Biology subjects

Bahn, M.

Publications and source records attributed to Bahn, M..

6 recordsLinked to original sources

bioRxiv2026

Who and how much? Quantifying the role of trophic guilds in soil organic carbon mineralization

Understanding the biotic processes that drive soil organic carbon (SOC) mineralization is essential for predicting the climate warming-carbon cycle feedback. Here, we combined Tree-of-life sequencing (TOLseq; cross-domain profiling using ribosomal RNA) with quantitative conversion factors linking rRNA transcript abundance to biomass, to understand how soil food web changes affect SOC mineralization in an in situ soil warming experiment. Field observations showed that warming reduced SOC stocks, but after decades of warming SOC mineralization had acclimated. An energetic soil food web model revealed both bottom-up and top-down controls in the trophic cascades, shifting C flows from fungal and plant-associated channels towards the bacterial channel. This caused an increase in SOC mineralization rate in warmed soils of 30% per-unit biomass across the year.

microbiology↗

bioRxiv2025

Global Change Factors differentially impact Floral and Leaf Economic Traits

Background and AimsSince the Industrial Revolution, rising atmospheric CO{square}, warming, and more frequent droughts have significantly impacted ecosystems. While the response of leaf functional traits to these climate change factors have been widely studied, reproductive traits remain relatively understudied, despite their key role in the diversification and distribution of flowering plants. Here, we investigated how elevated CO{square}, warming, drought, and their interactions affect floral, leaf and seed traits in two model grassland species. We also examined how these factors influence trait coordination. MethodsTwo common grassland species, Lotus corniculatus and Crepis capillaris, were sampled from a 10-year climate manipulation experiment. We measured resource economic traits related to organ size, construction cost, and dry matter content in both leaves and flowers, along with seed size and number. Univariate and multivariate analyses were used to assess trait responses, and rank-abundance curves were employed to visualize changes in trait coordination across treatments. Key ResultsTrait responses to climate change factors varied between species. Drought emerged as the most influential factor, affecting only leaf traits in L. corniculatus, but impacting leaf, floral, and seed traits in C. capillaris. Across both species, climate change conditions increased leaf construction costs and reduced flower size. In addition, it led to larger leaves in L. corniculatus, and fewer seeds in C. capillaris. Under extreme climate change conditions, trait coordination became stronger in both species, although C. capillaris showed no coordination response specifically to drought. ConclusionOur results show that floral economic traits, like leaf traits, are responsive to individual and combined effects of climate change factors. This highlights their importance in shaping plant strategies under environmental stress and emphasizes the need to better integrate floral traits into the whole-plant economic framework.

ecology↗

bioRxiv2024

Recurrent drought increases grassland community seasonal synchrony

1. Climate change increases the frequency and severity of drought events with strong repercussions on grassland ecosystems. While the effects of single drought events on ecosystem structure and functioning are well understood, it is largely unknown whether and how drought frequency modifies ecosystem responses to drought. 2. Here, we assessed how the increase in frequency of severe, annual summer drought impacted grassland communities. We examined these effects in a species-rich sub-alpine mountain meadow with a drought frequency of one, three, and 13 years, as well as ambient conditions. 3. We found that high drought frequency increased seasonal plant community synchrony through a reduction in species richness, a shift of plant functional groups, a loss of early-seasonal plant species, and the constrained establishment of seedlings throughout the growing season. These changes were associated with a decreased fraction of biomass as drought frequency increased. 4. Furthermore, we show that negative drought effects were enhanced with an increasing drought frequency, and that negative drought effects on plant communities outweighed the weak adaptive effects of species. 5. Synthesis. We conclude that single and low-frequency drought studies may not adequately predict longer-term changes in our rapidly shifting climate. With the ongoing increase in drought frequency due to climate change, we predict that grassland plant communities will increase in seasonal synchrony. We suggest that this increase in synchrony will leave ecosystems highly vulnerable to future disturbances, because asynchrony is a critical component of stability. Moreover, given the weak adaptive effects of plant species to long-term recurrent drought, we conclude that plant communities are unlikely to be able to adapt to the rapid increase in recurrent drought events.

ecology↗

bioRxiv2023

Soil fungi remain active and invest in storage compounds during drought independent of future climate conditions

Microbial growth is central to soil carbon cycling. However, how microbial communities grow under climate change is still largely unexplored. In an experiment simulating future climate conditions (increased atmospheric CO2 and temperature) and drought, we traced 2H or 18O applied via water-vapor exchange into fatty acids or DNA, respectively, allowing to measure community- and group-level adjustments in soil microbial physiology (replication, storage product synthesis, and carbon use efficiency, CUE). We show, that while overall community-level growth decreased by half during drought, fungal growth remained stable demonstrating an astonishing resistance of fungal activity against soil moisture changes. In addition, fungal investment into storage triglycerides increased more than five-fold under drought. CUE (the balance between anabolism and catabolism) was unaffected by drought but decreased in future climate conditions. Our results highlight that accounting for different growth strategies can foster our understanding of soil microbial contribution to C cycling and feedback to climate change.

microbiology↗

bioRxiv2018

Does the leaf economic spectrum hold within plant functional types? A Bayesian multivariate trait meta-analysis

We investigated whether global leaf economic relationships are also present within plant functional types (PFTs), and the extent to which this hierarchical structure can be used to constrain trait estimates. We developed a hierarchical multivariate Bayesian model that assumes separate means and covariance structures within and across PFTs and fit this model to seven leaf traits from the TRY database related to leaf morphology, biochemistry, and photosynthetic metabolism. Trait correlations were generally consistent in direction within and across PFTs, and consistent with predictions of the leaf economic spectrum. However, correlation strength varied substantially across PFTs indicating that leaf economic relationships within PFTs are often confounded by the unique physiology of certain plant types or environmental conditions in certain biomes. Leveraging covariance in multivariate models reduced uncertainties in mean trait estimates, particularly for undersampled trait-PFT combinations. However, additional constraint from the across-PFT hierarchy was limited.\n\nData accessibilityThe R code and ancillary data for running these analyses is publicly available online via the Open Science Framework at https://osf.io/w8y73/. The TRY data request used for this analysis has been archived at http://try-db.org, and can be retrieved by providing the TRY data request ID (#1584). Alternatively, the exact preformatted data used in this analysis are available on request to Alexey Shiklomanov (alexey.shiklomanov@pnnl.gov).

ecology↗

bioRxiv2017

Does circadian regulation lead to optimal gas exchange regulation?

Optimal stomatal theory is an evolutionary model proposing that leaves trade-off Carbon (C) for water to maximise C assimilation (A) and minimise transpiration (E), thereby generating a marginal water cost of carbon gain ({lambda}) that remains constant over short temporal scales. The circadian clock is a molecular timer of metabolism that controls A and stomatal conductance (gs), amongst other processes, in a broad array of plant species. Here, we test whether circadian regulation contributes towards achieving optimal stomatal behaviour. We subjected bean (Phaseolus vulgaris) and cotton (Gossypium hirsutum) canopies to fixed, continuous environmental conditions of photosynthetically active radiation, temperature and vapour pressure deficit over 48 hours. We observed a significant and self-sustained circadian oscillation in A and in stomatal conductance (gs) which also led to a circadian oscillation in{lambda} . The lack of constant marginal water cost indicates that circadian regulation does not directly lead to optimal stomatal behaviour. However, the temporal pattern in gas exchange, indicative of either maximizing A or of minimizing E, depending upon time of day, indicates that circadian regulation could contribute towards optimizing stomatal responses. More broadly, our results add to the emerging field of plant circadian ecology and show that molecular controls may partially explain leaf-level patterns observed in the field.

ecology↗