Biology subjects

Striebel, M.

Publications and source records attributed to Striebel, M..

6 recordsLinked to original sources

bioRxiv2026

Lake ecosystem responses to runoff variability across time and space

Inland waters in the Northern Hemisphere are experiencing increased annual runoff due to higher overall precipitation as well as intensified short-term events such as heavy rainfall, floods and storms. These events affect the total loading and variability of inputs of allochthonous, coloured dissolved organic matter (cDOM) and inorganic nutrients into lakes. Previous studies have shown that increased total cDOM and inorganic nutrient loads affect phytoplankton biomass and metabolic rates, but it is unknown how the effects of different cDOM and nutrient pulse scenarios are modified by spatial and seasonal differences in lake characteristics. Here, we conducted a coordinated, standardized mesocosm experiment across three lakes with different ambient cDOM and nutrient concentrations. In two of these lakes, the experiment was implemented in two seasons. The same total amounts of cDOM, nitrate and phosphate were added to all mesocosms, but in pulses that differed in intensity and frequency. We found that pulse intensity and frequency affected chlorophyll a and phycocyanin concentrations and metabolic rates, i.e. gross primary production and respiration, differently. Specifically, more pronounced effects were found in response to the extreme pulse scenario compared to those with more frequent, smaller pulse additions. Furthermore, the effects were mainly temporary and varied more among lakes than between seasons. The clearest differences between the extreme and more gradual runoff scenarios were found in the lake with the lowest background cDOM and nitrate concentrations, likely because lower light limitation and possibly stronger initial N-limitation caused a faster response to the nutrient addition. Our results highlight that both antecedent lake conditions and characteristics of runoff events can affect phytoplankton biomass and metabolic rates and that comparative experimental approaches are needed to reveal the complexity of the responses.

ecology↗

bioRxiv2025

Phase separation strength controls actin filament treadmilling

Cellular motility relies on the dynamic turnover of actin filaments, which treadmill through continuous polymerization at the barbed end and disassembly at the pointed end. Yet, the underlying physical principles remain poorly understood. A long-standing challenge has been experimentally reconstituting stable, persistent treadmilling leading to higher-order actin organization. Here, we reconstitute a minimal in vitro system, in which liquid-liquid phase-separated condensates of zyxin and VASP balance cofilin-driven disassembly to enable persistent treadmilling-like movement of actin bundles. The condensates crosslink filaments into dynamic bundles while promoting barbed-end polymerization. The localized stabilization based on condensate-mediated bundling competes against the activity of cofilin and CAP1, enabling selective disassembly at pointed ends and recycling of monomers. To elucidate the physical basis underlying this emergent behavior, we complement our experiments with agent-based simulations that quantitatively recapitulate key experimental findings. This combined approach demonstrates that an intermediate range of zyxin-VASP self-affinity, driving the phase separation, enables robust treadmilling-like movement. A weakened zyxin-VASP self-affinity fails to stabilize the bundles, whereas an excessive affinity impedes filament dynamics. Experimental reconstitution and theoretical modeling together reveal a physical mechanism by which the material properties of multivalent protein condensates govern cytoskeletal turnover, and suggest a general design principle by which biomolecular condensates can spatiotemporally organize cytoskeletal structures.

biophysics↗

bioRxiv2025

Quantifying the net effect of biodiversity on stability

Understanding the relationship between biodiversity and both the functioning and stability of ecosystems has been a central focus of ecologists for decades. A step-change in our understanding of the biodiversity-ecosystem functioning relationship was enabled by explicit measurement of the additional functioning provided by biodiversity through comparing expected and observed yields in multi-species communities. However, we lack an equivalent measure for stability. Here, we quantify the net biodiversity effect on stability using model simulations and a microcosm experiment that exposed different phytoplankton species and their combinations to temperature increases and fluctuations. As an emergent property of communities, stability frequently exceeded the expected stability of the combined component species, leading to a net biodiversity effect on stability analogous to the effect on functioning. In our simulations, these effects depended on the strength of competitive interactions as well as species composition and their thermal niche. Experimentally, the stabilising effect of diversity was, however, non-linear, greatest for two-species combinations, and varied with both community composition and disturbance regime. Quantifying the net biodiversity effect on stability advances our mechanistic understanding of the biodiversity-stability relationship, and provides crucial information to support ecosystem management and conservation.

ecology↗

bioRxiv2024

Body size is a better predictor of intra- than interspecific variation of animal stoichiometry across realms

Animal stoichiometry affects fundamental processes ranging from organismal physiology to global element cycles. However, it is unknown whether animal stoichiometry follows predictable scaling relationships with body mass and whether adaptation to life on land or water constrains patterns of elemental allocation. To test both interspecific and intraspecific body-size scaling relationships of the nitrogen (N), phosphorus (P), and N:P content of animals, we used a subset of the StoichLife database encompassing 9,933 individual animals (vertebrates and invertebrates) belonging to 1,543 species spanning 10 orders of magnitude of body size from terrestrial, freshwater, and marine realms. Across species, body mass did not explain much variation in %N and %P composition, although the %P of invertebrates decreased with size. The effects of body size on species elemental content were small in comparison to the effects of taxonomy. Body size was a better predictor of intraspecific than interspecific elemental patterns. Between 42 to 45% in intraspecific stoichiometric variation was explained by body size for 27% of vertebrate species and 35% of invertebrate species. Further, differences between organisms inhabiting aquatic and terrestrial realms were observed only in invertebrate interspecific %N, suggesting that the realm does not play an important role in determining elemental allocation of animals. Based on our analysis of the most comprehensive animal stoichiometry database, we conclude that (i) both body size and realm are relatively weak predictors of animal stoichiometry across taxa, and (ii) body size is a good predictor of intraspecific variation in animal elemental content, which is consistent with tissue-scaling relationships that hold broadly across large groups of animals. This research reveals a lack of general scaling patterns in the elemental content across animals and instead points to a large variation in scaling relationships within and among lineages.

ecology↗

bioRxiv2022

Growth, organic matter release, aggregation and recycling during a diatom bloom: A model-based analysis of a mesocosm experiment

Mechanisms terminating phytoplankton blooms are often not well understood. Potentially involved processes such as consumption by grazers, flocculation, and viral lysis each have different post-bloom consequences on the processing of the organic material, therefore it is important to develop a better understanding of the relevance of these processes, and potential interactions between them. In this study, we present a model-based analysis of a spring bloom observed in a mesocosm experiment. The intermediate-complexity (27-state variable) numerical model we extended from an earlier version to this end can resolve C, N, P and Si cycles, and relevant processes like formation of various organic material size classes (low and high molecular weight (hereafter small and large) dissolved organic carbon (DOC), transparent exopolymer particles (TEP), and small/large detritus) and their degradation by two bacterial sub-communities (free-living and particle-attached) and planktonic protists (heterotrophic flagellates and ciliates). The model can explain > 90% of the variation of a rich set of observations consisting of 11 independent variables over the course of 13 days during which a bloom largely dominated by diatoms develops, and disappears almost entirely. Fluxes estimated by the model point to the importance of coagulation (TEP formation) as a sink term for DOC, and a source term for POC. Consequently, aggregation with TEPs constitute an important loss term for phytoplankton. The flocculated phytoplankton, and detrital material, in turn become rapidly degraded by the particle attached bacteria and other protist heterotrophs. Through a scenario analysis, the relevance of nutrient-stress enhanced lysis rates; alterations between small and large DOC in phytoplankton exudates; and coagulation of smaller DOC molecules were investigated. Our results suggest that the former two processes have negligible effects in isolation, but when combined with the latter, they can synergistically cause substantial deviations in TEP formation, hence, in flocculation rates; and consequently in the peak magnitude of the diatom bloom, and in timing of its termination. Our results point to a need for better understanding of processes governing the termination of phytoplankton blooms, their inter-dependencies, and consequences on the global biogeochemical cycles.

microbiology↗

bioRxiv2019

A mechanistic view of collective filament motion in active nematic networks

Protein filament networks are structures crucial for force generation and cell shape. A central open question is how collective filament dynamics emerges from interactions between individual network constituents. To address this question we study a minimal but generic model for a nematic network where filament sliding is driven by the action of motor proteins. Our theoretical analysis shows how the interplay between viscous drag on filaments and motor-induced forces governs force propagation through such interconnected filament networks. We find that the ratio between these antagonistic forces establishes the range of filament interaction, which determines how the local filament velocity depends on the polarity of the surrounding network. This force propagation mechanism implies that the polarity-independent sliding observed in Xenopus egg extracts, and in-vitro experiments with purified components, is a consequence of a large force propagation length. We suggest how our predictions can be tested by tangible in vitro experiments whose feasibility is assessed with the help of simulations and an accompanying theoretical analysis.

biophysics↗