Total Ecosystem Respiration Research Articles

Eddy Covariance Measurements of Carbon dioxide (CO2) Exchange in Pichavaram Mangrove Ecosystem, Southeast Coast of India

Net Ecosystem Productivity (NEP) and Net Ecosystem Exchange (NEE) of carbon dioxide (CO2) between the mangrove forest and the atmosphere were assessed during May 2016 to April 2017 in the Pichavaram mangrove ecosystem in India. An eddy covariance (EC) flux tower of about 10 m height was established in the middle portion of the mangrove forests to have a maximum carbon footprint from the mangroves. The EC tower was established to investigate whether the mangrove ecosystem acts as a sink or source of CO2. The monthly mean CO2 concentration varied from 376 ppm in July 2016 (during day time) to 466 ppm in December 2016 at night time. The EC based NEE showed a positive CO2 flux ranging from 4 μmol m-2s-1 in July 2016 to 6 μmol m-2s-1 in February 2017 during the night time. This was mainly due to respiration of the mangrove ecosystem. Negative CO2 flux values ranging from – 8 μmol m-2 s-1 (March 2017) to -18 μmol m-2 s-1 (August 2016) was observed during daytime, due to photosynthesis. The monthly analysis of the NEE during the daytime and night clearly indicate that the NEP of the Pichvaram mangrove was found to be positive throughout the study period suggesting that the Pichvaram mangrove ecosystem acts as a sink for CO2.The measured annual Net Ecosystem Productivity during the study period was 345 g Cm-2year-1, which is higher than the NEP reported for Sundraban mangroves (249 g C m-2 year-1). The total Gross Primary Productivity (GPP) and ecosystem respiration (Re) of the study area for the annual cycle was 2305 g C m-2 year-1and 1072 g C m-2 year-1, respectively. A long term study is needed to draw a logical conclusion on carbon sequestration potentials of this mangrove as well as to find out the role of environmental factors controlling CO2 fluxes.Keywords: Pichavaram Mangrove, Carbon dioxide, Eddy covariance, Net Ecosystem Productivity, Carbon sequestration

Hydrology and microtopography control carbon dynamics in wetlands: Implications in partitioning ecosystem respiration in a coastal plain forested wetland

Wetlands store a disproportionately large fraction of organic carbon relative to their areal coverage, and thus play an important role in global climate mitigation. As destabilization of these stores through land use or environmental change represents a significant climate feedback, it is important to understand the functional regulation of respiratory processes that catabolize them. In this study, we established an eddy covariance flux tower project in a coastal plain forested wetland in North Carolina, USA, and measured total ecosystem respiration (Re) over three years (2009–2011). We evaluated the magnitude and variability of three respiration components – belowground (Rs), coarse woody debris (RCWD), and aboveground plant (Ragp) respiration at the ecosystem scale, by accounting microtopographic variation for upscaling and constraining the mass balance with Re. Strong hydrologic control was detected for Rs and RCWD, whereas Ragp and Re were relatively insensitive to water table fluctuations. In a relatively dry year (2010), this forested wetland respired a total of about 2000g CO2-C m-2 y-1 annually, 51% as Rs, 37% as Ragp, and 12% as RCWD. During non-flooded periods Rs contributed up to 57% of Re and during flooded periods Ragp contributed up to 69%. The contribution of Rs to Re increased by 2.4% for every cm of decrease in water level at intermediate water table level, and was nearly constant when flooded or when the water level more than 15cm below ground. The contrasting sensitivity of different respiration components highlights the need for explicit consideration of this dynamic in ecosystem and Earth System Models.

The SMAP Level 4 Carbon Product for Monitoring Ecosystem Land–Atmosphere CO2 Exchange

The National Aeronautics and Space Administration’s Soil Moisture Active Passive (SMAP) mission Level 4 Carbon (L4C) product provides model estimates of the Net Ecosystem CO2 exchange (NEE) incorporating SMAP soil moisture information. The L4C product includes NEE, computed as total ecosystem respiration less gross photosynthesis, at a daily time step posted to a 9-km global grid by plant functional type. Component carbon fluxes, surface soil organic carbon stocks, underlying environmental constraints, and detailed uncertainty metrics are also included. The L4C model is driven by the SMAP Level 4 Soil Moisture data assimilation product, with additional inputs from the Goddard Earth Observing System, Version 5 weather analysis, and Moderate Resolution Imaging Spectroradiometer satellite vegetation data. The L4C data record extends from March 31, 2015 to present with ongoing production and 8–12 day latency. Comparisons against concurrent global CO2 eddy flux tower measurements, satellite solar-induced canopy florescence, and other independent observation benchmarks show favorable L4C performance and accuracy, capturing the dynamic biosphere response to recent weather anomalies. Model experiments and L4C spatiotemporal variability were analyzed to understand the independent value of soil moisture and SMAP observations relative to other sources of input information. This analysis highlights the potential for microwave observations to inform models where soil moisture strongly controls land CO2 flux variability; however, skill improvement relative to flux towers is not yet discernable within the relatively short validation period. These results indicate that SMAP provides a unique and promising capability for monitoring the linked global terrestrial water and carbon cycles.

Carbon budget measurement over 12 years at a crop production site in the silty-loam region in Belgium

Carbon dioxide (CO2) exchanges between crops and the atmosphere are influenced by both climatic and management drivers. In this study, a site at the Lonzée Terrestrial Observatory (candidate ICOS site) in Belgium that had been managed for more than 70 years using conventional farming practices, was monitored over three complete rotation cycles (sugar beet/winter wheat/seed potato/winter wheat) from 2004 to 2016. Continuous eddy-covariance measurements and regular biomass samplings were performed in order to obtain the daily and seasonal Net Ecosystem Exchange (NEE), Gross Primary Productivity (GPP), Total Ecosystem Respiration (TER), Net Primary Productivity (NPP) and Net Biome Production (NBP). Meteorological data and crop management practices were also recorded.Over the 12 crop seasons, total NEE varied both between and within crop types. Crop type influenced net carbon (C) sequestration, with the seed potato crop exhibiting the smallest C fluxes. Despite differences in CO2 assimilation response to weather variables and in cumulated TER/GPP dynamics, the sugar beet, winter wheat and maize crops had similar seasonal NEE values. The NEE inter-annual variability, both between and within crop types, was explained mainly by the length of the active vegetation period, as well as the cumulated photosynthetic photon flux density and average air temperature during this period.The establishment of the C budget over the 12 years of study showed that NEE was a downward (negative) flux (−4.40±0.05kgCm−2), but NBP was an upward (positive) flux (0.99±0.22kgCm−2). That is, as soon as C exportation at harvest and C importation (manure, slimes) were included in the budget, the site behaved as a C source. The intercrop periods contributed significantly to the total C budget, and the C fluxes generated during these periods were positively related to crop residue amount and temperature. The largest uncertainties about the crop C budget were those relating to biomass measurements. Carrying out a soil C inventory would help to validate the NBP-based estimate of soil C loss.

Net CO2 emissions from a primary boreo-nemoral forest over a 10 year period

Primary forests play an important role in the global carbon balance. With little to no human intervention, primary forests are shaped and characterised by disturbances such as weather extremes, fire, insect and pathogen attacks. Such disturbances have a direct impact on the volume of coarse woody debris (CWD) which contributes to the total ecosystem respiration (Re). There are currently few studies that present continuous long term measurements of the carbon balance of northern primary forests. We used the eddy covariance method to measure continuous carbon dioxide (CO2) fluxes from a Swedish primary boreo-nemoral forest over a ten year period. By mapping the measured CO2 fluxes to the forest ecosystem we could indicate that small areas that had some form of disturbance and areas with significant levels of CWD within the eddy covariance footprint contributed to the total Re resulting in the forest being a net carbon source. A weighing algorithm was used to account for directional ecosystem heterogeneity and to estimate a representative carbon balance for the ecosystem. The forest ecosystem was a continuous source of CO2 to the atmosphere, losing around 25Mg per hectare of CO2 over a ten year period.

Short- and Long-term Influence of Litter Quality and Quantity on Simulated Heterotrophic Soil Respiration in a Lowland Tropical Forest

Heterotrophic soil respiration (SRH) alone can contribute up to 50% of total ecosystem respiration in tropical forests. Whereas the abiotic controls of SRH have been extensively studied, the influence of plant traits is less well characterised. We used field experiments and a modelling approach to test the relative influence of plant traits on SRH in lowland tropical forest in French Guiana. We measured leaf- and root litter traits for five common tree species and conducted a root decomposition experiment to evaluate the influence of root chemistry on decay rates. We measured SRH in trenched plots and used our field measurements to parameterize and test the Century model of soil C dynamics. Overall, the Century model performed well in simulating SRH, and species-specific root decomposition in Century corresponded well to decomposition rates measured in situ. Root litter characterized by low lignin-to-nitrogen ratios decomposed more rapidly than low-quality root litter during the first 6 months. Model runs over different time scales revealed that litter quality substantially influenced SRH on an annual time-scale by determining the rates of root- and leaf litter decomposition. However, litter mass had an overriding influence on SRH over the longer term in 20-year model runs. Synthesis Using simple plant trait data to parameterise the Century model, we were able to accurately simulate changes in SRH in a lowland tropical forest. Our results suggest that this approach could be used to predict changes in tropical soil C dynamics under global change scenarios by including data on changes in plant productivity and C inputs to the soil (for example litterfall and root turnover).

Simulating of carbon fluxes in bamboo forest ecosystem using BEPS model based on the LAI assimilated with Dual Ensemble Kalman Filter

LAI is one of the most important observation data in the research of carbon cycle of forest ecosystem, and it is also an important parameter to drive process-based ecosystem model. The Moso bamboo forest (MBF) and Lei bamboo forest (LBF) were selected as the study targets. Firstly, the MODIS LAI time series data during 2014-2015 was assimilated with Dual Ensemble Kalman Filter method. Secondly, the high quality assimilated MBF LAI and LBF LAI were used as input dataset to drive BEPS model for simulating the gross primary productivity (GPP), net ecosystem exchange (NEE) and total ecosystem respiration (TER) of the two types of bamboo forest ecosystem, respectively. The modeled carbon fluxes were evaluated by the observed carbon fluxes data, and the effects of different quality LAI inputs on carbon cycle simulation were also studied. The LAI assimilated using Dual Ensemble Kalman Filter of MBF and LBF were significantly correlated with the observed LAI, with high R2 of 0.81 and 0.91 respectively, and lower RMSE and absolute bias, which represented the great improvement of the accuracy of MODIS LAI products. With the driving of assimilated LAI, the modeled GPP, NEE, and TER were also highly correlated with the flux observation data, with the R2 of 0.66, 0.47, and 0.64 for MBF, respectively, and 0.66, 0.45, and 0.73 for LBF, respectively. The accuracy of carbon fluxes modeled with assimilated LAI was higher than that acquired by the locally adjusted cubic-spline capping method, in which, the accuracy of mo-deled NEE for MBF and LBF increased by 11.2% and 11.8% at the most degrees, respectively.

Different harvest intensity and soil CO2 efflux in sessile oak coppice forests

Soil CO2 efflux accounts for about 45-80% of total ecosystem respiration and is therefore an important part of the ecosystem carbon cycle. Soil CO2 efflux has been poorly studied in forests managed in the ancient coppicing manner. In our study, soil CO2 efflux, temperature, and moisture were measured in sessile oak stands with different harvesting intensity (control: 0% intensity; V1: 75%; V2: 80 %; V3: 85%; and V4: 100%) during the fifth and sixth years after harvesting. Soil CO2 efflux was in the range 2-8 µmol CO2 m-2 s-1 and indicated an increasing pattern with increasing harvesting intensity. The slope of that pattern became less steep from the fifth to the sixth year after harvesting, thus indicating gradual recovery of soil carbon dynamics in the coppiced stand toward the equilibrium state existing before harvesting. Temperature sensitivity of soil CO2 efflux ranged between 2.1 and 2.8, with the lowest values measured in the control stand. Soil CO2 efflux in the control stand was more sensitive to changes in soil moisture than was that on harvested plots. By our calculations, 6.2 tC ha-1 was released from the control stand and 6.2-6.8 tC ha-1 from the harvested stands during the sixth year after harvesting. If mean temperature were to rise by 1 °C, the amount of soil carbon released would increase by 7.7% in the control stand and, depending on harvesting intensity, by 9.0-10.8% in the harvested stands.

Sensitivity of the annual net ecosystem exchange to the cospectral model used for high frequency loss corrections at a grazed grassland site

Given the increasing use of the eddy covariance technique to estimate CO2 fluxes, more attention needs to be paid to the measurement method used. Among other procedures, the way high frequency loss corrections are established and, more particularly, the choice of the cospectrum shape that is used to implement the correction appears particularly important in this regard. In this study, we compared three approaches to high frequency loss correction for CO2 fluxes measured by a closed path eddy covariance system and evaluated their impact on the carbon balance at the Dorinne Terrestrial Observatory (DTO), an intensively grazed grassland site in Belgium. In the first approach, the computation of correction factors was based on the local cospectra, whereas the other two were based on Kansas cospectra models. The correction approaches were validated by comparing the nighttime eddy covariance CO2 fluxes corrected with each approach and chamber-based total ecosystem respiration estimates. We found that the local cospectra differed from the Kansas cospectra shape, although the site could not be considered as difficult (i.e., fairly flat, homogeneous, low vegetation, sufficient measurement height). The Kansas cospectra have more spectral power at high frequencies than the local cospectra under (un) stable conditions. This difference greatly affected the correction factor, especially for night fluxes. Night fluxes measured by eddy covariance were found to be in good accord with total chamber based ecosystem respiration estimates when corrected with local cospectra and to be overestimated when corrected with Kansas cospectra. As the difference between correction factors was larger in stable than unstable conditions, it acts as a selective systematic error and has an important impact on annual carbon fluxes. On the basis of a 4-year average, at DTO the errors reach 71–150gCm−2y−1 for net ecosystem exchange (NEE), 280–562gCm−2y−1 for total ecosystem respiration (TER) and 209–412gCm−2y−1 for gross primary productivity (GPP), depending on the approach used. We finally encourage site PIs to check the cospectrum shape at their sites and, if necessary, compute frequency correction factors on the basis of local cospectra rather than on Kansas cospectra.

Carbon and water exchange over a temperate semi-arid shrubland during three years of contrasting precipitation and soil moisture patterns

Water is considered a key factor affecting ecosystem carbon exchange in dryland regions. However, the relationship between inter-annual variations in precipitation and ecosystem productivity remains to be clarified for arid and semi-arid areas. Based on eddy-covariance measurements, we examined how ecosystem production in a shrubland of northern China varied over three years (2012–2014) with contrasting precipitation and soil moisture patterns. Net ecosystem production (NEP) was 77±10 (±standard deviation), −4±10 and −22±5gCm−2 in 2012–2014, respectively, indicating a rapid shift from an annual sink to a source of carbon. Gross ecosystem production (GEP), total ecosystem respiration (TER) and evapotranspiration (ET) also declined over the three years. Annual carbon and water fluxes appeared to be suppressed in years with low spring soil moisture, which declined dramatically from 2012 to 2014. GEP declined more than TER and ET, leading to reduced carbon sequestration capacity and water use efficiency (WUE=GEP/ET). Neither annual nor growing-season precipitation could explain the year-to-year variations in carbon fluxes, whereas at our site ET was a better proxy for water available to ecosystem carbon exchange on an annual basis. Autumn soil moisture levels were carried over winter to the following spring, and, thus, may affect the rates of leafout, plant growth and carbon uptake in the early- to mid-growing season. Our conclusions were drawn from only three years of measurements and are therefore preliminary. Longer timeseries encompassing a wider range of precipitation and soil moisture conditions are needed to confirm or refine these conclusions. Our findings highlight the importance of precipitation timing and soil moisture carry-over in controlling ecosystem productivity. Winter warming and decreases in autumn and winter precipitation may induce spring drought and thus impair the carbon sequestration potential of shrubland and steppe ecosystems in semi-arid and arid Eurasia.

A wildfire event influences ecosystem carbon fluxes but not soil respiration in a semi-arid woodland

The importance of arid and semi-arid ecosystems for global net carbon uptake has recently been highlighted. More information about the drivers of carbon fluxes in these ecosystems is required to advance our understanding of the contribution of dry ecosystems to the global carbon budget. In this study, eddy covariance flux data was used to calculate net ecosystem productivity (NEP), gross primary productivity (GPP) and ecosystem respiration (Reco) in a semi-arid woodland on sandy soil. In January 2014 a wildfire severely damaged the area around the flux tower, burning trees and spinifex and consuming aboveground bark and leaf litter. The flux tower recorded data for one year before the fire (January–December 2013) and more than one year after the fire (May 2014–July 2015). Soil respiration was measured in-situ monthly after the fire (July 2014–June 2015), in burnt and unburnt areas under Eucalyptus tree canopy and inter-canopy representing 25 and 75% of the area, respectively. Before the fire the ecosystem was a net carbon sink, sequestering 81gCm−2 yr−1 in 2013, but became a carbon source after the fire. Reco and GPP declined by about 35% and 65%, respectively, after the fire. Net carbon uptake resumed 12–15 months after the fire with NEP approaching values similar to those before the fire. Soil respiration was significantly higher under tree canopies (1.5μmol CO2 m−2s−1) than in inter-canopy areas (0.9μmol CO2 m−2s−1). Soil respiration was mainly driven by soil water content and thus magnitude and distribution of precipitation, but was not influenced by the wildfire. Accounting for differences in area, soil respiration from inter-canopy and under canopy contributed 51 and 32% to total ecosystem respiration. It can be concluded that carbon flux in this semi-arid woodland was strongly influenced by precipitation and wildfire, with net carbon uptake of the ecosystem beginning approximately one year after the fire.

Partitioning of ecosystem respiration of CO2 released during land‐use transition from temperate agricultural grassland to Miscanthus × giganteus

AbstractConversion of large areas of agricultural grassland is inevitable if European and UK domestic production of biomass is to play a significant role in meeting demand. Understanding the impact of these land‐use changes on soil carbon cycling and stocks depends on accurate predictions from well‐parameterized models. Key considerations are cultivation disturbance and the effect of autotrophic root input stimulation on soil carbon decomposition under novel biomass crops. This study presents partitioned parameters from the conversion of semi‐improved grassland to Miscanthus bioenergy production and compares the contribution of autotrophic and heterotrophic respiration to overall ecosystem respiration of CO2 in the first and second years of establishment. Repeated measures of respiration from within and without root exclusion collars were used to produce time‐series model integrations separating live root inputs from decomposition of grass residues ploughed in with cultivation of the new crop. These parameters were then compared to total ecosystem respiration derived from eddy covariance sensors. Average soil surface respiration was 13.4% higher in the second growing season, increasing from 2.9 to 3.29 g CO2‐C m−2 day−1. Total ecosystem respiration followed a similar trend, increasing from 4.07 to 5.4 g CO2‐C m−2 day−1. Heterotrophic respiration from the root exclusion collars was 32.2% lower in the second growing season at 1.20 g CO2‐C m−2 day−1 compared to the previous year at 1.77 g CO2‐C m−2 day−1. Of the total respiration flux over the two‐year time period, aboveground autotrophic respiration plus litter decomposition contributed 38.46% to total ecosystem respiration while belowground autotrophic respiration and stimulation by live root inputs contributed 46.44% to soil surface respiration. This figure is notably higher than mean figures for nonforest soils derived from the literature and demonstrates the importance of crop‐specific parameterization of respiration models.

Longer thaw seasons increase nitrogen availability for leaching during fall in tundra soils

Climate change has resulted in warmer soil temperatures, earlier spring thaw and later fall freeze-up, resulting in warmer soil temperatures and thawing of permafrost in tundra regions. While these changes in temperature metrics tend to lengthen the growing season for plants, light levels, especially in the fall, will continue to limit plant growth and nutrient uptake. We conducted a laboratory experiment using intact soil cores with and without vegetation from a tundra peatland to measure the effects of late freeze and early spring thaw on carbon dioxide (CO2) exchange, methane (CH4) emissions, dissolved organic carbon (DOC) and nitrogen (N) leaching from soils. We compared soil C exchange and N production with a 30 day longer seasonal thaw during a simulated annual cycle from spring thaw through freeze-up and thaw. Across all cores, fall N leaching accounted for ∼33% of total annual N loss despite significant increases in microbial biomass during this period. Nitrate leaching was highest during the fall (5.33 ± 1.45 mg N m−2 d−1) following plant senescence and lowest during the summer (0.43 ± 0.22 mg N m−2 d−1). In the late freeze and early thaw treatment, we found 25% higher total annual ecosystem respiration but no significant change in CH4 emissions or DOC loss due to high variability among samples. The late freeze period magnified N leaching and likely was derived from root turnover and microbial mineralization of soil organic matter coupled with little demand from plants or microbes. Large N leaching during the fall will affect N cycling in low-lying areas and streams and may alter terrestrial and aquatic ecosystem nitrogen budgets in the arctic.

Simulating the net ecosystem CO2 exchange and its components over winter wheat cultivation sites across a large climate gradient in Europe using the ORCHIDEE-STICS generic model

Over the last decade, efforts have been carried on to develop and evaluate versions of global terrestrial ecosystem models (GTEM) in which crop specificities are represented. The goal of this study is to evaluate the ability of the ORCHIDEE-STICS (Organising Carbon and Hydrology In Dynamic EcosystEms—Simulateur mulTIdisciplinaire pour les Cultures Standard) GTEM in simulating the observed seasonal variations and annual budgets of net ecosystem exchange (NEE), gross primary production (GPP) and total ecosystem respiration (TER) fluxes over seven wheat sites spanning a large climate gradient in Europe. Overall, the seasonal variations of GPP are well represented by the model, with 5 sites out of 7 exhibiting a correlation coefficient (R) value higher than 0.9 and a normalized standard deviation (NSTD) between 0.8 and 1.2. In comparison, the model performances for catching the seasonal variations of TER are lower, especially in terms of NSTD. Regarding the annual budgets, mean simulated deviations averaged over all sites do not exceed 10% and 15% of the observed annual mean budget, for GPP and TER, respectively. For NEE, the model capacity at estimating annual budgets is low, its mean deviation corresponding to ∼35% of the observed mean value. This clearly shows that more accurate model estimates of GPP and especially TER are required for estimating NEE annual budgets. In this respect, past land-use and land-management changes are probably the most crucial processes to add, for getting soil carbon disequilibrium and more accurate NEE annual budgets.From a sensitivity analysis of the modelled fluxes to three management practices (plant variety, sowing date and fertilization intensity), we found that the fertilization is the most sensitive practice impacting the model performances of any flux, both in terms of seasonal variations and annual budgets.

Changing temperature response of respiration turns boreal forest from carbon sink into carbon source

Seventeen years (1997–2013) of carbon dioxide (CO2) fluxes were measured in a boreal forest stand in northern Sweden using the eddy covariance technique. During the measurement period the forest turned from a net carbon sink into a net carbon source. The net ecosystem exchange (NEE) was separated using values from periods of darkness into the gross components of total ecosystem respiration (TER) and gross primary productivity (GPP), which was calculated as GPP=−NEE+TER. From the gross components we could determine that an increase in TER during the autumn (September to end of November) and spring (March to end of May) periods resulted in the forest becoming a net source of CO2. We observed no increase in the GPP from the eddy covariance measurements. This was further supported by measurements of tree growth rings. The increased TER was attributed to a change in the forest’s temperature response at lower temperatures (−5 to 10°C) rather than to a temperature increase. This study shows that changes in ecosystem functioning can have a larger impact on the carbon balance than climate warming per se.

Carbon dioxide exchange of a perennial bioenergy crop cultivation on a mineral soil

Abstract. One of the strategies to reduce carbon dioxide (CO2) emissions from the energy sector is to increase the use of renewable energy sources such as bioenergy crops. Bioenergy is not necessarily carbon neutral because of greenhouse gas (GHG) emissions during biomass production, field management and transportation. The present study focuses on the cultivation of reed canary grass (RCG, Phalaris arundinacea L.), a perennial bioenergy crop, on a mineral soil. To quantify the CO2 exchange of this RCG cultivation system, and to understand the key factors controlling its CO2 exchange, the net ecosystem CO2 exchange (NEE) was measured from July 2009 until the end of 2011 using the eddy covariance (EC) method. The RCG cultivation thrived well producing yields of 6200 and 6700 kg DW ha−1 in 2010 and 2011, respectively. Gross photosynthesis (GPP) was controlled mainly by radiation from June to September. Vapour pressure deficit (VPD), air temperature or soil moisture did not limit photosynthesis during the growing season. Total ecosystem respiration (TER) increased with soil temperature, green area index and GPP. Annual NEE was −262 and −256 g C m−2 in 2010 and 2011, respectively. Throughout the study period from July 2009 until the end of 2011, cumulative NEE was −575 g C m−2. Carbon balance and its regulatory factors were compared to the published results of a comparison site on drained organic soil cultivated with RCG in the same climate. On this mineral soil site, the RCG had higher capacity to take up CO2 from the atmosphere than on the comparison site.

Development of the BIOME-BGC model for the simulation of managed Moso bamboo forest ecosystems

Numerical models are the most appropriate instrument for the analysis of the carbon balance of terrestrial ecosystems and their interactions with changing environmental conditions. The process-based model BIOME-BGC is widely used in simulation of carbon balance within vegetation, litter and soil of unmanaged ecosystems. For Moso bamboo forests, however, simulations with BIOME-BGC are inaccurate in terms of the growing season and the carbon allocation, due to the oversimplified representation of phenology. Our aim was to improve the applicability of BIOME-BGC for managed Moso bamboo forest ecosystem by implementing several new modules, including phenology, carbon allocation, and management. Instead of the simple phenology and carbon allocation representations in the original version, a periodic Moso bamboo phenology and carbon allocation module was implemented, which can handle the processes of Moso bamboo shooting and high growth during “on-year” and “off-year”. Four management modules (digging bamboo shoots, selective cutting, obtruncation, fertilization) were integrated in order to quantify the functioning of managed ecosystems. The improved model was calibrated and validated using eddy covariance measurement data collected at a managed Moso bamboo forest site (Anji) during 2011–2013 years. As a result of these developments and calibrations, the performance of the model was substantially improved. Regarding the measured and modeled fluxes (gross primary production, total ecosystem respiration, net ecosystem exchange), relative errors were decreased by 42.23%, 103.02% and 18.67%, respectively.

Variations of carbon dioxide exchange in paddy field ecosystem under water-saving irrigation in Southeast China

Based on the results of continuous flux measurements in the Taihu Lake Region of China, the carbon dioxide (CO2) exchange of paddy fields under water-saving irrigation and its influence factors were analyzed. The net ecosystem exchange of CO2 (NEE) were negative during the daytime and positive at night, and the minimum value appeared around noon. The peak CO2 uptake in the flourishing period was approximately 1.5 times the values observed in the tillering and ripening stages. Frequent alternation of wetting and drying in paddy fields with water-saving irrigation resulted in larger NEE for the typical day before soil rewatering than that for the day after soil rewatering in the early growth stage. These alterations had a minimal effect on diurnal variation of NEE in the late rice growth stage. The average NEE for the typical days after soil rewatering in July and August were 2.30 and 1.38 times that before soil rewatering, respectively. CO2 exchange in paddy field ecosystem under water-saving irrigation displayed seasonal variation with the change of rice plant growth. The total ecosystem respiration (Reco), NEE and gross primary productivity (GPP) were 1996.88, −1284.15 and 3281.03gm−2, respectively, throughout the growth stage. These results showed that the paddy field ecosystem under water-saving irrigation was a sink for atmospheric CO2. Frequent alternation of wetting and drying processes increased the ecosystem reparation of paddy fields under water-saving irrigation and produced smaller net CO2 absorption compared to that of flooding irrigation. The net CO2 absorption because of plant photosynthesis during the daytime and the net CO2 release at night measured by static transparent chamber method were larger than those measured by eddy covariance method (P<0.05). The nighttime respiration of paddy field ecosystem under water-saving irrigation increased exponentially with temperature. Additionally, a larger temperature sensitivity coefficient (Q10) was observed for paddy fields under water-saving irrigation compared to that under flooding irrigation. The photosynthetic photon flux density (PPFD) was the most important factor for regulating daytime GPP. And the light saturation point during the heading-flowering and milk stages of paddy field ecosystem with water-saving irrigation (1500μmolm−2s−1) was higher than that of fields with flooding irrigation in previous studies. A significant positive correlation was found between the leaf area index (LAI) and the daily GPP.

Assessing carbon and water dynamics of no-till and conventional tillage cropping systems in the inland Pacific Northwest US using the eddy covariance method

Analysis of carbon and water budgets in cropping systems is important for understanding the impacts of different management practices and meteorological conditions, in the context of climate change, on agriculture. We have established a pair of long-term eddy covariance flux towers at the R. J. Cook Agronomy Farm (CAF) near Pullman, Washington, US. The tower sites have similar crop rotation, weather conditions, and management practices except tillage. One site has been under no-till management (CAF-NT) since 1998, while the other site has used conventional tillage practice (CAF-CT) over the same time period. Measurements conducted above a garbanzo bean crop (Cicer arietinum) between October 2012 and September 2013 showed the CAF-NT site was close to CO2 neutral with an annual cumulative net ecosystem exchange of CO2 (NEE) of −20±38gCm−2. By contrast, the CAF-CT site was a CO2 source with an annual NEE of 117±39gCm−2 during the same time period. The annual NEE values at each site were significantly different (p<0.05). When carbon losses via harvest export were taken into account, the net rates of carbon loss from each ecosystem to the atmosphere were 32±50 and 178±48gCm−2 for CAF-NT and CAF-CT, respectively, indicating CAF-NT was close to carbon neutral and CAF-CT was a net carbon source during the measurement period. Partitioning of NEE into gross primary productivity (GPP) and total ecosystem respiration (Reco) shows that the annual cumulative GPP of each site did not differ much, but CAF-NT had lower annual cumulative Reco compared to CAF-CT during the period of October 2012–September 2013. Water budget analyses presented similar magnitudes of annual sums of evapotranspiration (ET), 425 and 416mm for CAF-NT and CAF-CT, respectively. ET was partitioned into evaporation (E) and transpiration (T) for both sites, and CAF-CT had a larger fraction of annual E compared to CAF-NT during the measurement period. Relationships between carbon and water fluxes were investigated, and for the period of October 2012–September 2013, high correlations were found in GPP vs. T and NEE vs. ET at both sites. In summary, the site deploying no-till practices had lower total ecosystem respiration and evaporation throughout the measurement period, more net carbon uptake and a greater ratio of transpiration over evapotranspiration (T/ET) during the growing season.

Coarse woody debris and the carbon balance of a moderately disturbed forest

Forested landscapes are shaped by disturbances varying in severity and source. Moderate disturbance from weather, pathogens, insects, and age-related senescence that kills only a subset of canopy trees may increase standing woody debris and alter the contribution of coarse woody debris (CWD) to total ecosystem respiration (RE). However, woody debris carbon (C) dynamics are rarely examined following moderate disturbances that increase standing dead wood pools. We used an experimental manipulation of moderate disturbance in an upper Great Lakes forest to: (1) examine multi-year changes in CWD mass through a moderate disturbance; (2) quantify in situ CWD respiration during different stages of decay for downed and standing woody debris and; (3) estimate the annual contribution of CWD respiration to the ecosystem C balance through comparison with RE and net ecosystem production (NEP). Six years following disturbance, we found that the standing dead wood mass of 24.5MgCha−1 was an order of magnitude greater than downed woody debris mass and a large source of ecosystem C flux. Instantaneous in situ respiration rates from standing and minimally decayed downed woody debris were not significantly different from one another. Separate estimates of ecosystem CWD respiration of 1.1–2.1MgCha−1yr−1 six years following disturbance were comparable in magnitude to NEP and 12.5–23.8% of RE, representing a substantial increase relative to pre-disturbance levels. Ecosystem respiration and NEP were stable following moderate disturbance even though ecosystem CWD respiration increased substantially, suggesting a reduction in the respiratory C contribution from other sources. We conclude that standing and downed CWD can be essential components of the ecosystem C balance following moderate severity disturbance.