of mycorrhizal fungi is not fully clear (Cairney and Meharg, 1999), many of the fungi observable in the field are the reproductive structures of mycorrhizal fungi. Reduction in mycorrhizal vitality may therefore be most apparent in loss of above ground diversity of fungal fruiting bodies.
The experimental evidence of interactive effects of ozone and acidification on mycorrhizal fungi appears to be equivocal with some studies finding effects and others not (Cairney and Meharg 1999).
|Critical Load/ Level|
No estimate available