Variation in fungal endophyte communities of pedunculate oak (Quercus robus L.) : spatial, temporal and environmental aspects

Abstract: Fungal endophytes are a taxonomically and ecologically heterogeneous group of ubiquitous intercellular fungi that live part of their life within the tissues of the plants without causing apparent harm to the host. They may contribute to the stress tolerance and resistance of the plants, and endophytes may also be involved in decomposition processes. Thus, these fungi are an interesting part of biodiversity e.g. in forest ecosystems. Little is still known about the temporal and spatial patterns in endophyte community structures in trees. Moreover, while it is known that endophytes spread to trees from the environment (horizontally) it is not clear at which scales their spreading occurs, and if e.g. neighbouring vegetation determines endophyte communities in trees. In addition, it is not known if the general vitality of the trees affects the frequency and diversity of endophyte infections in trees. Using culture-dependent method (isolations), endophyte communities were compared in young pedunculate oak (Quercus robur L.) trees that were surrounded by herbs and shrubs in different combinations and that showed different vitality status. The isolations were done from current and previous year’s twigs (xylem and bark) in early and late summer to study the temporal and within-tree spatial patterns. A total of 384 samples were plated with bark and xylem pieces. Altogether 172 of them produced a total number of 285 isolates, which could be grouped in 22 morphological groups (morphotypes). The colonisation and isolation rate values showed the succession of endophyte communities during the season and inside the twigs but there were no significant effects of tree vitality on these rates. However, in June the declining trees had higher morphotype evenness, indicating that declining trees were compromised in their ability to defend themselves against fungal infections, which may have reduced the competition between the different invading fungi. The Jaccard’s similarity index and Shannon’s diversity index showed that there was no clear pattern of infection from the closest surrounding vegetation, suggesting that the spreading of these fungi occurs at a larger scale.