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1. Microanatomical traits track climate gradients for a dominant C4 grass species across the Great Plains, USA

   https://doi.org/10.1093/aob/mcaa146  

   Bachle, Seton; Nippert, Jesse B (August 2020, Annals of Botany)

   null (Ed.)

   Abstract Background and Aims Andropogon gerardii is a highly productive C4 grass species with a large geographic range throughout the North American Great Plains, a biome characterized by a variable temperate climate. Plant traits are often invoked to explain growth rates and competitive abilities within broad climate gradients. For example, plant competition models typically predict that species with large geographic ranges benefit from variation in traits underlying high growth potential. Here, we examined the relationship between climate variability and leaf-level traits in A. gerardii, emphasizing how leaf-level microanatomical traits serve as a mechanism that may underlie variation in commonly measured traits, such as specific leaf area (SLA). Methods Andropogon gerardii leaves were collected in August 2017 from Cedar Creek Ecosystem Science Reserve (MN), Konza Prairie Biological Station (KS), Platte River Prairie (NE) and Rocky Mountain Research Station (SD). Leaves from ten individuals from each site were trimmed, stained and prepared for fluorescent confocal microscopy to analyse internal leaf anatomy. Leaf microanatomical data were compared with historical and growing season climate data extracted from PRISM spatial climate models. Key Results Microanatomical traits displayed large variation within and across sites. According to AICc (Akaike’s information criterion adjusted for small sample sizes) selection scores, the interaction of mean precipitation and temperature for the 2017 growing season was the best predictor of variability for the anatomical and morphological traits measured here. Mesophyll area and bundle sheath thickness were directly correlated with mean temperature (annual and growing season). Tissues related to water-use strategies, such as bulliform cell and xylem area, were significantly correlated with one another. Conclusions The results indicate that (1) microanatomical trait variation exists within this broadly distributed grass species, (2) microanatomical trait variability appears likely to impact leaf-level carbon and water use strategies, and (3) microanatomical trait values vary across climate gradients, and may underlie variation in traits measured at larger ecological scales. 

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2. Finding genes responsible for evolution of complex 3D leaf anatomy using tomographic microscopy

   Muir, CD; Bonnin A; Buckley TN; Conesa, MÀ; Galmés J; McKlin S; Rippner DA; Schmeltz M; Théroux-Rancourt G (January 2022, Botany)

   Traits in wild relatives of crop species can help breed sustainable crop varieties that produce more food with fewer resources. To make use of this variation, we need to find the genetic regions that allow wild species to use water and nutrients more efficiently. Leaf anatomy has a major effect on photosynthesis by determining rates of carbon gain and water loss. However, finding the genetic regions underlying leaf anatomical evolution has been limited by low-throughput and low-resolution trait measurements. 3D imaging using X-ray microcomputed tomography (μCT) may overcome these obstacles by providing high-throughput, high-resolution data on leaf anatomy. Compared to traditional 2D methods for leaf anatomy, 3D imaging captures physiologically important volumetric traits, is less biased, and encompasses a larger leaf area. We used synchrotron μCT to measure leaf anatomy on two tomato species Solanum lycopersicum (cultivated tomato) and S. pennellii (wild, drought-tolerant species), and four introgression lines containing loci that alter leaf anatomy. We measured stomatal density, size, and 3D arrangement, as well as leaf thickness and mesophyll porosity. Preliminary analyses show that synchrotron μCT can identify previously described quantitative trait loci for stomatal traits and leaf thickness and show how those traits are related to 3D leaf anatomy. We will use finite element models to show how these anatomical differences may contribute to genetic variation leaf CO2 and water vapour exchange. 

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3. Limited hydraulic adjustments drive the acclimation response of Pteridium aquilinum to variable light

   https://doi.org/10.1093/aob/mcaa006  

   Baer, Alex; Wheeler, James K; Pittermann, Jarmila (January 2020, Annals of Botany)

   Abstract Background and Aims The success of invasive plants can be attributed to many traits including the ability to adapt to variable environmental conditions. Whether by adaptation, acclimation or phenotypic plasticity, these plants often increase their resource-use efficiency and, consequently, their fitness. The goal of this study was to examine the hydraulic and eco-physiological attributes of sun and shade populations of Pteridium aquilinum, a weedy fern, to determine whether the presence of vessels and other hydraulic attributes affects its success under a variety of light conditions. Methods Hydraulic traits such as cavitation resistance, hydraulic conductivity, photosynthesis and water potential at turgor loss point were measured on fronds from sun and shade populations. Anatomical and structural traits such as conduit diameter and length, stomatal density and vein density were also recorded. Diurnal measures of leaf water potential and stomatal conductance complement these data. Key Results Gas exchange was nearly double in the sun plants, as was water-use efficiency, leaf-specific conductivity, and stomatal and vein density. This was largely achieved by a decrease in leaf area, coupled with higher xylem content. There was no significant difference in petiole cavitation resistance between the sun and shade leaves, nor in xylem-specific conductivity. Hydraulic conduit diameters were nearly equivalent in the two leaf types. Conclusions Shifts in leaf area and xylem content allow P. aquilinum to occupy habitats with full sun, and to adjust its physiology accordingly. High rates of photosynthesis explain in part the success of this fern in disturbed habitats, although no change was observed in intrinsic xylem qualities such as cavitation resistance or conduit length. This suggests that P. aquilinum is constrained by its fundamental body plan, in contrast to seed plants, which show greater capacity for hydraulic adjustment. 

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4. Spatio-temporal differences in leaf physiology are associated with fire, not drought, in a clonally integrated shrub

   https://doi.org/10.1093/aobpla/plab037  

   Wedel, Emily R; O’Keefe, Kimberly; Nippert, Jesse B; Hoch, Braden; O’Connor, Rory C (August 2021, AoB PLANTS)

   Mitchell, Patrick (Ed.)

   Abstract In highly disturbed environments, clonality facilitates plant survival via resprouting after disturbance, resource sharing among interconnected stems and vegetative reproduction. These traits likely contribute to the encroachment of deep-rooted clonal shrubs in tallgrass prairie. Clonal shrubs have access to deep soil water and are typically thought of as relatively insensitive to environmental variability. However, how leaf physiological traits differ among stems within individual clonal shrubs (hereafter ‘intra-clonal’) in response to extreme environmental variation (i.e. drought or fire) is unclear. Accounting for intra-clonal differences among stems in response to disturbance is needed to more accurately parameterize models that predict the effects of shrub encroachment on ecosystem processes. We assessed intra-clonal leaf-level physiology of the most dominant encroaching shrub in Kansas tallgrass prairie, Cornus drummondii, in response to precipitation and fire. We compared leaf gas exchange rates from the periphery to centre within shrub clones during a wet (2015) and extremely dry (2018) year. We also compared leaf physiology between recently burned shrubs (resprouts) with unburned shrubs in 2018. Resprouts had higher gas exchange rates and leaf nitrogen content than unburned shrubs, suggesting increased rates of carbon gain can contribute to recovery after fire. In areas recently burned, resprouts had higher gas exchange rates in the centre of the shrub than the periphery. In unburned areas, leaf physiology remained constant across the growing season within clonal shrubs (2015 and 2018). Results suggest single measurements within a shrub are likely sufficient to parameterize models to understand the effects of shrub encroachment on ecosystem carbon and water cycles, but model parameterization may require additional complexity in the context of fire. 

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5. Divergent resource‐use strategies of encroaching shrubs: Can traits predict encroachment success in tallgrass prairie?

   https://doi.org/10.1111/1365-2745.14456  

   Wedel, Emily_R; Ratajczak, Zak; Tooley, E_Greg; Nippert, Jesse_B (December 2024, Journal of Ecology)

   Abstract Changes in climate and land management over the last half‐century have favoured woody plants native to grasslands and led to the rapid expansion of woody species. Despite this being a global phenomenon, it is unclear why some woody species have rapidly expanded while others have not. We assessed whether the most abundant woody encroaching species in tallgrass prairie have common growth forms and physiology or unique traits that differentiate their resource‐use strategies.We characterized the abundance, above‐ground carbon allocation, and leaf‐level physiological and structural traits of seven woody encroaching species in tallgrass prairie that span an order of magnitude in abundance. To identify species‐specific increases in abundance, we used a 34‐year species composition dataset at Konza Prairie Biological Station (Central Great Plains, USA). We then compared biomass allocation and leaf‐level traits to determine differences in carbon and water use strategies among species.While all focal species increased in abundance over time, encroachment in this system is primarily driven by three species:Cornus drummondii,Prunus americanaandRhus glabra. The most dominant species,Cornus drummondii, had the most extreme values for several traits, including the lowest leaf:stem mass ratios, lowest photosynthetic capacity and highest turgor loss point.Two of the most abundant species,Cornus drummondiiandRhus glabra, had opposing growth forms and resource‐use strategies. These species had significantly different above‐ground carbon allocation, leaf‐level drought tolerance and photosynthetic capacity. There were surprisingly few interspecific differences in specific leaf area and leaf dry matter content, suggesting these traits were poor predictors of species‐level encroachment.Synthesis. Woody encroaching species in tallgrass prairie encompass a spectrum of growth forms and leaf physiology. Two of the most abundant woody species fell at opposite ends of this spectrum. Our results suggest niche differences among a community of woody species facilitate the rapid encroachment by a few species. This study shows that woody encroaching species do not conform to a ‘one‐size‐fits‐all’ strategy, and a diversity of growth forms and physiological strategies may make it more challenging to reach management goals that aim to conserve or restore grassland communities. 

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