Dialytrichia undetermined

Philippe, Marc, Bittebiere, Anne-Kristel & Hugonnot, Vincent, 2019, Do Dialytrichia mucronata and D. saxicola share the same ecological preferences? A case study in the Rhône Valley (France) and possible application for river incision biomonitoring, Cryptogamie, Bryologie 20 (13), pp. 141-152 : 145-146

DIALYTRICHIA SPECIES ECOLOGICAL REQUIREMENTS

The moss D. saxicola prevailed in the relevés, occurring alone in 96 relevés (54%). Seventy-six relevés (42%) had D. mucronata only, and seven relevés (4%) included both species. See Table 1 and Supplementary material.

Both species were more frequently observed north of 45°N, with 151 of the relevés (81%) made north of this latitude. It was indeed quite difficult to find the genus south of 45°N (35 relevés, 39%), and populations there were smaller. Dialytrichia saxicola was more frequent than expected under the null hypothesis north of 45°N, and symmetrically D. mucronata was more frequent than expected under the null hypothesis south of 45°N ( Table 1, Chi-square test Χ² = 6.1, p-value = 0.01, df = 1).

On average, D. saxicola was apparently found at lower altitudes (167.02 m a.s.l.) than D. mucronata (186.34 m a.s.l.). The same is true if maximum altitude is considered ( Table 1). However, linear regression did not show any significant relationship between the abundances of each species and altitude (R² <0.01, p-value> 0.05 for the two species).

Various substrates were associated with Dialytrichia species, including the bark of 22 woody species ( Table 2) and five types of mineral substrates: migmatite (4 relevés), limestone (20), dolomitic sandstone (1), iron (1) and concrete (13).

Dialytrichia mucronata was more frequently observed on mineral substrate than expected under the null hypothesis, while D. saxicola was more frequent on trees ( Table 1, Chi-square test, Χ² = 15.4, p-value <0.001, df = 1).

Occurrences on the types of mineral substrates were too infrequent to be compared statistically (29 and 10 relevés for D. mucronata and D. saxicola , respectively, on total on mineral substrates, Table 1). Although the two species had almost the same number of occurrences on concrete, D. saxicola was observed only once on limestone (vs 20 times for D. mucronata ), and D. mucronata only once on migmatite (vs.three times for D saxicola ).

Dialytrichia mucronata was found on 12 different tree species and D. saxicola on 17 ( Table 2). The two species were not randomly distributed on the different phorophyte species, D. mucronata being less frequent than expected under the null hypothesis on bark, and symmetrically D. saxicola being more frequent than expected ( Tables 1 and 2; Chi-square test, Χ² = 33.9, p-value = 0.04, df = 21; phorophyte species in Table 2 are ranked according to the difference theoretical – observed for D. mucronata ). It can be noted that tree species that rarely occur in riparian forests ( Acer monspessulanum L., Buxus sempervirens L. and Juglans regia L.), as they do not withstand long-term soil water logging, were found in the middle part of the Table 2 only. They are thus phorophytes for which the number of observed trees bearing D. mucronata was more or less equal to the theoretically expected number. This suggests that outside riparian forests the two Dialytrichia species do not differ much in phorophyte choice. The three tree species (i.e. Quercus pubescens Willd. , Q. robur L. and Salix alba L.) with the lowest D. mucronata frequencies are all known to be particularly rich in tannic acid ( Kraus et al. 2003). Strictly riparian tree species were encountered at both ends of the Table 2 (e.g. Alnus glutinosa (L.) Gaertner and Salix alba ), thus being phorophytes for which the number of observed trees bearing D. mucronata differs much from the theoretically expected number.