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1. Resolving the contrasting leaf hydraulic adaptation of C₃ and C₄ grasses

   https://doi.org/10.1111/nph.20341  

   Baird, Alec_S; Taylor, Samuel_H; Pasquet‐Kok, Jessica; Vuong, Christine; Zhang, Yu; Watcharamongkol, Teera; Cochard, Hervé; Scoffoni, Christine; Edwards, Erika_J; Osborne, Colin_P; et al (January 2025, New Phytologist)

   Summary Grasses are exceptionally productive, yet their hydraulic adaptation is paradoxical. Among C₃grasses, a high photosynthetic rate (A_area) may depend on higher vein density (D_v) and hydraulic conductance (K_leaf). However, the higherD_vof C₄grasses suggests a hydraulic surplus, given their reduced need for highK_leafresulting from lower stomatal conductance (g_s).Combining hydraulic and photosynthetic physiological data for diverse common garden C₃and C₄species with data for 332 species from the published literature, and mechanistic modeling, we validated a framework for linkages of photosynthesis with hydraulic transport, anatomy, and adaptation to aridity.C₃and C₄grasses had similarK_leafin our common garden, but C₄grasses had higherK_leafthan C₃species in our meta‐analysis. Variation inK_leafdepended on outside‐xylem pathways. C₄grasses have highK_leaf : g_s, which modeling shows is essential to achieve their photosynthetic advantage.Across C₃grasses, higherA_areawas associated with higherK_leaf, and adaptation to aridity, whereas for C₄species, adaptation to aridity was associated with higherK_leaf : g_s. These associations are consistent with adaptation for stress avoidance.Hydraulic traits are a critical element of evolutionary and ecological success in C₃and C₄grasses and are crucial avenues for crop design and ecological forecasting. 

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2. Carbon isotope trends across a century of herbarium specimens suggest CO ₂ fertilization of C ₄ grasses

   https://doi.org/10.1111/nph.19868  

   del_Toro, Isa; Case, Madelon_F; Tyler_Karp, A.; Slingsby, Jasper_A; Staver, A_Carla (May 2024, New Phytologist)

   Summary Increasing atmospheric CO₂is changing the dynamics of tropical savanna vegetation. C₃trees and grasses are known to experience CO₂fertilization, whereas responses to CO₂by C₄grasses are more ambiguous.Here, we sample stable carbon isotope trends in herbarium collections of South African C₄and C₃grasses to reconstruct¹³C discrimination.We found that C₃grasses showed no trends in¹³C discrimination over the past century but that C₄grasses increased their¹³C discrimination through time, especially since 1950. These changes were most strongly linked to changes in atmospheric CO₂rather than to trends in rainfall climatology or temperature.Combined with previously published evidence that grass biomass has increased in C₄‐dominated savannas, these trends suggest that increasing water‐use efficiency due to CO₂fertilization may be changing C₄plant–water relations. CO₂fertilization of C₄grasses may thus be a neglected pathway for anthropogenic global change in tropical savanna ecosystems. 

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3. Consumer roles of small mammals within fragmented native tallgrass prairie

   https://doi.org/10.1002/ecs2.3441  

   Hope, Andrew_G; Gragg, Sabrina_F; Nippert, Jesse_B; Combe, Fraser_J (March 2021, Ecosphere)

   Abstract Grassland ecosystems globally are being negatively impacted by changes in climate, disturbance regimes, nutrient flux, and consumer guilds. Changes in the trophic ecology of consumers can substantially influence local resources, contributing to shifting diversity, community turnover, and other processes of ecosystem change. Small mammals are diverse and abundant within grasslands and yet the impact of changing ecosystems on small mammals and the role of these mammals as consumers are still both under‐studied. We assessed small mammal resource use within grassland and woodland vegetation types that have resulted from landscape‐scale experimental disturbance through fire treatments within the tallgrass prairie ecoregion of the North American Great Plains. We predicted that resource use would vary significantly among grassland vs. woodland communities, in turn reducing the role of small mammals in contributing to future maintenance of native prairies. We sampled five dominant species of rodents across three years and multiple habitats. Using stable isotope analysis, we investigated isotopic niche area and overlap to infer variation in diet, both within and among species. Resource use shifted in bivariate isotopic space seasonally but not across years when combining all species and habitats. Inferred spring diet (based on fur samples) was highly diverse and overlapping. Summer isotopic values (based on liver tissue) in woody habitat treatments were narrower and overlapped less than within grassland habitats. Consumers generally shifted from C₄herbivory to C₃herbivory, or greater omnivory, when analyzing grassland, shrubland, and woodland habitats respectively. Within the tallgrass prairie ecosystem, small mammal populations in herbaceous‐dominated habitats use a broader variety of resources than small mammals in proximate woody‐dominated habitats. As native grasslands experience woody encroachment, small mammal assemblages experience turnover of dominant species and associated changes in diet. Ecosystem changes such as cessation of frequent fire resulting in more woody habitats may include reduced roles by native small mammals as consumers/dispersers/propagators of native grassland plants. 

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4. IsoSeq transcriptome assembly of C ₃ panicoid grasses provides tools to study evolutionary change in the Panicoideae

   https://doi.org/10.1002/pld3.203  

   Carvalho, Daniel S.; Nishimwe, Aime V.; Schnable, James C. (February 2020, Plant Direct)

   Abstract The number of plant species with genomic and transcriptomic data has been increasing rapidly. The grasses—Poaceae—have been well represented among species with published reference genomes. However, as a result the genomes of wild grasses are less frequently targeted by sequencing efforts. Sequence data from wild relatives of crop species in the grasses can aid the study of domestication, gene discovery for breeding and crop improvement, and improve our understanding of the evolution of C₄photosynthesis. Here, we used long‐read sequencing technology to characterize the transcriptomes of three C₃panicoid grass species:Dichanthelium oligosanthes,Chasmanthium laxum, andHymenachne amplexicaulis. Based on alignments to the sorghum genome, we estimate that assembled consensus transcripts from each species capture between 54.2% and 65.7% of the conserved syntenic gene space in grasses. Genes co‐opted into C₄were also well represented in this dataset, despite concerns that because these genes might play roles unrelated to photosynthesis in the target species, they would be expressed at low levels and missed by transcript‐based sequencing. A combined analysis using syntenic orthologous genes from grasses with published reference genomes and consensus long‐read sequences from these wild species was consistent with previously published phylogenies. It is hoped that these data, targeting underrepresented classes of species within the PACMAD grasses—wild species and species utilizing C₃photosynthesis—will aid in future studies of domestication and C₄evolution by decreasing the evolutionary distance between C₄and C₃species within this clade, enabling more accurate comparisons associated with evolution of the C₄pathway. 

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5. Strong photosynthetic acclimation and enhanced water‐use efficiency in grassland functional groups persist over 21 years of CO ₂ enrichment, independent of nitrogen supply

   https://doi.org/10.1111/gcb.14714  

   Pastore, Melissa A.; Lee, Tali D.; Hobbie, Sarah E.; Reich, Peter B. (June 2019, Global Change Biology)

   Abstract Uncertainty about long‐term leaf‐level responses to atmospheric CO₂rise is a major knowledge gap that exists because of limited empirical data. Thus, it remains unclear how responses of leaf gas exchange to elevated CO₂(eCO₂) vary among plant species and functional groups, or across different levels of nutrient supply, and whether they persist over time for long‐lived perennials. Here, we report the effects of eCO₂on rates of net photosynthesis and stomatal conductance in 14 perennial grassland species from four functional groups over two decades in a Minnesota Free‐Air CO₂Enrichment experiment, BioCON. Monocultures of species belonging to C₃grasses, C₄grasses, forbs, and legumes were exposed to two levels of CO₂and nitrogen supply in factorial combinations over 21 years. eCO₂increased photosynthesis by 12.9% on average in C₃species, substantially less than model predictions of instantaneous responses based on physiological theory and results of other studies, even those spanning multiple years. Acclimation of photosynthesis to eCO₂was observed beginning in the first year and did not strengthen through time. Yet, contrary to expectations, the response of photosynthesis to eCO₂was not enhanced by increased nitrogen supply. Differences in responses among herbaceous plant functional groups were modest, with legumes responding the most and C₄grasses the least as expected, but did not further diverge over time. Leaf‐level water‐use efficiency increased by 50% under eCO₂primarily because of reduced stomatal conductance. Our results imply that enhanced nitrogen supply will not necessarily diminish photosynthetic acclimation to eCO₂in nitrogen‐limited systems, and that significant and consistent declines in stomatal conductance and increases in water‐use efficiency under eCO₂may allow plants to better withstand drought. 

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