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Nitrogen (N) deficiency limits the net carbon assimilation rate (A N), but the relative N sensitivities of photosynthetic component processes and carbon loss mechanisms remain relatively unexplored for field-grown cotton. Therefore, the objective of the current study was to define the relative sensitivity of individual physiological processes driving N deficiency-induced declines in A N for field-grown cotton. Among the potential diffusional limitations evaluated, mesophyll conductance was the only parameter substantially reduced by N deficiency, but this did not affect CO2 availability in the chloroplast. A number of metabolic processes were negatively impacted by N deficiency, and these effects were more pronounced at lower leaf positions in the cotton canopy. Ribulose bisphosphate (RuBP) regeneration and carboxylation, A N, and gross photosynthesis were the most sensitive metabolic processes to N deficiency, whereas photosynthetic electron transport processes, electron flux to photorespiration, and dark respiration exhibited intermediate sensitivity to N deficiency. Among thylakoid-specific processes, the quantum yield of PSI end electron acceptor reduction was the most sensitive process to N deficiency. It was concluded that A N is primarily limited by Rubisco carboxylation and RuBP regeneration under N deficiency in field-grown cotton, and the differential N sensitivities of the photosynthetic process and carbon loss mechanisms contributed significantly to photosynthetic declines. [ABSTRACT FROM AUTHOR]

IntroductionThe rapid increase in sea-water temperatures and frequency of extreme thermal events have amplified the risk of functional extinction of Mediterranean species such as the endemic long-lived seagrass Posidonia oceanica. Because of the valuable ecological functions and ecosystem services the species provides, understanding the life-stage specific thermal vulnerability is crucial to accurately predict the consequences of current and future global climate change and to protect and conserve existing meadows.MethodsTo this end, here we report a study on the ontogeny-specific thermal sensitivity of important physiological functions (i.e. respiration and net production) of three different early life history stages of P. oceanica, namely seed, seedling (4-month-old individuals) and 16-month-old plantlet by measuring thermal performance curves (eleven temperatures treatments between 15-36°C with n=8).ResultsAll three stages examined showed photosynthetic activity during light exposure with similar optimal temperatures for both net and gross production. Gross photosynthesis increased with rising temperature up to 28-30°C, subsequently declining at higher temperatures until complete inhibition at 36°C. The metabolic response of seeds was found to be temperature-dependent up to 26°C, while respiration of seedlings and plantlets was almost stable up to 28-30°C, but increased markedly at higher temperatures, resulting in a negative whole-plant C balance at temperatures above 32°C. Overall, our results show that seedlings and plantlets tolerate a wider temperature range (15 - 32°C) than seeds, which experience metabolic and physiological dysfunction from 26-28°C onwards.DiscussionThese findings suggest that the impact of warming on recruitment in P. oceanica meadows may vary depending on the timing of marine heatwaves (i.e. mid-spring to mid-autumn) and provide useful knowledge to inform restoration programs using early life stages of the species. In conclusion, the study of physiological responses during the early life stages of species is key to identify life history stages that are particularly vulnerable to climate change, which is vital knowledge for ecosystem management and conservation.

Background and Aims Leaflet shapes of tomato plants (Solanum lycopersicum) have been reduced to simple geometric shapes in previous functional–structural plant models (FSPMs) in order to facilitate measurements and reduce the time required to reconstruct the plant virtually. The level of error that such simplifications introduce remains unaddressed. This study therefore aims to quantify the modelling error associated with simplifying leaflet shapes. Methods Realistic shapes were implemented in a static tomato FSPM based on leaflet scans, and simulation results were compared to simple geometric shapes used in previous tomato FSPMs in terms of light absorption and gross photosynthesis, for both a single plant and a glasshouse scenario. Key Results The effect of simplifying leaflet shapes in FSPMs leads to small but significant differences in light absorption, alterations of canopy light conditions and differences in photosynthesis. The magnitude of these differences depends on both the type of leaflet shape simplification used and the canopy shape and density. Incorporation of realistic shapes requires a small increase in initial measurement and modelling work to establish a shape database and comes at the cost of a slight increase in computation time. Conclusions Our findings indicate that the error associated with leaflet shape simplification is small, but often unpredictable, and is affected by plant structure but also lamp placement, which is often a primary optimization goal of these static models. Assessment of the cost–benefit of realistic shape inclusion shows relatively little drawbacks for a decrease in model uncertainty. [ABSTRACT FROM AUTHOR]

The paper presents the results regarding the phytomonitoring of physiological processes in hair plants. Among the physiological processes that characterize the activity of the production process is photosynthesis, which, like other physiological processes, is influenced by light, temperature and other ecological factors. Based on these considerations, the saturation curve of the light for photosynthesis was monitored. The modern RTM-48A phytomonitor was used, which allowed the measurement of physiological indices in the form of film-phytodiagram in automatic regime that allowed the diagnosis of the properties of the genotype and the physiological state of the plants. The saturation curve of light for photosynthesis in hair trees was determined as a result of assessing the intensity of photosynthesis, sweating, respiration and conductivity of stomata depending on temperature, humidity and CO2 content in air. The minimum value of the light at which the photosynthesis process is initiated was established. With the increase of the light intensity (to 1/3 of the total light) the intensity of the photosynthesis increases after the essential optimization of the process took place. In hair plants, the intensity of photosynthesis begins with the appearance of light and continues to increase until the illumination of 100-150 micromol / m2 s, decreasing to 500 after maintaining at the same level until the illumination of 1500, then it increases to 1800. It was been established that the effect of temperature influence on photosynthesis in hair plants depended on the intensity of light. Respiration, transpiration and conductivity of the stomata confirmed light saturation curves for photosynthesis. As a result of the research, the positive influence of SBA Reglalg and microelements (B, Zn, Mn, Mo) on the activity of physiological processes in hair plants was established. The more pronounced stimulation of the activity of the physiological processes takes place under the influence of the Reglalg preparation in the presence of microelements. [ABSTRACT FROM AUTHOR]

Northern peatlands form a major soil carbon (C) stock. With climate change, peatland C mineralization is expected to increase, which in turn would accelerate climate change. A particularity of peatlands is the importance of soil aeration, which regulates peatland functioning and likely modulates the responses to warming climate. Our aim is to assess the impacts of warming on a southern boreal and a sub‐arctic sedge fen carbon dioxide (CO2) exchange under two plausible water table regimes: wet and moderately dry. We focused this study on minerotrophic treeless sedge fens, as they are common peatland types at boreal and (sub)arctic areas, which are expected to face the highest rates of climate warming. In addition, fens are expected to respond to environmental changes faster than the nutrient poor bogs. Our study confirmed that CO2 exchange is more strongly affected by drying than warming. Experimental water level draw‐down (WLD) significantly increased gross photosynthesis and ecosystem respiration. Warming alone had insignificant impacts on the CO2 exchange components, but when combined with WLD it further increased ecosystem respiration. In the southern fen, CO2 uptake decreased due to WLD, which was amplified by warming, while at northern fen it remained stable. As a conclusion, our results suggest that a very small difference in the WLD may be decisive, whether the C sink of a fen decreases, or whether the system is able to adapt within its regime and maintain its functions. Moreover, the water table has a role in determining how much the increased temperature impacts the CO2 exchange. [ABSTRACT FROM AUTHOR]

The review discusses up-to-date concepts of interrelations between photosynthesis and respiration. It considers the quantitative ratio of the processes in the leaf and that in the whole plant reported by Russian and other researches. Special attention is paid to performance of dark respiration in the light and to the methods of its exploration, which employ classical gas exchange, chlorophyll fluorescence, and carbon isotopes. Possible causes of conservatism and variability in the total respiration to gross photosynthesis ratio under stationary and stress conditions are also discussed along with prospects in further investigations. [ABSTRACT FROM AUTHOR]

As atmospheric CO2 concentrations increase, so too does the dissolved CO2 and HCO3– concentrations in the world's oceans. There are still many uncertainties regarding the biological response of key groups of organisms to these changing conditions, which is crucial for predicting future species distributions, primary productivity rates, and biogeochemical cycling. In this study, we established the relationship between gross photosynthetic O2 evolution and light-dependent O2 consumption in Trichodesmium erythraeum IMS101 acclimated to three targeted pCO2 concentrations (180 µmol mol–1=low-CO2, 380 µmol mol–1=mid-CO2, and 720 µmol mol–1=high-CO2). We found that biomass- (carbon) specific, light-saturated maximum net O2 evolution rates (PnC,max) and acclimated growth rates increased from low- to mid-CO2, but did not differ significantly between mid- and high-CO2. Dark respiration rates were five times higher than required to maintain cellular metabolism, suggesting that respiration provides a substantial proportion of the ATP and reductant for N2 fixation. Oxygen uptake increased linearly with gross O2 evolution across light intensities ranging from darkness to 1100 µmol photons m–2 s–1. The slope of this relationship decreased with increasing CO2, which we attribute to the increased energetic cost of operating the carbon-concentrating mechanism at lower CO2 concentrations. Our results indicate that net photosynthesis and growth of T. erythraeum IMS101 would have been severely CO2 limited at the last glacial maximum, but that the direct effect of future increases of CO2 may only cause marginal increases in growth. [ABSTRACT FROM AUTHOR]

Results of eddy covariance measurements of carbon dioxide and water fluxes above a spruce forest in the middle taiga subzone from April to August 2013 and 2016 are presented. The ecosystem of the spruce forest turned from source to sink CO2 at mean daily air temperatures below zero in late March and early April; in 2016, it was 2 weeks earlier than in 2013. The maximum net ecosystem exchange of CO2 (NEE) was recorded at the end of June and beginning of July. In 2016, the mean daily NEE of spruce forest decreased at a high air temperature and a low amount of precipitation in the beginning of the growing season; turning from the sink CO2 to the source was observed in early August. The net exchange of CO2 between spruce and the atmosphere from April to August 2013 reached 327 g C/m2 and, in 2016, 174 g C/m2. The seasonal evapotranspiration of the spruce forest in these years was 239–247 mm/m2 and the mean value of water-use efficiency for photosynthesis (WUE) in the season was 2.3–3.3 g C/kg H2O. WUE was relatively constant during the growing season, resulting from a close relationship between the exchange of CO2 and water, the main processes that ensure the production of organic matter in the spruce-forest ecosystem. [ABSTRACT FROM AUTHOR]

Recent climatic projections predict a decline in rainfall mainly during the summer period and an increase in air temperature for the Mediterranean basin, resulting in extended periods of soil water deficit. Mediterranean evergreen species attain drought resistance through different traits or combination of traits. The main objective of this research is to analyze the response of the evergreen species co-occurring in the Mediterranean maquis to variations in water availability and air temperature during the year. The results show that leaf structural traits significantly affect physiological traits as confirmed by the Partial Least Squares Regression analysis (PLS). In particular, the considered species have a similar leaf respiration (RL) trend during the year with the lowest rates in winter (mean 0.95 ± 0.44 µmol m-2 s-1) and the highest in drought (mean 3.05 ± 0.96 µmol m-2 s-1). Nevertheless, a different RL effect on gross photosynthesis (PG) during drought was observed. C. incanus, E. multiflora, R. officinalis and S. aspera have the highest RL/PG ratio (mean 0.54 ± 0.08), while Q. ilex, P. latifolia, P. lentiscus, A. unedo and E. arborea have the lowest (mean 0.22 ± 0.07). RL/PG ratio variations depend on the sensitivity of both the two parameters to drought. Considering the increase of the length and intensity of drought in the Mediterranean basin, and that the photosynthesis of Mediterranean evergreen species is frequently limited by sub-optimal conditions (i.e., water deficit, high light intensity and high air temperature), it is important to improve knowledge on RL, since it has a critical function in modulating carbon balance of Mediterranean species.

Biocrusts are a critical biological community that represents one of the most important photosynthetic biomass pools in dryland regions. Thus, they play an important role in CO 2 fluxes in these regions, where water availability limits vascular plant growth and development. The effect of biocrusts on CO 2 fluxes was expected to be controlled by the interplay of several environmental factors, as well as biocrust developmental stage and coverage. To test this hypothesis, we performed an in situ study during which we measured net CO 2 fluxes and dark respiration over biocrusted soils at different successional stages in two semiarid ecosystems, where biocrusts are one of the main surface components. In addition, CO 2 flux was measured in annual plants, which were an abundant interplant cover in one of the study sites during the measurement period. Field campaigns were conducted from early morning to dusk on selected days with different environmental conditions over the year. Gross photosynthesis was calculated from net CO 2 flux and dark respiration. Biocrusts showed contrasting responses in CO 2 exchange depending on environmental conditions during the day and the year and depending on biocrust developmental stage. CO 2 flux in biocrusts was highly correlated with soil moisture, but also with photosynthetically active radiation and temperature. During dry soil periods, soils colonized by biocrusts had net CO 2 fluxes close to zero, but after precipitation events (light or heavy) all the biocrust types began to photosynthesize. When the rainfall was right after an extended drought, the respiration by biocrusts themselves and underlying soil exceeded the biocrust gross photosynthesis, and consequently soils colonized by biocrusts behaved as CO 2 sources. On the contrary, consecutive precipitation events and mild temperatures caused soil colonization by biocrusts to behave as CO 2 sinks. Annual plants were measured during their senescence and acted as CO 2 sources during all measurement campaigns. The time of day when the biocrusts showed net CO 2 fixation depended on the interplay of humidity just above them, air temperature and photosynthetically active radiation. The biocrust type also significantly influenced CO 2 fluxes in both semiarid ecosystems. In general, during wet periods, late successional biocrusts (i.e. lichens and mosses) had higher gross photosynthesis than early successional biocrusts (developed and incipient cyanobacteria crusts). Nevertheless, dark respiration from late successional biocrusts and underlying soils was also higher than from early successional biocrusts, so both biocrust types had similar net CO 2 fluxes. These results highlight the importance of considering the whole soil profile under biocrusts with their associated microbial communities as well as the temporal variability of CO 2 fluxes in soils covered by biocrusts in carbon balance studies in semiarid regions. [ABSTRACT FROM AUTHOR]

Increasing atmospheric CO2 concentrations are leading to increases in dissolved CO2 and HCO3- concentrations and decreases in pH and CO32- in the world's oceans. There remain many uncertainties as to the magnitude of biological responses of key organisms to these chemical changes. In this study, we established the relationship between photosynthetic carbon fixation rates and pH, CO2, and HCO3- concentrations in the diazotroph, Trichodesmium erythraeum IMS101. Inorganic 14C-assimilation was measured in TRIS-buffered artificial seawater medium where the absolute and relative concentrations of CO2, pH, and HCO3- were manipulated. First, we varied the total dissolved inorganic carbon concentration (TIC) (<0 to ~5 mM) at constant pH, so that ratios of CO2 and HCO3- remained relatively constant. Second, we varied pH (~8.54 to 7.52) at constant TIC, so that CO2 increased whilst HCO3- declined. We found that 14C-assimilation could be described by the same function of CO2 for both approaches, but it showed different dependencies on HCO3- when pH was varied at constant TIC than when TIC was varied at constant pH. A numerical model of the carbon-concentrating mechanism (CCM) of Trichodesmium showed that carboxylation rates are modulated by HCO3- and pH. The decrease in assimilation of inorganic carbon (Ci) at low CO2, when TIC was varied, was due to HCO3- uptake limitation of the carboxylation rate. Conversely, when pH was varied, Ci assimilation declined due to a high-pH mediated increase in HCO3- and CO2 leakage rates, potentially coupled to other processes (uncharacterised within the CCM model) that restrict Ci assimilation rates under high-pH conditions. [ABSTRACT FROM AUTHOR]

Fluxes of carbon dioxide in the old-growth bilberry spruce forest in the European Taiga are measured by the eddy covariance technique. A carbon dioxide sink to the ecosystem was observed from April until September; the maximum net-exchange rate of carbon dioxide was recorded in July. During the cold period of the year from October to March, the biogenic flux of CO was directed from the forest canopy to the atmosphere. According to measurements at u* > 0.2, the total annual NEE was 219 g C m; the annual values of the ecosystem respiration R and the gross photosynthesis P were 483 and 966 g C m, respectively. The conclusion is that the old-growth bilberry spruce forest in the middle taiga subzone was the sink of carbon from the atmosphere during the year of observation. [ABSTRACT FROM AUTHOR]

Accumulation of arsenic in plants is a serious South-east Asian environmental problem. Photosynthesis in the small aquatic angiosperm Wolffia arrhiza is very sensitive to arsenic toxicity, particularly in water below pH 7 where arsenite (As (OH) 3 ) (AsIII) is the dominant form; at pH >7 AsO 4 2− (As(V) predominates). A blue-diode PAM (Pulse Amplitude Fluorometer) machine was used to monitor photosynthesis in Wolffia . Maximum gross photosynthesis (Pg max ) and not maximum yield (Y max ) is the most reliable indicator of arsenic toxicity. The toxicity of arsenite As(III) and arsenate (H 2 AsO 4 2− ) As(V) vary with pH. As(V) was less toxic than As(III) at both pH 5 and pH 8 but both forms of arsenic were toxic (>90% inhibition) at below 0.1 mol m −3 when incubated in arsenic for 24 h. Arsenite toxicity was apparent after 1 h based on Pg max and gradually increased over 7 h but there was no apparent effect on Y max or photosynthetic efficiency (α 0 ). [ABSTRACT FROM AUTHOR]

Single polyps of Galaxea fascicularis were fixed to glass vials with underwater epoxy resin. After regeneration into microcolonies they were used for microsensor measurements of photosynthesis and calcification under different incubating temperatures. Gross photosynthesis was found highest at temperatures of 23 and 26°C (ca. 0.022 mole O2 m-3 s–1), close to the ambient temperature (i.e. 26°C). At 35°C, gross photosynthesis was irreversibly inhibited as the microcolonies bleached. The net photosynthesis rapidly decreased with temperature and became negative at temperatures higher than 29°C. Profiles of O2 and Ca2+ showed a strong effect of temperature on them. The concentrations of Ca2+ measured on the polyp surface also showed temperature dependence of Ca2+ uptake. In the dark and below 29°C, the surface Ca2+ concentration was temperature independent. During illumination, the surface Ca2+ concentration showed a dip at 26°C (ca. 8.7 mM), indicating maximum uptake rates at ambient temperature. However, at 32°C and higher, Ca2+ was slightly higher at the tissue surface than in the seawater, in both light and dark, resulting from calcium dissolution. The surface pH in light increased gradually from 8.3 to 8.6 with increasing temperature to 23°C, and thereafter remained constant to 29°C. At 32°C, the pH became slightly acidic compared with the water phase, probably due to a decrease in the uptake of CO2 by photosynthesis. The largest difference in pH between light and dark incubations was at temperatures between 23 and 29°C (7.5-7.7 in dark versus 8.6-8.7 in light), which indicate high rates of photosynthesis and respiration in this temperature range. It is concluded that photosynthetic activity in the coral is maintained up to rather high temperatures (32°C), but corals at super-optimum temperatures (above 26°C) consume more O2 than they produce, decalcify and produce CO2

Water motion drives the flux of suspended and dissolved material (e.g., nutrients, gametes, and dissolved oxygen) to and from macrophyte canopies, and is one of the most important mechanisms that can regulate the growth, survival, and persistence of marine macrophytes populations. At small spatial scales (e.g., lamina or leaves and individuals), increasing flow-rates have been demonstrated to enhance physiological processes, especially photosynthesis rates, and we expected a similar response at the canopy scale. We conducted seven experiments over 25 days using a pair of open-air flow-chambers under natural light, temperature, and seawater conditions. In the four marine macrophyte ( Sargassum piluliferum, S. siliquastrum, S. thunbergii, and Zostera marina) canopies examined, an increase in flow-rate did not enhance photosynthesis rates. The odds that daily gross photosynthesis rates increase with a decrease in flow-rates was 1.77 to 1. We also examined if two non-linear equations and one linear equation, often used to describe the relationship between photosynthesis to photosynthetic photon flux density ( PPFD), biased estimates of the daily rates of photosynthesis and respiration. It was revealed that the functional form of the equation strongly influenced photosynthesis and respiration rate estimates at short time scales (i.e., minutes), however, daily rates were insensitive to the type of equation used to model the relationship between photosynthesis and PPFD. We suggest that the predominance of photosynthesis rates occurring in under-saturating PPFD conditions (> 40 % of daylight hours) may be one of the reasons for this insensitivity. [ABSTRACT FROM AUTHOR]

Premise of research. The encrusting arboreal lichen Dirinaria picta (Sw.) Schaer.ex Clem. (Physiaceae) is commonly found growing on tree trunks in Thailand and globally in the tropics and subtropics. Trebouxia sp. is its chlorophyte symbiont. Pulse amplitude modulation (PAM) techniques have been used to measure photosynthesis of a tropical lichen as well as its cultured symbiont. PAM technology has not been used to full advantage in lichens. Methodology. Absorptance of the thalli and glass fiber disks impregnated with cultured Trebouxia was measured with a leaf absorptance meter. PAM fluorometers measure the light reactions of photo-organisms to estimate gross photosynthesis (Pg; mol O2 m-2 s-1) from the measured electron transport rate through PSII (4 electrons per O2), provided that the absorptance of the photo-organism is known. Photosynthesis-versus-irradiance curves were measured with a blue-diode PAM machine and fitted to the waiting-in-line function. Pivotal results. The absorptance of moist active lichen in blue light is Abt%465 nm = 92.5 ± 0.529 ( ± 95% confidence limit [CL]; n = 48). Maximum yield, maximum Pg (Pg max), quantum efficiency, and nonphoto-chemical quenching do not show a strong diel cycle. Dirinaria has an optimum irradiance of ≈500 /amol m-2 s-1 PPFD and a Pgmax of ≈227 /amol O2 mg Chl a-1 h-1 (Chl a = chlorophyll a). Respiration of Dirinaria is ≈16.2 /amol O2 mg (Chl a) -1 h-1, so net photosynthesis is ≈211 /amol O2 mg Chl a-1 h-1. The Pg of Trebouxia is comparable to that of the Dirinaria lichen, but the two have different nonphotochemical quenching properties. Photosynthesis revives in dry Trebouxia in vitro within a few minutes after wetting. On a chlorophyll basis, the electron transport rates of dry and in vivo Trebouxia are closely comparable: hyphal absorption of light appears to be negligible. Conclusions. Dirinaria can tolerate high irradiances in natural conditions but is dry and dormant most of the time (poikilohydric). The desiccation resistance of Trebouxia is constitutive. [ABSTRACT FROM AUTHOR]

Chlorine (reactive chlorine: Cl+OCl) is used as a disinfectant on prawn farms but the environmental effects of discharged chlorine is of environmental concern. Toxicity of chlorine on prawn farm phytoplankton populations was monitored using the pulse amplitude fluorometer technique to measure phytoplankton photosynthesis. The dominant phytoplankton species found in the ponds of a prawn farm in Pang-Nga Province (Thailand) were Chlorella sp. (>95 %), with some Tetraselmis and Chaetoceros. Cells were suspended in clean sea water with (chlorine) of 15, 30, 45, 60, 75 and 90 ppm, respectively, in short-term experiments for 10 min (ST) and for long-term (24 h) exposure. Photosynthesis of Chlorella, Tetraselmis and Chaetoceros in clean sea water was inhibited by 50 % at (chlorine) of 4.68 ± 0.6, 7.26 ± 1.14 and 7.81 ± 0.78 ppm (mean ± SEM), respectively, in ST experiments. The chlorine consuming reactions with the large amounts of dissolved organic matter and ammonia in prawn farm pond water decreases toxicity but would form organochlorines and chloramine. Thiosulphate, often used to neutralise chlorine, was found to be of very limited toxicity to Chlorella in both short-term 1-h and 24-h experiments (up to ≈500 mmol m, 124 ppm). Environmental effects of Chlorine in discharges from ponds are short term. Chlorine quickly disappears in the environment, particularly during daylight and so only has effects close to effluent points. Standard practice was to discharge on a falling tide in daylight. The long effluent channel (1 km) also ensured that very little reactive chlorine reached the estuary. [ABSTRACT FROM AUTHOR]

Abstract: We carried out batch culture studies with seven species of marine phytoplankton and chemostat studies with two of the seven species to determine whether and to what extent 14C uptake approximated net photosynthesis. In two of seven cases, Isochrysis galbana and Dunaliella tertiolecta, cells uniformly labeled with 14C lost no activity when they were transferred to a 14C-free medium and allowed to grow in the light. In similar experiments with four other species, uniformly labeled cells lost activity when incubated in the light, but the loss rates were only a few percent per day. Thus these six species appear to respire primarily recently fixed carbon. In the case of the remaining species, Chlorella kessleri, loss rates of 14C in the light from uniformly labeled cells were about 29% per day, the apparent ratio of respiration to net photosynthesis being 0.4. Follow-up chemostat studies with I. galbana and C. kessleri grown under both light- and nitrate-limited conditions produced results consistent with the implications of the batch culture work: uptake of 14C by I. galbana after incubations of 24h yielded estimates of photosynthetic carbon fixation equal to the product of the chemostat dilution rate and the concentration of organic carbon in the growth chamber. Similar experiments with C. kessleri produced 14C-based estimates of photosynthetic carbon fixation that exceeded the net rates of organic carbon production in the growth chamber by roughly 55%. Time-course studies with both species indicated that at high growth rates recently fixed carbon began to enter the respiratory substrate pool after a time lag of several hours, a result consistent with previous work with D. tertiolecta. The lag time appeared to be much shorter at low growth rates. The results with C. kessleri are similar to results previously reported for Chlorella pyrenoidosa and Amphidium carteri. Collectively these results suggest that 14C uptake by species with relatively high ratios of respiration to photosynthesis may tend to substantially overestimate net photosynthesis, perhaps because a substantial percentage of the carbon respired by such species is old carbon. [Copyright &y& Elsevier]

Mechanistic understanding of the costs and benefits of photoacclimation requires knowledge of how photophysiology is affected by changes in the molecular structure of the chloroplast., We tested the hypothesis that changes in the light dependencies of photosynthesis, nonphotochemical quenching and PSII photoinactivation arises from changes in the abundances of chloroplast proteins in Emiliania huxleyi strain CCMP 1516 grown at 30 (Low Light; LL) and 1000 (High Light; HL) μmol photons m−2 s−1 photon flux densities., Carbon-specific light-saturated gross photosynthesis rates were not significantly different between cells acclimated to LL and HL. Acclimation to LL benefited cells by increasing biomass-specific light absorption and gross photosynthesis rates under low light, whereas acclimation to HL benefited cells by reducing the rate of photoinactivation of PSII under high light. Differences in the relative abundances of proteins assigned to light-harvesting (Lhcf), photoprotection ( LI818-like), and the photosystem II ( PSII) core complex accompanied differences in photophysiology: specifically, Lhcf: PSII was greater under LL, whereas LI818: PSII was greater in HL., Thus, photoacclimation in E. huxleyi involved a trade-off amongst the characteristics of light absorption and photoprotection, which could be attributed to changes in the abundance and composition of proteins in the light-harvesting antenna of PSII. [ABSTRACT FROM AUTHOR]

Cultivation of bioenergy crops has been suggested as a promising option for reduction of greenhouse gas ( GHG) emissions from arable organic soils (Histosols). Here, we report the annual net ecosystem exchange ( NEE) fluxes of CO2 as measured with a dynamic closed chamber method at a drained fen peatland grown with reed canary grass ( RCG) and spring barley ( SB) in a plot experiment ( n = 3 for each cropping system). The CO2 flux was partitioned into gross photosynthesis ( GP) and ecosystem respiration ( RE). For the data analysis, simple yet useful GP and RE models were developed which introduce plot-scale ratio vegetation index as an active vegetation proxy. The GP model captures the effect of temperature and vegetation status, and the RE model estimates the proportion of foliar biomass dependent respiration ( Rfb) in the total RE. Annual RE was 1887 ± 7 (mean ± standard error, n = 3) and 1288 ± 19 g CO2-C m−2 in RCG and SB plots, respectively, with Rfb accounting for 32 and 22% respectively. Total estimated annual GP was −1818 ± 42 and −1329 ± 66 g CO2-C m−2 in RCG and SB plots leading to a NEE of 69 ± 36 g CO2-C m−2 yr−1 in RCG plots (i.e., a weak net source) and −41 ± 47 g CO2-C m−2 yr−1 in SB plots (i.e., a weak net sink). Standard errors related to spatial variation were small (as shown above), but more significant uncertainties were related to the modelling approach for establishment of annual budgets. In conclusion, the bioenergy cropping system was not more favourable than the food cropping system when looking at the atmospheric CO2 emissions during cultivation. However, in a broader GHG life-cycle perspective, the lower fertilizer N input and the higher biomass yield in bioenergy cropping systems could be beneficial. [ABSTRACT FROM AUTHOR]

Abstract: We analyzed net CO2 exchange data from 13 flux tower sites with 27 site-years of measurements over maize and wheat fields across midcontinent North America. A numerically robust “light-soil temperature-VPD”-based method was used to partition the data into photosynthetic assimilation and ecosystem respiration components. Year-round ecosystem-scale ecophysiological parameters of apparent quantum yield, photosynthetic capacity, convexity of the light response, respiration rate parameters, ecological light-use efficiency, and the curvature of the VPD-response of photosynthesis for maize and wheat crops were numerically identified and interpolated/extrapolated. This allowed us to gap-fill CO2 exchange components and calculate annual totals and budgets. VPD-limitation of photosynthesis was systematically observed in grain crops of the region (occurring from 20 to 120 days during the growing season, depending on site and year), determined by the VPD regime and the numerical value of the curvature parameter of the photosynthesis-VPD-response, σ VPD. In 78% of the 27 site-years of observations, annual gross photosynthesis in these crops significantly exceeded ecosystem respiration, resulting in a net ecosystem production of up to 2100g CO2 m−2 year−1. The measurement-based photosynthesis, respiration, and net ecosystem production data, as well as the estimates of the ecophysiological parameters, provide an empirical basis for parameterization and validation of mechanistic models of grain crop production in this economically and ecologically important region of North America. [Copyright &y& Elsevier]

Water lilies, such as the blue Egyptian water lily (Nymphaea caerulea Savigny), are ubiquitous aquatic plants. Leaves of mature plants normally unfold at the surface and are ?oating or emergent. Some aquatic vascular plants have a form of CAM (crassulacean acid metabolism) known as submerged aquatic metabolism (SAM). The presence of aerenchyma in water lily leaves and petioles makes it very difficult to measure photosynthesis in water lily plants by gas exchange. Pulse amplitude modulation (PAM) fluorometer techniques provide direct information on the light reactions of plants. PAM technology calculates photosynthesis as the electron transport rate (ETR) through PSII (4 electrons per O2 produced) in mol m-2 s-1 . Here, relative ETR (rETR) was based on an assumed leaf absorptance factor of 0.84. Photosynthesis-versus-irradiance (P vs. E) curves were fitted with the waiting-in-line function (rETR = rETRmax x E/Eopt) x e 1-E/Eopt Maximum effective quantum yield, maximum relative ETR (rETRmax), and quantum efficiency all vary on a diurnal cycle. The nonphotochemical quenching parameters qNmax and NPQmax are highly correlated with each other (r = 0:7476, p << 0:001) but do not show a systematic variation over a diurnal cycle. Nymphaea is a "sun plant" with optimum irradiance (Eopt) of 1000 µmol m-2 s-1 PPFD or higher . Titratable acid of leaves varied from ~50 to 70 mol H+ m-3 (leaf water basis) and was depleted at ~0600 and 1800 hours each day, a diel pattern inconsistent with SAM/CAM physiology. The N. caerulea C4 acid pool is too small to support substantial SAM-type metabolism. Gross photosynthesis of Nymphaea leaves had a high value of ~5.3 g C m-2 d-1. For a daily irradiance of 56 mol m-2 PPFD, this works out to a 3.3% conversion efficiency in terms of moles of carbon. [ABSTRACT FROM AUTHOR]

Irradiance data software developed by the NREL Solar Radiation Laboratory (Simple Model of Atmospheric Radiative Transfer of Sunshine, SMARTS) has been used for modelling photosynthesis. Spectra and total irradiance were expressed in terms of quanta [mol m s, photosynthetic photon flux density, PPFD (400-700 nm)]. Using the SMARTS software it is possible to ( 1) calculate the solar spectrum for a planar surface for any given solar elevation angle, allowing for the attenuating effects of the atmosphere on extraterrestrial irradiance at each wavelength in the 400-700 nm range and for the thickness of atmosphere the light must pass through during the course of a day, ( 2) calculate PPFD vs. solar time for any latitude and date and ( 3) estimate total daily irradiance for any latitude and date and hence calculate the total photon irradiance for a whole year or for a growing season. Models of photosynthetic activity vs. PPFD are discussed. Gross photosynthesis ( P) vs. photosynthetic photon flux density (PPFD) ( P vs. I) characteristics of single leaves compared to that of a canopy of leaves are different. It is shown that that the optimum irradiance for a leaf (I) is the half-saturation irradiance for a battery of leaves in series. A C plant, with leaves having an optimum photosynthetic rate at 700 μmol m s PPFD, was used as a realistic worked example. The model gives good estimates of gross photosynthesis ( P) for a given date and latitude. Seasonal and annual estimates of P can be made. Taking cloudiness into account, the model predicts maximum P rates of about 10 g(C) m d, which is close to the maximum reported P experimental measurements. [ABSTRACT FROM AUTHOR]

PAM ( Pulse Amplitude Modulation) fluorometer techniques directly measure the light reactions of photosynthesis that are otherwise difficult to estimate in CAM (Crassulacean Acid metabolism) plants such as pineapple ( Ananas comosus comosus cv. Phuket). PAM machines calculate photosynthesis as the Electron Transport Rate (ETR) through PSII (4 electrons per O produced) as mol m s. P vs. E curves fitted the waiting-in-line function (an equation of the form $$ {\hbox{ETR}} = \left( {{\hbox{ET}}{{\hbox{R}}_{{ \max }}} \times {\hbox{E}}/{{\hbox{E}}_{\rm{opt}}}} \right).{{\hbox{e}}^{{1} - {\rm{E}}/{\rm{Eopt}}}} $$) allowing half-saturating and optimal irradiances (E) to be estimated. Effective Quantum Yield (Y), Electron Transport Rate (ETR) and the Non-Photochemical Quenching parameter, NPQ all vary on a diurnal cycle but the parameter qN does not show a systematic variation over a diurnal period. Phuket pineapple is a 'sun plant' with Optimum Irradiance (E) from 755 to 1,130 μmol m s (400-700 nm) PAR but photosynthetic capacity is very low in the late afternoon even though light conditions are favourable for rapid photosynthesis. Total CO fixed nocturnally as C4-dicarboxylic acids by leaves of the Phuket pineapple was only ≈0.14 gC m d (0.012 mol C m d). Titratable acid of leaves was depleted about 3 pm (15:00) and shows a classical CAM diurnal cycle. The Phuket pineapple variety only stored enough CO as C4 acids to account for only about 2.5% of photosynthesis (P) estimated using the PAM machine (≈5.6 gC m d). Phuket pineapples are classifiable as CAM-Cycling plants but nocturnal fixation of CO is so low compared to the more familiar Smooth Cayenne variety that it probably recycles only a small proportion of the respiratory CO produced in leaves at night and so even CAM-cycling is only of minor importance to the carbon economy of the plant. Unlike the Smooth Cayenne pineapple variety, which fixes large amounts of CO nocturnally, the Phuket pineapple is for practical purposes a C3 plant. [ABSTRACT FROM AUTHOR]

Biological soil crusts (biocrusts) are an integral part of the soil system in arid regions worldwide, stabilizing soil surfaces, aiding vascular plant establishment, and are significant sources of ecosystem nitrogen and carbon. Hydration and temperature primarily control ecosystem CO2 flux in these systems. Using constructed mesocosms for incubations under controlled laboratory conditions, we examined the effect of temperature (5–35 °C) and water content (WC, 20–100%) on CO2 exchange in light (cyanobacterially dominated) and dark (cyanobacteria/lichen and moss dominated) biocrusts of the cool Colorado Plateau Desert in Utah and the hot Chihuahuan Desert in New Mexico. In light crusts from both Utah and New Mexico, net photosynthesis was highest at temperatures >30 °C. Net photosynthesis in light crusts from Utah was relatively insensitive to changes in soil moisture. In contrast, light crusts from New Mexico tended to exhibit higher rates of net photosynthesis at higher soil moisture. Dark crusts originating from both sites exhibited the greatest net photosynthesis at intermediate soil water content (40–60%). Declines in net photosynthesis were observed in dark crusts with crusts from Utah showing declines at temperatures >25 °C and those originating from New Mexico showing declines at temperatures >35 °C. Maximum net photosynthesis in all crust types from all locations were strongly influenced by offsets in the optimal temperature and water content for gross photosynthesis compared with dark respiration. Gross photosynthesis tended to be maximized at some intermediate value of temperature and water content and dark respiration tended to increase linearly. The results of this study suggest biocrusts are capable of CO2 exchange under a wide range of conditions. However, significant changes in the magnitude of this exchange should be expected for the temperature and precipitation changes suggested by current climate models. [ABSTRACT FROM AUTHOR]

Pulse amplitude modulation (PAM) fluorometer techniques provide unique information on photosynthetic activity of CAM (crassulacean acid metabolism) plants such as the orchid Dendrobium spp. (cv. Viravuth Pink). CAM plants close their stomata for at least part of the day, creating a sealed compartment in the stems and leaves that precludes measurement of the light reactions of photosynthesis by any gas exchange-based method. PAM machines calculate photosynthesis as the electron transport rate (ETR) through PSII (four electrons per O2 produced) as mol m-2 s-1. Photosynthesis-versus-irradiance (P-vs.-E) curves fitted the waiting-in-line function (ETR = (ETRmaxx E/opt) x e1-E/Eopt), allowing half-saturating and optimal irradiances (Eopt) to be estimated. Effective quantum yield (Ymax), ETR (ETRmax), and the nonphotochemical quenching parameter NPQmax all vary on a diurnal (circadian) cycle, but the parameter qNmax does not show a systematic variation over a diurnal period. Dendrobium Viravuth is a "sun plant," with Eopt between 404 and 539 μmol m-2 s-1 PAR but photosynthetic capacity is very low in the late afternoon. Total CO2 fixed nocturnally as C4-dicarboxylic acids by leaves was only ≈120 mg C m-2 d-1. Titratable acid of leaves was depleted by 1500 hours and shows a classical CAM diurnal cycle. Dendrobium Viravuth stores only enough CO2 as C4 acids to account for 10% of the daily gross photosynthesis estimated with the PAM machine (≈1.4 g C m-2 d-1). Dendrobium Viravuth is an orchid cultivar with very limited capacity to fix and store C4 acids at night. It is probably a CAM-cycling orchid. [ABSTRACT FROM AUTHOR]

Population variation in ecophysiological traits of four co-occurring montane conifers was measured on a large latitudinal gradient to quantitatively assess their potential for response to environmental change. White fir (Abies concolor) had the highest variability, gross photosynthetic rate (Pg), and foliar carbon (C) and nitrogen (N) content. Despite low water use efficiency (WUE), stomatal conductance (gs) of fir was the most responsive to unfavorable environmental conditions. Pinus lambertiana exhibited the least variability in Pg and WUE, and is likely to be the most vulnerable to environmental changes. Pinus ponderosa had an intermediate level of variability, and high needle growth at its higher elevational limits. Pinus Jeffreyi also had intermediate variability, but high needle growth at its southern latitudinal and lower elevational limits. The attributes used to assess tree vigor were effective in predicting population vulnerability to abiotic (drought) and biotic (herbivore) stresses. [Copyright &y& Elsevier]

This study has two main objectives, the first being the determination of net phytoplankton primary production to explain the phytoplankton’s function in a wetland carbon cycle, while the second objective is to relate this function with the phytoplankton assemblage composition. The annual variation in the phytoplankton production was monitored monthly for more than a year (2007–2008) in the semiarid eutrophic, hydrologically-perturbed “Tablas de Daimiel” National Park wetland. The phytoplankton fraction considered in this study comprised all organisms between the size 3 and 100 μm. The total biomass of phytoplankton was obtained by counting algae and calculating their volume, while net primary production and respiration were quantified by in situ incubations with the Winkler method. The respiration ranged from undetectable to 0.07 mgO2 l−1 h−1; net photosynthesis reached 0.20 mgO2 l−1 h−1. Net primary production was maximum at the end of the warm period (October 2007), and other peaks occurred at the start of summer (July 2007) or spring (March 2008). When maximum production took place, phytoplankton was mainly composed of small fast-growing chlorophytes ( Tetraselmis cf. fontiana or Chlamydomonas sp.), in addition to some of the large, S-strategist algae ( Peridinium umbonatum, Microcystis flos-aquae, Euglena sp.). The phytoplankton metabolism in “Tablas de Daimiel” was autotrophic as a whole due to changing contributions of algal groups. Only chlorophyte biomass was statistically related to net primary production. The conclusion reached is that this shallow eutrophic semiarid wetland possessed an annual net autotrophic production of phytoplankton fraction resulting from the small, fast-growing algae enhanced by hydrological perturbations that interrupted the autogenic course of S strategists. [ABSTRACT FROM AUTHOR]

Many current models of ecosystem carbon exchange based on remote sensing, such as the MODIS product termed MOD17, still require considerable input from ground based meteorological measurements and look up tables based on vegetation type. Since these data are often not available at the same spatial scale as the remote sensing imagery, they can introduce substantial errors into the carbon exchange estimates. Here we present further development of a gross primary production (GPP) model based entirely on remote sensing data. In contrast to an earlier model based only on the enhanced vegetation index (EVI), this model, termed the Temperature and Greenness (TG) model, also includes the land surface temperature (LST) product from MODIS. In addition to its obvious relationship to vegetation temperature, LST was correlated with vapor pressure deficit and photosynthetically active radiation. Combination of EVI and LST in the model substantially improved the correlation between predicted and measured GPP at 11 eddy correlation flux towers in a wide range of vegetation types across North America. In many cases, the TG model provided substantially better predictions of GPP than did the MODIS GPP product. However, both models resulted in poor predictions for sparse shrub habitats where solar angle effects on remote sensing indices were large. Although it may be possible to improve the MODIS GPP product through improved parameterization, our results suggest that simpler models based entirely on remote sensing can provide equally good predictions of GPP. [Copyright &y& Elsevier]

Photosynthesis–irradiance relationships of macroalgal communities and thalli of dominant species in shallow coastal Danish waters were measured over a full year to test how well community production can be predicted from environmental (incident irradiance and temperature) and community variables (canopy absorptance, species number and thallus metabolism). Detached thalli of dominant species performed optimally at different times of the year, but showed no general seasonal changes in photosynthetic features. Production capacity of communities at high light varied only 1.8-fold over the year and was unrelated to incident irradiance, temperature and mean thallus photosynthesis, while community absorptance was a highly significant predictor. Actual rates of community photosynthesis were closely related to incident and absorbed irradiance alone. Community absorptance in turn was correlated to canopy height and species richness. The close relationship of community photosynthesis to irradiance is due to the fact that (1) large differences in thallus photosynthesis of individual species are averaged out in communities composed of several species, (2) seasonal replacement of species keeps communities metabolically active, and (3) maximum possible absorptance at 100% constrains the total photosynthesis of all species. Our results imply that the photosynthetic production of macroalgal communities is more predictable than their complex and dynamic nature suggest and that predictions are possible over wide spatial scales in coastal waters by measurements of vegetation cover, incoming irradiance and canopy absorptance. [ABSTRACT FROM AUTHOR]

Microbial mats are characterized by high primary production but low growth rates, pointing to a limitation of growth by the lack of nutrients or substrates. We identified compounds that instantaneously stimulated photosynthesis rates and oxygen consumption rates in a hypersaline microbial mat by following the short-term response ( c. 6 h) of these processes to addition of nutrients, organic and inorganic carbon compounds, using microsensors. Net photosynthesis rates were not stimulated by compound additions. However, both gross photosynthesis and oxygen consumption were substantially stimulated (by a minimum of 25%) by alanine (1 mM) and glutamate (3.5 mM) as well as by phosphate (0.1 mM). A low concentration of ammonium (0.1 mM) did not affect photosynthesis and oxygen consumption, whereas a higher concentration (3.5 mM) decreased both process rates. High concentrations of glycolate (5 mM) and phosphate (1 mM) inhibited gross photosynthesis but not oxygen consumption, leading to a decrease of net photosynthesis. Photosynthesis was not stimulated by addition of inorganic carbon, nor was oxygen consumption stimulated by organic compounds like glycolate (5 mM) or glucose (5 mM), indicating that carbon was efficiently cycled within the mat. Photosynthesis and oxygen consumption were apparently tightly coupled, because stimulations always affected both processes to the same extent, which resulted in unchanged net photosynthesis rates. These findings illustrate that microsensor techniques, due to their ability to quantify all three processes, can clarify community responses to nutrient enrichment studies much better than techniques that solely monitor net fluxes. [ABSTRACT FROM AUTHOR]

Abstract: An empirical method to measure respiratory CO2 recycling using a fast growing agricultural cover crop as a model system was tested and compared with a theoretical method which uses a variation of the Keeling plot. Both methods gave values which were high and similar to each other. The theoretical method gave a value of respiratory based CO2 recycling of 0.41, while the empirical method gave a value of 0.49. Therefore close to half of the respired CO2 is refixed during daytime photosynthesis in this densely planted cover crop. Refixation of respired CO2 during the day should lead to an isotopic enrichment of the remaining respired CO2 leaving the canopy of the cover crop. Therefore, calculations of gross respiration and photosynthesis using isotopic mass balance equations that do not take this isotopic fractionation into account could be in error. We tested this premise by using isotopic mass balance equations to estimate average gross photosynthesis and respiration in this cover crop under two scenarios: (1) no recycling and (2) recycling of respired CO2. Values of gross photosynthesis and respiration were unrealistically low when it was assumed that no recycling occurs. On the other hand, realistic values similar to previous publications were observed when recycling was taken into account. [Copyright &y& Elsevier]

gThe decline of growth rate with increasing species size of unicellular algae grown under uniform conditions is quantified by applying to published data the equation, growth (cell · time)[sup-1] = a (cell carbon)[subb] where a and b are coefficients. The degree of size dependence might be highest under optimal conditions of growth where b is 0.75. Respiration rate is shown to decline with size in the same manner. It is postulated that gross photosynthesis and processes underlying growth are similarly size-dependent. Growth efficiency (net over gross photosynthesis) cannot be shown to be size-dependent. Cell size, expressed as carbon, is proposed as a scaling factor in comparative algal physiology. [ABSTRACT FROM AUTHOR]

Northern peatlands form a major soil carbon (C) stock. With climate change, peatland C mineralization is expected to increase, which in turn would accelerate climate change. A particularity of peatlands is the importance of soil aeration, which regulates peatland functioning and likely modulates the responses to warming climate. Our aim is to assess the impacts of warming on a southern boreal and a sub-arctic sedge fen carbon dioxide (CO 2 ) exchange under two plausible water table regimes: wet and moderately dry. We focused this study on minerotrophic treeless sedge fens, as they are common peatland types at boreal and (sub)arctic areas, which are expected to face the highest rates of climate warming. In addition, fens are expected to respond to environmental changes faster than the nutrient poor bogs. Our study confirmed that CO 2 exchange is more strongly affected by drying than warming. Experimental water level draw-down (WLD) significantly increased gross photosynthesis and ecosystem respiration. Warming alone had insignificant impacts on the CO 2 exchange components, but when combined with WLD it further increased ecosystem respiration. In the southern fen, CO 2 uptake decreased due to WLD, which was amplified by warming, while at northern fen it remained stable. As a conclusion, our results suggest that a very small difference in the WLD may be decisive, whether the C sink of a fen decreases, or whether the system is able to adapt within its regime and maintain its functions. Moreover, the water table has a role in determining how much the increased temperature impacts the CO 2 exchange., (© 2019 John Wiley & Sons Ltd.)

Abstract Net ecosystem carbon dioxide (CO2 ) exchange (NEE) was measured in a northern temperate grassland near Lethbridge, Alberta, Canada for three growing seasons using the eddy covariance technique. The study objectives were to document how NEE and its major component processes—gross photosynthesis (GPP) and total ecosystem respiration (TER)—vary seasonally and interannually, and to examine how environmental and physiological factors influence the annual C budget. The greatest difference among the three study years was the amount of precipitation received. The annual precipitation for 1998 (481.7 mm) was significantly above the 1971–2000 mean (± SD, 377.9 ± 97.0 mm) for Lethbridge, whereas 1999 (341.3 mm) was close to average, and 2000 (275.5 mm) was significantly below average. The high precipitation and soil moisture in 1998 allowed a much higher GPP and an extended period of net carbon gain relative to 1999 and 2000. In 1998, the peak NEE was a gain of 5 g C m-2 d-1 (day 173). Peak NEE was lower and also occurred earlier in the year on days 161 (3.2 g C m-2 d-1 ) and 141 (2.4 g C m-2 d-1 ) in 1999 and 2000, respectively. Change in soil moisture was the most important ecological factor controlling C gain in this grassland ecosystem. Soil moisture content was positively correlated with leaf area index (LAI). Gross photosynthesis was strongly correlated with changes in both LAI and canopy nitrogen (N) content. Maximum GPP (A max: value calculated from a rectangular hyperbola fitted to the relationship between GPP and incident photosynthetic photon flux density (PPFD)) was 27.5, 12.9 and 8.6 µmol m-2 s-1 during 1998, 1999 and 2000, respectively. The apparent quantum yield also differed among years at the time of peak photosynthetic activity, with calculated values of 0.0254, 0.018 and 0.018 during 1998, 1999 and 2000, respectively. The ecosystem accumulated a total of 111.9 g C m-2 from the time the eddy covariance measurements were initiated in June 1998 until the end of December 2000, with most of that C gained during 1998. There was a net uptake of almost 21 g C m-2 in 1999, whereas a net loss of 18 g C m-2 was observed in 2000. The net uptake of C during 1999 was the combined result of slightly higher GPP (287.2 vs. 272.3 g C m-2 year-1 ) and lower TER (266.6 vs. 290.4 g C m-2 year-1 ) than occurred in 2000. [ABSTRACT FROM AUTHOR]