Effect of Rice Residues on Carbon Dioxide and Nitrous Oxide Emissions from a Paddy Soil of Subtropical China

A pot incubation experiment with rice residues (straw and root) was conducted under aerobic condition (60% of WHC, water holding capacity) for a period of 55 days in a greenhouse. The emissions of carbon dioxide (CO₂) and nitrous oxide (N₂O) were determined by the closed chamber method in a paddy soil. The soil was derived from quaternary red clay, and collected from the Ecological Station of Red Soil, the Chinese Academy of Sciences, located in Jiangxi Province, a subtropical region of China. The emissions of CO₂ and N₂O were increased by the amendment of rice residues. Significantly positive correlation was found between N₂O and CO₂ fluxes (R = 0.650*?0.870*, P ≤ 0.05). The cumulative emissions during the early stage of the incubation (<25 days after residue addition) accounted for about 67%–86% and 67%–80% of the total amount of CO₂ and N₂O emissions, respectively. Cumulative emissions and emission factors of the two gases were higher in the soils amended with rice straw than those with rice root. The two gas fluxes were positively correlated with microbial biomass C and N, as well as soluble organic C. N₂O flux was positively correlated with NH₄ ⁺–N content at the early stage (<25 days), and negatively with NO₃ ^?–N content at the later stage of this incubation (25–55 days), implying that both nitrification and denitrification may have contributed to N₂O production.     

Soil Air Permeability and Carbon Dioxide Flux Measurements from the Soil Surface

Abstract

Air permeability has been recognized as an index of soil structure and used in attempts to characterize soil pore geometry. The importance of increased carbon dioxide in soil to agriculture comes from the direct effects of carbon dioxide (CO₂) on root respiration of agricultural crops. In this study, the soil air permeability and CO₂ flux values were obtained using two different apparatuses built and designed to measure air permeability and CO₂ flux. Air permeability was obtained in clay soil using two different aggregate sizes. The average values obtained were 9.55×10^?8 and 1.78×10^?7 cm² for the <2-mm and 2- to 5-mm fractions, respectively. Carbon dioxide flux from the soil surface of no‐till and bare plots under winter conditions was measured using another apparatus. The average CO₂ flux for the no‐till plot was 2.88 g/m²‐day and for the bare plot was 1.31 g/m²‐day. These values were within the range of values obtained from other studies.     

农业开垦对中国土壤有机碳的影响

以中国土种志资料为基础,分析了耕地和非耕地表层土壤有机碳含量的变异性,以及各大区域土壤有机碳含量在耕地和非耕地、水田和旱地之间的差异;同时结合非耕地有机碳含量和耕地面积数据,估算了由于耕地的开垦而导致的土壤表层有机碳贮量的变化。结果表明,耕地土壤有机碳含量的变异性小于非耕地,水田小于旱地;耕地土壤有机碳含量明显低于非耕地土壤,平均减少了51.5%,水田却明显高于旱地;水田和旱地的开垦分别导致土壤表层有机碳贮量减少了0.67,3.63 Pg,共计4.3 Pg。最后还分析了土壤有机碳库减少量的空间分布格局,探讨了东北和华北这两大区域土壤有机碳贮量下降程度最大的原因,是由于黑土、黑钙土、暗棕壤等富含有机碳的草原草甸和湿地土壤大量开垦以及耕作管理措施粗放所致。     

农业开垦对中国土壤有机碳的影响

以中国土种志资料为基础,分析了耕地和非耕地表层土壤有机碳含量的变异性,以及各大区域土壤有机碳含量在耕地和非耕地、水田和旱地之间的差异;同时结合非耕地有机碳含量和耕地面积数据,估算了由于耕地的开垦而导致的土壤表层有机碳贮量的变化。结果表明,耕地土壤有机碳含量的变异性小于非耕地,水田小于旱地;耕地土壤有机碳含量明显低于非耕地土壤,平均减少了51.5%,水田却明显高于旱地;水田和旱地的开垦分别导致土壤表层有机碳贮量减少了0.67,3.63 Pg,共计4.3 Pg。最后还分析了土壤有机碳库减少量的空间分布格局,探讨了东北和华北这两大区域土壤有机碳贮量下降程度最大的原因,是由于黑土、黑钙土、暗棕壤等富含有机碳的草原草甸和湿地土壤大量开垦以及耕作管理措施粗放所致。     

亚热带森林转换对不同粒径土壤有机碳的影响

以亚热带天然阔叶林和由其转换而来的针阔混交人工林和杉木人工林为研究对象,探讨森林转换对土壤有机碳(Soilorganiccarbon,SOC)含量和分布格局的影响。选取不同土层(0～20cm、20～40cm、40～60cm)土壤作为样本,运用物理分组方法研究森林转换对土壤粗颗粒有机碳(Coarse particulate organic carbon,CPOC)、细颗粒有机碳(Fine particulate organic carbon,FPOC)、矿物结合态有机碳(Mineral-associatedorganiccarbon,MOC)含量及其分配比例的影响。结果表明:天然林转换为人工林后(1)各土层土壤有机碳含量均呈下降趋势;(2)0～20cm土层土壤粗颗粒有机碳含量和分配比例均显著降低,土壤细颗粒有机碳含量和比例呈增加趋势;矿物结合态有机碳含量呈减少趋势,比例呈增加趋势;(3)各土层土壤颗粒有机碳/矿物结合态有机碳(POC/MOC)和矿物结合态有机碳/土壤有机碳(MOC/SOC)比值均呈下降趋势,0～20 cm土层土壤CPOC与SOC相关性最好,40～60cm土层MOC与SOC相关性最好。因此,亚热带天然阔叶林转换为针阔混交人工林和杉木人工林,土壤总有机碳含量降低,土壤有机碳的稳定性增强;土壤CPOC更能反映森林转换对表层土壤有机碳的影响;而MOC更能反映森林转换对深层土壤有机碳的影响。     

中国亚热带地区土壤可蚀性的季节性变化研究

开展土壤可蚀性K值季节性变化规律的研究,对于精确预报土壤侵蚀及深入了解土壤可蚀性K值的机理具有重要意义.基于14个自然降雨条件下的田间小区实测数据.研究了中国亚热带有代表性的不同类型土壤可蚀性K值季节性变化规律,并对其季节性变化的原因作了初步分析.结果表明:各小区土壤可蚀性K值在不同季节间都存在动态变化,总体变化趋势是春、夏季高.而秋、冬季低,并且不同小区土壤其可蚀性K值的变动趋势和变动幅度不同,同一土壤可蚀性K值不同季节间最高和最低值之间相差最高达6倍.     

湘中丘陵区4种森林土壤水溶性有机碳含量及其与土壤养分的关系

为了解亚热带天然次生林保护对森林土壤有机碳库的影响,研究了湘中丘陵区杉木人工林和3种天然次生林(马尾松+石栎针阔混交林、南酸枣落叶阔叶林、石栎+青冈常绿阔叶林)土壤水溶性有机碳(DOC)含量季节动态及其与土壤自然含水率、p H、养分含量的相关性。结果表明:土壤DOC含量0~15 cm土层高于15~30 cm土层,秋季土层之间的含量差异最小,土壤DOC的分配比例15~30 cm土层高于0~15 cm土层;马尾松+石栎针阔混交林、南酸枣落叶阔叶林、石栎+青冈常绿阔叶林土壤DOC含量分别较杉木人工林高3.15%~9.81%,3.85%~8.19%和11.24%~12.00%,夏季不同森林类型之间的含量差异最大;4种森林土壤DOC的分配比例在2.00%~2.54%之间,杉木人工林土壤DOC的分配比例高于3种次生林;4种森林土壤DOC含量季节变化明显,均表现为:春、夏、冬季较高,秋季最低,秋季与春(除杉木人工林外)、夏季之间差异显著;各森林土壤DOC含量与土壤自然含水率、有机碳(SOC)、全N、全P、全K、水解N、有效P、速效K含量之间呈极显著或显著正相关。可见,地带性常绿阔叶林或天然次生林转变为杉木人工林后,土壤DOC含量下降,土壤DOC含量可作为衡量土壤潜在生产力的敏感指标。     

中亚热带4种森林类型土壤有机碳氮贮量及分布特征

对湖南省长沙县大山冲省级森林公园立地条件基本一致的4种森林土壤有机碳(SOC)、全氮(N)含量、贮量及土层分布进行研究。结果表明:不同森林、同一森林的不同土层SOC、N含量和贮量均存在显著差异(p<0.05)。各土层SOC含量的变化范围分别为杉木林8.66～22.96g/kg,马尾松林13.33～37.50g/kg,南酸枣林13.78～43.58g/kg,青冈林13.33～36.87g/kg。土壤全N含量的变化范围分别为杉木林1.37～2.29g/kg,马尾松林1.29～2.65g/kg,南酸枣林1.69～3.96g/kg,青冈林1.23～3.26g/kg。4种林地SOC和N含量均随土层深度增加而逐渐下降。4种森林土壤SOC贮量差异不显著(p=0.177 6),N贮量差异极显著(p=0.000 7)。4种森林土壤SOC含量与N含量存在极显著相关性(p<0.01),除青冈林外,其余3种森林土壤SOC与C/N存在极显著相关关系(p<0.01)。马尾松土壤N与C/N之间呈极显著相关(p<0.01),南酸枣林的存在显著关系(p<0.05),青冈林和杉木林的相关性不显著。     

长期施肥红壤稻田有机碳演变规律及影响因素

利用1981年起设置的水稻土长期施肥定位试验,分析了CK(不施肥)、N(单施氮肥)、NPK(氮磷钾配施)、NPK2(2倍氮磷钾配施)和NPKM(有机无机肥配施)等施肥措施下土壤有机碳的演变规律及其与作物产量和土壤养分(全氮、碱解氮、全磷、速效磷、全钾和速效钾)的相关性.结果表明:试验30年后,各个处理的土壤有机碳含量均有上升,其中CK、N、NPK、NPK2和NPKM的土壤有机碳在试验30年分别比试验前增加18.95％、17.72％、23.36％、16.92％和32.68％.与CK处理相比,NPK、NPK2和NPKM处理的土壤有机碳平均提高了4.09％、4.03％和25.68％.土壤有机碳含量与水稻产量呈显著相关(P＜0.001),相关系数r为0.410,这说明土壤有机碳含量的增加可以促进水稻增产.土壤有机碳与土壤养分中的碱解氮、速效磷和全磷含量均表现出极显著相关(P＜0.001),相关系数r分别为0.452、0.559和0.487,但是与钾含量相关不显著.这表明:有机无机肥配施可以持续快速提高红壤性水稻土的有机碳含量,同时在有机无机肥配施过程中应适当增施钾肥,从而促进土壤肥力平衡和维持作物高产稳产,实现农业可持续性.     

亚热带3种森林对土壤碳氮储量及酶活性的影响

[目的]探明森林类型对土壤碳氮含量和酶活性的影响,为亚热带针叶林改造过程中的树种选择和营林方式选择提供科学依据。[方法]研究相同海拔高度和相近环境条件下的亚热带常绿阔叶林(米槠林)、常绿—落叶阔叶混交林(闽桦—闽楠林)和针叶林(马尾松林)3种森林类型对土壤碳氮储量和酶活性的影响。[结果](1)马尾松林的土壤总有机碳含量显著高于其他两种林分类型,土壤全氮含量与闽桦—闽楠林无显著差异,但二者均显著高于米槠林,马尾松林和闽桦—闽楠林的土壤氮储量和碳储量显著高于米槠林;马尾松林和闽桦—闽楠林的土壤可溶性有机碳含量显著高于米槠林。马尾松林的土壤可溶性有机氮含量显著小于米槠林和闽桦—闽楠林,米槠林和马尾松林的土壤微生物量碳氮含量均显著高于闽桦—闽楠林,3种林分的土壤铵态氮含量无显著差异,而闽桦—闽楠林的土壤硝态氮含量显著高于其他两种林分;(2)米槠林的土壤脲酶活性显著高于闽桦—闽楠林。3种林分的土壤蔗糖酶活性差异显著,表现为：马尾松林>米槠林>闽桦—闽楠林,马尾松林和米槠林的土壤过氧化氢酶活性均显著高于闽桦—闽楠林。3种林分的土壤磷酸酶活性无显著差异,马尾松林的土壤β-葡糖糖苷酶活性显...     

Organic Carbon Storage in Soils of Tropical and Subtropical China

Tropical and subtropical China occupies a total area of about215 Mha, but the contents and storage of soil organic carbon (C)on this land have not been well studied. This research wasconducted in this concern by jointly using soil survey data andthe regional soil map. It was estimated that the 0–20 cm Cdensity of the soil subgroups in the region varied from 1.2 to9.7 kg C m^-2. In the major zonal soils, soil subgroup`young ～' had generally a C density about 1.2–4.4 timeslower than its other natural counterparts. Furthermore, subgroups of thecultivated soil gave a C density about 20–63% lower than theirnatural counterparts (except subgroup `young ～'), showingremarkable C losses caused by cultivation. For soil groups inthe east, brown soil had the highest C density (6.8 and 21.4 kgC m^-2, for the upper 20 and 100 cm soil, respectively),followed by yellow soil, yellow brown soil and limestone soil (4.6–5.5 and 12.3–14.5 kg C m^-2, idem). Torrid red soil, purplishsoil and fluvo-aquic soil had the lowest C density (2.0–2.2 and5.8–7.5 kg C m^-2, idem) with the others ranking at amedium level. In the west, podzolic soil ranked the highest(17.9 and 55.8 kg C m^-2, idem), followed by dark brownsoil, brown soil and limestone soil (6.9–11.6 and 21–29 kg Cm^-2, idem), and again torrid red soil, purplish soiland fluvo-aquic soil ranked the lowest (3.9–5.1 and 11.4–14.1 kg C m^-2, idem). Finally, a total of about 26.8±7.4 Pg organic C was estimated being stored in soils of the entire region.     

长期施肥下红壤中类芬顿反应及其对碳储存的影响

以祁阳红壤长期定位试验站的施用有机肥和化肥的土壤为研究对象,结合不同孔径(1000μm、20μm和0.45μm)的原位微宇宙培养试验,通过高效液相色谱、高通量测序、同步辐射红外显微成像和X射线光电子能谱等技术手段研究了长期施肥处理对红壤中类芬顿反应的调控能力及其对红壤有机碳储存的影响。结果表明,长期施用化肥的红壤中H_2O_2、H O·及Fe(II)含量均显著高于长期施用有机肥。根系分泌物和微生物的参与也能够调控H_2O_2、H O·和Fe(II)含量,且H_2O_2和HO·含量呈线性关系。长期施用有机肥的红壤具有很好的H_2O_2缓冲性能,而长期施用化肥的红壤可能由于发生了退化(如土壤有机质含量低),H_2O_2缓冲性能较差。长期施用有机肥的红壤中微生物丰富度和多样性指数均显著高于长期施用化肥的红壤。植物根系和微生物的进入对长期施用有机肥的红壤中细菌群落结构影响较小,而对长期施用化肥的红壤中细菌群落结构影响较大。长期施用有机肥的细菌群落影响了土壤p H、可溶性有机碳、可溶性Fe和CO2释放;而长期施用化肥的细菌群落可能通过产生H_2O_2和还原态Fe(II)引发了土壤中的芬顿反应。根-土界面上黏土矿物(36 1 9c m-1)、脂肪碳(29 1 4c m-1)、羧酸碳(1 725 cm-1)、羟基碳(1 135 cm-1)的分布模式有较大差异,其中根系的出现增加了根-土界面上Fe(II)比例。综上,本文提出了有效增加亚热带红壤土壤有机碳的概念模型。     

土壤无机离子对CO2封存泄漏的响应

[目的]旨在研究土壤中无机离子含量对CO2封存泄漏的响应。[方法]在CO2人工气候箱中分别种植绿豆、荞麦两种作物,模拟10 000,20 000,40 000和80 000μl/L这4个浓度梯度,外加一个空白浓度对照组,观测土壤无机离子含量变化及作物生长情况。[结果]随着大气中CO2浓度升高,土壤中的Cl-,K+,Ca2+含量基本先降后升,SO2-4呈现先升后降再升再降的M型变化趋势,Na+,Mg2+,HCO-3变化不显著,而CO2-3始终未检出。绿豆、荞麦的光合速率及生物量均在CO2浓度10 000μl/L时达到最大。[结论]大气中CO2浓度升高一方面会直接影响土壤溶液酸碱度、碳平衡,发生离子沉淀;另一方面还会影响作物和微生物生长,改变其对土壤离子的吸收和代谢。     

库布齐沙漠植被恢复对风沙土壤碳通量与碳储量的影响

为阐明库布齐沙漠植被恢复过程中土壤碳通量的时空动态特征及主控因子，明确土壤有机碳含量和储量的变化趋势，本研究以流动沙地、半固定沙地、藻结皮固定沙地和地衣苔藓混合结皮固定沙地为研究对象，运用静态暗箱–气相色谱法对风沙土壤碳通量及水热因子进行观测，并对土壤有机碳含量和密度进行测定和计算。结果表明，生长季内风沙土壤碳通量变异较大，季节动态与土壤温度基本一致，且随植被恢复碳通量呈递增趋势：混合结皮固定沙地(210.28 mg/(m~2·h))>藻结皮固定沙地(177.45 mg/(m~2·h))>半固定沙地(117.34 mg/(m~2·h))>流动沙地(65.61mg/(m~2·h))；土壤碳通量与各层土壤温度均显著正相关，除流动沙地土壤碳通量与深层土壤含水量显著负相关外，其余样地碳通量均与表层土壤含水量显著负相关；风沙土壤有机碳含量和密度随植被恢复而递增：混合结皮固定沙地(1.32 g/kg,0.94 kg/m~2)>藻结皮固定沙地(1.03 g/kg,0.74 kg/m~2)>半固定沙地(0.45 g/kg,0.36 kg/m~2)>流动沙地(0.27...     

Environmental Controls on Fallow Carbon Dioxide Flux in a Single‐Crop Rice Paddy,Japan

Soil organic carbon (SOC) is one of the important measures of soil fertility and sustainability in arable lands. With continuous CO₂ flux measurements, this study assessed the SOC decomposition and its environmental controls at both half‐hourly and season‐long scales in a single‐crop rice (Oryza sativa L.) paddy during three fallow periods between 2004 and 2007. Measurements were made on a gray lowland soil sited in eastern Japan using the eddy covariance method. Ecosystem respiration was strongly affected by soil water content measured at 0–0·1 m depth. At 0·5 m³ m^{− 3} or more of soil water content, the baseline of ecosystem respiration decreased by 50% compared with that at 0·2 m³ m^{− 3} . The effect was quantified at half‐hourly scale using an empirical multiple regression model, together with the soil surface temperature and the time after residue incorporation. At season‐long scale, net biome production, which is equivalent to the change in the SOC pool during the fallow period, was estimated from the flux and ancillary data at 150 g C m^{− 2} in 2004–2005, 70 g m^{− 2} in 2005–2006, and 270 g C m^{− 2} in 2006–2007. Apparently, as much as 46 to 79% of the soil organic matter incorporated (crop residues, ratoon, and stable manure) was decomposed during the fallow period. Precipitation, or associated soil water content, was important for the carbon balance of the field at season‐long scale because of its large interannual variability and relatively low permeability of the paddy soil. Copyright © 2013 John Wiley & Sons, Ltd.     

中亚热带退化林地土壤有机碳及不同粒径土壤颗粒有机碳的变化

采用土壤颗粒分级方法,以湘中丘陵区地域相邻、环境条件基本一致的4种林地:檵木—南烛—满山红灌草丛(LVR)、檵木—杉木—白栎灌木林(LCQ)、马尾松—石栎—檵木针阔混交林(PLL)和石栎-红淡比-青冈常绿阔叶林(LAG)为对象,研究土壤有机碳(SOC)及不同粒径土壤颗粒有机碳含量随着林地退化的变化特征,剖析林地退化对中亚热带森林SOC库的影响机制。结果表明:随着林地退化,2μm砂粉粒百分含量增高,而2μm黏粒百分含量下降,土壤质地粗砂化;林地SOC含量呈负指数函数下降,LAG林地SOC库以粉粒、黏粒有机碳为分配主体,PLL、LCQ、LVR林地以粉粒、砂粒有机碳为分配主体;随着林地退化,同一土层同一粒径有机碳含量呈下降趋势,砂粒有机碳含量的分配比例明显增加,黏粒有机碳含量的分配比例明显下降,同一土层颗粒有机碳(POC)/矿物结合有机碳(MOC)值增加,SOC固持和保护作用减弱,SOC稳定性下降。群落物种组成、生物量和土壤颗粒组成随着林地退化的变化是导致林地SOC含量和稳定性下降的主要因素。     

Soil Carbon and Nutrient Dynamics Following Cessation of Anthropogenic Disturbances in Degraded Subtropical Forests

Soil carbon (C) and nutrient availability is fundamental to terrestrial biodiversity and functionality. In recent decades, the restoration of degraded forests has become a major concern worldwide, and recent studies have demonstrated that soil C and nitrogen (N) increase over time following restoration. However, our understanding of the responses of soil phosphorus (P), calcium (Ca), potassium (K) and magnesium (Mg) and elemental stoichiometric ratios to restoration remains elusive. We employed a chronosequence to examine the responses of C and macronutrients in three soil layers (0–10 cm, 10–20 cm and 20–30 cm) to the time (0 to 31 years) since the cessation of anthropogenic disturbances in the degraded subtropical forests of Eastern China. We found that stand basal area, soil water content, organic matter content and C concentration and stock increased, while soil pH and bulk density decreased over time, with the most pronounced effects within the 0–10 cm layer. Total and available N and K as well as available P and total Mg increased, while total P in the 20–30 cm layer and Ca in all soil layers decreased over time. The mass concentration ratios of soil C to total N and available N, P and K decreased, whereas those for C to total P and Ca as well as total N to total P and available N to available P increased over time. Our results suggest that soil C accumulation and biologically driven nutrients increase, while nutrients that are driven primarily through geochemical mechanisms decrease with live biomass accumulation following restoration. Copyright © 2017 John Wiley & Sons, Ltd.