The Decrease of Leaf Dark Respiration during Water Stress Is Related to Leaf Non-Structural Carbohydrate Pool in Vitis vinifera L.

Dark respiration (Rd) is a fundamental plant process used to gain biomass and maintain plant physiological activity. It accounts for the metabolization of a large share of the carbon fixed by photosynthesis. However, Rd during conditions of severe plant water stress is still poorly understood. The decrease in leaf transpiration increases temperature, one of the most important drivers of leaf Rd. On the other hand, water stress decreases the pool of leaf carbohydrates, which are the most important substrate for respiration. The aim of the present work was to determine the impact of water shortage on leaf Rd in grapevine and understand the driving factors in modulating leaf Rd response under plant water stress conditions. Water stressed vines had lower Rd as the water shortage severity increased. Rd was correlated with leaf temperature in well-watered vines. Instead, in water stressed vines, Rd correlated with leaf soluble sugars. The decrease of leaf Rd in water stressed vines was due to the decrease of leaf non-structural carbohydrate that, under water stress conditions, exerted a limiting effect on Rd.

Determination of respiration and photosynthesis fractionation coefficients for atmospheric dioxygen inferred from a vegetation-soil-atmosphere analog of the terrestrial biosphere in closed chambers

The isotopic composition of dioxygen in the atmosphere is a global tracer which depends on the biosphere flux of dioxygen toward and from the atmosphere (photosynthesis and respiration) as well as exchanges with the stratosphere. When measured in fossil air trapped in ice cores, the relative concentration of 16O, 17O and 18O of O2 can be used for several applications such as ice core dating and past global productivity reconstruction. However, there are still uncertainties about the accuracy of these tracers as they depend on the integrated isotopic fractionation of different biological processes of dioxygen production and uptake, for which we currently have very few independent estimates. Here we determined the respiration and photosynthesis fractionation coefficients for atmospheric dioxygen from experiments carried out in a replicated vegetation-soil-atmosphere analog of the terrestrial biosphere in closed chambers with growing Festuca arundinacea. The values for 18O discrimination during soil respiration and dark respiration in leave are equal to −12.3 ± 1.7 ‰ and −19.1 ± 2.4 ‰, respectively. We also found a value for terrestrial photosynthetic fractionation equal to +3.7 ± 1.3 ‰. This last estimate suggests that the contribution of terrestrial productivity in the Dole effect may have been underestimated in previous studies.

Dark respiration rates are not determined by differences in mitochondrial capacity, abundance and ultrastructure in C4 leaves

Our understanding of the regulation of respiration in C plants, where mitochondria play different roles in the different types of C photosynthetic pathway, remains limited. We examined how leaf dark respiration rates (R), in the presence and absence of added malate, vary in monocots representing the three classical biochemical types of C photosynthesis (NADP-ME, NAD-ME and PCK) using intact leaves and extracted bundle sheath strands. In particular, we explored to what extent R are associated with mitochondrial number, volume and ultrastructure. We found that the respiratory response of NAD-ME and PCK type bundle sheath strands to added malate was associated with differences in mitochondrial number, volume, and/or ultrastructure, while NADP-ME type bundle sheath strands did not respond to malate addition. In general, mitochondrial traits reflected the contributions mitochondria make to photosynthesis in the three C types. However, despite the obvious differences in mitochondrial traits, no clear correlation was observed between these traits and R. We suggest that R is primarily driven by cellular maintenance demands and not mitochondrial composition per se, in a manner that is somewhat independent of mitochondrial organic acid cycling in the light.

Photosynthesis, Growth and Dry Biomass Production in Euglena gracilis Klebs as Affected by Three Growth Irradiance Levels

Aims: The research aimed to investigate the shade response of E. gracilis Klebs while making the irradiance a crucial factor for photosynthesis based physiological activities and its applicability for industrial level culture conditions. Study Design: Euglena was cultured at three different light intensities of 30, 90, and 210 mol m-2s-1 photoautotrophically and axenically in modified Cramer-Meyer medium at 25 ˚C as batch cultures. Methodology: The photosynthesis O2 evaluation of Euglena cultures was measured under exponential (EP), transitional (TP), and stationary phases (SP). The light compensation point (LCP), light saturation point (LSP), and dark respiration rate (DRR) were obtained. Cell volume and cell number in each culture were measured simultaneously. Cells were collected and obtained dry mass (DM) after drying aliquots at 80˚C. Specific growth rate (SGR) and relative growth rate (RGR) were calculated. Tests for homogeneity of variance were performed on all parameters and LSDs were used for the mean separation. Results: In the TP, the lowest LCP was achieved in the higher light culture. The values of both the DRR and the LSP were the same as in EP. The DRR, LCP and LSP are lower in lower PFD cultures and decreased with increasing cell titers. The cellular growth levels were lower in lower light culture and decreased as each culture grew. Cellular DM was maintained constant in the EP, where SGR almost equaled RGR. In the EP, SGR was maintained constant in each culture, SGR displayed a saturation phenomenon. In the later TP, SGR became equal to RGR and all the cultures revealed constant DM. Conclusion: Euglena photoautotrophic cultures can tolerate low light intensities. With the SGR and RGR behavior under the shade conditions, they can maintain the constant photosynthesis rate and constant dry matter level.

Effect of pH on Photosynthesis of Euglena mutabilis Schmitz, an Acidophilic Benthic Flagellate

The dependence of the photosynthetic rate of Euglena mutabilis Schmitz on pH across a range of 2.0–10.0 was investigated. Populations of E. mutabilis isolated from sediments of acidic mine drainage in Sensui (pH = 3.95) and a volcanic cold spring in Bougatsuru (pH = 5.32) were cultured in a pH-adjusted growth media for 96 h, and photosynthetic rate and dark respiration rate were measured. The maximum gross photosynthetic rate of E. mutabilis cells from the Sensui drainage population did not vary significantly over the pH range of 2.0–7.0, and their dark respiration rate showed high values at pH = 7.0. The maximum gross photosynthetic rate of E. mutabilis cells from the Bougatsuru spring population did not vary significantly within the pH range of 2.0–6.0, and their dark respiration rate tended to show high values at pH = 7.0. E. mutabilis can colonize under circumneutral conditions up to and including pH = 6.0.

Photosynthetic Physiology Comparisons between No Tillage and Sod Culture of Citrus Farming in Different Seasons under Various Light Intensities

Sod culture (SC) and no tillage (NT) are modern orchard management systems, and are two different bases for the sustainable development and production of citrus orchards in Taiwan. However, there is no information about the efficiency of either NT or SC on the photosynthetic physiology of farmed citrus under different seasons and varying light intensities. The objective of this study was to clarify the impacts of SC and NT under eco-friendly farming management on the photosynthetic apparatus of an important plantation citrus species in response to varying light intensities over the seasons. The results showed that Rd (dark respiration rate of CO2), Qy (light quantum yield of CO2), LCP (light compensation point), Amax (maximum net assimilation of CO2), and Fv/Fm values of citrus plants under SC were somewhat higher under NT in the same season, particularly in the fall and in winter. As light intensity increased from 200 to 2000 μmol photon m−2 s−1 PPFD, higher Pn (net photosynthesis rate), Gs (stomatal conductance), ETR (electron transport rate), NPQ (non-photochemical quenching), and Fv/Fm (potential quantum efficiency of PSII) values were observed in spring and summer compared to the fall and winter, and increasing NPQ and decreasing Fv/Fm values were observed in all seasons. Positive and significant correlations were shown between the Pn and Gs under NT and SC in all seasons with all light illuminations, whereas significant and negative relationships were observed between the ETR and NPQ under NT in fall and winter at 1200~2000 PPFD. In short, ETR was useful for non-destructive estimations of Pn and NPQ since these indices were significantly and positively correlated with ETR in citrus leaves exposed to 0~1200 PPFD in all seasons and 1200~2000 PPFD in spring, the fall, and winter, providing a quick means to identify the physiological condition of plants under various seasons and tillages. The precise management of photosynthetic parameters such as ETR in response to light irradiances under varied seasons also provides implications for sustainable citrus production for tillage cropping systems in future higher CO2 and potentially wetter or drier environments. The tillages may hold promise for maximizing the economic efficiency of the growth and development of citrus plants grown in the field.

Variation in white spruce needle respiration across the species range

White spruce (Picea glauca) spans a massive range from arctic treeline to temperate forests. Yet the variability in respiratory physiology and the implications for tree carbon balance at the extremes of this distribution remain enigmasWorking at Arctic and Temperate sites more than 5000 km apart, we measured the short-term temperature response of dark respiration (R/T) at upper and lower canopy positions. R/T curves were fit to a polynomial model and model parameters (a, b, and c) were compared between locations, canopy positions, or with published data. Respiration measured at 25°C (R25) was 68% lower at the southern location than the northern location, resulting in a significantly lower a parameter of the R/T response in temperate trees Only at the southern location did upper canopy leaves have a steeper temperature response than lower canopy leaves, likely reflecting steeper canopy gradients in light. No differences were manifest in the maximum temperature of respiration. At the northern range limit, respiration appears extreme. This high carbon cost likely contributes to the current location of northern treeline. We find that respiration will increase with end-of-the-century warming and will likely continue to constrain the future range limits of this important boreal species.

Effects of Throughfall Exclusion on Photosynthetic Traits in Mature Japanese Cedar (Cryptomeria japonica (L. f.) D. Don.)

As climate change progresses, it is becoming more crucial to understand how timber species respond to increased drought frequency and severity. Photosynthetic traits in a 40-year-old clonal Japanese cedar (Cryptomeria japonica) plantation were assessed under artificial drought stress using a roof to exclude rainfall and a control with no exclusion. C. japonica is a commercial tree that is native to Japan and has high growth on mesic sites. The maximum carboxylation rate (Vcmax), maximum electron transfer rate (Jmax), and dark respiration rate (Rd) in current-year shoots in the upper canopy were determined from spring to autumn over two growing seasons. In addition, the photosynthetic rate at light saturation (Pmax), stomatal conductance (gs), and intrinsic water use efficiency (WUEi) were measured in the morning and afternoon during the same period. Leaf mass per unit area (LMA) and nitrogen concentration (N) were also measured. The values of Vcmax, Jmax, Rd, N, and LMA did not differ between the two plots. By contrast, significantly lower Pmax and gs and higher WUEi were found in the drought plot, and the reduction in Pmax was accompanied by low gs values. Midday depressions in Pmax and gs were more pronounced in the drought plot relative to the control and were related to higher WUEi. Under drought conditions, mature Japanese cedar experienced little change in photosynthetic capacity, foliar N, or LMA, but they did tend to close the stomata to regulate transpiration, thus avoiding drought-induced damage to the photosynthetic machinery and improving WUEi.

Effects of Foliage Spraying with Sodium Bisulfite on the Photosynthesis of Orychophragmus violaceus

Sulphurous acid derived from sulfur dioxide (SO2) emission leads to the pollution of irrigation water and the inhibition of plant growth. The safe concentration threshold of NaHSO3 in plants should be clarified to promote agricultural production. In this study, Orychophragmus violaceus seedlings were used as experimental materials and five NaHSO3 concentrations (i.e., 0, 1, 2, 5, 10 mmol·L−1) were simultaneously sprayed on the leaf surface of different seedlings separately. Leaf physiology responses under different concentrations were analyzed. The NaHSO3 did not promote photosynthesis in O. violaceus under the 1 and 2 mmol·L−1 treatments. It was conducive to the net photosynthetic rate (PN), photorespiration rate (Rp), chlorophyll content, actual photochemical quantum yield (YII) and photochemical quenching (qP) under the 5 mmol·L−1 treatment. However, quantum yield of regulated energy dissipation (YNPQ) and nonphotochemical quenching (NPQ) were inhibited. Under the 10 mmol·L−1 treatment, PN, chlorophyll content, YII, qP, dark respiration rate (Rd) and electron transport rate (ETR) showed significant decreases, while the photorespiration portion (Sp) significantly increased. Our results demonstrated that NaHSO3 provided a sulfur source for plant growth and interfered with the redox reaction of the plant itself, and its role as a photorespiratory inhibitor might be masked.

Opposite Growth Responses of Alexandrium minutum and Alexandrium catenella to Photoperiods and Temperatures

Shift of phytoplankton niches from low to high latitudes has altered their experienced light exposure durations and temperatures. To explore this interactive effect, the growth, physiology, and cell compositions of smaller Alexandrium minutum and larger A. catenella, globally distributed toxic red tide dinoflagellates, were studied under a matrix of photoperiods (light:dark cycles of 8:16, 16:8, and 24:0) and temperatures (18 °C, 22 °C, 25 °C, and 28 °C). Under continuous growth light condition (L:D 24:0), the growth rate (µ) of small A. minutum increased from low to medium temperature, then decreased to high temperature, while the µ of large A. catenella continuously decreased with increasing temperatures. Shortened photoperiods reduced the µ of A. minutum, but enhanced that of A. catenella. As temperature increased, cellular Chl a content increased in both A. minutum and A. catenella, while the temperature-induced effect on RubisCO content was limited. Shortened photoperiods enhanced the Chl a but reduced RubisCO contents across temperatures. Moreover, shortened photoperiods enhanced photosynthetic capacities of both A. minutum and A. catenella, i.e., promoting the PSII photochemical quantum yield (FV/FM, ΦPSII), saturation irradiance (EK), and maximum relative electron transfer rate (rETRmax). Shortened photoperiods also enhanced dark respiration of A. minutum across temperatures, but reduced that of A. catenella, as well as the antioxidant activities of both species. Overall, A. minutum and A. catenella showed differential growth responses to photoperiods across temperatures, probably with cell size.