Growing season surface–atmosphere exchange of carbon dioxide and methane were quantified at Fish Island, a wetland site in the lower northeast Mackenzie River Delta, Northwest Territories, Canada. The terrain consists of low-center polygonal tundra and is subject to infrequent flooding in high water years. Carbon dioxide and methane fluxes were continuously measured using eddy covariance and the relevance of different environmental controls were identified using neural networks. Net daily carbon dioxide uptake peaked in mid-July before gradually decreasing and transitioning to net daily emissions by September. Variations in light level and temperature were the main controls over diurnal net carbon dioxide uptake, whereas thaw depth and phenology were the main seasonal controls. Methane emissions measured at Fish Island were higher than comparable studies on river delta sites in the Arctic and were influenced by the interaction of a large number of factors including thaw and water table depth, soil temperatures, and net radiation. Spikes in methane emissions were associated with strong winds and turbulence. The Fish Island tundra was a net sink for carbon during the growing season and methane emissions only slightly reduced the overall sink strength.

Despite its monotonous structure, sea-island plays a crucial role in sustaining biodiversity and ecosystem functioning. The objectives of this study were to explore the altitudinal variation of soil carbon (C), nitrogen (N), and phosphorus (P) pools in forests across 14 islands spanning temperate zone (TZ), northern subtropical zone (NSZ), mid-subtropical zone (MSZ), and sou-thern subtropical zone (SSZ) in eastern China. The relationships of soil C and nutrient pools with climatic factors and plant species diversity were examined across islands. Our results showed that soil C, N and P pools differed significantly across climatic zones. Soil C and N pools were the lowest in TZ (49.35 and 1.08 t·hm^-2) and the highest in NSZ (137.25 and 4.63 t·hm^-2). Soil P pool was the lowest in SSZ (1.3 t·hm^-2) and the highest in NSZ (5.19 t·hm^-2). There were significant difference in soil C, N and P pools among vegetation types. Soil C, N and P pools in deciduous forests were significantly higher in subtropical than in temperate islands. Soil C and N pools in evergreen broadleaved forests did not differ among sub-climatic zones, and soil P pool was lower in SSZ than that in NSZ and MSZ. The interactions across mean annual temperature, mean annual precipitation, soil water content, and plant species diversity positively affected latitudinal variation in soil C, N, and P pools. Plant species diversity positively associated with soil N pool, but negatively linked with soil P pool. In conclusion, the latitudinal trend of soil C pool is different, but that of soil N and P pools are identical between sea-island and mainland. The main abiotic and biotic dri-vers of soil C, N and P pools are water availability, temperature and plant species diversity across sea-islands in eastern China.

The atmospheric input of carbon dioxide from burning wood, in particular from forest fires in boreal and temperate regions resulting from both natural and man-made causes and predominantly from forest fires in tropical regions caused by shifting cultivation, is estimated to be 5.7 x 10(15) grams of carbon per year as gross input and 1.5 x 10(15) grams of carbon per year as net input. This is a significant amount as compared to the fossil fuel carbon dioxide produced from the utilization of oil, gas, coal, and limestone, and bears on the hypothesis of the enhanced sedimentation of marine detritus as a removal mechanism of excess atmospheric carbon dioxide.

. With the eddy covariance (EC) technique, net fluxes of carbon dioxide (CO2) and other trace gases as well as water and energy fluxes can be measured at the ecosystem level. These flux measurements are a main source for understanding biosphere–atmosphere interactions and feedbacks through cross-site analysis, model–data integration, and upscaling. The raw fluxes measured with the EC technique require extensive and laborious data processing. While there are standard tools1 available in an open-source environment for processing high-frequency (10 or 20 Hz) data into half-hourly quality-checked fluxes, there is a need for more usable and extensible tools for the subsequent post-processing steps. We tackled this need by developing the REddyProc package in the cross-platform language R that provides standard CO2-focused post-processing routines for reading (half-)hourly data from different formats, estimating the u* threshold, as well as gap-filling, flux-partitioning, and visualizing the results. In addition to basic processing, the functions are extensible and allow easier integration in extended analysis than current tools. New features include cross-year processing and a better treatment of uncertainties. A comparison of REddyProc routines with other state-of-the-art tools resulted in no significant differences in monthly and annual fluxes across sites. Lower uncertainty estimates of both u* and resulting gap-filled fluxes by 50 % with the presented tool were achieved by an improved treatment of seasons during the bootstrap analysis. Higher estimates of uncertainty in daytime partitioning (about twice as high) resulted from a better accounting for the uncertainty in estimates of temperature sensitivity of respiration. The provided routines can be easily installed, configured, and used. Hence, the eddy covariance community will benefit from the REddyProc package, allowing easier integration of standard post-processing with extended analysis. 1http://fluxnet.fluxdata.org/2017/10/10/toolbox-a-rolling-list-of-softwarepackages-for-flux-related-data-processing/, last access: 17 August 2018\n

红树林是生长在热带和亚热带地区潮间带的特殊的湿地森林，在防风固田、促进淤泥沉积、抵御海啸和台风等自然灾害和保护海岸线方面起着重要的作用.全球约有红树林152000 km²，占陆地森林面积的0.4%，我国约有230 km².热带红树林湿地的碳储量平均高达1023 Mg C·hm^-2，全球红树林湿地的碳汇能力在0.18～0.228 Pg C·a^-1.影响红树林碳储量和碳汇能力的主要因子除了植物种类组成以外，气温、海水温度、海水盐度、土壤理化性质、大气CO₂浓度及人类干扰等均有着重要作用.红树林湿地碳储量、碳汇能力的研究方法以实测法为基础，包括异速方程、遥感反演和模型模拟等.研究红树林湿地碳储量及碳汇能力，有利于深入认识红树林湿地碳循环过程及其调控机制，对红树林湿地的保护和合理利用具有重要意义. 

Mangrove forest is a special wetland forest growing in the inter-tidal zone of tropical and subtropical regions, playing important roles in windbreak, promoting silt sedimentation, resisting extreme events such as cyclones and tsunamis, and protecting coastline, <em>etc</em>. The total area of global mangrove forests is about 152000 km², only accounting for 0.4% of all forest area. There are about 230 km² mangrove forests in China. The mangrove forests in the tropics have an average carbon storage as high as 1023 Mg&middot;hm^-2, and the global mangrove forests can sequestrate about 0.18-0.228 Pg C&middot;a^-1. In addition to plant species composition, a variety of factors such as air temperature, seawater temperature and salinity, soil physical and chemical properties, atmospheric CO₂ concentration, and human activities have significant effects on the carbon storage and sink ability of mangrove forests. Many approaches based on field measurements, including allometric equations, remote sensing, and model simulation,&nbsp; are applied to quantify the carbon storage and sink ability of mangrove forest wetland. To study the carbon storage and sink ability of mangrove wetland can promote the further understanding of the carbon cycle of mangrove wetland and related controlling mechanisms, being of significance for the protection and rational utilization of mangrove wetland.

. We have carried out an inter-comparison between EddyUH and EddyPro®, two public software packages for post-field processing of eddy covariance data. Datasets including carbon dioxide, methane and water vapour fluxes measured over 2 months at a wetland in southern Finland and carbon dioxide and water vapour fluxes measured over 3 months at an urban site in Helsinki were processed and analysed. The purpose was to estimate the flux uncertainty due to the use of different software packages and to evaluate the most critical processing steps, determining the largest deviations in the calculated fluxes. Turbulent fluxes calculated with a reference combination of processing steps were in good agreement, the systematic difference between the two software packages being up to 2.0 and 6.7 % for half-hour and cumulative sum values, respectively. The raw data preparation and processing steps were consistent between the software packages, and most of the deviations in the estimated fluxes were due to the flux corrections. Among the different calculation procedures analysed, the spectral correction had the biggest impact for closed-path latent heat fluxes, reaching a nocturnal median value of 15 % at the wetland site. We found up to a 43 % median value of deviation (with respect to the run with all corrections included) if the closed-path carbon dioxide flux is calculated without the dilution correction, while the methane fluxes were up to 10 % lower without both dilution and spectroscopic corrections. The Webb–Pearman–Leuning (WPL) and spectroscopic corrections were the most critical steps for open-path systems. However, we found also large spectral correction factors for the open-path methane fluxes, due to the sensor separation effect.\n

. Eddy covariance technique to measure CO2, water and energy fluxes between biosphere and atmosphere is widely spread and used in various regional networks. Currently more than 250 eddy covariance sites are active around the world measuring carbon exchange at high temporal resolution for different biomes and climatic conditions. In this paper a new standardized set of corrections is introduced and the uncertainties associated with these corrections are assessed for eight different forest sites in Europe with a total of 12 yearly datasets. The uncertainties introduced on the two components GPP (Gross Primary Production) and TER (Terrestrial Ecosystem Respiration) are also discussed and a quantitative analysis presented. Through a factorial analysis we find that generally, uncertainties by different corrections are additive without interactions and that the heuristic u*-correction introduces the largest uncertainty. The results show that a standardized data processing is needed for an effective comparison across biomes and for underpinning inter-annual variability. The methodology presented in this paper has also been integrated in the European database of the eddy covariance measurements.

Li, X., Ziadi, N., Bélanger, G., Cai, Z. and Xu, H. 2011. Cadmium accumulation in wheat grain as affected by mineral N fertilizer and soil characteristics. Can. J. Soil Sci. 91: 521–531. Cadmium (Cd) is a heavy metal distributed in soil by natural processes and anthropogenic activities. It can accumulate in crops, such as spring milling wheat (Triticum aestivum L.), and its accumulation depends on crop species, soil factors, and agricultural practices like fertilizer inputs. Our objective was to study the effect of mineral N fertilizer and soil characteristics on wheat grain Cd concentration. A field study was conducted over 12 site-years (2004–2006) in Québec, with four N application rates (0, 40, 120, and 200 kg N ha−1). Wheat grain samples (n=192) were analysed for their Cd and N concentrations. Soil samples (n=48) taken before N fertilizer application were characterised for their chemical and physical properties, including Mehlich-3 extractable Cd concentration. Wheat grain Cd concentration increased significantly with increasing N application rates at 11 of the 12 site-years. Averaged across the 12 site-years, Cd concentration ranged from 53 µg kg−1dry matter (DM) without N applied up to 87 µg kg−1DM when 200 kg N ha−1was applied. Wheat grain Cd concentration also varied significantly with site-years (34–99 µg kg−1DM), but never exceeded the proposed tolerance for wheat grain of 235 µg kg−1DM. Wheat grain Cd concentration was significantly related to Mehlich-3 extractable Cd in soil (R2=0.44, P=0.021) and nitrogen nutrition index (R2=0.69, P=0.001). We conclude that soil Cd concentration and the crop N nutrition status affect Cd accumulation in spring wheat grain produced in eastern Canada.

\n\n\t\t\t\tVariation in the oxygen isotope composition of within-canopy CO2 has potential to allow partitioning of the ecosystem respiratory flux into above- and below-ground components. Recent theoretical work has highlighted the sensitivity of the oxygen isotope composition of leaf-respired CO2 (δRl) to nocturnal stomatal conductance. When the one-way flux model was tested on Ricinus communis L. large enrichments in δRl were observed. However, most species for which the isotope flux partitioning technique has been or would be applied (i.e. temperate tree species) are much more conservative users of water than R. communis. So, high stomatal conductance and very high enrichment of δRl observed may not be typical for temperate tree species. Using existing gas-exchange measurements on six temperate tree species, we demonstrate significant water loss through stomata for all species (i.e. statistically significantly greater than cuticular loss alone) at some time for some leaves during the night. δRl values predicted by the one-way flux model revealed that δRl might be very much more enriched than when the net flux alone is considered, particularly close to sunrise and sunset. Incorporation of the one-way flux model into ecosystem respiration partitioning studies will affect model outputs and interpretation of variation in the oxygen isotope composition of atmospheric CO2.\n\t\t\t

Selecting an appropriate model for simulating ecosystem respiration is critical in modeling the carbon cycle of terrestrial ecosystems due to their magnitude and high variations in time and space. There is no consensus on the ideal model for estimating ecosystem respiration in different ecosystems. We evaluated the performances of six respiration models, including Arrhenius, logistic, Gamma, Martin, Concilio, and time series model, against measured ecosystem respiration during 2014–2018 in four grassland ecosystems on the Mongolian Plateau: shrubland, dry steppe, temperate steppe, and meadow ecosystems. Ecosystem respiration increased exponentially with soil temperature within an apparent threshold of ~19.62 °C at shrubland, ~16.05 °C at dry steppe, ~16.92 °C at temperate steppe, and ~15.03 °C at meadow. The six models explained approximately 50–80% of the variabilities of ecosystem respiration during the study period. Both soil temperature and soil moisture played considerable roles in simulating ecosystem respiration with R square, ranging from 0.5 to 0.8. The Martin model performed better than the other models, with a relatively high R square, i.e., R2 = 0.68 at shrubland, R2 = 0.57 at dry steppe, R2 = 0.74 at temperate steppe, and R2 = 0.81 at meadow. These models achieved good performance for around 50–80% of the simulations. No single model performs best for all four grassland types, while each model appears suitable for at least one type of ecosystem. Models that oil moisture include models, especially the Martin model, are more suitable for the accurate prediction of ecosystem respiration than Ts-only models for the four grassland ecosystems.