氮素类型和剂量对寒温带针叶林土壤N2O排放的影响

大气氮沉降输入会增加森林生态系统氮素有效性,进而改变土壤N_2O产生与排放,然而有关不同氮素离子(氧化态NO_3~--N与还原态NH_4~+-N)沉降对土壤N_2O排放的影响知之甚少。以大兴安岭寒温带针叶林为研究对象,构建了3种类型(NH_4Cl、KNO_3、NH_4NO_3)和4个施氮水平(0、10、20、40 kg N hm~(-2)a~(-1))的增氮控制试验,利用流动化学分析仪和静态箱-气相色谱法4次/月测定凋落物层和矿质层土壤无机氮含量、土壤-大气界面N_2O净交换通量以及相关环境因子,分析施氮类型和剂量对土壤氮素有效性、土壤N_2O通量的影响探讨氮素富集条件下土壤N_2O通量的环境驱动机制。结果表明:施氮类型和剂量均显著影响土壤无机氮含量,土壤NH_4~+-N的积累效应显著高于NO_3~--N。施氮一致增加寒温带针叶林土壤N_2O排放,NH_4NO_3促进效应最为明显,增幅为442%-677%,高于全球平均水平(134%)。土壤N_2O通量与土壤温度、凋落物层NH_4~+-N含量正相关,且随着施氮水平增加而增加。结果表明大气氮沉降短期内不会导致寒温带针叶林土壤NO_3~--N大量流失,但会显著促进土壤N_2O的排放。此外,外源性NH_4~+和NO_3~-输入对土壤N_2O排放的促进作用具有协同效应,在未来森林生态系统氮循环和氮平衡研究中应该区分对待。     

模拟SO42-沉降对闽江口淡水感潮野慈姑湿地甲烷排放通量的影响

2015年12月—2016年10月,每月小潮日原位定期向闽江口塔礁洲淡水感潮野慈姑(Sagittaria trifolia L.)湿地施加剂量为60、120 kg S hm~(-2)a~(-1)的K_2SO_4溶液(分别记做S-60和S-120),探讨模拟硫酸根(SO_4~(2-))沉降对河口淡水感潮湿地甲烷(CH4)排放通量及间隙水SO_4~(2-)浓度的影响。对照、S-60和S-120处理组CH_4排放通量年均值分别为(7.88±1.00)mg h~(-1)m~(-2)、(6.55±0.97)mg h~(-1)m~(-2)和(6.66±1.49)mg h~(-1)m~(-2)。在年尺度上,两个高强度模拟SO_4~(2-)沉降处理组均未显著降低闽江口淡水感潮野慈姑湿地CH_4排放通量(P0.05),即高强度SO_4~(2-)沉降不会对河口淡水感潮湿地CH_4排放通量产生类似于其对泥炭湿地和水稻田的显著抑制效应。在年尺度以及秋、冬季,两个施加K_2SO_4溶液处理显著增加了野慈姑湿地10 cm深度土壤间隙水SO_4~(2-)浓度。对于各个处理组,温度较高的夏、秋季CH_4排放通量均显著高于温度相对较低的冬、春季(P0.05)。不同处理组CH_4排放通量均与土壤温度呈显著正相关关系,温度仍然是影响亚热带河口淡水感潮湿地CH_4排放通量的重要环境因子。     

增温和CO2浓度加倍对川西亚高山针叶林土壤可溶性氮的影响

采用全自动微气候控制的"人工模拟气候实验系统"研究了增温和CO2浓度加倍对川西亚高山针叶林土壤硝态氮(NO_3~--N)、铵态氮(NH_4~+-N)、游离氨基酸(FAA)、可溶性有机氮(DON)和可溶性总氮(TSN)的影响。结果表明:1在种植油松苗木组,增温处理显著降低了土壤NO_3~--N含量,不同处理0—15 cm土层NO_3~--N含量均显著小于15—30 cm层;而在未种树组,增温处理显著增加了土壤NO_3~--N含量,0—15 cm土层NO_3~--N含量显著高于15—30 cm层,这表明增温促进了油松苗对NO_3~--N的吸收。2在种植油松苗木组,增温(ET)、增CO_2(EC)及两者的共同作用(ETC)均显著增加了土壤NH_4~+-N、DON和TSN含量;在未种树组,ET显著增加了土壤NH_4~+-N、FAA、DON和TSN含量,EC和ETC对NH_4~+、FAA、DON和TSN含量具有微弱影响或没有显著影响。不同处理0—15cm层土壤NH_4~+-N、FAA、DON和TSN的含量显著大于15—30 cm层。3种植油松苗木组土壤NO_3~--N、NH_4~+-N、FAA、DON和TSN含量均显著低于未种树组,这是由植物对氮素的吸收消耗造成的。研究结果表明,EC、ETC主要通过植物根系作用促进了NH_4~+-N、DON和TSN含量增加,而ET处理通过影响土壤微生物和植物根系来促进NH_4~+-N、FAA、DON和TSN含量的增加。     

冬季水分管理和水稻覆膜栽培对川中丘陵地区冬水田CH4排放的影响

采用静态箱-气相色谱法观测冬季水分管理和水稻覆膜栽培对川中丘陵地区冬水田全年的CH_4排放通量。试验设置持续淹水(CF)、冬季直接落干+稻季淹水(TF)与冬季覆膜落干+稻季覆膜(PM)3个处理。结果表明,冬季休闲期,CF、TF和PM处理CH_4排放分别为16.1、1.4 g/m~2和2.7 g/m~2;水稻生长期,CF、TF和PM处理CH_4排放分别为57.7、27.7 g/m~2和13.5 g/m~2。相较于CF处理,TF与PM处理分别减少其全年CH_4排放60.6%和78.0%。TF与PM处理水稻生长期CH_4排放峰值分别较CF处理低33.0%和56.1%。休闲期,TF、PM处理厢面与厢沟区域CH_4排放与土壤温度显著正相关(P0.05),与土壤氧化还原电位(土壤Eh)显著负相关(P0.05),而CF处理CH_4排放仅与土壤温度显著正相关(P0.05)。水稻生长期,CF处理CH_4排放与土壤温度显著正相关(P0.05),与土壤Eh显著负相关(P0.05),TF处理CH_4排放仅与土壤Eh显著负相关(P0.05),PM处理厢沟CH_4排放与土壤Eh显著正相关(P0.05)。各处理水稻生长期土壤可溶性有机碳含量(DOC)与微生物生物量碳含量(MBC)显著高于休闲期(P0.05)。研究结果为进一步研究冬水田全年CH_4排放规律及寻求有效的减排措施提供数据支撑和科学依据。     

模拟氮沉降对藏北高寒草甸温室气体排放的影响

目前,高寒草甸对全球温室效应的贡献仍具有不确定性,而随着N沉降的增加,该系统温室体气排放也必将发生变化。为揭示高寒草甸对N沉降的响应机制,探讨其对全球变化的反馈作用,利用人工添加氮素的方法,于2014年生长季(6-9月)在那曲地区那曲县设置不同水平N添加梯度(0、7、20kg hm~(-2)a~(-1)和40 kg hm~(-2)a~(-1)),模拟氮沉降增加对藏北高寒草甸温室气体排放的影响。经过1a的研究结果表明:1)施氮显著促进了CO_2排放但对CH_4的吸收和N_2O的排放无显著影响。总体而言,添加氮素明显增加了温室气体排放总量,其中N2O处理下高寒草甸温室气体排放总量最高。2)回归分析结果表明,CO_2与NPP(总生物量)和TOC(土壤有机碳)线性相关(P0.05),而与TN(总氮)、NH_4~+-N和NO_3~--N均无显著相关关系(P0.05),CH_4与TN/NPP/TOC/NH_4~+-N/NO_3~--N均不相关(P0.05),N_2O与NPP/TOC/NO_3~--N均显著线性相关(P0.05),而与TN/NH_4~+-N不相关。综合初步研究结果,未来氮沉降增加条件下,藏北高寒草甸温室气体排放通量将有可能明显增加,从而对气候变化产生重要的反馈作用。     

氮磷添加对杉木林土壤碳氮矿化速率及酶动力学特征的影响

以江西杉木林红壤为研究对象,开展野外长期氮(N)、磷(P)添加控制试验,设置对照(CK)、N(50kg N hm~(-2)a~(-1))、P(50kg P hm~(-2)a~(-1))、NP(50kg N hm~(-2)a~(-1)+50kg P hm~(-2)a~(-1))处理,分析N、P添加对土壤碳矿化速率(C_(min))、氮矿化速率(N_(min))和相关的β-1,4-葡萄糖苷酶(βG)和β-1,4-N-乙酰葡糖氨糖苷酶(NAG)动力学参数的影响。结果表明:(1)N添加明显降低了C_(min)和N_(min),比CK分别减少了25%和18%;N添加减小了NAG的潜在最大酶活性(V_(max))、半饱和常数(K_m)、催化效率(V_(max)/K_m),但差异不显著(P0.05);N添加显著增加了βG的V_(max)、K_m,但对V_(max)/K_m有抑制作用。(2)P输入(P、NP)较CK使NAG的V_(max)、K_m减小26%—60%;NP同时添加明显提高βG和NAG的V_(max)/K_m(P0.05),但P输入(P、NP)对C_(min)和N_(min)影响不显著(P0.05)。(3)C_(min)与土壤溶解性有机碳正相关,N_(min)与pH显著正相关,与土壤NH_4~+-N、NO_3~--N显著负相关;βG和NAG的V_(max)/K_m均与NH_4~+-N、NO_3~--N负相关(P0.05),K_m均与NH_4~+-N、NO_3~--N正相关(P0.05)。βG的V_(max)与NH_4~+-N、NO_3~--N正相关(P0.05),NAG的V_(max)与有机碳、全氮、全磷、有效磷负相关(P0.05)。研究结果表明,在亚热带杉木人工林中,N添加降低土壤pH,增加土壤有效氮含量,抑制βG和NAG的V_(max)/K_m,对土壤C_(min)和N_(min)产生抑制作用;而NP添加增加土壤有效磷含量,增加土壤βG和NAG的V_(max)/K_m。     

退化设施蔬菜地修复过程中土壤可溶性有机碳与无机氮动态

土壤强还原处理(reductive soil disinfestation,RSD)可以有效修复退化设施蔬菜地土壤,但实施过程中亦会存在可溶性有机碳(DOC)与无机氮(NO_3~--N和NH_4~+-N)的淋溶风险。本研究选用水稻秸秆及其制备的生物质炭(biochar,BC)作为修复材料,采用BC、RSD以及RSD+BC三种方法修复退化蔬菜地土壤,探究修复过程中土壤基本性质、DOC与无机氮的动态变化。结果表明,与对照土壤相比,BC处理显著提高了土壤pH、EC和DOC含量(P0.05),但对土壤NO_3~--N和NH_4~+-N无显著影响。对于RSD和RSD+BC处理,土壤NO_3~--N含量在1～3 d内快速下降,之后维持在较低水平;土壤DOC含量呈先上升后下降趋势,在整个培养时段均显著高于对照处理(P0.05)。方差分析表明,BC与RSD处理对土壤DOC、全碳(TC)、全氮(TN)和C/N存在交互作用。可见,RSD和RSD+BC处理能有效去除NO_3~--N,但DOC含量大幅度增加,存在淋溶风险。     

氮沉降对温带森林土壤甲烷氧化菌的影响

大量研究显示氮沉降影响森林甲烷吸收量,但其中的微生物驱动机制仍缺乏研究。基于长白山典型温带森林长期氮沉降模拟实验平台样地,采用定量PCR和克隆测序技术,研究了长期施加不同形态氮((NH_4)_2SO_4、NH_4Cl和KNO_3)处理下森林土壤甲烷氧化菌的数量和群落组成随季节变化的特征。结果表明,夏季,森林土壤甲烷氧化菌pmo A基因丰度在不同施氮处理之间无显著性差异(每克干土1.54×10~6-3.20×10~6拷贝数);秋季,pmo A基因丰度在施加NH_4Cl和(NH_4)_2SO_4处理小区(每克干土1.93×10~5-7.6×10~5拷贝数)与对照(每克干土(4.03×10~6±1.2×10~6)拷贝数)相比有所降低,尤其在(NH_4)_2SO_4处理小区(每克干土(4.61×10~5±2.61×10~5)拷贝数)显著降低;无论夏季还是秋季,施加不同形态氮处理土壤甲烷氧化菌均以Type I型为主(相对丰度在70.6%-85.4%之间),并以Methylobacter-group(Type I)为优势类群,占Type I型的55.1%-91.7%;Methylobacter-group(Type I)的相对丰度在夏季不同形态氮处理土壤样品中无显著差异,但秋季样品中在施加(NH_4)_2SO_4(52.7%±6.5%)和NH_4Cl(56.1%±8.9%)的处理显著低于对照土壤(77.0%±2.9%),Methylococcus-group(Type I)的相对丰度则在(NH_4)_2SO_4和NH_4Cl处理土壤呈增加的趋势。这些结果表明铵态氮肥添加对温带森林土壤甲烷氧化菌的生长具有抑制作用并导致其群落结构发生改变,受夏季温度和水分的影响,这种抑制作用在秋季表现更明显,而NO_3~--N添加对土壤甲烷氧化菌的群落组成和丰度无显著影响。这些结果解释了以往观测到的施铵态氮肥显著降低秋季温带林地土壤甲烷净吸收量,而在夏季无显著影响的观测结果,解释了长期氮沉降影响森林土壤甲烷吸收的微生物机制。     

模拟氮沉降对温带森林土壤酶活性的影响

森林土壤酶作为土壤中最活跃组分,能影响生态系统的物质循环过程,其活性能快速反映氮沉降对土壤环境的变化。以北京地带性植被辽东栎林为研究对象,利用模拟氮沉降方法,原位设计低氮(50 kg N hm~(-2)a~(-1),N50)、高氮(150 kg N hm~(-2)a~(-1),N150)两个施氮水平,每个施氮水平设置Na NO_3、(NH_4)_2SO_4、NH4NO_33个不同的施氮类型,另设置空白对照(0 kg N hm~(-2)a~(-1),N0)。从时间格局上研究不同氮素化学形态和剂量对温带森林土壤6种酶(脲酶、酸性磷酸酶、碱性磷酸酶、β-葡萄糖苷酶、多酚氧化酶和过氧化氢酶)活性的影响。结果表明:在氮形态和水平的交互作用下,NH4NO3-N处理的脲酶活性显著高出NO~-_3-N处理的24.20%(N50),NH~+_4-N处理对酸性磷酸酶活性的影响显著高出NO~-_3-N处理的13.82%(N150);在NH~+_4-N和NH_4NO_3-N处理中,N50水平下的脲酶活性分别高出N0处理的38.90%和24.20%,差异显著。对无氮形态和水平交互作用的酶活性分析得出,不同的施氮水平,对碱性磷酸酶和多酚氧化酶的酶活性有显著促进作用,碱性磷酸酶活性在N50和N150处理下分别比N0高20.2%和11.5%,N50和N150处理对多酚氧化酶活性的促进作用分别比N0处理高64.3%和41.8%,差异显著(P0.05);NH~+_4-N处理对β-葡萄糖苷酶活性具有显著促进作用(P0.05),不同的施氮形态,对碱性磷酸酶、多酚氧化酶和过氧化氢酶的酶活性无显著影响。6种酶活性均呈现了显著的时间变化,氮添加对森林土壤酶活性的时间分异规律没有显著影响。此外,土壤微生物量碳、硝态氮和铵态氮含量与酶活性具有显著相关性(P0.05)。以上结果表明,氮添加通过改变森林土壤的环境因子,影响了土壤中的水解酶和氧化酶活性,进而改变了土壤有机碳库和养分循环。     

中亚热带天然林土壤CH_4吸收速率对模拟N沉降的响应

陆地森林土壤是重要的大气甲烷(CH4)汇,大气氮(N)沉降增加对森林土壤CH4吸收速率影响突出。运用静态箱-气相色谱法对中亚热带天然林土壤CH4吸收速率对模拟N沉降的响应进行连续3a的观测;试验作3种N处理,分别为对照(CK,0 kg N·hm-2·a-1)、低氮(LN,50 kg N·hm-2·a-1)和高氮(HN,100 kg N·hm-2·a-1),每种处理重复3次,每个月采集气体1次,同时测定0—5 cm土壤温度和0—12 cm土壤含水量;分析不同N沉降水平土壤CH4吸收速率的差异、动态变化以及对土壤含水量和土壤温度响应,并探讨N沉降对土壤理化性质的影响。结果显示:天然林土壤(CK)平均CH4吸收速率为(-62.78±14.39)μg·m-2·h-1,LN和HN土壤平均CH4吸收速率分别下降了30.21%、7.24%,CK、LN和HN处理土壤CH4吸收速率季节变化趋势相似;观测期间土壤CH4吸收速率对LN响应达到显著水平(P0.05),对HN响应则不显著(P0.05);LN、HN处理前两年对土壤CH4吸收速率抑制作用均不显著(P0.05),但在第3年LN极显著降低了土壤CH4吸收速率(P0.01),HN处理对土壤CH4吸收速率的影响则在第3年表现为显著抑制作用(P0.05),表明土壤CH4吸收速率对N沉降的响应随着N沉降时间的持续呈抑制效应加剧的趋势。相关分析表明:CK与HN土壤CH4吸收速率与土壤温度和土壤含水量均有显著相关性(P0.05),但LN土壤CH4吸收速率仅与土壤含水量显著相关(P0.05),表明土壤含水量是控制各N沉降处理土壤CH4吸收速率动态的主要环境因子。此外,LN、HN处理下土壤pH均极显著降低(P0.01),但LN土壤pH极显著低于HN(P0.01);LN处理极显著提高了土壤C/N比(P0.01),HN处理则相反;LN和HN处理对土壤NH+4-N、NO-3-N、可溶性总N(TDN)、可溶性有机碳(DOC)、地面凋落物量、地下0—10 cm细根生物量影响均不显著(P0.05),表明一定时期内N沉降首先引起了土壤pH和土壤C/N比的显著变化。     

Mineralization-immobilization and plant uptake of nitrogen as influenced by the spatial distribution of cattle slurry in soils of different texture

The effect of incorporating cattle slurry in soil, either by mixing or by simulated injection into a hollow in soil, on the ryegrass uptake of total N and ¹⁵NH₄ ⁺-N was determined in three soils of different texture. The N accumulation in Italian ryegrass (Lolium multiflorum L.) from slurry N and from an equivalent amount of NH₄ ⁺-N in (¹⁵NH₄) SO₄ (control) was measured during 6 months of growth in pots. After this period the total recovery of labelled N in the top soil plus herbage was similar in the slurry and the control treatments. This indicated that gaseous losses from slurry NH₄ ⁺-N were insignificant. Consequently, the availability of slurry N to plants was mainly influenced by the mineralization-immobilization processes. The apparent utilization of slurry NH₄ ⁺-N mixed into soil was 7%, 14% and 24% lower than the utilization of (NH₄)₂SO₄-N in a sand soil, a sandy loam soil and a loam soil, respectively. Thus, the net immobilization of N due to slurry application increased with increasing soil clay content, whereas the recovery in plants of ¹⁵N-labelled NH₄ ⁺-N from slurry was similar on the three soils. A parallel incubation experiment showed that the immobilization of slurry N occurred within the first week after slurry application. The incorporation of slurry N by simulated injection increased the plant uptake of both total and labelled N compared to mixing the slurry into the soil. The apparent utilization of injected slurry NH₄ ⁺-N was 7% higher, 8% lower and 4% higher than the utilization of (NH₄)₂SO₄-N in the sand, the sandy loam and the loam soil, respectively. It is concluded that the spatial distribution of slurry in soil influenced the net mineralization of N to the same degree as did the soil type.     

Effect of experimental nitrogen load on methane and nitrous oxide fluxes on ombrotrophic boreal peatland

Methane (CH₄) and nitrous oxide (N₂O) dynamics were studied in a boreal Sphagnum fuscum pine bog receiving annually (from 1991 to 1996) 30 or 100 kg NH₄NO₃-N ha^–1. The gas emissions were measured during the last three growing seasons of the experiment. Nitrogen treatment did not affect the CH₄ fluxes in the microsites where S. fuscum and S. angustifolium dominated. However, addition of 100 kg NH₄NO₃-N ha^–1 yr^–1 increased the CH₄ emission from those microsites dominated by S. fuscum. This increase was associated with the increase in coverage of cotton grass (Eriophorum vaginatum) induced by the nitrogen treatment. The differences in the CH₄ emissions were not related to the CH₄ oxidation and production potentials in the peat profiles. The N₂O fluxes were negligible from all microsites. Only minor short-term increases occurred after the nitrogen addition.     

Effects of ammonium on the activity and community of methanotrophs in landfill biocover soils

The influence of NH₄⁺ on microbial CH₄ oxidation is still poorly understood in landfill cover soils. In this study, effects of NH₄⁺ addition on the activity and community structure of methanotrophs were investigated in waste biocover soil (WBS) treated by a series of NH₄⁺-N contents (0, 100, 300, 600 and 1200 mg kg⁻¹). The results showed that the addition of NH₄⁺-N ranging from 100 to 300 mg kg⁻¹ could stimulate CH₄ oxidation in the WBS samples at the first stage of activity, while the addition of an NH₄⁺-N content of 600 mg kg⁻¹ had an inhibitory effect on CH₄ oxidation in the first 4 days. The decrease of CH₄ oxidation rate observed in the last stage of activity could be caused by nitrogen limitation and/or exopolymeric substance accumulation. Type I methanotrophs Methylocaldum and Methylobacter, and type II methanotrophs (Methylocystis and Methylosinus) were abundant in the WBS samples. Of these, Methylocaldum was the main methanotroph in the original WBS. With incubation, a higher abundance of Methylobacter was observed in the treatments with NH₄⁺-N contents greater than 300 mg kg⁻¹, which suggested that NH₄⁺-N addition might lead to the dominance of Methylobacter in the WBS samples. Compared to type I methanotrophs, the abundance of type II methanotrophs Methylocystis and/or Methylosinus was lower in the original WBS sample. An increase in the abundance of Methylocystis and/or Methylosinus occurred in the last stage of activity, and was likely due to a nitrogen limitation condition. Redundancy analysis showed that NH₄⁺-N and the C/N ratio had a significant influence on the methanotrophic community in the WBS sample.     

Effects of increased CO2 and N on CH4 efflux from a boreal mire: a growth chamber experiment

Increases in the supply of atmospheric CO₂ and N are expected to alter the carbon cycle, including CH₄ emissions, in boreal peatlands. These effects were studied in a glasshouse experiment with peat monoliths cored from an oligotrophic pine fen. The cores with living plants were kept in 720 ppm_v and 360 ppm_v CO₂ atmospheres for about 6 months under imitated natural temperature cycle. Fertilisation with NH₄NO₃ (3 g m⁻² for 25 weeks) was applied to 18 of the 36 monoliths. The rate of CH₄ flux was non-linearly dependent on the number of Eriophorum vaginatum shoots growing in the monoliths, probably due to the gas transport properties of the aerenchyma. The average CH₄ efflux rate, standardised by the number of shoots, was increased by a maximum of 10–20% in response to the raised CO₂ level. In the raised-NH₄NO₃ treatment, the increase in CH₄ release was lower. The effect of combined CO₂+NH₄NO₃ on CH₄ release was negligible and even lower than in the single treatments. Both potential CH₄ production and oxidation rates at 5, 15 and 25°C were higher near the surface than at the bottom of the core. As expected, the rates clearly depended on the incubation temperature, but the different treatments did not cause any consistent differences in either CH₄ production or oxidation. The determination of potential CH₄ production and oxidation in the laboratory is evidently too crude a method of differentiating substrate-induced differences in CH₄ production and oxidation in vivo. These results indicate that an increase in atmospheric CO₂ or N supply alone, at least in the short term, slightly enhances CH₄ effluxes from boreal peatlands; but together their effect may even be restrictive. Received: 18 June 1998 / Accepted: 25 January 1999     

Effects of Elatobium abietinum on nutrient fluxes in Sitka spruce canopies receiving elevated nitrogen and sulphur deposition

1 In a field acid mist simulation experiment, Sitka spruce (Picea sitchensis) was sprayed with different pollutant treatments: N, NH₄NO₃; S, Na₂SO₄; NS Acid, NH₄NO₃ + H₂SO₄ and control, no spray. Treatment effects on the abundance of the green spruce aphid Elatobium abietinum and honeydew production were assessed. In addition, needles were sampled for phyllosphere micro‐organisms. In a manipulative experiment, shoots were established and maintained as with or without E. abietinum infestation in order to determine the effects of infestation on needle loss and throughfall nutrient fluxes. 2 Aphid numbers were highest during the end of May and early June, with almost twice as many needles infested in the NS Acid treatment compared with the other treatments. Honeydew production was not affected by the treatments. 3 On infested shoots, increasing numbers of yellowing and dead needles were recorded above the throughfall collectors as the season progressed. The numbers of dead needles falling into the collectors were significantly higher beneath infested shoots. There were strong positive correlations between aphid numbers above the throughfall collectors, the number of yellowing and dead needles on the shoots and the number of needles in the funnels of the throughfall collectors. Litter production was more affected by aphid number than by pollutant treatment. 4 Bacteria, yeasts and filamentous fungi were more prolific on infested needles and treatment effects on colony forming units (CFUs) were most pronounced in the NS Acid treatment. 5 Fluxes of inorganic nitrogen beneath infested shoots were generally lower than beneath uninfested shoots. This effect was more pronounced in those treatments that supplied N i.e. N, NS Acid. The combination of aphid infestation and N‐addition exerted the strongest influence on nutrient fluxes. The fluxes of potassium and of organic carbon (DOC) were higher beneath infested shoots in all treatments, through most of the survey period.     

增氮对青藏高原东缘高寒草甸土壤甲烷吸收的早期影响

研究大气氮沉降对青藏高原高寒草甸土壤CH4吸收的影响,对于揭示氮素调节土壤CH4吸收的机制和评价氮沉降增加背景下大气CH4收支平衡至关重要.通过构建多形态、低剂量的增氮控制试验,测定土壤CH4净交换通量和相关土壤理化性质,分析高寒草甸土壤CH4通量变化特征及其主要驱动因子.研究结果表明:自然状态下高寒草甸土壤是大气CH4汇,CH4平均吸收量为(35.40±1.92) μg· m-2· h-1.土壤CH4吸收主要受水分驱动,其次为土壤NH4+-N和NO3-N含量.NH4+-N抑制CH4吸收,NO3--N促进CH4吸收;不同剂量氮素输入对土壤CH4吸收影响也不尽相同,低氮处理促进土壤CH4吸收,而中氮和高氮处理抑制土壤CH4吸收.结果显示青藏高原高寒草甸土壤是重要的大气CH4汇,在未来大气氮沉降加倍的情景下CH4汇功能增强,但当氮沉降量增加两倍以上时CH4汇功能将会减弱.     

不同氮处理下速生柳对水体氮的吸收、分配及生理响应

采用水培法,研究了旱柳苗在外源添加不同氮水平(贫氮、中氮、富氮、过氮)的铵态氮(NH+4-N)和硝态氮(NO-3-N)的生长、氮吸收、分配和生理响应。结果表明:一定范围氮浓度的增加能够促进旱柳苗的生长,但过量氮会抑制其生长,且NH+4-N的抑制作用大于NO-3-N;两种氮处理下,旱柳表现出对NH+4-N的吸收偏好,在同一氮水平时,旱柳各部位氮原子百分含量Atom%15N(AT%)、15N吸收量和来自氮源的N%(Ndff%)均为NH+4-N处理大于NO-3-N处理,且随着氮浓度的增加,差异增大,且在旱柳各部位的分布为根﹥茎﹥叶;2种氮素过量和不足均会对旱柳根和叶生理指标产生不同的影响,其中在过氮水平时,NH+4-N和NO-3-N处理下根系活力比对照减少了50.61%和增加了19.53%;在过氮水平时,NH+4-N处理柳树苗根总长、根表面积、根平均直径、根体积和侧根数分别对照下降了30.92%、29.48%、19.44%、27.01%和36.41%,NO-3-N处理柳树苗相应的根系形态指标分别对对照下降了1.66%、5.65%、1.49%、5.06%和25.72%。可见,高浓度NH+4-N对旱柳苗的胁迫影响大于NO-3-N,在应用于水体氮污染修复时可通过改变水体无机氮的比例,削弱其对旱柳的影响,从而提高旱柳对水体氮污染的修复效果。     

Evaluation of thiosulfate as a nitrification inhibitor for manures and fertilizers

Nitrogen from poultry manure (PM) and ammoniacal fertilizers undergoes rapid nitrification upon addition to soils, making it highly susceptible to leaching and thus creating a potential for groundwater contamination by nitrate-N. Any management technique that could delay nitrification would be desirable. A laboratory incubation study was conducted to determine the effect of thiosulfate, a known nitrification inhibitor, on nitrification in a loamy sand soil amended with five N sources, including two poultry manures and three N fertilizers [(NH₄)₂SO₄, NH₄NO₃, CO(NH₂)₂]. The manures or fertilizers were added to a soil-sand mixture alone or in combination with Na₂S₂O at a rate of 100 mg N kg^-1 for the inorganic N sources and 147 mg N kg^-1 and 122 mg N kg^-1 for PM-1 and PM-2 respectively. All treatments were incubated for 12 weeks and analyzed periodically for NO₃-N and NH₄-N.Thiosulfate was most effective with NH₄NO₃, maintaining 100% inhibition of nitrification throughout the 12 week study, and with (NH₄)₂SO₄ (89% inhibition at 12 weeks). Thiosulfate also inhibited nitrification from urea and poultry manure, but the inhibitory effect diminished later in the incubation. Urea had 81% inhibition of nitrification after eight weeks, decreasing to 26% by week 12, while the manures averaged 89% inhibition after four weeks and 20% at week 12. Net mineralization of organic N from PM was also reduced by the use of thiosulfate, particularly for PM-1 where the percentage of organic N mineralized decreased from 42% after four weeks incubation to 3% at week 12. Therefore, while thiosulfate can reduce nitrification from manures, and thus the potential for nitrate leaching, the timing of manure application will influence the effect of thiosulfate on the availability of manure N for plant uptake or leaching.     

马尾松组培苗对氮素形态的生长响应

马尾松属高氮需求树种,然而在苗木培育中马尾松对氮素,尤其是不同形态氮素的需求尚不明确。该文以马尾松组培苗为试验材料,采用基质培养方法,针对硝态氮、铵态氮两种氮素形态均分别设置了2、4、8、16 mmol·L~(-1)4个处理,以不添加氮素为对照,对苗木的高径生长、根构型参数(总根长、总表面积、总体积、平均直径和根尖数)以及生物量的变化进行了分析。结果表明:(1)在2～8 mmol·L~(-1)硝态氮处理下,除根冠比外,苗高、地径、根构型参数、生物量均不低于对照,其中以2 mmol·L~(-1)水平下苗木生长效果最好,苗高、地径、根构型参数、生物量均高于对照;在16 mmol·L~(-1)硝态氮处理下,苗高、总根长与根尖数低于对照。(2)在2～16 mmol·L~(-1)供试范围内,铵态氮处理下的苗木根冠比小于对照,但其苗高、地径、根构型参数、生物量均不低于对照,整体上以4 mmol·L~(-1)处理下的苗木生长表现最佳。(3)在任一供氮水平,除根冠比和2mmol·L~(-1)处理下的根总表面积与根尖数在两种氮素形态间无明显差异外,铵态氮处理下的苗木生长情况显著优于硝态氮处理,这说明马尾松组培苗偏好于吸收和利用铵态氮。综上结果表明,外施硝态氮、铵态氮均能促进马尾松组培苗生长,但需控制在适宜浓度范围内,其中以2 mmol·L~(-1)硝态氮和4 mmol·L~(-1)铵态氮处理效果较佳。高浓度硝态氮会抑制苗木高度及根系发育,且在相同施肥水平下,对苗木生长的促进效果大多弱于铵态氮。因此,今后为达到培育优质壮苗和提高肥效、减少肥害的目的,可考虑使用铵态氮肥。