Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher.
Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?
Some links on this page may take you to non-federal websites. Their policies may differ from this site.
-
more » « less
Abstract Background While a considerable amount of research has explored plant community composition in primary successional systems, little is known about the microbial communities inhabiting these pioneer plant species. Fungal endophytes are ubiquitous within plants, and may play major roles in early successional ecosystems. Specifically, endophytes have been shown to affect successional processes, as well as alter host stress tolerance and litter decomposition dynamics—both of which are important components in harsh environments where soil organic matter is still scarce.
Results To determine possible contributions of fungal endophytes to plant colonization patterns, we surveyed six of the most common woody species on the Pumice Plain of Mount St. Helens (WA, USA; Lawetlat'la in the Cowlitz language; created during the 1980 eruption)—a model primary successional ecosystem—and found low colonization rates (< 15%), low species richness, and low diversity. Furthermore, while endophyte community composition did differ among woody species, we found only marginal evidence of temporal changes in community composition over a single field season (July–September).
Conclusions Our results indicate that even after a post-eruption period of 40 years, foliar endophyte communities still seem to be in the early stages of community development, and that the dominant pioneer riparian species Sitka alder (
Alnus viridis ssp.sinuata ) and Sitka willow (Salix sitchensis ) may be serving as important microbial reservoirs for incoming plant colonizers. -
Litter decomposition rates are affected by a variety of abiotic and biotic factors, including the presence of fungal endophytes in host plant tissues. This review broadly analyzes the findings of 67 studies on the roles of foliar endophytes in litter decomposition, and their effects on decomposition rates. From 29 studies and 1 review, we compiled a comprehensive table of 710 leaf-associated fungal taxa, including the type of tissue these taxa were associated with and isolated from, whether they were reported as endo- or epiphytic, and whether they had reported saprophytic abilities. Aquatic (i.e., in-stream) decomposition studies of endophyte-affected litter were significantly under-represented in the search results (p < 0.0001). Indicator species analyses revealed that different groups of fungal endophytes were significantly associated with cool or tropical climates, as well as specific plant host genera (p < 0.05). Finally, we argue that host plant and endophyte interactions can significantly influence litter decomposition rates and should be considered when interpreting results from both terrestrial and in-stream litter decomposition experiments.more » « less
-
more » « less
Abstract Although most lotic ecosystems experience frequent and sometimes large disturbances, opportunities are uncommon to study primary succession in streams. Exceptions include new stream channels arising from events such as glacial retreat, volcanism, and catastrophic landslides. In 1980, the eruption and massive landslide at Mount St. Helens (WA, U.S.A.) created an entire landscape with five new catchments undergoing primary succession. We asked if riparian and lotic assemblages at early successional stages (36 years after the eruption) showed predictable change along longitudinal gradients within catchments, and whether assemblages were similar among five replicate catchments.
In July 2016, we collected environmental data and characterised riparian, algal, and benthic macroinvertebrate assemblages at 21 stream reaches distributed within and among five neighbouring catchments. We evaluated patterns of richness, abundance, biomass, multivariate taxonomic community structure, and functional traits both longitudinally and among catchments.
We found minimal evidence that longitudinal gradients had developed within catchments at 36 years post‐eruption. Increases in diatom and macroinvertebrate richness with downstream distance were the only biological responses with longitudinal trends. Conversely, we documented substantial variation in community structure of riparian plants, soft‐bodied algae, diatoms, and macroinvertebrates at the among‐catchment scale. Among‐catchment differences consistently separated two eastern catchments from three western catchments, and these two groups also differed in stream water chemistry, water temperature, and geomorphology.
Overall, we documented greater diversity in the young catchments than predicted by ecologists in the years immediately following the eruption, yet functional traits indicate that these catchments are still in relatively early stages of succession. Variation at the among‐catchment scale is likely to be driven in part by hydrological source variation, with the two eastern catchments showing environmental signatures associated with glacial ice‐melt and the three western catchments probably fed primarily by springs from groundwater aquifers. Contemporary flow disturbance regimes also varied among catchments and successional trajectories were probably reset repeatedly in streams experiencing more frequent disturbance.
Similar to new stream channels formed following glacial retreat, our results support a tolerance model of succession in streams. However, contrasting abiotic templates among Mount St. Helens catchments appear to be driving different successional trajectories of riparian plant, algal, and macroinvertebrate assemblages among neighbouring small catchments sharing the same catastrophic disturbance history.
