Current understanding of the species richness and community structure of arbuscular mycorrhizal fungi (AMF) is primarily based on studies of grasses, herbs, and especially agricultural crops, typically in disturbed environments. Very few studies have considered AMF associated with long-lived woody perennial species in undisturbed ecosystems. Here we examined AMF communities associated with western redcedar (Thuja plicata) in the ancient forests of British Columbia. We sampled seedlings, mature trees, and ancient trees, using their diameter at breast height as a proxy for age, at two sites separated by hundreds of kilometers in the interior temperate rainforests of the Canadian Rocky Mountains. A pyrosequencing approach was used to analyse the fungal communities of both root and soil samples collected along this host chronosequence. Community structure was assessed using a number of different statistical techniques, such as beta diversity partitioning between age classes, and two different methods for defining the identity of AMF taxa.
Results/Conclusions
Using the most conservative approach to species delimitation we found that the species richness of western redcedar AMF was consistently high regardless of life stage. Out of the pool of 80-90 AMF taxa found across all samples a mean of 27.5 (s.e.m. 2.21) AMF taxa were obtained from root samples. Soil samples were significantly less diverse than root samples. In addition there was a significant pattern of community divergence between seedlings (overdispersion) and convergence between ancient trees (autocorrelation). The same pattern occurred at both sites, even though the identity of the fungi (community composition) differed significantly between them. After searching the literature for comparable data we report that western redcedar roots typically harbour significantly more AMF than other woody plants. Species diversity of AMF was most similar to that of breadfruit (Artocarpus spp.), but the two hosts differed in the richness and composition of AMF between age classes. Examining the mycorrhizal communities of old growth forests yields insights into the community structure of mutualists in undisturbed ecosystems and associated with long-lived hosts. With the Anthropocene leading to increased levels of disturbance it is important to understand the baseline with which novel ecosystems can be compared.