Methane consumption by montane soils: implications for positive and negative feedback with climatic change

PDF HTML阅读 XML下载 导出引用 引用提醒 太湖流域农田稻季CH4通量特征及影响因子 DOI: 10.5846/stxb201911062340 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金面上项目（41771571）；中科院南京地理与湖泊研究所前沿探索与基础性研究（NIGLAS2016QY02）；江苏省自然资源科技项目（KJXM2019007） Characteristics and impact factors of methane flux in the paddy fields of Taihu Lake Basin Author: Affiliation: Fund Project: 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:开展太湖流域农田稻季CH4排放研究，深入了解稻田CH4排放规律，为稻田CH4减排、制定合理稻田管理措施提供科学依据。以太湖流域稻麦轮作农田为研究区域，运用涡度相关法观测其稻季CH4通量变化，分析其通量变化特征及影响因子。结果表明：太湖流域典型稻麦轮作区稻季为CH4的源，CH4排放总量为28.95 g/m2，稻季CH4通量日变化表现为无规则型与单峰型两种模式；稻季CH4排放整体集中在水稻生长前期（81.61%）及中期（16.16%）、后期排放相对较弱（2.23%），返青期排放量较低（日均0.102 μmol m-2 s-1），分蘖期较强（日均0.451 μmol m-2 s-1），成熟期最低（日均0.006 μmol m-2 s-1）；模型所模拟的累计CH4排放通量比累计测量CH4通量低6.69%，较好地模拟了太湖流域稻田CH4的排放，土壤温度、土壤水分、土壤电导率、摩擦风速可确认为太湖流域农田稻季CH4排放的主要驱动因子。 Abstract:Methane emissions play a key role in global warming and climate change. The mechanism of methane emission in the paddy fields of the Taihu Lake Basin-a typical rice-wheat rotation region of China and also an area with one of the highest rates of land use change in the country-is still unclear, largely due to limited observation and the spatial heterogeneity of the environment. Eddy covariance, one of most popular approaches to observing methane flux, has many advantages, including long-term continuous observation, high frequency, and large monitoring range, without destruction of the original soil environment. We utilized the eddy covariance method to observe the methane flux in rice-wheat rotation paddy fields in the Taihu Lake Basin. The missing flux values were interpolated with the GA-BPNN model. The characteristics and influencing factors of methane flux were then analyzed, and a semi-empirical multiplicative model was built. The results showed that the rice-wheat rotation paddy fields were the main source of methane in the Taihu Lake Basin. During the observation period, the total amount of emitted methane was 28.95 g/m2, and methane flux values varied in the range of 0-0.861 μmol m-2 s-1. The diurnal variation in methane flux during the rice season appears under two modes:irregular and unimodal. In the irregular mode, methane flux was unstable throughout the day, and in the unimodal mode, the emissions during the day were significantly higher than that at night. The emission of methane in the rice season is concentrated in the early and middle stages of rice growth, relatively weak in the later stage, relatively low in the green stage (0.102 μmol m-2 s-1 per day), strong in the tillering stage (0.451 μmol m-2 s-1 per day), and lowest in the maturity stage (0.006 μmol m-2 s-1 per day). The results of the analysis of various impact factors are as follows:The methane flux in the rice season increased exponential with air temperature and soil temperature at 10/20/40 cm depth (R2=0.589, 0.584, 0.521, 0.459, P<0.0001). Methane flux increased with increasing temperature. Methane flux showed a weak exponential relationship with soil moisture at 10/20 cm depth (R2=0.362, 0.372, P<0.0001). With the rise in soil moisture, methane flux increased. Methane flux has a quadratic relationship with soil moisture at a depth of 40 cm (R2=0.378, P<0.0001). When the soil moisture is less than 0.41 m3 m-3, methane flux decreases with the increase in soil moisture, and when the soil moisture is greater than 0.41 m3 m-3, methane flux increased with the rise in soil moisture. Methane flux showed a power relationship with soil conductivity at 10/20/40 cm depth (R2=0.309, 0.54, 0.439, P<0.0001). As the soil conductivity increases, the methane flux increases. Methane flux and friction wind speed are only significantly correlated on a half-hour scale. The methane flux estimated by the model 2 is 6.69% lower than measured flux. The model 2 well simulates the methane emission from paddy fields in the Taihu Lake Basin. The main driving factors of methane emission from paddy fields in the Taihu Lake Basin include soil temperature, soil moisture, soil conductivity, and friction wind speed. 参考文献 相似文献 引证文献

Ammonia-oxidizing archaea and bacteria (AOA, AOB) catalyze the first and rate-limiting step of nitrification. To examine their differential responses to the wetting of dry and salty arid soil, AOA and AOB amoA genes (encoding subunit A of the ammonia monooxygenase) and transcripts were enumerated in dry (summer) and wet (after the first rainfall) soil under the canopy of halophytic shrubs and between the shrubs. AOA and AOB were more abundant under shrub canopies than between shrubs in both the dry and wetted soil. Soil wetting caused a significant decrease in AOB abundance under the canopy and an increase of AOA between the shrubs. The abundance of the archaeal amoA gene transcript was similar for both the wet and dry soil, and the transcript-to-gene ratios were < 1 independent of niche or water content. In contrast, the bacterial amoA transcript-to-gene ratios were between 78 and 514. The lowest ratio was in dry soil under the canopy and the highest in the soil between the shrubs. The results suggest that the AOA are more resilient to stress conditions and maintain a basic activity in arid ecosystems, while the AOB are more responsive to changes in the biotic and abiotic conditions.

Net methane (CH4) flux from coastal wetlands is an equilibrium product of methanogenesis by anerobic methanogenic microbes and methane oxidation by aerobic and anaerobic methanotrophic microbes. 75-95% of the methane produced is consumed by anaerobic methane oxidation in the deep, anoxic soil layers. Meanwhile, aerobic methane oxidation, which needs both oxygen (O2) and methane as substrates, occurs in the upper soil layer. Aerobic methanotrophy has mostly been studied in temperate grasslands. The well-aerated saltmarshes of the Wadden Sea coast might show a similar effect as such grasslands regarding methane consumption. However, this is a largely understudied process, since salt marshes are known for net methane emission rather than for net methane uptake. We hypothesize that (1) methane consumption vs. emission is driven by the oxygen concentration in the soil and is reflected in the ratio of methanotrophic vs. methanogenic microbes and (2) methane consumption occurs in the rhizosphere of salt marsh soil and in the plant tissue itself. A salt marsh plant-soil pot experiment will be conducted where S. anglica is exposed to different soil oxygen concentrations due to different hydrological conditions (5x waterlogged, 5x intermittently waterlogged, 5x drained), thereby triggering various methane dynamics. To determine methane consumption and emission, chamber measurements, using a MGGA Trace Gas Analyzer, will be performed regularly throughout the experiment. The ratio and location of methanotrophic to methanogenic microbes in the plant-soil system will be determined by quantitative polymerase chain reaction (qPCR) using pmoA189-F/pmoA661-R (methanotrophic bacteria) and mlas-F/mcrA-R (methanogenic archaea) primer pairs. Further analysis will include 16S sequencing on extracted DNA and rRNA from soil and plant tissue to differentiate between the total and the active community, respectively. Results from a pre-study show net methane consumption in the drained pots while net methane emission was measured in the waterlogged pots. We attribute this effect to upregulated methanotrophic processes under oxic conditions, resulting in a higher methane oxidation rate. First results of qPCR reveal methanotrophic bacteria in the rhizosphere and within the plant stem, while methanogenic archaea were only detected in the soil. Our results suggest a previously overlooked role of plant stem associated methanotrophic microbess in salt marshes greenhouse gas dynamics.

17β-estradiol (17β-E2), a widespread and natural estrogen in the environment, has imposed a serious threat to the safety and function of aquatic ecosystems because of worsening pollution and high potential toxicity. In the present study, the authors focus on the impact of 17β-E2 pollution on water microbial methane oxidation function. The authors investigated the mechanism of its influence on water microbial activity and discuss the growth rate of methane-oxidizing bacteria. The results showed that 17β-E2 could significantly inhibit the function of water microbial methane oxidation. When 17β-E2 concentration was ≥ 5 ng L(-1) , the methane oxidation rate increased with increasing 17β-E2 and finally settled to a constant value. Furthermore, the authors found no significant linear correlation between 17β-E2 concentrations and its methane oxidation rate. However, increasing 17β-E2 dramatically improved water microbial community activity, because a significant or highly significant promotion in the generation rate of CO2 was measured. Moreover, within a certain period of time and at certain concentrations, positive linear correlation existed between water CO2 generation rate and 17β-E2 concentrations. In addition, the growth rate of culturable methane-oxidizing bacteria was promoted when 17β-E2 pollution concentration from 2 ng L(-1) to 20 ng L(-1) . Therefore, 17β-E2 pollution can inhibit microbial methane oxidation function in water, which indirectly promotes the release of water methane and directly contributes to the rate of water-generated and released CO2 . Specifically, 17β-E2 pollution can promote water emissions of greenhouse gases. Environ

Mountain ecosystems contribute substantially to global carbon and nitrogen biogeochemical cycles. Although soil respiration, and microbial biomass, activities and diversity have been extensively studied at different altitudes worldwide, little is known on causal link between environmental drivers, microbial functions and emissions of greenhouse gases (GHGs) in soils of different elevation. Here, by measuring in-situ GHG fluxes, soil properties, organic matter (OM) quality, microbial enzyme activities, biomass and gene abundances, we investigate factors that control long-term GHG fluxes (carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O)) in natural soils with an elevational gradient of ~2400 m across Switzerland with different vegetation covers. Results showed that CO2 and N2O fluxes increased significantly with elevation from top to the treeline, but slightly decreased from the treeline to bottom. Contrastingly, no significantly patterns of CH4 fluxes across the whole elevation were observed. Spearman correlations revealed that the increased CO2 and N2O fluxes were highly correlated to the significant increases in soil temperature, moisture, organic matter (OM) quantity and quality (increases in the relative contribution of humic-like vs. fresh-like OM), bacterial and fungal biomass and gene abundances. Structural equation model, hierarchical partitioning and random forest regression further confirmed that, in addition to soil temperature and moisture, SOM quantity and quality are the most driving factors of microbial activity and respiration. Our study highlights the importance of OM quality as a driving factor of soil microbial metabolic activities in Alpine soils across the elevation, and predicts a potential increase in GHG emissions in high-altitudinal soils with the expected upwarding-shifting treeline under climate warming.

Soil organic carbon ( SOC ) and selected soil properties were measured in fringe and ditch marshes and cropland of old and young reclaimed areas in a subtropical estuary in China in order to investigate the effects of land use and reclamation history on SOC. The results show that after the conversion of wetlands to cropland, a longer reclamation history (&gt;20 yr) resulted in greater soil bulk density, salinity, clay and silt, and lower soil moisture, SOC and sand content, whereas a shorter reclamation history (&lt;20 yr) induced smaller values for soil pH , moisture and sand. Ditch marshes had greater average SOC in the top 50 cm than fringe marshes and cropland. SOC decreased generally down soil profiles from 0 to 50 cm in depth, except for the obvious accumulation of SOC in deeper soils from old fringe and young ditch marshes. Ditch marshes had the greatest SOC densities in the top 50 cm in both regions compared to the other land uses. SOC densities in the top 50 cm were less in croplands than in fringe marshes in the young region, while there were no significant differences between them in the older one. Except for cropland, SOC densities in the top 50 cm of the fringe or ditch marshes in the old region were not significantly different from those in the young region. SOC in both regions was reduced by 13.53 × 10 4 t (12.98%) in the top 50 cm of the marshes after conversion to cropland, whereas the regional SOC storage increased by 29.25 t when ditch marshes were included. The results from regression analysis show that bulk density and soil moisture significantly influenced SOC . The total SOC stored in both ditch marshes and croplands was higher compared to fringe marshes. The regional SOC storage in the top 50 cm was not reduced after reclamation due to C accumulation in the ditch marshes. The regional effects of cultural practices should be taken into account in devising strategies for managing soils in coastal wetlands, particularly in the developing world.

Redistribution of water within plants could mitigate drought stress of roots in zones of low soil moisture. Plant internal redistribution of water from regions of high soil moisture to roots in dry soil occurs during periods of low evaporative demand. Using minirhizotrons, we observed similar lifespans of roots in wet and dry soil for the grapevine 'Merlot' (Vitis vinifera) on the rootstock 101-14 Millardet de Gramanet (Vitis riparia x Vitis rupestris) in a Napa County, California vineyard. We hypothesized that hydraulic redistribution would prevent an appreciable reduction in root water potential and would contribute to prolonged root survivorship in dry soil zones. In a greenhouse study that tested this hypothesis, grapevine root systems were divided using split pots and were grown for 6 months. With thermocouple psychrometers, we measured water potentials of roots of the same plant in both wet and dry soil under three treatments: control (C), 24 h light + supplemental water (LW) and 24 h light only (L). Similar to the field results, roots in the dry side of split pots had similar survivorship as roots in the wet side of the split pots (P = 0.136) in the C treatment. In contrast, reduced root survivorship was directly associated with plants in which hydraulic redistribution was experimentally reduced by 24 h light. Dry-side roots of plants in the LW treatment lived half as long as the roots in the wet soil despite being provided with supplemental water (P < 0.0004). Additionally, pre-dawn water potentials of roots in dry soil under 24 h of illumination (L and LW) exhibited values nearly twice as negative as those of C plants (P = 0.034). Estimates of root membrane integrity using electrolyte leakage were consistent with patterns of root survivorship. Plants in which nocturnal hydraulic redistribution was reduced exhibited more than twice the amount of electrolyte leakage in dry roots compared to those in wet soil of the same plant. Our study demonstrates that besides a number of ecological advantages to protecting tissues against desiccation, internal hydraulic redistribution of water is a mechanism consistent with extended root survivorship in dry soils.

The disappearance of EPTC (ethyl N,N-di-n-propylthiolcarbamate) from soils was studied by steam distilling the remaining EPTC from the soil samples and analyzing the distillates. The most important factor affecting the loss of EPTC from soil was the amount of moisture in the soil. During the first 15 minutes after spraying on the soil surface, 20% of the applied EPTC disappeared from dry soil, 27% from moist soil and 44% from wet soil. The loss was 23, 49, and 69% after one day and 44, 68, and 90% after six days on dry, moist, and wet soils, respectively. No significant loss of EPTC occurred the first few hours after applying granular EPTC to dry soil or soil containing 4 to 6% moisture, but on soil at 15% moisture the loss from granules was 60% in two hours. There appeared to be a critical moisture level for each soil, above which large losses of EPTC occurred after application to the surface or after shallow incorporation. Depth of incorporation was the second most important factor in EPTC loss from soils. Incorporation to at least 2 to 3 inches was necessary to prevent large losses of EPTC when light rain or sprinkler irrigation followed treatment. EPTC was lost at a faster rate on sunny days than cloudy days. Increasing the temperature from 32 to 60 F, increased the rate of EPTC vaporization from moist soil but had no effect on the loss from dry soil.

Free‐air carbon dioxide enrichment (FACE) experiments in terrestrial ecosystems have demonstrated ecological responses of key ecosystem processes to rising atmospheric carbon dioxide (CO2). However, CO2 fertilization responses in field conditions have seldom included methane (CH4) and nitrous oxide (N2O), particularly in natural and mature forests, which are expected to have an important role in climate change mitigation. Herein, we aimed to capture the effect of elevated CO2 (eCO2; ambient vs. +150 ppm) on long‐term temporal dynamics of CH4 and N2O fluxes, followed by identification of climo‐edaphic factors explaining feedback responses. To achieve this, continuous monitoring of greenhouse gas (GHG) fluxes using a manual chamber technique, over a 3‐year period was implemented in a mature dryland Eucalypt forest FACE (EucFACE) facility in Australia. The relationship between CH4 and N2O fluxes with rainfall indices and soil properties was also explored since they directly impact the microbial communities in the soil responsible for CH4 and N2O net emissions. Our results showed that in 3 years of eCO2 treatment, the amount and frequency of rainfall predicted GHG emissions in this native forest. We also found a significant reduction in CH4 sink (15%–25%) for some of the years as well as an overall treatment effect index reduction in N2O emissions under eCO2. Higher frequency of rain events with lower intensity led to highest CH4 sink followed by lowest N2O emissions due to fewer wet–dry cycles. Of all the environmental variables included, soil moisture, rainfall and pH were the main predictors of net CH4 and N2O emissions. Methane flux was also strongly influenced by soil texture. Our findings highlight the need to account for reduced forest CH4 sink under eCO2 in dryland ecosystems, which has implications for GHG budget predictions under future climate conditions. A free Plain Language Summary can be found within the Supporting Information of this article.

The effect of soil moisture content and evaporative demand on diurnal variations of leaf resistance to water vapor diffusion were studied at two heights in a soybean (Glycine max L. (Merr.)) canopy. Under soil moisture stress, leaf resistance to water‐vapor diffusion of middle leaves in the canopy increased approximately 2 hr earlier in the day and to a greater extent than the resistance of upper leaves. This indicated a preferential flow of water to upper leaves. It is speculated that the degree of out‐of‐phase change in leaf resistance under stress conditions is related to canopy density.Leaf resistances of middle leaves decreased at a slower rate under adequate soil water supply than under drier conditions. On days with low evaporative demand, leaf resistances of upper leaves tended to be less (0.8 sec/cm) under the low soil moisture than under the high soil moisture supply. The apparent reduction of stomatal activity in leaves under low evaporative demand and high soil moisture supply is believed related to the lack of development of a small leaf‐water deficit necessary for maximal stomatal opening.

Climate change has resulted in an increased occurrence of summer droughts in large parts of the world. Low soil moisture has marked impacts on the physiology of soil invertebrates and lowers degradation rates of organic contaminants in soil. Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic contaminants that readily accumulate in the lipids of soil organisms. Here, we exposed springtails (Collembola, small soil living arthropods) to phenanthrene (a common PAH) in combination with a range of soil water contents to investigate the combined effects of these factors on the bioaccumulation, survival, recruitment, and body growth in a full factorial experiment. The results showed that phenanthrene up to 60 mg/kg dry soil had moderate effects on survival (<20%), whereas dry soil (4% soil water content) caused approximately 60% mortality. The bioaccumulation of phenanthrene increased almost 3-fold when soil water content decreased from 22 to 4%. We observed a joint effect of low soil water content and phenanthrene on recruitment, suggesting a synergistic interaction. The recruitment EC50 values of phenanthrene decreased from approximately 40 mg/kg dry soil at 22% soil water content to approximately 10 mg/kg dry soil at 12% soil water content. Our results show that the effects of phenanthrene are more pronounced in dry soil partly because bioaccumulation is enhanced when soils become dry.

PDF HTML阅读 XML下载 导出引用 引用提醒 新疆天山高寒草原不同放牧管理下的CO2,CH4和N2O通量特征 DOI: 10.5846/stxb201209221338 作者: 作者单位: 中国科学院干旱区生物地理与生物资源重点实验室 中国科学院新疆生态与地理研究所;中国科学院研究生院;中国农业大学资源与环境学院,中国科学院干旱区生物地理与生物资源重点实验室 中国科学院新疆生态与地理研究所,中国科学院干旱区生物地理与生物资源重点实验室 中国科学院新疆生态与地理研究所,中国科学院干旱区生物地理与生物资源重点实验室 中国科学院新疆生态与地理研究所,中国科学院新疆生态与地理研究所 中国农业大学资源与环境学院,中国科学院干旱区生物地理与生物资源重点实验室 中国科学院新疆生态与地理研究所,中国科学院干旱区生物地理与生物资源重点实验室 中国科学院新疆生态与地理研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（41005001）；国家重点基础研究发展计划（973）资助项目（2009CB825103）；中国科学院百人计划资助项目（304）资助 The fluxes of carbon dioxide, methane and nitrous oxide in alpine grassland of the Tianshan Mountains, Xinjiang Author: Affiliation: Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences,,,,Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences. College of Resources and Environmental Sciences, China Agricultural University.,, Fund Project: 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:以中国科学院新疆巴音布鲁克草原生态站为依托，于2010年5月-2011年10月利用静态箱-气相色谱法对短期禁牧（2005年围封）、长期禁牧（1984年围封）和自由放牧（冬季放牧）3种草地的CO2、CH4、N2O气体通量进行了野外连续试验研究。结果表明：新疆天山高寒草原对CO2，CH4和N2O通量表现出明显的季节排放特点。在植物的生长季（5-10月），新疆天山高寒短期禁牧、长期禁牧和自由放牧草原的CO2通量平均值分别为：（89.8±49.3）、（52.8±28.7）、（57.0±30.7）mg · m-2 · h-1，CH4通量平均值分别为：（-66.3±21.3）、（-104.5±32.8）、（-103.0±39.0）μg · m-2 · h-1，N2O通量平均值分别为：（21.2±11.8）、（13.6±6.9）、（13.2±6.2）μg · m-2 · h-1；短期禁牧草原与长期禁牧和自由放牧草原CH4平均通量具有显著性差异（P < 0.05），但CO2和N2O差异不显著（P > 0.05）。在植物的非生长季（11月-翌年4月），新疆天山高寒短期禁牧、长期禁牧以及自由放牧草原的3种温室气体的通量较低且差异均不显著。 Abstract:With growing concerns on impacts of human activities and global warming on Alpine grasslands, comprehensive understanding of the sources and sinks of greenhouse gases becomes increasingly more important. The understanding is closely related to the progress on biogeochemical cycles of carbon and nitrogen in terrestrial ecosystems. Carbon dioxide, methane and nitrous oxide are the three most important greenhouse gases, which are considered to account for 80% contribution to global warming potential. The alpine grassland of Xinjiang is a typical temperate arid region of grasslands. The study was conducted at the Bayinbuluk Grassland Eco-system Research Station, Chinese Academy of Sciences(83°43'E,42°54'N). Bayinbuluk alpine grassland is located in the southern Tianshan mountains. Xinjiang Uygur AutonoMous Region, central Asia and covers a total area of approximately 2.3×104 km2. Bayinbuluk alpine grassland is the typical temperate arid alpine grassland, which is the second largest grassland of China after Inner Mongolia Grassland. As we all know, the grassland ecosystem has degenerated seriously and grazing prohibition is a frequently-used solution to prevent grass grassland degradation. While, it is still unknown that grazing prohibition impacts greenhouse gases fluxes in some degree. The study of carbon dioxide, methane and nitrous oxide of long-term grazing-prohibition grass(1984), short-term grazing-prohibition grass(2005) and free grazing grass in Bayinbuluk alpine grassland is meaningful, which will deepen our understanding of greenhouse gases fluxes in the alpine grassland ecosystem, help us assess global warming, parameterize Earth System models and get more comprehensive grasp of the impact of grazing prohibition on the grassland ecosystem. Using opaque, static, manual stainless steel chambers and gas chromatography, the fluxes of carbon dioxide, methane and nitrous oxide of long-term grazing-prohibition grass, short-term grazing-prohibition grass and free grazing grass were measured through the continuous experiment in situ from May 2010 to October 2011(no sampling in January and February 2011 because of the very low temperatures, about -40℃). Four times per month during the growing season(from May to October) and twice per month during non-growing (from November to next year April) season at all sites. According to the results of field experiment, the alpine grassland of Xinjiang is the sources of carbon dioxide and nitrous oxide; it is the sinks of methane. In the growing season, CO2 average fluxes of short-term grazing-prohibition, long-term grazing-prohibition and free grazing are (89.8±49.3),(52.8±28.7), (57.0±30.7)mg · m-2 · h-1; CH4 fluxes averaged out to (-66.3±21.3), (-104.5±32.8), (-103.0±39.0) μg · m-2 · h-1; CH4 fluxes averaged out to (21.2±11.8), (13.6±6.9), (13.2±6.2) μg · m-2 · h-1. Our results indicated that: (1) Nitrous oxide fluxes showed a significant correlation with carbon dioxide fluxes in three kinds of grasslands. (2) In the growing season, the difference of greenhouse gases fluxes between long-term grazing-prohibition grass and free grazing grass were not significant, while short-term grazing-prohibition grass has higher fluxes of carbon dioxide and nitrous oxide and lower fluxes of methane. (3) In growing season, the fluxes of methane of short-term grazing-prohibition grass showed significant difference with long-term grazing-prohibition grass and free grazing grass. But the difference of growing-season average carbon dioxide and nitrous oxide fluxes did not reach the significance level of 0.05. (4) In non-growing season, no significant differences between the fluxes of carbon dioxide, methane and nitrous oxide were found in long-term grazing-prohibition grassland, short-term grazing-prohibition grassland and free grazing grassland. 参考文献 相似文献 引证文献

Nowadays heat waves are a growing issue, causing detrimental effects on society, people&amp;#8217;s health and environment in several parts of the world. Slow drivers such as spring soil moisture and sea surface temperature are known to impact the probability of occurrence of heatwaves in many areas of the globe. However, their influence remains still little understood and studied. Even fewer has been said on the cross effect and relative impact of both factors.&amp;#160;Our work aims at analysing and comparing the effects of spring soil moisture deficit in Europe and sea surface temperature decadal variability in the North Atlantic (AMV) on the occurrence of typical and more extreme European heat waves. To do that, we use the outputs from three climate models, namely IPSL-CM6A-LR, EC-Earth3 and CNRM-CM6-1, in which North Atlantic sea surface temperatures are nudged to the observed AMV anomalies.At a methodological level, previous studies mainly focused on typical heat waves. Our work goes beyond that and proposes a new methodology to study events with larger return times. By introducing return time maps we can study rare heatwaves with return time from 10 to 50 years. We find that the temperature and duration of typical and extreme heatwaves are influenced by the AMV and soil moisture. In general, the changes induced by typical AMV or soil moisture anomalies are of comparable amplitude. In many areas of Europe, the influence of AMV and soil moisture over duration or temperature of extreme heatwaves increases when the return time is longer and is statistically significant even for return times of 50 years. In general, the three models give consistent results.&amp;#160;With positive AMV phase or low soil moisture, the temperature and duration of extreme heatwaves are changed according to regional patterns. As might be expected, positive AMV phase or low soil moisture often induce hotter and longer typical and extreme heatwaves. However, counter-intuitively, they also induce cooler and shorter heatwaves over part of Northern-Eastern Europe. For more extreme events, the impact of the AMV and soil moisture increases, according to rather similar regional patterns. However, the regions with decreased temperature or duration impact extend in size.In this work, we have improved the study of extreme heat waves and better understood their slow drivers. Studying those drivers is important to enhance heat wave predictability. To move further in this direction, we need to improve the statistics of the events. In this context, developing and using new tools such as rare event simulations might be the right path to follow.

Charcoal rot, caused by the soilborne fungus Macrophomina phaseolina, is one of the most economically important diseases affecting strawberry (Fragaria × ananassa) production in California. Previous studies on nonstrawberry hosts have shown that proper soil moisture management can limit pathogen colonization of plants and decrease disease severity. We performed field and greenhouse studies for two seasons with the objective of investigating the role of soil moisture in disease development and management of charcoal rot of strawberries. Bare-root transplants of cultivars Monterey and Fronteras were inoculated or not inoculated and maintained at a high, optimal, or low soil moisture level using tensiometers. Randomly selected plants from each treatment were sampled for pathogen colonization every 4 weeks after planting, and all plants were visually rated for disease severity every 2 weeks after symptom onset. In both seasons, low soil moisture significantly increased charcoal rot mortality among inoculated plants compared with optimal soil moisture by 16 and 24 percentage points, respectively. In the first season, mortality was significantly lower in the high- compared with the optimal-soil-moisture treatment. Colonization of crowns was increased by low soil moisture among inoculated plants in the first season, but soil moisture did not influence root colonization in either year of the study. In the greenhouse, charcoal rot severity was highest in the low-soil-moisture treatment. These results indicate that soil moisture has a limited influence on colonization of strawberries by M. phaseolina and that maintaining optimal soil moisture can help prevent excess charcoal rot mortality.

Lakes represent a considerable natural source of methane to the atmosphere compared to their small global surface area. Methanotrophs in sediments and in the water column largely control methane fluxes from these systems, yet the diversity, electron accepting capacity, and nutrient requirements of these microorganisms have only been partially identified. Here, we investigated the role of electron acceptors alternative to oxygen and sulfate in microbial methane oxidation at the oxycline and in anoxic waters of the ferruginous meromictic Lake La Cruz, Spain. Active methane turnover in a zone extending well below the oxycline was evidenced by stable carbon isotope-based rate measurements. We observed a strong methane oxidation potential throughout the anoxic water column, which did not vary substantially from that at the oxic/anoxic interface. Both in the redox-transition and anoxic zones, only aerobic methane-oxidizing bacteria (MOB) were detected by fluorescence in situ hybridization and sequencing techniques, suggesting a close coupling of cryptic photosynthetic oxygen production and aerobic methane turnover. Additions of nitrate, nitrite and to a lesser degree iron and manganese oxides also stimulated bacterial methane consumption. We could not confirm a direct link between the reduction of these compounds and methane oxidation and we cannot exclude the contribution of unknown anaerobic methanotrophs. Nevertheless, our findings from Lake La Cruz support recent laboratory evidence that aerobic methanotrophs may be able to utilize alternative terminal electron acceptors under oxygen limitation.