Diversity patterns and host shifts in ectomycorrhizal fungi across an agricultural disturbance gradient in the mid-Zambezi area, Zimbabwe

Fallowing creates land mosaics characterised by vegetation communities at different stages of succession. Such mosaics are expected to harbour mycorrhizal associations that reflect host species composition and diversity. Ectomycorrhizal fungi are often a neglected group of the ecosystem despite their importance as bioindicators of disturbance. The present study investigated the diversity of ectomycorrhizal fungi and their host associations across a fallow chrono-sequence of 1-14 years in the mid-Zambezi Valley area, Zimbabwe. A total of ten ectomycorrhizal fungaltaxa that included Lactarius gymnocarpus, Lactarius sp., Boletus sp., Thelephora terrestris and Amphinema byssoides were recorded from 13 tree species from six families (Combretaceae, Ebenaceae, Fabaceae, Simaroubaceae, Rhamnaceae and Tiliaceae). The Spearman rank correlation test showed no significant correlation (p=0.002) between fallow age and ectomycorrhizal fungi status of host tree species. The generalised linear model (GLM) showed no significant relationship (p=0.079) among ectomycorrhizal fungi in any tree species and fallow age. The Raup-Crick similarity index indicated that there was an interaction between fallow age and the mycorrhizal status of the tree species, as opposed to host specificity. These results support previously reported low host specificity for ectomycorrhizal fungi among tropical African plant communities. Theyfurther indicate that selective tree felling negatively impacts host specific ectomycorrhizal fungi. The results also indicate that an increase in host tree species does not necessarily lead to increased ectomycorrhizal species diversity, thus implying the influence of other factors. Genetic similarity tests (using Nei and Li similarity coefficients) based on RAPDs and RFLPs showed varying relationships among the collected fungi. PCR-RFLPs confirmed genetic polymorphisms among samples of the recorded taxa. The intra- and inter-specific genetic diversity among the sampled ectomycorrhizal fungi partly explains the low host specificity among the collected ectomycorrhizal fungi and the dominance of a few ectomycorrhizal species in the study area