Biology subjects

Brodersen, C. R.

Publications and source records attributed to Brodersen, C. R..

12 recordsLinked to original sources

bioRxiv2026

Divergence in wilt tolerance across the range of Mimulus guttatus in the absence of stomatal regulation

Whether phenotypes and environments predict performance under stress is central to ecology and evolution and can reveal species' vulnerability to global change. We sampled Mimulus guttatus range-wide to test whether reproductive, morphological, and physiological traits predict drought responses. Surprisingly, we find that stomatal response, a key mediator of water balance, did not change as drought intensified. Climate, however, predicted survival after turgor loss: plants from regions with large daily relative to seasonal temperature ranges survived wilting longer. Stress responses also depended on life history: where summers are dry, perennials withstood lower water potentials, whereas annuals increased leaf cooling as they wilted. Known trait associations were not fixed: although many baseline traits tracked climate, none predicted drought responses. Drought performance therefore cannot be inferred from traits measured under well-watered conditions. Lacking stomatal regulation, riparian drought escapers like M. guttatus may be vulnerable if shorter growing seasons bring drought before reproduction.

plant biology↗

bioRxiv2025

High-resolution microCT reveals relationships between stomata and interior leaf anatomy in Sorghum

Stomata are pores in the leaf epidermis that regulate the trade-off between CO2 uptake for photosynthesis and water vapor loss to the atmosphere. Stomatal patterning therefore influences water use efficiency and is a target for engineering to avoid drought stress. However, there is limited understanding of how internal leaf anatomy is coordinated with stomatal development, in part due to the technical challenges of assessing three-dimensional anatomy with sufficient resolution. C4 grasses are understudied, and this is a significant knowledge gap given their file-like stomatal distribution and unique mesophyll organization. In this study, wild-type sorghum and a low-stomatal density transgenic line expressing a synthetic Epidermal Patterning Factor (EPFsyn) were studied. High-resolution microCT was paired with machine learning to characterize three-dimensional traits of mesophyll, epidermis, and airspace, which together determine gias. Sorghum internal leaf airspace is an arrangement of large sub-stomatal airspaces with thin air passageways. Adaxial and abaxial surfaces differed in stomatal patterning relative to mesophyll structures, sub-stomatal crypts and airspace CO2 conductance (gias). Surprisingly, adaxial stomata were consistently located above rather than between vascular bundles. Unexpectedly, gias was not significantly different in wild-type versus EPFsyn. EPFsyn plants had larger crypts and shifts in internal leaf anatomy, indicating a potential compensation mechanism for predicted impacts of reduced stomatal density on gias. These findings provide a new understanding of the interplay between leaf surface specific anatomy and internal structural patterning of the mesophyll in a C4 species, and provides knowledge relevant to engineering water use efficiency in crop species.

plant biology↗

bioRxiv2025

Tree microbiomes and methane emissions in upland forests

RationaleUpland forest trees emit CH , but whether emissions derive from internal microbial production or soil-derived transport remains debated. Methanogens have been detected in heartwood of several species, yet the prevalence of wood-associated methanogenesis, its metabolic basis, and its relationship to co-occurring methanotrophy are poorly understood. MethodsWe measured 1,148 stem fluxes and 276 soil fluxes, sampled internal stem gases including {delta}{superscript 1}3CH , quantified methanogens and methanotrophs via ddPCR in 564 samples, characterized communities via 16S rRNA sequencing, and upscaled fluxes. Key resultsMethanogens were detected in 97% of heartwood samples (up to 10 copies g {superscript 1}) at concentrations exceeding soil by [~]2 orders of magnitude; methane consumers were likewise near-ubiquitous across forest compartments. Wood harbored distinct microbial communities dominated by hydrogenotrophic Methanobacteriaceae, corroborated by depleted {delta}{superscript 1}3CH . Vertical flux profiles indicated soil transport only in wet microsites, with uniform emissions across height consistent with internal production across most upland species. Species-level methanogen:methanotroph ratios predicted emissions (R{superscript 2} = 0.51), indicating net flux reflects the balance between production and oxidation. Main conclusionMethane-cycling microbes are widespread in upland trees, and net methane flux reflects the species-level balance between production and consumption. Internal methanogenesis contributes widely to upland tree emissions; resolving ecosystem-scale magnitude requires improved quantification of woody surface area and vertical flux variability.

ecology↗

bioRxiv2024

Ice and air: Visualisation of freeze-thaw embolism and freezing spread in young L. tulipifera leaves

Spring freezing is an unforgiving stress for young leaves, often leading to death, with consequences for tree productivity and survival. While both the plant water transport system and living tissues are vulnerable to freezing, we do not know whether damage to one or both of these systems causes death in leaves exposed to freezing. Whole saplings of Liriodendron tulipifera were exposed to freezing and thawing trajectories designed to mimic natural spring freezes. We monitored the formation of freeze-thaw xylem embolism and damage to photosynthetic tissues to reveal a predictable progression of ice formation across the leaf surface that is strongly influenced by leaf vein architecture, notably the presence or absence of bundle sheath extensions. Our data also show that freeze-thaw embolism occurs only in the largest vein orders where mean vessel diameter exceeds 30{micro}m. With evidence of both freeze-thaw embolism and damage to photosynthetic tissue, we conclude that this dual-mode lethality may be common among other wide-vesseled angiosperm-leaves, potentially playing a role in limiting geographic distributions, and show that bundle sheath extensions may stall or even prevent freezing spread. HighlightBoth ice and air lead likely lead to death in young L.tulipfera leaves exposed to freezing, with the spread of both governed by physical characteristics of these leaves.

physiology↗

bioRxiv2024

Transpirational water loss from flowers is low but unregulated

Flowers play a critical role in reproduction for most of the flowering plants, and maintaining flowers throughout their lifespan can require substantial resources, such as carbon and water. Increases in temperature and aridity due to climate change are shifting the atmospheric conditions experienced by flowers, potentially altering the costs of floral maintenance. However, little is known about floral physiology and the capacity of flowers to regulate water loss. Because many flowers have few, if any, stomata, flowers may not be able to curtail water loss when the atmospheric demand for water vapor is high. Here, we tested whether the surface conductance of of flower petals, tepals, and showy bracts responds dynamically to changes in the vapor pressure gradient driving water loss. We measure the responses of flower surface conductance (gs) to step changes in the vapor pressure gradient on nine species. Across species, gs was low among all species, and there was little, if any, response in gs to step changes in humidity. The lack of response in gs resulted in linear responses of transpirational water loss to variation in vapor pressure deficit. These results suggest that unusually hot, dry conditions could elevate water loss from flowers, leading to premature wilting and senescence, thereby shortening floral longevity.

plant biology↗

bioRxiv2024

A diverse and distinct microbiome inside living trees

Despite significant advances in microbiome research across various environments1, the microbiome of Earths largest biomass reservoir- the wood of living trees2- remains largely unexplored. This oversight neglects a critical aspect of global biodiversity and potentially key players in tree health and forest ecosystem functions. Here we illuminate the microbiome inhabiting and adapted to wood, and further specialized to individual host species. We demonstrate that a single tree can host approximately a trillion microbes in its aboveground internal tissues, with microbial communities partitioned between heartwood and sapwood, each maintaining a distinct microbiome with minimal similarity to other plant tissues or nearby ecosystem components. Notably, the heartwood microbiome emerges as a unique ecological niche, distinguished in part by endemic archaea and anaerobic bacteria that drive consequential biogeochemical processes. Our research supports the emerging idea of a plant as a "holobiont"3,4--a single ecological unit comprising host and associated microorganisms--and parallels human microbiome research in its implications for host health, disease, and functionality5. By mapping the structure, composition, and potential sources and functions of the tree internal microbiome, our findings pave the way for novel insights into tree physiology and forest ecology, and establish a new frontier in environmental microbiology.

ecology↗

bioRxiv2023

Wind speed affects the rate and kinetics of stomatal conductance

Understanding the relationship between wind speed and gas exchange in plants is a longstanding challenge. Our aim was to investigate the impact of wind speed on maximum rates of gas exchange and the kinetics of stomatal responses. We conducted experiments using an infrared gas analyzer equipped with a controlled leaf fan, enabling precise control of the boundary layer conductance. We first showed that the chamber was adequately mixed even at extremely low fan speeds (down to 200 rpm, equivalent to a wind speed of 0.0005 m s-1) and evaluated the link between fan speed, wind speed, and boundary layer conductance. We observed that higher wind speeds led to increased gas exchange of both water vapor and CO2 in Arabidopsis, presumably due to its effect on transpiration and the consequential reduction in epidermal pressure that led to stomatal opening. We documented that stomatal opening in response to light was three times faster at a fan speed of 10000 rpm (wind speed of 2 m s-1) compared with 500 rpm (0.25 m s-1) in Vicia faba, while the latter exhibited an opening rate that was similar to those of epidermal peels. The increase of stomatal conductance under high wind was observed in four species under field conditions. Our findings demonstrate the importance of the size of the boundary layer on determining maximum rates of gas exchange and the kinetics of gas exchange responses to environmental changes.

plant biology↗

bioRxiv2020

Natural selection maintains species despite widespread hybridization in the desert shrub Encelia

Natural selection is an important driver of genetic and phenotypic differentiation between species. A powerful way to test the role of natural selection in the formation and maintenance of species is to study species complexes in which potential gene flow is high but realized gene flow is low. For a recent radiation of New World desert shrubs (Encelia: Asteraceae), we use fine-scale geographic sampling and population genomics to determine patterns of gene flow across two hybrid zones formed between two independent pairs of species with parapatric distributions. After finding evidence for extremely strong selection at both hybrid zones, we use a combination of field experiments, high-resolution imaging, and physiological measurements to determine the ecological basis for selection at one of the hybrid zones. Our results identify multiple ecological mechanisms of selection (drought, salinity, herbivory, and burial) that together are sufficient to maintain species boundaries despite high rates of hybridization. Given that multiple pairs of species hybridize at ecologically divergent parapatric boundaries in the adaptive radiation of Encelia, such mechanisms may maintain species boundaries throughout this group. SIGNIFICANCE STATEMENTIn Baja California, the deserts meet the coastal dunes in a narrow transition visible even from satellite images. We study two species pairs of desert shrubs (Encelia) that occur across this transition. Although these species can interbreed, they remain distinct. Using a combination of genetics, field experiments, 3D-imaging, and physiological measurements, we show that natural selection counteracts the homogenizing effects of gene exchange. The different habitats of these species create multiple mechanisms of selection - drought, salinity, herbivory, and burial, which together maintain these species in their native habitats and their hybrids in intermediate habitats. This study illustrates how environmental factors influence traits and fitness and how this in turn maintain species, highlighting the importance of natural selection in speciation.

evolutionary biology↗

bioRxiv2020

Maximum CO2 diffusion inside leaves is limited by the scaling of cell size and genome size

Maintaining high rates of photosynthesis in leaves requires efficient movement of CO2 from the atmosphere to the chloroplasts inside the leaf where it is converted into sugar. Throughout the evolution of vascular plants, CO2 diffusion across the leaf surface was maximized by reducing the sizes of the guard cells that form stomatal pores in the leaf epidermis1,2. Once inside the leaf, CO2 must diffuse through the intercellular airspace and into the mesophyll cells where photosynthesis occurs3,4. However, the diffusive interface defined by the mesophyll cells and the airspace and its coordinated evolution with other leaf traits are not well described5. Here we show that among vascular plants variation in the total amount of mesophyll surface area per unit mesophyll volume is driven primarily by cell size, the lower limit of which is defined by genome size. The higher surface area enabled by smaller cells allows for more efficient CO2 diffusion into photosynthetic mesophyll cells. Our results demonstrate that genome downsizing among the flowering plants6 was critical to restructuring the entire pathway of CO2 diffusion, facilitating high rates of CO2 supply to the leaf mesophyll cells despite declining atmospheric CO2 levels during the Cretaceous.

plant biology↗

bioRxiv2019

Digitally Deconstructing Leaves in 3D Using X-ray Microcomputed Tomography and Machine Learning

Premise of the studyX-ray microcomputed tomography (microCT) can be used to measure 3D leaf internal anatomy, providing a holistic view of tissue organisation. Previously, the substantial time needed for segmenting multiple tissues limited this technique to small datasets, restricting its utility for phenotyping experiments and limiting our confidence in the conclusion of these studies due to low replication numbers. Methods and ResultsWe present a Python codebase for random-forest machine learning segmentation and 3D leaf anatomical trait quantification which dramatically reduces the time required to process single leaf microCT scans into detailed segmentations. By training the model on each scan using 6 hand segmented image slices out of >1500 in the full leaf scan, it achieves >90% accuracy in background and tissue segmentation. ConclusionOverall, this 3D segmentation and quantification pipeline can reduce one of the major barriers to using microCT imaging in high-throughput plant phenotyping.

plant biology↗

bioRxiv2019

The scaling of genome size and cell size limits maximum rates of photosynthesis with implications for ecological strategies

A central challenge in plant ecology is to define the major axes of plant functional variation with direct consequences for fitness. Central to the three main components of plant fitness (growth, survival, and reproduction) is the rate of metabolic conversion of CO2 into carbon that can be allocated to various structures and functions. Here we (1) argue that a primary constraint on the maximum rate of photosynthesis per unit leaf area is the size and packing density of cells and (2) show that variation in genome size is a strong predictor of cell sizes, packing densities, and the maximum rate of photosynthesis across terrestrial vascular plants. Regardless of the genic content associated with variation in genome size, the simple biophysical constraints of encapsulating the genome define the lower limit of cell size and the upper limit of cell packing densities, as well as the range of possible cell sizes and densities. Genome size, therefore, acts as a first-order constraint on carbon gain and is predicted to define the upper limits of allocation to growth, reproduction, and defense. The strong effects of genome size on metabolism, therefore, have broad implications for plant biogeography and for other theories of plant ecology, and suggest that selection on metabolism may have a role in genome size evolution.

ecology↗

bioRxiv2017

Water relations of Calycanthus flowers: hydraulic conductance, capacitance, and embolism resistance

Introduction Introduction Materials Methods Results Discussion Conclusions References Flowers are developmentally and morphologically complex structures whose primary function is to promote sexual reproduction (Specht & Bartlett 2009). Coevolution with animal pollinators has long been considered the primary selective agent responsible for the many, diverse forms apparent among angiosperm flowers (Sprengel 1793, 1996; Fenster et al. 2004). Yet, floral adaptations to pollinators may not be as frequent as commonly considered, and non-pollinator agents of selection, such as the resource costs of building and maintaining flowers, may also influence floral form and function (Herrera 1996; Strauss & Whittall 2006). Fo ...

ecology↗