棉花幼苗AsA-GSH循环对低温胁迫的响应机制研究

为探究棉花幼苗营养器官抗坏血酸-谷胱甘肽(AsA-GSH)循环系统对低温胁迫的响应机制,以新陆早57号为试验材料,研究4℃低温胁迫不同时间(0、1和2 d)对根、茎和叶中抗氧化物质含量和酶活性的影响。结果表明,与对照(0 d)相比,随着低温胁迫时间延长,棉花幼苗根中还原型抗坏血酸(AsA)含量及单脱氢抗坏血酸还原酶(MDHAR)和谷胱甘肽还原酶(GR)活性呈上升趋势,氧化型抗坏血酸(DHA)含量先减少后增加,氧化型谷胱甘肽(GSSG)含量和脱氢抗坏血酸还原酶(DHAR)活性先升高后降低,谷胱甘肽氧化还原状态(GSH/GSSG比率)和抗坏血酸过氧化物酶(APX)活性总体呈下降趋势,抗坏血酸氧化还原状态(AsA/DHA比率)、还原型谷胱甘肽(GSH)含量和谷胱甘肽过氧化物酶(GPX)活性无显著性差异;茎和叶中AsA和GSH含量、AsA/DHA比率及APX、MDHAR和GR活性总体呈上升趋势,且茎中DHAR活性升高,DHA和GSSG含量先减少后增加,GSH/GSSG比率和GPX活性无显著性差异,而叶中DHA含量和GSH/GSSG比率先不变后增加,DHAR活性先升高后降低,GSSG含量和GPX活性无显著性差异。综合分析显示,棉花幼苗通过调节根、茎和叶中抗氧化物质含量和酶活性来清除活性氧,从而适应低温胁迫,减轻低温伤害。此外,低温对根中AsA-GSH循环影响最大。本研究结果为揭示低温胁迫对棉花幼苗AsA-GSH循环代谢机制提供了理论依据。     

H_2S对低温胁迫下甜樱桃柱头和子房AsA-GSH循环的响应

为了探究H_2S对甜樱桃花器官低温伤害的缓解机理,以甜樱桃品种早大果为试材,分析了不同浓度H_2S供体NaHS对低温胁迫下甜樱桃柱头和子房AsA-GSH循环系统的影响。结果表明,喷施0.02、0.05、0.1 mmol·L~(-1)的NaHS均可降低低温胁迫下甜樱桃柱头和子房超氧阴离子(O_2~-)、过氧化氢(H_2O_2)、丙二醛(MDA)含量,显著提高还原型抗坏血酸(AsA)和还原型谷胱甘肽(GSH)含量(P0.05),降低氧化型抗坏血酸(DHA)和氧化型谷胱甘肽(GSSG)含量,使AsA/DHA和GSH/GSSG比值显著升高(P0.05),以0.05 mmol·L~(-1)NaHS效果最显著;0.02、0.05、0.1 mmol·L~(-1)的NaHS均显著提高低温胁迫下柱头和子房AsA-GSH循环中抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)、单脱氢抗坏血酸还原酶(MDAR)、谷胱甘肽还原酶(GR)、谷胱甘肽过氧化物酶(GPX)和谷胱甘肽-S-转移酶(GST)的活性(P0.05),以0.05 mmol·L~(-1)NaHS提高上述酶活性的幅度最大。NaHS的浓度大于0.2 mmol·L~(-1)不再提高低温胁迫下AsA-GSH循环效率;低温胁迫下添加NaHS的同时添加H_2S清除剂HT可解除H_2S的效果。综上所述,喷施适量外源H_2S可有效降低低温胁迫下O_2~-、H_2O,和MDA积累,提高AsA-GSH循环效率,减轻低温对甜樱桃柱头和子房的氧化伤害。本研究结果为明确H_2S缓解甜樱桃花器官低温伤害作用机制以及生产上花期低温伤害预防提供了理论依据。     

NaCl胁迫对菜用大豆种子抗坏血酸-谷胱甘肽循环的影响

采用蛭石栽培,在100 mmol/L NaCl胁迫下,对耐盐性不同的两个菜用大豆[Glycine max(L.)Merr.]品种种子的过氧化氢(H2O2)含量及抗坏血酸-谷胱甘肽(AsA-GSH)循环进行了研究。结果显示,NaCl胁迫显著增加了菜用大豆种子的H2O2含量,但耐盐品种"绿领特早"的增幅低于盐敏感品种"理想高产95-1"。NaCl胁迫期间,"绿领特早"种子中抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)、谷胱甘肽还原酶(GR)活性,AsA、GSH含量以及AsA/DHA值和GSH/GSSG值的增幅高于同期的"理想高产95-1",或降幅低于同期的"理想高产95-1";脱氢抗坏血酸(DHA)、氧化型谷胱甘肽(GSSG)含量的增幅低于同期的"理想高产95-1"。表明"绿领特早"种子在胁迫期间能够保持较高的AsA-GSH循环效率,可有效地抑制H2O2的积累,这可能是其耐盐性较强的重要原因之一。     

胁迫对菜用大豆种子抗坏血酸-谷胱甘肽循环的影响

采用蛭石栽培,在100 mmol/L NaCl 胁迫下,对耐盐性不同的两个菜用大豆［Glycine max (L.)Merr.］品种种子的过氧化氢（H2O2）含量及抗坏血酸-谷胱甘肽（AsA-GSH）循环进行了研究。结果显示,NaCl胁迫显著增加了菜用大豆种子的H2O2含量,但耐盐品种 绿领特早的增幅低于盐敏感品种理想高产95-1。NaCl胁迫期间,绿领特早种子中抗坏血酸过氧化物酶（APX）、脱氢抗坏血酸还原酶（DHAR）、谷胱甘肽还原酶（GR）活性,AsA、GSH含量以及AsA/DHA值和GSH/GSSG值的增幅高于同期的理想高产95-1,或降幅低于同期的理想高产95-1; 脱氢抗坏血酸（DHA）、氧化型谷胱甘肽（GSSG）含量的增幅低于同期的理想高产95-1。表明 绿领特早种子在胁迫期间能够保持较高的AsA-GSH循环效率,可有效地抑制H2O2的积累,这可能是其耐盐性较强的重要原因之一。     

硒镉伴生对富硒土壤柑橘生长及生理代谢的影响

为保障富硒柑橘的安全生产,明确富硒土壤硒镉伴生现象对柑橘生长、硒镉吸收转运和抗氧化能力的影响,采用盆栽试验,以一年生大雅柑橘为试验材料,研究添加硒代蛋氨酸(SeMet,CK,模拟富硒土壤)和添加SeMet与镉(模拟富硒土壤硒镉伴生)对富硒土壤柑橘的生长指标、硒镉含量、叶片还原型抗坏血酸-谷胱甘肽(AsA-GSH)循环效率的影响。结果表明,与CK相比,富硒土壤中,硒镉伴生增加了柑橘叶片叶绿素a+b、叶绿素a、叶绿素b和类胡萝卜素含量,但对株高、新梢长度、新梢数量以及根茎叶的干物质量影响不显著;在富硒土壤中,硒镉伴生显著增加了大雅柑橘硒含量和硒的富集系数(BCF),降低了硒的转运系数(TF);硒和镉主要分布在根系,其次是叶片和茎;在AsA-GSH循环中,硒镉伴生使过氧化氢(H₂O₂)和还原型抗坏血酸(AsA)含量显著上升,脱氢抗坏血酸(DHA)含量上升但未达到显著水平,抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)活性和脱氢抗坏血酸还原酶(DHAR)活性显著上升,而GSH和氧化型谷胱甘肽(GSSG)含量下降,AsA/(AsA+DHA)和GSH/(GSH+GSSG)比值降低,谷胱甘肽过氧化物酶(GPX)活性显著降低。本研究为阐明镉胁迫对富硒土壤柑橘的生理影响机制提供了理论依据。     

水杨酸对栝楼AsA-GSH循环系统及耐寒性的影响

以耐寒性较强的三门峡栝楼和耐寒性较弱的安庆栝楼为对比试验材料,分析低温(4℃)胁迫下喷施不同浓度(0,0.5,1,2 mmol/L)水杨酸对栝楼幼苗叶片的生长特性、抗氧化物质含量以及抗氧化酶活性的影响.结果表明:栝楼幼苗在低温胁迫下,对照组,2个栝楼品种幼苗的冷害指数、MDA含量、H2 O2含量、APX活性均明显增加;DHA、GSH、GSSG含量以及GR、MDHAR、DHAR活性呈升—降—升的趋势;AsA含量、GSH/GSSG、AsA/GSH比则在胁迫5d时呈相反的变化趋势,显示出2个栝楼品种的耐寒性差异;而喷施适宜浓度的SA能够降低植株的冷害指数、细胞内的MDA、H2 O2、DHA和GSSG含量,增加AsA、GSH含量和AsA/DHA、GSH/GSSG比,维持较高且相对协调平衡的APX、GR、MDHAR和DHAR活性.由隶属函数分析得出,适宜浓度的SA具有缓解栝楼低温胁迫的效果,但不能消除低温胁迫对栝楼生长的抑制作用.通过灰色关联分析可知,喷施SA对栝楼的AsA/GSH比影响很大.     

烟嘧磺隆胁迫对甜玉米幼苗活性氧积累、抗氧化系统及相关基因表达的影响

为减轻烟嘧磺隆对甜玉米(Zea mays L. seccharata Sturt)的药害作用,探究甜玉米幼苗抗氧化系统对烟嘧磺隆胁迫的响应机制,本研究以一对甜玉米姊妹系(对烟嘧磺隆表现耐药性的甜玉米自交系HK301和对烟嘧磺隆表现敏感的甜玉米自交系HK320)为试材,研究烟嘧磺隆胁迫对不同耐药性甜玉米品种氧化压力、抗氧化酶、抗氧化系统非酶类物质和抗氧化酶关键基因表达量的影响。结果表明,烟嘧磺隆胁迫后,与对照(HK301-CK)相比,HK301的超氧阴离子自由基( {\mathrm{O}}_2^{\frac{-}{·}} )产生速率、过氧化氢(H₂O₂)含量和丙二醛(MDA)含量先增加后减少,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、单脱氢抗坏血酸还原酶(MDHAR)、脱氢抗坏血酸还原酶(DHAR)、谷胱甘肽还原酶(GR)活性均呈先升高后降低的趋势,抗坏血酸(AsA)含量、脱氢抗坏血酸(DHA)、还原型谷胱甘肽(GSH)含量先增加后减少,氧化型谷胱甘肽(GSSG)含量持续增加,抗坏血酸氧化还原状态(AsA/DHA比值)显著降低,谷胱甘肽氧化还原状态(GSH/GSSG比值)无显著差异。与对照(HK320-CK)相比,HK320的 {\mathrm{O}}_2^{\frac{-}{·}} 产生速率和H₂O₂含量显著增加, CAT、APX、DHAR、GR活性先升高后下降,SOD、MDHAR活性和GSH含量、GSH/GSSG 比值、AsA/DHA 比值呈下降趋势,DHA含量持续增加,GSSG含量无显著差异。烟嘧磺隆胁迫后,相较于HK320,HK301显著上调了SOD、CAT、APX、MDHAR、DHAR和GR基因的相对表达量。综合分析显示,不同耐药性甜玉米幼苗通过调节体内抗氧化物质含量和酶活性来清除活性氧,从而提高幼苗对除草剂的耐药性。本研究为揭示烟嘧磺隆胁迫下甜玉米幼苗抗氧化系统的代谢机制提供了理论依据。     

高温强光下Ca2+对西葫芦幼苗膜质过氧化、抗氧化酶系统及热耗散的影响

为探明不同浓度外源Ca2+对高温强光胁迫下西葫芦植株幼苗的影响,本试验选用西葫芦(Cucurbitapepo L.)品种"阿兰一代"为试验材料,通过外源喷施不同浓度CaCl2溶液,研究了Ca2+对高温强光胁迫下西葫芦幼苗叶绿素荧光特性、膜质过氧化及抗氧化酶系统的影响。结果表明,较低浓度Ca2+处理(5~20 mmol.L 1)可有效提高高温强光下西葫芦幼苗超氧化物歧化酶(SOD)、过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)和过氧化氢酶(CAT)活性,降低丙二醛(MDA)、过氧化氢(H2O2)、超氧阴离子自由基(O2&)含量和膜透性,还原型谷胱甘肽(GSH)含量升高;同时西葫芦叶片PSII的最大光化学效率(Fv/Fm)、PSⅡ实际光化学效率(ΦPSⅡ)和光化学猝灭系数(qP)较高,而非光化学猝灭系数(NPQ)较低。说明5~20 mmol.L 1Ca2+处理对高温强光胁迫具有明显的缓解作用,同时其热耗散较小。当Ca2+处理浓度超过40 mmol.L 1时对高温强光胁迫缓解效应不明显。     

钙对盐胁迫下水稻幼苗抗氧化酶活性和膜脂过氧化作用的影响

研究了外源Ca2 对盐胁迫下耐盐性不同的两个水稻品种(武育粳3号和IR36)几种抗氧化酶活性及膜脂过氧化的影响。结果表明:适量的Ca2 供应能有效提高水稻叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)以及抗坏血酸过氧化物酶(APX)的活性,使之维持在较高的水平上,并降低了丙二醛(MDA)含量和细胞膜透性。此外,外源Ca2 还增加了抗坏血酸(AsA)的含量,增强了水稻幼苗的根系活力。这表明适量的外源Ca2 供应提高水稻耐盐性的原因之一,在于其增强了植株的活性氧清除能力以及对细胞膜的稳定作用。     

外源硫化氢对PEG模拟干旱胁迫下玉米种子萌发及幼苗生长的影响

为明确干旱胁迫下外源硫化氢(H2S)对植物幼苗的缓解作用,以玉米自交系郑58为试验材料,研究了不同浓度(0、0.3、0.6、0.9、1.2及1.5 mmol·L-1)的H2S供体硫氢化钠(Na HS)对15%PEG模拟干旱胁迫下玉米种子萌发的影响,并以筛选到的最佳Na HS浓度对幼苗进行叶面喷施,研究其对幼苗叶片抗氧化酶活性、抗氧化剂含量、游离脯氨酸(Pro)和活性氧(ROS)的积累特征及膜质过氧化水平的影响。结果表明,不同浓度的Na HS处理在一定程度上提高了干旱胁迫下玉米种子的发芽势、发芽率及幼苗的生物量,其中以0.6 mmol·L-1的Na HS处理效果最佳。叶面喷施0.6 mmol·L-1Na HS溶液显著增强了叶片中超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)及抗坏血酸过氧化物酶(APX)活性,提高了叶片中抗坏血酸(As A)和谷胱甘肽(GSH)的含量。同时,外源H2S处理增强了玉米叶片中△1-吡咯啉-5-羧酸合成酶(P5CS)的活性,提高了叶片中游离Pro含量,显著降低了叶片中过氧化氢(H2O2)及丙二醛(MDA)含量。综上,外源H2S处理通过提高幼苗的抗氧化水平,减少干旱胁迫对玉米叶片造成的氧化损伤,在一定程度上提高了玉米幼苗对干旱胁迫的适应能力。本研究为进一步探索H2S缓解玉米干旱胁迫的机理提供了理论依据。     

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.     

重塑Q3黄土K0三轴蠕变特性的试验研究

[目的]研究陕西省延安地区重塑Q_3黄土高填方工程的后期沉降变形特性,为高填方工程的设计、施工提供一定的技术和理论支撑。[方法]通过改进K0三轴蠕变仪,对所取黄土进行了不同压实度、不同含水量、不同竖向应力下的室内土的静止侧压力系数K_0三轴固结排水蠕变试验。[结果]重塑Q_3黄土具有明显的蠕变特性,在低应力条件下,呈现出典型的衰减蠕变;在K_0条件下,随着含水量增大、竖向应力的增大,压实度的减小,蠕变呈增强趋势,蠕变变形量增大;在低水平应力的条件下,土体所受侧向应力与竖向应力成线性关系。[结论]建立了重塑Q_3黄土关于竖向应力的自定义蠕变模型,通过试验数据拟合获得了模型参数,所建模型能很好地描述延安地区重塑Q_3黄土的蠕变特性。     

A new technique to measure soil CO2 efflux at constant CO2 concentration

A new principle for measuring soil CO₂ efflux at constant ambient concentration is introduced. The measuring principle relies on the continuous absorption of CO₂ within the system to achieve a constant CO₂ concentration inside the soil chamber at ambient level, thus balancing the amount of CO₂ entering the soil chamber by diffusion from the soil. We report results that show reliable soil CO₂ efflux measurements with the new system. The novel measuring principle does not disturb the natural gradient of CO₂ within the soil, while allowing for continuous capture of the CO₂ released from the soil. It therefore holds great potential for application in simultaneous measurements of soil CO₂ efflux and its δ¹³C, since both variables show sensitivity to a distortion of the soil CO₂ profile commonly found in conventional chamber techniques.     

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。     

Short-term effects of clearfelling on soil CO2, CH4, and N2O fluxes in a Sitka spruce plantation

We examined the effects of forest clearfelling on the fluxes of soil CO₂, CH₄, and N₂O in a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation on an organic-rich peaty gley soil, in Northern England. Soil CO₂, CH₄, N₂O as well as environmental factors such as soil temperature, soil water content, and depth to the water table were recorded in two mature stands for one growing season, at the end of which one of the two stands was felled and one was left as control. Monitoring of the same parameters continued thereafter for a second growing season. For the first 10 months after clearfelling, there was a significant decrease in soil CO₂ efflux, with an average efflux rate of 4.0 g m⁻² d⁻¹ in the mature stand (40-year) and 2.7 g m⁻² d⁻¹ in clearfelled site (CF). Clearfelling turned the soil from a sink (−0.37 mg m⁻² d⁻¹) for CH₄ to a net source (2.01 mg m⁻² d⁻¹). For the same period, soil N₂O fluxes averaged 0.57 mg m⁻² d⁻¹ in the CF and 0.23 mg m⁻² d⁻¹ in the 40-year stand. Clearfelling affected environmental factors and lead to higher daily soil temperatures during the summer period, while it caused an increase in the soil water content and a rise in the water table depth. Despite clearfelling, CO₂ remained the dominant greenhouse gas in terms of its greenhouse warming potential.     

模拟CCS技术CO2泄露对C4作物种子萌发的影响

模拟CCS技术CO₂泄露对C₄作物种子萌发的影响,以期为CCS技术CO₂泄露后可能产生的环境影响提供基础性资料。利用CO₂人工气候箱,模拟CCS技术CO₂泄露产生的高浓度CO₂环境,研究在CO₂分别为正常大气CO₂浓度(对照组),10000,20000,40000,80000 mg/kg时,对玉米、高粱、谷子、糜子4种C₄作物发芽率、发芽势以及平均发芽天数的影响。高浓度CO₂对玉米发芽率无明显影响,而高粱、谷子和糜子分别在10000,20000, 20000 mg/kg时发芽率达到最高值;高浓度CO₂对玉米发芽势亦无明显影响,而高粱、谷子和糜子均在20000 mg/kg时发芽势达到最高值;高浓度CO₂对4种C₄作物发芽天数均产生较小影响,其中,对糜子影响较为显著。在不同CO₂浓度范围内对C₄作物种子发芽率分别有促进和抑制作用,促进和抑制作用不是很显著,其中,促进范围1%~5%,抑制范围1%~4%;高浓度CO₂对C₄作物种子发芽势有比较显著的促进作用,较对照组,发芽势的促进范围为9%~16%;高浓度CO₂对4种C₄作物发芽天数均产生较小影响。     

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.     

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.     

La(NO3)3 对盐胁迫下黑麦草幼苗生长及抗逆生理特性的影响

为探讨稀土元素镧(La)对牧草盐胁迫伤害的缓解作用, 采用水培法研究了叶面喷施20 mg·L^-1La(NO₃)₃ 对NaCl 胁迫下黑麦草幼苗生长及其抗逆生理特性的影响。结果表明: 盐胁迫显著抑制黑麦草幼苗的生长, 提高叶片电解质渗漏率及丙二醛(MDA)、O₂^- 和H₂O₂ 含量, 其作用随盐浓度的增大而增强。超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)活性和抗坏血酸(AsA)、谷胱甘肽(GSH)、可溶性蛋白质、脯氨酸含量随盐浓度增大呈先升后降趋势, 可溶性糖和Na⁺/K⁺比逐渐增大, 质膜H⁺-ATP 酶活性逐渐降低, 过氧化物酶(POD)活性及POD 同功酶数量表达增强。喷施La(NO₃)₃ 处理可降低盐胁迫下黑麦草幼苗叶片的O₂^- 和H₂O₂ 含量, 提高SOD、CAT、POD、APX 和质膜H⁺-ATP 酶的活性及POD 同功酶的表达, 使AsA、GSH、可溶性蛋白质、可溶性糖和游离脯氨酸含量及幼苗生物量增加, Na⁺/K⁺比降低。表明La(NO₃)₃ 可通过提高抗氧化系统的活性和积累渗透溶质减轻盐胁迫伤害, 从而提高黑麦草的耐盐性。