Carbon Dioxide Exchange Rates Research Articles

Using eddy covariance observations to determine the carbon sequestration characteristics of subalpine forests in the Qinghai–Tibet Plateau

Abstract. Subalpine forests are a crucial component of the carbon cycling system in the Qinghai–Tibet Plateau (QTP). However, there are currently significant data gaps in the QTP, and it is essential to enhance continuous monitoring of forest carbon absorption processes in the future. This study investigates 2 years' carbon exchange dynamics of a subalpine forest on the QTP using an eddy covariance method. We first characterized the seasonal carbon dynamics of the subalpine forest, revealing the higher carbon dioxide (CO2) exchange rates in summer and autumn and lower rates in winter and spring, and found that autumn is the peak period for carbon sequestration in this subalpine forest, with the maximum measured value of CO2 absorption reaching 10.70 µmol m−2 s−1. Subsequently, we examined the environmental factors influencing the carbon sequestration function. Principal component analysis (PCA) shows that photosynthetically active radiation (PAR) was the major environmental factor driving the net ecosystem exchange (NEE) of CO2, significantly influencing forest carbon absorption, and the increase in relative humidity decreases the rate of carbon fixation. In addition, we explored NEE and its influencing factors at the regional scale and found that air temperature promotes carbon dioxide absorption (negative NEE values), while the average annual precipitation shows a minor effect on NEE. At the annual scale, the subalpine forest functions as a strong carbon sink, with an average NEE of −332 to −351 g C m−2 (from November 2020 to October 2022). Despite the challenges of climate change, forests remain robust carbon sinks with the highest carbon sequestration capacity in the QTP, with an average annual CO2 absorption rate of 368 g C m−2. This study provides valuable insights into the carbon cycling mechanism in subalpine ecosystems and the global carbon balance.

A Wearable Bracelet for Simultaneous Monitoring of Transcutaneous Carbon Dioxide and Pulse Rates

AbstractDaily monitoring of psychological parameters, encompassing chemical and physical signals, has become increasingly valuable for the management of chronic diseases. Among various vital signs, carbon dioxide exchange and pulse rate (PR) serve as critical indicators for the comprehensive assessment of the cardiopulmonary system. However, simultaneous monitoring of these chemical and physical signals in a nonintrusive manner is challenging. This study presents a wearable bracelet that enables simultaneous monitoring of transcutaneous carbon dioxide (TcCO2) and PR using a nanomaterials‐modified lensless CMOS imager. The proposed bracelet exhibits exceptional sensitivity, selectivity, and anti‐humidity interference in TcCO2 detection, and achieves reliable tracking of TcCO2 and PR fluctuations induced by daily activities, demonstrating great potential in the comprehensive assessment of cardiopulmonary system. In addition, the proposed compact imaging approach is multiplexed and extensible, providing a promising sensing platform for the future development of multifunctional wearable devices.

Effects of biochar and ligneous soil amendments on greenhouse gas exchange during extremely dry growing season in a Finnish cropland

Organic soil amendments such as manure, biochar and compost are among the most efficient and widely used methods to increase soil carbon sequestration in agricultural soils. Even though their benefits are well known, many wood-derived materials are not yet utilized in Nordic agriculture due to a lack of incentives and knowledge of their effects in the local climate. We studied greenhouse gas exchange, plant growth and soil properties of a clay soil cultivated with oat in southern Finland in an extremely dry year. Two years earlier, the field was treated with three ligneous soil amendments—lime-stabilized fiber from the pulp industry, willow biochar and spruce biochar—which we compared against fertilized and non-fertilized controls. We found that the soil amendments increased porosity and the mean soil water holding capacity, which was most noticeable in plots amended with spruce biochar. There was a trend indicating that the mean yield and overall biomass production were larger in plots with soil amendments; however, the difference to unamended control was seldom significant due to the high variance among replicates. Manual chamber measurements revealed that carbon dioxide and methane exchange rates were reduced most probably by the exceptionally hot and dry weather conditions, but no differences could be found between the amended and unamended treatments. The nitrous oxide emissions were significantly smaller from the vegetated soil amended with willow biochar compared with the unamended control. Emissions from non-vegetated soil, representing heterotrophic respiration, were similar but without significant differences between treatments. Overall, the studied soil amendments indicated positive climatic impact two years after their application, but further research is needed to conclusively characterize the specific effects of organic soil amendments on processes affecting greenhouse gas exchange and plant growth.

The nexus between Egyptian renewable energy resources and economic growth for achieving sustainable development goals

This study contributes to the conceptual and empirical studies by investigating the relation between the electricity generated from renewables, carbon dioxide (CO2) emission, exchange rate and unemployment on Egyptian economic growth (EEC). Developing countries are in pursuit of economic growth as it is the path for sustainable economies. The study applies autoregressive distributed lag model (ARDL) using the dataset for the period from 1990–2019. The empirical results highlight the main driving forces that accelerate economic growth. The main findings confirmed that government support is one of the key drivers for positive and significant impacts of electricity generated from renewable energy sources, CO2 emission, and exchange rate in Egypt on economic growth. However, the positive and significant impact of carbon dioxide still plays a challenging aspect to achieve sustainability. Policies have been identified to develop the required energy network of the future

Double cropping inVitis viniferaL. cv. Pinot Noir: agronomical and physiological validation

Background and Aims Environmental effects of global warming are leading to extended ripening seasons, which may either require or allow new vineyard management techniques. An innovative double-cropping technique is proposed for temperate climate areas. Methods and Results The principle technique was to maintain the primary crop as well as to obtain a second, late ripening crop through release of dormancy of the auxiliary buds during the current season. Potted Pinot Noir vines were subjected to two forcing treatments over 2 years: trimming all the primary shoots at six nodes and removing any developing laterals at the end of the flowering and pea size stages. Vine growth, yield components and grape composition were monitored on both primary and forced shoots. In the second season, seasonal whole-vine gas exchange was evaluated in detail. Forced shoots carried 40–50% of the vine crop compared to primary shoots and fruit quality was greatly enhanced and higher TA was observed. Forcing treatments reached a similar net carbon dioxide exchange rate per vine compared to unforced Control about 2 weeks following auxiliary budburst. For the remainder of the season, forcing treatments maintained much higher net carbon dioxide exchange rate and water-use efficiency than unforced Control vines. Conclusions Detailed agronomical and physiological evaluation for 2 years confirmed the reliability of the double-cropping technique without compromising the pruning point selection for the next cropping year. Significance of the Study Future field application may disclose that this forcing technique is able to warrant two crops potentially suited to different wine styles within a single season.

The Intensifying Role of High Wind Speeds on Air‐Sea Carbon Dioxide Exchange

AbstractWhile it has been known that wave breaking and bubble generation at high wind speeds enhance air‐sea carbon dioxide (CO2) exchange rates (F), quantification of their contribution at the global scale remains a formidable challenge. There is urgency to make progress on this issue as a significant uptick in both magnitude and frequency of high wind events (HW) has been documented over the last 3 decades. Using a wind‐wave dependent expression for gas transfer velocity (k) that explicitly considers bubbles and a widely used wind‐only parameterization, the spatial pattern of k at high winds can be explained by sea surface temperature distribution. The HW, which represent some 3% of wind conditions, contribute disproportionally to the global F (18%) with an increasing trend. Approximately 50% of the global F at high winds is attributed to bubble contribution. The findings are of significance to quantifying CO2 transfer to the ocean interior.

Three new methods indicate that CO2 concentration affects plant respiration in the range relevant to global change.

Short-term responses of plant dark respiration to carbon dioxide concentration ([CO2]) in the range anticipated in the atmosphere with global change remain controversial, primarily because it is difficult to convincingly eliminate the many possible sources of experimental error in measurements of carbon dioxide or oxygen exchange rates. Plant dark respiration is a major component of the carbon balance of many ecosystems. In seedlings without senescent tissue, the rate of loss of dry mass during darkness indicates the rate of respiration. This method of measuring respiration was used to test for [CO2] effects on respiration in seedlings of three species with relatively large seeds. The time it took respiration to exhaust substrates and cause seedling death in darkness was used as an indicator of respiration rate in four other species with smaller seeds. The third method was measuring rates of CO2 exchange in excised petioles sealed in a cuvette submerged in water to prevent leaks. Petioles were utilized as the plant tissue type with the most reliable rates of respiration, for excised tissue. The rate of loss of dry mass in the dark decreased with increasing [CO2] in the range of 200-800 μmol mol-1 in all three large-seeded species. The seedling survival time in the dark increased with [CO2] in the same concentration range in all four of the smaller-seeded species. Respiration rates of excised petioles of several species also decreased over this [CO2] range. The data provide new evidence that the rate of dark respiration in plant tissue often decreases with increasing [CO2] in the 200-800 μmol mol-1 range.

Influence of trace elements, applied in classical and nano forms, on photosynthesis of higher plants in relation to enhancement of crop productivity

One of the main factors of increasing the productivity of agricultural plants is intensifying the activity of the photo- synthetic apparatus, since the productivity of crops depends on the ability to absorb solar radiation and convert it into the energy of chemical bonds for further use in metabolic processes. The amount of photosynthetically active radia- tion absorbed by crops, in its turn, depends on the area, duration, and activity of the assimilation surface functioning. The use of fertilizers, that contain trace elements, can further achieve both raising the yield of cultivated plants and environmental protection. In this regard, the state-of-the-art research on the infl uence of the main trace elements (iron, zinc, manganese, molybdenum, cobalt, selenium, boron, titanium) and one macroelement - magnesium - on photosynthetic characteristics of plants and crops is discussed. Based on the literature data and the results of our own research, we documented the effect of trace elements on leaves carbon dioxide exchange rates, the content of photo- synthetic pigments, the antioxidant enzymes activity, as well as the traits of the photosynthetic apparatus capacity. The infl uence of nanometals on the content and ratio of pigments, net CO 2 assimilation rate, and the photochemical activity of photosystems, including the effect of stress factors, is discussed. The specifi cities of the infl uence of nanometals are discussed and possible mechanisms of the effect of low concentrations of trace elements on plant metabolism are analyzed. It is shown that trace elements infl uence photosynthetic processes in plants and the systems of their antioxi- dant protection. The relevance of trace elements in the development of new strategies to elaborate the technologies of cultivating next-generation plants, including those that will be based on new physical and chemical properties of macro- and micronutrients in a nano form, is highlighted

The Rate of Oxygen Release from Freshwater Bodies

The annual regimes of estimated rates of oxygen and carbon dioxide exchange between water surface and the atmosphere was compared for two water bodies with different sizes and hydroecological conditions: the deep oligotrophic Lake Baikal and the small mesotrophic–eutrophic Mozhaisk Reservoir with water exchange rate 150 times greater than that of Baikal. The obtained, very large, differences between the rates of gas evasions and invasions in the lake and the reservoir allow the rates of these processes to be used as integral characteristics for the parameterization of the self-purification capacity of freshwater bodies from organic pollutants.

Diurnal carbon dioxide exchange rates of Saccharina latissima and Laminaria digitata as affected by salinity levels in Norwegian fjords

The Norwegian fjords are strongly influenced by freshwater runoff from the mountain regions as a result of high precipitation. The macroalgae growing in the fjords may therefore be frequently exposed to low salinity levels. This may affect the potential for cultivating kelp in the fjords. In the present study, the sensitivity to salinity levels of 10, 16, 24 or 34‰ was studied by measuring the carbon dioxide exchange rate (CER) in young sporophytes of Saccharina latissima and Laminaria digitata continuously over several days. A positive CER was found down to the freezing point of −2 °C as well as a positive CER during darkness depending on the irradiance level of the previous day. Decreasing the salinity from 34 to 24, 16 or 10‰ reduced the daily CO2 uptake by 50, 85 or 100%, respectively, in S. latissima. The negative effect of decreasing salinity to 10‰ was irreversible. In L. digitata, the daily CO2 uptake was reduced by 20, 30 or 40% by decreasing the salinity from 34‰ to the respective salinity levels. The reduction in the CER at 10‰ was fully reversible. These results were consistent with the observations in a fjord dominated by brackish water where L. digitata was abundant and S. latissima absent.

Net carbon dioxide exchange rate of wild blueberries is influenced by carbon dioxide concentration, light intensity and air temperature

Net carbon dioxide exchange rate of wild blueberries is influenced by carbon dioxide concentration, light intensity and air temperature

Decadal trends in the seasonal-cycle amplitude of terrestrial CO2 exchange resulting from the ensemble of terrestrial biosphere models

The seasonal-cycle amplitude (SCA) of the atmosphere–ecosystem carbon dioxide (CO2) exchange rate is a useful metric of the responsiveness of the terrestrial biosphere to environmental variations. It is unclear, however, what underlying mechanisms are responsible for the observed increasing trend of SCA in atmospheric CO2 concentration. Using output data from the Multi-scale Terrestrial Model Intercomparison Project (MsTMIP), we investigated how well the SCA of atmosphere–ecosystem CO2 exchange was simulated with 15 contemporary terrestrial ecosystem models during the period 1901–2010. Also, we made attempt to evaluate the contributions of potential mechanisms such as atmospheric CO2, climate, land-use, and nitrogen deposition, through factorial experiments using different combinations of forcing data. Under contemporary conditions, the simulated global-scale SCA of the cumulative net ecosystem carbon flux of most models was comparable in magnitude with the SCA of atmospheric CO2 concentrations. Results from factorial simulation experiments showed that elevated atmospheric CO2 exerted a strong influence on the seasonality amplification. When the model considered not only climate change but also land-use and atmospheric CO2 changes, the majority of the models showed amplification trends of the SCAs of photosynthesis, respiration, and net ecosystem production (+0.19 % to +0.50 % yr−1). In the case of land-use change, it was difficult to separate the contribution of agricultural management to SCA because of inadequacies in both the data and models. The simulated amplification of SCA was approximately consistent with the observational evidence of the SCA in atmospheric CO2 concentrations. Large inter-model differences remained, however, in the simulated global tendencies and spatial patterns of CO2 exchanges. Further studies are required to identify a consistent explanation for the simulated and observed amplification trends, including their underlying mechanisms. Nevertheless, this study implied that monitoring of ecosystem seasonality would provide useful insights concerning ecosystem dynamics.

El Niño Southern Oscillation (ENSO) enhances CO2 exchange rates in freshwater Marsh ecosystems in the Florida everglades.

This research examines the relationships between El Niño Southern Oscillation (ENSO), water level, precipitation patterns and carbon dioxide (CO2) exchange rates in the freshwater wetland ecosystems of the Florida Everglades. Data was obtained over a 5-year study period (2009–2013) from two freshwater marsh sites located in Everglades National Park that differ in hydrology. At the short-hydroperiod site (Taylor Slough; TS) and the long-hydroperiod site (Shark River Slough; SRS) fluctuations in precipitation patterns occurred with changes in ENSO phase, suggesting that extreme ENSO phases alter Everglades hydrology which is known to have a substantial influence on ecosystem carbon dynamics. Variations in both ENSO phase and annual net CO2 exchange rates co-occurred with changes in wet and dry season length and intensity. Combined with site-specific seasonality in CO2 exchanges rates, El Niño and La Niña phases magnified season intensity and CO2 exchange rates at both sites. At TS, net CO2 uptake rates were higher in the dry season, whereas SRS had greater rates of carbon sequestration during the wet season. As La Niña phases were concurrent with drought years and extended dry seasons, TS became a greater sink for CO2 on an annual basis (−11 to −110 g CO2 m−2 yr−1) compared to El Niño and neutral years (−5 to −43.5 g CO2 m−2 yr−1). SRS was a small source for CO2 annually (1.81 to 80 g CO2 m−2 yr−1) except in one exceptionally wet year that was associated with an El Niño phase (−16 g CO2 m−2 yr−1). Considering that future climate predictions suggest a higher frequency and intensity in El Niño and La Niña phases, these results indicate that changes in extreme ENSO phases will significantly alter CO2 dynamics in the Florida Everglades.

Creeping Bentgrass Field Response to Pigment‐Containing Products

Reducing summer stress on creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.)] putting greens is a major goal of many turf managers. Use of colorants and pigment‐containing products has been proposed as a means of protecting the plant from environmental stress, especially on bentgrass putting greens grown in heat‐stressed environments. The objective of this research was to investigate the physiological effects of four pigment‐containing products–a combination of zinc oxide (ZnO), green pigment, and titanium dioxide (TiO2) (TurfScreen); Cu‐based pigments (PAR and Foursome); and a Cu‐pigmented paint designed to provide green color to dormant turfgrass in winter months–have on creeping bentgrass under stressful field conditions. Products were applied weekly for 10 wk to two separate studies repeated in time. TurfScreen, PAR, Foursome, and paint all lowered carbon dioxide exchange rate (CER), reduced normalized difference vegetation index (NDVI), and raised canopy temperature relative to nontreated controls. Only paint lowered visual quality and percent turf cover compared to the untreated controls. TurfScreen reduced evapotranspiration (ET) in one of two studies. Root mass was unaffected by any treatment. Zinc (∼800 mg kg−1) and Cu (>155 mg kg−1) concentrations in leaf tissue and soil increased dramatically after TurfScreen and paint application, respectively, and potential toxicity should be considered during long‐term use of these products. The products tested failed to enhance physiological processes normally associated with improved turf health and quality.

Soil pore-water environment and CO2 emission in a Luvisol as influenced by contrasting tillage

Little is known how contrasting tillage (deep ploughing, top- and sub-soil loosening with straight or bent leg cultivator [BLC], direct drilling [DD]) affect important soil physical properties (total porosity [TP], pore size distribution [PSD], water release characteristics [WRC]) and CO2 emissions from a Luvisol. The study was aimed to alleviate compaction on land that had been under reduced tillage for 4 successive years. Undisturbed core samples were collected from 5–10, 15–20 and 25–30 cm depths for soil WRCs, TP and pore-size distribution determination. A closed chamber method was used to quantify the CO2 emissions from the soil. Soil loosening with straight or BLC produced the highest total soil porosity (on average 0.48 m3 m−3) within 5–30 cm soil layer, while conventional tillage (CT) gave 6%, DD up to 25% reduction. Sub-surface loosening with a BLC was the most effective tool to increase the amount of macro- and mesopores in the top- and sub-soil layers. It produced 21% more macro- and mesopores within 25–30 cm soil layer as compared to the soil loosened with a straight leg cultivator. Plant available water content under CT and DD was lower as compared to that under deep loosening with straight or BLC (23% and 18%, respectively). DD produced 12% lower soil surface net carbon dioxide exchange rate than CT and by 25–28% lower than deep soil loosening with straight or BLC. The increase in micropores within 25–30 cm soil layer caused net carbon dioxide exchange rate reduction. The amount of mesopores within the whole 5–30 cm soil layer acted as a direct dominant factor influencing net CO2 exchange rate (NCER) (Pxy = −3.063; r = 0.86).

The Effect of Wide-Range Photosynthetic Active Radiations on Photosynthesis, Growth and Flowering of <i>Rosa sp.</i> and <i>Kalanchoe blossfeldiana</i>

Miniature roses (Rosa sp.) and Kalanchoe blossfeldiana were grown at photon flux densities (PFD) ranging from 60 to 670 μmol·m-2·s-1 (associated with a temperature gradient from 20.0°C to 24.0°C [TEMP1]) and from 50 to 370μmol·m-2-s-1 (associated with a temperature gradient from 22.5°C to 26.5°C [TEMP2]). The experiment was conducted in a greenhouse compartment at latitude 59° north in mid-winter. The daily photosynthetic active radiations (PAR) ranged from 4.3 to 48.2 and 3.6 to 26.6 mol·m-2·day-1 in the TEMP1 and TEMP2 treatments, respectively. Time until flowering in miniature roses decreased from about 50 to 35 days in the TEMP1 treatment and from 50 to 25 days in the TEMP2 treatment, when the PFD increased from 50 to 370μmol·m-2·s-1. In Kalanchoe time until flowering was decreased to the same extent (about 15 days) in both temperature treatments when PFD increased from 50 to 370 μmol·m-2·s-1. The number of flowers and the plant dry weight in miniature roses increased up to 300 – 400 μmol·m-2·s-1 PFD (21.6 - 28.8 mol·m-2 day-1 PAR), while flower stem fresh weight and plant dry weight in Kalanchoe increased up to 200 – 300 μmol·m-2·s-1 at TEMP1. Measurements of the diurnal carbon dioxide exchange rates (CER) in daylight in small plant stands of roses in summertime showed that CER was saturated at about 300 μmol·m-2·s-1 PFD at 370 μmol·mol-1 CO2 and at 400 – 500 μmol·m-2·s-1 PFD at 800 μmol·mol-1 CO2. For Kalanchoe similar results were obtained. Increasing the CO2 concentration from 370 to 800 μmol·mol-1 increased the CER in roses (48%) as well in Kalanchoe (69%). It was concluded that 15 to 20 mol·m-2·day-1 combined with about 24°C air temperature and high CO2 concentration will give a very good growth with lot of flowers within a short production time in miniature roses. For Kalanchoe 10 to 15 mol·m-2·day-1 combined with about 20°C and high CO2 produced a similar result.

Measuring daytime CO2 fluxes from the inter-tidal mangrove soils of Indian Sundarbans

The aim of this research was to measure the rate of carbon dioxide (CO2) exchange between the soil and atmosphere in the inter-tidal forest floor of the Indian Sundarbans mangrove ecosystem and to study its response with soil temperature and soil water content. Soil CO2 effluxes were monitored every month at two stations (between April, 2011 and March, 2012); one situated at the land–ocean boundary of the Bay of Bengal (outer part of the mangrove forest) and the other lying 55 km inshore from the coast line (inner part of the mangrove forest). The static closed chamber technique was implemented at three inter-tidal positions (landward, seaward and bare mudflats) in each station. Fluxes were measured in the daytime every half an hour by circulating chamber headspace air through a sampling manifold assembly and a closed-path non-dispersive infrared gas analyser. The fluxes ranged between 0.15 and 2.34 μmol m−2 s−1 during the annual course of sampling. Effluxes of higher magnitude were measured during summer; however, it abruptly decreased during the monsoon. CO2 flux from the forest floor was strongly related to soil temperature, with the highest correlation found with temperature at 2 cm depth. No such significant relationship between soil water content and CO2 efflux could be properly ascertained; however, excessively high soil water content was found to be the only reason which hampered the rate of effluxes during the monsoon. On the whole, landward (LW) sites of the mangrove forest emitted more than the seaward (SW) sites. Q 10 values (obtained from simple exponential model) which denote the multiplicative factor by which the efflux rate increases for a 10 °C rise in temperature ranged between 2.07 and 4.05.

Physiological Responses of Creeping Bentgrass to Pigment‐Containing Products

Providing relief from summer stress is a constant goal when maintaining creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.)] golf putting greens. Colorants and other pigment‐containing products are marketed as a means of relieving summer stress but research supporting such claims is limited and was the objective of this study. Pigment‐containing products evaluated on bentgrass maintained under supraoptimal (>30°C) temperature stress included: TurfScreen (a combination of zinc oxide [ZnO], a green pigment, and titanium dioxide [TiO2]) and PAR (a commercial copper‐based pigment). Carbon dioxide exchange rate (µmol CO2 cm–2 s–1) was reduced >100% following Turfscreen and PAR applications and evapotranspiration rate (µmol H2O cm–2 s–1) was reduced ∼10% compared to nonstressed control plants. Fluorescence (Fv/Fm) was reduced ∼16% following Turfscreen and PAR application. Products (including a commercial paint and an additional copper‐based pigment, Foursome) were also applied to acrylic sheets to measure the transmission of photosynthetically active radiation. PAR and Foursome reduced the transmission of photosynthetically active radiation ∼20%, while TurfScreen and paint reduced it by 39 and 46%, respectively. Microscopy images revealed TurfScreen (higher viscosity) remained on the leaf surface, and covered stomata while PAR (lower viscosity) entered the leaf via stomata. Overall, products evaluated provided little consistent physiological benefit to creeping bentgrass in a heat‐stressed environment.

Estimating carbon dioxide exchange rates at contrasting northern peatlands using MODIS satellite data

Northern hemisphere peatlands play an important role in the global carbon (C) cycle, accounting for about 30% of global soil C and ~10–25% of global natural methane (CH4) emissions. Satellite remote sensing has the potential for extracting continuous information related to C exchange rates at regional and global extents, yet, few studies have focused on peatlands. In this study we examined the potential of moderate resolution imaging spectroradiometer (MODIS) vegetation indices (normalized difference vegetation index, NDVI and simple ratio, SR), MODIS light use efficiency (LUE) based gross primary production (GPP) and a MODIS derived phenological index (annual peak photosynthetic rate) for the estimation of eddy covariance (EC) flux-derived GPP and net ecosystem production (NEP) at four contrasting northern peatlands. At the four sites of this study MODIS NDVI and SR explained between 39% and 71%, and between 42% and 69% of the variation in EC-derived GPP, respectively; and between 25% and 53%, and between 29% and 39% of the variation in EC-derived NEP, respectively. The relationships were mostly consistent across sites and within sites, suggesting that data may be pooled across years and sites, which could simplify the prediction of gross and net C dioxide (CO2) uptake over large areas dominated by northern peatlands based on MODIS data. MODIS GPP explained between 68% and 89% of the variation in EC-derived GPP at the four study sites. The root mean square errors ranged between 0.62 and 1.16gCm−2d−1 and were similar to errors from ecosystem process model estimates reported in the literature. Annual peak MODIS GPP, NDVI and SR rates explained up to 50% of the variations in annual cumulative EC-derived GPP and NEP at two of the study sites. Our results show the potentials and limitations of MODIS data to monitor the C dynamics of northern peatlands; among the three studied approaches the MODIS LUE-based GPP approach showed better performance as a predictor of GPP and NEP. The other approaches (VIs and phenology) can provide important input data for LUE models.

Influence of Water Regimes and Potassium Chlorate on Floral Induction, Leaf Photosynthesis and Leaf Water Potential in Longan

This study verifies the influence of water regimes and potassium chlorate (KC1O3) on photosynthetic rate, flower emergence and media moisture content of longan trees. The trees were grown in 150 liters lysimeter tanks filled with fine sand. The experimental design was a 2x2 factorial in completely randomized design (CRD) with 2 factors; 1) two levels of water regimes (well-watered and water deficit) and 2) two levels of KClO3 at 10 and 0 g. The results revealed that the well-watered treatment produced faster days of terminal bud break than that of the water deficit treatment. The 10 g KClO3 treatment induced 91 % flower emergence at 35 days after commencing the treatment, while the 0 g KClO3 treatment had 82 % leaf flushing and had no flower emergence. Water deficit or KClO3 treatments reduced the net carbondioxide (CO2) exchange, transpiration and stomatal conductance rates. Moreover, the combination of well-watered and 0 g KClO3 treatments gave the greatest values of the parameters. The well-watered treatment had higher volumetric water content in the growing medium and leaf water potential than the water deficit treatment, while for the 10 g and 0 g KClO3 treatments had similar the media moisture content.