Local variations in microfungal populations on Pinus sylvestris needles.

We studied the fungal colonization of Pinus sylvestris needles in two neighbouring sites, comparing stands of isolated and grouped trees. We observed large variations among the proportions of needles bearing fruit bodies of Cyclaneusma minus, Lophodermium pinastri, Verticicladium trifidum and black lines characteristic of L. pinastri colonization. Variations between sites and within trees were greater than that between stands or between trees. The frequency of L. pinastri colonization was negatively correlated with C. minus fruit body frequency, while the frequency of V. trifidum conidiophores was positively correlated with L. pinastri colonization frequency without fruiting, and negatively correlated with C. minus apothecia frequency. Although L. pinastri black lines and C. minus apothecia were nearly randomly associated on individual needles in each sample, the two fungi occupied different segments when they occupied the same needle. These patterns at needle and sample scales do not explain the negative correlation between the frequencies of these two species observed at larger scales. In each sample, frequency of V. trifidum conidiophores was highest on needles colonized by L. pinastri without fruiting. On individual needles, V. trifidum conidiophores developed on segments colonized by L. pinastri without fruiting, but not on segments bearing fruit bodies of L. pinastri or C. minus. These patterns at needle and sample scales were consistent with the correlations between frequencies observed at larger scales. These results were compared to variations observed with stand age and climate in others studies. The observed variations might result from both microclimate variations and fungal interactions.