Biology subjects

Engelmann, R. A.

Publications and source records attributed to Engelmann, R. A..

3 recordsLinked to original sources

bioRxiv2026

Traversing the canopy: phenology-driven changes and within-canopy transport shape the phyllosphere microbiome in a temperate floodplain hardwood forest

O_LIPhyllosphere microbiomes are subject to microbial import from various sources and undergo substantial changes during phenological changes of plants. However, these processes are still poorly understood for forest canopies. We propose that phenology-driven changes in host properties, and rainwater-mediated, within-canopy transport shape the phyllosphere microbiome in temperate forests. Leaves and throughfall samples were collected from oak, ash and linden trees at top, mid, and bottom canopy positions at the Leipzig canopy crane facility (Germany) at time points representing early, mid and late phenological stages. Bacterial community composition was assessed by 16S rRNA gene amplicon sequencing. C_LIO_LIPhenological stages explained 19% of phyllosphere bacterial community variation, followed by tree species identity (12%) and canopy position (2%). Later phenological stages exhibited more homogeneous and functionally redundant phyllosphere communities along with a strong decline of plant pathogens and increasing potential for microbially mediated biocontrol mechanisms. Throughfall transported up to 1011 bacterial cells per litre with maximum bacterial fluxes at the canopy top. C_LIO_LIOur findings demonstrate that in temperate forests, phenology-driven effects on the phyllosphere microbiome are far more important than tree species specific effects. Extent and selectivity of throughfall-mediated mobilization may play a crucial role for the spatial heterogeneity of microbial communities in tree crowns. C_LI

ecology↗

bioRxiv2021

Cumulative growth and stress responses to the 2018-2019 drought in a European floodplain forest

Droughts increasingly threaten the worlds forests and their potential to mitigate climate change. In 2018-2019, Central European forests were hit by two consecutive hotter drought years, an unprecedented phenomenon that is likely to occur more frequently with climate change. Here, we examine tree growth and physiological stress responses (increase in carbon isotope composition; {Delta}{delta}13C) to this consecutive drought based on tree-rings of dominant tree species in a Central European floodplain forest. Tree growth was not reduced for most species in 2018, indicating that water supply in floodplain forests can partly buffer meteorological water deficits. Drought stress responses in 2018 were comparable to former single drought years but the hotter drought in 2018 induced drought legacies in tree growth while former droughts did not. We observed strong decreases in tree growth and increases in {Delta}{delta}13C across all tree species in 2019, which are likely driven by the cumulative stress both consecutive hotter droughts exerted. Our results show that consecutive hotter droughts pose a novel threat to forests under climate change, even in forest ecosystems with comparably high levels of water supply.

ecology↗

bioRxiv2021

Climate, latitude, and land cover predict flying insect biomass across a German malaise trap network

O_LIAmong the many concerns for biodiversity in the Anthropocene, recent reports of flying insect loss are particularly alarming, given their importance as pollinators and as a food source for many predators. Few insect monitoring programs cover large spatial scales required to provide more generalizable estimates of insect responses to global change drivers. C_LIO_LIWe ask how climate and surrounding habitat affect flying insect biomass and day of peak biomass using data from the first year of a new standardized distributed monitoring network at 84 locations across Germany comprising spatial gradient of land-cover types from protected to urban areas. C_LIO_LIFlying insect biomass increased linearly with monthly temperature across Germany. However, the effect of temperature on flying insect biomass flipped to negative in the hot months of June and July when local temperatures most exceeded long-term averages. C_LIO_LILand-cover explained little variation in insect biomass, but biomass was lowest in forested sites. Grasslands, pastures and orchards harbored the highest insect biomass. The date of peak biomass was primarily driven by surrounding land-cover type, with grasslands especially having earlier insect biomass phenologies. C_LIO_LIStandardized, large-scale monitoring is pivotal to uncover underlying processes of insect decline and to develop climate-adapted strategies to promote insect diversity. In a temperate climate region, we find that the benefits of temperature on flying insect biomass diminish in a German summer at locations where temperatures most exceeded long-term averages. These results highlighting the importance of local adaptation in climate change-driven impacts on insect communities. C_LI

ecology↗