Bart F. Van Tooren

Bio: Bart F. Van Tooren is an academic researcher. The author has contributed to research in topics: Lichen & Vascular plant. The author has an hindex of 1, co-authored 1 publications receiving 143 citations.

Canonical Correspondence Analysis with variation partitioning: some comments and an application

Abstract: . This study presents an alternative treatment of data from a comprehensive vegetation study in which the main gradient structure of boreal coniferous forest vegetation in southern Norway was investigated by ordination techniques. The data sets include vegetation samples of different plot sizes, supplied with measurements of 33 environmental explanatory variables (classified in four groups) and nine spatial explanatory variables derived from geographical coordinates. Partitioning the variation of the species-sample plot matrices on different sets of explanatory variables is performed by use of (partial) Canonical Correspondence Analysis. Several aspects of vegetation-environment relationships in the investigation area are discussed on the basis of results obtained by the new method. Generally, ca. 35% of the variation in species abundances are explained by environmental and spatial variables. The results indicate support for the hypothesis of macro-scale topographic control over the differentiation of the vegetation, more strongly so in pine than in spruce forest where soil nutrients play a major role. Towards finer scales, the primary topographical and topographically dependent factors lose importance, and vegetational differentiation is more strongly affected by the accumulated effects of the vegetation (including the tree stand) on soils, shading, litter fall, etc. The fraction of variation in species abundance explained by significant environmental variables was found to be ca. twice as large as the fraction explained by spatial variables. The fraction of variation explained by the supplied variables differed between data sets; it was lower for cryptogams than for vascular plants, and lower for smaller than for larger sample plots. Possible reasons for these patterns are discussed. Some methodological aspects of CCA with variation partitioning are discussed: improvements, necessary precautions, and the advantages over alternative methods.

Host and geographic structure of endophytic and endolichenic fungi at a continental scale

Abstract:  Premise of the study: Endophytic and endolichenic fungi occur in healthy tissues of plants and lichens, respectively, playing potentially important roles in the ecology and evolution of their hosts. However, previous sampling has not comprehensively evaluated the biotic, biogeographic, and abiotic factors that structure their communities.  Methods: Using molecular data we examined the diversity, composition, and distributions of 4154 endophytic and endolichenic Ascomycota cultured from replicate surveys of ca. 20 plant and lichen species in each of fiNorth American sites (Madrean coniferous forest, Arizona; montane semideciduous forest, North Carolina; scrub forest, Florida; Beringian tundra and forest, western Alaska; subalpine tundra, eastern central Alaska).  Key results: Endolichenic fungi were more abundant and diverse per host species than endophytes, but communities of endophytes were more diverse overall, refl ecting high diversity in mosses and lycophytes. Endophytes of vascular plants were largely distinct from fungal communities that inhabit mosses and lichens. Fungi from closely related hosts from different regions were similar in higher taxonomy, but differed at shallow taxonomic levels. These differences refl ected climate factors more strongly than geographic distance alone.  Conclusions: Our study provides a fi rst evaluation of endophytic and endolichenic fungal associations with their hosts at a continental scale. Both plants and lichens harbor abundant and diverse fungal communities whose incidence, diversity, and composition refl ect the interplay of climatic patterns, geographic separation, host type, and host lineage. Although culture-free methods will inform future work, our study sets the stage for empirical assessments of ecological specifi city, metabolic capability, and comparative genomics.

The ecological significance of organochemical compounds in Sphagnum

Abstract: The bryophyte genus Sphagnum occurs as a dominant vegetation component in peat-forming bogs and fens worldwide. The peat mosses are known to have physical and chemical properties which keep their environment wet, acidic and unfavourable for most higher plants and microbes. In this paper, the production and further fate of secondary metabolites produced by Sphagnum representatives are reviewed, with special reference to their ecological significance for the Sphagnum plants and for the bog ecosystem as a whole. The organochemical compounds produced by Sphagnum discussed here can be roughly divided into two groups. A first major group of compounds are the phenolics, secondary metabolites, the most important of which is sphagnum acid (p-hydroxy-(i(carboxymethyl)-cinnamic acid). This is a monophenolic which is specific for this genus and has been found in all representatives studied so far. This phenolic is present in the cell fluids but also in three-dimensional polymeric networks, together with other phenolics such as gallic acid, in the cell walls. The second group of compounds are carbohydrates, in particular uronic acids such as galacturonic acid, which also form large polymeric molecules, named ‘sphagnan’, associated with the cell walls. The polymeric phenols give the cell walls the rigor needed for the large water-holding capacity of the hyaline cells. They also will provide a defence against herbivores and diseases, although this has not been investigated in any systematic way. The monomeric phenolics are excreted into the bog water and may have allelopathic functions. The polyuronic acids in the cell walls give the peat mosses their high cation exchange capacity, which enables them to firmly bind metals and nutrients. The effects of these metabolites on the functioning of the bog ecosystem are mostly associated with their inhibitory effect on decomposition, which is of great importance for the peat storage function. The monophenolics excreted in the bog water slow down microbial decomposition in the acrotelm, and recycling of nutrients is relatively rapid after the death of the cells. The phenolics in the cell walls prohibit the microbial breakdown of all cell wall polysaccharides, and this protective action may persist in deep peat layers for thousands of years. The polymeric networks of phenolics release tannins in deep peat layers. These tannins, together with the sphagnan which is released in the catotelm, have a tanning effect on proteins and further slow down the peat decomposition.

Community Analysis Reveals Close Affinities Between Endophytic and Endolichenic Fungi in Mosses and Lichens

Abstract: Endolichenic fungi live in close association with algal photobionts inside asymptomatic lichen thalli and resemble fungal endophytes of plants in terms of taxonomy, diversity, transmission mode, and evolutionary history. This similarity has led to uncertainty regarding the distinctiveness of endolichenic fungi compared with endophytes. Here, we evaluate whether these fungi represent distinct ecological guilds or a single guild of flexible symbiotrophs capable of colonizing plants or lichens indiscriminately. Culturable fungi were sampled exhaustively from replicate sets of phylogenetically diverse plants and lichens in three microsites in a montane forest in southeastern Arizona (USA). Intensive sampling combined with a small spatial scale permitted us to decouple spatial heterogeneity from host association and to sample communities from living leaves, dead leaves, and lichen thalli to statistical completion. Characterization using data from the nuclear ribosomal internal transcribed spacer and partial large subunit (ITS-LSU rDNA) provided a first estimation of host and substrate use for 960 isolates representing five classes and approximately 16 orders, 32 families, and 65 genera of Pezizomycotina. We found that fungal communities differ at a broad taxonomic level as a function of the phylogenetic placement of their plant or lichen hosts. Endolichenic fungal assemblages differed as a function of lichen taxonomy, rather than substrate, growth form, or photobiont. In plants, fungal communities were structured more by plant lineage than by the living vs. senescent status of the leaf. We found no evidence that endolichenic fungi are saprotrophic fungi that have been "entrapped" by lichen thalli. Instead, our study reveals the distinctiveness of endolichenic communities relative to those in living and dead plant tissues, with one notable exception: we identify, for the first time, an ecologically flexible group of symbionts that occurs both as endolichenic fungi and as endophytes of mosses.