The fate of xylem-transported CO2 in plants

The concentration of carbon dioxide in tree stems can be ~30-750 times higher than current atmospheric [CO2]. Dissolved inorganic carbon enters the xylem from root and stem respiration and travels with water through the plant. However, the fate of much of this xylem-transported CO2 is unknown. In these studies I examined the fate of xylem-transported CO2 traveling through the petiole and leaf. This was accomplished by placing cut leaves from a woody and herbaceous C3 species, and a Kranz-type C4 species, in a solution of dissolved NaH13CO3 at concentrations similar to those measured in nature. This allowed me to track the efflux of 13CO2 using tunable diode laser absorption spectroscopy and compare this with 12CO2 fluxes derived from plant metabolism. The objective of the first study was to measure the efflux of xylem-transported CO2 out of the woody species Populus deltoides and the herbaceous C3 species Brassica napus in the dark by testing the relationship among the concertation of bicarbonate in the xylem, the rate of transpiration, and the rate of gross CO2 efflux. I found when the concentration of CO2 in the xylem is high and when the rate of transpiration is also high, the magnitude of 13CO2 efflux can approach half of the rate of respiration in the dark. The second study extends measurements of the fate of xylem-transported CO2 into lighted conditions where photosynthesis is active. I measured 12CO2 and 13CO2 fluxes across light- and CO2-response curves with the objectives of: 1) determining how much and under what conditions xylem-transported CO2 exited cut leaves in the light, and 2) determining how much xylem-transported CO2 was used for photosynthesis and when the overall contribution to photosynthesis was most important. I found that in the light the contribution of xylem-transported CO2 is most important when intercellular [CO2] is low which occurs under high irradiance and low [CO2]. The last study focused on the efflux and use of xylem-transported CO2 in the Kranz-type C4 species, Amaranthus hypochondriacus. Species with Kranz anatomy have highly active photosynthetic cells surrounding the vascular bundle, which is where xylem-transported CO2 would first interact with photosynthetic cells. The objectives of this study were to determine: 1) the rate and total efflux of xylem-transported CO2 exiting a cut leaf of the Kranz-type C4 species, A. hypochondriacus, in the dark and 2) the rate and contribution of xylem-transported CO2 to total assimilation in the light for A. hypochondriacus. Rates of dark efflux of xylem-transported CO2 out of A. hypochondriacus leaves were lower in the dark compared to rates observed in B. napus across the same rates of transpiration and bicarbonate concentrations. In the light a higher portion of xylem-transported CO2 was used for photosynthesis in A. hypochondriacus compared to B. napus suggesting that Kranz anatomy influences how C4 plants use xylem-transported CO2 for photosynthesis

Can improved canopy light transmission ameliorate loss of photosynthetic efficiency in the shade An investigation of natural variation in Sorghum bicolor

Previous studies have found that maximum quantum yield of CO2 assimilation (φCO2,max,app) declines in lower canopies of maize and miscanthus, a maladaptive response to self-shading. These observations were limited to single genotypes, leaving it unclear whether the maladaptive shade response is a general property of this C4 grass tribe, the Andropogoneae. We explored the generality of this maladaptation by testing the hypothesis that erect leaf forms (erectophiles), which allow more light into the lower canopy, suffer less of a decline in photosynthetic efficiency than drooping leaf (planophile) forms. On average, φCO2,max,app declined 27% in lower canopy leaves across 35 accessions, but the decline was over twice as great in planophiles than in erectophiles. The loss of photosynthetic efficiency involved a decoupling between electron transport and assimilation. This was not associated with increased bundle sheath leakage, based on 13C measurements. In both planophiles and erectophiles, shaded leaves had greater leaf absorptivity and lower activities of key C4 enzymes than sun leaves. The erectophile form is considered more productive because it allows a more effective distribution of light through the canopy to support photosynthesis. We show that in sorghum, it provides a second benefit, maintenance of higher φCO2,max,app to support efficient use of that light resource

The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra

This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17)

The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra

This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17)

The 16th Data Release of the Sloan Digital Sky Surveys : First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra

This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library "MaStar"). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17).Peer reviewe

The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar and APOGEE-2 Data

This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library (MaStar) accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) survey which publicly releases infra-red spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the sub-survey Time Domain Spectroscopic Survey (TDSS) data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey (SPIDERS) sub-survey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated Value Added Catalogs (VACs). This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper (MWM), Local Volume Mapper (LVM) and Black Hole Mapper (BHM) surveys

Growth of the single-cell C₄ plant, Bienertia sinuspersici, under light-limited conditions

Generally, C4 photosynthesis requires two cell types (Kranz-anatomy) to concentrate CO2 within the leaf. However, several species have been identified that lack Kranz-anatomy and perform C4 photosynthesis using dimorphic chloroplasts within an individual cell. In both Kranz-type and single-cell C4 plants some of the concentrated CO2 around Rubisco leaks out of the leaf (leakiness), reducing photosynthetic efficiency. In single-cell C4 plants the distance between dimorphic chloroplasts is predicted to affect the resistance of CO2 diffusion and therefore leakiness. When grown under optimal growth conditions the single-cell C4 plants have similar photosynthetic efficiencies compared with Kranz-type plants, but it is not known how growth under limited light affects the leaf structure and efficiency of the single-cell CO2 concentrating mechanism. The single-cell C4 plant, Bienertia sinuspersici, was grown under medium- and low-light, and measurements of leaf CO2 isotope exchange in response to irradiance, and O2 concentrations were used to determine how the efficiency of the single-cell CO2 concentrating mechanism changes in response to growth light conditions. Additionally, enzyme assays, chlorophyll content and light microscopy were used to further determine how B. sinuspersici responds to light-limited growth conditions. Photosynthetic enzyme activity and the specific leaf areas were higher in medium-light compared to low-light plants. Chlorophyll content and leaf thickness did not change significantly between light treatments. Photosynthesis and respiration rates were higher in medium-light compared to low-light plants but photosynthetic carbon isotope discrimination was similar in medium- and low-light plants under high irradiance measurement conditions and 21% O2. However, photosynthesis decreased with increasing O2 concentration for both mediumand low-light plants. Additionally, carbon isotope discrimination increased with O2 concentration under both light treatments but more so in the low-light plants. In general, it appears that the low-light growth conditions decreased the efficiency of the CO2 concentrating mechanism, particularly in response to changing O2 concentrations, in the single-cell C4 plant B. sinuspersici

Impact of pod and seed photosynthesis on seed filling and canopy carbon gain in soybean

Abstract There is a limited understanding of the carbon assimilation capacity of nonfoliar green tissues and its impact on yield and seed quality since most photosynthesis research focuses on leaf photosynthesis. In this study, we investigate the photosynthetic efficiency of soybean (Glycine max) pods and seeds in a field setting and evaluate its effect on mature seed weight and composition. We demonstrate that soybean pod and seed photosynthesis contributes 13% to 14% of the mature seed weight. Carbon assimilation by soybean pod and seed photosynthesis can compensate for 81% of carbon loss through the respiration of the same tissues, and our model predicts that soybean pod and seed photosynthesis contributes up to 9% of the total daily carbon gain of the canopy. Chlorophyll fluorescence (CF) shows that the operating efficiency of photosystem II in immature soybean seeds peaks at the 10 to 100 mg seed weight stage, while that of immature pods peaks at the 75 to 100 mg stage. This study provides quantitative information about the efficiency of soybean pod and seed photosynthesis during tissue development and its impact on yield.<br><br>This is a pre-copyedited, author-produced PDF of an article accepted for publication in Plant Physiology following peer review. The version of record [Impact of pod and seed photosynthesis on seed filling and canopy carbon gain in soybean. Plant Physiology 193, 2 p966-979 (2023)] is available online at: https://doi.org/10.1093/plphys/kiad324. <br><br>Deposited by shareyourpaper.org and openaccessbutton.org. We've taken reasonable steps to ensure this content doesn't violate copyright. However, if you think it does you can request a takedown by emailing [email protected]

Increased bundle sheath leakiness of <scp> CO ₂ </scp> during photosynthetic induction shows a lack of coordination between the <scp> C ₄ </scp> and <scp> C ₃ </scp> cycles

Use of a complete dynamic model of NADP-ME C4 photosynthesis indicated during dark or shade to high-light transitions induction of the C4 pathway was more rapid than that of the C3, resulting in a predicted transient increase in bundle-sheath CO2 leakiness (ϕ) Previously, ϕ was measured at steady-state, here we developed a new method, coupling a tunable diode laser absorption spectroscope (TDL) with a gas exchange system, to track ϕ in sorghum and maize through the non-steady-state condition of photosynthetic induction. In both species, ϕ showed a transient increase to >0.35 before declining to a steady-state of 0.2 by 1500 s after illumination. Average ϕ was 60% higher than at steady-state over the first 600 s of induction and 30% higher over the first 1500 s. The transient increase in ϕ, which was consistent with the model prediction, indicated that capacity to assimilate CO2 into the C3 cycle in the bundle-sheath failed to keep pace with the rate of dicarboxylate delivery by the C4 cycle. Because non-steady-state light conditions are the norm in field canopies, the results suggest that ϕ in these major crops in the field is significantly higher and energy conversion efficiency lower than previous measured values under steady-state conditions