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Post-fire Colonization of Cistus creticus L. Seedlings by Ectomycorrhizal Fungi in Aleppo Pine Forests in Central Greece
Jeremy Milne
2002
PhD Thesis, The University of Edinburgh
Supervisors: Colin Legg (School of GeoSciences)
Philip Mason (Centre for Ecology and Hydrology)
Margarita Arianoutsou (The University of Athens)
Abstract
In mature forests, ectomycorrhizal fungal mycelia tend to be concentrated in the litter and upper soil layers and are therefore prone to damage by fires. Sources of fungal inoculum required by ectomycorrhizal tree and shrub seedlings re-establishing in burned forest sites may thus be reduced and patchily distributed.
Cistus creticus L is an ectomycorrhizal woody perennial that establishes after fires in Aleppo pine (Pinus halepensis Mill.) forests from small, hard-coated seeds that are stored in the soil. Field observations, and field and greenhouse bioassays were used to assess spatial and temporal variation in post-fire colonization of Cistus creticus seedlings by ectomycorrhizal fungi and to investigate the potential of resprouting shrubs to act as refugia of ectomycorrhizal fungal inoculum.
Six months after fire, there was spatial stratification of ectomycorrhizal fungal inoculum that was strongly related to depth in the soil profile and weakly to proximity to resprouting shrubs. Results show that the earliest post-fire colonization of Cistus seedlings throughout the forest is strongly dominated by E-strain fungi and an unidentified fungus (Unknown 1) that form weak ectomycorrhizas predominantly in the upper few centimetres of root systems. Early colonization of long roots in addition to short roots appears to be an important process in Unknown 1 which is replaced on short roots by a wide range of mature forest fungi by the sixth month after host seed germination. E-strain fungi, on the other hand appear able to persist, at least for the first six months of seedling establishment.
Results of a greenhouse bioassay suggest that the weak ectomycorrhiza-forming fungi colonize from spores or other resistant propagules while the mature forest fungi colonize from mycelia that are attached to an existing resource-base that may be either living or dying roots of mature forest plants. These strategies for fire survival are somewhat analagous to the ‘seeding’ and ‘resprouting’ of the aboveground vegetation.
Proximity to resprouting shrubs had little quantifiable effect on percentage colonization or ectomycorrhizal community structure associated with Cistus creticus seedlings though there was some circumstantial evidence to suggest that some mature forest fungi, particularly basidiomycetes, are restricted to soils around both ectomycorrhizal and non-ectomycorrhizal resprouting shrubs in the early stages of post-fire recovery. New roots of ectomycorrhizal resprouting shrubs such as Quercus coccifera are likely to be locally important sources of carbohydrate for ectomycorrhizal fungi recovering after fires. However, it is suggested that by establishing in large numbers after fires and exhibiting broad receptivity to ectomycorrhizal associates, Cistus seedlings facilitate the post-fire recovery of mature forest fungi.
Early colonization of Cistus by weak ectomycorrhiza-forming fungi may provide quick access to the external sources of nutrition required by this small-seeded species yet at a low carbon cost to the establishing seedlings. Thus early interaction between plant seeders and their mycological counterparts facilitates the establishment of the Cistus seedlings that in turn facilitate the recovery of mature forest fungi.
As with the aboveground vegetation, the ectomycorrhizal fungal community in Mediterranean pine forests appears to be resilient to the effects of fire under natural conditions. However, perturbations to the fire regime could act to break the cycle of interaction that has evolved to confer that resilience.
For further information contact Jeremy Milne.