氮添加对樟子松人工林氮转化及相关功能基因丰度的影响

土壤氮(N)的有效性是影响土壤微生物群落结构以及土壤氮循环的重要因子。为探索N添加对樟子松人工林氮素转化及N功能基因(NFGs)表达的影响及其作用机制,该文以塞罕坝千层板林场的樟子松人工林为研究对象,进行了2年的氮添加处理,设置4个不同氮添加水平0、1、5、10 g N·m^-2·a^-1,分别记作N0、N1、N5、N10,采用功能基因微阵GeoChip 5.0系统及室内土壤培养法,探讨了土壤NFGs对氮添加的反应及其对氮转化过程的影响。结果表明:(1)与N0相比,中低N添加处理(N1、N5)促进了氨化(ureC、nirA、nrfA)、硝化(amoA)和反硝化(norB)相关基因的相对丰度,高N处理(N10)则抑制了所有NFGs的表达。(2)相关分析表明,N1、N5的促进作用与土壤有机碳(SOC)、硝态氮(NO₃^--N)和微生物生物量碳(MBC)显著相关,N10处理显著降低了所有氮转化过程NFGs的相对丰度,这种负面影响与溶解性有机碳(DOC)、MBC含量的减少有关。(3)与氮转化基因丰度规律趋势相似,N1和N5处理显著增加了净N硝化、净N矿化以及N₂O的排放速率,但N10促进作用不明显,表明氮添加对氮转化的促进作用存在阈值。(4)多元回归分析进一步表明,amoA-AOB和MBC是影响净N硝化的关键因素,ureC、nirK和MBC是影响净氮矿化的关键因素,narG、nirS是影响N₂O排放的关键因素。综上,N添加可提高促进樟子松人工林的氮转化及提高部分特定酶功能基因的相对丰度,但氮添加水平存在阈值,当施用10 g N·m^-2·a^-1时,氮转化受到抑制,添加5 g N·m^-2·a^-1是促进樟子松人工林土壤N转化的较佳水平。     

二氧化钛纳米颗粒对沼泽土壤反硝化和N2O排放的影响

近年来,二氧化钛纳米颗粒（TiO₂NPs）环境释放量不断增加,并通过多种途径进入湿地生态系统,不可避免地影响到湿地生态系统环境和功能。然而,关于TiO₂NPs对沼泽土壤反硝化作用和氧化亚氮（N₂O）排放的影响机及制尚不明确。选择典型沼泽土壤,通过室内培养实验研究土壤理化性质、反硝化酶活性、反硝化速率（DNR）和N₂O排放对不同剂量TiO₂NPs 0 mg/kg （CK）、10 mg/kg （A10）、100 mg/kg （A100）、1000 mg/kg （A1000）输入的响应,探讨TiO₂NPs输入对沼泽土壤反硝化作用和N₂O排放影响的内在机制。结果表明：不同剂量TiO₂NPs处理显著降低了土壤pH （P<0.05）,A10处理显著降低土壤总有机碳（TOC）含量（P<0.01）,A1000处理显著降低硝态氮（NO₃^--N）和亚硝态氮（NO₂^--N）含量（P<0.05）。TiO₂NPs处理抑制硝酸盐还原酶（NAR）活性,促进一氧化氮还原酶（NOR）和氧化亚氮还原酶（NOS）活性（P<0.01）,A1000处理先促进后抑制了亚硝酸盐还原酶（NIR）活性（P<0.05）。不同剂量TiO₂NPs处理抑制了土壤DNR,促进了N₂O排放,TiO₂NPs处理通过抑制NIR活性,降低土壤DNR,同时通过促进NOR活性,提高N₂O排放。综上,TiO₂NPs输入通过影响反硝化还原酶活性改变沼泽土壤反硝化过程,导致沼泽土壤N₂O排放增加,改变湿地氮的源、汇功能,影响全球气候变化。为TiO₂NPs输入的湿地环境风险评估研究提供理论基础。     

城市化地区典型水体的N2O排放通量特征——以南京市为例

内陆淡水水体是大气中N₂O的重要排放源,然而目前对于内陆典型城市水体N₂O排放通量的监测数据依然匮乏,典型城市水体的N₂O排放特征及驱动因素尚不清楚。本研究选取了南京市江北新区的典型水体,包括湖库、河流、养殖池塘和景观池塘,在2020年5月-2021年4月利用漂浮箱法连续监测了不同水体类型的水-气界面N₂O排放特征,并通过测定水环境特征,探究驱动水体N₂O排放通量的关键因素。研究结果表明,典型城市水体整体均表现为N₂O排放源,河流和养殖池塘的日平均排放通量最大,分别为（503±1236）μg m^-2 d^-1和（508±797）μg m^-2 d^-1,其次为景观池塘（（179±989）μg m^-2 d^-1）,而湖库的N₂O排放通量最小,仅表现为微弱的N₂O排放源（（54±212）μg m^-2 d^-1）。水体的N₂O排放呈现季节性差异,河流和养殖池塘夏季的N₂O排放通量显著高于其他季节（P<0.01）。水体全年N₂O排放数据与水体温度和溶解氧含量（DO）呈显著相关。而在温度较高的5月份-9月份（>20℃）,氮输入成为影响N₂O排放通量的关键因素（P<0.01）,因此控制城市水体的氮输入尤其是在水温较高的夏季是减少N₂O排放的有利措施。此外,由于水文化学条件差异等因素,小型封闭水体包括养殖池塘和景观池塘的N₂O排放通量差异较大,未来应加强监测不同水体的水文化学特征和N₂O的时空排放特征,探讨影响小型封闭水体水-气界面N₂O排放通量的具体驱动因素。此研究为城市区域N₂O排放的精准核算提供了数据支撑,为N₂O排放模型的修正提供了科学依据。     

黄河上游灌区稻田N2O排放特征

黄河上游灌区稻田高产区过量施肥现象十分突出,氮肥过量施用引起土壤氮素盈余,导致N₂O排放量增大,由此引起的温室效应引起广泛关注。采用静态箱-气相色谱法研究黄河上游灌区稻田不同施肥处理下N₂O排放特征。试验设置5个施肥处理,包括常规氮肥300 kg/hm²下单施尿素和有机肥配施2个处理,分别用N300和N300-OM代表;优化氮肥240 kg/hm²下单施尿素和有机肥配施2个处理,分别用N240和N240-OM代表;对照不施氮肥用N0代表。试验结果得出,灌区水稻生长季稻田土壤N₂O排放主要集中在水稻分蘖前及水稻生长的中后期,稻田氮肥施用、灌水及土壤温度的变化对N₂O排放通量影响较大,不同处理水稻各生育阶段N₂O累积排放量与稻田土壤耕层NO^-₃-N含量动态变化显著相关。稻田N₂O排放不是黄河上游灌区稻田氮素损失的主要途径,但灌区稻田N₂O排放的增温潜势较大;稻田氮肥过量施用会显著增加N₂O排放量,在相同氮素水平下,有机肥配施会显著增加稻田土壤N₂O的排放量(P＜0.01)。优化施氮能有效减少灌区稻田水稻生长季N₂O排放量。稻田不同处理的水稻整个生长季土壤N₂O排放总量为2.69-3.87 kg/hm²,肥料氮通过N₂O排放损失的百分率仅为0.43%-0.64%。在灌区习惯灌水和高氮肥300 kg/hm²时,N300-OM处理的稻田N₂O排放量达3.87 kg/hm²,在100 a时间尺度上的全球增温潜势(GWPs)为20.76×10⁷ kg CO₂/hm²;优化施氮240 kg/hm²水平下,N240和N240-OM处理的N₂O累计排放量较N300-OM处理,分别降低了1.18 kg/hm²和0.57 kg/hm²,在100 a尺度上每年由稻田N₂O排放引起的GWPs分别降低了6.33×10⁷ kg CO₂/hm²和3.06×10⁷ kg CO₂/hm²。     

城市小型景观水体溶存N2O浓度及排放通量特征

淡水生态系统是大气中N₂O的重要排放源,受到国内外广泛关注。城市小型景观水体作为区域淡水系统的重要组成,具有环境容量小,受人类活动干扰强烈,其N₂O排放特征及影响机制并不清楚。选择重庆大学城8个典型景观水体和2个城市外围的自然水体（对照）作为研究对象,利用顶空法和漂浮箱法对水体溶存N₂O浓度及排放通量进行季节性监测,并通过分析生境特征及水环境特征,探究城市小型景观水体N₂O排放特征及关键影响因素。结果表明：1）小型景观水体TN、NO₃^--N、NH₄⁺-N、NO₂^--N含量总体偏低但变异性极强（变化范围分别为0.31-1.47 mg/L、0.05-0.79 mg/L、0.03-0.14 mg/L、0.00-0.04 mg/L）,硝态氮是主要的氮形态;景观水体氮丰度远高于外围的自然水体;2）10个小型水体N₂O浓度范围为16.51-158.96 nmol/L,平均为（47.60±21.47） nmol/L,均处于过饱和状态;漂浮箱法实测8个景观水体N₂O排放通量均值为（0.13±0.05）mmol m^-2 d^-1,是对照水体的1.3-5.2倍,高于大部分已有研究结果,是大气N₂O的排放热源;3）景观水体N₂O排放通量与水体各形态氮含量呈显著的正相关关系,较高的N负荷和强烈的氮转化过程是导致景观水体成为N₂O排放热源的主要因子,水体N含量可以作为景观水体N₂O排放强度的有效指示因子;同时水生植物分布对水体N₂O排放影响显著,有植物分布的水域比开敞水域高1.4倍;4）漂浮箱法和边界层模型法对小型景观水体N₂O排放通量的监测结果呈较好的线性关系,但不同季节仍存在着一定差异,需要进一步优化模型估算方法;5）水体N₂O排放通量对温度的季节性变化较为敏感,呈夏季最高,春、秋季次之,冬季最低的季节模式。本研究强调,城市小型景观水体具有较高的N₂O排放速率,在区域氮循环及全球淡水系统温室气体排放清单中具有不可忽视的作用,在未来研究中应得到更多关注。     

双季稻田种植不同冬季作物对甲烷和氧化亚氮排放的影响

研究双季稻收获后填闲种植不同冬季作物在其生长季节内CH₄和N₂O的排放特征,对合理利用冬闲稻田,发展冬季作物生产及合理评价不同种植模式具有重要意义。采用静态箱-气相色谱法对冬季免耕直播黑麦草、紫云英、油菜以及翻耕移栽油菜和冬闲的双季稻田中甲烷(CH₄)和氧化亚氮(N₂O)排放进行了分析。结果表明:在冬季作物生长期,CH₄、N₂O平均排放通量和总排放量均表现为翻耕移栽油菜＞免耕直播黑麦草＞免耕直播油菜＞免耕直播紫云英＞冬闲。不同冬季作物稻田CH₄和N₂O总排放量与对照(冬闲)的差异均达到极显著水平(P<0.01);翻耕移栽油菜的双季稻田中CH₄和N₂O排放量最高,分别达2.989 g/m²和0.719 g/m²。翻耕移栽油菜稻田的CH₄和N₂O温室效应总和也最大,为2893.92 kg CO₂/hm²;免耕直播黑麦草和免耕直播油菜处理次之,而免耕直播紫云英处理最低。种植不同冬季作物促进了稻田生态系统CH₄和N₂O的排放。     

好氧氨氧化过程中的关键酶及N2O排放研究进展

氧化亚氮(nitrous oxide, N₂O)排放量的持续增加对全球生态平衡造成了严重的威胁。微生物N₂O排放占主要来源。其中,好氧氨氧化过程是氨在有氧的条件下氧化为亚硝酸盐,其直接或间接地影响着全球产生N₂O与释放量。氨氧化古菌(ammonia-oxidizing archaea, AOA)、氨氧化细菌(ammonia-oxidizing bacteria, AOB)、全程氨氧化菌(complete ammonia oxidization, Comammox)和异养氨氧化菌(heterotrophic ammonium oxidizing bacteria, HAOB)是氨氧化过程中主要的参与者,明确这四类微生物N₂O产生的机制对缓解全球N₂O排放是必要的。本文综述了AOA、AOB、Comammox和HAOB在好氧氨氧化过程中驱动的N₂O产生途径,并结合酶学分析了一些关键酶在N₂O产生途径中的作用。本文旨在为调控生物N₂O排放提供理论基础。     

不同水位管理对恢复泥炭地土壤CO2、CH4排放的影响

泥炭地水文条件影响泥炭地生物地球化学循环,控制和维持着泥炭地生态系统的结构和功能,是泥炭地生态恢复的重要前提。然而,目前关于恢复泥炭地土壤碳排放对不同水位的响应尚不明确。以长白山区天然（NP）、退耕（DP）及实施不同水文管理的恢复泥炭地（低水位（LR）、高水位（HR）与高低交替水位（H-LR））为研究对象,采用静态箱-气相色谱法对研究区泥炭地进行生长季（6-10月）土壤CO₂、CH₄排放监测。结果表明：温度和水位变化是研究区泥炭地土壤CO₂、CH₄排放季节变化的主控因子。H-LR受水位控制的影响,生长季土壤CO₂排放速率波动剧烈,其它水位管理恢复区土壤CO₂排放速率呈单峰型排放模式,且均与近地表温度呈指数相关（P<0.05）。除HR外,土壤CO₂排放速率与水位呈显著负相关（P<0.05）。生长季,研究区HR土壤CH₄排放速率呈双峰型,H-LR与NP的土壤CH₄排放呈单峰型,与近地表温度呈指数相关（P<0.05）,LR水位与CH₄排放速率显著正相关（P<0.05）。研究区不同水位管理恢复泥炭地土壤碳排放差异显著,虽然HR的土壤CO₂-C累积碳排放量显著低于其它水位恢复区,但其土壤CH₄-C累积碳排放量和综合增温潜势显著高于其它水位恢复区（P<0.05）。LR的累积碳排放量显著低于退化泥炭地,且其综合增温潜势最低。因此,建议在泥炭地恢复初期将低水位管理作为短期策略,以更好地恢复泥炭地碳汇功能,减弱其增温潜势。     

川西平原小流域不同水体N2O排放特征及驱动因素

氧化亚氮（N₂O）是一种潜在的、强大的温室气体,应该根据京都议定书规定开展监测和削减。河流、水库、鱼塘和沟渠等受人类影响的小流域水生生态系统是氮素生物地球化学循环的活跃区域,更是N₂O重要的源和汇。然而,同一流域不同水体N₂O的排放特征差异及其驱动因素尚不清楚。因此,选择川西平原西河流域作为研究区,于2016年6月到2017年5月连续监测不同水体水气界面的N₂O排放强度,并结合聚类分析解析N₂O排放特征的驱动因素。结果显示,不同水体的N₂O年排放通量差异显著,沟渠的N₂O年排放通量最高（（52.68±36.09）μg m^-2 h^-1）,城市段河流和鱼塘次之（（34.16±23.97）μg m^-2 h^-1和（29.03±31.41）μg m^-2 h^-1）,乡镇段和农区段河流再次（（8.32±28.60）μg m^-2 h^-1和（8.52±9.43）μg m^-2 h^-1）,水库最低（（-16.45±29.76）μg m^-2 h^-1）。除水库表现为N₂O的汇,其他水体均表现为N₂O的排放源。另外,不同水体N₂O排放的季节特征差异显著,农区段河流和农业沟渠表现为夏天最高,冬春最低（P<0.05）,而其他水体均表现为冬春显著高于夏秋（P<0.05）。根据N₂O排放季节特征及其驱动因素可将西河流域水体分为四类：第一类农业类水体的N₂O排放季节特征受气象因素和农业活动的联合驱动;第二类城乡类河流和第三类鱼塘分别受控于人类活动和养殖活动,与降雨温度等气象指标关系较弱;第四类水库主要受控于气象因素。并且,第一类农业类水体已成为大气N₂O排放的重要源,农业氮素管控是区域控制N₂O排放的重点。     

不同季节艾比湖湿地盐角草根际nirS-型与nirK-型反硝化细菌群落组成分析

旨在了解艾比湖湿地盐生植物盐角草根际与非根际中不同类型反硝化细菌的分布及其随季节变化情况,为温带干旱地区荒漠盐化生态系统的代表-艾比湖湿地在生态植被恢复过程中,由微生物推动的土壤氮素循环过程提供数据支撑。采集了艾比湖湿地夏、秋、春三个季节的盐角草根际和非根际土壤样本,通过高通量测序技术,比较分析了nirS-型和nirK-型两种类型的反硝化细菌的多样性和群落结构特点;利用RDA (redundancy analysis)探究了土壤理化因素对反硝化细菌多样性及群落结构的影响。艾比湖湿地盐角草根际与非根际中,nirS-型和nirK-型反硝化细菌多样性最高的为秋季根际土壤样本;各土壤样本中的反硝化细菌多样性均呈现根际>非根际。盐角草各土壤样本中的nirS-型反硝化细菌在门分类水平上隶属于变形菌门(Proteobacteria),厚壁菌门(Firmicutes)和放线菌门(Actinobacteria),而nirK-型反硝化细菌在门水平上分类仅包括了Proteobacteria和Firmicutes。Proteobacteria在各土壤样本中的占比均较高;其中Gamma-Proteobacteria的盐单胞菌属(Halomonas)和假单胞菌属(Pseudomonas)是各土壤样本所共有的nirS-型反硝化菌的优势菌属,但它们在每个土壤样本中的相对丰度各有差异。Alpha-Proteobacteria的根瘤菌属(Rhizobium)是盐角草各土壤样本中较为广泛存在的nirK-型反硝化细菌。艾比湖湿地盐角草各土壤样本中的反硝化细菌群落结构存在着一定的差异。RDA结果显示含水量、有机质、全氮和铵态氮等对各土壤样本中的nirS-型反硝化细菌的多样性影响较大,含水量、有机质、全氮、碱解氮等是nirK-型反硝化细菌多样性的主要影响因素。土壤电导率、全磷、全钾、全氮和碱解氮协同影响nirS-型反硝化细菌的群落结构,有机质、速效钾、速效磷、pH和硝态氮是nirK-型反硝化细菌群落结构组成的主要影响因素。艾比湖湿地反硝化细菌呈现季节性变化,nirS-型和nirK-型反硝化细菌以不同的主要菌属,共同推进湿地反硝化作用。而对于湿地生态系统的保护,则需要进行长期而广泛的土壤状态评估和土壤反硝化微生物菌群的动态监测。     

不同土地利用方式土壤氨氧化微生物和反硝化微生物时空分布特征

研究不同土地利用方式下氮循环相关微生物在不同土壤剖面的分布,可为认识和理解土壤氮转化过程提供科学依据。土壤氨氧化微生物和反硝化微生物在调节氮肥利用率、硝态氮淋溶和氧化亚氮(N₂O)排放等方面有着重要作用。以北京郊区农田和林地两种土地利用方式为研究对象,分析土壤氨氧化潜势和亚硝酸盐氧化潜势在0—100 cm土壤剖面上的季节分布(春季和秋季),并通过实时荧光定量PCR方法表征土壤氨氧化和反硝化微生物的时空分布特征。结果表明,农田土壤氨氧化潜势、亚硝酸盐氧化潜势、氨氧化微生物和反硝化微生物丰度均显著高于林地土壤,且随土壤深度增加而显著降低。除氨氧化古菌amoA基因丰度在不同季节间无显著差异外,春季土壤氨氧化细菌(amoA基因)、反硝化微生物nirS、nirK和典型nosZ I基因的丰度均显著高于秋季。土壤有机质、总氮、NH~+₄-N、NO~-₃-N含量与氨氧化微生物和反硝化微生物的功能基因丰度显著相关。综上,不同土地利用方式下土壤氮循环相关微生物的丰度与土壤氮素的可利用性和转化过程紧密相关,研究结果对土壤氮素利用和养分管理提供...     

The Impact of Using Mature Compost on Nitrous Oxide Emission and the Denitrifier Community in the Cattle Manure Composting Process

The diversity and dynamics of the denitrifying genes (nirS, nirK, and nosZ) encoding nitrite reductase and nitrous oxide (N₂O) reductase in the dairy cattle manure composting process were investigated. A mixture of dried grass with a cattle manure compost pile and a mature compost-added pile were used, and denaturing gradient gel electrophoresis was used for denitrifier community analysis. The diversity of nirK and nosZ genes significantly changed in the initial stage of composting. These variations might have been induced by the high temperature. The diversity of nirK was constant after the initial variation. On the other hand, the diversity of nosZ changed in the latter half of the process, a change which might have been induced by the accumulation of nitrate and nitrite. The nirS gene fragments could not be detected. The use of mature compost that contains nitrate and nitrite promoted the N₂O emission and significantly affected the variation of nosZ diversity in the initial stage of composting, but did not affect the variation of nirK diversity. Many Pseudomonas-like nirK and nosZ gene fragments were detected in the stage in which N₂O was actively emitted.     

Can differences in microbial abundances help explain enhanced N2O emissions in a permanent grassland under elevated atmospheric CO2?

Long‐term effects of elevated atmospheric CO₂ on the ammonia‐oxidizing and denitrifying bacteria in a grassland soil were investigated to test whether a shift in abundance of these N‐cycling microorganisms was responsible for enhanced N₂O emissions under elevated atmospheric CO₂. Soil samples (7.5 cm increments to 45 cm depth) were collected in 2008 from the University of Giessen Free Air Carbon dioxide Enrichment (GiFACE), a permanent grassland exposed to moderately elevated atmospheric CO₂ (+20%) since 1998. GiFACE plots lay on a soil moisture gradient because of gradually changing depth to the underlying water table and labeled as the DRY block (furthest from water table), MED block (intermediate to water table), and WET block (nearest to water table). Mean N₂O emissions measured since 1998 have been significantly higher under elevated CO₂. This study sought to identify microbial and biochemical parameters that might explain higher N₂O emissions under elevated CO₂. Soil biochemical parameters [extractable organic carbon (EOC), dissolved organic nitrogen (DON), NH₄⁺, NO₃^?], and abundances of genes encoding the key enzymes involved in ammonia oxidation (amoA) and denitrification (nirK, nirS, nosZ) depended more on soil depth and block (underlying soil moisture gradient) than on elevated CO₂. Ammonia oxidation and denitrification gene abundances, relative abundances (ratios) of nirS to nirK, of nosZ to both nirS and to nirK, and of the measured soil biochemical properties DON and NO₃^? tended to be lower in elevated CO₂ plots as compared with ambient plots in the MED and WET blocks while the DRY block exhibited an opposite trend. High N₂O emissions under elevated CO₂ in the MED and WET blocks correlated with lower nosZ to nirK ratios, suggesting that increased N₂O emissions under elevated CO₂ might be caused by a higher proportion of N₂O‐producing rather than N₂O consuming (N₂ producing) denitrifiers.     

Genetic and Environmental Controls on Nitrous Oxide Accumulation in Lakes

We studied potential links between environmental factors, nitrous oxide (N₂O) accumulation, and genetic indicators of nitrite and N₂O reducing bacteria in 12 boreal lakes. Denitrifying bacteria were investigated by quantifying genes encoding nitrite and N₂O reductases (nirS/nirK and nosZ, respectively, including the two phylogenetically distinct clades nosZ _I and nosZ _II) in lake sediments. Summertime N₂O accumulation and hypolimnetic nitrate concentrations were positively correlated both at the inter-lake scale and within a depth transect of an individual lake (Lake Vanajavesi). The variability in the individual nirS, nirK, nosZ _I, and nosZ _II gene abundances was high (up to tenfold) among the lakes, which allowed us to study the expected links between the ecosystem’s nir-vs-nos gene inventories and N₂O accumulation. Inter-lake variation in N₂O accumulation was indeed connected to the relative abundance of nitrite versus N₂O reductase genes, i.e. the (nirS+nirK)/nosZ _I gene ratio. In addition, the ratios of (nirS+nirK)/nosZ _I at the inter-lake scale and (nirS+nirK)/nosZ _I+II within Lake Vanajavesi correlated positively with nitrate availability. The results suggest that ambient nitrate concentration can be an important modulator of the N₂O accumulation in lake ecosystems, either directly by increasing the overall rate of denitrification or indirectly by controlling the balance of nitrite versus N₂O reductase carrying organisms.     

Dominance of bacterial ammonium oxidizers and fungal denitrifiers in the complex nitrogen cycle pathways related to nitrous oxide emission

Organic compounds and mineral nitrogen (N) usually increase nitrous oxide (N₂O) emissions. Vinasse, a by‐product of bio‐ethanol production that is rich in carbon, nitrogen, and potassium, is recycled in sugarcane fields as a bio‐fertilizer. Vinasse can contribute significantly to N₂O emissions when applied with N in sugarcane plantations, a common practice. However, the biological processes involved in N₂O emissions under this management practice are unknown. This study investigated the roles of nitrification and denitrification in N₂O emissions from straw‐covered soils amended with different vinasses (CV: concentrated and V: nonconcentrated) before or at the same time as mineral fertilizers at different time points of the sugarcane cycle in two seasons. N₂O emissions were evaluated for 90 days, the period that occurs most of the N₂O emission from fertilizers; the microbial genes encoding enzymes involved in N₂O production (archaeal and bacterial amoA, fungal and bacterial nirK, and bacterial nirS and nosZ), total bacteria, and total fungi were quantified by real‐time PCR. The application of CV and V in conjunction with mineral N resulted in higher N₂O emissions than the application of N fertilizer alone. The strategy of vinasse application 30 days before mineral N reduced N₂O emissions by 65% for CV, but not for V. Independent of rainy or dry season, the microbial processes were nitrification by ammonia‐oxidizing bacteria (AOB) and archaea and denitrification by bacteria and fungi. The contributions of each process differed and depended on soil moisture, soil pH, and N sources. We concluded that amoA‐AOB was the most important gene related to N₂O emissions, which indicates that nitrification by AOB is the main microbial‐driven process linked to N₂O emissions in tropical soil. Interestingly, fungal nirK was also significantly correlated with N₂O emissions, suggesting that denitrification by fungi contributes to N₂O emission in soils receiving straw and vinasse application.     

Terrestrial N2O emissions and related functional genes under climate change: A global meta‐analysis

Nitrous oxide (N₂O) emissions from soil contribute to global warming and are in turn substantially affected by climate change. However, climate change impacts on N₂O production across terrestrial ecosystems remain poorly understood. Here, we synthesized 46 published studies of N₂O fluxes and relevant soil functional genes (SFGs, that is, archaeal amoA, bacterial amoA, nosZ, narG, nirK and nirS) to assess their responses to increased temperature, increased or decreased precipitation amounts, and prolonged drought (no change in total precipitation but increase in precipitation intervals) in terrestrial ecosystem (i.e. grasslands, forests, shrublands, tundra and croplands). Across the data set, temperature increased N₂O emissions by 33%. However, the effects were highly variable across biomes, with strongest temperature responses in shrublands, variable responses in forests and negative responses in tundra. The warming methods employed also influenced the effects of temperature on N₂O emissions (most effectively induced by open‐top chambers). Whole‐day or whole‐year warming treatment significantly enhanced N₂O emissions, but daytime, nighttime or short‐season warming did not have significant effects. Regardless of biome, treatment method and season, increased precipitation promoted N₂O emission by an average of 55%, while decreased precipitation suppressed N₂O emission by 31%, predominantly driven by changes in soil moisture. The effect size of precipitation changes on nirS and nosZ showed a U‐shape relationship with soil moisture; further insight into biotic mechanisms underlying N₂O emission response to climate change remain limited by data availability, underlying a need for studies that report SFG. Our findings indicate that climate change substantially affects N₂O emission and highlights the urgent need to incorporate this strong feedback into most climate models for convincing projection of future climate change.     

Nitrification,denitrification, and related functional genes under elevated CO2: A meta-analysis in terrestrial ecosystems

Global change may have profound effects on soil nitrogen (N) cycling that can induce positive feedback to climate change through increased nitrous oxide (N₂O) emissions mediated by nitrification and denitrification. We conducted a meta-analysis of the effects of elevated CO₂ on nitrification and denitrification based on 879 observations from 58 publications and 46 independent elevated CO₂ experiments in terrestrial ecosystems. We investigated the effects of elevated CO₂ alone or combined with elevated temperature, increased precipitation, drought, and N addition. We assessed the response to elevated CO₂ of gross and potential nitrification, potential denitrification, and abundances of related functional genes (archaeal amoA, bacterial amoA, nirK, nirS, and nosZ). Elevated CO₂ increased potential nitrification (+28%) and the abundance of bacterial amoA functional gene (+62%) in cropland ecosystems. Elevated CO₂ increased potential denitrification when combined with N addition and higher precipitation (+116%). Elevated CO₂ also increased the abundance of nirK (+25%) and nirS (+27%) functional genes in terrestrial ecosystems and of nosZ (+32%) functional gene in cropland ecosystems. The increase in the abundance of nosZ under elevated CO₂ was larger at elevated temperature and high N (+62%). Four out of 14 two-way interactions tested between elevated CO₂ and elevated temperature, elevated CO₂ and increased precipitation, and elevated CO₂ and N addition were marginally significant and mostly synergistic. The effects of elevated CO₂ on potential nitrification and abundances of bacterial amoA and nirS functional genes increased with mean annual temperature and mean annual precipitation. Our meta-analysis thus suggests that warming and increased precipitation in large areas of the world could reinforce positive responses of nitrification and denitrification to elevated CO₂ and urges the need for more investigations in the tropical zone and on interactive effects among multiple global change factors, as we may largely underestimate the effects of global change on soil N₂O emissions.     

氮磷添加对草甸草原土壤氮磷转化功能基因丰度的影响

氮添加是提高退化草地生产力的主要养分管理措施,而过量的氮输入会导致土壤酸化、增加硝酸盐淋溶损失和温室气体排放。旨在明确草原割草利用下土壤氮、磷转化功能基因丰度对氮磷添加的响应规律,为定向调控打草场土壤氮、磷转化过程,提高养分利用效率,减少温室气体N₂O排放提供科学依据。2018—2020年在呼伦贝尔草甸草原打草场设置了5个施氮水平(0、1.55、4.65、13.95、27.9 g N m^-2 a^-1)和3个磷水平(0、5.24、10.48 g P m^-2 a^-1),裂区试验设计,在植物不同生长时期测定土壤氨氧化(amoA-AOA和amoA-AOB)、反硝化(narG、nirK、nirS和nosZ)和磷转化(phoD)基因丰度。结果表明,土壤氮转化基因丰度受到氮、磷添加的调控,而氮、磷添加对土壤磷转化功能基因丰度无显著影响(P>0.05)。氮添加可提高amoA-AOB基因丰度,增加氨氧化细菌调控土壤总硝化速率的相对重要性,因此能增加硝酸盐淋溶损失潜势。高氮处理下添加磷可降低...     

Abundance and Structure Composition of nirK and nosZ Genes as Well as Denitrifying Activity in Heavy Metal-polluted Paddy Soils

Denitrification is an important microbial process in soils and leads to the emission of nitrous oxide (N₂O). However, studies about the microbial community involved in denitrification processes in polluted paddy fields are scarce. Here, we studied two rice paddies which had been polluted for more than three decades by metal mining and smelter activities. Abundance and community composition were determined using real-time polymerase chain reaction (PCR) assay and denaturing gradient gel electrophoresis of nitrite reductase and nitrous oxide reductase gene amplicons (nirK and nosZ), while denitrifying activities were assessed by measuring potential denitrifier enzyme activity. We found that the community structure of both nirK and nosZ containing denitrifiers shifted under pollution in the two rice paddies. All the retrieved nirK sequences did not group into either α- or β-proteobacteria, while most of the nosZ species were affiliated with α-proteobacteria. While the abundance of both nirK and nosZ was significantly reduced in the polluted soils at “Dexing” (with relatively higher Cu levels), these parameters did not change significantly at “Dabaoshan” (polluted with Cd, Pb, Cu, and Zn). Furthermore, total denitrifying activity and N₂O production and reduction rates also only decreased under pollution at “Dexing.” These findings suggest that nirK and nosZ containing denitrifier populations and their activities could be sensitive to considerable Cu pollution, which could potentially affect N₂O release from polluted paddy soils.