Determinants of annual fluxes of CO2 and N2O in long-term no-tillage and conventional tillage systems in northern France

The greenhouse gases CO₂ and N₂O emissions were quantified in a long-term experiment in northern France, in which no-till (NT) and conventional tillage (CT) had been differentiated during 32 years in plots under a maize–wheat rotation. Continuous CO₂ and periodical N₂O soil emission measurements were performed during two periods: under maize cultivation (April 2003–July 2003) and during the fallow period after wheat harvest (August 2003–March 2004). In order to document the dynamics and importance of these emissions, soil organic C and mineral N, residue decomposition, soil potential for CO₂ emission and climatic data were measured. CO₂ emissions were significantly larger in NT on 53% and in CT on 6% of the days. From April to July 2003 and from November 2003 to March 2004, the cumulated CO₂ emissions did not differ significantly between CT and NT. However, the cumulated CO₂ emissions from August to November 2003 were considerably larger for NT than for CT. Over the entire 331 days of measurement, CT and NT emitted 3160 ± 269 and 4064 ± 138 kg CO₂-C ha⁻¹, respectively. The differences in CO₂ emissions in the two tillage systems resulted from the soil climatic conditions and the amounts and location of crop residues and SOM. A large proportion of the CO₂ emissions in NT over the entire measurement period was probably due to the decomposition of old weathered residues. NT tended to emit more N₂O than CT over the entire measurement period. However differences were statistically significant in only half of the cases due to important variability. N₂O emissions were generally less than 5 g N ha⁻¹ day⁻¹, except for a few dates where emission increased up to 21 g N ha⁻¹ day⁻¹. These N₂O fluxes represented 0.80 ± 0.15 and 1.32 ± 0.52 kg N₂O-N ha⁻¹ year⁻¹ for CT and NT, respectively. Depending on the periods, a large part of the N₂O emissions occurred was probably induced by nitrification, since soil conditions were not favorable for denitrification. Finally, for the period of measurement after 32 years of tillage treatments, the NT system emitted more greenhouses gases (CO₂ and N₂O) to the atmosphere on an annual basis than the CT system.     

农田土壤N2O排放和减排措施的研究进展

氧化亚氮(N2O)是一种受人类活动影响的重要温室气体。农业土壤是其主要的排放源之一,土壤中硝化和反硝化作用是N2O产生的主要过程。N2O的排放受多种因素的影响,农业活动尤其是施用化学氮肥是农田N2O排放量增加的主要因素。提高氮肥利用率,使用硝化抑制剂等措施将有助于减少N2O的排放量,更有效的减排措施还有待进一步的研究与应用。     

下辽河平原潮棕壤撂荒地和人工林N2O、CH4排放研究

采用静态箱(暗箱)气相色谱法对下辽河平原潮棕壤撂荒地和人工林N2O、CH4排放进行了为期1年的原位测量,同时测量了土壤温湿度、气温,土壤NO3-N、NH4 -N含量等相关因子.结果表明,在观测期间内人工林地土壤的N2O排放通量明显高于撂荒地.撂荒地是大气CH4的源,而人工林则是CH4的汇.对人工林的观测结果表明,N2哦O排放与CH4排放之间存在负相关关系(R2=-0.351,p＜0.05,n=36);而撂荒地两种气体排放之间无明显相关关系.N2O排放通量和温度变化有很好的相关性.当土壤含水量在200 g/kg以上时,土壤含水量与CH4气体排放具有较好的正相关关系.     

Response of denitrifying communities to successive soil freeze–thaw cycles

The effect of soil freeze–thaw cycles on the denitrification potential was examined based on the C₂H₂ inhibition method. The gross N₂O production curve of the soil sample (incubation with C₂H₂) showed minor changes between the freeze–thaw treatment and the unfrozen control. However, kinetics analysis revealed that the initial production rate, an indicator of the population density of denitrifying communities, decreased (P = 0.043) and the specific growth rate constant, an indicator of the activity of denitrifying communities, increased (P = 0.039) as a result of the freeze–thaw cycles in five of six soil samples examined. The increase in the specific growth rate constant suggested the stimulation of the activity of denitrifying communities that survived after the freeze–thaw cycles and may explain the minor suppression on the gross N₂O production in spite of decreasing the population density of denitrifying communities that was suggested by the initial production rate. The net N₂O production curve of the soil sample (incubation without C₂H₂) showed a remarkable change in one out of six soil samples, and in that one soil sample, N₂O release to the atmosphere was largely stimulated (7.6 times) by the freeze–thaw cycles. However, the stimulation of the N₂O release by the freeze–thaw cycles was even observed in two other selected soil samples (4.6 and 1.8 times), suggesting that an imbalance in the N₂O-producing and N₂O-reducing activities of denitrifying communities might complementally explain the N₂O release stimulated by the freeze–thaw cycles.     

转5-烯醇式丙酮酰莽草酸-3-磷酸合酶(EPSPS)基因抗草甘膦烟草和棉花的获得

以从抗草甘膦的荧光假单胞菌(Pseudomonas fluorescens)G2中克隆的、并按双子叶植物偏爱密码子改造的5-烯醇式丙酮酰莽草酸-3-磷酸合酶(EPSPS)基因aroAG2M为目的基因,用菊花Rubisco小亚基的启动子驱动,在基因的5'端加叶绿体定位信号肽,构建植物表达载体。用根癌农杆菌(Agrobacterium tumefaciens)介导的叶盘法转化烟草(Nicotiana tabacum)获得转基因植株,PCR检测表明,外源基因已整合到烟草基因组中。转基因和非转基因植株6～8叶龄苗的叶片涂抹不同浓度的草甘膦异丙胺盐,表明转基因植株可抗4‰浓度的草甘膦,而非转基因对照植株则在2‰草甘膦时即死亡。花粉管通道法转化棉花(Gossypium hirsutum),得到3株具有草甘膦抗性的转基因植株,PCR和Southern检测显示,外源基因已整合到棉花基因组中,田间喷洒草甘膦异丙胺盐水剂,表明T1代转基因植株具有草甘膦抗性。     

大颗粒木质成型燃料燃烧过程烟气排放特性

选用大颗粒木质燃料为研究对象,通过管式加热炉对单颗粒木质燃料进行燃烧试验,研究不同空气流量和温度下木质燃料燃烧过程CO、NO、SO_2等气体动态排放特性。试验结果表明:800℃时,挥发分着火时间滞后,着火前即有CO随挥发分析出,CO排放浓度曲线呈双峰状;随着温度升高,CO析出峰明显变窄,从挥发分析出至焦炭燃烧完成所需时间缩短:NO排放浓度及其排放量在温度为900℃时达到最大值,燃料N至NO的转化率最高可达41.79%,随着温度升高和燃烧过程还原性气氛增强,NO析出浓度及其排放量减少,转化率可低至12.32%;木质燃料充分燃烧时,几乎无SO_2排出,S主要转化为硫酸盐固存于灰分中或于高温下随烟气排出;贫氧燃烧状态下,S02析出主要源自挥发分析出初期有机硫的分解、氧化,但燃料中更多的s以H2S、CaS等形式排出。     

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。     

基于变量优选与机器学习的干旱区湿地土壤盐渍化数字制图

土壤盐渍化是导致土壤退化和生态系统恶化的主要原因之一,对干旱区的可持续发展构成主要威胁。为了尽可能精确地监测土壤盐渍化的空间变异性,该研究收集新疆艾比湖湿地78个典型样点,其中选取54个样本作为训练集,24个样本作为独立验证集。基于Sientinel-2多光谱传感器(Multi-Spectral Instrument,MSI)、数字高程模型(Digital Elevation Model,DEM)数据提取3类指数(红边光谱指数、植被指数和地形指数),经过极端梯度提升(Extreme Gradient Boosting,XGBoost)算法筛选有效特征变量,构建了关于土壤电导率(Electrical Conductivity,EC)的随机森林(Random Forest,RF)、极限学习机(Extra Learning Machine,ELM)和偏最小二乘回归(Partial Least Squares Regression,PLSR)预测模型,并选择最优模型绘制了艾比湖湿地盐渍化分布图。结果表明:优选的红边光谱指数基本能够预测EC的空间变化;红边光谱指数与植被指数组合建模效果总体上优于...     

再植枸杞根际真菌群落对长期连作的响应研究

受枸杞自身种植特点和道地产区土地资源限制,连作障碍已成为制约宁夏枸杞产业可持续发展的主要因素之一,导致严重的经济损失和生态问题。前期研究表明,连作能够显著影响再植枸杞根际土壤细菌的群落结构和多样性,但就连作对真菌群落结构和功能的影响目前仍不清楚。本文利用实时荧光定量PCR和高通量测序技术,研究连作对再植枸杞根际真菌群落丰度及多样性的影响。实时荧光定量PCR分析表明,与对照样地相比,连作显著促进再植枸杞根际及非根际土壤中细菌和真菌的丰度。但连作对真菌的促进作用明显高于细菌,导致细菌/真菌比例失衡,使再植枸杞根际及非根际土壤微生物环境偏向于真菌型。对测序结果的分析发现,所测定样地中枸杞根际及非根际土壤中的优势真菌门分别为子囊菌门、担子菌门、接合菌门、壶菌门及球囊菌门,其中连作地再植枸杞根际子囊菌门的相对丰度较对照样地显著降低,而接合菌门的相对丰度则显著增加(P0.05)。FUNGuild真菌功能预测也证实连作显著抑制再植枸杞根际土壤丛枝菌根真菌的相对丰度(P0.05)。基于距离的冗余分析(db-RDA)结果表明,土壤pH、电导率、硝态氮和有效磷含量是影响枸杞根际土壤真菌群落变化的主要因子(P0.05),而土壤硝态氮和有效磷含量则是解释非根际土壤真菌群落变化的主要因子(P0.05)。这些结果说明长期施用化肥可能是改变连作地再植枸杞根际土壤真菌群落结构及枸杞-真菌互作关系的主要因素之一。这一研究结果为理解枸杞连作障碍的形成机制提供理论基础。     

铁皮石斛PRC2复合体成员的鉴定及对胁迫响应的表达分析

为了探讨PRC2复合体在铁皮石斛生长发育和胁迫响应中的功能,通过生物信息学方法筛选了铁皮石斛PRC2核心成员DcCLF、DcSWN、DcEMF2、DcFIE和DcMSI1,借助酵母双杂交技术分析了它们之间的互作关系,利用半定量PCR分析了PRC2核心成员的组织表达谱,通过荧光定量PCR检测了它们对非生物胁迫(低温、高温、脱水)和病害胁迫(齐整小核菌、灰葡萄孢霉菌)的响应情况。结果表明,铁皮石斛PRC2复合体包含5个成员:E(z)同源基因DcCLF和DcSWN、Su(z)12基因DcEMF2、ESC基因DcFIE、p55基因DcMSI1,且这5个成员间的互作关系基本符合模式植物的互作模式,也存在物种特异性,表明PRC2复合体在进化中既有保守性也有特殊性。PRC2核心成员在铁皮石斛根、茎、叶、花蕾、成花中均有表达,但不同基因的表达存在组织差异性。同时,PRC2成员响应不同的环境和病害胁迫:DcCLF受低温、高温和脱水等各种环境胁迫的显著诱导;DcMSI1和DcEMF2在齐整小核菌侵染下表达明显上调,而DcSWN在灰葡萄孢霉菌侵染下受诱导程度最大。铁皮石斛PRC2复合体在生长发育和胁迫应答中...