Fungal diversity in restoration sites
Restored communities or simply poor imitations?
The tea-tree species manuka and kanuka are important colonisers of disturbed habitats, and nursery-raised seedlings of these plants are often used as pioneer species for site restoration. Around Auckland, manuka and kanuka are dominant elements in early successional communities that may eventually develop to climax podocarp or Agathis forests.
Restoration projects typically use locally sourced seed in an attempt to recreate as closely as possible 'natural' local communities. However, microbes associated with the plants are rarely considered, despite constituting a high proportion of the biodiversity in tea-tree communities. Microorganisms also play key roles in the most basic ecosystem processes of decomposition, nutrient flow, and disease.
The results presented here show that microbial communities associated with tea-tree in restoration sites differ from those in natural sites. We ask questions relating to the impact that these differences might have on site restoration projects.
Significance of these results to site restoration projects
- Do the differences in diversity of these two groups of fungi indicate more widespread differences in the microbial biota as a whole?
- What effect might the lack of microbial diversity in planted stands be having on tea-tree nutrition and health, and on the resilience of these trees to environmental stress?
- Do planted stands of tea-tree represent tea-tree communities, or are they simply teatree plantations?
- What effect might this lack of microbial diversity be having on other parts of the community, e.g., the invertebrates that feed on fungi, or the birds that feed on the invertebrates?
- Will the microbial diversity within planted stands increase naturally as the stands age?
- Has the early establishment of high populations of weedy microbes buffered the stands so that they resist the establishment of the diverse group of species normally expected within them?
The fungi sampled
Two distinct functional groups of fungi (ectomycorrhizal mushrooms and leaf endophytes of manuka) were sampled from natural stands of tea-tree, and from stands planted using nursery-raised seedlings. These groups are biologically important to the health of tea-tree communities, and their diversity is relatively easy to measure.
|Ectomycorrhizal mushrooms||Leaf endophytes|
|Position in community||below ground||above ground|
|Ecological role||symbionts, living in close association with the roots of their tree hosts||ecological role uncertain|
|major role in nutrient supply to hosts||found at all levels in the aboveground parts of the forest|
|protect hosts againstsoil-borne pathogens||live within the healthy, symptomless leaves of their hosts|
|increase tolerance of hosts to environmental||at some stages of their life cycle typically inhabit litter on the forest|
Ectomycorrhizal mushrooms of Manuka and KanukaFungal diversity is lower in planted than in natural stands.
Examples of ectomycorrhizal genera that are commonly seen in natural stands of tea-tree
Leaf endophytes of Manuka
- Fungal species dominant in planted stands are opportunistic, weedy generalists (e.g., Alternaria, Botryosphaeria and Epicoccum), found on a wide range of different plants. High populations of these kinds of fungi may indicate that host plants are under stress.
- Fungal species dominant in natural stands are generally absent from planted stands.
- For example:
- a Phyllosticta sp. was found in all natural stands of manuka sampled
- typically, 15-45% of symptomless, apparently healthy leaves were infected with this single species
- samples from natural stands in Bay of Islands and Marlborough Sounds showed similar levels of infection
- in contrast, the Phyllosticta sp. was recovered from only one planted stand (from < 5% of the leaves)
- the reason for this difference is not yet understood, but does not relate to environmental differences such as plant age, degree of exposure of leaves, associated understorey plants, etc., factors considered important for endophyte distribution in some other studies (for details see Johnston, P.R. 1998: Leaf endophytes of manuka (Leptospermum scoparium).Mycological Research 102: 1009-1016)