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Mesophyll resistance for CO2 diffusion (rm) is one of the main limitations for photosynthesis and plant growth. Breeding new varieties with lower rm requires knowledge of its distinct components.We tested new method for estimating the relative drawdowns of CO2 concentration (c) across hypostomatous leaves of Fagus sylvatica. This technique yields values of the ratio of the internal CO2 concentrations at the adaxial and abaxial leaf side, cd/cb, the drawdown in the intercellular air space (IAS), and intracellular drawdown between IAS and chloroplast stroma, cc/cbd. The method is based on carbon isotope composition of leaf dry matter and epicuticular wax isolated from upper and lower leaf sides. We investigated leaves from tree‐canopy profile to analyse the effects of light and leaf anatomy on the drawdowns and partitioning of rm into its inter‐ (rIAS) and intracellular (rliq) components. Validity of the new method was tested by independent measurements of rm using conventional isotopic and gas exchange techniques.73% of investigated leaves had adaxial epicuticular wax enriched in 13C compared to abaxial wax (by 0.50‰ on average), yielding 0.98 and 0.70 for average of cd/cb and cc/cbd, respectively. The rIAS to rliq proportion were 5.5:94.5% in sun‐exposed and 14.8:85.2% in shaded leaves. cc dropped to less than half of the atmospheric value in the sunlit and to about two‐thirds of it in shaded leaves.This method shows that rIAS is minor but not negligible part of rm and reflects leaf anatomy traits, i.e. leaf mass per area and thickness. [ABSTRACT FROM AUTHOR]

Quantifying carbon dioxide (CO2) fluxes between soil and atmosphere is key in understanding net ecosystem C exchange and biogeochemical C cycling in plant‐soil systems. In ecosystems with low primary production and sparse vegetation, for example, dry lands or subpolar regions where C fluxes are small, measurement sensitivity is key—even so when measurements are combined with isotopic labeling. Here, we present a simplified gas sampling system developed to facilitate sampling and measurement of low soil CO2 fluxes as well as in situ 13CO2 labeling in the same setup. The capacity of the system was tested in a set of feature tests along with gas measurements of dryland soil‐biocrust systems. The system's sensitivity to capture minor changes in CO2 concentration was confirmed in respiration and photosynthesis measurements of soil‐biocrust systems, where fluxes down to 0.1 μmol CO2 m−2 s−1 were quantified. A balloon, implemented to counterbalance underpressure build‐up during gas withdrawal, mitigated 72% of pressure differences at sampling. The overall system volume was reduced to a minimum to limit contamination caused by residual air, and the design enabled one‐step flushing and evacuation of system compartments and gas sample bags, successfully ruling out cross‐contamination between samples. Ultimately, this system offers a flexible and accessible solution for CO2 measurements that can be applied not only on arid soils with low biological activity and turnover rates, but also on plant‐soil systems. The modifications enabled larger, and thereby more representative, sample volumes to be collected while limiting incubation, contamination, and pressure effects on the intact soil system. Plain Language Summary: Measurements of carbon dioxide (CO2) fluxes between soil and atmosphere are crucial to understand the terrestrial carbon cycle. In dry regions, these fluxes are rather small as both the release of CO2 via microbial respiration and uptake of CO2 via photosynthesis is limited by lack of water and sparse vegetation cover. We have developed a simplified CO2 gas sampling setup suitable for incubation experiments of soils with low biological activity and turnover rates, for example, soils from dry lands or subpolar regions, using only cost‐effective, easily available and replaceable system compartments. We tested system parameters in a set of feature tests and could rule out leakage and cross‐contamination. We further confirmed the suitability of the system for capturing small CO2 fluxes in photosynthesis and respiration measurements of soils with biocrusts. A balloon was installed to counterbalance pressure build‐up during sampling, allowing for larger gas volumes to be collected, which resulted in a mitigation of 72% of the underpressure build‐up. This system offers a straightforward and accessible solution for CO2 measurements, with features limiting contamination and pressure effects on the research sample. Key Points: We present a simplified and low‐cost gas sampling system, developed for quantifying CO2 fluxes in soil incubation experimentsRespiration rates down to 0.1 μmol CO2 m−2 s−1 were quantified, confirming the suitability of the system for low‐CO2 flux measurementsA balloon was installed, mitigating 72% of pressure changes in the headspace during sampling [ABSTRACT FROM AUTHOR]

Common oak trees display endogenous rhythmic growth with alternating shoot and root flushes. To explore the mechanisms involved, microcuttings of the Quercus robur L. clone DF159 were used for 13C/15N labelling in combination with RNA sequencing (RNASeq) transcript profiling of shoots and roots. The effect of plant internal resource availability on the rhythmic growth of the cuttings was tested through inoculation with the ectomycorrhizal fungus Piloderma croceum. Shoot and root flushes were related to parallel shifts in above- and below-ground C and, to a lesser extent, N allocation. Increased plant internal resource availability by P. croceum inoculation with enhanced plant growth affected neither the rhythmic growth nor the associated resource allocation patterns. Two shifts in transcript abundance were identified during root and shoot growth cessation, and most concerned genes were down-regulated. Inoculation with P. croceum suppressed these transcript shifts in roots, but not in shoots. To identify core processes governing the rhythmic growth, functions [Gene Ontology (GO) terms] of the genes differentially expressed during the growth cessation in both leaves and roots of non-inoculated plants and leaves of P. croceum-inoculated plants were examined. Besides genes related to resource acquisition and cell development, which might reflect rather than trigger rhythmic growth, genes involved in signalling and/or regulated by the circadian clock were identified. The results indicate that rhythmic growth involves dramatic oscillations in plant metabolism and gene regulation between below- and above-ground parts. Ectomycorrhizal symbiosis may play a previously unsuspected role in smoothing these oscillations without modifying the rhythmic growth pattern. [ABSTRACT FROM AUTHOR]

The present study compares the dynamics in carbon (C) allocation of adult deciduous beech (Fagus sylvatica) and evergreen spruce (Picea abies) during summer and in response to seven-year-long exposure with twice-ambient ozone (O3) concentrations (2 x O3). Focus was on the respiratory turn-over and translocation of recent photosynthates at various positions along the stems, coarse roots and soils. The hypotheses tested were that (1) 2 x O3 decreases the allocation of recent photosynthates to CO2 efflux of stems and coarse roots of adult trees, and that (2) according to their different O3 sensitivities this effect is stronger in beech than in spruce. Labeling of whole tree canopies was applied by releasing 13C depleted CO2 (δ13C of -46.9 ‰) using a free-air stable carbon isotope approach. Canopy air δ13C was reduced for about 2.5 weeks by ca. 8 ‰ in beech and 6 ‰ in spruce while the increase in CO2 concentration was limited to about 110 µl 1-1 and 80 µl 1-1, respectively. At the end of the labeling period, δ13C of stem CO2 efflux and phloem sugars was reduced to a similar extend by ca. 3-4 ‰ (beech) and ca. 2- 3 ‰ (spruce). The fraction of labeled C (f E, new) in stem CO2 efflux amounted to 0.3 to 0.4, indicating slow C turnover of the respiratory supply system in both species. Elevated O3 slightly stimulated the allocation of recently fixed photosynthates to stem and coarse root respiration in spruce (rejection of hypothesis I for spruce), but resulted in a significant reduction in C flux in beech (acceptance of hypotheses I and II). The distinct decrease in C allocation to beech stems indicates the potential of chronic O3 stress to substantially mitigate the C sink strength of trees on the long-term scale. [ABSTRACT FROM AUTHOR]

Stable isotope analysis is a powerful tool for tracing biogeochemical processes in the carbon and water cycles. One particularly powerful approach is to employ multiple isotopes where the simultaneous assessment of the D/H,18O/16O and/or 13C/12C in different compounds provide a unique means to investigate the coupling of water and 5 carbon fluxes at various temporal and spatial scales. Here, we present a research update on recent advances in our process-based understanding of the utilization of carbon, oxygen and hydrogen isotopes to lend insight into carbon and water cycling. We highlight recent technological developments and approaches, their strengths and methodological precautions with examples covering scales from minutes to centuries and from the leaf to the globe. [ABSTRACT FROM AUTHOR]

The occurrence of oxidative stress and oxidative damage in the halophyte Mesembryanthemum crystallinum during C3/crassulacean acid metabolism (CAM) transition evoked by salinity and high irradiance was investigated. The hypothesis tested was that CAM induction will effectively protect M. crystallinum against oxidative damage even under additionally applied oxidative stress via ozone (150 p.p.b.) exposure. Salinity (0.4 m NaCl), high irradiance and ozone induced the cytosolic CuZn-superoxide dismutase (SOD; EC 1.15.1.1) transcript abundance and activity indicating oxidative stress. However, ozone did not induce CAM. Contrary to the hypothesis, that ethylene may be involved in CAM induction, gassing with ethylene (200 p.p.b.) did not lead to CAM, but revealed that in M. crystallinum ethylene biosynthesis is induced by autostimulation. A putative fragment of the hitherto unknown nu-cleotide sequence of 1-aminocyclopropane-1-carboxylate oxidase (ACC; EC 4.4.1.14) was isolated and used as a specific probe against the ACC oxidase transcript to monitor oxidative damage. Ozone exposure increased the ACC oxidase expression only in plants with C3-photosynthesis which also showed severe necrosis and reduced photosynthetic activity, whereas plants in CAM mode (salt induced) remained unaffected. Natural stressors such as salinity and high irradiance induce CAM and up-regulate the ARS component CuZn-SOD very effectively to protect M. crystallinum from oxidative damage even when additional oxidative stress such as ozone is present. [ABSTRACT FROM AUTHOR]

Four different Clusia species showing C3 photosynthesis (C. multiflora) or crassulacean acid metabolism (CAM) (C. rosea, an unidentified Clusia sp. and C. alata) co-occur in the same habitat in the northwest of Venezuela. The aim of this field study was to correlate the adaptive changes in chlorophyll a fluorescence with gas exchange patterns and deacidification of nocturnally accumulated organic acids. The results indicate that in C. rosea and Clusia sp. a lowering of the potential quantum yield, measured as Fv/Fm after 10 min of dark adaptation, is restricted to the early morning hours. With the onset of deacidification there was no further decline in Fv/Fm, although the irradiance upon the leaves remained high. For the C3-plant, C. multiflora, changes in Fv/Fm were correlated with changes in irradiance incident on the leaves before predarkening for 10 min for Fv/Fm measurements. The fast relaxation of Fv/Fm under low light indicates that C. multiflora was not suffering photoinhibitory damage. Effective quantum yield as determined by ΔF/Fm, was low under high irradiances for C. rosea and Clusia sp. and did not change significantly for C. rosea during phase III of CAM. During the time of low incident irradiance C. alata and C. multiflora reached an effective quantum yield that was close to the optimal quantum yield of electron transport. It is noteworthy that apparent electron transport rates through photosystem II (PS II) ((ΔF/F'm) × PPFD) were highest for C. rosea, Clusia sp. and C. alata during phase III of CAM. Electron transport rates in C. multiflora were under high irradiance and did not differ from those in phase II and IV of CAM. The possible role of CO2 evolution from acid decarboxylation with respect to photosynthetic efficiency is discussed. [ABSTRACT FROM AUTHOR]

Presents a correction for the article on different species of Clusia, published in the 1997 issue of the journal "The New Phytologist."