Total Soil CO2 Emissions Research Articles

Different pipe burial depths associated with subsurface drip irrigation significantly affected soil gas emissions

AbstractEfforts are needed to reduce soil greenhouse gas emissions from irrigated croplands. Thus, in this study, patterns of soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions in the root zone of tomato plants grown under subsurface drip irrigation (SDI) involving different pipe burial depths were studied, with surface drip irrigation (DI) used as a control (CK). The soil CO2 and N2O emission curves under DI and SDI with pipe burial depths of 10 and 20 cm tended to be similar. In contrast, SDI with a pipe depth of 30 cm resulted in peak CO2 and N2O emissions occurring at different times. The different pipe burial depths led to significantly different spatial distributions of soil water‐filled pore space, which indirectly affected root–soil interactions and soil gas emissions through direct effects on total tomato root fork numbers and microbial community composition. The SDI treatments involving 10‐ and 20‐cm pipe burial depths increased the number of root forks to 1.85 and 2.77 times that in the DI treatment, respectively, and increased the Shannon index of the fungal community by 11.9 and 7.29% compared with that in the DI treatment, respectively. The SDI treatment involving the 30‐cm pipe burial depth resulted in 2.22 times the number of root forks compared with that in the DI treatment; however, the Shannon index of the fungal community decreased by 13.6% compared with that in the DI treatment. As a result, the total soil CO2 emissions and total soil N2O emissions in the SDI treatment involving the 10‐cm pipe burial depth were 1.37 and 2.03 times those in the DI treatment, and those in the SDI treatment involving the 20‐cm pipe burial depth were 1.33 and 2.17 times those in the DI treatment, respectively. In the SDI treatment involving the 30‐cm pipe burial depth, the total amount of soil CO2 emissions was similar to that in the DI treatment; however, the total amount of soil N2O emissions was 28.98% lower than that in the DI treatment. Therefore, soil gas emissions can be reduced by increasing the burial depth of irrigation pipes. These results provide insights into the control of soil gas emissions in agroecosystems.

Substrate availability regulates the suppressive effects of Canada goldenrod invasion on soil respiration

AbstractInvasive alien plants not only decrease riparian vegetation diversity but also alter wetland ecosystem carbon processes, especially when they displace the original vegetation. Invasive Canada goldenrod (Solidago canadensis L.) has colonized large areas of disturbed and undisturbed land in southeastern China, yet little is known regarding how it affects soil carbon cycling. To explore the response patterns of soil respiration following S. canadensis invasion and their driving mechanisms, an observational field study and a greenhouse experiment simulating invasion were performed. In the field study, soil respiration was measured weekly from 21th July 2018 to 15th December 2018. In the greenhouse experiment, soil, autotrophic and heterotrophic respiration were measured every 1st and 15th of the month from 15th July 2019 to 15th December 2019. Soil, autotrophic and heterotrophic respiration were measured using a closed-chamber system with the deep gauze collar root exclusion method. Solidago canadensis invasion appeared to decrease the total soil CO2 emissions in both the field study and the greenhouse experiment. The suppressive effects on soil respiration may be attributed to S. canadensis invasion-induced alterations in the quality and quantity of available soil substrate, suggesting that S. canadensis invasion may impact soil carbon cycling via plant-released substrates and by competing for the soil available substrate with native plant and/or soil microbes. These results have substantial implications for estimations of the effects of invasive plants on belowground carbon dynamics and their contribution to the warming world.

Influences of temperature and moisture on abiotic and biotic soil CO2 emission from a subtropical forest

BackgroundSoil CO2 efflux is considered to mainly derive from biotic activities, while potential contribution of abiotic processes has been mostly neglected especially in productive ecosystems with highly active soil biota. We collected a subtropical forest soil to sterilize for incubation under different temperature (20 and 30 °C) and moisture regimes (30%, 60 and 90% of water holding capacity), aiming to quantify contribution of abiotic and biotic soil CO2 emission under changing environment scenarios.Main findings:Results showed that abiotic processes accounted for a considerable proportion (15.6−60.0%) of CO2 emission in such a biologically active soil under different temperature and moisture conditions, and the abiotic soil CO2 emission was very likely to derive from degradation of soil organic carbon via thermal degradation and oxidation of reactive oxygen species. Furthermore, compared with biotically driving decomposition processes, abiotic soil CO2 emission was less sensitive to changes in temperature and moisture, causing reductions in proportion of the abiotic to total soil CO2 emission as temperature and moisture increased.ConclusionsThese observations highlight that abiotic soil CO2 emission is unneglectable even in productive ecosystems with high biological activities, and different responses of the abiotic and biotic processes to environmental changes could increase the uncertainty in predicting carbon cycling.

Methane and Carbon Dioxide Flux Heterogeneity Mediated by Termite Mounds in Moist Tropical Forest Soils of Himalayan Foothills, India

Termites are dominant soil macro-fauna in tropical forests, yet remain an uncertain component of the carbon budget in many regions. We investigated CH4 and CO2 flux patterns from termite mounds and background soils of moist tropical deciduous forests in Indian lower Himalaya from April 2015 till March 2016 using static closed chamber technique. The relation between gas fluxes and soil moisture as well as temperature were examined. Termite (Odontotermes obesus) mounds were significant localized source of CH4 (0.38 ± 0.01 mg m−2 h−1) and CO2 (1837 ± 40 mg m−2 h−1) amidst CH4 consuming (– 0.028 ± 0.001 mg m−2 h−1) or lower CO2 emitting (1120 ± 19 mg m−2 h−1) background forest soils. Gas fluxes from termite mounds were seasonally bimodal (monsoon flux being highest followed by a second mild peak in winter) and diurnally variable. Soil moisture was a significant determinant of CH4 and CO2 fluxes from termite mounds, explaining more than 50% variability. In the case of background forest soils, the combined effect of soil moisture and temperature best explained CO2 and CH4 flux variation. On scaling up, termite mounds contributed negligibly (0.3%) to total soil CO2 emission while mound-mediated CH4 emission offset net soil CH4 uptake by 2.0%. Our results suggest considerable role of termite mounds in influencing source–sink capacity of forest soils. Present data are crucial in reducing error and uncertainty due to spatiotemporal variations in case of large-scale predictions. We suggest careful future land use decisions to minimize the contribution of mound-building termites to net soil CO2 and CH4 flux from this region.

Contrasting responses of soil C-acquiring enzyme activities to soil erosion and deposition

Soil C-acquiring enzymes are good indicators for the biological mechanism of soil nutrients and organic matter cycles. However, they have been used less frequently to assess the ecological stability and soil C cycle in eroding landscapes due to a lack of knowledge of the responses of C-acquiring enzyme activities to soil erosion and deposition. In the present study, a 3-year field simulation experiment was conducted to examine the variations in the activities of C-acquiring enzymes (β-1,4-xylosidase (βX), β-1,4-glucosidase (βG) and β-D-cellobiohydrolase (CBH)) from erosion-deposition plots with different slope gradients (5°, 10° and 20°) on the Loess Plateau in China (2016–2018). The activities of βX, βG and CBH were higher in the depositional plots than in the erosional plots, and those differences were enlarged with increasing slope gradients. Compared to the 5°-erosional plot, the activities of βX, βG and CBH respectively declined by 3.2–4.5%, 14.3–37.5% and 12.7–29.1% in the 10°-and 20°-erosional plots. The βX, βG and CBH activities were 2.2–18.1%, 17.3–32.1% and 14.8–86.2% higher in the 10°- and 20°-depositional plots than in the 5°-depositional plot. Moreover, the total soil CO2 emissions from the whole erosion-deposition plots decreased as slopes steepened. The displaced runoff and sediment depleted soil moisture, SOC, clay and microbial biomass in the erosional plots but enhanced these resources in the depositional plots, which can account for the changes in C-acquiring enzyme activities. The spatial distribution of enzyme activities affected soil CO2 emissions in a positive linear function. The sensitive responses of the C-acquiring enzyme activities and the controlling effects of C-acquiring enzyme activities on soil CO2 emissions during erosion and deposition processes, should be properly considered in assessing the biological mechanism for nutrition cycling in regions predominated with fragmented eroding landscapes.

Effect of biochar addition on CO2 exchange in paddy fields under water-saving irrigation in Southeast China

Biochar has been widely applied to paddy fields to improve soil fertility, crop productivity and carbon sequestration, thereby leading to variations in the CO2 exchange between the paddy fields under flooding irrigation and the atmosphere, as indicated by many previous reports. However, few relevant reports have focused on paddy fields under water-saving irrigation. This study conducted a field experiment to investigate the effects of three biochar addition rates (0, 20 and 40 t ha−1) on the CO2 exchange between paddy fields under controlled irrigation (CI, a water-saving irrigation technique) and the atmosphere in the Taihu Lake region of Southeast China. Our results showed that biochar addition increased the paddy field ecosystem respiration (Reco) and the soil respiration rate (Rs) in the CI paddy fields. And biochar application increased the total CO2 emissions and the total soil CO2 emissions, especially at a rate of 40 t ha−1. In contrast, gross primary productivity (GPP) was decreased and the net ecosystem exchange of CO2 (NEE) was increased with biochar addition. However, biochar addition at a rate of 20 t ha−1 significantly increased the total CO2 absorption and the net CO2 absorption of the CI paddy fields (p < 0.05), whereas biochar addition at a rate of 40 t ha−1 had no effect on the total CO2 absorption and decreased the total net CO2 absorption. At the same time, biochar addition significantly increased soil catalase, invertase and urease activities and contributed substantially to the increase in soil invertase activity. In addition, the soil bacterial, fungal and actinomycetal abundances were evidently increased with biochar addition, of which the soil fungal abundance showed the greatest increase. A high correlation was observed between soil catalase and invertase activities and soil microbial abundance. Reco was highly correlated with air and soil temperatures and soil enzyme activity. A significant quadratic polynomial correlation was observed between GPP and leaf area index (p < 0.01). The combination of biochar addition at a rate of 20 t ha−1 and water-saving irrigation has the potential to increase the size of the carbon sink and promote soil enzyme and microbial activities in paddy field ecosystems.

Steel slag and biochar amendments decreased CO2 emissions by altering soil chemical properties and bacterial community structure over two-year in a subtropical paddy field

Waste amendments, such as steel slag and biochar, have been reported as a strategy for improving soil fertility, crop productivity, and carbon (C) sequestration in agricultural lands. However, information regarding the subsequent effects of steel slag and biochar on C cycling and the underlying microbial mechanisms in paddy soils remains limited. Hence, this study aimed to examine the effect of these waste amendments (applied in 2015–2017) on total soil CO2 emissions, total and active soil organic C (SOC) contents, and microbial communities in the early and late seasons in a subtropical paddy field. The results showed that despite the exogenous C input from these waste amendments (steel slag, biochar and slag + biochar), they significantly (P < 0.05) decreased total CO2 emissions (e.g., by 41.9–59.6% at the early season), compared to the control soil. These amendments also significantly (P < 0.001) increased soil salinity and pH. The increased soil pH had a negative effect (r = −0.37, P < 0.05) on microbial biomass C (MBC). The biochar and slag + biochar treatments (cf. control) significantly (P < 0.001) increased SOC contents in the both seasons. The amendments altered the soil microbial community structure that associated with soil C cycling: (1) all three amendments increased the relative abundance of Agromyces and Streptomyces, which was associated with higher soil pH (cf. control); and (2) biochar and slag + biochar treatments caused a higher relative abundance of Sphingomonas, which was supported by high SOC contents under those amendments. Overall, this study demonstrated that the steel slag and biochar amendments altered microbial community composition due to changes in key soil properties, such as salinity, pH and SOC contents, with implications for increasing soil C stocks while mitigating CO2 emissions in the paddy field.

Organic carbon decomposition rates with depth and contribution of inorganic carbon to CO2emissions under a Mediterranean agroforestry system

AbstractAgroforestry systems have been much studied for their potential to store soil organic carbon (SOC). However, few data are available on their specific impact on potential SOC mineralization, especially at depth in subsoils. Moreover, many soils of the world, especially in arid and semiarid environments, also contain large stocks of soil inorganic carbon (SIC) as carbonates. Consequently, the organic carbon dynamics have been poorly investigated in these soils due to the complexity of measurements and of the processes involved. To assess mineralization rates of SOC with depth, we incubated soil samples from an 18‐year‐old agroforestry system (both tree row and alley) and an adjacent agricultural plot established on a calcareous soil in France. Soil samples were taken at four different depths: 0–10, 10–30, 70–100 and 160–180 cm. Total CO2emissions, the isotopic composition (δ13C, ‰) of the CO2and microbial biomass were measured. The SIC concentrations ranged from 48 to 63 g C kg−1soil and the SOC concentrations ranged from 4 to 17 g C kg−1soil. The contribution of SIC‐derived CO2represented about 20% in the topsoil and 60% in the subsoil of the total soil CO2emissions. The microbial biomass and the SOC‐derived CO2emissions were larger in the topsoil, but the decomposition rates (day−1) remained stable with depth, suggesting that only the size of the labile carbon pool was modified with depth. Subsoil organic carbon seems to be as prone to decomposition as surface organic carbon. No difference in CO2emissions was found between the agroforestry and the control plot, except in the tree row at 0–10 cm. Our results suggest that the measurement of soil respiration in calcareous soils could be overestimated if the isotopic signature of the CO2is not taken into account. It also advocates more in‐depth studies on carbonate dissolution–precipitation processes and their impact on CO2emissions.HighlightsWe measured SOC mineralization and inorganic carbon contribution to CO2emissions in agroforestrySubsoil organic carbon was as prone to decomposition as surface organic carbonInorganic carbon contribution to CO2emissions ranged from 20 to 60% depending on soil depthMeasurement of soil respiration in calcareous soils could be overestimated

Soil respiration in paludified forests of European Russia

Soil respiration studies in paludified forests of the European part of Russia are quite rare in comparison with those of open peat bogs, which make long-term observations in this region highly relevant. In this study, soil CO2 emissions were measured by the close chamber method in different microlandscapes of paludified forests. For four summer seasons with different environments, soil respiration ranged from 1078 to 248 mg CO2 m−2 h−1 in a paludified spruce forest site with coarse woody debris to 659–820 mg CO2 m−2 h−1 in a paludified boggy pine forest. The most intensive soil respiration was observed during the hot summer of 2013 and the lowest in the hot and humid summer of 2016. Annual total soil CO2 emissions in paludified forests in 2015–2016 were approximately 2000–3000 g CO2 m−2. During the year, the lowest CO2 emission values were observed from November to April (14–84 mg CO2 m−2 h−1) and the maximum were in July and August (522–1205 mg CO2 m−2 h−1). The contributions of CO2 emissions in the cold November–April period were 6–8.5%. The impacts of temperature on soil respiration were higher (r2 = 0.45–0.57) than those of groundwater levels (r2 = 0.17–0.49). Soil respiration in the paludified spruce forest and in the pine bog generally were higher than emissions from ecosystems with similar hydrothermal conditions in the boreal zone.

Emergy analysis, water-heat utilization, and carbon emission of typical cropping patterns in the oasis irrigation area.

Reasonable cropping pattern can improve resource utilization efficiency, reduce environmental risks in agricultural production, and achieve the goal of resource saving coupled with high production and efficiency. We evaluated the production effects of typical cropping patterns in an arid irrigation region from several aspects, including resource utilization, carbon emissions, economic benefit, emergy self-sufficiency ratio and net emergy yield ratio, with the method of emergy theory, to provide theoretical and practical basis for the establishment of efficient cropping with lower resource investment and carbon emissions but higher yield and resource utilization efficiency combined with the sustainability of agricultural production. The results showed that, high-efficient wheat-maize intercropping production pattern (integration of no tillage with 25 to 30 cm height of wheat straw covering in the wheat strip and two-year plastic mulching in the maize strip, NTSI) had the best performance in grain yield boosting, with the yields 13.5% to 16.9% and 13.8% to 17.1% higher than that in local traditional production patterns (i.e., wheat-maize intercropping, CTI, and monoculture maize, CTM), respectively. Moreover, NTSI increased water use efficiency and solar energy use efficiency by 12.4% to 17.2% and 6.1% to 8.1%, compared to CTI, respectively. Compared to CTI and CTM, NTSI improved the effect on carbon emission reduction by decreasing total soil CO2 emission by 618 to 895 kg·hm-2 and 1804 to 2002 kg·hm-2 with the ratio of 12.1% to 16.4% and 28.6% to 31.0%, but increased carbon emission efficiency by 29.3% to 40.1% and 58.9 to 71.4%, respectively. Meanwhile, the NTSI pattern had obvious resources saving potential. Compared with CTI and CTM, NTSI reduced total input by 1424 to 1431 yuan·hm-2 and 501 to 1547 yuan·hm-2, with the proportional reduction being 12.6% to 13.6% and 4.9% to 14.6%; however, increased total output by 4309 to 4603 yuan·hm-2 and 8439 to 11057 yuan·hm-2, the increased ratio was 11.2% to 11.8% and 24.4% to 36.3%; also, increased net return by 5740 to 6027 yuan·hm-2 and 9544 to 11558 yuan·hm-2, and the improved percentage was 19.6% to 22.4% and 40.1% to 57.7%, respectively. Therefore, the high-efficient NTSI pattern had greater input-output ratio by 27.9% to 29.0% and 40.5% to 45.6% than CTI and CTM, respectively, similarly, greater benefit per cubic meter of water by 19.9% to 23.2% and 27.7% to 39.3%, respectively. The emergy self-sufficiency ratio of NTSI pattern was 57.2%, being 4.0% and 12.2% higher than CTI and CTM, respectively. NTSI pattern's net emergy yield ratio was 0.173, being 10.0% greater than CTI but 11.7% lower than CTM. With respect to resource utilization, carbon emission reduction, economic benefits and the sustainable development of high-efficient intercropping pattern, the integration of no tillage with straw covering and two-year plastic film mulching measures had higher economic activity, better function of agricultural system, greater production efficiency, and higher returns on energy value. We concluded that NTSI could be a high-efficiency farming system pattern on resources saving, carbon emission reduction, high yield and efficiency in arid oasis irrigation areas.

Spatial Variability of Carbon Dioxide Emission by Soils in the Main Types of Forest Ecosystems at the Zvenigorod Biological Station of Moscow State University

Carbon dioxide (CO2) emission from the soil surface in forest biogeocenoses of the Zvenigorod Biological Station of Moscow State University in summer varies on average from 120 to 350 mg C–CO2/(m2 h) and depends on the hydrothermal conditions (soil moisture and temperature) and the type of phytocenosis. The intensity of CO2 emission in the biogeocenosis does not depend on its parcel structure and varies with respect to plant microgroups: it is maximum in oxalis pine–spruce and maple–lime forests and bracken spruce–birch forests and minimum in areas of forest fall without vegetation. The upper (from 0 to 20 cm thick) soil layer provides up to 50% of the total soil CO2 emission. The role of microbial respiration in the total CO2 emission from soils is determined by weather conditions and varies from 9–33% in a dry summer to 55–75% in a summer with favorable temperature and moisture.

Thinning but not understory removal increased heterotrophic respiration and total soil respiration in Pinus massoniana stands

Quantifying soil respiration (Rs) and its components [autotrophic respiration (Ra) and heterotrophic respiration (Rh)] in relation to forest management is vital to accurately evaluate forest carbon balance. Thus, Rs, Ra, and Rh were continuously monitored from November 2013 to November 2016 in Pinus massoniana forests subjected to four different management practices in China. We hypothesized that understory removal and thinning decrease Ra and Rh and thus Rs, and these decreases will change with time following UR and thinning. Mean values of Rs, Ra, and Rh in light thinned plots (LT=15% of tree basal area thinned) and heavily thinned plots (HT=70% of tree basal area thinned) were significantly higher than in control (CK) and understory removal plots (UR). The annual Rh/Rs ratio ranged from 58% to 70% across all treatments, and this ratio was significantly higher in HT and LT than in UR and CK. Only HT significantly increased soil temperature. Soil temperature could better explain Rh (R2=0.69–0.96) than Ra (R2=0.51–0.86). HT and LT increased Q10 for both Ra and Rh, except for Rh in UR. Soil moisture content (W; %) was significantly higher in HT than in other treatments, but W had limited effects on soil respiration in that rain-rich subtropical China. This result suggests that global warming alone, or in combination with clear-cutting or canopy tree thinning will markedly increase soil heterotrophic respiration and thus the total soil CO2 emission. To get firewood for local people and to reduce soil CO2 emissions under global warming, canopy trees are needed to be protected and understory shrubs may be allowed to be used in the subtropical China.

How winter cover crops and tillage intensities affect nitrogen availability in eggplant

This study evaluates the fate of nitrogen (N) content in winter cover crops under different tillage intensities. Field trials were conducted over a 2-year period in a Mediterranean environment adopting a cover crop–eggplant sequence. The treatments were: three cover crops (hairy vetch, oat and oilseed rape); three tillage intensities (residue left on soil surface, shallow green manure and deep green manure). The measurements included: cover crop and eggplant characteristics, N mineralization from cover crops, soil inorganic N and soil CO2 emission. At cover crop termination, N accumulated in the cover crops was 207, 77 and 77 kg N ha−1 in hairy vetch, oat and oilseed rape, respectively. Tillage intensity affected biomass decomposition and N mineralization from cover crop residues which were slower when residues were left on soil surface (54 and 71%, respectively) than when incorporated into the soil (66 and 79%, respectively). Hairy vetch showed a greater ability to supply N to eggplant (151 kg N ha−1), due to the fast decay of its residues, consequently, the N balance index was always high after hairy vetch throughout eggplant cultivation. N mineralized by cover crops was positively correlated with total soil CO2 emission and soil inorganic N. Placing cover crop residues on soil surface enhances synchronization between N mineralized and eggplant N demand in hairy vetch, while in oat it appears to mitigate the shortage of soil inorganic N for the following vegetable. These findings may also be extended to other summer vegetables which have similar requirements to the eggplant.

Can Partial Cultivation of Only The Sugarcane Row Reduce Carbon Dioxide Emissions in an Oxisol and Ultisol?

Core Ideas The use of soil management at line (alone) reduces the CO2 emission. The higher soil aggregation favorece the higher CO2 emission. The soil management at line (alone) improve the lower soil desegregation. The objective was to determine the influence of partial cultivation of only the crop row on carbon dioxide (CO2) emissions in an Oxisol and Ultisol. The experimental design was a large paired‐plot design with treatments consisting of targeted chiseling to only the planting row to chiseling the whole field. Soil CO2 emissions, soil temperature, and soil moisture were measured daily for 12 d after tillage. In the Oxisol, CO2 emissions were higher on the second day after tillage and then decreased until Day 6. When analyzing the effect of tillage, chiseling in the planting row (CPR) showed, in general, lower CO2 emissions (2.54 µmol m−2 s−1) when compared to chiseling in total area (CTA) (3.32 µmol m−2 s−1), regardless of the day after tillage. However, the linear regression analysis between soil CO2 emissions and soil moisture in the Ultisol was significant for CPR (R2 = 0.79, p &lt; 0.01) and CTA (R2 = 0.58, p &lt; 0.01). Total soil CO2 emissions were higher in the Oxisol for both tillage systems (CPR = 1020.9 kg CO2 ha−1 and CTA = 1336.3 kg CO2 ha−1) than the Ultisol (CPR = 587.0 kg CO2 ha−1 and CTA = 649.3 kg CO2 ha−1). These results indicate that soil tillage by using CPR favors a lower soil CO2 emission to the atmosphere and contributes to a reduction in soil degradation when cultivated with sugarcane (Saccharum officinarum L.).

Experimental analysis of CO2 emissions from agricultural soils subjected to five different tillage systems in Lithuania

Intensive agricultural production strongly influences the global processes that determine climate change. Thus, tillage can play a very important role in climate change. The intensity of soil carbon dioxide (CO2) emissions, which contribute to the greenhouse effect, can vary depending on the following factors: the tillage system used, meteorological conditions (which vary in different regions of the world), soil properties, plant residue characteristics and other factors. The main purpose of this research was to analyse and assess the effects of autumn tillage systems with different intensities on CO2 emissions from soils during different seasons and under the climatic conditions of Central Lithuania. The research was conducted at the Experimental Station of Aleksandras Stulginskis University from 2009 to2012; and in 2014. The soils at the experimental site were classified as Eutric Endogleyic Planosol (Drainic). The investigations were conducted using five tillage systems with different intensities, typical of the Baltic Region. Deep conventional ploughing was performed at a depth of 230–250mm, shallow ploughing was conducted at a depth of 120–150mm, deep loosening was conducted at depths of 250–270mm, and shallow loosening was conducted at depths of 120–150mm. The fifth system was a no-tillage system. Overall, autumn tillage resulted in greater CO2 emissions from the soil over both short- and long-term periods under the climatic conditions of Central Lithuania, regardless of the tillage system applied. The highest soil CO2 emissions were observed for the conventional deep ploughing tillage system, and the lowest emissions were observed for the no-tillage system. The meteorological conditions greatly influenced the CO2 emissions from the soil during the spring. Soil CO2 emissions were enhanced as precipitation and the air and soil temperatures increased. Long-term investigations regarding the dynamics of CO2 emissions from soils during the maize vegetation period indicated that autumn tillage systems affect the total soil CO2 emissions. The highest (2.17μmolm−2s−1) soil CO2 emissions during the vegetation period were observed in the deep ploughing tillage system, and the lowest values were observed (1.59μmolm−2s−1) in the no-tillage system.

Biochar suppressed the decomposition of organic carbon in a cultivated sandy loam soil: A negative priming effect

Conversion of plant residues to biochar is an attractive strategy for mitigation of atmospheric carbon dioxide (CO2) emission and enhancement of carbon (C) storage in soil. However, the effect of biochar application on the decomposition of soil organic C (SOC) as well as its mechanisms is not well understood in the sandy loam soil of North China Plain. We investigated how biochar affected the decomposition of native SOC, using stable δ13C isotope analyses by applying biochar produced from corn straw (a C4 plant, δ13C = −11.9‰) to a sandy loam soil (δ13C of SOC = −24.5‰) under a long-term C3 crop rotation. The incubation experiment included four treatments: no amendment (Control), biochar amendment (BC, 0.5% of soil mass), inorganic nitrogen (N) amendment (IN, 100 mg N kg−1) and combined biochar and N amendments (BN). Compared with Control, N amendment significantly (P < 0.05) increased total soil CO2 emission, even when combined with biochar amendment. In contrast, biochar alone amendment did not affect total soil CO2 emission significantly. However biochar, even when combined with N amendment, significantly (P < 0.05) reduced CO2 emission from native SOC by 64.9–68.8%, indicating that biochar inhibited the decomposition of native SOC and the stimulation effect of inorganic N on native SOC degradation, a negative priming effect. N addition immediately stimulated the growth of microorganisms and altered microbial community structure by increasing Gram-positive bacteria compared to Control as measured by phospholipid fatty acid. Biochar amendment did not alter microbial biomass during the 720-h incubation period except at 168 and 720 h, but significantly (P < 0.05) lowered dissolved organic C (DOC) content in soil, primarily due to sorption of DOC by the biochar. Our study suggested that biochar application could effectively reduce the decomposition of native organic C and a potential effective measure for C sequestration in the test soil of the North China Plain.

Temporal patterns of soil CO2 efflux in a temperate Korean Larch (Larix olgensis Herry.) plantation, Northeast China

There is little information available regarding seasonal and annual variations in soil CO2 efflux from Korean Larch plantations, which are an important component of forests’ carbon balance in temperate China. In this study, the soil respiration rate (R s), soil temperature (T 10) and soil moisture (SM10) at 10 cm depth were observed in a Korean Larch (Larix olgensis Herry.) plantation in Northeast China from 2008 to 2012. Mean R s in growing season (GS) varied greatly, ranged from 2.32 ± 0.08 to 3.88 ± 0.09 μmol CO2 m−2 s−1 (mean ± SE) over the period of 2008–2012. In comparison with T-model, the increase of explained variability by applying both T 10 and SM10 to the T-M model is very small. It is indicated that R s was controlled largely by T 10 in the present study. By accounting for 22.2 and 17.7 % of the total soil CO2 emissions in 2010/2011 and 2011/2012, respectively, the soil CO2 efflux in dormant season (DS) was an essential component of the total soil CO2 efflux. The Q 10 value in the study period was always smaller for GS than DS, suggesting that soil carbon cycling may be more sensitive to the temperature changes at low than at high temperature range. These results indicated that climate changes may have great potential impacts on temperate Larch plantations in Northeast China, owing to soil carbon emissions of Larch plantation during the long period of DS being more sensitive to T 10 than in GS, and played a significant role in the annual forest ecosystems carbon budget.

Responses of Soil CO2 Fluxes to Short-Term Experimental Warming in Alpine Steppe Ecosystem, Northern Tibet

Soil carbon dioxide (CO2) emission is one of the largest fluxes in the global carbon cycle. Therefore small changes in the size of this flux can have a large effect on atmospheric CO2 concentrations and potentially constitute a powerful positive feedback to the climate system. Soil CO2 fluxes in the alpine steppe ecosystem of Northern Tibet and their responses to short-term experimental warming were investigated during the growing season in 2011. The results showed that the total soil CO2 emission fluxes during the entire growing season were 55.82 and 104.31 g C m-2 for the control and warming plots, respectively. Thus, the soil CO2 emission fluxes increased 86.86% with the air temperature increasing 3.74°C. Moreover, the temperature sensitivity coefficient (Q 10) of the control and warming plots were 2.10 and 1.41, respectively. The soil temperature and soil moisture could partially explain the temporal variations of soil CO2 fluxes. The relationship between the temporal variation of soil CO2 fluxes and the soil temperature can be described by exponential equation. These results suggest that warming significantly promoted soil CO2 emission in the alpine steppe ecosystem of Northern Tibet and indicate that this alpine ecosystem is very vulnerable to climate change. In addition, soil temperature and soil moisture are the key factors that controls soil organic matter decomposition and soil CO2 emission, but temperature sensitivity significantly decreases due to the rise in temperature.

Increased CO2 emission and organic matter decomposition by leaf-cutting ant nests in a coastal environment

Leaf-cutting ants perform a vital role in the cycling of carbon and nutrients in tropical ecosystems. Nests have high levels of organic matter and refuse dumps host up to two times more soil micro-organisms than non-nest soil. The increased levels of organic matter in the soil of nests, however, can affect CO2 emissions from soil and alter the balance of atmospheric CO2. We aimed at assessing the effect of nests of the leaf-cutting ant Acromyrmex balzani on CO2 emissions in a coastal area of Northeast Brazil. Results show that A. balzani nests emitted up to four times more CO2 than the surrounding soil and emissions were positively correlated with soil moisture and soil organic matter (SOM) content. In addition, field experiments demonstrated that refuse material has a lower residence time than the leaf material brought to the colonies. Despite the high density of nests and high content of SOM compared to adjacent control soil, CO2 emissions by A. balzani nests represent only 0.3% of the total CO2 efflux by the studied ecosystem. Although these effluxes account for a relative small portion of the total soil CO2 emission, they are still important for the understanding of C balance, especially when one considers the thousands of tons of CO2 emitted each day, across entire Neotropical regions where leaf-cutting ants occur.

Estimating Root Plus Rhizosphere Contributions to Soil Respiration in Annual Croplands

Although soil respiration represents an important C transfer from terrestrial ecosystems to the atmosphere, the effects of environmental and biological factors on soil respiration rates are not adequately understood. This is due primarily to the variety of processes that produce CO2 within the soil. Thus, separating the main CO2–producing processes is needed to improve our understanding of soil C cycling and dynamics. Here, we describe and test a model that estimates soil CO2 emissions derived from anabolic and catabolic processes, representing organic matter decomposition and root + rhizosphere respiration, respectively. Our model is based on the exponential response of organic matter decomposition with respect to temperature, and it requires only measurements of total soil CO2 emissions and soil temperature as inputs. To test the model, we relied on published measurements of soil respiration rates and soil temperatures in a maize (Zea mays L.) field in Ottawa, Canada, and on independent estimations of soil and root contributions for this field made on the basis of stable‐C isotope measurements of soil‐derived CO2 Model‐based and isotope estimations correlated significantly (r2 = 0.91, P &lt; 10−9) on a daily basis. Model‐based estimations for root + rhizosphere respiration rates for the entire growing season totaled 145 g C m−2 or 27% of CO2 emissions, and those based on C isotopes totaled 158 g C m−2 or 30% of the total emissions. The excellent correspondence between model‐based and isotope‐based estimations suggests that this relatively simple model can be used to distinguish root from soil contributions to soil CO2 emissions in temperate‐zone, annual croplands free of significant water stress.