菜地土壤施用铵态氮肥后 N2O 排放来源及其动态

氧化亚氮(N2O)是重要的农业源温室气体,菜地土壤施肥量高、施肥次数多,且肥水同期,是重要的N2O排放源。采用室内培养实验,测定在70%田间持水量条件下菜地土壤施用铵态氮肥后3周内N2O排放动态,利用不同气体抑制剂(低浓度乙炔、纯氧、纯氦、纯氧+乙炔)对N2O排放过程抑制效果各不相同的特点,经合理组合计算得出自养硝化、硝化细菌的反硝化、生物反硝化等主要过程对土壤N2O排放的相对贡献及其动态,以探索菜地土壤施用铵态氮肥后土壤N2O排放的来源及动态。结果表明,(1)在70%田间持水量条件下,菜地土壤施用铵态氮肥后2d内(48h内)的N2O排放通量最高,为314.4ng·g-1·d-1,到第4天时N2O排放通量已迅速降至前两天的1/6,且随培养时间的延长其排放通量不断降低。(2)自养硝化作用是菜地施用铵态氮肥后N2O排放的主要来源,施肥培养后2周内的贡献率在50%以上,2周后其贡献率降至40%左右。(3)硝化细菌的反硝化作用对N2O排放的贡献主要在施铵氮后2d内,其贡献率达44%,之后其贡献率一直保持在14%~27%。反硝化作用对N2O排放的贡献随着土壤中铵态氮含量的下降和硝态氮含量的升高而逐渐从开始时不到1%增至30%,但由于施肥培养2周后N2O的排放通量绝对数值很低(仅为施肥后2d内排放高峰的1/20),故其对N2O排放的贡献有限。土壤N2O排放通量及其来源与土壤中铵态氮和硝态氮含量的动态变化密切相关,施用铵态氮肥后土壤短期内呈现酸化趋势。因此,合理控制硝化作用是有效控制菜地土壤N2O排放的关键措施。     

砖红壤不同温度、水分及碳氮源条件下硝化和反硝化特征

采用气压分离技术,研究了海南橡胶林砖红壤土壤总硝化速率和反硝化速率对温度、水分及碳氮源的响应。结果表明,在10~30℃的土壤温度范围内,温度的升高促进了土壤总硝化速率,反硝化速率随着温度的升高呈现先增加后降低的趋势。随着土壤水分的升高,土壤总硝化速率和反硝化速率均呈线性增加。当土壤孔隙度水达到70%后,总硝化速率呈下降趋势,却进一步地促进了反硝化速率。添加硝态氮抑制了总硝化速率;在N 0~40 g m~(-2)的范围内,除低量硝态氮的添加(N 1 g m~(-2))降低了反硝化速率外,反硝化速率大致随硝态氮浓度的增加而增加。低量铵态氮的添加(N 0.5 g m~(-2))促进了总硝化速率,高量铵态氮(N 4、20和40 g m~(-2))则抑制了总硝化速率;除低量铵态氮的添加(N 1 g m~(-2))抑制了反硝化速率外,添加铵态氮对反硝化速率影响不大。添加C(C 10~40 g m~(-2))激发了土壤总硝化速率和反硝化速率,碳源的缺乏可能是橡胶林酸性砖红壤限制土壤硝化和反硝化速率的主要因素。     

不同土地利用方式土壤温室气体排放对碳氮添加的响应

揭示不同土地利用方式下土壤N2O产生机制及其CO2和CH4的排放,有助于土壤温室气体减排措施的制定。本研究以长沙金井河流域酸性红壤上菜地、稻田、茶园和林地土壤为研究对象,控制温度和土壤含水量,采用静态培养-气相色谱法,研究4种利用方式土壤N2O、CO2和CH4的排放对不同碳氮和硝化抑制剂添加的响应。结果表明,由于土壤pH较低,酸性红壤外加氮源后仅有较小的N2O排放。葡萄糖能够促进尿素添加后N2O的排放及土壤反硝化作用N2O的排放。异养硝化作用可能是酸性红壤N2O产生的主要途径。硝化抑制剂双氰胺（DCD）对酸性红壤N2O减排无明显效果。碳氮添加后土壤N2O的总排放量表现为茶园 > 菜地 > 稻田 > 林地。外源有机碳能够显著促进4种利用方式土壤CO2的排放,表现为茶园、稻田 > 菜地、林地。但除稻田土壤CH4排放增加外,菜地、茶园和林地土壤CH4排放对外源有机碳无明显响应。     

尿素不同配施处理对棕壤茶园土壤尿素转化及硝化作用影响的研究

采用好气土壤培养试验,以单施尿素为对照,研究了尿素配施双氰胺（UD）、菌剂（UJ）、复混肥（UY）、菌剂+复混肥（UYJ）以及表面覆盖茶末（UF）处理对尿素转化和硝化作用的影响,测定了土壤铵态氮、硝态氮、脲酶活性、氨氧化菌数量并计算表观硝化率,结果表明:各种处理均能提高土壤中铵态氮含量,降低硝态氮含量,延迟脲酶活性高峰期,减小表观硝化率,抑制氨氧化菌。其中以覆盖茶末（UF）处理效果最好,其土壤铵态氮含量最高,硝态氮和硝化率最低;其次为UD处理,配施DCD能明显推迟脲酶活性高峰出现时间并降低前期活性,同时能显著抑制氨氧化菌生长。此外,比较UYJ和UJ处理结果可以推测:在有机质丰富的茶园中施用菌剂来抑制硝化作用的效果不显著。     

不同培肥措施下复垦土壤氮素转化特征

为揭示不同复垦年限和培肥措施对采煤塌陷区复垦土壤氮素转化特征影响,分别采用间歇淋洗好气培养法、室内恒温控湿好气培养法和硝酸盐消失法研究了5种培肥措施下复垦4,8年土壤矿化、硝化、反硝化作用规律。结果表明:随复垦年限增加,土壤的矿化量(Nt)和矿化势(N0)均有增加,但土壤矿化率(Nt/N)及矿化势占全氮的比例(N0/N)无明显变化;不同培肥措施下,复垦8年土壤生物有机肥配施化肥处理(MCFB)Nt、N0、Nt/N和N0/N分别较单施化肥处理(CF)提高65.22%,65.21%,60.42%和60.76%。土壤硝化率和达到最大硝化速率需要的时间(Tmax)受复垦年限影响较小,不同施肥措施均可提高土壤硝化率,但处理间差异不显著;最大硝化速率(Vmax)随复垦年限增加而增大,复垦4,8年土壤Vmax和Tmax总体以MCFB效果优于其他培肥处理。土壤硝态氮损失率和硝酸盐消失速率随复垦年限的增加而增加,经过7天培养,不同培肥措施下复垦4年土壤硝态氮损失率以单施有机肥处理(M)最高,达78.72%,硝酸盐消失速率以MCFB处理最低,与不施肥对照(CK)一致;复垦8年土壤反硝化作用在不同处理下无显著差异。通过短期氮素转化作用强度比较,复垦土壤硝化作用>反硝化作用>矿化作用。综合来看,培肥对复垦土壤氮素转化作用提升效果明显,生物有机肥配施化肥更有利于土壤有效氮的保持和提高,减少氮素损失。     

硝态氮浓度对亚热带土壤反硝化潜力和产物组成的影响

在实验室条件下,采用密闭、淹水、充 N2 的严格厌氧培养方法研究了NO3--N?浓度对亚热带土壤反硝化潜力和产物组成的影响。研究表明,在NO3-?-N?浓度为 10 ~ 200 mg /kg 范围内,该土壤的反硝化势变化于 0.024 ~ 0.224 mg/(kg×h) 之间,随着NO3--N?浓度的增加而呈显著线性增加(R2 = 0.94,P<0.01)。N2O 始终是反硝化的主要产物,占反硝化产物的 56% ~ 92%;NO 是次要产物,占 6% ~ 40%。在野外原位状态下,土壤的还原条件难以达到供试实验室条件,由此估计,亚热带森林土壤反硝化的主要产物并非 N2,而是 N2O 和 NO,这可能是该类土壤虽反硝化作用弱,但 N2O 排放量大的主要原因。     

碳源与底物对不同层次土壤产生N2O能力的影响

底层土壤的反硝化作用是土壤排放N2O的重要来源，同时也是影响浅层地下水硝酸盐含量的重要因素，通过一系列室内培养试验，研究了一种农用土壤不同土层在碳源和NO3含量不同情况下产生N2O的能力。结果表明，试验用土壤的不同土层均具有进行反硝化作用产生N2O的能力，底层土壤产生N2O的能力大于根区土壤；单独添加葡萄糖、NO3或同时添加葡萄糖和NO3，对土壤N2O和CO2释放的影响与土壤层次和观测时间有关；向土壤添加葡萄糖和NO3，各个土层释放N2O的能力均显著提高；从产生N2O和CO2能力的角度而言，不同层次土壤的微生物区系间存在较大差异。采用短期（24h之内）饱和泥浆好气培养法，可以区分土壤微生物区系在产生N2O方面的差异。     

砖红壤区橡胶林地土壤硝化作用研究初报

以尿素为氮源,采用土壤好气培养试验,研究了砖红壤区橡胶林短期内不同培肥方式下土壤硝化作用特征。结果表明,尿素加入胶园土壤后即迅速水解,加入橡胶树行间未经培肥区土壤(a)中4天水解99.0%,生成的铵态氮14天后开始较强的硝化作用,最大硝化率为46.2%,培养63天后NH4+-N含量仍保持在63.2 mg kg-1的较高水平;而尿素加入经有机无机肥培肥土壤(c)中1天水解99.8%,加入单用化肥培肥的土壤(b)中4天水解98.6%以上,水解生成的铵态氮培养至第4天即开始较强的硝化作用,14天基本硝化完全,最大硝化率都在99%以上,使得培肥区土壤中的无机氮主要以硝态氮形式存在。     

长期不同化肥氮用量对设施菜地土壤氮素矿化和硝化作用的影响

为揭示长期施用不同化肥氮对设施菜地土壤供氮能力的影响，选取连续种植15年不同化肥氮用量下的设施菜地土壤，采用好气密闭培养法研究长期不同化肥氮用量对设施菜地土壤氮素矿化和硝化作用的影响。供试土壤为5个氮施用水平，分别为：不施化肥氮（CK），常规化肥氮（100% N），常规化肥氮上减氮20%（80% N）、40%（60% N）、60%（40% N）。结果表明：与初始矿质氮量相比，培养结束后CK、40% N、60% N、80% N和100% N处理土壤矿质氮变化量分别为38.9、44.7、20.6、-32.7、-87.6 mg/kg；CK、40% N和60% N处理土壤矿质氮变化量分别占各自土壤全氮量的2.7%、2.5%和1.0%，80% N和100% N处理土壤矿质氮量与初始矿质氮量相比下降1.3%和3.1%；CK、40%、60% N、80% N和100% N处理土壤硝化速率分别为19.3、11.2、4.9、5.2、1.2 mg/（kg·d）。长期高量化肥氮（80% N和100% N）投入下，设施菜地土壤氮素矿化和硝化速率显著降低，土壤供氮能力下降，土壤pH降低可能是导致土壤矿化和硝化作用受到抑制的原因之一。鉴于此，设施蔬菜种植体系在现有施氮水平上应减少化肥氮投入，科学优化施肥，维持土壤的供氮能力，确保设施土壤的可持续利用。     

亚热带稻田土壤反硝化动力学参数估算

反硝化作用是土壤氮素损失的重要途径,对反硝化潜势的准确估算是农业精准施肥的必然要求。以亚热带典型红壤稻田土作为研究对象,足量添加外源氮进行室内淹水厌氧培养获取反硝化作用动态,并分别用米氏方程和一级动力学方程对其拟合,最后利用土壤基本理化性质对反硝化动力学参数进行估算。结果表明:米氏方程更适合反硝化动力学拟合,最佳的米氏常数(Km)为35mg/kg;米氏最大速率常数(vmax)与一级动力学速率常数(K)具有显著的相关性(r=0.96, P0.05)。土壤总氮,砂粒和粉粒以及土壤容重对vmax影响最大。利用总氮和粉粒含量作为输入参数估算了vmax,准确度达66%。所构建的参数方程既充分挖掘了土壤基础数据潜能,又能快速地获取土壤反硝化动力学曲线,省时省力。     

Role of nitrite and nitric oxide in the processes of nitrification and denitrification in soil: Results from N tracer experiments

Recent research has proven soil nitrite to be a key element in understanding N-gas production (NO, N₂O, N₂) in soils. NO is widely accepted to be an obligatory intermediate of N₂O formation in the denitrification pathway. However, studies with native soils could not confirm NO as a N₂O precursor, and field experiments mainly revealed ammonium nitrification as the source of NO. The hypothesis was constructed, that the limited diffusion of NO in soil is the reason for this contradiction. To test this diffusion limitation hypothesis and to verify nitrite and NO as free intermediates in native soils we conducted through-flow (He/O₂ atmosphere) ¹⁵N tracer experiments using black earth soil in an experimental set up free of diffusion limitation. All of the three relevant inorganic N soil pools (ammonium, nitrite, nitrate) were ¹⁵N labelled in separate incubation experiments lasting 81 h based on the kinetic isotope method. During the experiments the partial pressure of O₂ was decreased in four steps from 20% to about 0%. The net NO emission increased up to 3.7 μg N kg⁻¹ h⁻¹ with decreasing O₂ partial pressure. Due to the special experimental set up with little to no obstructions of gas diffusion, only very low N₂O emission could be observed. As expected the content of the substrates ammonium, nitrate and nitrite remained almost constant over the incubation time. The ¹⁵N abundance of nitrite revealed high turnover rates. The contribution of nitrification of ammonium to the total nitrite production was approx. 88% under strong aerobic soil conditions but quickly decreased to zero with declining O₂ partial pressure. It is remarkable that already under the high partial pressure of 20% O₂ 12 % of nitrite is generated by nitrate denitrification, and under strict anaerobic conditions it increases to 100%. Nitrite is present in two separate endogenous pools at least, each one fed by the nitrification of ammonium or the denitrification of nitrate. The experiments clearly revealed that nitrite is almost 100% the direct precursor of NO formation under anaerobic as well as aerobic conditions. Emitted N₂O only originated to about 100% from NO under strict anaerobic conditions (0-0.2% O₂), providing evidence that NO is a free intermediate of N₂O formation by denitrification. To the best of our knowledge this is the first time that NO has been detected in a native soil as a free intermediate product of N₂O formation at denitrification. These results clearly verify the “diffusion limitation” hypothesis.     

粪产碱菌(Alcaligenes faecalis)的反硝化及固氮作用

粪产碱菌生长在NH_4~+和NO_3~-两种氮源的介质中时,优先利用NH_4~+,在好气条件下,NH_4~+的存在抑制了粪产碱菌对NO_3~-的同化作用。在厌氧条件下,粪产碱菌能以乳酸为碳源,NH_4~+为唯一氮源进行反硝化作用,NO_3~-作为最终电子受体,接受无氧呼吸链传递的末端电子,经NO_2~-等氮氧化物最终还原为N_2。在好气和厌气条件下,低浓度的NO_2~-对粪产碱菌生长有一定抑制作用,但NH_4~-的存在并不抑制细菌对NO_2~-的利用。粪产碱菌在厌氧条件下还具有需硝酸盐的固氮酶活性。当氧存在或以NO_2~-代替NO_3~-时,固氮活性均受抑制,硝酸盐或亚硝酸盐浓度愈高,抑制愈强。反硝化作用产生的N_2能为微好氧条件下生长的粪产碱菌所重新固定。     

不同氮素添加对不同土地利用方式黑土氮素转化特征的影响

以吉林省典型黑土区的玉米、果树、森林、水稻和菜地土壤为研究对象,采用室内培养法研究氮素在不同土地利用方式黑土中的形态转化特征。结果表明:施加氮肥使不同土地利用方式黑土的铵态氮和硝态氮含量均有不同程度的提高,其中铵态氮含量差异不显著,硝态氮含量差异显著。对于施加尿素的处理而言,S2(129.82 mg/kg)和C2(138.01 mg/kg)硝态氮含量显著高于G2(111.89 mg/kg)和D2(105.35 mg/kg),且Y2(126.92 mg/kg)显著高于D2。对于施加磷酸二铵的处理而言,各土壤硝态氮含量由大到小的顺序为C3(160.23 mg/kg)>Y3(150.00 mg/kg)>S3(140.12 mg/kg)>G3(133.45 mg/kg)>D3(126.70 mg/kg),且C3和Y3显著高于G3和D3。土壤净矿化速率和净硝化速率分别与土壤C/N,土壤微生物量碳、土壤微生物量氮呈显著负相关。整个培养期间,Y、G、C和D土壤平均NMR由大到小的顺序均为处理2>处理3>CK处理,S土壤平均NMR由大到小的顺序为处理3>处理2>CK处理。Y、G和D土壤平均NR由大到小的顺序均为处理2>处理3>CK处理,S和C土壤平均NR由大到小的顺序为处理3>处理2>CK处理。土壤理化性质对黑土氮素转化特征有重要影响。     

Relationships between the denitrification capacities of soils and total,water-soluble and readily decomposable soil organic matter

The relationships between the denitrification capacities of 17 surface soils and the amounts of total organic carbon, mineralizable carbon, and water-soluble organic carbon in these soils were investigated. The soils used differed markedly in pH, texture, and organic-matter content. Denitrification capacity was assessed by determining the N evolved as N₂ and N₂O on anaerobic incubation of nitrate-treated soil at 20°C for 7 days, and mineralizable carbon was assessed by determining the C evolved as CO₂ on aerobic incubation of soil at 20°C for 7 days. The denitrification capacities of the soils studied were significantly correlated (r = 0·7771) with total organic carbon and very highly correlated (r = 0·9971) with water-soluble organic carbon or mineralizable carbon. The amount of nitrate N lost on anaerobic incubation of nitrate-treated soils for 7 days was very closely related (r = 0·99971) to the amount of N evolved as N₂ and N₂O.The work reported indicates that denitrification in soils under anaerobic conditions is controlled largely by the supply of readily decomposable organic matter and that analysis of soils for mineralizable carbon or water-soluble organic carbon provides a good index of their capacity for denitrification of nitrate.     

Effect of cellulose and straw incorporation in soil on total denitrification and nitrogen immobilization at initially aerobic and permanent anaerobic conditions

Summary Laboratory experiments were used to examine the influence of cellulose and straw on denitrification and N immobilization in a sandy loam soil. The soil was mixed with 300 g nitrate-N/g and incubated in a special vessel under conditions that changed from aerobic to anaerobic or in the permanent absence of O₂. Gases (O₂, CO₂, N₂, N₂O, NO and CH₄) were analysed by gas chromatography at regular intervals and the soil was examined for nitrate, nitrite, ammonium and cellulose. Compared with controls, the application of straw and cellulose (0.5% and 1.0%, respectively) enhanced nitrate immobilization and decreased denitrification, under both anaerobic and originally aerobic (PO₂ = 20 vol%) conditions. However, a comparison of results from the aerobic and the anaerobic incubations shows that an increase in denitrification and N immobilization was apparent at an original O₂ concentration of 20 vol%. N₂ was the major product of denitrification in all experiments. Free methane was apparent as soon as nitrate was respired. The stimulating effect of O₂ on total denitrification in the presence of relatively high amounts of easily decomposable cellulose is ascribed to a higher turnover and an intensified mineralization rate (CO₂ production), which increased the total demand for electron acceptors.     

Estimation of the total gaseous nitrogen losses from clay soils under laboratory and field conditions

Acetylene blockage was evaluated as a method for measuring losses of N₂O + N₂ from two Denchworth series clay soils. The denitrification potential in anaerobic, dark incubations at 20°C with nitrate (equivalent to 100 kg N ha^?1 0–20 cm depth), maximum water holding capacity, and acetylene (1%), was equivalent to 32 ± 11 and 39 ± 6 kg N ha^?1 per day for the two 0–20 cm soils and was positively correlated with carbon content (r= 0.98). After 4 days N₂O was reduced to N₂ in the presence of C₂H₂. In April 1980 following irrigation (24 mm) and applications of ammonium nitrate (70 kg N ha^?1) and acetylene, the mean nitrous oxide flux from soil under permanent grass was 0.05 ± 0.01 kg N₂O-N ha^?1 per day for 8 days. In June 1980, the losses of nitrogen from cultivated soils under winter wheat after irrigation (36 mm) and acetylene treatment were 0.006 ± 0.002 and 0.04–0.07 ± 0.01 kg N ha^?1 per day respectively before and after fertilizer application (70 kg N ha^?1). The nitrous oxide flux in the presence of acetylene decreased briefly, indicating that nitrification was rate determining in drying soil.     

设施菜田土壤pH和初始C/NO3– 对反硝化产物比的影响

【目的】设施菜田土壤反硝化作用是N₂O排放和氮素损失的重要途径。本研究通过室内厌氧培养试验,在不同pH和初始C/NO₃–条件下,比较设施菜田土壤反硝化氮素气体排放及产物比的变化特征。【方法】以设施菜田土壤为研究对象,通过添加一定量低浓度的酸碱溶液调节土壤pH分别为酸性、中性和碱性条件,调节后的实测pH分别为5.63、6.65和7.83;同时以谷氨酸钠作为有效性碳,除未添加有效性碳作为对照处理 (CK) 外,其他有效性碳与硝酸盐 (C/NO₃–) 的比值分别调节为5∶1、15∶1和30∶1,三种pH条件下均设置 4 个 C/NO₃– 水平,每个水平3次重复。利用自动连续在线培养系统 (Robot系统),在厌氧条件下监测不同处理土壤产生的 N₂O、NO、N₂和CO₂浓度的动态变化,通过计算N₂O/(N₂O + NO + N₂)指数估算反硝化过程N₂O的产物比。【结果】增加土壤的pH能显著减少设施菜田土壤N₂O和NO的产生量,酸性 (pH 5.63) 土壤的N₂O、NO产生量峰值在不同初始C/NO₃– 比下均显著高于中性 (pH 6.65) 和碱性 (pH 7.83) 土壤 (P < 0.05)。中性和碱性土壤在高C/NO₃– 下有利于减少反硝化过程N₂O的产生,而酸性土壤条件下差异并不显著。中性土壤条件下增加有机碳含量会降低NO产生量,而在酸性和碱性土壤上有机碳的添加对NO产生量没有显著影响。土壤pH和初始C/NO₃– 比对土壤N₂O的产生有极显著的交互效应 (P < 0.001)。酸性和中性土壤上添加有机碳能够显著增加土壤N₂的产生速率 (P < 0.05),且与对照相比,不同pH的土壤添加有机碳后均显著促进反硝化过程中N₂O向N₂的转化。在不同初始C/NO₃– 下碱性土壤的CO₂产生量显著高于酸性和中性土壤,同时与对照相比,添加有机碳显著增加了土壤的CO₂产生量 (P < 0.05)。酸性土壤的N₂O产物比在不同初始C/NO₃– 下均极显著高于碱性土壤 (P < 0.01),且不同初始C/NO₃– 下的土壤N₂O产物比随pH的增加显著下降,二者呈极显著线性负相关关系 (P < 0.01)。【结论】土壤pH降低是设施菜田土壤N₂O和NO排放量较高的重要原因。而且,增加初始土壤有效碳含量促进了土壤的反硝化损失,并在中性和碱性土壤中N₂O的产生量减少。土壤pH升高和初始C/NO₃– 增加均降低了产物比,但增加了土壤反硝化作用速率。在利用N₂O排放通量和产物比估算土壤反硝化氮素损失时,土壤pH和有效碳含量是必须考虑的两个重要因素。     

镉污染下不同类型水稻土氮素供应特征及其影响因素

污染条件下的土壤氮素供应影响了作物生产和植物生态修复。采用温室盆栽试验,研究了两种剂量镉污染下我国21种水稻土无机氮的供应特征和影响因素。结果表明：淹水10天后,不同水稻土土壤溶液无机态氮含量变幅为1.42 ~ 70.40 mg/L （(平均值为16.76 mg/L）),其中NH4+-N和NO3--N分别占62.5% 和33.7%;与施肥对照相比,镉污染降低了大多数水稻土土壤溶液无机态氮的含量,平均降幅为58.4%,主要是由土壤溶液NH4+-N含量下降所致;土壤溶液NO3--N含量受镉污染的影响程度则因土壤类型而异。基于典范对应分析的偏因子分析（(VPA）)表明镉污染对水稻土土壤溶液无机氮含量的影响最大,其次是土壤类型,施肥影响最小,三类因子单独作用的影响比例分别为40.38%、6.51% 和0.05%。镉污染下,pH、CEC和土壤质地显著影响水稻土无机氮供应,其中土壤pH是镉污染条件下影响NH4+-N含量变化的首要因子。     

不同氮形态对镉胁迫下小白菜生长及镉含量的影响

【目的】研究施用速效氮肥（全铵、全硝、硝铵复合和尿素）对镉（Cd）污染土壤小白菜生长和Cd含量的影响,为合理选择氮肥,缓解Cd对植物生长的胁迫并减少Cd在作物体内的积累提供依据。【方法】以小白菜为试材,采用菜园土进行了盆栽试验。以CdCl2溶液模拟土壤Cd胁迫,设土壤Cd含量0、1、3和5 mg/kg 4个水平,每个胁迫水平分别供应小白菜铵态氮、硝态氮、硝铵（1:1）和尿素4种氮形态,总氮添加量均为N 400 mg/kg土。收获后分析各处理间小白菜的生长、光合、氧化胁迫及Cd含量的差异。【结果】 1）与无Cd对照相比,Cd 1 mg/kg处理水平下,全铵、全硝、硝铵和尿素处理的小白菜可食部分鲜重分别下降了31%、16%、21%和26%;Cd 3 mg/kg处理水平下分别下降了58%、28%、35%和39%;Cd 5 mg/kg处理水平下分别下降了83%、38%、52%和69%。全硝和硝铵处理间小白菜Cd耐受系数（TICd）差异不显著,但均高于全铵和尿素处理。2）与无Cd对照相比,Cd 1 mg/kg处理下,全铵、全硝、硝铵和尿素处理小白菜叶片的光合速率分别下降了14%、10%、12%和13%;Cd 3 mg/kg处理分别下降了33%、22%、25%和40%;Cd 5 mg/kg处理分别下降了53%、42%、41%和56%。与无Cd对照相比,1 mg/kg Cd浓度时全铵、全硝、硝铵和尿素处理小白菜叶片的丙二醛含量分别增加了11%、4%、9%和11%;超氧自由基产生速率分别增加了5%、1%、2%和4%,综合比较,以全硝处理下小白菜受Cd的光合抑制及氧化胁迫相对最小。3）3个Cd处理水平,均以施用全铵和尿素处理的小白菜体内Cd含量最高,硝铵处理次之,全硝处理最低。【结论】在供试菜园土上,小白菜施用铵态氮和尿素易引起Cd在小白菜体内的积累。施用硝态氮可缓解Cd诱导的光合抑制和氧化胁迫,减轻Cd对小白菜的生长胁迫,降低作物体内Cd的含量。     

Influence of nitrogen concentration and form in the nutrient solution N20 and N2 emissions from a soilless culture system

The influence of nitrogen concentration and form in the nutrient solution on the N₂O and N₂ emissions from a closed rockwool system with cucumber crops was investigated. At optimum, nitrate-accented nitrogen supply of plants (120 mg N l^?1) on average 0.59 kg N per hectare greenhouse area and day was released. Comparable emission rates occurred with moderate sub- and supraoptimum nitrogen fertilization. Thus, in this range the N supply was non-limiting for the gaseous nitrogen losses. Only in the case of severe suboptimum N supply (40 mg N l^?1) the N₂O N₂ emissions were clearly lower, probably as a result of diminished plant growth and therefore reduced root respiration and exudation of organic carbon sources for microorganisms. The proportion of nitrous oxide in the gaseous nitrogen losses increased on average from 5 to 13% with increasing N supply, possibly because of an impaired N₂O reduction in denitrification due to high nitrate concentrations. Short-term shifting with optimum nitrogen supply from nitrate- accented composition to pure nitrate did not affect the gaseous nitrogen emissions, whereas an exclusive ammonium supply resulted in a considerable decrease. The results indicated that the N₂O emission and the total nitrogen losses from the soilless culture system were predominantly caused by denitrification.