Variability of CO2 and N2O emissions during freeze‐thaw cycles: results of model experiments on undisturbed forest‐soil cores

The amounts of N₂O released in periods of alternate freezing and thawing depend on site and freezing conditions, and contribute considerably to the annual N₂O emissions. However, quantitative information on the N₂O emission level of forest soils in freeze‐thaw cycles is scarce, especially with regard to the direct and indirect effect of tree species and the duration of freezing. Our objectives were (i) to quantify the CO₂ and N₂O emissions of three soils under beech which differed in their texture, C and N contents, and humus types in freeze‐thaw cycles, and (ii) to study the effects of the tree species (beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.)) for silty soils from two adjacent sites and the duration of freezing (three and eleven days) on the emissions. Soils were adjusted to a matric potential of –0.5 kPa, and emissions were measured in 3‐hr intervals for 33 days. CO₂ emissions of all soils were similar in the two freeze‐thaw cycles, and followed the temperature course. In contrast, the N₂O emissions during thawing differed considerably. Large N₂O emissions were found on the loamy soil under beech (Loam‐beech) with a maximum N₂O emission of 1200 μg N m^–2 h^–1 and a cumulative emission of 0.15 g N m^–2 in the two thawing periods. However, the sandy soil under beech (Sand‐beech) emitted only 1 mg N₂O‐N m^–2 in the two thawing periods probably because of a low water‐filled pore space of 44 %. The N₂O emissions of the silty soil under beech (Silt‐beech) were small (9 mg N m^–2 in the two thawing periods) with a maximum emission of 150 μg N m^–2 h^–1 while insignificant N₂O emissions were found on the silty soil under spruce (0.2 mg N m^–2 in the two thawing periods). The cumulative N₂O emissions of the short freeze‐thaw cycles were 17 % (Sand‐beech) or 22 % (Loam‐beech, Silt‐beech) less than those of the long freeze‐thaw cycles, but the differences between the emissions of the two periods were not significant (P ≤ 0.05). The results of the study show that the amounts of N₂O emitted in freeze‐thaw cycles vary markedly among different forest soils and that the tree species influence the N₂O thawing emissions in forests considerably due to direct and indirect impacts on soil physical and chemical properties, soil structure, and properties of the humus layer.     

草鱼不同混养模式下围隔底泥反硝化、硝化和氨化速率

应用乙炔抑制法测定了草鱼(Ctenopharyngodon idellus)不同混养模式围隔底泥的硝化、反硝化和氨化速率,以探究草鱼不同混养模式对池塘底泥－水界面N元素动态变化的影响,并为草鱼养殖模式的优化提供必要的参考依据.混养组合分别为一元组（草鱼）、二元组（草鱼+鲢、草鱼+凡纳滨对虾）、三元组（草鱼+鲢+凡纳滨对虾,设2种放养比例）.结果显示:1）草鱼不同混养模式中底泥的反硝化速率范围为0～734.15 μmol/(m2·d),硝化速范围为0～1 209.20 mmol/(m2·d),化速率范围为0～41.25 mmol/(m2·d).2)草鱼不同混养模式底泥的反硝化速率较高,与很多河口和湖泊数值接近；在养殖中期,底泥的硝化速率很小甚至检测不到；底泥的氨化速率呈逐月递增趋势,以三元混养组最高.3）混养组中凡纳滨对虾(Litopenaeus vannamei)的放养密度越大,草鱼的放养密度越小,反硝化作用出现得越早,但反硝化速率很难保持开始的水平；反之,反硝化作用出现得较晚,并会随着养殖周期的推移迅速升高；放养种类越单一,底泥的硝化速率越低,且鲢(Hypophthalmichthys molitrix)放养密度越高,硝化速率越高.从养殖模式优化的角度来看,草鱼三元混养组要优于单养和二元混养组,但三元混养组中两种放养密度各有优劣,有待进一步优化以确定最佳放养比例.     

Co-incorporation of biodegradable wastes with crop residues to reduce nitrate pollution of groundwater and decrease waste disposal to landfill

Return of high nitrogen (N) content crop residues to soil, particularly in autumn, can result in environmental pollution resulting from gaseous and leaching losses of N. The EU Landfill Directive will require significant reductions in the amounts of biodegradable materials going to landfill. A field experiment was set up to examine the potential of using biodegradable waste materials to manipulate losses of N from high N crop residues in the soil. Leafy residues of sugar beet were co‐incorporated into soil with materials of varying C:N ratios, including molasses, compactor waste, paper waste, green waste compost and cereal straw. The amendment materials were each incorporated to provide approximately 3.7 t C per hectare. The most effective material for reducing nitrous oxide (N₂O) production and leaching loss of NO₃^? was compactor waste, which is the final product from the recycling of cardboard. Adding molasses increased N₂O and NO₃^? leaching losses. Six months following incorporation of residues, the double rate application of compactor waste decreased soil mineral N by 36 kg N per hectare, and the molasses increased soil mineral N by 47 kg N per hectare. Compactor waste reduced spring barley grain yield by 73% in the first of years following incorporation, with smaller losses at the second harvest. At the first harvest, molasses and paper waste increased yields of spring barley by 20 and 10% compared with sugar beet residues alone, and the enhanced yield persisted to the second harvest. The amounts of soil mineral N in the spring and subsequent yields of a first cereal crop were significantly correlated to the lignin and cellulose contents of the amendment materials. Yield was reduced by 0.3–0.4 t/ha for every 100 mg/g increase in cellulose or lignin content. In a second year, cereal yield was still reduced and related to the cellulose content of the amendment materials but with one quarter of the effect. Additional fertilizer applied to this second crop did not relieve this effect. Although amendment materials were promising as tools to reduce N losses, further work is needed to reduce the negative effects on subsequent crops which was not removed by applying 60 kg/ha of fertilizer N.     

Analysis of Nitrite Accumulation During Denitrification

To realize the purpose of enhanced nitrogen removal (TN<5 mg·L-1) in step feed process treating urban wastewater, by using SBR reactor, the nitrite accumulation, variation of pH and ORP as well as dynamic properties during denitrification with methanol and glucose as the sole carbon sources are investigated in details. The results show that for both carbon sources, serious nitrite accumulations are observed during denitrification under different ratios of nitrogen and carbon (C/N). With identical C/N, when glucose is used as carbon source there is more maximum NO2--N accumulation concentration. However, NO3--N reduction rate is faster than NO2--N reduction rate for both carbon sources. Furthermore, with the increase of C/N, the maximum NO2--N concentration increases and the time in which the NO2--N achieves the highest concentration is accordingly shortened. For glucose, however, under high C/N ratio (C/N=29.3) both the denitrification rate and NO2--N accumulation concentration decrease. Besides, the changes of pH and ORP reflect the variation of NO2--N accumulation concentration well because pH and ORP have the significant relationship with NO2--N concentration. The second inflexion on curves indicates the real end of denitrification process.     

氨氮质量浓度及附着基筛选对硝化细菌氨氮净化影响

将带有试验硝化细菌——食油假单胞菌X14-1-1的等面积陶粒、聚氯乙烯、纤维、火山岩、无纺布和流化床6种材料的附着基分别放入1 L的充气瓶内,在36℃、130 r/m in的摇床上混合培养48 h后,洗脱计数测定菌种附着数量.模拟氨氮去除率试验中氨氮初始质量浓度为0(不加硫酸铵)、10、20、30、40、50、60 m...     

利用膜进样质谱仪测定水稻土几种厌氧氮转化速率

为了在同一体系下区分和测定水稻土反硝化、厌氧氨氧化(Anammox)和硝酸根异化还原成铵(DNRA)过程发生速率和相互关系,并获取近似原位情况下的净脱氮速率,本研究通过将~(15)NH_4~+化学氧化法测定DNRA速率和添加尿素模拟原位土柱测定净脱氮速率与膜进样质谱法(MIMS)进行联用,完善了一套基于膜进样质谱法(MIMS)的稻田硝态氮转化测定方法体系,利用该方法测定了5种典型的水稻土[辽宁营口(YK)、江苏宜兴(YX)、浙江金华(JH)、广西桂林(GL)和四川广安(GA)]的反硝化、Anammox、DNRA和净脱氮4种氮转化速率。结果显示:基于MIMS的方法体系可实现对水稻土中反硝化、Anammox、DNRA和净脱氮速率的测定,5种水稻土反硝化、Anammox、DNRA和净脱氮速率范围分别为(358.63±25.37)～(479.96±22.12)、(-14.81±0.22)～(5.29±1.22)、(25.76±12.71)～(109.87±3.88)g N·hm~(-2)·h~(-1)和(33.33±11.16)～(72.74±14.18)g N·hm~(-2)·h~(-1),相关结果与其他方法研究结果具有可比性。相关性分析显示:水稻土NO_3~-、可溶性有机碳(DOC)和土壤Fe~(2+)含量是反硝化过程的主要限制因素;NO_3~-是Anammox的关键限制因素;而土壤DOC和Fe~(2+)含量是DNRA过程的主要限制因素。基于MIMS的方法体系可以在短时间内(1周)测定水稻土四种厌氧氮转化速率,且所需样品量低、精确度高,在稻田或湿地土壤厌氧氮转化过程研究中有很好的应用前景。     

Characterization of vegetable nitrogen uptake and soil nitrogen transformation in response to continuous molybdenum application

Molybdenum (Mo), a plant micronutrient, is involved in nitrogen (N) cycling of global ecosystem, but little is known about its effect on soil N transformation especially the key processes nitrification and denitrification. A long‐term field experiment was carried out to investigate the effects of continuous sufficient soil available Mo on vegetable N uptake and soil N transformation. The experiment consisted of three treatments: control (CK), Mo deficiency (NPK), and Mo application (NPK+Mo). The results show that (1) after a 7‐year‐experiment, continuous Mo application significantly increased soil available Mo content. (2) Compared to the NPK treatment, NPK+Mo treatment showed an increase of 11, 18, and 8% in the cumulative crop yield, plant N uptake, and N fertilizer use efficiency. (3) With continuous Mo application, the soil , , microbial biomass N, and total N contents were reduced by 14, 29, 40, and 12%, the soil nitrate reductase (NR) and nitrite reductase (NiR) activities were reduced by 14 and 8%, as well as the potential denitrification activity (PDA) and gross nitrification rate (GNR) were decreased by 64 and 80%, respectively. Additionally, continuous Mo application decreased the abundance of ammonia‐oxidizing archaea (AOA) and increased the abundance of narG‐containing denitrifiers (narG) and nirK‐type nitrite reducers (nirK) significantly. The data suggest that a deficiency in soil available Mo may induce the risk of soil N accumulation and environmental N emission in vegetable soil, whereas continuous Mo application could mitigate this risk by increasing crop yield and N uptake and, by decreasing soil N residues, soil nitrification and denitrification.     

复合益生菌发酵液的功能特性及对对虾诱食效果

为探求复合菌发酵液的多种功能,该试验选择具有脱氮、产酶、抑菌等优良性能的酵母菌、乳酸菌及芽孢杆菌各1株,利用已优化的HJ培养基进行共培养,实时监测发酵过程,分时段取样,对复合菌发酵液的脱氮、产酶、抑菌、培藻及诱食等功能进行研究。结果表明,酿酒酵母菌NJ-02、屎肠球菌SC-01及枯草芽孢杆菌M7-1能够在HJ培养基中进行共发酵,连续培养24 h后3株微生物活菌数量分别达到3.88×10~8、2.41×10~(10)、5.38×10~9 CFU/mL。复合菌发酵液的脱氮、培藻性能同复合菌中枯草芽孢杆菌M7-1的活菌数相关较大,发酵至16h其降解亚硝态氮和培藻性能最为理想,亚硝态氮降解率为89%,并使小球藻叶绿素a质量分数提升49.6%。复合菌发酵液具有同枯草芽孢杆菌M7-1相当的产酶(蛋白酶、淀粉酶、纤维素酶)活性及同屎肠球菌SC-01相当的抑菌(副溶血弧菌)活性。复合菌发酵液饲喂对虾,诱食效果明显好于对照组(P0.05),同化学诱食剂二甲基-β-丙酸噻亭(dimethyl-beta-propiothetin hydrochloride, DMPT)差异不显著,其肠道中乳酸菌、酵母菌数目显著高于对照组及化学诱食剂组(P 0.05)。该研究所制备的脱氮、培藻、抑菌及诱食功能复合菌发酵液,为可持续生态水产养殖提供了新的微生物资源和技术方法。     

稻田生态系统氧化亚氮(N_2O)排放微生物调控机制研究进展及展望

氧化亚氮(N_2O)是第三大温室气体,对全球气候变化具有显著影响。稻田是重要的N_2O排放源,追踪稻田N_2O产生及排放关键过程的微生物调控机制,可以为农田土壤氮素循环研究以及稻田N_2O减排提供有价值的信息。微生物调控的硝化作用和反硝化作用是稻田N_2O排放的主要来源。基于此,我们在过去十年的研究中,依托中国科学院桃源农业生态试验站,以水稻田淹水-落干和施肥为关键过程,从水稻根际、土层深度、反应底物浓度等方面探明了土壤硝化反硝化过程和N_2O排放特征及其微生物调控机制;提出了开发稻田土壤微生物资源,提高土壤N_2O消纳能力的可能策略;构建了可以有效降低稻田氮素损失和N_2O排放的基于化肥一次性深施的减氮控磷施肥技术,并在实际农业生产中进行了示范推广。本文对上述研究取得的成果,以及国内外相关研究结果进行了全面综述。结合分子生物技术在土壤科学研究中的应用,今后的研究工作将会从以下几个方面开展:1)解析土壤微生物与土壤生产力和生态环境之间的关系;2)在基因组和转录组水平构建农田土壤碳氮循环功能微生物分析平台;3)解析土壤微生物分布与生态功能之间的关联机制;4)根系—土壤—微生物之间的协同机制以及植物—内生菌—土壤微生物之间相互影响的分子机制;5)加强对实用技术的研发,把基础研究成果转化为生产力,服务农业生产和生态文明建设。     

长江三角洲农田地下水反硝化对硝酸盐的去除作用

长江三角洲(简称"长三角")农田氮素投入量高,但是否像其他高氮投入农田一样在土壤剖面累积了大量硝酸盐尚不清楚。通过连续两年的野外观测结合室内培养实验,发现长三角地区3种不同类型的高氮投入农田1～4 m地下水硝态氮(NO_3~--N)剖面分布特征存在明显差异,水稻田地下水NO_3~--N浓度始终很低(1mg·L~(-1)),不同深度之间无差异。蔬菜地和葡萄园1 m处地下水NO_3~--N年平均浓度分别为5.6和17.5 mg·L~(-1),但是地下水NO_3~--N浓度随着深度增加急剧下降,至4m处,NO_3~--N浓度降至小于1 mg·L~(-1),与水稻田无差异。蔬菜地和葡萄园地下水高浓度NO_3~--N仅出现在施肥期间,非施肥期地下水NO_3~--N浓度较低,这表明长三角农田不存在明显的NO_3~--N累积。原状土柱培养实验结果表明,0～4 m土壤均存在较强的反硝化活性。通过对地下水中反硝化产物N2及N2O的直接定量测定,发现反硝化对地下水NO_3~--N的去除效率随着深度而增加,至4m处,反硝化对地下水NO_3~--N的去除效率分别为86%(水稻田)、93%(蔬菜地)和89%(葡萄园)。这表明反硝化能有效去除地下水NO_3~--N,是长三角地区农田土壤剖面未产生NO_3~--N累积的重要原因。反硝化产生的溶解性气态氮主要通过地下水流入临近水域,对于蔬菜地和葡萄园而言,溶解性气态氮流失量与NO_3~--N淋溶损失量相当,是一个重要的氮素去向,值得关注。