Bekæmpelsesmiddelforskning fra Miljøstyrelsen, 103 – Fungiciders påvirkning af mykorrhizasvampes diversitet og funktion

Fungiciders påvirkning af mykorrhizasvampes diversitet og funktion

Summary

This study describes studies on fungicide effects on arbuscular mycorrrhizal fungi. Previous studies have compared various fungicides effects on specific fungal isolates, and only few studies have included dose-response experiments. The experiments described in this report include fungicide effects on individual, population and community level. This integrative approach should provide a more realistic demonstration of the impact of agricultural fungicides on the importance of mycorrhiza as a plant growth promoting factor.

At the individual level fungicides were found to inhibit mycorrhizal fungi. The NOAEL-limit (no observed adverse effect level) was lower for carbendazim (0,1 – 0,5 x field dose) than for mancozeb (5-25 x field dose). Low doses (< NOAEL) of both fungicides had a stimulating effect on the fungi. The physiological background for this stimulation was not elucidated, but an over compensation in the reaction of the fungi to low stress levels could be involved. The experiments showed that different species and genotype may react differently to the fungicides.

Studies at the population level revealed a significant number of genotypes in the field. The genotypic variation and distribution within the fields explained most of the variation. Comparison of adjacent fields grown conventionally or organic, showed that most of the variation was attributable to variation within the field. Differences between conventionally and organic praxis did not influence the genetic diversity within the species. Consequently, fungicides can not be expected to influence the fungi at the population level.

A more pronounced effect of the soil management (conventionally or organic) was seen on the diversity at the community level, though some variation in diversity was seen within the fields. These field and site differences were more pronounced that the fungicide induced effects. It was also shown that the fungicide treatment could change the result of the interaction in the possible combination of the three fungi. The outcome of the interactions could not be concluded from the knowledge obtained from experiments with the fungi alone. The fungicide treatment could increase the phosphorus uptake by inhibition of an inefficient fungus in some of the combinations.

In conclusion the complexity in the fungal communities in agricultural fields, can explain why the use of fungicides in Danish agriculture have limited effects on the community of mycorrhizal fungi in soil and plant roots. Field doses of mancozeb and low doses of carbendazim could stimulate the development and the function of mycorrhiza. This hormesis effect can partly explain why fungicide effects on mycorrhiza under field conditions are rarely observed. The pronounced complexity in communities and the genetic variation at the population level will conceal effects of external factor as fungicides on the functional properties of the communities.