Soil CO2 Concentration Research Articles

Subsoiling reduces CO2 concentrations in soil profile of winter wheat – summer maize rotation ecosystem in the North China Plain: a strategy to achieve carbon neutrality in farmland

ABSTRACT Reducing CO2 emissions from agricultural soils is a key component of the overall carbon reduction strategy. The closed chamber method was used to continuously monitor CO2 concentration in soil profiles of winter wheat-summer maize rotation fields in the North China Plain (NCP) during 2015–2017. Additionally, we evaluated the contribution of different tillage methods (Rotary tillage (RT), Subsoiling (SS), No- tillage (ZT), and conventional tillage (CT) in combination with Straw return (s) and straw removal (0)) to reducing soil CO2 emission. The results showed that the concentration of CO2 increased with the soil depth and peaked at the 150 cm layer. The trend of CO2 concentration in soil profiles under different tillage treatments was CTS > RTS > ZTS > SSS, and the average concentration in maize season was higher than that in wheat season. In addition, soil moisture and temperature in the 0–10 cm soil layer were significantly correlated with soil CO2 concentrations. Thus, our results highlight that the SSs plays a critical role in moderating soil CO2 emissions. This process merits further study to effectively regulate soil CO2 release and achieve carbon neutrality with less carbon emissions in farmland ecosystems.

Soil Moisture Assimilation Improves Terrestrial Biosphere Model GPP Responses to Sub-Annual Drought at Continental Scale

Due to the substantial gross exchange fluxes with the atmosphere, the terrestrial carbon cycle plays a significant role in the global carbon budget. Drought commonly affects terrestrial carbon absorption negatively. Terrestrial biosphere models exhibit significant uncertainties in capturing the carbon flux response to drought, which have an impact on estimates of the global carbon budget. Through plant physiological processes, soil moisture tightly regulates the carbon cycle in the environment. Therefore, accurate observations of soil moisture may enhance the modeling of carbon fluxes in a model–data fusion framework. We employ the Carbon Cycle Data Assimilation System (CCDAS) to assimilate 36-year satellite-derived surface soil moisture observations in combination with flask samples of atmospheric CO2 concentrations. We find that, compared to the default model, the performance of optimized net ecosystem productivity (NEP) and gross primary productivity (GPP) has increased with the RMSEs reduced by 1.62 gC/m2/month and 10.84 gC/m2/month, which indicates the added value of the ESA-CCI soil moisture observations as a constraint on the terrestrial carbon cycle. Additionally, the combination of soil moisture and CO2 concentration in this study improves the representation of inter-annual variability of terrestrial carbon fluxes as well as the atmospheric CO2 growth rate. We thereby investigate the ability of the optimized GPP in responding to drought by comparing continentally aggregated GPP with the drought index. The assimilation of surface soil moisture has been shown to efficiently capture the influences of the sub-annual (≤9 months drought durations) and large-scale (e.g., regional to continental scales) droughts on GPP. This study highlights the significant potential of satellite soil moisture for constraining inter-annual models of the terrestrial biosphere’s carbon cycle and for illustrating how GPP responds to drought at a continental scale.

岩溶区不同土地利用方式下土壤CO2排放模拟研究

PDF HTML阅读 XML下载 导出引用 引用提醒 岩溶区不同土地利用方式下土壤CO2排放模拟研究 DOI: 10.5846/stxb202111223290 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（42072278，42177248）；贵州省科技计划项目（黔科合支撑[2020]4Y013号） Simulation experiment on soil CO2 emission by different land uses in karst area Author: Affiliation: Fund Project: The national natural science foundation of China(42072278,42177248); Guizhou Science and Technology Supporting Plan (No. 2020-4Y013) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土地利用变化作为全球气候变化研究的重要内容之一，对土壤CO2的排放具有重要影响。岩溶区石漠化治理过程中植被恢复伴随着土地利用方式的转变，其对土壤CO2排放的影响有待进一步研究。基于控制性实验，以土壤、岩溶含水介质初始条件相同，仅土地利用方式不同的贵州普定沙湾模拟试验场为研究对象，通过1年的土壤CO2浓度和通量数据，研究岩溶区不同土地利用方式下土壤CO2的排放规律及其影响因素。结果表明：（1）土壤CO2的浓度和通量具有明显的季节变化规律，不同季节下的土壤CO2通量呈现昼夜变化规律，温度和降雨影响着土壤CO2的排放，前者可促进排放量，后者可抑制排放量，且不同土地利用方式受影响的程度不同；（2）耕作活动也会影响土壤CO2的排放，耕作使得土壤变得松散，加上岩溶区下伏基岩的溶蚀作用，增加了土壤CO2向含水层的扩散，导致春季耕地表现为负通量；（3）不同土地利用方式下土壤CO2的年排放量不同，具体为草地（897.53 tC km-2 a-1）>灌木地（258.15 tC km-2 a-1）>耕地（207.66 tC km-2 a-1）>裸土地（92.68 tC km-2 a-1），究其原因，主要受不同土地利用下植被生物量和土壤有机碳含量的影响；（4）不同土地利用下的土壤有机碳含量为草地（29.33 g/kg）>灌木地（23.31 g/kg）>耕地（22.08 g/kg）>裸土地（19.00 g/kg），鉴于这些土壤的初始性质相同，研究发现随着土地利用方式的改变，除无植被的裸土地土壤有机碳含量减小外，其余有植被的类型均有增加，且增加的程度和植被覆盖的程度有关。综上，不同土地利用类型可以通过影响上覆植被的生物量和土壤有机碳含量，进而控制土壤CO2的排放，而排放强弱与温度、降雨和耕作活动有关，可以通过土地利用方式的调整来增加土壤有机质含量和土壤储碳。 Abstract:As one of the important parts of global climate change research, land use change plays a significant role in soil CO2 emission. In karst area, vegetation has been restored in the process of rocky desertification control, accompanied by the change of land use, and its impact on soil CO2 emission needs to be further clarified. Based on the controlled experiment, with the same initial conditions of soil and karst aqueous media but different land uses, the Shawan Test Site at Puding, Guizhou was chosen to study the emission law and influencing factors of soil CO2. Through the soil CO2 concentration and flux data in a hydrological year, our results demonstrated that:(1) the soil CO2 concentration and flux showed obviously seasonal variations, and the soil CO2 flux had apparent diurnal variation in different seasons. They were mainly controlled by temperature and rainfall. The former could increase the emission, while the latter could decrease the emission, and the increased or decreased degrees were related to land uses. (2) Farming activities affected the soil CO2 emission as well. Due to the dissolution of the underlying carbonate rock in karst area, farming activities could make the soil loose and increase the diffusion of soil CO2 to the aquifer, resulting in negative soil CO2 flux of cultivated land in spring. (3) The annual emission of soil CO2 under different land uses were grassland (897.53 tC km-2 a-1) > shrub land (258.15 tC km-2 a-1) > cultivated land (207.66 tC km-2 a-1) > bare soil land (92.68 tC km-2 a-1). It was found that they were mainly dominated by vegetation biomass and soil organic carbon content under different land uses. (4) The contents of soil organic carbon were grassland (29.33 g/kg) > shrub land (23.31 g/kg) > cultivated land (22.08 g/kg) > bare soil land (19.00 g/kg). Given the same initial properties of these soils, we found that with the change of land use, except for the soil organic carbon content in non-vegetated bare soil land decreased, the other types increased, and the increased degree was related to the degree of vegetation coverage. Therefore, land use types could control soil CO2 emission by affecting the biomass of overlying vegetation and the soil organic carbon content, and the emission intensity is related to temperature, rainfall process and farming activities. Further, we think that the content of soil organic matter and soil carbon storage could be increased through the adjustment of land use. 参考文献 相似文献 引证文献

Impacts of thinning activities on boreal peatland forests

Boreal peatland forests are an important source of timber. Recently, timber harvesting has been extended to warmer months, resulting in machinery traffic over unfrozen soils, and leading to higher levels of soil disturbance, such as deeper ruts. Despite this, our knowledge of the impact of soil disturbance on peat physical properties and soil biochemistry is still limited. To address this gap, I conducted a study to examine the effects of soil disturbance caused by harvesting machinery during thinning operations on the soil physical, chemical, and biological properties and vegetation of drained boreal peatland forests. To assess the rate of recovery, I sampled six sites that formed a chronosequence covering 15 years since thinning. The results showed that soil disturbance caused an increase in the bulk density and field capacity of peat, along with a decrease in total porosity. In the vegetation, moss biomass and root production were reduced, but sedge cover increased. Furthermore, recently disturbed areas exhibited greater soil CO2 production potential, as well as higher soil CO2 and CH4 concentrations compared to control areas. However, CO2 and CH4 emissions, microbial communities, and cellulose decomposition rate were not impacted. Although the rate of recovery varied, all studied properties impacted by disturbance were fully recovered within 15 years. As the water retention characteristic (WRC) describes soil structure and its alterations, it a useful for disturbance assessment. Thus, I propose how WRC can be predicted using artificial neural networks. Overall, the study demonstrated that while drained boreal peatlands are sensitive to disturbance, they are also resilient to mechanical soil disturbance caused by thinnings.

Soil CO2 Concentration and Efflux in Pine Forest Plantation Region in South Korea

Soil CO2 Concentration and Efflux in Pine Forest Plantation Region in South Korea

Black Plastic Film Mulching Increases Soil Nitrous Oxide Emissions in Arid Potato Fields

Black plastic film mulching is a common practice for potato production in the arid area of Northwest China. Many studies have reported the significant positive effect of black plastic film mulch on potato harvest, while the effect of black plastic film mulch treatment on soil nitrous oxide (N2O) emissions is still unclear. As a consequence, this study aimed to examine the effect of black plastic film mulch treatment on N2O emission from arid upland potato fields. With the static chamber-gas chromatography method, soil N2O emissions were measured. The results showed that black plastic film mulching treatment significantly increased cumulative soil N2O emissions by 21-26% compared with non-mulched treatment. Cumulative N2O emission positively correlated with soil temperature, soil moisture, soil CO2 concentration, and amoA-AOB abundance. This study indicated that black plastic film mulching, mainly through increasing soil temperature and soil moisture, increasing soil carbon dioxide (CO2) concentration, and promoting the abundance of nitrification-related functional gene of amoA-AOB, regulated N2O emissions. This study also highlighted that the specific soil environment under black plastic film mulch is conducive to N2O emissions and lay the foundation for settling the contradiction between food production and greenhouse gas mitigation in upland soils. The negative effects of black plastic film mulching on the environment should be considered in future applications in food production.

Positive response of nitrite-dependent anaerobic methane oxidation to both gradual and abrupt increases of atmospheric CO2 concentration in paddy soils

The global ongoing increase in the atmospheric CO2 concentration is a gradual rather than an abrupt process. Although the abrupt increase in atmospheric CO2 concentration has been reported to greatly affect nitrite-dependent anaerobic methane oxidation (n-damo), the effect of a gradual increase in atmospheric CO2 concentration on n-damo remains unclear. To better evaluate the role of n-damo in paddy soils, this study investigated the responses of n-damo to different CO2 treatments: the ambient CO2 concentration (CK), a gradual increase (GI), and an abrupt increase (AI) in the CO2 concentration across different growth periods and soil depths. The 13CH4 stable isotope and quantitative PCR results revealed that compared to the CK, GI and AI significantly increased the activity of n-damo by 91.6 % and 90.0 % (p < 0.05), respectively, and also significantly increased the abundance of Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria by 67.7 % and 98.6 % (p < 0.05), respectively. Although there was no significant variation between GI and AI. In addition, the activity and abundance differed significantly between growth period and soil depth. The high-throughput sequencing results showed that GI and AI had little effect on bacterial community, while the soil depth had a significant impact on bacterial community. The changes in several soil physiochemical factors (e.g., the contents of soil water, organic carbon, and inorganic nitrogen) had important impacts on n-damo activity and the bacterial community structure. Overall, the results indicate a positive and similar response of n-damo to both gradual and abrupt increases in the atmospheric CO2 concentration in paddy soils.

Dynamic characteristics of near-surface spontaneous combustion gas flux and its response to meteorological and soil factors in coal fire area

Accurate identification of the early stages of coal-fire combustion is important for effectively controlling the spread of coal fires. CO2 and CO, as characteristic gases in the early stage of coal fire combustion, can be effectively monitored by in-situ monitoring near the surface. However, in the previous in-situ monitoring methods, the influence of surface meteorological and soil factors on the release law of characteristic gases is often ignored. Therefore, this paper considers the complexity of the geological conditions in the coal fire area, a system, and equipment for obtaining the near-surface CO2 and CO variation laws in the early stage of coal fire combustion proposed by the concentration gradient method (CGM). The system and equipment realize the simultaneous online coupling of multi-area and multi-parameter data and conduct field investigations on the Wuda coal fire area. The results show that in the early stage of coal combustion, the change patterns of CO2 and CO concentrations in different regions are anomalous, and the CO2 concentration was higher than the CO concentration. The CO2 and CO concentrations in shallow soil increased with the increase of soil depth, and compared with other areas, the CO2 and CO concentration was the highest. The shallow soil and CO2 were identified as the key areas and characteristic gases for identifying the early stage of coal-fire combustion. The CO2 flux (CF) of different shallow soil depths decreased with increased soil layer depth. Variation of soil-surface CO2 flux (S-SCF) estimated by flux extrapolation method (FLEM). The change of S-SCF is controlled by meteorological and soil factors, and there is a certain connection between it and the “respiration phenomenon” in the fissure area. Thus, this study provides a theoretical basis for effectively identifying the early stages of coal-fire combustion.

Study of carbon dioxide (co2) concentration distribution in the soil on mixed vegetation area land cover at specific sites of jonggrangan karst zone

Karstification and soil physical factor in the soil at Jonggrangan Karst zone induces carbon dioxide (CO2) concentration dynamics. This research aimed to measuring soil CO2 concentration varieties on mixed vegetation area at specific sites of Jonggrangan Karst zone and analyze the relation among soil physical factors with CO2 concentration. The data were collected between the dry season and rainy season, as well as in different of soil depths at 20 cm, 40 cm, and 60 cm. The data was performed and explained graphically, comparatively, and built upon statistic descriptive. The result shows that the soil moisture has strong relation to CO2 concentration and shows a proportional trend vertically. The soil organic matter shows an inversely trend to CO2 concentration. The increase in CO2 concentration happens during the rainy season and is influenced by land cultivation.

Tree organ growth and carbon allocation dynamics impact the magnitude and δ13C signal of stem and soil CO2 fluxes.

Incomplete knowledge of carbon (C) allocation dynamics in trees hinders accurate modeling and future predictions of tree growth. We studied C allocation dynamics in a mature Pinus sylvestris L. dominated forest with a novel analytical approach, allowing the first comparison of: (i) magnitude and δ13C of shoot, stem and soil CO2 fluxes (Ashoot, Rstem and Rsoil), (ii) concentration and δ13C of compound-specific and/or bulk non-structural carbohydrates (NSCs) in phloem and roots and (iii) growth of stem and fine roots. Results showed a significant effect of phloem NSC concentrations on tracheid growth, and both variables significantly impacted Rstem. Also, concentrations of root NSCs, especially starch, had a significant effect on fine root growth, although no effect of root NSC concentrations or root growth was detected on Rsoil. Time series analysis between δ13C of Ashoot and δ13C of Rstem or δ13C of Rsoil revealed strengthened C allocation to stem or roots under high C demands. Furthermore, we detected a significant correlation between δ13C of Rstem and δ13C of phloem sucrose and glucose, but not for starch or water-soluble carbohydrates. Our results indicate the need to include C allocation dynamics into tree growth models. We recommend using compound-specific concentration and δ13C analysis to reveal C allocation processes that may not be detected by the conventional approach that utilizes bulk organic matter.

Nitrogen addition increases CO2, CH4, and N2O concentrations of topsoils and subsoils in a subtropical Moso bamboo forest

Forest soils play a vital role in regulating the balance between the production and consumption of global soil greenhouse gases (GHGs), such as CO2, CH4, and N2O. However, the effect of N addition on GHGs concentrations at different soil depths in subtropical forests has never been elucidated. We conducted a two-year field study to investigate the effects of different N addition rates (0, 30, 60, and 90 kg N ha−1 year−1, defined as Control, N30, N60, and N90) on CO2, CH4, and N2O concentrations in the topsoil (0–20 cm) and subsoil (20–40 cm) in a subtropical Moso bamboo (Phyllostachys edulis) forest. Soil CO2 and N2O concentrations increased with soil depth and showed patterns of seasonal variation, being higher in summer and lower in winter. Soil CH4 concentrations declined with soil depth and showed erratic patterns of seasonal variations. N addition significantly increased the annual topsoil concentrations of CO2 (23.2–81.5%), CH4 (28.1–93.8%), and N2O (52.1–210.9%) and the annual subsoil concentrations of CO2 (21.5–74.2%), CH4 (36.8–109.2%), and N2O (54.5–249.2%), but did not change the seasonal patterns of the three GHGs. The CO2 concentration of the topsoil was more responsive to N addition than that of the subsoil, whereas the CH4 and N2O concentrations showed the opposite response pattern. Soil CO2 concentration was significantly and positively correlated with soil temperature and volumetric water content (VWC). Soil CH4 concentration was significantly negatively correlated with soil pH. Soil N2O concentration was significantly positively correlated with soil temperature, VWC, and soil total nitrogen. These findings indicate that N addition increased CO2, CH4, and N2O concentrations at different soil depths in Moso bamboo forests. These results contribute to a better understanding of GHG fluxes from forest ecosystem, and their responses to the increasing atmospheric N deposition.

Effects of plastic mulching on soil CO2 efflux in a cotton field in northwestern China

In Northwestern China, more and more traditional cultivation system (TC) with no mulching and flood irrigation have been replaced by modern cultivation technology (MC) combining plastic film mulching with drip irrigation. Does plastic film mulching increase or reduce soil CO2 emission in arid areas? In order to study the effects of plastic mulching on soil CO2 efflux, a field study was conducted to compare soil CO2 concentration, soil CO2 efflux, soil temperature and moisture between the TC treatment and the MC treatment during a cotton growing season in Northwestern China. The seasonal patterns of soil profile temperature and soil moisture in the TC treatment were similar to that in the MC treatment. The mean value of soil profile temperature in the MC treatment was higher than that in the TC treatment. Except for soil moisture at 15 cm depth, the mean value of soil moisture at 5 cm and 10 cm depths in the MC treatment was higher than that in the TC treatment. The variation patterns of soil CO2 concentration and soil CO2 efflux in MC treatment were different to that in the TC treatment. Although the peak of soil CO2 concentration in the TC treatment was earlier than that in the MC treatment, the duration of soil CO2 concentration with high values in TC treatment was shorter than that in the MC treatment. Based on the model of Fick’s first diffusion law, soil surface CO2 efflux in the MC and TC treatments were determined. The surface CO2 efflux in the TC treatment calculated by Fick’s first diffusion law model was in good agreement with the value measured by chamber method. The seasonal curve of soil surface CO2 efflux in the MC treatment indicate the similar pattern with that in the TC treatment, and the rate of CO2 efflux was lower in the MC system. In the MC treatment, the seasonal variation of soil surface efflux was explained more by soil moisture than by soil temperature. However, in the TC treatment, the seasonal variation of soil surface efflux was explained more by soil temperature than by soil moisture. Over the completely experimental period, accumulated rates of soil CO2 efflux were 361 g C m−2 and 474 g C m−2 for the MC and TC system, respectively. We concluded that converting agricultural practices from traditional cultivation to the plastic mulching cultivation could reduce soil CO2 efflux by approximately 110 g C m−2 year−1 in agricultural land in arid areas of Northwestern China.

Health impact of natural gas emission at Cava dei Selci residential zone (metropolitan city of Rome, Italy)

Natural gas hazard was assessed at Cava dei Selci, a residential neighbourhood of Marino (Rome) by a joint study of gas emissions and related health problems. Here a densely urbanized zone with 4000 residents surrounds a dangerous natural gas discharge where, along the years, dozens of animals were killed by the gas. Gas originates from Colli Albani volcano and consists mostly of CO2 with ~ 1 vol% of H2S. In recent years, several gas-related accidents occurred in the urbanized zone (gas blowouts and road collapses). Some houses were evacuated because of hazardous indoor air gas concentration. Gas hazard was assessed by soil CO2 flux and concentration surveys and indoor and outdoor air CO2 and H2S concentration measurements. Open fields and house gardens release a high quantity of CO2 (32.23 tonnes * day−1). Inside most houses, CO2 air concentration exceeds 0.1 vol%, the acceptable long-term exposure range. In several houses both CO2 and H2S exceed the IDLH level (Immediately Dangerous to Life and Health). An epidemiological cohort study was carried out on the residents of two Cava dei Selci zones with high (zone A) and medium (zone B) gas hazard exposure, using the rest of Marino as reference zone. We found excess mortality and emergency room visits (ERV) related to high exposure to CO2 and H2S; in particular, an increased risk of mortality and ERV for diseases of central nervous system (HR 1.57, 95% CI 0.76–3.25 and HR 5.82, 95% CI 1.27–26.56, respectively) was found among men living in zone A.

Response of vegetation and soil biological properties to soil deformation in logging trails of drained boreal peatland forests

In the boreal region, peatland forests are a significant resource of timber. Under pressure from a growing bioeconomy and climate change, timber harvesting is increasingly occurring over unfrozen soils. This is likely to cause disturbance in the soil biogeochemistry. We studied the impact of machinery-induced soil disturbance on the vegetation, microbes, and soil biogeochemistry of drained boreal peatland forests caused by machinery traffic during thinning operations. To assess potential recovery, we sampled six sites that ranged in time since thinning from a few months to 15 years. Soil disturbance directly decreased moss biomass and led to an increase in sedge cover and a decrease in root production. Moreover, soil CO2 production potential, and soil CO2 and CH4 concentrations were greater in recently disturbed areas than in the control areas. In contrast, CO2 and CH4 emissions, microbial biomass and structure, and the decomposition rate of cellulose appeared to be uncoupled and did not show signs of impact. While the impacted properties varied in their rate of recovery, they all fully recovered within 15 years covered by our chronosequence study. Conclusively, drained boreal peatlands appeared to have high biological resilience to soil disturbance caused by forest machinery during thinning operations.

Effect of Heavy Machine Traffic on Soil CO2 Concentration and Efflux in a Pinus koraiensis Thinning Stand

Mechanized timber harvesting is cost efficient and highly productive. However, mechanized harvesting operations are often associated with several environmental problems, including soil compaction and disturbance. Soil compaction impedes air circulation between the soil and atmosphere, which in turn results in increased concentrations of CO2 within soil pores. In this study, we investigated the impact of forest machine traffic on soil conditions to determine soil CO2 efflux (Fc), and soil CO2 concentrations (Sc). Field measurements included soil bulk density (BD), soil temperature (ST), soil water content (SWC), Fc, and Sc over a 3-year period at a specific thinning operation site (Hwacheon-gun) in the Gangwon Province of Korea. To assess the soil impacts associated with machine traffic, we established four machine-treatment plots (MT) characterized by different geographical and traffic conditions. The results revealed that BD, Sc, and SWC increased significantly on the disturbed track areas (p &lt; 0.05). Furthermore, reduced soil Fc values were measured on the soil-compacted (machine disturbed) tracks in comparison with undisturbed (control) areas. Variations in BD, SWC, and Sc were significantly different among the four MT plots. Additionally, in comparison with undisturbed areas, lower Fc and higher Sc values were obtained in compacted areas with high soil temperatures.

Soil Ventilation Benefited Strawberry Growth via Microbial Communities and Nutrient Cycling Under High-Density Planting

In order to increase O2 concentration in the rhizosphere and reduce the continuous cropping obstacles under high-density cultivation, ventilation is often used to increase soil aeration. Yet, the effect of ventilation on soil microbial communities and nutrient cycling and, further, the extent to which they influence strawberry growth under greenhouse conditions are still poorly understood. Thus, four treatments—no ventilation + low planting density (LD), ventilation + LD, no ventilation + high planting density (HD), and ventilation + HD—of strawberry “Red cheeks” (Fragaria × ananassa Duch. cv. “Benihopp”) were studied in a greenhouse for 3 years. The ventilation pipe (diameter = 10 cm) was buried in the soil at a depth of 15 cm from the surface and fresh air was sent to the root zone through the pipe by a blower. Ten pipes (one pipeline in a row) were attached to a blower. Soil samples were collected using a stainless-steel corer (five-point intra-row sampling) for the nutrient and microbial analyses. The composition and structure of the soil bacterial and fungal communities were analyzed by high-throughput sequencing of the 16S and 18S rRNA genes, and functional profiles were predicted using PICRUSt and FUNGuild, respectively. The results showed that soil ventilation increased the net photosynthetic rate (Pn), transpiration rate (Tr), and water use efficiency (WUE) of strawberry plants across two growth stages [vegetative growth stage (VGS) and fruit development stage (FDS)]. Soil ventilation increased its available nutrient contents, but the available nutrient contents were reduced under the high planting density compared with low planting density. Both the O2 concentration and O2:CO2 ratio were increased by ventilation; these were positively correlated with the relative abundance of Bacilli, Gamma-proteobacteria, Blastocatella, as well as Chytridiomycota and Pezizomycetes. Conversely, ventilation decreased soil CO2 concentration and the abundance of Beta-proteobacteria and Gemmatimonadetes. The greater planting density increased the relative abundance of Acidobacteria (oligotrophic group). Ventilation altered soil temperature and pH along with carbon and nitrogen functional profiles in the VGS (more nitrogen components) and FDS (more carbon components), which benefited strawberry plant growth under high planting density. The practice of soil ventilation provides a strategy to alleviate hypoxia stress and continuous cropping obstacles for improving crop production in greenhouse settings.

Soil Carbon Dioxide Flux Partitioning in a Calcareous Watershed With Agricultural Impacts

AbstractPredicting the partitioning between aqueous and gaseous C across landscapes is difficult because many factors interact to control carbon dioxide (CO2) concentrations and removal as dissolved inorganic carbon (DIC). For example, carbonate minerals buffer soil pH and allow CO2 dissolution in porewaters, but nitrification of fertilizers may decrease pH so that carbonate weathering results in a gaseous CO2 efflux. Here, we investigate CO2 partitioning in an agricultural, first‐order, mixed‐lithology humid, temperate watershed. We quantified soil mineralogy and measured porewater chemistry, soil moisture, and soil pCO2 and pO2 as a function of depth at three hillslope positions. Variation of soil moisture along the hillslope was the dominant control on the concentration of soil CO2, but mineralogy acted as a secondary control on the partitioning of CO2 between gaseous and aqueous phases. Regression slopes of pCO2 versus pO2 in the carbonate‐bearing soils indicate a deficit of aerobically respired CO2 relative to O2 (p &lt; 0.05). Additionally, nitrification of upslope fertilizers did not lower soil pH and therefore did not cause a gaseous CO2 flux from carbonate weathering. We concluded that in the calcareous soils, up to 43% of respired C potentially dissolves and drains from the soil rather than diffusing out to the atmosphere. To explore the possible implications of the reactions we evaluated, we used databases of carbonate minerals and land uses to map types of soil degassing behaviors. Based on our maps, the partitioning of respired soil CO2 to the aqueous phase could be important in estimating ecosystem C budgets and models.

The triple oxygen isotope composition of phytoliths, a new proxy of atmospheric relative humidity: controls of soil water isotope composition, temperature, CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentration and relative humidity

Abstract. Continental atmospheric relative humidity is a major climate parameter whose variability is poorly understood by global climate models. Models' improvement relies on model–data comparisons for past periods. However, there are no truly quantitative indicators of relative humidity for the pre-instrumental period. Previous studies highlighted a quantitative relationship between the triple oxygen isotope composition of phytoliths, particularly the 17O excess of phytoliths, and atmospheric relative humidity. Here, as part of a series of calibrations, we examine the respective controls of soil water isotope composition, temperature, CO2 concentration and relative humidity on phytolith 17O excess. For that purpose, the grass species Festuca arundinacea was grown in growth chambers where these parameters were varying. The setup was designed to control the evolution of the triple oxygen isotope composition of phytoliths and all the water compartments of the soil–plant–atmosphere continuum. Different analytical techniques (cavity ring-down spectroscopy and isotope ratio mass spectrometry) were used to analyze water and silica. An inter-laboratory comparison allowed to strengthen the isotope data matching. Water and phytolith isotope compositions were compared to previous datasets obtained from growth chamber and natural tropical sites. The results show that the δ′18O value of the source water governs the starting point from which the triple oxygen isotope composition of leaf water, phytolith-forming water and phytoliths evolves. However, since the 17O excess varies little in the growth chamber and natural source waters, this has no impact on the strong relative humidity dependency of the 17O excess of phytoliths, demonstrated for the 40 %–80% relative humidity range. This relative humidity dependency is not impacted by changes in air temperature or CO2 concentration either. A relative humidity proxy equation is proposed. Each per meg of change in phytolith 17O excess reflects a change in atmospheric relative humidity of ca. 0.2 %. The ±15 per meg reproducibility on the measurement of phytolith 17O excess corresponds to a ±3.6 % precision on the reconstructed relative humidity. The low sensitivity of phytolith 17O excess to climate parameters other than relative humidity makes it particularly suitable for quantitative reconstructions of continental relative humidity changes in the past.

Identification of CO2 leakage from geological storage based on maize spectral characteristic indexes

CO2 capture and storage (CCS) is an important technical strategy to reduce global CO2 emission from heavy industries. However, the risk of CO2 leakage in CCS-related projects cannot be ignored and it is crucial to identify and monitor CO2 leakage in CCS project areas in a timely and effective manner. So here we investigate the biological characteristics (plant height, leaf length, leaf width and SPAD value) and leaf spectral characteristics of maize under soil CO2 concentration of 10, 30, and 50%, with normal soil condition as control (CK). By analysing the original spectrum and first derivative spectrum of maize leaves, spectral parameters relatively sensitive to soil CO2 stress were extracted. Further, eight composite spectral characteristic indexes that are expected to identify CO2 leakages were constructed and analyzed. Besides, the normalized pigment chlorophyll index (NPCI) and modified chlorophyll absorption in reflectance index (MCARI) were also investigated for the indication role in CO2 leakage. The results showed that maize morphological traits had a significant hysteresis effect for the indication of CO2 leakage; the SPAD value was difficult to indicate the lower concentration of soil CO2 early. But it was found that three spectral characteristic indexes REP-BEP, RGP/RRV and RGP-RRV/RGP+RRV can effectively identify CO2 leakage, and three spectral characteristic indexes (RVP-GPP, REP-BEP and MCARI) can be used for quantitative inversion of soil CO2 concentration. Especially, REP-BEP index could both indicate CO2 leakage and quantitatively inverse soil CO2 concentration. In sum, the spectral characteristic indexes of maize leaves can be used as effective indicators to quickly and effectively identify CO2 leakage and quantitatively invert the CO2 concentration in soil.

Temperature controls diel oscillation of the CO2 concentration in a desert soil

The diel dynamic of the CO2 concentration in soils in relation to temperature is not yet fully understood. Air temperature might control the soil CO2 concentration due to thermal convective venting at sites experiencing large temperature differences between the atmosphere and the soil. Therefore, the objective of this study was to determine the soil CO2 concentration and its temporal dynamic in a deep desert soil in relationship to soil and air temperature based on high frequency measurements. For this purpose, CO2 concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a coarse-textured desert soil in the North of Chile every 60 min together with precipitation and air temperature for one year. The mean CO2 concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm depth. We observed a strong diel oscillation of the CO2 concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO2 concentration and both air and soil temperature. The Rayleigh-Darcy number calculated for different times indicates that thermal convective venting of the soil occurred during the night and in the early morning. A small precipitation event (4 mm) increased the CO2 concentrations in 15, 30, and 50 cm depths for several days but did not alter the amplitude of the diel oscillation of the CO2 concentration. The diel oscillation of the CO2 concentration and the hysteretic relationship between soil CO2 concentration and air temperature were likely caused by thermal convection, leading to transport of CO2-rich air from the soil to the atmosphere at night. In conclusion, our results indicate that the soil CO2 concentration can be largely controlled by convection caused by temperature differences, and not only by diffusion. The results have important implications as they provide further evidence that thermal convective venting contributes to gas exchange at sites experiencing large temperature differences between the atmosphere and the soil, which is relevant for soil chemical reactions.