Biology subjects

Walden, S.

Publications and source records attributed to Walden, S..

3 recordsLinked to original sources

bioRxiv2021

A parasite's paradise: Biotrophic species prevail oomycete community composition in tree canopies

Oomycetes (Stramenopiles, Protista) are among the most severe plant pathogens, comprising species with a high economic and ecologic impact on forest ecosystems. Their diversity and community structures are well studied in terrestrial habitats, but tree canopies as huge and diverse habitats have been widely neglected. A recent study highlighted distinct oomycete communities in the canopy region compared to forest soils when taking oomycete abundances into account, in contrast to the homogeneity at the incidence level. It remains however unknown if this homogeneity also leads to a functional homogenisation among microhabitats. In this study, we supplemented functional traits to oomycete canopy and ground communities, which were determined over a time period of two years with a metabarcoding approach. Our results showed that even though most oomycetes occurred in all habitats, a strong discrepancy between the strata and correspondingly the distribution of oomycete lifestyles could be observed, which was constant over time. Obligate biotrophic species, exclusively feeding on living host tissue, dominated the canopy region, implying tree canopies to be a hitherto neglected reservoir for parasitic protists. Parasites highly specialised on hosts that were not sampled could be determined in high abundances in the canopy and the surrounding air, challenging the strict host dependencies ruled for some oomycetes. Our findings further contribute to the understanding of oomycete ecosystem functioning in forest ecosystems.

microbiology↗

bioRxiv2021

On the phenology of protists: Recurrent patterns reveal seasonal variation of protistan (Rhizaria: Cercozoa, Endomyxa) communities in tree canopies

Tree canopies are colonized by billions of highly specialized microorganisms that are well adapted to the extreme microclimatic conditions, caused by diurnal fluctuations and seasonal changes. In this study we investigated seasonality patterns of protists in tree canopies of a temperate floodplain forest via high-throughput sequencing with group-specific primers for the phyla Cercozoa and Endomyxa. We observed consistent seasonality and identified divergent spring and autumn taxa. Tree crowns were characterized by a dominance of bacterivores and omnivores, while eukaryvores gained a distinctly larger share in litter and soil communities on the ground. Seasonality was largest among communities detected on the foliar surface. Higher variance within alpha diversity of foliar communities in spring indicated greater heterogeneity during community assembly. However, communities underwent distinct changes during the aging of leaves in autumn, reflecting recurring phenological changes during microbial colonization of leaves. Surprisingly, endomyxan root pathogens appeared to be exceptionally abundant across tree canopies during autumn season, demonstrating a potential role of the canopy surface as an important reservoir for wind-dispersed propagules. Overall, about 80% of detected OTUs could not be assigned to known species - representing only a fraction of dozens of microeukaryotic taxa whose canopy inhabitants are waiting to be discovered.

ecology↗

bioRxiv2020

To the canopy and beyond: Air samples reveal wind dispersal as a driver of ubiquitous protistan pathogen assembly in tree canopies

We analyzed air dispersal of the protistan phyla Cercozoa and Oomycota with an air sampler near the ground (~2 m) and in tree crowns (~25 m) of three tree species (oak, linden and ash) in a temperate floodplain forest in March (before leafing) and May (after leaf unfolding) with a cultivation-independent high throughput metabarcoding approach. Both, Cercozoa and Oomycota, contain important pathogens of forest trees and other vegetation. We found a high diversity of Cercozoa and Oomycota in air samples with 122 and 81 OTUs, respectively. Especially oomycetes showed a high temporal variation in beta diversity between both sampling dates. Differences in community composition between air samples in tree canopies and close to the ground were however negligible, and also tree species identity did not affect communities in air samples, indicating that the distribution of protistan propagules through the air was not spatially restricted in the forest ecosystem. OTUs of plant pathogens, whose host species that did not occur in the forest, demonstrate wind dispersal of propagules from outside the forest biome. Overall, our results lead to a better understanding of the stochastic processes of wind dispersal of protists and protistan pathogens, a prerequisite to understand the mechanisms of their community assembly in forest ecosystems. ImportanceWind dispersal has been shown to play a crucial role in protistan community assembly. The protistan taxa Cercozoa and Oomycota contain important plant parasites with a major ecologic and economic impact. However, comprehensive assessments of cercozoan and oomycete diversity in forest air samples were lacking. Using a cultivation-independent high throughput metabarcoding approach, we analyzed cercozoan and oomycete air dispersal in forest floors and the canopy region - a potential filter for microbial propagules. Our study provides insights into the diversity and community assembly of protists within the air, contributing to a better understanding which factors drive the distribution of plant pathogens within forest ecosystems.

ecology↗