The effect of AMF suppression on plant species composition in a nutrient-poor dry grassland

Abstract

Arbuscular mycorrhizal fungi (AMF) are expected to be one of the key drivers determining the diversity of natural plant communities, especially in nutrient-poor and dry habitats. Several previous studies have explored the importance of AMF for the composition of plant communities in various types of habitats. Surprisingly, studies of the role of AMF in nutrient-poor dry grassland communities dominated by less mycotrophic plant species are still relatively rare. We present the results of a 3-year study in which a plant community in a species-rich dry grassland was subjected to the fungicide carbendazim to suppress AMF colonization. We tested the effect of the fungicide on the following parameters: the plant species composition; the number of plant species; the cover of the rare, highly mycorrhiza-dependent species Aster amellus; the cover of the dominant, less mycorrhiza-dependent species Brachypodium pinnatum; and the cover of graminoids and perennial forbs. In addition, we examined the mycorrhizal inoculation potential of the soil. We found that the suppression of AMF with fungicide resulted in substantial changes in plant species composition and significant decrease in species richness, the cover of A. amellus and the cover of perennial forbs. In contrast the species increasing their cover after fungicide application were graminoids--the C3 grasses B. pinnatum and Bromus erectus and the sedge Carex flacca. These species appear to be less mycorrhiza dependent. Moreover, due to their clonal growth and efficient nutrient usage, they are, most likely, better competitors than perennial forbs under fungicide application. Our results thus suggest that AMF are an essential part of the soil communities supporting a high diversity of plant species in species-rich dry grasslands in nutrient-poor habitats. The AMF are especially important for the maintenance of the populations of perennial forbs, many of which are rare and endangered in the area.

Figure 1. Species most positively and negatively affected by fungicide application.

Graph shows change in the absolute cover of particular species after 3 years of fungicide application, averaged over 10 plots. Asterisks indicate significant (P ≤ 0.05) differences in species cover in the last year of the experiment between plots with and without fungicide application tested with a factorial ANOVA with block used as a covariate.

Figure 2. Number of plant species in plots with fungicide application and in control plots.

The graph shows means and standard errors (n = 10). Columns marked by the same letter are not significantly different (P > 0.05). Tests were performed using a GLM with a Poisson distribution, with block as a covariate.

Figure 3. Effect of fungicide treatment on plant growth.

Comparison of cover of Aster amellus (A), cover of Brachypodium pinnatum (B), cover of graminoids (C) and cover of perennial forbs (D) in plots with fungicide application and in control plots during the 3 years of the experiment. The graph shows means and standard errors (n = 10). Columns marked by the same letter are not significantly different (P > 0.05) in a factorial ANOVA. Data from 2007 were collected before fungicide application.

Figure 4. Effect of cover of graminoids on species richness.

Significant negative correlation between change in cover of graminoids and change in species richness in plots with and without 3 years of fungicide application (F_1,18 = 19.51; P < 0.001; linear regression).