Terms Of Carbon Gain Research Articles

There Is No Carbon Transfer Between Scots Pine and Pine Mistletoe but the Assimilation Capacity of the Hemiparasite Is Constrained by Host Water Use Under Dry Conditions.

Pine mistletoe is a hemiparasitic shrub that can produce its own photosynthates. There is a lack of knowledge about the interaction of mistletoe and host under varying environmental condition that might influence carbon gain and allocation. In a 13C-pulse labeling experiment with mature Pinus sylvestris (pine) infected by mistletoes grown in naturally dry or irrigated conditions, (1) mistletoe clusters were shielded from 13CO2 added, and (2) mistletoes or host needles were removed to manipulate the local assimilate and water availability. No 13C signal was found in shielded mistletoes, indicating no carbon transfer from the host to the mistletoe. When the pine needles were removed from girdled branches, no 13C signal was found in the host tissues, implying no carbon transfer from mistletoe to the host. However, mistletoes on needle-removed pine trees accumulated more labeled assimilates and had higher non-structural carbohydrate (NSC) concentrations only under naturally dry conditions but not in irrigated plots. Our results suggest that mistletoes show full carbon autonomy, as they neither receive carbon from nor provide carbon resource to the host trees. Moreover, the high assimilation capacity of mistletoes seems to be constrained by the host water use under dry conditions, suggesting that drought stress is not only negatively impacting trees but also mistletoes. Therefore, we conclude that the hemiparasites live on their own in terms of carbon gain which, however, depends on the water provided by the host tree.

Optimization can provide the fundamental link between leaf photosynthesis, gas exchange and water relations.

Tight coordination in the photosynthetic, gas exchange and water supply capacities of leaves is a globally conserved trend across land plants. Strong selective constraints on leaf carbon gain create the opportunity to use quantitative optimization theory to understand the connected evolution of leaf photosynthesis and water relations. We developed an analytical optimization model that maximizes the long-term rate of leaf carbon gain, given the carbon costs in building and maintaining stomata, leaf hydraulics and osmotic pressure. Our model demonstrates that selection for optimal gain should drive coordination between key photosynthetic, gas exchange and water relations traits. It also provides predictions of adaptation to drought and the relative costs of key leaf functional traits. Our results show that optimization in terms of carbon gain, given the carbon costs of physiological traits, successfully unites leaf photosynthesis and water relations and provides a quantitative framework to consider leaf functional evolution and adaptation.

Wintertime photosynthesis and spring recovery of Ilex aquifolium L.

Abstract: Former studies using the chlorophyll fluorescence technique on evergreen Ilex aquifolium L. showed that its photosynthetic potential for electron transport in winter recovers quickly when exposed to more favorable conditions. Since little is known, however, about its photosynthetic carbon gain in winter, we investigated its leaf gas exchange over an entire winter and spring period. Measurements were made rotationally in the field and in the laboratory to also investigate if I. aquifolium profits from warmer phases during winter in terms of net carbon gain. From the end of autumn until the end of spring, three different climate-driven phases of photosynthetic responses could be distinguished: first, an acclimation phase which lasted until February and was characterized by a gradually decreasing light-saturated gross photosynthesis (Amax(gross)), decreasing apparent quantum yield of CO2-assimilation (ΦΦi) and a decreasing ability of these parameters to recover overnight inside the laboratory. At the same time, maximal quantum yield of PSII (Fv/Fm) could fully regenerate. In this phase, single warmer days had a positive effect on carbon assimilation. Second, a phase of relatively constant but low photosynthesis which was virtually unaffected by temperature, lasting for almost two months occurred. Here, Amax(gross) and Φi had lost their ability to recover from winter conditions in the field, while Fv/Fm was much less affected. I. aquifolium was still able to conduct positive light-saturated net photosynthesis at a leaf temperature of -0.5 °C, but during this time it could not profit from milder temperatures in terms of carbon gain. Third, a phase of increasing photosynthesis (spring recovery) occurred, starting in March when the 5-day average temperature was above 5 °C and radiation in the field increased, and where all parameters slowly recovered from winter depressions. Our findings show that I. aquifolium is photosynthetically active over the whole winter, even at temperatures around 0 °C. In terms of carbon gain, however, I. aquifolium does not profit from warmer phases during winter, despite the fast recovery seen in chlorophyll fluorescence measurements.

Multiple Consequences Induced by Epidermally-Located Anthocyanins in Young, Mature and Senescent Leaves of Prunus.

Anthocyanic morphs are generally less efficient in terms of carbon gain, but, in turn, are more photoprotected than anthocyanin-less ones. To date, mature leaves of different morphs or leaves at different developmental stages within the same species have generally been compared, whereas there is a lack of knowledge regarding different stages of development of red vs. green leaves. Leaves (1-, 7-, and 13-week-old) of red- (RLP) and green-leafed (GLP) Prunus in terms of photosynthetic rate, carbon metabolism and photoprotective mechanisms were compared to test whether anthocyanin-equipped leaves perform better than anthocyanin-less leaves and whether photoprotection is the primary role of epidermally-located anthocyanins, using for the first time a recently-developed parameter of chlorophyll fluorescence (qPd). GLP leaves had a higher photosynthetic rate in 1- and 7-week-old leaves, but RLP leaves performed better at an early stage of senescence and had a longer leaf lifespan. Anthocyanins contributed to leaf photoprotection throughout the leaf development, but were tightly coordinated with carotenoids. Besides photoprotecting, we propose that epidermal anthocyanins may be principally synthetized to maintain an efficient carbon-sink strength in young and senescent leaves, thus extending the RLP leaf lifespan.

Suboptimal Acclimation of Photosynthesis to Light in Wheat Canopies.

Photosynthetic acclimation (photoacclimation) is the process whereby leaves alter their morphology and/or biochemistry to optimize photosynthetic efficiency and productivity according to long-term changes in the light environment. The three-dimensional architecture of plant canopies imposes complex light dynamics, but the drivers for photoacclimation in such fluctuating environments are poorly understood. A technique for high-resolution three-dimensional reconstruction was combined with ray tracing to simulate a daily time course of radiation profiles for architecturally contrasting field-grown wheat (Triticum aestivum) canopies. An empirical model of photoacclimation was adapted to predict the optimal distribution of photosynthesis according to the fluctuating light patterns throughout the canopies. While the photoacclimation model output showed good correlation with field-measured gas-exchange data at the top of the canopy, it predicted a lower optimal light-saturated rate of photosynthesis at the base. Leaf Rubisco and protein contents were consistent with the measured optimal light-saturated rate of photosynthesis. We conclude that, although the photosynthetic capacity of leaves is high enough to exploit brief periods of high light within the canopy (particularly toward the base), the frequency and duration of such sunflecks are too small to make acclimation a viable strategy in terms of carbon gain. This suboptimal acclimation renders a large portion of residual photosynthetic capacity unused and reduces photosynthetic nitrogen use efficiency at the canopy level, with further implications for photosynthetic productivity. It is argued that (1) this represents an untapped source of photosynthetic potential and (2) canopy nitrogen could be lowered with no detriment to carbon gain or grain protein content.

Relationships Between Vegetation Carbon Use Efficiency and Climatic Factors on the Tibetan Plateau

. Temperature, water, and sunshine conditions affect vegetation efficiency in terms of carbon gain. Responses of annual carbon use efficiency (CUE; i.e., the ratio of net primary production to gross primary production) to annual temperature, precipitation, vapor pressure, relative humidity, and sunshine were examined from 2000 to 2012 on the Tibetan Plateau. The response magnitudes of CUE to climatic factors varied with vegetation types, and might be related to changed climates with vegetation types. Spatially averaged CUE increased with increasing temperature and vapor pressure deficit, but decreased with actual vapor pressure and relative humidity. The vapor pressure deficit had the strongest effect on spatially averaged CUE. Specifically, air humidity conditions dominated the interannual variation of spatially averaged CUE. Warming and drying climatic changes will likely be conductive to an increased vegetation carbon storage efficiency of the Tibetan Plateau.Résumé. Les conditions de température, d’eau, et d’ensoleillement affectent l’efficacité de la végétation en matière de gain de carbone. Les réponses de l’efficacité de l’utilisation de carbone annuelle (CUE; soit, le rapport de la production primaire nette à la production primaire brute) en fonction de la température annuelle, des précipitations, de la pression de vapeur, de l’humidité relative, et de l’ensoleillement ont été examinées de 2000 à 2012 sur le plateau tibétain. Les amplitudes des réponses de la CUE aux facteurs climatiques ont varié selon les types de végétation, qui peuvent être liés aux changements de climats avec des types de végétation. La CUE moyenne spatiale a augmenté avec l’augmentation de la température et du déficit de pression de vapeur, mais a diminué avec la pression de vapeur et l’humidité relative. Le déficit de pression de vapeur a eu le plus fort effet sur la CUE moyenne spatiale. Plus précisément, les conditions d’humidité de l’air ont dominé la variation interannuelle de la CUE moyenne spatiale. Le réchauffement et l’assèchement causé par les changements climatiques amèneront probablement une augmentation de l’efficacité du stockage de carbone pour la végétation du plateau tibétain.

Photosynthesis and water use by two Sedum species in green roof substrate

Different succulent plants have been shown to exhibit varying degrees of crassulacean acid metabolism (CAM). This variation has not been consistently shown to relate to water use efficiency (WUE) by these species. This raises fundamental questions about the ecophysiological implications of switching between C3 photosynthesis and CAM metabolism. More information is also needed for Sedum species that utilize CAM to varying degrees on green roofs so that plant water use can be included in water balance equations that predict green roof performance. We monitored carbon dioxide exchange and water use by two common green roof species, Sedum album and Sedum kamtschaticum, for three weeks without water under strictly controlled environmental conditions in order to (1) compare daily carbon gain, rates of evapotranspiration (ET), and WUE for these two species and (2) assess the effect of CAM cycling on WUE with increasing drought for entire plant stands. Under similar environmental conditions, S. album and S. kamtschaticum canopies exhibited CAM metabolism to different extents with different ecophysiological consequences. S. kamtschaticum exhibited C3 photosynthesis for the first 14 days without water and outperformed S. album in terms of carbon gain and WUE above a volumetric water content (VWC) of 0.08m3m−3. S. album was the more drought tolerant species under the conditions of this experiment, gaining at least as much carbon and using water more efficiently at VWC below 0.08m3m−3. By switching from C3 to CAM at lower VWC, S. kamtschaticum had an overall greater WUE even though this species used as much if not more water overall compared to S. album. These data further support suggestions that a major adaptive function of CAM is to prolong plant-available water while maintaining a consistent, albeit low level of carbon gain. These findings also demonstrate why Sedum species should be treated independently of each other when considered in green roof designs.

Trade‐offs between global warming and day length on the start of the carbon uptake period in seasonally cold ecosystems

[1] It is well established that warming leads to longer growing seasons in seasonally cold ecosystems. Whether this goes along with an increase in the net ecosystem carbon dioxide (CO2) uptake is much more controversial. We studied the effects of warming on the start of the carbon uptake period (CUP) of three mountain grasslands situated along an elevational gradient in the Alps. To this end, we used a simple empirical model of the net ecosystem CO2 exchange, calibrated, and forced with multiyear empirical data from each site. We show that reductions in the quantity and duration of daylight associated with earlier snowmelts were responsible for diminishing returns, in terms of carbon gain, from longer growing seasons caused by reductions in daytime photosynthetic uptake and increases in nighttime losses of CO2. This effect was less pronounced at high, compared to low, elevations, where the start of the CUP occurred closer to the summer solstice when changes in day length and incident radiation are minimal.

Seasonal dynamics of CO2 balance and water consumption of C3 and C4-type cover crops compared to bare soil in a suitability study for their use in vineyards in Germany and Argentina

Cover crops are used in vineyards to maintain soil structure, minimise soil erosion and optimise vineyard mechanisation, yet few data are available on water consumption and carbon dioxide assimilation (CO2). Whereas cover crop use is common in the grape growing regions of Germany it is uncommon in Argentina. To obtain some information on the suitability of a selected number of species in terms of carbon gain and water expenditure under the climatic conditions of Germany and Argentina, we first quantified evapotranspiration (EvT), CO2 assimilation and water use efficiency of Trifolium repens L. (white clover) (TR), Festuca arundinacea Schreb (tall fescue) (FE), Sorghum sudanense (Piper) Stapf (Sudan grass) (SO), and Digitaria californica (Benth) Henr. (Arizona cotton top) (DI) in a field trial in Geisenheim, Germany. We then compared the performance of TR, FE and DI together with Sorghum halepense L. (Johnson grass) (SH) in a pot experiment under the warmer climatic conditions of Mendoza, Argentina, where water supply could be controlled. In all cases bare soil served as a reference for soil water loss. Gas-exchange of plants and soil were measured with customised open system canopy chambers and an infrared gas analyser and water dynamics in the soil with soil moisture probes (field) or gravimetrically (pots). SO and TR were the two species that reached the highest degree of soil coverage in Germany and substantially reduced soil moisture in the first 0.40m of depth. TR showed high EvT and CO2 assimilation rates in both climates when water supply was sufficient and maintained relative high rates when water status was reduced under cool conditions in Germany, yet performed poorly when high temperatures occurred concomitant to low water supply in Argentina. DI, being a C4 species from arid regions, had difficulties to get established in the cool conditions of Germany and there was no clear tendency for more efficient water use than the other cover crops. However under the warm condition of Argentina, especially when water supply was reduced, DI displayed higher WUE which was entirely related to the maintenance of higher assimilation rates at substantially reduced EvT. FE being common in German vineyards had low assimilation rates combined with high evapotranspiration rates under Argentinian conditions and was very sensitive to water deficit in combination with high temperature.

Cost-efficient light control for production of two campanula species

A cost-efficient light control system based on weather forecasts, electricity prices and daily photosynthesis integral (DPI) was evaluated for application in the commercial production of the long-day (LD) plant Campanula portenschlagiana ‘Blue Get Mee’ and C. cochlearifolia ‘Blue Wonder’. Experiments were conducted under both autumn and spring conditions and included four treatments. Three treatments were controlled by the software system DynaLight Desktop which automatically defined the most cost-efficient use of supplemental light, -based on a predefined set point of DPI, forecasted solar irradiance and the market price on electricity. The set points of DPI in the three treatments were 300, 450 and 600 mmol CO 2 m −2 leaf d −1 and the treatments were compared with a traditional LD 19-h treatment. The DPI-based light control strategy resulted in very irregular light patterns including daily periods of solar irradiance combined with supplemental light in low light periods and a night period interrupted by irregular light breaks (NB-lighting). Both campanula species flowered in the DPI-based treatments during spring, but the flowering percentage was low and non-uniform during autumn. This was caused by a combination of the irregular light, low natural light intensities and a decrease in daily light integral (DLI), and could be restored by maintaining a continuous 19 h photoperiod with incandescent lamps (<5 μmol m −2 s −1), illustrating that photoperiod was an important factor for flowering in LD species grown under low light intensities. Growth in terms of carbon gain was marginally affected by the irregular light and a 25% reduction in electricity costs was achieved without major reductions in plant quality in spring. Our results illustrate that plant production of LD species can be maintained in a cost-efficient light control system where the use of supplemental light is based on weather forecasts and electricity prices.

Influence of irradiance on photosynthesis and PSII photochemical efficiency in maize during short-term exposure at high CO&lt;sub&gt;2&lt;/sub&gt; concentration

This work aimed to evaluate if gas exchange and PSII photochemical activity in maize are affected by different irradiance levels during short-term exposure to elevated CO2. For this purpose gas exchange and chlorophyll a fluorescence were measured on maize plants grown at ambient CO2 concentration (control CO2) and exposed for 4 h to short-term treatments at 800 &mu;mol(CO2) mol-1 (high CO2) at a photosynthetic photon flux density (PPFD) of either 1,000 &mu;mol m-2 s-1 (control light) or 1,900 &mu;mol m-2 s-1 (high light). At control light, high-CO2 leaves showed a significant decrease of net photosynthetic rate (P N) and a rise in the ratio of intercellular to ambient CO2 concentration (C i/C a) and water-use efficiency (WUE) compared to control CO2 leaves. No difference between CO2 concentrations for PSII effective photochemistry (&Phi;PSII), photochemical quenching (qp) and nonphotochemical quenching (NPQ) was detected. Under high light, high-CO2 leaves did not differ in P N, C i/C a, &Phi;PSII and NPQ, but showed an increase of WUE. These results suggest that at control light photosynthetic apparatus is negatively affected by high CO2 concentration in terms of carbon gain by limitations in photosynthetic dark reaction rather than in photochemistry. At high light, the elevated CO2 concentration did not promote an increase of photosynthesis and photochemistry but only an improvement of water balance due to increased WUE.

Growth of Chrysanthemum in Response to Supplemental Light Provided by Irregular Light Breaks during the Night

Circadian rhythms are believed to be of great importance to plant growth and performance under fluctuating climate conditions. However, it is unclear how plants with a functioning circadian clock will respond to irregular light environments that disturb circadian-regulated parameters related to growth. Chrysanthemum (Chrysanthemum morifolium ‘Coral Charm’) was exposed to supplemental light provided as irregular light breaks during the night, achieved by controlling the light based on forecasted solar irradiance and electricity prices. Growth, in terms of carbon gain, was linearly correlated to both daylength and daily light integral. This response was observed irrespective of the irregularity of the light breaks and despite circadian-regulated processes of carbohydrate metabolism, chlorophyll fluorescence, and leaf chlorophyll content being affected. Leaf expansion and stem elongation occurred at a faster rate in plants grown in short days with irregular light breaks during the night period compared with plants grown in a climate with a consecutive long light period, showing that low average light intensity promoted expansion of the photosynthetic area of the plants. These results are important to gain an understanding of the relationship between circadian-regulated processes and plant growth. These results will also contribute to increased energy savings in the use of supplemental light in greenhouse production.

Water relations and CO 2 exchange of the terrestrial lichen Teloschistes capensis in the Namib fog desert: Measurements during two seasons in the field and under controlled conditions

Although the coastal zone of the Central Namib Desert (Namibia) has negligible rainfall, frequent fog, dew and high air humidity support a luxurious lichen flora. Large areas of soil crust communities are dominated by the multibranched, fruticose Teloschistes capensis interspersed by a (still indeterminable) Ramalina species. In earlier communications, based on field measurements in autumn, we began the analysis of functional mechanisms that allow these lichens to exist under the special conditions of a fog desert. We have extended this work by monitoring lichen CO 2 exchange and water relations in spring and by experiments under controlled conditions. In both seasons, nocturnal hydration, by fog and/or dew, activated dark respiration of the lichens which was followed, after sunrise, by a short period of positive net photosynthesis (NP) that continued until metabolic inactivation occurred from desiccation. Dry thalli of T. capensis were able to reactivate NP through water vapour uptake alone, beginning at an air relative humidity of 82%, i.e. at a water potential of −26.3 MPa; the moisture compensation point during desiccation was at 13% thallus water content (WC, dry weight related). Optimal WC for photosynthesis was around 100%, and both species showed a large and extended suprasaturation depression of CO 2 assimilation. Light response showed “sun-plant” characteristics with saturation >1000 μmol m −2 s −1 photosynthetically active photon flux density (PPFD). However, due to rapid desiccation, the combination of light saturation with optimal WC very rarely occurred under field conditions. Light compensation point after sunrise was highly dependent on actual WC: at low hydration, it amounted to only ca. 10 μmol m −2 s −1 PPFD so that even the smallest levels of hydration could be used for carbon gain before desiccation took place again. This phenomenon was probably due to a hydration gradient in the thallus branches during transient moistening so that the outer photobiont layer was favoured in contrast to the internal mycobiont which remained dry longer and did not contribute respiratory CO 2 loss. Fully hydrated thalli had light compensation points around 50 μmol m −2 s −1 PPFD. Extended desiccation of 1–3 days had no impact on the magnitude and recovery of photosynthesis but, imposed desiccation of 10 days reduced NP in lab and field experiments and caused an extended period of recovery. “Resaturation respiration” was not detected in the field data, although it was present after experimental moistening of dry thalli. In spring, the higher fog frequency and intensity increased maximal nocturnal WC, maximal attained NP as well as integrated daily carbon income (ΣNP) compared to the autumn measurements. NP max and ΣNP depended on maximal nocturnal WC with a saturation-type response. In terms of carbon gain both species seem to be optimally adapted to nocturnal moistening up to 160% WC and were not able to make use of higher degrees of hydration, a feature that might well influence their habitat selection. Maximal daily carbon-related ΣNP for T. capensis was 4.6 mg C (g C) −1 day −1. A rough estimate of the annual (projected) area-related carbon balance (photosynthetic income minus respiratory losses) based on published fog and dew frequencies and personal observations was 15–34 mg C m −2 yr −1.

Radiative transfer and carbon assimilation in relation to canopy architecture, foliage area distribution and clumping in a mature temperate rainforest canopy in New Zealand

The objective of this study was to characterize the forest canopy in terms of species composition, tree size classes and spatial distribution of leaf area of a mature temperate rainforest to provide a basis for scaling up shoot-level processes of energy and mass exchange using a one-dimensional canopy model. Stem number per unit area was high (1660 stems ha −1) but species diversity was low ( n = 10). Two species ( Dacrydium cuppressinum and Weinmannia racemosa) equally accounted for 70% of the stem numbers, with the remaining 30% distributed among the other eight tree species. However, D. cuppressinum alone accounted for 72% of basal area and 75% of crown volume. Across the site L e (“effective” leaf area index, uncorrected for foliage clumping and woody surface interceptance) varied between 2.2 and 5.6, with a mean value of 3.5. Half total woody surface area per unit ground area ( W) was 1.1. The mean foliage clumping index within shoot elements ( γ E) was 1.2, while that between shoot elements ( Ω E) was 0.87, giving an overall foliage clumping factor ( Ω = Ω E/ γ E) of 0.73. After corrections for foliage clumping and woody surface interceptance, half total leaf area per unit ground area ( L hc = L e/ Ω − W) was 3.7. For individual shoots, γ E increased from 1.0 to 1.5 with height in the canopy, possibly reflecting shoot structural adaptation to local irradiance. Simulations with the canopy model over 1 year using mean clumping factors revealed that clumping reduced total canopy radiation interception by 5%. Shoot-level irradiance was reduced at the top of the canopy but increased in lower canopy layers resulting in a more even canopy irradiance distribution. This enhanced annual canopy photosynthesis by 8% over a canopy with randomly distributed foliage. When the simulations were repeated to include the observed variation of γ E with height, total canopy radiation absorption was 11% lower than for a random canopy and canopy photosynthesis was 12% greater than a random canopy. The combination of reduced canopy radiation absorption and increased photosynthesis due to foliage clumping resulted in a considerable enhancement of canopy light-use efficiency. These analyses reveal a significant advantage of clumped foliage over randomly distributed foliage in terms of carbon gain, even for a forest canopy with moderate leaf area index.

Photoinhibition, acclimation and New Zealand's divarication plants: a reply to Lusk

Photoinhibition, acclimation and New Zealand's divarication plants: a reply to Lusk

Scaling sun and shade photosynthetic acclimation ofAlocasia macrorrhizato whole‐plant performance – I. Carbon balance and allocation at different daily photon flux densities

ABSTRACTWe determined the carbon allocation patterns and construction costs ofAlocasia macrorrhizaplants grown at different photon flux densities (PFD) as well as the whole‐plant carbon gain of these plants at different daily PFDs. Growth at high PFD resulted in thicker leaves with a higher leaf mass per unit area, and increased biomass allocation to petioles and roots, as compared to growth at low PFD. Increased allocation to petioles may have been necessary to support the heavier leaves, whereas increased allocation to roots may have been necessary to supply sufficient water for the higher transpiration rates in high PFD. Root biomass was highly correlated with the daily, whole‐plant transpiration rate. Tissue construction costs per unit dry mass were unchanged by acclimation, but, since the mass per unit areas of leaves, roots and petioles all increased, construction costs per unit leaf area were much higher for plants grown at high PFD. On a per unit leaf area basis, daily whole‐plant carbon gain measured at high daily PFD was higher in high‐ than in low‐PFD‐grown plants. However, on a per unit leaf mass basis, low‐PFD‐grown plants had a daily carbon gain at least as high as that of high‐PFD‐grown plants at high daily PFD. At low daily PFD, low‐PFD‐grown plants maintained an advantage over high‐PFD‐grown plants in terms of carbon gain because of their larger leaf area ratios. Thus, in terms of carbon gain, low‐PFD‐grown plants performed better than sun plants at low PFD and as well as high‐PFD‐grown plants at high PFD, despite their lower photosynthetic capacities per unit area. For high‐PFD‐grown plants, the higher construction costs per unit leaf area resulted in lower leaf area ratios, which counteracted the advantage of higher photosynthetic rates per unit leaf area.