Arbuscular mycorrhizal colonisation of roots of grass species differing in invasiveness

Recent research indicates that the soil microbial community, particularly arbuscular mycorrhizal fungi (AMF), can influence plant invasion in several ways. We tested if 1) invasive species are colonised by AMF to a lower degree than resident native species, and 2) AMF colonisation of native plants is lower in a community inhabited by an invasive species than in an uninvaded resident community. The two tests were run in semiarid temperate grasslands on grass (Poaceae) species, and the frequency and intensity of mycorrhizal colonisation, and the proportion of arbuscules and vesicles in plant roots have been measured. In the first test, grasses representing three classes of invasiveness were included: invasive species, resident species becoming abundant upon disturbance, and non-invasive native species. Each class contained one C3 and one C4 species. The AMF colonisation of the invasive Calamagrostis epigejos and Cynodon dactylon was consistently lower than that of the non-invasive native Chrysopogon gryllus and Bromus inermis, and contained fewer arbuscules than the post-disturbance dominant resident grasses Bothriochloa ischaemum and Brachypodium pinnatum. The C3 and C4 grasses behaved alike despite their displaced phenologies in these habitats. The second test compared AMF colonisation for sand grassland dominant grasses Festuca vaginata and Stipa borysthenica in stands invaded by either C. epigejos or C. dactylon, and in the uninvaded natural community. Resident grasses showed lower degree of AMF colonisation in the invaded stand compared to the uninvaded natural community with F. vaginata responding so to both invaders, while S. borysthenica responding to C. dactylon only. These results indicate that invasive grasses supposedly less reliant on AMF symbionts have the capacity of altering the soil mycorrhizal community in such a way that resident native species can establish a considerably reduced extent of the beneficial AMF associations, hence their growth, reproduction and ultimately abundance may decline. Accumulating evidence suggests that such indirect influences of invasive alien plants on resident native species mediated by AMF or other members of the soil biota is probably more the rule than the exception

Effects of land use on the fungal spore richness in small crater-lake basins of western Uganda

Mycological tools to estimate the effects of diverse land-use practices on fungal diversity are scarce, because of poor knowledge of the taxonomic diversity of tropical fungi and their response to anthropogenic habitat change. Here, we investigate assemblages of fungal spores, recently deposited in the bottom sediments of 24 small crater lakes in western Uganda, to assess the relationship between the local richness of fungi and environmental variation in the crater basin along regional gradients of natural vegetation and land use. We recovered similar to 9500 fungal spore specimens, which could be attributed to 216 morphotypes. Using an information-theoretic approach based on the corrected Akaike Information Criterion (AICc), we determined the environmental factors which best explained variation in the diversity of fungal spores among three datasets: (i) the full set of 24 crater basins, (ii) the subset of 22 basins with freshwater lakes, and (iii) the subset of 17 basins partly or completely in agricultural use (cropland, fallow land, pasture and plantation). In these 17 human-impacted crater basins our results revealed a negative relationship between fungal spore richness and the areal fraction of basins in agricultural use. However, this detrimental effect of land use on fungal spore richness was not apparent across the full set of both disturbed and (presently) undisturbed basins. This was due to large variation in fungal spore richness among the undisturbed basins covered either with forest or savannah vegetation, probably resulting from site-specific controls on fungal habitat diversity, such as climatic moisture balance and the composition of natural and/or secondary vegetation. The land-use effects on fungal spore diversity, as documented in this study, suggest that communities of tropical fungi progressively exposed to land-use practices are threatened by species loss. Hence, our study demonstrates the need to develop conservation strategies mitigating the impacts of agriculture on the biodiversity of tropical fungi