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The flux-variance similarity (FVS) partitioning method to estimate transpiration/photosynthesis and evaporation/respiration, using only high frequency Eddy Covariance (EC) measurements, was studied. The FVS method was applied to two crops in successive growing seasons of a typical cropping system in Mediterranean region: fava bean followed by winter wheat. FVS applies the flux-variance arguments derived from Monin-Obukhov similarity theory separately to the stomatal (photosynthesis and transpiration) and non-stomatal (respiration and evaporation) processes. The leaf-level water use efficiency, an input of FVS method, is here calculated by using EC outputs and estimated humidity after the direct measurement of surface infrared temperature. The two experimental seasons were characterized by exceptionally rainy periods (262 mm in 85 days in 2014, 344 mm in 149 days in 2015). Nevertheless, the partitioning results are consistent with expected trends and absolute values of flux components throughout both seasons. In particular, heterotrophic soil respiration measured by chamber systems and modelled FVS respiration components are comparable at the beginning and at the end of the growing crop cycles, when crop biomass and leaf area are very low. Furthermore, the coupling of FVS method and root exclusion method for measuring soil respiration is able to give the heterotrophic and autotrophic components of respiration. Finally, the results showed that the succession fava bean to wheat permits a mitigation of the loss of carbon to the atmosphere and increases carbon sequestration. [ABSTRACT FROM AUTHOR]

It is important to quantify carbon decomposition to assess the reforestation impact on the forest floor C stocks. Estimating the loss of C stock in a short-term perspective requires measuring changes in soil respiration. This is not trivial due to the contribution of both soil microbes and vegetation to the measured CO2 flux. However, C stable isotopes can be used to partition the respiration and potentially to assess how much of the recalcitrant C stock in the forest floor is lost. Here, we measured the soil respiration at two forest sites where different regeneration methods were applied, along with an intact forest soil for reference. In so doing, we used a closed dynamic chamber for measuring respiration and the 13C composition of the emitted CO2. The chamber measurements were then supplemented with the soil organic carbon analysis and its δ13C content. The mean δ13C-CO2 estimates for the source of the CO2 were -26.4, -27.9 and -29.5‰, for the forest, unploughed and ploughed, respectively. The 13C of the soil organic carbon did, not differ significantly between sites. The higher soil respiration rate at the forest, as compared to the unploughed site, could be attributed to the autotrophic respiration by the forest floor vegetation. [ABSTRACT FROM AUTHOR]

Microbial community plays critical roles in driving soil carbon (C) cycling in terrestrial ecosystems. However, we lack empirical evidence to demonstrate the role of microbial community in driving soil respiration - a key ecosystem process for global sustainability and climate regulation. Here, we used a long-term field experiment including multiple management practices, to identify, via statistical modeling, the role of microbial community composition in influencing soil respiration. We analyzed major soil properties and microbial (both bacterial and fungal) abundance, diversity and community composition. We found that different management regimes led to different soil respiration rates. Most importantly, microbial community composition explained a unique portion of the variation in soil respiration, which cannot be accounted for by key respiration drivers such as soil properties and other microbial attributes (richness and total abundance). Microbial biomass and fungal richness were also identified as key drivers of soil respiration. Our results indicate that inclusions of microbial compositional data in Earth system models can be potentially used to improve our capacity to predict changes in soil C balance under changing environments. [ABSTRACT FROM AUTHOR]

Abstract: The impact of grazing on C fluxes from pastures in subtropical and tropical regions and on the environment is uncertain, although these systems account for a substantial portion of global C storage. We investigated how cattle grazing influences net ecosystem CO2 and CH4 exchange in subtropical pastures using the eddy covariance technique. Measurements were made over several wet‐dry seasonal cycles in a grazed pasture, and in an adjacent pasture during the first three years of grazer exclusion. Grazing increased soil wetness but did not affect soil temperature. By removing aboveground biomass, grazing decreased ecosystem respiration (Reco) and gross primary productivity (GPP). As the decrease in Reco was larger than the reduction in GPP, grazing consistently increased the net CO2 sink strength of subtropical pastures (55, 219 and 187 more C/m2 in 2013, 2014, and 2015). Enteric ruminant fermentation and increased soil wetness due to grazers, increased total net ecosystem CH4 emissions in grazed relative to ungrazed pasture (27–80%). Unlike temperate, arid, and semiarid pastures, where differences in CH4 emissions between grazed and ungrazed pastures are mainly driven by enteric ruminant fermentation, our results showed that the effect of grazing on soil CH4 emissions can be greater than CH4 produced by cattle. Thus, our results suggest that the interactions between grazers and soil hydrology affecting soil CH4 emissions play an important role in determining the environmental impacts of this management practice in a subtropical pasture. Although grazing increased total net ecosystem CH4 emissions and removed aboveground biomass, it increased the net storage of C and decreased the global warming potential associated with C fluxes of pasture by increasing its net CO2 sink strength. [ABSTRACT FROM AUTHOR]

Soil plays an important role in carbon storage. Accordingly, urban soil carbon and its storage have great impacts on urban carbon balance and future urban sustainable development. In this study, 151 traffic road soils in five urban functional areas were selected. The discrepancies of field soil respiration, soil physiochemical conditions among urban functional areas were calculated. Factor analysis and the Geographic Detector (GeoD) factor model showed that heavy metals had the most important impacts on soil respiration, followed by organic matter and urban function. Using the geographic detector method, individual factors and their interaction effects on soil respiration were tested. The GeoD interaction model demonstrated that no-linear enhanced interaction exhibited between C and ecological function, between N and residential function, S and industrial function. Moreover, no-linear enhanced interaction existed between Ti and ecological function, between Hg, Zn, Ni and residential function. The GeoD risk detector indicated that Soil temperature, N and Hg in different categories had obvious traffic road soil respiration impacts discrepancy. Overall, the results of this study will be useful for further investigation of urban soil treatment to enable healthy urban functional development. [ABSTRACT FROM AUTHOR]

Photosynthesis and respiration of biological soil crusts (BSCs) sampled along a mobile inland dune catena were determined to evaluate the applicability of Odum's P/R ratio, determined under controlled conditions, for estimation of ecosystem maturity. The theory is that in the early stages of ecological succession, the total photosynthesis (P) exceeds the rate of community respiration (R), so that the P/R ratio is > 1, and that P/R approaches 1 as succession occurs. In the special case of organic pollution, the P/R ratio is typically < 1. Samples were collected in the deflation zone of the dune near the crest (BSC1, thickness 2–3 mm), at the lee side of grass tussocks at the slope (BSC2, thickness 2–4 mm) and near the base (BSC3, thickness 4–6 mm). Non-crusted sand was used as control (BSC0). Photosynthesis, respiration, crust biomass, as well as fossil and allochthonous pedogenic carbon entering the system with mineral substrate were determined. The respiration of the BSC1 was dominated by the degradation of allochthonous organic matter, leading to a diminished P/R ratio. The better developed BSC2 and BSC3 were less influenced by allochthonous organic matter, where BSC maturity increased downslope with biomass increase. No significant relation between the P/R ratio and soil water tension was found. Crust carbon pools increased and flows intensified, but mineralization constants decreased with system maturation. It was concluded that Odum's P/R ratio and accumulation of recalcitrant to biodegradation organic matter are indicative for biocrust maturity. [ABSTRACT FROM AUTHOR]

We measured total soil CO2 efflux (RS) and efflux from the forest floor layers (RFF) in red pine (Pinus resinosa Ait.) stands of different ages to examine relationships between stand age and belowground C cycling. Soil temperature and RS were often lower in a 31-year-old stand (Y31) than in 9-year-old (Y9), 61-year-old (Y61), or 123-year-old (Y123) stands. This pattern was most apparent during warm summer months, but there were no consistent differences in RFF among different-aged stands. RFF represented an average of 4–13% of total soil respiration, and forest floor removal increased moisture content in the mineral soil. We found no evidence of an age effect on the temperature sensitivity of RS, but respiration rates in Y61 and Y123 were less sensitive to low soil moisture than RS in Y9 and Y31. Our results suggest that soil respiration’s sensitivity to soil moisture may change more over the course of stand development than its sensitivity to soil temperature in red pine, and that management activities that alter landscape-scale age distributions in red pine forests could have significant impacts on rates of soil CO2 efflux from this forest type. [ABSTRACT FROM AUTHOR]

Forests are structurally complex ecosystems with several canopy layers, each with distinct functional properties contributing differently to the net ecosystem CO 2 exchange. A large number of studies have addressed ecosystem-scale net CO 2 fluxes in forests, but only few studies have investigated the role of the forest understory. The goal of this study was to quantify the below-canopy contribution to ecosystem CO 2 fluxes of a mixed deciduous forest in Switzerland. Below- and above-canopy eddy-covariance (EC) measurements were made continuously over two years, complemented by within canopy wind and CO 2 concentration profile measurements. On an annual basis, the below-canopy fluxes indicated a net carbon source dominated by soil respiration, while the above-canopy fluxes were dominated by tree photosynthesis leading to a net carbon sink. Below-canopy fluxes showed a net carbon sink only in spring, with the early emergence of understory plants before overstory canopy leaf-out. Below-canopy respiration partitioned from the EC measurements agreed well with previous chamber-based soil respiration measurements. However, below- and above-canopy fluxes became decoupled under full canopy closure, thus leading to unaccounted below-canopy fluxes when measured only above the canopy. Wind and CO 2 concentration profile measurements supported this finding. Decoupling was independent of low turbulence conditions and decoupled periods could be identified using the relationship between the below- and above-canopy standard deviation in vertical wind velocity. A decoupling correction was applied to the above-canopy measurements during decoupled periods and corrected annual net ecosystem production (NEP) agreed well with independent estimates from biomass inventory combined with models. Overall, the below-canopy fluxes contributed 79% to annual ecosystem respiration, but only 9% to annual ecosystem photosynthesis. The decoupling correction reduced annual NEP for the site from about 760 to 330 g C m −2 yr −1 . Our results showed that below-canopy EC measurements are essential in this mixed deciduous forest, and likely in many other forests, to fully understand the carbon dynamics within structurally complex ecosystems. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2 ) fluxes between terrestrial ecosystems and the atmosphere are primarily measured with eddy covariance (EC), biometric, and chamber methods However, it is unclear why the estimates of the CO 2 -fluxes, when measured using different methods, converge at some sites but diverge at others. We synthesized a novel global dataset of forest CO 2 -fluxes to evaluate the consistency between EC and biometric or chamber methods for quantifying the CO 2 budget in forest ecosystems. The EC approach, compared with the other two methods, overestimated net ecosystem production (NEP) by 25% (0.52 Mg C ha −1 yr −1 ), and underestimated ecosystem respiration (Re) by 10% (1.39 Mg C ha −1 yr −1 ) and gross primary production by 3% (0.48 Mg C ha −1 yr −1 ). The differences between EC and the other methods were greater at the sites with complex topography and dense canopy than at the sites with flat topography and open canopy. Forest age also influenced the differences mainly through changes in leaf area index. Open-path EC system induced large positive bias in the NEP estimated by EC, presumably due to its surface-heating effect. These results suggest that EC method likely produce biased estimates of NEP and Re in forest ecosystems. A global extrapolation suggests that the differences in the forest CO 2 -fluxes measured with different methods be consistent with the global overestimation of NEP and underestimation of Re by EC method. Accounting for these differences would substantially improve our estimates of the forest carbon budget. The uncertainties involved in each method were also discussed. To reduce uncertainty in quantifying both local and global carbon budgets, we recommend cross-validation of forest CO 2 -fluxes measured by different methods with more accurate measurements and careful data processing strategies. [ABSTRACT FROM AUTHOR]

The responses of soil respiratory components to global warming are poorly understood particularly in high altitude forest ecosystems. To examine the different responses of soil respiration ( R S ) components, i.e., autotrophic ( R A ) and heterotrophic ( R H ) respirations, in a mountainous temperate forest to elevated temperature, we conducted an open-field soil warming experiment combined with trenching treatments in a 60-year-old cool-temperate deciduous broadleaved forest in central Japan. Here we particularly focused on the temporal variations of respirations under remarkable seasonal change of air and soil temperatures in the region. R S was divided into R A and R H by trenching method in both warmed and control plots (three subplots for each treatment). We installed heating cables at 5 cm below the soil surface to increase soil temperature by 3.0 °C during snow-free seasons in the four experimental years from 2012 to 2015. The soil warming significantly increased R S , however, the soil warming did not alter fine root biomass, carbon concentrations nor nitrogen availability in the soils, which were positively related to R S . The magnitude of the warming effects on R H was negatively correlated to both soil temperature and soil moisture content. In this cool-temperate forest characterized by monsoon climate in summer, the high soil moisture level may not be a limiting factor for the soil warming effect on R H . The effect of soil warming on R S did not vary throughout the daytime, but the effect on R S varied seasonally because R H showed more sensitive response to soil warming in the late-growing season when compared to other seasons. We demonstrated that the season-specific Q 10 model is able to quantify the warming impacts on annual respiration rates more accurately than apparent annual Q 10 model. The soil warming increased annual R S , R H , and R A for the second year by 18.1%, 25.6%, and 5.3%, respectively, but the magnitude of those increments declined in the fourth year to 9.9%, 19.5%, and −2.8%, respectively. Our results suggest that soil warming did not alter the temperature sensitivity of R H in this forest soil, but might have induced thermal acclimation of R A . This 4-year soil warming study in a mountainous forest contributes to the better understanding of the different responses of R H and R A to changing soil temperature conditions, and we highlight that the seasonal variations in the warming effects on R H and R A to future climate conditions should be taken into consideration in projecting the future soil carbon cycle. [ABSTRACT FROM AUTHOR]

Although knowledge of the impact of N enrichment on soil C fluxes is scant, such information is highly critical for estimating the global C budget under elevated N deposition. To quantify the effects of short-term N addition on soil C sequestration in an alpine scrub ecosystem, we conducted a field experiment for Sibiraea angustata scrub on the eastern margin of the Qinghai-Tibetan Plateau in China. We quantified the soil C pool (0–30 cm) and C fluxes in litterfall, fine root (<2 mm diameter) production (FRP), and soil CO 2 emission (heterotrophic respiration, R h ) over four years with four levels of N addition (N 0 ; control, N 20 ; 20, N 50 ; 50, and N 100 , 100 kg N ha −1 year −1 ). The results showed that at control plots the total C-input (433 ± 33 g C m −2 year −1 ) via FRP (360 ± 34 g C m −2 year −1 ) and litterfall (73 ± 1 g C m −2 year −1 ) was close to the C-output via R h (466 ± 5 g C m −2 year −1 ), which demonstrates that the S. angustata scrub soil C is at equilibrium status. However, adding N, particularly the N 100 treatment, significantly affected the soil C balance; the soil became a C sink (163 ± 46 g C m −2 year −1 ) by increasing FRP (+63%) rather than by increasing litterfall ( P > 0.05) or reducing R h ( P > 0.05). As a result, the soil C pool (0–30 cm) increased significantly. In conclusion, these results suggest that fine roots play a dominant role in the C balance of an alpine scrub ecosystem due to large C-inputs to the soil. Moreover, short-term high N enrichment causes sequestration of additional atmospheric CO 2 , largely because of the stimulation of fine root growth rather than increased inputs of aboveground plant litterfall or reductions in soil CO 2 emission. [ABSTRACT FROM AUTHOR]

Color sensor technologies offer opportunities for affordable and rapid assessment of soil organic carbon (SOC) and total nitrogen (TN) in the field, but the applicability of these technologies may vary by soil type. The objective of this study was to use an inexpensive color sensor to develop SOC and TN prediction models for the Russian Chernozem (Haplic Chernozem) in the Kursk region of Russia. Twenty-one dried soil samples were analyzed using a Nix ProTM color sensor that is controlled through a mobile application and Bluetooth to collect CIEL*a*b* (darkness to lightness, green to red, and blue to yellow) color data. Eleven samples were randomly selected to be used to construct prediction models and the remaining ten samples were set aside for cross validation. The root mean squared error (RMSE) was calculated to determine each model's prediction error. The data from the eleven soil samples were used to develop the natural log of SOC (lnSOC) and TN (lnTN) prediction models using depth, L*, a*, and b* for each sample as predictor variables in regression analyses. Resulting residual plots, root mean square errors (RMSE), mean squared prediction error (MSPE) and coefficients of determination (R², adjusted R²) were used to assess model fit for each of the SOC and total N prediction models. Final models were fit using all soil samples, which included depth and color variables, for lnSOC (R² = 0.987, Adj. R² = 0.981, RMSE = 0.003, p-value < 0.001, MSPE = 0.182) and lnTN (R² = 0.980 Adj. R² = 0.972, RMSE = 0.004, p-value < 0.001, MSPE = 0.001). Additionally, final models were fit for all soil samples, which included only color variables, for lnSOC (R² = 0.959 Adj. R² = 0.949, RMSE = 0.007, p-value < 0.001, MSPE = 0.536) and lnTN (R² = 0.912 Adj. R² = 0.890, RMSE = 0.015, p-value < 0.001, MSPE = 0.001). The results suggest that soil color may be used for rapid assessment of SOC and TN in these agriculturally important soils. [ABSTRACT FROM AUTHOR]

Purpose This study investigated soil respiration ( R s ) in adjacent ecosystems with a cascade distribution in the semi-arid region of the Horqin Sandy Land (HSL) and determined the spatio-temporal distribution of R s as well as its relationship with the influencing factors. Methods Four ecosystems with a cascade distribution (i.e., cascade ecosystems) were selected from the dune–meadow area of the HSL, including sandy bare ground (SBG), a sandy Caragana microphylla community (SCC), transitional artificial Populus forest (TPF), and a meadow Phragmites communis community (MPC). In 2014 and 2015, R s , soil temperature ( T s ) and soil moisture content ( M s ) were measured every 10–15 days during the growing season, and 24-h continuous observations were carried out during the early, middle and late stages of growth. In addition, landforms, soil properties, vegetation characteristics and groundwater table depths of the cascade ecosystems were surveyed. Results The R s values of the cascade ecosystems showed significantly different seasonal variations (P < 0.05). During the growing season, the mean, coefficient of variation, and temperature sensitivity of R s were in order of SBG < SCC < TPF < MPC, which was consistent with landforms, soil properties and vegetation characteristics. Due to the differences in landforms, soil properties, vegetation characteristics and groundwater table depth, the R s values of SBG and SCC were significantly positively correlated with M s. but not with T s . TPF had the optimum M s. for R s , while the R s value of MPC was significantly negatively correlated with M s . Further, the R s values of TPF and MPC were significantly positively correlated with T s . T s and M s. together explained 49.9%, 74.8%, 79.5%, 92.1% of R s in the cascade ecosystems(SBG, SCC, TPF, MPC). At the diurnal scale, the R s values of SBG, TPF and MPC had different relationships with T s and M s. during different stages of the growing season. The R s values of SBG and TPF also had different diurnal patterns during these stages. Conclusion The critical factors that led to the spatial variation of R s in the cascade ecosystems in the study area were root biomass, vegetation cover, soil organic matter and M s . These factors also resulted in the complex relationships of R s with its influencing factors. The critical factors that led to the temporal variation of R s in the cascade ecosystems were T s , M s. and plant growth. Cascade ecosystems should be considered when estimating the terrestrial carbon balance, and caution must be taken to select the appropriate relation between R s and its influencing factors. Results of this study will contribute to the accurate estimation of terrestrial carbon emissions and our understanding of the carbon cycle process. [ABSTRACT FROM AUTHOR]

Using collars for measuring soil respiration and its component fluxes in closed chamber systems relies on two main assumptions. Firstly, it is assumed that shallow collars prevent lateral soil gas leakage beneath the chamber's walls and the underestimation of soil CO fluxes, and secondly, the insertion of deeper collars excises all living roots and the autotrophic flux is eliminated. It was hypothesised that previous findings on collar insertion impacts on autotrophic and total soil respiration also apply to afforested peatlands. In these ecosystems, a large fraction of fine roots grow close to the soil surface. Therefore, the use of shallow collars may sever some fine roots and hyphae of mycorrhizal fungi, and therefore, it may lead to underestimation of total soil respiration. It was also hypothesised that this underestimation may be greater than a possible CO leakage from lateral diffusion of soil gas as a result of not using collars. In this study, we measured soil CO efflux in a Sitka spruce and a lodgepole pine plantation on blanket peat in southern Ireland. A surface collar (not inserted into the ground) and six insertion depths (5, 10, 15, 25, 35 and 45 cm) were established to assess the effect of the collar insertion depth on autotrophic and total soil respiration. The insertion depth of 5 cm reduced total soil respiration by 47 and 32% in the spruce and pine stands, respectively. Using nonlinear equations, it was estimated that a frequently used shallow insertion of 1.5 cm would have reduced this efflux by 35 and 20% in each stand, respectively. Moreover, it was demonstrated that this reduction was greater than a possible lateral soil gas leakage. These results suggest that the insertion of shallow collars should be avoided and surface collars permanently anchored in the soil should be used instead. [ABSTRACT FROM AUTHOR]

Soil heterotrophic respiration (R H ) is usually modeled using simple temperature dependence equations where the temperature sensitivity of R H could vary for different soils and climate conditions. The temperature sensitivity is expressed as a function of the base rate of heterotrophic respiration (R H − 0 ) and the respiration change rate over a 10 °C temperature shift (Q 10 ). A methodology was developed to better quantify these two parameters, and was validated using seven contrasting year-site soil respiration datasets collected in wheat fields. The data were acquired using soil respiration chambers and eddy flux towers in three mid-latitude European sites and one North American site. The first step consisted in parameterizing and initializing a semi-mechanistic process-based model then validating the prediction performance using 2/3 of the datasets. The coefficient of determinations between the predictions and the observations of daily soil respiration (R s ) was 0.71 and was 0.73 for its heterotrophic component (R H ). The second step consisted in using the daily semi-mechanistic model predictions of R H for each growing season and site to calibrate a simple empirical model describing R H response to soil temperature and water content. It was shown with the contrasting years-sites that coherent results were only obtained when a common average Q 10 value was determined prior to fit the base rate of heterotrophic respiration coefficient. Using a common Q 10 value of 2.2 provided more stable R H − 0 for each site over time. It reflected the strong relationship between the R H − 0 and the slow decomposing C in the first 30-cm soil layer. The simple empirical model, which was validated using 1/3 of the data, explained between 42% and 92% of the variability of R H over the different sites. [ABSTRACT FROM AUTHOR]

Background: An acceleration of model-data synthesis activities has leveraged many terrestrial carbon datasets, but utilization of soil respiration (R) data has not kept pace. Scope: We identify three major challenges in interpreting R data, and opportunities to utilize it more extensively and creatively: (1) When R is compared to ecosystem respiration (R) measured from EC towers, it is not uncommon to find R > R. We argue this is most likely due to difficulties in calculating R, which provides an opportunity to utilize R for EC quality control. (2) R integrates belowground heterotrophic and autotrophic activity, but many models include only an explicit heterotrophic output. Opportunities exist to use the total R flux for data assimilation and model benchmarking methods rather than less-certain partitioned fluxes. (3) R is generally measured at a very different resolution than that needed for comparison to EC or ecosystem- to global-scale models. Downscaling EC fluxes to match the scale of R, and improvement of R upscaling techniques will improve resolution challenges. Conclusions: R data can bring a range of benefits to model development, particularly with larger databases and improved data sharing protocols to make R data more robust and broadly available to the research community. [ABSTRACT FROM AUTHOR]

Aims: Soil respiration (Rs) is a major process controlling soil carbon loss in forest ecosystems. However, the underlying mechanisms leading to variation in Rs along forest successional gradients are not well understood. In this study, we investigated the effects of biotic and abiotic factors on Rs along a forest successional gradient in southeast China. Methods: We selected 16 plots stratified by forest age, ranging from 20 to 120 years. In each plot, six shallow collars and six deep collars were permanently inserted into the soil. Shallow and deep collars were used to measure Rs and heterotrophic respiration (Rh), respectively. Autotrophic soil respiration (Ra) was estimated as the difference between Rs and Rh. Litter layer respiration (RL) was calculated by subtracting soil respiration measured in collars without leaf litter layer (RNL) from Rs. Rs was measured every 2 months, and soil temperature (ST) and soil volumetric water content (SVWC) were recorded every hour for 19 months. We calculated daily Rs using an exponential model dependent on ST. Daily Rs was summed to obtain cumulative annual Rs estimates. Structural equation modelling (SEM) was applied to identify the drivers of Rs during forest succession. Important Findings: Rs showed significant differences among three successive stages and it was the highest in the young stage. Ra was higher in the young stage than in the medium stage. Cumulative annual Rs and Ra peaked in the young and old stages, respectively. Cumulative annual Rh and respiration measured from soil organic matter (RSOM) decreased, whereas RL increased with forest age. The SEM revealed that cumulative annual Rs was influenced by fine root biomass and SVWC. Our results indicated that the dominant force regulating Rs on a seasonal scale is ST; however, on a successional scale, belowground carbon emerges as the dominant influential factor. [ABSTRACT FROM AUTHOR]

This study was conducted to evaluate the effects of fertilizer application on heterotrophic soil respiration (Rh) in soil respiration (Rs) components in red pine stands. Two types of fertilizer (N3P4K1 = 113:150:37 kg_ha-1.year-1; P4K1 = 150:37 kg.ha-1.year-1) were applied manually on the forest floor for two years. Rs and Rh rates were monitored from April 2011 to March 2013. Mean Rs and Rh rates were not significantly affected by fertilizer applications. However, Rh in the second year following fertilizer application fell to 27% for N3P4K1 and 17% in P4K1 treatments, while there was an increase of 5% in the control treatments compared with the first fertilization year. The exponential relationships between Rs or Rh rates and the corresponding soil temperature were significant (Rh: R2 = 0.86-0.90; p < 0.05; Rs: R2 = 0.86-0.91; p < 0.05) in the fertilizer and control treatments. Q10 values (Rs increase per 10 .C increase in temperature) in Rs rates were lowest for the N3P4K1 treatment (3.47), followed by 3.62 for the P4K1 treatment and 3.60 in the control treatments, while Rh rates were similar among the treatments (3.59-3.64). The results demonstrate the importance of separating Rh rates from Rs rates following a compound fertilizer application. [ABSTRACT FROM AUTHOR]

The response of soil respiration (Rs) to nitrogen (N) addition is one of the uncertainties in modelling ecosystem carbon (C). We reported on a long-term nitrogen (N) addition experiment using urea (CO(NH)) fertilizer in which Rs was continuously measured after N addition during the growing season in a Chinese pine forest. Four levels of N addition, i.e. no added N (N0: 0 g N m year), low-N (N1: 5 g N m year), medium-N (N2: 10 g N m year), and high-N (N3: 15 g N m year), and three organic matter treatments, i.e. both aboveground litter and belowground root removal (LRE), only aboveground litter removal (LE), and intact soil (CK), were examined. The Rs was measured continuously for 3 days following each N addition application and was measured approximately 3-5 times during the rest of each month from July to October 2012. N addition inhibited microbial heterotrophic respiration by suppressing soil microbial biomass, but stimulated root respiration and CO release from litter decomposition by increasing either root biomass or microbial biomass. When litter and/or root were removed, the 'priming' effect of N addition on the Rs disappeared more quickly than intact soil. This is likely to provide a point of view for why Rs varies so much in response to exogenous N and also has implications for future determination of sampling interval of Rs measurement. [ABSTRACT FROM AUTHOR]

A reliable approach for the rapid and simple estimation of global microbial respiration of soils is described for determining trends in improvement or deterioration of soil quality for various environmental scenarios. Considering the initial respiratory response of microbial populations to glucose, the method quantifies CO 2 production by impedance measurements. The effect of key operational conditions on the rate of CO 2 produced was evaluated by response surface methodology. The method provides reproducible estimates of biomass (relative standard deviation < 10%) using a relatively small soil sample (5 g). The procedure consisted on pre-wetting the soil samples at 70% of field capacity for 2 h, mixing with 10 mg g − 1 glucose, incubating at 30 °C into the respirometer system and measuring substrate induced respiration (SIR) rates over 6 h. Results from soil samples under different anthropogenic perturbations showed significant ( P < 0.001) differences in CO 2 contents (mg h − 1 100 g − 1 ) produced by agricultural (3.3) and mining soils (1.3). Factor analysis revealed a strong relationship between SIR, soil pH, cation exchange capacity and electrical conductivity. The results evidence the method's capacity to discriminate different human activities using the CO 2 rate as indicator. [ABSTRACT FROM AUTHOR]

Numerous studies have documented that soil respiration and nitrogen cycling show a distinct seasonal dependence regulated by environmental factors (e.g., soil temperature and soil water content). The mechanisms controlling the seasonal dependence of these two key ecosystem processes have rarely been linked to both soil microbial community and soil environmental factors. Here, we present results on the seasonal patterns of soil respiration and gross nitrification rates in three subtropical plantations of Pinus massoniana, Castanopsis hystrix and Erythrophleum fordii over a period of 11 months. Turnover rates were measured with the Barometric Process Separation technique (BaPS). We elucidated how soil respiration and gross nitrification are controlled by the soil microbial community and by soil environmental factors. Soil respiration and gross nitrification showed strong seasonal dynamics, although no significant differences were observed among plantations. The turnover rates were the highest during the wet season and the lowest during the dry season. Microbial biomass, total phospholipid fatty acids (PLFAs), fungal PLFAs and bacterial PLFAs peaked during the dry season. Both soil respiration and gross nitrification rates were positively correlated with soil temperature and soil water content. Microbial biomass decreased with increasing turnover rates. Our findings highlight that carbon and nitrogen turnover rates were mostly controlled by soil temperature and soil water content. [ABSTRACT FROM AUTHOR]

Soil respiration (Rs) is the second largest carbon flux next to GPP between the terrestrial ecosystem (the largest organic carbon pool) and the atmosphere at a global scale. Given their critical role in the global carbon cycle, Rs measurement and modeling issues have been well reviewed in previous studies. In this paper, we briefly review advances in soil organic carbon (SOC) decomposition processes and the factors affecting Rs. We examine the spatial and temporal distribution of Rs measurements available in the literature and found that most of the measurements were conducted in North America, Europe, and East Asia, with major gaps in Africa, East Europe, North Asia, Southeast Asia, and Australia, especially in dry ecosystems. We discuss the potential problems of measuring Rs on slope soils and propose using obliquely-cut soil collars to solve the existing problems. We synthesize previous estimates of global Rs flux and find that the estimates ranged from 50 PgC/yr to 98 PgC/yr and the error associated with each estimation was also high (4 PgC/yr to 33.2 PgC/yr). Using a newly integrated database of Rs measurements and the MODIS vegetation map, we estimate that the global annual Rs flux is 94.3 PgC/yr with an estimation error of 17.9 PgC/yr at a 95% confidence level. The uneven distribution of Rs measurements limits our ability to improve the accuracy of estimation. Based on the global estimation of Rs flux, we found that Rs is highly correlated with GPP and NPP at the biome level, highlighting the role of Rs in global carbon budgets. [ABSTRACT FROM AUTHOR]

It is well known that soil microbial biomass and activity and nutrient availability following plant residue addition are influenced by residue composition. In a previous study, Marschner et al. (2015) showed that in soil amended twice with residues of different C/N, the C/N of the previous residue addition influenced nutrient release after the second amendment which can be referred to as legacy effect. In that study, the interval between residue additions was 20 days. In this study, high C/N residue (mature wheat shoots, C/N 120, H) or low C/N residue (young kikuyu shoots, C/N 22, L) were added at 10 g kg −1 on day 0 to a silt loam followed by a second amendment (at 10 g kg −1 ) on days 10, 20 or 30 with low C/N residue following high C/N residue or vice versa (HL or LH). Respiration was measured between residue additions and over 30 days after the second addition of residues. Microbial biomass C, N and P and available N and P were measured every 10 days. Cumulative respiration over 30 days after the second residue addition was higher in HL than LH and higher when the second amendment occurred 10 days after the first compared to 30 days. There were no differences in microbial biomass C, N and P and available N and P between HL and LH when the second residue was added 10 days after the first, indicating a strong legacy effect. When the second residue was added 20 or 30 days after the first, available N concentrations were lower in LH than HL, but the MBC concentration was higher in LH than HL thus a legacy effect was present for MBC, but not for available N. It can be concluded that the legacy effect on N availability is short-lived (10 days), but the C/N ratio of a previously added low C/N residue can stimulate microbial growth after addition of high C/N residue even when added 30 days before. [ABSTRACT FROM AUTHOR]

Electromagnetic Induction (EMI), a non-invasive geophysical technique, can be a useful tool to study soil distribution of physical–chemical characters that strongly influence total soil respiration. Soil respiration emission flux (FCO 2 ) was followed in an orchard (0.7 ha) with olive trees placed at irregular distances. FCO 2 was measured in four different days at 6:00 and 15:00 h. Correlations between soil respiration and soil apparent electrical conductivity (EC a ), measured by the EMI technique, were assessed. Statistically significant linear relationships were found between EC a , measured at 7 kHz, and FCO 2 (R 2 > 0.6). The strong relations found between daily FCO 2 and EC a values allowed to spatialize soil respiration rate at field scale. The EMI technique combined with the statistical software called ESAP (Electrical conductivity Sampling, Assessment, and Prediction) seemed to be a very efficient tool to choose representative soil sites within the field on where to measure FCO 2. The EMI/ESAP procedure was also compared with two soil sampling procedures, Joint Research Centre European Method (JRC-EU) and regular grid sampling, in order to estimate average soil organic carbon (SOC) value within the olive orchard. Results suggested that the above mentioned approach could be an interesting solution to reduce number of samplings and their cost reaching, in the meantime, reliable assessments of FCO 2 and SOC at field scale. [ABSTRACT FROM AUTHOR]

Rapid and accurate estimations of the heterotrophic and autotrophic components of total soil respiration (Rs) are important for calculating forest carbon budgets and for understanding carbon dynamics associated with natural and management-related disturbances. The objective of this study was to use deep (60 cm) root exclusion tubes and paired control (i.e., no root exclusion) collars to estimate heterotrophic respiration (Rh) and Rs, respectively, in three 26-year-old longleaf pine (Pinus palustris Mill.) stands in western Georgia. Root biomass was measured in root exclusion tubes and control collars after 102-104 days of incubation and fine root biomass loss from root exclusion was used to quantify root decay. Mean Rs from control collars was 3.3 micromol·CO2·m-2·s-1. Root exclusion tubes decreased Rs, providing an estimate of Rh. Mean Rh was 2.7 micromol·CO2·m-2·s-1 when uncorrected by pretreatment variation, root decay, or soil moisture compared to 2.1 micromol-·CO2·m-2·s-1 when Rh was corrected for root decay. The corresponding ratio of Rh to Rs ranged from 66% to 82%, depending on the estimation method. This study provides an estimate of Rh in longleaf pine forests, and demonstrates the potential for deep root exclusion tubes to provide relatively rapid assessments (i.e., ~40 days post-treatment) of Rh in similar forests. The range in Rh to Rs is comparable to other reports for similar temperate coniferous ecosystems. [ABSTRACT FROM AUTHOR]

Our objective was to examine the effects of inter-annual variation of precipitation on productivity of two dominant species (Chuquiraga avellanedae, an evergreen shrub, andNassella tenuis, a perennial grass) in two communities of contrasting soil degradation: a herbaceous steppe with shrubs (HSS) and a degraded shrub steppe (SS). Data were collected during two consecutive years with different annual precipitation. Aboveground productivity was determined nondestructively using a double sampling approach. The number of inflorescences per plant was recorded too. Perennial grass productivity was lower in SS than in HSS in both years, while shrub productivity was lower in SS only during the year of below average precipitation. With rising precipitation the perennial grass increased the number of inflorescences while the evergreen shrub augmented vegetative biomass. In summary, the effects of precipitation on plant productivity are community dependent; abiotic factors, such as superficial and sub-superficial soil characteristics, and biotic factors, such as leaf area index (LAI) or tussock sizes, may interact to influence the responses of species to precipitation. Our results suggest that if precipitation increased, this would favor the dominance of shrubs over grasses. [ABSTRACT FROM AUTHOR]

Soil respiration (Rs) and its biophysical controls were measured over a fixed sand dune in a desert-shrub ecosystem in northwest China in 2012 to explore the mechanisms controlling the spatial heterogeneity in Rs and to understand the plant effects on the spatial variation in Rs in different phenophases. The measurements were carried out on four slope orientations (i.e., windward, leeward, north- and south-face) and three height positions on each slope (i.e., lower, upper, and top) across the phenophases of the dominant shrub species (Artemisia ordosica). Coefficient of variation (i.e., standard deviation/mean) of Rs across the 11 microsites over our measurement period was 23.5 %. Soil respiration was highest on the leeward slope, but lowest on the windward slope. Over the measurement period, plant-related factors, rather than micro-hydrometeorological factors, effected the topographic variation in Rs. During the flowering-bearing phase, root biomass effected Rs most, explaining 72% of the total variation. During the leaf coloration-defoliation phase, soil nitrogen content effected Rs the most, explaining 56%of the total variation. Our findings highlight that spatial pattern in Rs was dependent on plant distribution over a desert sand dune, and plant-related factors largely regulated topographic variation in Rs, and such regulations varied with plant phenology. [ABSTRACT FROM AUTHOR]

Background: Our previous studies documented how soil CO efflux, one of the main carbon pathways in forest ecosystems, is affected by soil moisture and forest structure in an aseasonal tropical rainforest in Borneo, Malaysia. Aim: In this study, we clarify the effect of short-term drought treatment on the spatial variation of soil CO efflux in a forest, and to interpret the changes in soil CO efflux caused by root activities. Methods: Experimental plots (15 m radius) were established around six emergent trees and a drought treatment was conducted for three of the six plots. Soil CO efflux was measured along with environmental factors and root biomass, respiration and production in each plot. Results: Soil CO efflux at 0.5 m of the emergent trees was nearly three times higher than at 5 and 10 m away from the trees. Root respiration and biomass had no correlation with the spatial variation. Soil water content decreased by nearly 30 % during the drought treatment, although soil CO efflux was unchanged between drought and control plots. Conclusions: Our result suggests a strong spatial variation exists in soil CO efflux around emergent trees, but short-term severe drought has little effect on it. [ABSTRACT FROM AUTHOR]

Potential consequences of climate change on crop production can be studied using mechanistic crop simulation models. While a broad variety of maize simulation models exist, it is not known whether different models diverge on grain yield responses to changes in climatic factors, or whether they agree in their general trends related to phenology, growth, and yield. With the goal of analyzing the sensitivity of simulated yields to changes in temperature and atmospheric carbon dioxide concentrations [ CO2], we present the largest maize crop model intercomparison to date, including 23 different models. These models were evaluated for four locations representing a wide range of maize production conditions in the world: Lusignan (France), Ames ( USA), Rio Verde (Brazil) and Morogoro (Tanzania). While individual models differed considerably in absolute yield simulation at the four sites, an ensemble of a minimum number of models was able to simulate absolute yields accurately at the four sites even with low data for calibration, thus suggesting that using an ensemble of models has merit. Temperature increase had strong negative influence on modeled yield response of roughly −0.5 Mg ha−1 per °C. Doubling [ CO2] from 360 to 720 μmol mol−1 increased grain yield by 7.5% on average across models and the sites. That would therefore make temperature the main factor altering maize yields at the end of this century. Furthermore, there was a large uncertainty in the yield response to [ CO2] among models. Model responses to temperature and [ CO2] did not differ whether models were simulated with low calibration information or, simulated with high level of calibration information. [ABSTRACT FROM AUTHOR]

Anthropogenic activities have increased nitrogen (N) deposition by threefold to fivefold over the last century, which may considerably affect soil respiration ( Rs). Although numerous individual studies and a few meta-analyses have been conducted, it remains controversial as to how N addition affects Rs and its components [i.e., autotrophic ( Ra) and heterotrophic respiration ( Rh)]. To reconcile the difference, we conducted a comprehensive meta-analysis of 295 published studies to examine the responses of Rs and its components to N addition in terrestrial ecosystems. We also assessed variations in their responses in relation to ecosystem types, environmental conditions, and experimental duration ( DUR). Our results show that N addition significantly increased Rs by 2.0% across all biomes but decreased by 1.44% in forests and increased by 7.84% and 12.4% in grasslands and croplands, respectively ( P < 0.05). The differences may largely result from diverse responses of Ra to N addition among biomes with more stimulation of Ra in croplands and grasslands compared with no significant change in forests. Rh exhibited a similar negative response to N addition among biomes except that in croplands, tropical and boreal forests. Methods of partitioning Rs did not induce significant differences in the responses of Ra or Rh to N addition, except that Ra from root exclusion and component integration methods exhibited the opposite responses in temperate forests. The response ratios ( RR) of Rs to N addition were positively correlated with mean annual temperature ( MAT), with being more significant when MAT was less than 15 °C, but negatively with DUR. In addition, the responses of Rs and its components to N addition largely resulted from the changes in root and microbial biomass and soil C content as indicated by correlation analysis. The response patterns of Rs to N addition as revealed in this study can be benchmarks for future modeling and experimental studies. [ABSTRACT FROM AUTHOR]

Aims: The objective of this study is to determine the effect of treefall gap size on carbon and nitrogen biogeochemistry in the Northern hardwood forest. The size of the gap controls the microclimate, particularly solar radiation, soil temperature, and soil moisture, which can alter nutrient cycling. However, in Northern hardwood forests, our understanding of the relation between biogeochemistry and gap size is incomplete. Methods: Twelve natural treefall gaps ranging in size from 27 to 590 m and four control plots located under closed canopy were identified in Upper Michigan in May 2008. Concentrations of ammonium and nitrate were measured in throughfall and soil leachates; soil respiration rates were measured in soil; and nutrient pools were measured in vegetative biomass, forest floor (Oe, Oi horizons), mineral soil, and microbial biomass. Results: Gap size was positively correlated with sapling biomass density and throughfall ammonium concentration but negatively correlated with microbial biomass, endomycorrhizal biomass, and soil respiration. Gap size was unrelated to all other parameters measured. Conclusions: The results of this study suggest that in the Northern hardwood forest, vegetative recovery and a reduction in microbial biomass may limit the influence larger gaps have on nutrient cycling. [ABSTRACT FROM AUTHOR]

A range of factors has been identified that affect the temperature sensitivity (Q10 values) of the soil-to-atmosphere CO2 flux. However, the factors influencing the spatial distribution of Q10 values within warm temperate forests are poorly understood. In this study, we examined the spatial variation of Q10 values and its controlling factors in both a naturally regenerated oak forest (OF) and a pine plantation (PP). Q10 values were determined based on monthly soil respiration (RS) measurements at 35 subplots for each stand from Oct. 2008 to Oct. 2009. Large spatial variation of Q10 values was found in both OF and PP, with their respective ranges from 1.7 to 5.12 and from 2.3 to 6.21. In PP, fine root biomass (FR) (R = 0.50, P = 0.002), non-capillary porosity (NCP) (R = 0.37, P = 0.03), and the coefficients of variation of soil temperature at 5 cm depth (CV of T5) (R = −0.43, P = 0.01) well explained the spatial variance of Q10. In OF, carbon pool lability reflected by light fractionation method (LLFOC) well explained the spatial variance of Q10 (R = −0.35, P = 0.04). Regardless of forest type, LLFOC and FR correlation with the Q10 values were significant and marginally significant, respectively; suggesting a positive relationship between substrate availability and apparent Q10 values. Parameters related to gas diffusion, such as average soil water content (SWC) and NCP, negatively or positively explained the spatial variance of Q10 values. Additionally, we observed significantly higher apparent Q10 values in PP compared to OF, which might be partly attributed to the difference in soil moisture condition and diffusion ability, rather than different substrate availabilities between forests. Our results suggested that both soil chemical and physical characters contributed to the observed large Q10 value variation. [ABSTRACT FROM AUTHOR]

Multiple substrate induced respiration (MSIR) assays which assess the response of soils to carbon source amendment are effective approaches to determine catabolic diversity of soils. Many assays are based on a single short term (<6 h) time point measurement and usually limited to CO2 production only. However, repeated measurements of both CO2 and O2 simultaneously can provide additional valuable information. In this study, a MSIR assay involving eight carbon sources was applied to three hydrocarbon contaminated soils using continuous CO2 and O2 respiration measurements. Based on cumulative CO2 and O2 measurements at 4, 24 and 120 h, the soils were found to be distinct in terms of their catabolic diversity. Most noteworthy, however, was the response to the addition of maleic acid which provided strong evidence of abiotic CO2 efflux to be the overriding process, raising questions about the interpretation of CO2 only responses from organic acid addition in MSIR assays. [Copyright &y& Elsevier]

Soil respiration rates were measured monthly (from April 2007 to March 2008) under four adjacent coniferous plantation sites [Oriental spruce ( Picea orientalis L.), Austrian pine ( Pinus nigra Arnold), Turkish fir ( Abies bornmulleriana L.), and Scots pine ( Pinus sylvestris L.)] and adjacent natural Sessile oak forest ( Quercus petraea L.) in Belgrad Forest-Istanbul/Turkey. Also, soil moisture, soil temperature, and fine root biomass were determined to identify the underlying environmental variables among sites which are most likely causing differences in soil respiration. Mean annual soil moisture was determined to be between 6.3 % and 8.1 %, and mean annual temperature ranged from 13.0°C to 14.2°C under all species. Mean annual fine root biomass changed between 368.09 g/m and 883.71 g/m indicating significant differences among species. Except May 2007, monthly soil respiration rates show significantly difference among species. However, focusing on tree species, differences of mean annual respiration rates did not differ significantly. Mean annual soil respiration ranged from 0.56 to 1.09 g C/m/day. The highest rates of soil respiration reached on autumn months and the lowest rates were determined on summer season. Soil temperature, soil moisture, and fine root biomass explain mean annual soil respiration rates at the highest under Austrian pine ( R = 0.562) and the lowest ( R = 0.223) under Turkish fir. [ABSTRACT FROM AUTHOR]

Highly sensitive Raman gas spectroscopy is introduced for simultaneous real time analysis of O2, CO2, CH4, and N2 in order to elucidate the dynamics of greenhouse gases evolving from climate-sensitive ecosystems. The concentrations and fluxes of this suite of biogenic gases were quantified in the head space of a water-saturated, raised peat bog ecotron. The intact peat bog, exhibiting various degradation stages of peat and sphagnum moss, was exposed to various light regimes in order to determine important ecosystem parameters such as the maximum photosynthesis rate of the sphagnum as well as the extent of soil and plant respiration. Miniaturized Raman gas spectroscopy was proven to be an extremely versatile analytical technique that allows for onsite multigas analysis in high temporal resolution. Therefore it is an urgently needed tool for elucidation of complex biochemical processes especially in climate-sensitive ecosystems and consequently for the estimation of climate-relevant gas budgets. [ABSTRACT FROM AUTHOR]

ABSTRACT In a tropical deciduous forest in northern Thailand, an area affected by the Asian monsoon, we made soil respiration measurements for 4 years to determine their inter-annual variability. We also made continuous measurements of soil moisture, soil temperature, and soil CO2 concentration. Annual soil respiration rates were estimated using two methods: multiple regression analysis and Fick's first law of diffusion. During the study period, between June 2000 and December 2004, the annual rainfall and the length of the wet period showed considerable year-to-year variation, differing by 1162-1435 mm year−1 falling over 146-189 days, respectively. In response to the inter-annual variability in rainfall, annual soil respiration rates estimated by the two models also showed large inter-annual variations for the 4 years (coefficient of variation = 14-17%). The range in the inter-annual variation for soil respiration was comparable with values for net ecosystem exchange reported in other Southeast Asian tropical forests. Historical rainfall records at this site showed further large inter-annual variations that occurred in times other than in the study period, suggesting that long-term monitoring would be required for a better understanding of the C balance at this site. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The main objective of this study was the evaluation of the impact of different sources of organic waste (used as an N source) on soil quality (as measured by CO2 release) and N transformation processes (available inorganic N forms) in a short-term field study of an almond tree plantation. Three compost types were used as organic fertilisers: EC compost constituted from organic agriculture farm (vegetables and manure), SC compost formed from sewage sludge and pruning waste composted, and XC compost comprised a mixture of composted sewage sludge plus slurry and manure from an intensive pig farm. The two compost doses were compared according to N content, and a high dose (H), corresponding to 210 kg N ha−1, and a low dose (L), equivalent to 105 kg N ha−1, were used. In addition, an N rate corresponding to 130 kg N ha−1, which resulted from the supplementation of NPK mineral fertiliser with compost application at a low dose (mixed fertilisation), was compared in a parallel study. Generally, almost all organically treated soils demonstrated an improvement in the levels of C, N and P, compared to controls (unfertilised soils). In addition, the nitrate content increased, predominating over ammonium content, with the highest values in the soils with the low dose application of SC. Furthermore, soil respiration improved in organically treated soils, which showed different responses according to the organic-exogenous source of the incorporated matter. In contrast, a mineral supplement promoted a decrease in biological activity and resulted in lower CO2 production in soils with XC and mineral fertiliser. Contrary to the organically treated soil, in soils with mix fertilisation the NH4 +–N was the primary available form of nitrogen. However, the application of SC plus mineral fertiliser to soil caused a positive effect on CO2 emissions compared to the control soil. Soil respiration behaviour was closely related to the form of inorganic N available in the soils due to the fertilisation practice type (organic or mixed), where both parameters seemed to depend on the mobilisations of cations (Na+ and Ca2+) to the soil solution. [Copyright &y& Elsevier]

Carbon storage (carbon density; kg C m2), concentrations of dissolved organic carbon (DOC) in soil pore water and soil respiration (g C m2 yr−1) were measured in a 35 year old urban lawn soil amended with a surface mulch application of green waste compost and compared to those in two newly created urban soils, manufactured by mixing different volumes of green waste compost with existing soils or soil forming materials. The aim was to determine C storage and calculate annual fluxes in two newly created urban soils compared to an existing urban soil, to establish the potential for maintaining and building carbon storage. In the lawn soil, organic carbon storage was largely limited to the upper 15cm of the soil, with material below 30cm consisting of substantial amounts of alkaline building debris augmenting sandstone parent material. Leaching of DOC directly from the surface applied compost mulch amendment was readily mobile within the upper 15cm of soil beneath, but not to 30cm depth, indicating limited vertical redistribution of the soluble organic C fraction to the deeper, technic horizons. Only a very small proportion of annual C losses were attributable to DOC export (≤0.5%) whilst a much greater amount was accounted for by soil respiration (∼20%). In the two newly created urban soils, ≤30% additions of compost mixed with existing soil forming materials trebled C densities from <2 to 6kg total carbon (TC) m2, surpassing those of the existing lawn soil (≤5kg TC m2). Adding 45% compost served only to reduce bulk density so that C densities did not increase further until >50% compost was applied. Combined increases in soil respiration losses and DOC leaching associated with higher compost application rates suggested that volumes of ∼30% compost were altogether optimal for sustainable C storage whilst minimising annual losses. Thus repeated applications of small amounts, rather than single applications of large amounts of green waste compost could be most effective at maintaining and building C storage in urban soils. [Copyright &y& Elsevier]

Microbial activity plays an important role in regulating soil fertility. Microbiological processes in soil have been measured using several parameters, such as microbial biomass, respiration, and enzymatic activities. Enzyme activity is essential in both mineralisation and transformation of organic C and plant nutrients. The aim of this study was to investigate dynamics of the number of microorganisms and dehydrogenase activity in the rhizosphere of maize in long-term monoculture. The study was conducted in the multi-year stationary field experiment at the Institute of Field and Vegetable Crops, Novi Sad at Rimski Šančevi. The study treatments were: control variant - maize in monoculture without fertilizer or organic fertilizers; NPK - maize in monoculture, fertilized only with mineral fertilizers; NPK + manure - maize grown in monoculture, with application of manure and mineral fertilizers; NPK + crop residue - maize grown in monoculture, with plowing crop residues (maize) and the application of mineral fertilizers. Soil samples were taken for microbiological analyses at two dates. The number of microorganisms was determined by the dilution method on agarized selective medium. Total number of microorganisms was determined by the dilution method on agarized soil extract and number of ammonifiers on MPA medium. Nitrogen-free medium was used for determination of free N-fixing bacteria and the method of fertile drops for Azotobacter. Actinomycetes were determined on a synthetic medium and the number of fungi on Czapek-Dox medium. The number of P-mobilizing bacteria was done in glucoseasparagine agar and the number of cellulolytic microorganisms in Waksman-Carey medium. Dehydrogenase activity was determined spectrophotometrically. The highest number of azotobacter and fungi was obtained on variant NPK. The highest number of cellulolytic bacteria and actinomycetes was on variant manure + NPK and crop residue + NPK on first date of sampling. On second date of sampling we obtained higher total number of microorganisms, number of azotobacter, amonifiers and fungi. The dehydrogenase activity was higher at the second date of sampling, too, which is in correlation with increase number of most examined groups of microorganisms. [ABSTRACT FROM AUTHOR]

The article discusses a study on effects of age of soil organic matter and soil respiration on belowground radiocarbon constraints. It states that radiocarbonic data from soil organic matter can be sude for analyzing magnitude and timing of soil carbon response to global change, and mentions use of data from well-drained soil and tropical forest in the study. It notes findings inferring contribution from decomposition of organic matter in soil respiration.

A correction to the article "The value of soil respiration measurements for interpreting and modeling terrestrial carbon cycling" that was published in the December 30, 2016 issue is presented.

Soil respiration is an important indicator of soil biological activity. Respiration rate can be influenced by soil temparature, moisture conditions, plant root densities and activities, soil organism population levels, soil physical and chemical properties, etc. The results obtained by measuring soil respiration evaporation on 10 soybean varieties in flowering phenophase shows significant differences for 8 of the 10 species considered in the study. [ABSTRACT FROM AUTHOR]

It will help understand the representation legality of soil temperature to explore the correlations of soil respiration with variant properties of soil temperature. Soil temperature at 10 cm depth was hourly logged through twelve months. Basing on the measured soil temperature, soil respiration at different temporal scales were calculated using empirical functions for temperate forests. On monthly scale, soil respiration significantly correlated with maximum, minimum, mean and accumulated effective soil temperatures. Annual soil respiration varied from 409 g C m−2 in coniferous forest to 570 g C m−2 in mixed forest and to 692 g C m−2 in broadleaved forest, and was markedly explained by mean soil temperatures of the warmest day, July and summer, separately. These three soil temperatures reflected the maximum values on diurnal, monthly and annual scales. In accordance with their higher temperatures, summer soil respiration accounted for 51% of annual soil respiration across forest types, and broadleaved forest also had higher soil organic carbon content (SOC) and soil microbial biomass carbon content (SMBC), but a lower contribution of SMBC to SOC. This added proof to the findings that maximum soil temperature may accelerate the transformation of SOC to CO2-C via stimulating activities of soil microorganisms. [ABSTRACT FROM AUTHOR]