► Forests are carbon sources until 10–20years of age, sinks from 20 to 70years, carbon neutral or weak sinks thereafter. ► Following planting, an afforested white pine stand offset initial carbon ...losses after 4years. ► Following disturbance and depending on forest type, forests offset initial carbon losses after 19–47years. ► The photosynthetic growing season length of forest stands increased with age until about 20years. ► GEP and ER of mature stands were driven by climate, fluxes of young stands were driven by LAI and climate.
Proper management and accounting of forest carbon requires good knowledge of how disturbances and climate affect the carbon dynamics of different stand types. We have investigated such relationships by measuring, over a 5-year period (2003–2007), the net ecosystem productivity (NEP), gross ecosystem productivity (GEP) and ecosystem respiration (ER) of 26 forest sites in Canada using the eddy covariance technique. The study included black spruce, jack pine, Douglas-fir, aspen, boreal mixedwood and white pine forest ecosystems ranging in age from 1- to 153-years. The dataset included six chronosequences (one afforested plantation, three harvested and two burned).
Following planting, the afforested white pine stands quickly became carbon sinks and offset initial carbon losses after 4years. Depending on forest type, the other forest stands were carbon sources for 10–18years following a disturbance, offset initial carbon losses after 19–47years, and showed net total gains ranging from 38 to 86MgCha−1 at 80years. Peak NEP ranged from 0.9 to 2.9MgCha−1year−1 at ages of 35–55years except for the afforested white pine where it was 6.9MgCha−1year−1 at 15–20years. Stepwise regression and Pearson correlation analyses indicated that the GEP and ER of mature stands (>70years old) were driven mainly by climate, while fluxes of young stands (<19years old) were driven by both leaf area index and climate.
Although stand age of the afforested white pine plantations did not affect the GEP growing season lengths, the growing season length of the other forests increased with age until about 20years and this coincided with the switch from carbon source to sink. With the exception of the afforested white pine, peak GEP/ER ratios of the youngest sites occurred later in the growing season compared to older sites. The strong influence of stand age on the seasonal dynamics of GEP fluxes needs to be considered to avoid confounding the impacts of climate change with those of disturbance. These age-related seasonality effects are continental in scope and should be important in interpreting the time series of atmospheric CO2 concentration measurements at regional and global scales.
The eddy-covariance (EC) micro-meteorological technique and the ecology-based biometric methods (BM) are the primary methodologies to quantify CO
exchange between terrestrial ecosystems and the ...atmosphere (net ecosystem production, NEP) and its two components, ecosystem respiration and gross primary production. Here we show that EC and BM provide different estimates of NEP, but comparable ecosystem respiration and gross primary production for forest ecosystems globally. Discrepancies between methods are not related to environmental or stand variables, but are consistently more pronounced for boreal forests where carbon fluxes are smaller. BM estimates are prone to underestimation of net primary production and overestimation of leaf respiration. EC biases are not apparent across sites, suggesting the effectiveness of standard post-processing procedures. Our results increase confidence in EC, show in which conditions EC and BM estimates can be integrated, and which methodological aspects can improve the convergence between EC and BM.
► Friction–velocity thresholds (u*Th) are commonly used to filter nighttime NEE. ► Change-point detection (CPD) is used to improve automated u*Th evaluation. ► The technique is evaluated at 38 sites ...from the North American Carbon Program. ► At most sites, CPD produced robust u*Th estimates that were comparable among years. ► The results support the pragmatic use of u*Th filters.
The eddy-covariance method often underestimates fluxes under stable, low-wind conditions at night when turbulence is not well developed. The most common approach to resolve the problem of nighttime flux underestimation is to identify and remove the deficit periods using friction–velocity (u*) threshold filters (u*Th). This study modifies an accepted method for u*Th evaluation by incorporating change-point-detection techniques. The original and modified methods are evaluated at 38 sites as part of the North American Carbon Program (NACP) site-level synthesis. At most sites, the modified method produced u*Th estimates that were higher and less variable than the original method. It also provided an objective method to identify sites that lacked a u*Th response. The modified u*Th estimates were robust and comparable among years. Inter-annual u*Th differences were small, so that a single u*Th value was warranted at most sites. No variation in the u*Th was observed by time of day (dusk versus mid or late night), however, a few sites showed significant u*Th variation with time of year. Among-site variation in the u*Th was strongly related to canopy height and the mean annual nighttime u*. The modified u*Th estimates excluded a high fraction of nighttime data – 61% on average. However, the negative impact of the high exclusion rate on annual net ecosystem production (NEP) was small compared to the larger impact of underestimating the u*Th. Compared to the original method, the higher u*Th estimates from the modified method caused a mean 8% reduction in annual NEP across all site-years, and a mean 7% increase in total ecosystem respiration (Re). The modified method also reduced the u*Th-related uncertainties in annual NEP and Re by more than 50%. These results support the use of u*Th filters as a pragmatic solution to a complex problem.
Spatio-temporal fields of land–atmosphere fluxes derived from data-driven models can complement simulations by process-based land surface models. While a number of strategies for empirical models ...with eddy-covariance flux data have been applied, a systematic intercomparison of these methods has been missing so far. In this study, we performed a cross-validation experiment for predicting carbon dioxide, latent heat, sensible heat and net radiation fluxes across different ecosystem types with 11 machine learning (ML) methods from four different classes (kernel methods, neural networks, tree methods, and regression splines). We applied two complementary setups: (1) 8-day average fluxes based on remotely sensed data and (2) daily mean fluxes based on meteorological data and a mean seasonal cycle of remotely sensed variables. The patterns of predictions from different ML and experimental setups were highly consistent. There were systematic differences in performance among the fluxes, with the following ascending order: net ecosystem exchange (R2 < 0.5), ecosystem respiration (R2 > 0.6), gross primary production (R2> 0.7), latent heat (R2 > 0.7), sensible heat (R2 > 0.7), and net radiation (R2 > 0.8). The ML methods predicted the across-site variability and the mean seasonal cycle of the observed fluxes very well (R2 > 0.7), while the 8-day deviations from the mean seasonal cycle were not well predicted (R2 < 0.5). Fluxes were better predicted at forested and temperate climate sites than at sites in extreme climates or less represented by training data (e.g., the tropics). The evaluated large ensemble of ML-based models will be the basis of new global flux products.
•Monitoring of carbon cycle crucially rely on remote sensing-based models of GPP.•We examined the potential of five mechanisms for improving model prediction.•Better representation of soil-moisture ...improved model performance.•However, at biome level the improvement was not large.•Accurately scaling up leaf level processes to the ecosystem scale are crucial.
Accurate and reliable estimates of gross primary productivity (GPP) are required for monitoring the global carbon cycle at different spatial and temporal scales. Because GPP displays high spatial and temporal variation, remote sensing plays a major role in producing gridded estimates of GPP across spatiotemporal scales. In this context, understanding the strengths and weaknesses of remote sensing-based models of GPP and improving their performance is a key contemporary scientific activity. We used measurements from 157 research sites (∼470 site-years) in the FLUXNET “La Thuile” data and compared the skills of 11 different remote sensing models in capturing intra- and inter-annual variations in daily GPP in seven different biomes. Results show that the models were able to capture significant intra-annual variation in GPP (Index of Agreement=0.4–0.80) in all biomes. However, the models’ ability to track inter-annual variation in daily GPP was significantly weaker (IoA<0.45). We examined whether the inclusion of different mechanisms that are missing in the models could improve their predictive power. The mechanisms included the effect of sub-daily variation in environmental variables on daily GPP, factoring-in differential rates of GPP conversion efficiency for direct and diffuse incident radiation, lagged effects of environmental variables, better representation of soil-moisture dynamics, and allowing spatial variation in model parameters. Our analyses suggest that the next generation remote sensing models need better representation of soil-moisture, but other mechanisms that have been found to influence GPP in site-level studies may not have significant bearing on model performance at continental and global scales. Understanding the relative controls of biotic vis-a-vis abiotic factors on GPP and accurately scaling up leaf level processes to the ecosystem scale are likely to be important for recognizing the limitations of remote sensing model and improving their formulation.
Selenium (Se) is an essential trace element with diverse physiological functions related to cellular homoeostasis, body metabolism and antioxidant defence. Se is an integral constituent of at least ...25 selenoproteins in the body that regulate cellular redox and antioxidant defence enzymes systems control free radicles of reactive oxygen species . Dietary Se plays key role in immunity, growth and fertility in chickens, which require optimum levels in their diets to maintain high reproductive and productive performance of birds. In the last decade, dietary supplementation with selenium nanoparticles (SeNPs) has enhanced the growth performance, feed conversion ratio, reproductive performance, egg production, immune response and antioxidant status, as well as improved the quality of meat and eggs and promoted microflora. Se has been shown to increase relative weights of immune-related organs (burse and thymus) to enhance immunity. Feeding Se-NPs can improve antioxidant status and glutathione peroxidase activities in both broilers and layers. Use of Se-NPs at 0.9 mg/kg diet in broilers improved the intestinal health via increasing the population of beneficial bacteria and producing short-chain fatty acids. This review focuses on the significance of SeNPs in poultry industry and provides insights about its comparative advantages over conventional sources of Se in poultry diets.
The allometry and partitioning of above- and belowground tree biomass was studied in an age-sequence of four eastern white pine (
Pinus strobus L.) forests (2-, 15-, 30-, and 65-year-old) in southern ...Ontario, Canada. Biomass in each tree component, i.e. foliage, branch (live and dead), bark, stem and root was quantified by destructive tree harvesting. Allometric biomass equations were developed for each tree component within each stand (age class) and across the entire age-sequence. Mean above- and belowground tree biomass was 0.3, 54, 105, and 529
kg
tree
−1 and 0.1, 13, 17, and 99
kg
tree
−1 in the 2-, 15-, 30-, and 65-year-old stands, respectively. The relative portion of stem biomass to total tree biomass increased from 25% for the 2-year-old stand to 69% for the 65-year-old stand, whereas the relative contribution of canopy biomass components (foliage and branches) decreased with stand age. Root to shoot biomass ratio decreased from 0.32 in the 2-year-old stand to 0.24, 0.16, and 0.22 in the 15-, 30-, and 65-year-old stands, respectively, indicating a decrease during the first few decades after stand establishment. Allometric relationships between biomass of individual aboveground tree components and tree diameter changed with stand age and thus resulted in age-specific allometric equations. In contrast, a single allometric equation could predict total aboveground and belowground, and total tree biomass from tree diameter only across the entire age-sequence. The relationship between tree component biomass and stem volume, expressed as biomass expansion factor (BEF), decreased for all above- and belowground tree components and total tree biomass with increasing stand age. Changes in tree biomass allocation and allometry throughout different stages of forest stand development need to be considered in order to improve forest biomass and carbon sequestration accounting on regional and national scale.
The mobility, availability and persistence of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in contaminated lake sediment samples were evaluated by means of sequential extraction scheme, proposed by the ...Community Bureau of Reference protocol (BCR). The metal content in the extracts was measured by atomic absorption spectrometry. The precision and accuracy of the proposed procedure were evaluated by using a certified reference material BCR 701. The maximum recoveries for heavy metals (HMs) were observed for all three steps of BCR protocol at 32
h total shaking period instead of previously reported 51
h, with
p
>
0.05. The lixiviation tests (DIN 38414-S4) were used to evaluate the leaching of HMs from sediment samples and it was observed that levels of water extractable HMs were low as compared to those values obtained by acid-soluble fraction of the BCR protocol.
Climate change is leading to a disproportionately large warming in the high northern latitudes, but the magnitude and sign of the future carbon balance of the Arctic are highly uncertain. Using 40 ...terrestrial biosphere models for the Alaskan Arctic from four recent model intercomparison projects – NACP (North American Carbon Program) site and regional syntheses, TRENDY (Trends in net land atmosphere carbon exchanges), and WETCHIMP (Wetland and Wetland CH4 Inter-comparison of Models Project) – we provide a baseline of terrestrial carbon cycle uncertainty, defined as the multi-model standard deviation (σ) for each quantity that follows. Mean annual absolute uncertainty was largest for soil carbon (14.0 ± 9.2 kg C m−2), then gross primary production (GPP) (0.22 ± 0.50 kg C m−2 yr−1), ecosystem respiration (Re) (0.23 ± 0.38 kg C m−2 yr−1), net primary production (NPP) (0.14 ± 0.33 kg C m−2 yr−1), autotrophic respiration (Ra) (0.09 ± 0.20 kg C m−2 yr−1), heterotrophic respiration (Rh) (0.14 ± 0.20 kg C m−2 yr−1), net ecosystem exchange (NEE) (−0.01 ± 0.19 kg C m−2 yr−1), and CH4 flux (2.52 ± 4.02 g CH4 m−2 yr−1). There were no consistent spatial patterns in the larger Alaskan Arctic and boreal regional carbon stocks and fluxes, with some models showing NEE for Alaska as a strong carbon sink, others as a strong carbon source, while still others as carbon neutral. Finally, AmeriFlux data are used at two sites in the Alaskan Arctic to evaluate the regional patterns; observed seasonal NEE was captured within multi-model uncertainty. This assessment of carbon cycle uncertainties may be used as a baseline for the improvement of experimental and modeling activities, as well as a reference for future trajectories in carbon cycling with climate change in the Alaskan Arctic and larger boreal region.
Anthocyanins are flavonoids widely spread in various plant species as a major phyto-pigment. In recent years, interest in using anthocyanins as a feed ingredient has increased markedly owing to their ...health and other benefits. Anthocyanins possess various pharmacological properties, including anti-inflammatory, immunomodulatory, anticancer, antidiabetic, neuroprotective, anti-obesity and antioxidant effects. Dietary consumption of anthocyanins has revealed benefits in animal performance. Little is known about health-promoting effects of anthocyanins in avian species, but anthocyanin-rich dried fruits have shown positive effects on certain pathological conditions and health promoting markers in human and other animals. This review aims to gather information regarding health benefits of anthocyanins and highlight therapeutic and potential health beneficial effects of anthocyanins for poultry. Additionally, it explores these biologically important flavonoids as alternative ingredients in poultry feed to replace synthetic nutrients and medicines. The available literature reports studies involving use of anthocyanins focused on human, mice and in vitro models. However, there is a need to explore mechanism of action at molecular level to understand potential beneficial effects of anthocyanins in avian species.
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