土壤溶解性有机物对CO_2和N_2O排放的影响

农田土壤是温室气体的重要排放源,溶解性有机物作为土壤微生物容易利用的基质,其含量变化与温室气体的产生和排放密切相关。基于室内培养试验,对溶解性有机物影响土壤CO2、N2O的排放过程进行了分析。设置空白(CK)、单施秸秆(S)、单施氮肥(N)、秸秆和氮肥(S+N)4个不同的处理,对添加不同物质条件下土壤溶解性有机碳(DOC)、溶解性有机氮(DON)和CO2、N2O的排放动态进行了研究,对DOC和DON影响CO2、N2O的排放过程进行了探讨。结果表明:不同处理的温室气体排放通量和土壤DOC、DON含量差异显著;各处理的CO2排放通量和DOC动态随培养时间的延长呈现逐渐减小的趋势,S和S+N处理的N2O排放和DON动态呈现先增大后减小的趋势;S+N处理的CO2排放量最高,DON含量也显著高于其他处理,单施秸秆(S)处理的N2O排放量和DOC含量显著高于其它处理,单施氮肥(N)对土壤CO2的排放量和DOC含量的影响较小;土壤CO2和N2O的排放通量与土壤DOC和DON含量呈显著的相关性,相关系数(R2)达0.6以上,说明溶解性有机物的含量和动态对CO2、N2O的排放过程产生显著影响。     

生物黑炭对旱地土壤CO2、CH4、N2O排放及其环境效益的影响

采用土柱室内模拟的方法,通过添加0%、0.5%、2%、4%、6%、8%生物黑炭于土壤中,测定土壤CO2、CH4、N2O排放通量,探讨生物黑炭对旱地土壤CO2、CH4、N2O排放及其环境效益的影响。结果表明:室内模拟土柱培养期内,施用生物黑炭能显著增加CO2排放,且生物黑炭添加百分数(x)与CO2累积排放量(y)之间满足线性方程:y=12.591x+235.02(R2=0.834,n=24);当生物黑炭添加量达到2%及以上时,基本抑制了CH4的排放和显著减少土壤N2O排放,并显著减少CH4和N2O的综合温室效应,当其达到4%以上时,CH4和N2O的综合温室效应降幅更大并趋于稳定,但施用少量生物黑炭(0.5%)可显著促进N2O排放,对减少CH4和N2O综合温室效应并无明显效果。生物黑炭表观分解率随其添加量的增加逐渐减少,生物黑炭添加比例越高,积累于土壤中的碳越多,从投入生物黑炭量与固碳量和减排比角度综合考虑,农业生产中推荐生物黑炭施用量为20 t/hm2,其固碳减排效果俱佳。     

线虫和蚯蚓对土壤微量气体排放的影响

线虫和蚯蚓是农业中广泛存在的土壤动物,由于它们与微生物的相互作用及对土壤生态系统能量传递和养分转化的影响,可能影响土壤微量气体代谢和温室气体的排放.通过在不同土壤线虫密度下接种蚯蚓的15d培养试验结果表明,土壤动物对土壤微量气体(CO2和N2O)代谢有显著促进作用.与灭线土相比,高密度线虫土壤处理与高密度线虫土壤加蚯蚓的处理导致CO2排放量分别增加了4.3倍和5.2倍,相应的N2O排放量增加了1.8倍和2.7倍.与低密度线虫土壤处理比较时,高密度线虫土壤处理导致CO2和N2O排放量分别增加了19%和21%.接种蚯蚓在高密度线虫土中较接种在低密度线虫土壤中的CO2和N2O排放量分别增加了12%和27%.5个处理中,除了低密度线虫加蚯蚓的处理和高密度线虫处理间差异不显著外,其余各处理间均达到极显著差异(P<0.01).两种气体的排放速率呈极显著正相关(R2=0.9414).高密度线虫土壤较低密度线虫土壤显著提高了土壤的DOC含量,不同线虫密度土壤中DOC显著性的差异与CO2和N2O排放密切相关(P<0.05).     

冻融对温带森林土壤碳、氮矿化作用的影响

秋末春初,中高纬度和高海拔地区普遍存在冻融现象。随着全球气候变暖,冻融对土壤碳/氮循环过程的影响日益受到重视。本研究以长白山地区典型阔叶红松林(Pinus koraiensis)、白桦林(Betula platyphylla)和长白山落叶松林(Larix olgensis)土壤为研究对象,采用室内模拟控制试验,研究低含水量(40%)和高含水量(过饱和)条件下,冻融循环(-10~10℃)对不同林型土壤碳/氮矿化作用的影响。结果表明,在不同含水量条件下(低含水量条件下的阔叶红松林土壤除外),冻融处理均显著降低土壤有机碳矿化速率,且土壤碳矿化速率随冻融次数的增加而显著降低。冻融与土壤水分对氮矿化存在交互影响;在低含水量条件下,冻融促进土壤氮矿化作用;但在高含水量条件下,该影响不一致。本研究表明,秋末和春初的冻融循环对长白山地区森林土壤碳、氮矿化过程有重要影响,且其影响程度很大程度上取决于冻融频率和土壤含水量。     

土地利用方式和培养温度对土壤氮转化及温室气体排放的影响

在好氧条件下研究土地利用方式(林地、草地)及培养温度(10、15 ℃)对加拿大和中国土壤的硝化作用、氮矿化作用以及N2O和CO2排放的影响.结果表明:草地土壤中的硝化作用和N2O排放量大于林地土壤,中国草地土硝化作用最强.10和15℃下中国草地土硝化速率分别为2.10和2.86 mg N·kg-1·d-1,15 d的N2O累积排放量分别为10.2和15.4μg N2O-N·kg-1.pH是影响土壤硝化作用强度和N2O排放的主要因素,与两者均呈显著正相关.林地土壤的矿化作用和CO2排放量高于草地,中国林地土壤的矿化作用最强,其平均矿化速率在10和15℃时分别为3.08和2.87mgN·kg-1 ·d-1.加拿大林地土壤CO2排放量最高,其15 d的累积排放量在10和15℃时分别为314和370 mg CO2-C·kg-1,土壤有机碳和水溶性有机碳含量分别与有机氮矿化作用和CO2排放量呈显著正相关.温度增加促进草地土壤硝化作用及林地和草地土壤中N2O的排放,也显著促进林地土壤中CO2的排放.     

东北温带次生林和落叶松人工林土壤CH4吸收和N2O排放通量

2007年6月-2008年6月,在帽儿山用静态箱/气相色谱法测定了相邻次生林和落叶松人工林土壤CH4和N2O通量,结果表明:次生林转变为落叶松人工林后土壤年CH4吸收和年N2O排放通量均显著增加,分别为次生林的1.2倍和3.6倍.两林分CH4和N2O通量表现相似的季节动态,生长季土壤CH4吸收通量和N2O排放通量均高于非生长季.次生林和落叶松人工林土壤CH4吸收通量与土壤温度均呈正相关关系,而与土壤含水量呈负相关关系.土壤N2O排放通量与土壤温度和土壤铵态氮含量均呈正相关关系,而与土壤含水量没有明显相关性.次生林转变为落叶松人工林后,落叶松林地较厚的凋落物层改变了林地土壤水分的格局,影响了土壤的CH4和N2O通量.     

冻融作用对我国东北湿地土壤碳排放与土壤微生物的影响

通过室内模拟冻融实验,探讨了冻融强度(-5和-15℃)和循环次数(0、1、5、10和15次)对我国东北连续多年冻土和季节性冻土湿地二氧化碳(CO2)、甲烷(CH4)产生以及土壤微生物生物量碳(MBC)的影响。结果表明,不同冻融条件下,2种冻土中CO2、CH4排放速率及MBC均表现为:在第1次冻融循环后有所降低,随后随着循环次数的增加,呈现先增高后降低并趋于稳定的趋势。总体上,循环次数显著影响2种冻土CO2、CH4排放和MBC。与对照和小幅度冻融循环相比,大幅温度波动显著促进2种冻土土壤碳排放,但冻融强度对MBC影响不大。实验期间,FTC(-15℃)处理中,连续多年冻土CO2累积排放量(679.99 mg·kg-1)高于季节性冻土(454.32 mg·kg-1),而对CH4累积排放量来说,在FTC(-5℃)处理时,连续多年冻土达到334.49μg·kg-1,略高于其他处理;而在FTC(-15℃)处理时,季节性冻土则最高(600.07μg·kg-1),可能意味着冻融过程中2种冻土产甲烷菌的温度敏感性具有一定差异。本研究为科学评估全球气候变化对我国东北主要冻土区的土壤碳周转提供了数据支持。     

黄淮海平原河北省范围内农田土壤二氧化碳和氧化亚氮排放量的估算

以黄淮海平原河北省范围内的农田土壤为研究对象,通过与田间实际观测数据进行比较发现,DNDC模型能够较好地反映农田土壤温室气体CO2和N2O的排放通量,可以用来模拟估算农田土壤CO2和N2O的排放通量.根据模型估算,2003年河北省111个县市农业土壤CO2排放量约3.758×106tC,各县市总的N2O排放量40.345×106kgN.全省释放的CO2和N2O中有40%左右来自冬小麦/夏玉米地.因此,减少该地区农业土壤CO2和N2O排放量的措施,应集中用于排放量高的县市和这些地区的冬小麦/夏玉米地,进行大范围的普遍减排可能收效甚微,并且没有必要.     

黄绵土N2O排放的温度效应及其动力学特征

以室内试验为手段,以黄绵土为供试土壤,研究了不同水热条件下农田土壤中N2O的排放特征,并借助于化学反应动力学理论对N2O排放的热效应机理进行了探讨.结果表明:在适宜的温度范围内,表现为土壤N2O排放量随温度升高而增大.14.50%水分时,20～25℃温区N2O排放呈现"跃增"现象,即温度效应较强,而18.70%和22%水分时,N2O排放的"跃增区"分别出现在15～20℃温区和25～30℃温区,即水分条件影响着N2O排放的温度效应.土壤N2O累积排放量随时间t的变化均符合修正的Elovich方程y=a+blnt,并应用表观排放速率b从动力学角度验证了N2O排放"跃增"现象的存在.在一定的水分条件下,随着温度的增加,土壤N2O排放出现最大值(此时温度为T0),在T1～T0温区内,随温度升高土壤N2O排放量增加,在T0～T2温区内,随温度升高土壤N2O排放量降低,对于黄土性土壤而言,这一转折点(T0)在30℃左右.7.86%水分时干燥土壤存在吸收N2O的现象.     

施氮对桉树人工林生长季土壤温室气体通量的影响

施肥是维持短期轮伐人工林生产量的重要手段,为了提高肥料利用效率,缓释氮肥逐渐成为广泛采用的氮肥种类。评估缓释肥施用对人工林生长季土壤温室气体通量的影响对于全面评估人工林施肥的环境效应具有重要意义。以我国南方广泛种植的桉树林为对象,采用野外控制实验研究了4种施氮处理(对照CK:0 kg/hm2;低氮L:84.2 kg/hm2;中氮M:166.8 kg/hm2;高氮H:333.7 kg/hm2)对土壤-大气界面3种温室气体(CO2、N2O和CH4)通量的影响,结果表明:(1)4种施氮水平下CO2排放通量、N2O排放通量和CH4吸收通量分别为276.84—342.84 mg m-2h-1、17.64—375.34μg m-2h-1和29.65—39.70μg m-2h-1;施氮显著促进了N2O的排放(P0.01),高氮处理显著增加CO2排放和显著减少CH4吸收(P0.05),且CO2排放通量与CH4吸收通量随着施氮量的增加分别呈现增加和减少的趋势;(2)生长季CO2和N2O排放呈现显著正相关(P0.01),CO2排放和CH4吸收呈现显著负相关(P0.05),N2O排放和CH4吸收呈现显著负相关(P0.01);(3)土壤温度和土壤水分是影响CO2、N2O排放通量和CH4吸收通量的主要环境因素。结果表明:施用缓释肥显著增加了桉树林生长季土壤N2O排放量,且高氮处理还显著促进CO2排放和显著抑制CH4吸收,上述研究结果可为人工林缓释肥对土壤温室气体通量评估提供参数。     

Reduced Snow Cover Increases Wintertime Nitrous Oxide (N<Subscript>2</Subscript>O) Emissions from an Agricultural Soil in the Upper U.S. Midwest

Throughout most of the northern hemisphere, snow cover decreased in almost every winter month from 1967 to 2012. Because snow is an effective insulator, snow cover loss has likely enhanced soil freezing and the frequency of soil freeze–thaw cycles, which can disrupt soil nitrogen dynamics including the production of nitrous oxide (N₂O). We used replicated automated gas flux chambers deployed in an annual cropping system in the upper Midwest US for three winters (December–March, 2011–2013) to examine the effects of snow removal and additions on N₂O fluxes. Diminished snow cover resulted in increased N₂O emissions each year; over the entire experiment, cumulative emissions in plots with snow removed were 69% higher than in ambient snow control plots and 95% higher than in plots that received additional snow (P < 0.001). Higher emissions coincided with a greater number of freeze–thaw cycles that broke up soil macroaggregates (250–8000 µm) and significantly increased soil inorganic nitrogen pools. We conclude that winters with less snow cover can be expected to accelerate N₂O fluxes from agricultural soils subject to wintertime freezing.     

N2O emission in a Norway spruce forest due to soil frost: concentration and isotope profiles shed a new light on an old story

In mountain regions of Central Europe an increase of soil frost periods is predicted for this century due to reduced snow fall. To investigate the effects of freezing and thawing on soil N₂O fluxes in a mature Norway spruce forest in the mountainous Fichtelgebirge, Germany, the natural snow cover on three experimental plots was removed to induce soil frost. Three plots with natural snow cover served as controls. Soil N₂O fluxes were recorded in biweekly to monthly intervals during the frost and subsequent thawing period of the below-average cold winter in 2005/2006 and in the above-average warm winter in 2006/2007. In addition, N₂O concentrations and isotope signatures in soil air were measured along soil profiles in six different depths (from 6 to 70 cm). The soil of the snow removal plots was frozen down to 15 cm depth from January to April 2006 while the soil of control plots remained unfrozen under snow cover. Both soil freezing and thawing resulted in almost tenfold enhanced N₂O fluxes on snow removal plots contributing 84% to annual N₂O emissions. In the subsequent winter without soil frost no effects were observed. Vertical gradients of N₂O concentrations together with isotope abundance suggest that the subsoil of all plots was a probably weak, but continuous N₂O source throughout the year. Isotope signatures and N₂O concentration gradients in the soil profile indicate that microbial N₂O production and reduction of N₂O to N₂ did not or just marginally occur in frozen soil layers of the snow removal plots. Consequently, elevated N₂O fluxes in the late winter were attributed to the release of accumulated N₂O originating from the subsoil. At unfrozen soil, however, N₂O emissions were reduced due to a shift of the N₂O production-consumption ratio towards more consumption in the topsoil of both the control and snow removal plots. These findings contradict the general assumption that N₂O production in the organic layer is responsible for bursts of N₂O due to soil frost.     

温带针阔混交林土壤碳氮气体通量的主控因子与耦合关系

中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧化碳(CO2)、甲烷(CH4)和氧化亚氮(N2O)净交换通量以及温度、水分等相关环境因子。研究结果表明:温带针阔混交林土壤整体上表现为CO2和N2O的排放源和CH4的吸收汇。土壤CH4、CO2和N2O通量的年均值分别为-1.3 kg CH4hm-2a-1、15102.2 kg CO2hm-2a-1和6.13 kg N2O hm-2a-1。土壤CO2通量呈现明显的季节性规律,主要受土壤温度的影响,水分次之;土壤CH4通量的季节变化不明显,与土壤水分显著正相关;土壤N2O通量季节变化与土壤CO2通量相似,与土壤水分、温度显著正相关。土壤CO2通量和CH4通量不存在任何类型的耦合关系,与N2O通量也不存在耦合关系;土壤CH4和N2O通量之间表现为消长型耦合关系。这项研究显示温带针阔混交林土壤碳氮气体通量主要受环境因子驱动,不同气体通量产生与消耗之间存在复杂的耦合关系,下一步研究需要深入探讨环境变化对其耦合关系的影响以及内在的生物驱动机制。     

Process-level controls on CO<Subscript>2</Subscript> fluxes from a seasonally snow-covered subalpine meadow soil,Niwot Ridge,Colorado

Fluxes of CO₂ during the snow-covered season contribute to annual carbon budgets, but our understanding of the mechanisms controlling the seasonal pattern and magnitude of carbon emissions in seasonally snow-covered areas is still developing. In a subalpine meadow on Niwot Ridge, Colorado, soil CO₂ fluxes were quantified with the gradient method through the snowpack in winter 2006 and 2007 and with chamber measurements during summer 2007. The CO₂ fluxes of 0.71 μmol m⁻² s⁻¹ in 2006 and 0.86 μmol m⁻² s⁻¹ in 2007 are among the highest reported for snow-covered ecosystems in the literature. These fluxes resulted in 156 and 189 g C m⁻² emitted over the winter, ~30% of the annual soil CO₂ efflux at this site. In general, the CO₂ flux increased during the winter as soil moisture increased. A conceptual model was developed with distinct snow cover zones to describe this as well as the three other reported temporal patterns in CO₂ flux from seasonally snow-covered soils. As snow depth and duration increase, the factor controlling the CO₂ flux shifts from freeze–thaw cycles (zone I) to soil temperature (zone II) to soil moisture (zone III) to carbon availability (zone IV). The temporal pattern in CO₂ flux in each zone changes from periodic pulses of CO₂ during thaw events (zone I), to CO₂ fluxes reaching a minimum when soil temperatures are lowest in mid-winter (zone II), to CO₂ fluxes increasing gradually as soil moisture increases (zone III), to CO₂ fluxes decreasing as available carbon is consumed. This model predicts that interannual variability in snow cover or directional shifts in climate may result in dramatically different seasonal patterns of CO₂ flux from seasonally snow-covered soils.     

Multivariate regulation of soil CO2 and N2O pulse emissions from agricultural soils

Climate and land‐use models project increasing occurrence of high temperature and water deficit in both agricultural production systems and terrestrial ecosystems. Episodic soil wetting and subsequent drying may increase the occurrence and magnitude of pulsed biogeochemical activity, affecting carbon (C) and nitrogen (N) cycles and influencing greenhouse gas (GHG) emissions. In this study, we provide the first data to explore the responses of carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes to (i) temperature, (ii) soil water content as percent water holding capacity (%WHC), (iii) substrate availability throughout, and (iv) multiple soil drying and rewetting (DW) events. Each of these factors and their interactions exerted effects on GHG emissions over a range of four (CO₂) and six (N₂O) orders of magnitude. Maximal CO₂ and N₂O fluxes were observed in environments combining intermediate %WHC, elevated temperature, and sufficient substrate availability. Amendments of C and N and their interactions significantly affected CO₂ and N₂O fluxes and altered their temperature sensitivities (Q₁₀) over successive DW cycles. C amendments significantly enhanced CO₂ flux, reduced N₂O flux, and decreased the Q₁₀ of both. N amendments had no effect on CO₂ flux and increased N₂O flux, while significantly depressing the Q₁₀ for CO₂, and having no effect on the Q₁₀ for N₂O. The dynamics across DW cycles could be attributed to changes in soil microbial communities as the different responses to wetting events in specific group of microorganisms, to the altered substrate availabilities, or to both. The complex interactions among parameters influencing trace gas fluxes should be incorporated into next generation earth system models to improve estimation of GHG emissions.     

Influence of nematodes and earthworms on the emissions of soil trace gases (CO2, N2O)

To determine effects of soil fauna on greenhouse gas emissions, soil inoculated with different populations of nematodes and earthworms was incubated for 15 d. Soil with greater populations of nematodes and earthworms enhanced CO₂ and N₂O emissions. Cumulative emission fluxes of the two gases in the treatment of greater populations of nematodes and the treatment of greater populations of nematodes and earthworms were increased by 4.3 and 5.2 times for CO₂, 1.8 and 2.7 times for N₂O, respectively in comparison of the nematode-killed treatment. The emission fluxes of CO₂ and N₂O in soil treated with greater populations of nematodes were 19% for CO₂ and 21% for N₂O higher than those in soil treated with lower populations of nematodes. Meanwhile, the emission fluxes of the two gases in soil treated with greater populations of nematodes and earthworms were 12% for CO₂ and 27% for N₂O higher than those in soil treated with lower populations of nematodes and earthworms. The two gas fluxes were significantly correlated (R² = 0.9414; p < 0.001). Cumulative emissions of CO₂ and N₂O from soil treated with different populations of nematodes were positively correlated with DOC (dissolved organic carbon) concentration measured at the start of gas sampling (p < 0.05).     

水肥一体化条件下设施菜地的N2O排放

在保证作物产量的前提下,研究减少农田土壤N_2O排放的水肥统筹管理措施对全球温室气体减排具有重要意义。以京郊典型设施菜地为例,设置了农民习惯(FP)、水肥一体化(FPD)、优化水肥一体化(OPTD)和对照(CK)4个处理,采用静态箱-气相色谱法,对果菜-叶菜(黄瓜-芹菜)轮作周期内土壤N_2O排放进行了观测,并分析了氮肥施用量、灌溉方式、土壤温度和湿度等因素对土壤N_2O排放的影响。结果表明:在黄瓜-芹菜种植模式中,各施氮处理除基肥施用后N_2O排放峰持续10—15d外,一般施肥、施肥+灌溉事件后土壤N_2O排放峰均呈现3—5d短而急促的情形。黄瓜生长季N_2O排放通量与土壤湿度(WFPS)之间呈现显著相关的关系;芹菜生长季N_2O排放通量与土壤温度之间呈现显著相关的关系。观测期内FP处理N_2O排放量为(31.00±2.15)kg N/hm~2,FPD处理与之相比N_2O排放量减少了4.2%,而OPTD处理在减少40%化肥氮量的情况下,N_2O累积排放量比FP处理减少了42.7%,且达到显著水平。说明在水肥一体化条件下,合理改变施肥体系是减少N_2O排放的前提,在此基础上进行水肥优化是设施菜地保持产量、减少N_2O排放的重要技术措施。     

渗滤液负荷和灌溉深度对土壤氧化亚氮与二氧化碳释放的影响

采用预设取样器和静态箱气相色谱法,对渗滤液灌溉条件下,土柱土壤不同深度剖面 N₂O的浓度以及N₂O和CO₂的表面释放通量进行了监测.结果表明: 渗滤液灌溉可促进N₂O的生成和释放,灌溉后24 h内土柱N₂O的释放通量与表土下10 cm（r=0.944,P< 0.01）、20 cm（r=0.799,P<0.01）、30 cm（r=0.666,P<0.01）和40 cm（r=0.482,P<0.05）处所生成的N₂O浓度呈显著相关,且相关程度依次递减.渗滤液灌溉还促进了CO₂的释放,但N₂O与CO₂释放通量之间无显著相关性（P>0.05）.渗滤液的灌溉负荷主要决定温室气体释放总量的强弱（N₂O和CO₂,以CO₂当量计）,灌溉负荷为6 mm·d^-1条件下温室气体释放总量为灌溉负荷2 mm·d^-1的3倍多.采用表土下20 cm处灌溉方式可比表土下10 cm处灌溉方式削减47%的温室气体释放总量.渗滤液灌溉土壤14 d内,N₂O释放量约占温室气体释放总量的57.0%～91.0%.     

Winter production of CO2 and N2O from alpine tundra: environmental controls and relationship to inter-system C and N fluxes

Fluxes of CO₂ and N₂O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C, but there was no significant relationship between flux for either gas and temperature within this range. While early developing snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest CO₂ fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal flux of CO₂ –C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO₂ –C loss ranged from 0.3 g C m⁻² season⁻¹ at sites characterized by inconsistent snow cover to 25.7 g C m⁻² season⁻¹ at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed with C loss, a hard freeze early in the winter did not result in greater N₂O–N loss. Both mean daily N₂O fluxes and the total over-winter N₂O–N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N₂O–N loss ranged from less 0.23 mg N m⁻² from the latest developing, short duration snowpacks to 16.90 mg N m⁻² from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N₂O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling in these environments. Received: 5 April 1996 / Accepted: 25 November 1996     

Influence of nematodes and earthworms on the emissions of soil trace gases (CO2, N2O)

To determine effects of soil fauna on greenhouse gas emissions, soil inoculated with different populations of nematodes and earthworms was incubated for 15 d. Soil with greater populations of nematodes and earthworms enhanced CO₂ and N₂O emissions. Cumulative emission fluxes of the two gases in the treatment of greater populations of nematodes and the treatment of greater populations of nematodes and earthworms were increased by 4.3 and 5.2 times for CO₂, 1.8 and 2.7 times for N₂O, respectively in comparison of the nematode-killed treatment. The emission fluxes of CO₂ and N₂O in soil treated with greater populations of nematodes were 19% for CO₂ and 21% for N₂O higher than those in soil treated with lower populations of nematodes. Meanwhile, the emission fluxes of the two gases in soil treated with greater populations of nematodes and earthworms were 12% for CO₂ and 27% for N₂O higher than those in soil treated with lower populations of nematodes and earthworms. The two gas fluxes were significantly correlated (R² = 0.9414; p < 0.001). Cumulative emissions of CO₂ and N₂O from soil treated with different populations of nematodes were positively correlated with DOC (dissolved organic carbon) concentration measured at the start of gas sampling (p < 0.05).