2.2.20
FUNGAL DYNAMICS ON CONIFEROUS NEEDLES: CLIMATIC FACTORS AND BIOLOGICAL INTERACTIONS IN CONTROL OF SPATIAL DISTRIBUTION

A VAN MAANEN and F GOURBIERE

Laboratoire d'Ecologie Microbienne des Sols UMR CNRS 5557, Université Claude Bernard Lyon I, 43 Blvd du 11 Novembre 1918, 69622 Villeurbanne cedex, France

Background and objectives
Lophodermium pinastri, Cyclaneusma minus and Verticicladium trifidum are frequent fungal colonizers of Pinus sylvestris needles. L. pinastri and C. minus infect green needles (as endophytes or parasites) and form ascocarps on dead ones. In the litter, their fructification could be controlled by saprophytes species such as V. trifidum, which colonizes the needles just after litterfall [1]. The objective of the present work was to explain the distribution of these three fungal species in terms of climatic conditions and biological interactions.

Materials and methods
Litter samples of P. sylvestris were examined for the presence or absence of L. pinastri, C. minus and V. trifidum. Data are given as pecentage of needles colonized by each species.

Results and conclusions
Climatic influence was studied by observing the frequencies of colonization along altitudinal transects in France. Results showed a decrease in frequencies of V. trifidum with increasing altitude; conversely, frequencies of L. pinastri (especially its fructifications) and C. minus increased. In order to test the climatic hypothesis, a mathematical model for fungal dynamics on a temporary resource unit was built; it included water as a disperser and growth factor. The simulation of three fungi dynamics is in good agreement with the observed data. This strengthens the role of the influence of climatic conditions (rainfall) on distribution of the fungus.

Biological interactions between L. pinastri and C. minus were studied in each litter sample at two spatial scales. Statistical analyses (chi-square tests) showed that L. pinastri and C. minus have a tendency to associate on needles. However, at one needle scale, they appeared to occupy separate areas of the resource unit, revealing spatial exclusion and competition processes.

Climatic factors and biological interactions appear therefore to play major roles in fungal distribution. We are now aiming to determine how climatic factors interfere with fungal competition.

References
1. van Maanen A, Gourbière F, 1997. Canadian Journal of Botany 75, 699-710.