庐山毛竹扩张及模拟氮沉降对土壤N_2O和CO_2排放的影响

毛竹是我国南方广泛分布的一种典型的森林资源,其扩张已引发了多方面的生态问题,但是目前关于氮沉降背景下毛竹扩张引起的土壤N_2O和CO_2气体排放变化的研究甚少,且无原位观测数据。采用静态箱-气相色谱法,分析江西庐山毛竹纯林、毛竹扩张形成的毛竹-日本柳杉混交林及日本柳杉纯林3种林分土壤的N_2O和CO_2排放速率和累积排放量及其对模拟氮沉降的响应。结果表明:(1)混交林土壤的NH_4~+-N含量、NO_3~--N含量及pH分别为14.39mg·kg~(-1)、8.65mg·kg~(-1)、4.88,显著高于日本柳杉纯林的9.75 mg·kg~(-1)、5.58 mg·kg~(-1)、4.05,但是混交林土壤DOC含量(236.5 mg·kg~(-1))却显著低于日本柳杉纯林(382.0mg·kg~(-1))。(2)混交林土壤N_2O累积排放量(393.6mg·m~(-2))显著高于毛竹纯林(202.5mg·m~(-2))和日本柳杉纯林(192.8mg·m~(-2)),混交林土壤CO_2累积排放量(4 655 g·m~(-2))显著高于日本柳杉纯林(2 815 g·m~(-2))。(3)模拟氮沉降未对3种林分类型土壤的CO_2排放速率和累积排放量产生显著影响,但明显增加了混交林和日本柳杉纯林的N_2O累积排放量。本研究表明:毛竹扩张不同阶段土壤的理化性质、N_2O及CO_2排放表现出不同特征。毛竹扩张过程中一定程度上增大了土壤N_2O和CO_2的排放量,但是完全扩张后N_2O排放出现明显下降趋势,而CO_2的排放未发生显著变化。同时,氮沉降促进了毛竹未扩张和扩张初期土壤的N_2O排放,而对CO_2排放未产生显著影响。表明在未来气候变化条件下管理亚热带毛竹扩张时,必须明确考虑这些生态系统组成、结构和影响因子之间的影响。     

硝态氮源及碳源有效性对土壤N_2O和CO_2排放的影响

以华北平原农田土壤为对象,通过室内静态培养系统研究NO_3~--N与不同碳源组合对土壤N_2O和CO_2排放的影响。结果表明,NO_3~--N作为氮源和不同碳源施入土壤,除NO_3~-+纤维素,其余土壤N_2O排放通量均高于对照组和只添加氮源土壤;NO_3~--N和不同碳源组合的CO_2累积排放量均高于对照和只添加氮源土壤。NO_3~-+果胶的N_2O排放量在第1 d达到最大值1 383.42μg N·kg~(-1)·d~(-1);NO_3~-+葡萄糖的CO_2排放量在第1 d达到最大值370.13 mg C·kg~(-1)·d~(-1),CO_2累积排放量顺序为:葡萄糖果胶秸秆纤维素淀粉木质素。土壤NO_3~--N含量与N_2O排放呈极显著正相关。总之,添加纤维素可以抑制N_2O的排放,促进CO_2排放,并增加土壤中NO_3~--N含量,添加其余碳源均会促进土壤N_2O和CO_2排放。     

土壤中羟胺和亚硝态氮非生物过程对N_2O排放的贡献

羟胺(NH_2OH)和亚硝态氮(NO_2~--N)均可以通过非生物过程产生N_2O,但是同一土壤中其对N_2O排放的相对贡献尚不明确。本文采用高压灭菌和室内培养方法,测定了采自6个不同地点的农业利用土壤在灭菌和非灭菌条件下添加NH_2OH或NO_2~--N后N_2O的排放量,以研究土壤中NH_2OH和NO_2~--N非生物过程对N_2O排放的相对贡献及其关键因子。结果表明,供试土壤中,NH_2OH非生物过程产生的N_2O贡献介于6%~73%,NO_2~--N非生物过程产生N_2O占的比例为3%~236%;在pH7的衢州茶园、鹰潭旱地、常熟菜地和海伦旱地土壤中,添加NO_2~--N后非生物过程产生N_2O比例大于添加NH_2OH的处理,但是在pH7的常熟果园和封丘旱地土壤中则相反;pH是影响NH_2OH和NO_2~--N非生物过程产生N_2O的关键因子,添加NH_2OH处理中非生物过程产生N_2O占N_2O总排放量的比例与土壤pH呈正相关(p0.05),而在添加NO_2~--N处理中呈负相关(p0.01)。上述结果说明,NO_2~--N在偏酸性土壤中可能主要通过非生物过程产生N_2O,而在偏碱性土壤中主要通过生物过程;NH_2OH则与之相反。     

减量施氮与秸秆添加对设施菜田N2O的减排效应

采用静态箱–气相色谱法,在宁夏灌区设施菜田研究了不施肥(CK)、单施有机肥(M)、常规施肥(CON)、减量优化化肥(OPT)、优化化肥+调节土壤碳氮比(OPT+C/N) 5种施肥方式对春茬黄瓜和夏休闲期土壤N_2O排放通量、累积排放量和排放系数的影响。结果表明:各施肥处理土壤N_2O排放通量高峰一般出现在黄瓜滴灌施肥或夏休闲期漫灌后第1天或第3天。春茬黄瓜基肥、追肥和夏休闲期,OPT、OPT+C/N处理土壤N_2O排放通量较CON处理分别降低了3.6%～47.2%、5.9%～49.9%和14.7%～46.6%。春茬黄瓜季和夏休闲期各施肥处理的N_2O累积排放量分别为2.05～9.98kg/hm~2和3.55～7.23 kg/hm~2,OPT、OPT+C/N处理较CON处理分别降低了26.2%～34.3%和29.6%～33.7%。春茬黄瓜当季肥料的N_2O排放系数为0.43%～0.71%,而春茬黄瓜–夏休闲期总排放系数为0.54%～1.04%。N_2O总排放量与施氮量呈显著正相关(R~2=0.778);N_2O排放通量与5cm表层地温呈显著或极显著相关(R~2=0.47～0.68),与0～20cm土壤含水量呈极显著相关(R~2=0.63～0.88)。因此,相对于农民常规施氮方式,减施50%化肥氮量或减氮配合添加7.5 t/hm~2的小麦秸秆来调节土壤碳氮比都能达到设施菜田土壤N_2O的减排目标。     

林地转变为耕地对紫色土N2O排放的影响

土地利用方式变化是造成大气中温室气体浓度变化的主要原因之一,但土地利用方式转变,如林地转变为耕地过程对土壤氧化亚氮(N_2O)排放的影响还缺乏系统研究。本研究于2016年7月中旬在四川盆地丘陵区将林地转变为耕地,并按照耕地冬小麦-夏玉米轮作方式,采用静态暗箱-气相色谱法,对比分析了耕地翻耕不施肥(CL-T)、翻耕施肥(CL-TF)和邻近林地(CK)的土壤N_2O排放过程特征。结果表明,试验期间CL-T、CL-TF土壤N_2O排放通量较CK均显著增加(P0.01),且二者的N_2O排放通量在林地转变为耕地初期均有明显的排放峰。小麦季和玉米季土壤N_2O排放通量[μg(N)·m-2·h-1]均值CK分别为2.52和4.60,CL-T分别为3.55和11.63,CL-TF分别为6.26和22.16,N_2O排放通量玉米季显著高于小麦季。CK、CL-T和CL-TF的土壤N_2O全年累积排放量[mg(N)·hm-2]分别为0.271、0.515和0.957,CL-T、CL-TF较CK分别显著增长89.8%、253.0%,说明林地转变为耕地,紫色土N_2O排放迅速增加。首先翻耕改变土壤结构并显著增加土壤无机氮含量(P0.05),其次施肥大幅增加土壤无机氮含量导致土壤N_2O的激发排放。而土壤温度和水分未发生显著改变(P0.05),种植作物短时间内也未显著改变土壤的N_2O排放。结果表明,林地转变为耕地激发土壤N_2O排放的根本机制可能是提高了土壤有机氮矿化速率。但土地利用转变对土壤氮转化过程的影响以及进而改变土壤N_2O的排放特征的机理有待进一步研究。     

氮肥配施纳米碳对植烟土壤氮素转化及N2O排放的影响

采用实验室静态培养方法,通过氮肥配施不同量纳米碳来探究纳米碳对植烟土壤氮素转化以及N_2O排放的影响。试验在等氮条件下共设置5个处理:CK,硝酸铵(N 200 mg/kg,下同);NC1,硝酸铵+纳米碳(2.5 g/kg);NC2,硝酸铵+纳米碳(5 g/kg);NC3,硝酸铵+纳米碳(10 g/kg);NC4,硝酸铵+纳米碳(15 g/kg)。结果表明:NC3和NC4处理较CK处理显著降低了土壤pH(P0.05);与CK处理相比,NC1、NC2、NC3和NC4处理在培养前期增加了土壤NH_4~+-N含量,相应降低了NO_3~–-N含量;在培养结束时,与CK处理相比,添加纳米碳处理显著降低了无机氮含量,而显著增加了CO_2累积排放量(P0.05);另外,添加纳米碳处理较CK处理增加了N_2O累积排放量,但仅NC4处理与CK处理间差异显著(P0.05),N_2O累积排放量与CO_2累积排放量呈显著正相关关系(R~2=0.50,P0.001)。可见,添加纳米碳能够降低土壤pH和无机氮含量,抑制土壤硝化作用,同时还可以提高微生物活性和增加N_2O排放量。     

等氮量下不同分施次数对燥红壤N2O排放的影响

通过室内培养试验研究等氮量下不同施肥次数对N_2O排放的影响。试验设一次性施氮(S1,将200 mg/kg氮肥一次性施入土壤),二次分施(S2,将200 mg/kg氮肥分两次平均施入土壤),三次分施(S3,将200 mg/kg氮肥分80、60、60 mg/kg 3次施入土壤)和空白(CK,不施肥)4个处理。培养在65%田间持水量,30℃恒温箱中进行。结果表明,氮肥施入显著促进土壤N_2O排放;等施氮量下,不同分施次数使土壤pH呈显著性差异,而土壤pH的差异又影响了土壤N_2O累积排放量;分施次数越多,土壤酸化程度越强,N_2O累积排放量越少。因此,在等施氮量下,要充分考虑土壤酸化、N_2O排放、NO–3-N积累以及施肥成本等,确定合理分施次数。     

秸秆与氮肥调节C/N比对潮土CH_4,CO_2和N_2O排放/吸收的影响

为了探讨秸秆还田与氮肥配施对砂质潮土CH_4,CO_2和N_2O排放/吸收规律及土壤碳、氮含量的影响,采用恒温培养的方法,在土壤中添加定量秸秆情况下,通过尿素调节不同C/N比(分别为9、12.5、25、40、71),并设单施氮肥处理(N),同时以原土(不施肥)为对照(CK),研究了玉米秸秆与氮肥调节C/N比对砂质潮土不同形态碳、氮含量的变化以及对CH_4,CO_2和N_2O等温室气体动态排放特征。结果表明,培养结束时,随着配施C/N比的增加,土壤可溶性有机碳(DOC)呈先增加后降低趋势,以C/N比为25时最高,可溶性有机氮(DON)呈增加趋势,以C/N比为9时最高;秸秆添加后对土壤NH_4^+-N和NO_3^--N含量具有一定的抑制作用,但随着配施氮肥量的增加NH_4^+-N和NO_3^--N含量呈增加趋势。同时发现,在37 d室内培养试验中,各处理土壤整体表现为对CH_4的吸收,单施N肥较CK对CH_4的排放无显著影响,C/N比为71(单独添加秸秆)促进了CH_4的吸收,而秸秆与氮肥配施抑制了土壤对CH_4的吸收。CO_2排放通量整体上随时间呈现出"上升-下降-稳定"的过程;各处理均在培养的第3 d达到排放峰值,且在添加秸秆情况下C/N比越小CO_2排放通量越高,最高达5.47mg kg^-1h^-1。不同处理N_2O的排放通量随时间变化具有不同的变化趋势,C/N比为71、40和25的3个处理在培养第1 d即达到排放最大值,而C/N比为12.5和9及单施N等3个处理排放峰值则出现在培养的第3 d,且排放峰值随氮肥用量的增加而增高,C/N比为9时达到最高,为2.64滋g kg^-1h^-1。CO_2和N_2O累积排放量最大的处理为C/N比为9,分别为1551.3 mg kg^-1和240.5 mg kg^-1。由此得出,秸秆与氮肥的配施促进了砂质潮土CO_2和N_2O的排放以及对CH_4的吸收,随着配施C/N的减小,砂质潮土对CO_2和N_2O的排放以及CH_4的吸收增强。     

冬季施用鸡粪和生物炭对南方稻田土壤CO2与CH4排放的影响

生物炭的利用近年来是农田土壤固碳减排研究中的热点。本研究通过在冬季稻田养鸡,结合生物炭添加,采用箱式法结合温室气体分析仪定量测定冬季稻田和双季稻期间土壤CO_2和CH_4排放通量,分别估算冬季稻田和双季稻期间土壤CO_2和CH_4排放总量,评估生物炭和鸡粪添加对土壤碳排放的影响。结果表明,鸡粪还田处理显著提高了土壤CO_2的排放,冬季稻田和水稻生育期排放量分别达9 935.39 kg·hm~(-2)和27 756.34kg·hm~(-2),比对照增加58.7倍(P0.01)和56%(P0.05);生物炭添加处理冬季稻田和水稻生育期CO_2累积排放量比对照高12.3倍(P0.01)和41%(P0.05)。鸡粪还田处理下冬季稻田和水稻生育期稻田的CH_4排放量均显著高于其他处理;而生物碳添加对冬季稻田CH_4排放无显著影响,但显著降低了水稻生育期稻田的CH_4排放。鸡粪还田配施生物炭处理也显著提高了稻田土壤CO_2的排放。冬季稻田时,鸡粪还田配施生物炭土壤CO_2累积排放量显著高于鸡粪还田处理;而水稻生育期时,鸡粪还田配施生物炭处理下土壤CO_2累积排放量显著低于鸡粪还田处理。鸡粪还田下添加生物碳可以降低因鸡粪还田引起的CH_4排放增加的效应。总之,鸡粪原位还田显著增加了冬季稻田和水稻生育期稻田的CO_2和CH_4排放;无论是冬季稻田还是水稻生育期,生物炭的添加都降低了土壤CH_4的排放,且生物炭添加后期有抑制土壤CO_2排放的作用。因此,从更长的时间尺度来看,生物炭施入土壤有利于土壤固碳减排。     

施氮及添加硝化抑制剂对苜蓿草地N2O排放的影响

为探究旱作紫花苜蓿(MedicagosativaL.)栽培草地氧化亚氮(N_2O)排放对施氮水平及添加硝化抑制剂的响应特征,采用传统静态箱法研究了不同施氮水平[0kg(N)·hm~(-2)(N0)、 50kg(N)·hm~(-2)(N50)、 100kg(N)·hm~(-2)(N100)和150kg(N)·hm~(-2)(N150)]以及添加硝化抑制剂双氰胺(DCD)150kg(N)·hm~(-2)(N150+DCD)对陇东苜蓿草地N_2O排放特征的影响。结果显示,监测期内N0、N50、N100和N150处理N_2O平均排放速率分别为3.5μg·m~(-2)·h~(-1)、4.1μg·m~(-2)·h~(-1)、5.0μg·m~(-2)·h~(-1)和6.1μg·m~(-2)·h~(-1),随着施氮梯度的增加, N_2O排放速率呈增加趋势。添加硝化抑制剂DCD对N_2O排放产生明显的抑制作用。与N150处理相比, N150+DCD处理下苜蓿草地N_2O平均排放速率下降50.7%, N_2O累计排放量显著降低61.6%(P0.05)。施氮对苜蓿产量没有显著影响,而N0、N50、N100和N150处理下单位苜蓿产量N_2O排放量随氮肥梯度的增加而增加,各处理分别为6.5 mg·kg~(-1)、7.8 mg·kg~(-1)、11.3 mg·kg~(-1)和12.5 mg·kg~(-1)。N_2O排放受土壤含水量影响深刻,生长季N_2O排放通量与土壤水分呈显著正相关关系(P0.05),而与土壤温度无显著相关性(P0.05)。综上,旱作紫花苜蓿栽培草地N_2O排放通量随施氮水平的增加明显增加,在相同施氮水平下添加硝化抑制剂DCD能显著抑制N_2O排放。相关研究结果对于该区域苜蓿草地合理施肥以及N_2O减排具有一定的实践指导意义。     

Chemical and colloidal stability of sols in the Al2O3-Fe2O3-SiO2-H2O system: their role in podzolization

Concentrations of dialysable silica in equilibrium with Al₂O₃-SiO₂-H₂O sols at pH 4.5–5.0 confirm the formation of a poorly ordered non-dialysable proto-imogolite species with an Al : Si ratio near 2, close to that of imogolite. Sols with Al : Si>2 give nearly constant levels of free silica in solution in the range 2–6 μg/cm³, indicating equilibrium between proto-imogolite and aluminium hydroxide species. These findings indicate that imogolite-like precipitates in acid soils will buffer silica in solution to within this range during leaching episodes. Imogolite is more stable than a previous estimate suggested, and a revised value for its free energy of formation is proposed: ΔG⁰_f(298.15) = -2929.7 kJ/mol. In Fe₂O₃-SiO₂-H₂O sols, the Fe : Si ratio of the non-dialysable species varies smoothly from 11 to 3 as free silica in solution ranges from 4 to 35 μg/cm³. Such sols are much less colloidally stable than hydroxyaluminium silicate sols, but mixed Al₂O₃—Fe₂O₃—SiO₂—H₂O sols are almost as stable as iron-free sols up to a Fe : Al ratio of 1.5. Thus migration of Al and Fe as mixed hydroxide sols can account for the almost constant ratio of Al to Fe with depth in oxalate extracts from Bs horizons of podzols.     

铁、锰、铝氧化物固体吸附剂对胡敏酸和富里酸吸附机理研究

研究了Fe2O3、MnO2或Al2O3固体吸附剂对胡敏酸和富里酸的吸附机制和影响因素。结果表明:相同pH下,Fe2O3、MnO2或Al2O3固体吸附剂对腐殖酸的吸附量随着腐殖酸(胡敏酸HA和富里酸FA)有机碳浓度的增加而增加;不同pH下,对HA的吸附量依照pH3·0>pH5·0>pH7·0的顺序递减。相同pH下,随着HA有机碳浓度的增加,三种固体吸附剂对HA的吸附百分率减小。相同pH下,三种固体吸附剂对FA的吸附百分率呈单峰形,随着酸度的降低,峰位向添加的有机碳低浓度处迁移。吸附量用Langumuir方程拟合能得到极显著相关的方程,在相同pH下,三种固体吸附剂吸附HA的最大吸附量Smax和吸附亲和力常数K小于FA,而标准自由能变ΔGmo却略大于FA;298·2K温度下,三种固体吸附剂吸附胡敏酸和富里酸的ΔGmo<0,表明在等温等压不做非体积功情况下吸附是自发进行的反应。     

添加H2O2改性和HNO3/H2SO4改性生物质炭对一种酸性水稻土吸附Cd (Ⅱ)的影响

选择稻草、玉米秸秆和油菜秸秆作为制备生物质炭的原料，分别用H2O2和HNO3/H2SO4对生物质炭进行改性处理，以未改性的生物质炭和HCl处理的生物质炭作为对照。按土重3%的比例向采自安徽郎溪的酸性水稻土中添加上述生物质炭，在经历一个干湿交替周期后，进行Cd(Ⅱ)吸附/解吸实验，研究添加生物质炭对水稻土吸附Cd(Ⅱ)的影响及其机制。结果表明，两种改性方法均有效增加了生物质炭表面的质子结合位点数，且HNO3/H2SO4改性对生物质炭表面羧基官能团的扩增效果更显著。官能团的增加使得添加了HNO3/H2SO4改性生物质炭的水稻土对Cd(Ⅱ)的专性吸附能力显著增强。因此，添加HNO3/H2SO4改性生物质炭可以作为酸性水稻土吸附固定重金属Cd的一种新型方法。     

碳酸氧镧改性生物炭材料的合成及对磷酸盐去除性能

为高效去除废水中过量的磷酸盐为目的，该研究将研究利用艾草生物质与镧溶液共生共热的方法制成具有大量纳米级碳酸氧镧突起的镧基复合生物炭材料，研究了材料投加量、初始磷酸盐浓度、吸附时间、初始溶液pH值和共存离子对其吸附磷酸盐性能的影响及饱和磷吸附镧基复合生物炭材料（La-CB2-P）对生菜种子发芽率的试验。试验结果表明：La-CB2最佳投加量为1 g/L，最佳吸附温度为25 ℃，对磷酸盐的吸附主要为多分子层吸附，Langmuir模型模拟最大吸附容量为126.82 mg/g，并在12h内达到吸附平衡，酸性至中性水环境中La-CB2吸附性能更优，并对碱性水环境的pH值具有缓冲作用，在pH值为3时La³⁺浸出率为7.66%，其他pH值条件下仅为0.029%左右，在磷吸附过程中La-CB2的DOC溶出量随着初始溶液pH值的升高呈先增后减的趋势，在多种共存阴离子中对磷酸盐具有很强的选择性吸附，水体中的腐殖酸会大幅度降低La-CB2对磷酸盐的吸附性能。饱和磷吸附镧基复合生物炭材料（La-CB2-P）能够作为磷缓释肥显著促进生菜发芽，对La-CB2在富营养水体的磷吸附及资源回收提供了大量的理论基础。     

Ureide production by N2-fixing and non-N2-fixing leguminous trees

Xylem-sap and stem and leaf extracts from 35 species, comprising 14 genera, of leguminous trees were analyzed for ureides, nitrate and -amino acids. Trees were either inoculated with Rhizobium or fertilized with NH₄NO₃. The dominant form of soluble N in stem and leaf extracts and xylem sap was 2-amino acids. Certain non-N₂-fixing species, i.e. Tamarindus indica and Adenantherapavonina, produced significant amounts of ureides. Several N₂-fixing species. Mimosa scabrella, Sesbania grandiflora. Acacia mearnsii and Gliricida sepium, grown on mineral-N had higher absolute amounts of ureides in both extracts and exudates than did most nodulated species. Nodulated A. meamsii and S. grandiflora, had the highest amounts of ureides in xylem sap. The relative abundance of ureides in stem and leaf extracts was lower than in xylem sap, but was correlated. Results indicated that the presence of ureides, per se, was not a reliable indicator of N₂-fixing activity. Moreover, the relative abundance of ureides in most of the species tested was too low to use as a presumptive test for, or as a means of, estimating N₂ fixation.     

Elevated CO2 stimulates N2O emissions in permanent grassland

To evaluate climate forcing under increasing atmospheric CO₂ concentrations, feedback effects on greenhouse gases such as nitrous oxide (N₂O) with a high global warming potential should be taken into account. This requires long-term N₂O flux measurements because responses to elevated CO₂ may vary throughout annual courses. Here, we present an almost 9 year long continuous N₂O flux data set from a free air carbon dioxide enrichment (FACE) study on an old, N-limited temperate grassland. Prior to the FACE start, N₂O emissions were not different between plots that were later under ambient (A) and elevated (E) CO₂ treatments, respectively. However, over the entire experimental period (May 1998–December 2006), N₂O emissions more than doubled under elevated CO₂ (0.90 vs. 2.07 kg N₂O-N ha⁻¹ y⁻¹ under A and E, respectively). The strongest stimulation occurred during vegetative growth periods in the summer when soil mineral N concentrations were low. This was surprising because based on literature we had expected the highest stimulation of N₂O emissions due to elevated CO₂ when mineral N concentrations were above background values (e.g. shortly after N application in spring). N₂O emissions under elevated CO₂ were moderately stimulated during late autumn–winter, including freeze–thaw cycles which occurred in the 8th winter of the experiment. Averaged over the entire experiment, the additional N₂O emissions caused by elevated CO₂ equaled 4738 kg CO₂-equivalents ha⁻¹, corresponding to more than half a ton (546 kg) of CO₂ ha⁻¹ which has to be sequestered annually to balance the CO₂-induced N₂O emissions. Without a concomitant increase in C sequestration under rising atmospheric CO₂ concentrations, temperate grasslands may be converted into greenhouse gas sources by a positive feedback on N₂O emissions. Our results underline the need to include continuous N₂O flux measurements in ecosystem-scale CO₂ enrichment experiments.     

Emissions of CO2, CH4 and N2O from Southern European peatlands

Peatlands play an important role in emissions of the greenhouse gases CO₂, CH₄ and N₂O, which are produced during mineralization of the peat organic matter. To examine the influence of soil type (fen, bog soil) and environmental factors (temperature, groundwater level), emission of CO₂, CH₄ and N₂O and soil temperature and groundwater level were measured weekly or biweekly in loco over a one-year period at four sites located in Ljubljana Marsh, Slovenia using the static chamber technique. The study involved two fen and two bog soils differing in organic carbon and nitrogen content, pH, bulk density, water holding capacity and groundwater level. The lowest CO₂ fluxes occurred during the winter, fluxes of N₂O were highest during summer and early spring (February, March) and fluxes of CH₄ were highest during autumn. The temporal variation in CO₂ fluxes could be explained by seasonal temperature variations, whereas CH₄ and N₂O fluxes could be correlated to groundwater level and soil carbon content. The experimental sites were net sources of measured greenhouse gases except for the drained bog site, which was a net sink of CH₄. The mean fluxes of CO₂ ranged between 139 mg m⁻² h⁻¹ in the undrained bog and 206 mg m⁻² h⁻¹ in the drained fen; mean fluxes of CH₄ were between −0.04 mg m⁻² h⁻¹ in the drained bog and 0.05 mg m⁻² h⁻¹ in the drained fen; and mean fluxes of N₂O were between 0.43 mg m⁻² h⁻¹ in the drained fen and 1.03 mg m⁻² h⁻¹ in the drained bog. These results indicate that the examined peatlands emit similar amounts of CO₂ and CH₄ to peatlands in Central and Northern Europe and significantly higher amounts of N₂O.     

Infrared spectra of Cu2+ Pb2+ and Ca2+ complexes of soil humic substances

An infrared spectroscopic investigation of the complexes of Cu²⁺, Pb²⁺, and Ca²⁺ with humic and fulvic acids demonstrated the participation of OH and CO groups in addition to COOH in the binding of heavy-metal cations. The degree to which metal-carboxylate linkages are ionic or covalent cannot be accurately determined from the positions of antisymmetric and symmetric carboxylate stretching vibrations due to interference from covalent bonding with other groups. The apparent order of the reaction of three divalent cations with humic and fulvic acids was Cu²⁺ > Pb²⁺ > Ca²⁺.     

Relationship between soil CO2 concentrations and forest-floor CO2 effluxes

To better understand the biotic and abiotic factors that control soil CO₂ efflux, we compared seasonal and diurnal variations in simultaneously measured forest-floor CO₂ effluxes and soil CO₂ concentration profiles in a 54-year-old Douglas fir forest on the east coast of Vancouver Island. We used small solid-state infrared CO₂ sensors for long-term continuous real-time measurement of CO₂ concentrations at different depths, and measured half-hourly soil CO₂ effluxes with an automated non-steady-state chamber. We describe a simple steady-state method to measure CO₂ diffusivity in undisturbed soil cores. The method accounts for the CO₂ production in the soil and uses an analytical solution to the diffusion equation. The diffusivity was related to air-filled porosity by a power law function, which was independent of soil depth. CO₂ concentration at all depths increased with increase in soil temperature, likely due to a rise in CO₂ production, and with increase in soil water content due to decreased diffusivity or increased CO₂ production or both. It also increased with soil depth reaching almost 10 mmol mol⁻¹ at the 50-cm depth. Annually, soil CO₂ efflux was best described by an exponential function of soil temperature at the 5-cm depth, with the reference efflux at 10 °C (F₁₀) of 2.6 μmol m⁻² s⁻¹ and the Q₁₀ of 3.7. No evidence of displacement of CO₂-rich soil air with rain was observed.Effluxes calculated from soil CO₂ concentration gradients near the surface closely agreed with the measured effluxes. Calculations indicated that more than 75% of the soil CO₂ efflux originated in the top 20 cm soil. Calculated CO₂ production varied with soil temperature, soil water content and season, and when scaled to 10 °C also showed some diurnal variation. Soil CO₂ efflux and concentrations as well as soil temperature at the 5-cm depth varied in phase. Changes in CO₂ storage in the 0–50 cm soil layer were an order of magnitude smaller than measured effluxes. Soil CO₂ efflux was proportional to CO₂ concentration at the 50-cm depth with the slope determined by soil water content, which was consistent with a simple steady-state analytical model of diffusive transport of CO₂ in the soil. The latter proved successful in calculating effluxes during 2004.