基于冬种不同作物的水旱轮作模式对水稻产量及稻田CH_4、N_2O排放的影响

为探究冬种不同作物、水旱轮作措施对稻田丰产及温室气体减排的影响,本研究设置5种种植模式,即紫云英-早稻-晚稻(CRR)、紫云英-早稻-甘薯‖晚大豆(CRI)、油菜-早稻-晚稻(RRR)、油菜-早稻-甘薯‖晚大豆(RRI)、马铃薯-早稻-晚稻(PRR),采用静态暗箱-气相色谱法测定稻田CH_4、N_2O的全年排放通量,研究基于冬季不同作物的不同水旱轮作模式对水稻产量、全球增温潜势(GWP)及温室气体排放强度(GHGI)的影响。结果表明,冬种不同作物均能提高早稻的产量,但对晚稻产量基本无影响,其中紫云英对早稻产量增效最好,CRI处理分别较其他处理高1.73%、12.08%、7.48%、10.95%;水旱轮作处理较双季稻处理可以获得更高的产量,RRI处理晚稻产量较其他4个处理分别高22.54%、5.37%、29.83%、27.24%。冬种不同作物对CH_4、N_2O排放无显著影响(P>0.05),水旱轮作显著增加了N_2O排放,显著降低了CH_4排放(P<0.05)。5种种植模式中,RRI处理的GWP最低,且显著低于CRR、RRR、PRR处理(P<0.05),分别低25.54%、29.76%、20.78%。RRI处理的GHGI最低,较其他处理分别显著低32.51%、18.18%、30.77%、20.59%(P<0.05)。综上,RRI处理在增加作物产量、减少稻田温室气体排放方面表现最好。本研究结果为长江中游双季稻区稻田丰产及温室气体减排提供了理论依据。     

Meta分析生物质炭对中国主粮作物痕量温室气体排放的影响

该文采用Meta分析方法定量分析生物质炭输入对中国主粮作物痕量温室气体的影响,研究可为农田痕量温室气体减排提供有效的途径.结果表明相对于不施加生物质炭,生物质炭输入对甲烷吸收/排放并无显著影响,而甲烷排放在不同耕作和施氮情况下发生显著变化.旋耕和不施氮情况下施加生物质炭分别显著提高稻田甲烷排放达30%和46%,而在翻耕和施氮的情况下施加生物质炭可减少稻田甲烷排放达9%和10%.生物质炭输入分别可显著减少主粮作物氧化亚氮、全球增温潜势(global warming potential,GWP)及温室气体排放强度(greenhouse gas intensity,GHGI)达41%、18%及25%.不同土地利用类型、耕作类型、生物质炭施用量及生物质炭类型均可显著影响农田氧化亚氮、GWP和GWPI.合理的管理主粮作物生物质输入可为减少温室气体排放做出贡献,建议生物质炭与施氮和翻耕2种农作措施相结合,施加小于10 t/hm2及碳氮比(C/N)低于80的生物质炭,以利于主粮作物综合温室效应的减排.     

基于DNDC模型模拟江汉平原稻田不同种植模式条件下温室气体排放

稻田被认为是温室气体CH_4和N_2O的主要排放源之一。湖北省江汉平原地区水稻常年种植面积约8×105 hm2,占湖北省水稻种植面积的40%左右。研究江汉平原地区稻田温室气体排放特征,对于评估区域稻田温室气体排放以及稻田温室气体减排具有重要意义。目前,DNDC模型已被广泛应用于模拟和估算田间尺度的温室气体排放,DNDC模型与地理信息系统(Arc GIS)结合,可进行区域尺度的温室气体排放模拟与估算。本研究以湖北省典型稻作区江汉平原为研究区域,运用DNDC模型模拟和估算江汉平原稻田区域尺度的温室气体排放。设置大田定点观测试验,监测中稻-小麦(RW)、中稻-油菜(RR)、中稻-冬闲(RF)3种种植模式下稻田温室气体CH_4和N_2O的周年排放特征。通过田间观测值与DNDC模拟值的比较进行模型验证,并利用获取DNDC模型所需的气象、土壤、作物及田间管理等区域数据,模拟江汉平原稻田不同种植模式下温室气体CH_4和N_2O的排放量。田间试验表明,江汉平原稻田RW、RR和RF模型的CH_4排放通量为-2.80~39.78 mg·m-2·h-1、-1.74~42.51 mg·m-2·h-1和-1.57~55.64 mg·m-2·h-1,N_2O周年排放通量范围分别为0~1.90 mg·m-2·h-1、0~1.76mg·m-2·h-1和0~1.49 mg·m-2·h-1;CH_4排放量RW和RR模式显著高于RF模式,N_2O排放量为RF显著低于RW和RR模式。模型验证结果表明,不同种植模式温室气体排放实测值与模拟值比较的决定系数(R2)为0.85~0.98,相对误差绝对值(RAE)为8.29%~16.42%。根据DNDC模型模拟和估算的结果,江汉平原区域稻田CH_4周年的排放量为0.292 9 Tg C,N_2O周年的排放量为0.009 2 Tg N,不同种植模式稻田CH_4排放量表现为RWRRRF,N_2O排放量表现为RWRFRR,增温潜势(GWP)表现为RWRRRF。不同地区稻田CH_4排放量表现为监利县荆门市公安县天门市仙桃市洪湖市松滋市汉川市潜江市石首市荆州市江陵县赤壁市嘉鱼县,N_2O排放量表现为监利县荆门市公安县洪湖市仙桃市天门市汉川市潜江市松滋市荆州市江陵县赤壁市石首市嘉鱼县。本研究结果表明DNDC模型能较好地应用于模拟江汉平原稻田温室气体排放,RR和RF模式相比RW模式可有效减少温室气体CH_4和N_2O的排放。     

不同农业管理措施对华北地区麦田温室气体排放的影响

利用静态暗箱-气相色谱法对华北地区4种农业管理措施下的小麦农田生态系统温室气体(CO_2、CH_4和N_2O)的排放通量进行了观测,并对其综合增温潜势进行了估算。结果表明,麦季农田土壤是N_2O和CO_2的排放源,CH_4的吸收汇。与秸秆不还田(SN)相比,秸秆还田(SR)显著提高了CO_2和N_2O的排放量,但增加了CH_4的吸收量。通过施用新型肥料(SRC)或采用氮肥条施(SRR)的施肥方式,可以降低22.4%~35.5%的N_2O排放量,并增加9.3%~44.2%的CH_4吸收量。尤其是SRR可以抵消由于秸秆还田引起的N_2O增排。4种管理措施下的麦田是大气总温室气体的吸收汇,在秸秆还田基础上施用新型氮肥品种或采用氮肥条施的施肥方式,能够达到温室气体减排,且增产增效的效果。     

深耕对土壤温室气体排放影响研究进展

深耕作为农业耕作措施的同时,也是重要的土壤污染修复方法,然而,其对土壤温室气体排放的影响尚不明确。总结了深耕条件下土壤二氧化碳(CO₂)、甲烷(CH4)和氧化亚氮(N2O)排放规律的相关研究。深耕主要通过影响土壤物理性质(如容重、团聚体稳定性)进而影响其化学和生物学性质,从而导致温室气体排放通量发生变化。深耕可显著增加土壤CO₂的排放量。土壤团聚体稳定性和容重是影响CO₂排放的重要因子。旱地土壤是CH4的“汇”,水田是CH4的“源”。深耕可降低旱地土壤对CH4的吸收,增加水田土壤CH4的排放。土壤通气性能以及产甲烷菌和甲烷氧化菌的大小和活性是影响CH4排放的重要因素。深耕对N2O的影响主要与土壤通气性能有关,在通气性较好的土壤中,深耕可显著增加N2O的排放,但在通气性不良的土壤中则表现为降低趋势,土壤硝化和反硝化作用是影响N2O排放的重要过程。此外,土壤改良方式、水分管理、气候因素和其他土壤性质等可进一步对土壤温室气体的排放产生影响。从农业可持续发展和土壤绿色低碳修复的角度出发,采用深耕方法进行农业耕作和土壤修复对气候变化的潜在影响值得进一步审慎商榷。     

除草剂对土壤温室气体排放的影响

试验设对照、尿素、尿素＋草甘膦和尿素＋丁草胺4个处理,尿素氮用量为200mg·kg-1干土,除草剂用量为10mg有效成分·kg-1干土。在实验室恒温培养条件下,研究除草剂对菜田土壤温室气体排放的影响。结果表明,菜田土壤中施用氮肥显著增加了温室气体N2O、CO2和CH4的排放。尿素氮肥中添加草甘膦显著抑制N2O、CO2的排放,分别比尿素处理降低48.4%和20.2%;添加丁草胺显著抑制N2O排放,比尿素处理降低23.2%,对CO2排放略有减少但不显著;草甘膦和丁草胺对CH4排放都无明显影响。这说明除草剂对土壤温室气体的排放具有显著影响,但不同除草剂品种的效应也存在明显差异。因此,在农田温室气体排放估算时应考虑除草剂的施用对温室气体减排所产生的效果。     

长期不同量秸秆炭化还田下水稻土孔隙结构特征

  【目的】  生物炭被认为是一种能够提高土壤固碳能力、改善土壤结构和减缓全球气候变化的土壤改良剂。土壤孔隙结构直接影响土壤中水、气、热的运动,因此,研究长期施用生物炭对土壤孔隙结构特征的影响,以期为秸秆炭化还田提供理论依据。  【方法】  研究基于2013年建立的水稻秸秆炭化还田长期定位试验,选取在等氮磷钾条件下不施用生物炭 (C0)、施用低量生物炭 (1.5 t/hm2,C1.5)、高量生物炭 (3.0 t/hm2,C3.0)的 3个处理。利用X射线CT扫描和图像处理技术,分析了土壤孔隙结构参数,包括土壤孔隙度、土壤孔隙大小分布、孔隙连通性指数 (欧拉特征值)、各向异性、分形维数、最紧实层孔隙度和最紧实层平均孔隙直径等参数。  【结果】  C1.5和C3.0处理均能显著增加土壤有机碳含量和土壤总孔隙度,降低土壤容重,平均增加或降低比例分别为15.5%、10.5%和7.4%。C1.5与C3.0处理之间的总孔隙度没有显著差异,但孔隙大小分布存在差异。C1.5处理显著增加了大孔隙中当量孔径为100～500 μm和 > 500 μm的孔隙度,增幅分别为81.6%和275.3%,而C3.0处理显著降低了大孔隙中当量孔径100～500 μm的孔隙度,降幅为32.9%。C3.0处理当量孔径 < 25 μm的孔隙度显著大于C0处理和C1.5处理,增幅分别为13.8%和16.3%。C1.5处理的欧拉特征值最低,分形维数、最紧实层孔隙度和平均孔隙直径最大。各处理土壤孔隙的各向异性没有显著差异。  【结论】  长期施用水稻秸秆生物炭能够显著增加稻田土壤有机碳含量和总孔隙度,降低土壤容重。施用适量生物炭会增加土壤大孔隙度和土壤孔隙的连通性,但是过量施用生物炭可能会降低土壤大孔隙度和土壤孔隙的通气导水能力。炭化秸秆还田量与孔隙结构之间的定量关系还需深入研究。     

有机物料还田对冬小麦农田土壤温室气体排放影响的研究

探讨有机物料还田对冬小麦田温室气体排放特性的影响,对提高经济效应和环境效应有积极意义。本研究应用静态箱-气相色谱法对秸秆还田（J）、秸秆还田+牛粪（JF）和秸秆还田+菌渣（JZ）3种有机物料还田下分别施氮肥243 kg （N）·hm^-2（减氮10%,N1）、216 kg （N）·hm^-2（减氮20%,N2）对冬小麦农田N₂O、CO₂和CH₄的排放通量进行监测,探讨了不同施肥措施对麦田温室气体累积排放量、增温潜势的影响。试验期间同步记录每项农事活动机械燃油量、施肥量和灌溉量,测定产量,地上部生物量,估算农田碳截留。结果表明,冬小麦农田土壤N₂O和CO₂是排放源,是CH₄的吸收汇,氮肥施入、灌溉以及强降水促进了土壤N₂O和CO₂的生成,却弱化了CH₄作为大气吸收汇的特征。牛粪+秸秆（JF）处理N₂O和CO₂排放总量最高,分别为3.5 kg （N₂O-N）·hm^-2和19 689.67 kg （CO₂-C）·hm^-2,但CH₄的吸收值最大,为5.33 kg （CH₄-C）·hm^-2,均显著高于菌渣+秸秆（JZ）和秸秆（J）处理（P<0.05）;各处理N₂O和CO₂的总量随施氮量的增加呈升高趋势,CH₄的总量随施氮量的增加而呈降低趋势。JFN2、JN2和JZN2处理农田综合增温潜势（GWP）均为负值,表明有机物料还田且减氮20%条件下农田生态系统为大气的碳汇,麦季净截留碳1 038~2 024 kg·hm^-2,其他处理GWP值均为正。JZN2处理小麦产量为8 061 kg·hm^-2,显著高于JFN2处理（P<0.05）。综上所述,JZN2处理不仅能够保证小麦产量,且对环境效应最有利,为本区域冬小麦较优的施肥管理模式。     

模拟搅浆对水稻土结构和有机氮矿化的影响

搅浆(Puddling)是传统水稻种植过程中的重要环节,搅浆会改变土壤结构,进而影响氮转化过程。通过室内模拟试验,设置不搅动(CK)、低强度搅动(LIS)和高强度搅动(HIS)三个处理,研究搅浆引起的土壤结构变化,及其对土壤有机氮矿化的影响。首先利用湿筛法测定不同处理团聚体分布及稳定性,采用CT扫描和图像分析方法研究不同处理土壤孔隙结构,并通过室内培养法测定土壤有机氮矿化量,进一步分析土壤结构与有机氮矿化之间的关系。结果显示,与CK相比,LIS和HIS两处理中大于1 mm的水稳性团聚体含量和平均重量直径(MWD)均显著降低,LIS和HIS处理间无显著差异。CK、LIS和HIS的土壤孔隙度分别为3.3%、3.2%和3.3%,各处理间无显著差异;但三个处理的土壤孔隙形态有明显差异,CK大孔隙分布较多且连通性好,LIS和HIS处理孔隙多为球状孔隙,连通性较差。矿化培养第一周,LIS和HIS处理矿化量均快速增加,高于CK处理;但是培养2周后CK矿化氮高于搅动处理,培养试验结束时(4周)CK累积矿化氮量(N28)和氮矿化潜势(N0)显著高于LIS和HIS处理,说明搅拌降低了有机氮的累积矿化量。相关分析表明,土壤有机氮矿化与粒径大于0.25 mm的团聚体含量和当量直径为30～100μm的孔隙数量具有显著正相关关系,其内在机制尚待进一步研究。     

秸秆还田对免耕稻田温室气体排放及土壤有机碳固定的影响

秸秆还田影响免耕稻田土壤固碳潜力,相应地改变了温室气体的排放,从而影响秸秆还田后稻田土壤固碳减排对减缓全球变暖的贡献。通过研究不同油菜秸秆还田量（0、3000、4000kg·hm-2和6000kg·hm-2）对免耕稻田温室气体（CO2、CH4和N2O）排放和土壤碳固定的影响,评估秸秆还田后温室气体增排的综合增温潜势对稻田固碳减缓全球变暖的贡献的抵消作用。结果表明,秸秆还田显著提高CO2和N2O排放,降低CH4排放,显著提高土壤有机碳含量,有效地提高土壤碳固定,从而有效地提高稻田土壤碳固定对温室气体增排的温室效应抵消作用。随着秸秆还田量的增加,稻田土壤固碳减缓全球变暖的贡献相应增加,因此必须考虑免耕稻田秸秆还田量的问题,以有效发挥免耕稻田秸秆还田的固碳潜力和降低温室气体的排放。     

施肥处理对春季冻融期灰漠土农田温室气体排放的影响

绿洲灰漠土冻融交替明显,但缺乏该时期气体通量及动态变化方面的研究。选取NPK(氮磷钾肥)、NPKS(0.9NPK+0.1秸秆氮)、NPKM(1/3NPK+2/3羊粪氮)和NPKM+(1.5倍NPKM)处理作为研究对象,利用静态箱气相色谱法开展2013—2014年春季冻融期温室气体排放观测试验。结果显示,春季冻融期间,有机肥添加处理CO_2排放量较高,其中NPKM+和NPKM处理CO_2平均排放量分别为C 113 mg m~(-2) h~(-1)和85 mg m~(-2) h~(-1),其次为NPKS(72 mg m~(-2) h~(-1))、NPK(75 mg m~(-2) h~(-1))和CK(35 mg m~(-2) h~(-1))。同样,NPKM+和NPKM处理有相对更高的N_2O排放,春冻平均排放通量分别为N 73μg m~(-2) h~(-1)和42μg m~(-2) h~(-1),显著高于NPKS(22μg m~(-2) h~(-1))和NPK(17μg m~(-2) h~(-1))处理(p0.05)。CH_4排放量相对较低,各处理无明显差异(p0.05)。分析发现,N_2O在冻融期呈现先增加后急剧减少的趋势,CO_2变幅不明显。与全年总排放量相比,冻融期(27 d)N_2O的排放量占全年的9%~18%,CH_4冻融期间排放比重占全年排放量的6%~14%。所以,冻融交替期是灰漠土农田温室气体排放的相对高发时期,估算温室气体排放时应充分考虑。     

不同利用方式红壤反硝化势和气态产物排放特征

采用厌氧培养-乙炔抑制法测定了4种不同利用方式红壤的反硝化势和气态产物N₂O和N₂的排放速率。结果表明，不同利用方式红壤反硝化势和N₂O和N₂的排放速率差异明显，土壤反硝化势强弱顺序依次为：竹林>茶园>林地>旱地。反硝化势与土壤有机碳(P<0.05)、厌氧培养期间土壤CO₂累积排放量(P<0.01)、nirS基因丰度( P<0.05)和nirK基因丰度(P<0.05) 呈显著正相关关系。逐步回归分析结果表明，CO₂累积排放量表征的易矿化碳是造成不同利用方式红壤反硝化势差异的主要原因，可以解释反硝化势变化的66%(P<0.01)。不同利用方式红壤N₂O和N₂排放速率差异明显，旱地红壤N₂O和N₂排放速率均最低，表明土壤pH的提升并没有增加旱地红壤的反硝化损失风险和N₂O排放速率。土壤易矿化有机碳含量也是影响不同利用方式红壤N₂O和N₂排放速率的主要因素。反硝化功能基因nirS、nirK和nosZ的丰度均与CO₂累积排放量呈显著正相关关系，进一步支持了土壤易矿化有机碳含量是影响不同利用方式红壤反硝化势和气态产物排放的主要因子。土壤pH是影响不同利用方式红壤反硝化气态产物N₂/N₂O的主要因素，但是pH影响红壤N₂/N₂O的微生物机制仍需要进一步研究。     

Greenhouse gas emissions in response to straw incorporation,water management and their interaction in a paddy field in subtropical central China

A field experiment was conducted to study the effects of combination of straw incorporation and water management on fluxes of CH₄, N₂O and soil heterotrophic respiration (Rh) in a paddy field in subtropical central China by using a static opaque chamber/gas chromatography method. Four treatments were set up: two rice straw incorporation rates at 0 (S1) and 6 (S2) t ha^?1 combined with two water managements of intermittent irrigation (W1, with mid-season drainage) and continuous flooding (W2, without mid-season drainage). The cumulative seasonal CH₄ emissions for the treatments of S1W2, S2W1 and S2W2 increased significantly by 1.84, 5.47 and 6.63 times, respectively, while seasonal N₂O emissions decreased by 0.67, 0.29 and 1.21 times, respectively, as compared to S1W1 treatment. The significant increase in the cumulative Rh for the treatments S1W1, S2W1 and S2W2 were 0.54, 1.35 and 0.52 times, respectively, in comparison with S1W2. On a seasonal basis, both the CO₂-equivalents (CO₂e) and yield-scaled CO₂e (GHGI) of CH₄ and N₂O emissions increased with straw incorporation and continuous flooding, following the order: S2W2>S2W1>S1W2>S1W1. Thus, the practices of in season straw incorporation should be discouraged, while mid-season drainage is recommended in paddy rice production from a point view of reducing greenhouse gas emissions.     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.     

Effect of dairy manure type and supplemental synthetic fertilizer on methane and nitrous oxide emissions from a grassland in Nasu,Japan

Abstract

It is well known that some fungal species are remarkably tolerant of high copper concentration, although copper is toxic to most fungi (Garraway and Evans 1984). Bedford (1936) and Jurkowska (1952) reported that Penicillium and Aspergillus species can grow in liquid media saturated or nearly saturated with copper sulfate. Okamoto and Fuwa (1974) isolated Penicillium ochro-chloron from the laboratory air, and found that the fungus was able to grow in a medium saturated with copper sulfate.     

Effects of water content and N addition on potential greenhouse gas production from two differently textured soils under laboratory conditions

GHGs production and emission may vary depending on soil physical properties, water management and fertilization. Two paddy soils characterized by different texture were incubated to evaluate the impact of flooding (permanent or intermittent) and N addition on potential N₂O, CH₄ and CO₂ production and release into atmosphere and soil solution. Relationships with volumetric water content (VWC) and water filled pore space (WFPS) were evaluated. Overall, the finer clayey soil (CL) produced 58% more CH₄ than the coarser sandy soil (SA) and showed an earlier sink to source transition; the difference was lower with N addition. Permanent flooding favoured the amount of dissolved CH₄. SA produced more N₂O emissions than CL under permanent flooding (31.0 vs. 3.7%); an opposite pattern was observed for dissolved N₂O (16.4 vs. 52.7%). Fertilization increased N₂O emissions under dry conditions in CL and under flooding in SA.

Our findings showed that i) VWC had a larger influence on N₂O and CH₄ emissions than WFPS, ii) soil type influenced the gas release into atmosphere or soil solution and the timing of sink to source transition in CH₄ emissions. Further investigation on timing of fertilization and drainage are needed to improve climate change mitigation strategies.     

Effect of intermittent drainage in reduction of methane emission from paddy soils in Hokkaido,northern Japan

ABSTRACT

Emission of methane (CH₄), a major greenhouse gas, from submerged paddy soils is generally reduced by introducing intermittent drainage in summer, which is a common water management in Japan. However, such a practice is not widely conducted in Hokkaido, a northern region in Japan, to prevent a possible reduction in rice grain yield caused by cold weather. Therefore, the effects of intermittent drainage on CH₄ emission and rice grain yield have not been investigated comprehensively in Hokkaido. In this study, we conducted a three-year field experiment in Hokkaido and measured CH₄ and nitrous oxide (N₂O) fluxes and rice grain yield to elucidate whether the reduction in CH₄ emission can be achieved in Hokkaido as well as other regions in Japan. Four experimental treatments, namely, two soil types [soils of light clay (LiC) and heavy clay (HC) textures] and two water management [continuous flood irrigation (CF), and intermittent drainage (ID)], were used, and CH₄ and N₂O fluxes were measured throughout the rice cultivation periods from 2016 to 2018. Cumulative CH₄ emissions in 2016 were markedly low, suggesting an initially low population of methanogens in the soils presumably due to no soil submergence or crop cultivation in the preceding years, which indicates a possible reduction in CH₄ emission by introducing paddy-upland crop rotation. Cumulative CH₄ emissions in the ID-LiC and ID-HC plots were 21–91% lower than those in the CF-LiC and CF-HC plots, respectively, whereas the cumulative N₂O emissions did not significantly differ between the different water managements. The amount of CH₄ emission reduction by the intermittent drainage was largest in 2018, with a comparatively long period of the first drainage for 12 days in summer. Rice grain yields did not significantly differ between the different water managements for the entire 3 years, although the percentage of well-formed rice grains was reduced by the intermittent drainage in 2018. These results suggest that CH₄ emission from paddy fields can be reduced with no decrease in rice grain yield by the intermittent drainage in Hokkaido. In particular, the first drainage for a long period in summer is expected to reduce CH₄ emission markedly.     

Elevated CO2 concentration and nitrogen fertilisation effects on N2O and CH4 fluxes and biomass production of Phleum pratense on farmed peat soil

The effects of elevated CO₂ supply on N₂O and CH₄ fluxes and biomass production of Phleum pratense were studied in a greenhouse experiment. Three sets of 12 farmed peat soil mesocosms (10 cm dia, 47 cm long) sown with P. pratense and equally distributed in four thermo-controlled greenhouses were fertilised with a commercial fertiliser in order to add 2, 6 or 10 g N m⁻². In two of the greenhouses, CO₂ concentration was kept at atmospheric concentration (360 μmol mol⁻¹) and in the other two at doubled concentration (720 μmol mol⁻¹). Soil temperature was kept at 15 °C and air temperature at 20 °C. Natural lighting was supported by artificial light and deionized water was used to regulate soil moisture. Forage was harvested and the plants fertilised three times during the basic experiment, followed by an extra fertilisations and harvests. At the end of the experiment CH₄ production and CH₄ oxidation potentials were determined; roots were collected and the biomass was determined. From the three first harvests the amount of total N in the aboveground biomass was determined. N₂O and CH₄ exchange was monitored using a closed chamber technique and a gas chromatograph. The highest N₂O fluxes (on average, 255 μg N₂O m⁻² h⁻¹ during period IV) occurred just after fertilisation at high water contents, and especially at the beginning of the growing season (on average, 490 μg N₂O m⁻² h⁻¹ during period I) when the competition of vegetation for N was low. CH₄ fluxes were negligible throughout the experiment, and for all treatments the production and oxidation potentials of CH₄ were inconsequential. Especially at the highest rates of fertilisation, the elevated supply of CO₂ increased above- and below-ground biomass production, but both at the highest and lowest rates of fertilisation, decreased the total amount of N in the aboveground dry biomass. N₂O fluxes tended to be higher under doubled CO₂ concentrations, indicating that increasing atmospheric CO₂ concentration may affect N and C dynamics in farmed peat soil.     

Boreal pine forest floor biogenic volatile organic compound emissions peak in early summer and autumn

In boreal forests, canopy-scale emissions of biogenic volatile organic compounds (BVOCs) are rather well characterised, but knowledge of ecosystem-scale BVOC emissions is still inadequate. We used adsorbent tubes to measure BVOCs from a boreal Scots pine (Pinus sylvestris L.) forest floor in southern Finland and analysed the compounds with a gas chromatograph-mass spectrometer. The most abundant compound group was the monoterpenes (averaging 5.04 μg m⁻² h⁻¹), in which α-pinene, Δ³-carene and camphene contributed over 90% of the emissions. Emissions of other terpenoids (isoprene and sesquiterpenes) were low (averaging 0.05 and 0.04 μg m⁻² h⁻¹, respectively). BVOC emissions from the forest floor varied seasonally, peaking in early summer and autumn, with most of the compounds following similar patterns. The emission pattern was sustained throughout the measurement period, suggesting that the main sources of the emissions remained more or less stable. We compared the BVOC fluxes with environmental parameters such as temperature, precipitation and PAR, and with fluxes of other trace gases (CO₂, CH₄, N₂O), as well as with ground vegetation photosynthesis and with litter input. Several of these parameters were correlated with the presence of BVOCs. The sources of soil BVOC emissions are very poorly understood, but our results suggest, that changes in litter quantity and quality, soil microbial activity and the physiological stages of plants are linked with changes in BVOC fluxes.