Seasonal and annual variation in nitrogen mineralization and nitrification along an elevational gradient in New Mexico

Patterns and amounts of nitrogen loss from disturbed ecosystems vary widely. The mineralization of organic nitrogen to ammonium and then nitrification to nitrate are important processes regulating nitrogen cycling rates and nitrogen losses. Nitrification is a significant process because of the production of the nitrate anion which is easily leached or denitrified. Most studies of these processes do not evaluate their seasonal and yearly variations. This study demonstrates that marked seasonal and yearly variations can occur in these processes in different ecosystems and suggests that nitrogen loss or other system properties correlated with one arbitrarily selected collection can be misleading. Spruce-fir and ponderosa pine ecosystems demonstrated little actual orpotential nitrification. Aspen and mixed conifer ecosystems demonstrated distinct seasonal patterns with increased rates of mineralization and nitrification during spring and summer months and a precipitous decline in both rates coincident with autumn foliage litterfall.The relative availability of soil nitrogen along with the amount of nitrogen circulating annually in litterfall prior to disturbance are useful predictors of the potential for nitrate production and loss following disturbance. However, other controls, including regulation by organic compounds, appear important in determining seasonal and annual variation in actual nitrification rates.     

四种温带森林土壤氮矿化与硝化时空格局

利用PVC管原位培养连续取样法测定了东北地区4种具有代表性的森林生态系统(硬阔叶林、蒙古栎林、红松林、落叶松林)土壤氮素矿化、硝化的时间动态及氮矿化的空间分布格局.结果表明:4种森林土壤氮素矿化存在明显的时空变异.蒙古栎和红松林土壤在6月份表现出强烈的氮矿化和硝化作用,而硬阔叶林及落叶松林7月份氮素矿化强烈.4种森林生态系统上层土壤的氮净矿(硝)化率显著高于下层土壤.4种林型土壤的硝化过程在氮矿化过程中占有重要地位,其NO-3-N在无机氮中的比例分别为:79.9%～91.1%(硬阔叶林)、50.7%～80.5%(蒙古栎林)、54.1%～92.0%(红松林)、63.7%～86.5%(落叶松林).生态系统构成决定了土壤氮素的矿化能力.阔叶林和针阔混交林生态系统矿化率大于纯针叶林生态系统.硬阔叶林、红松林、蒙古栎林、落叶松林的平均净矿化率分别为:(0.58±0.01) mg · kg-1 · d-1、(0.47±0.19) mg · kg-1 · d-1、(0.39±0.11) mg · kg-1 · d-1和(0.23±0.06) mg · kg-1 · d-1.4种林型氮素矿化作用与地下5 cm温度呈正相关,并受土壤表层 (0～10 cm)水分显著影响.土壤微生物量氮与土壤氮矿化呈显著正相关.     

三江平原典型小叶章湿地土壤氮素净矿化与硝化作用

2004年6月—2005年7月,利用PVC顶盖原位培育法研究了三江平原典型草甸小叶章湿地和沼泽化草甸小叶章湿地土壤(0~15cm)无机氮库、净矿化/硝化速率动态、影响因素及年净矿化/硝化量.结果表明:两种湿地土壤的无机氮均呈明显的动态变化特征,其NH4 -N、NO3-N含量均表现为典型草甸小叶章湿地>沼泽化草甸小叶章湿地.两种湿地土壤的净矿化/硝化速率均呈明显的波动变化,生物固持作用、反硝化作用以及雨季较多降水是导致净矿化/硝化速率出现负值的主要原因.温度、降水、土壤有机质含量、C/N和pH是引起二者土壤无机氮库、净矿化/硝化速率存在明显差异的重要原因.典型草甸小叶章湿地的年净矿化量(19.41kg·hm-2)、年净硝化量(4.27kg·hm-2)以及净硝化量占净矿化量的百分比(22.00%)明显高于沼泽化草甸小叶章湿地(5.51kg·hm-2、0.28kg·hm-2和5.08%),说明前者的氮有效性以及维持可利用氮的能力明显高于后者.     

模拟干旱和磷添加对热带低地雨林氮矿化过程的影响

土壤氮矿化作为氮转化的主要过程决定土壤供氮能力。热带森林生态系统往往受磷限制, 氮矿化过程对干旱的响应是否受磷限制的调控值得探讨。该研究以海南三亚甘什岭自然保护区热带低地雨林为研究对象, 利用2019年建立的林内穿透雨减少(50%)及磷添加双因素交互实验平台, 通过野外树脂芯原位培养法研究模拟干旱及磷添加对土壤无机氮(包括铵态氮和硝态氮)含量和氮矿化过程的影响。结果表明: 1)减雨处理显著降低了5和15 cm深度土壤的水分含量, 而对土壤温度没有显著影响。2)减雨处理和减雨与磷添加共同处理无论在旱季还是湿季对0-10 cm土壤无机氮含量均没有产生显著影响, 但磷添加处理在旱季显著降低了土壤硝态氮含量, 表明磷添加处理对氮有效性的影响主要体现在旱季, 而非湿季。3)干旱处理在旱季和湿季均显著降低了土壤净氨化速率和净氮矿化速率, 而磷添加处理和减雨与磷添加共同处理无论在旱季还是湿季对净氨化速率、净硝化速率和净氮矿化速率均没有产生显著影响, 结果表明了干旱能够显著降低土壤净氮矿化速率。4)土壤水分含量与土壤净氨化速率和净氮矿化速率呈显著正相关关系, 同时减雨处理显著影响了土壤净氨化速率与铵态氮含量的关系, 并且在铵态氮含量相等的情况, 随着干旱的影响净氨化速率下降得更快。这表明土壤水分含量变化是影响该研究样地土壤氮矿化的主要因素。上述研究结果说明, 降水变化对热带低地雨林中土壤氮矿化有重要影响, 短期磷添加没有显著影响, 减雨与磷添加对土壤氮矿化过程并没有交互效应。     

蚂蚁筑巢对西双版纳热带森林土壤有机氮矿化的影响

蚂蚁作为生态系统工程师能够调节土壤微生物及理化环境,进而对热带森林土壤有机氮矿化速率及其时间动态产生显著影响。以西双版纳白背桐热带森林群落为研究对象,采用室内需氧培养法测定土壤有机氮矿化速率,比较蚁巢和非蚁巢土壤有机氮矿化速率的时间动态,揭示蚂蚁筑巢活动引起土壤无机氮库、微生物生物量碳及化学性质改变对有机氮矿化速率时间动态的影响。结果表明：（1）蚂蚁筑巢显著影响土壤有机氮矿化速率（P<0.01）,相较于非蚁巢,蚁巢土壤有机氮矿化速率提高了261%;（2）土壤有机氮矿化速率随月份推移呈明显的单峰型变化趋势,即6月最大（蚁巢1.22 mg kg^-1 d^-1、非蚁巢0.41 mg kg^-1 d^-1）,12月最小（蚁巢0.82 mg kg^-1 d^-1、非蚁巢0.18 mg kg^-1 d^-1）;（3）两因素方差分析表明,不同月份及不同处理对土壤有机氮矿化速率、NH₄-N及NO₃-N产生显著影响（P<0.05）,但对NO₃-N的交互作用不显著;（4）蚂蚁筑巢显著提高了无机氮库（NH₄-N与NO₃-N）、微生物生物量碳、有机质、水解氮、全氮及易氧化有机碳等土壤养分含量,而降低了土壤pH值;（5）回归分析表明,铵态氮和硝态氮对土壤有机氮矿化速率产生显著影响,分别解释87.89%、61.84%的有机氮矿化速率变化;（6）主成份分析表明NH₄-N、微生物生物量碳及有机质是影响有机氮矿化速率时间动态的主要因素,而全氮、NO₃-N、易氧化有机碳、水解氮及pH对土壤有机氮矿化速率的影响次之,且pH与土壤有机氮矿化速率呈显著负相关。总之,蚂蚁筑巢活动主要通过影响土壤NH₄-N、微生物生物量碳及有机质的状况,进而调控西双版纳热带森林土壤有机氮矿化速率的时间动态。研究结果将有助于进一步提高对土壤氮矿化生物调控机制的认识。     

Soil N mineralization and nitrification in relation to nitrogen solution chemistry in a small forested watershed

Spatial variations in soil processes regulating mineral N losses to streams were studied in a small watershed near Toronto, Ontario. Annual net N mineralization in the 0–8 cm soil was measured in adjacent upland and riparian forest stands using in situ soil incubations from April 1985 to 1987. Mean annual rates of soil N mineralization and nitrification were higher in a maple soil (93.8 and 87.0 kg.ha^–1) than in a pine soil (23.3 and 8.2 kg.ha^–1 ). Very low mean rates of mineralization (3.3 kg.ha^–1) and nitrification (3.4 kg.ha^–1) were found in a riparian hemlock stand. Average NO₃-N concentrations in soil solutions were 0.3–1.0 mg.L^–1 in the maple stand and >0.06mg.L^–1 in the pine stand. Concentrations of NO₃–N in shallow ground water and stream water were 3–4× greater in a maple subwatershed than in a pine subwatershed. Rapid N uptake by vegetation was an important mechanism reducing solution losses of NO₃–N in the maple stand. Low rates of nitrification were mainly responsible for negligible NO₃–N solution losses in the pine stand.     

Comparison of soil nitrogen mineralization and nitrification in a mixed grassland and forested ecosystem in central Taiwan

We used the buried bag incubation method to study temporal patterns of net N mineralization and net nitrification in soils at Ta-Ta-Chia forest in central Taiwan. The site included a grassland zone, (dominant vegetation consists of Yushania niitakayamensis and Miscanthus transmorrisonensis Hayata) and a forest zone (Tsuga chinensis var. formosana and Yushania niitakamensis). In the grassland, soil concentration NH₄ ⁺ in the organic horizon (0.1–0.2 m) ranged from 1.0 to 12.4 mg N kg^–1 soil and that of NO₃ ^– varied from 0.2 to 2.1 mg N kg^–1 soil. In the forest zone, NH₄ ⁺ concentration was between 2.8 and 25.0 mg N kg^–1 soil and NO₃ ^–varied from 0.2 to 1.3 mg N kg^–1 soil. There were lower soil NH₄ ⁺ concentrations during the summer than other seasons. Net N mineralization was higher during the summer while net nitrification rates did not show a distinct seasonal pattern. In the grassland, net N mineralization and net nitrification rates were between –0.1 and 0.24 and from –0.04 to 0.04 mg N kg^–1 soil day^–1, respectively. In the forest zone, net N mineralization rates were between –0.03 and 0.45 mg N kg^–1 soil day^–1 and net nitrification rates were between –0.01 and 0.03 mg N kg^–1 soil day^–1. These differences likely result from differing vegetation communities (C₃ versus C₄ plant type) and soil characteristics.     

华北盐渍化草地土壤净氮矿化速率对不同水平氮添加的响应

对于养分贫瘠的盐渍化草地生态系统, 大气氮沉降如何影响土壤氮循环过程是一个目前尚未解决的问题。该研究在位于华北地区山西省右玉县境内的盐渍化草地建立了一个模拟氮沉降的试验平台, 设置8个氮添加水平, 分别为0、1、2、4、8、16、24、32 g·m^-2·a^-1 (N0、N1、N2、N4、N8、N16、N24、N32), 生长季5-9月, 每月月初以喷施的方式等量添加NH₄NO₃。从2017年5月到2019年10月, 运用顶盖PVC管法每月一次进行净氮矿化速率的测定同时计算了净氮矿化速率对不同水平氮添加的敏感性。主要结果表明: (1)高水平氮添加(N16、N24、N32)显著增加土壤无机氮库; (2)该盐渍化草地土壤氮矿化以硝化作用为主, 经过3年氮添加以后, 高氮添加(N24、N32)显著促进了土壤净硝化速率, 并且不同氮添加水平在不同的月份和年份中表现出差异性响应; (3)不同氮添加水平对土壤净氮矿化敏感性的影响在不同降水年份差异显著, 短期低水平氮添加提高了土壤净氮矿化的敏感性, 而高水平氮添加降低土壤净氮矿化敏感性; (4)盐渍化草地土壤净氮矿化速率与土壤温度和水分呈正相关关系, 与土壤pH呈负相关关系。因此, 在当前氮沉降增加的背景下, 北方盐渍化草地土壤氮矿化速率对低氮添加的敏感性较高, 结合氮沉降的特点, 未来模型预测应该同时考虑氮沉降对盐渍化草地的可能影响。     

Seasonal flooding,nitrogen mineralization and nitrogen utilization in a prairie marsh

Flooding can be an important control of nitrogen (N) biogeochemistry in wetland ecosystems. In North American prairie marshes, spring flooding is a dominant feature of the physical environment that increases emergent plant production and could influence N cycling. I investigated how spring flooding affects N availability and plant N utilization in whitetop (Scolochloa festucacea) marshes in Manitoba, Canada by comparing experimentally spring-flooded marsh inside an impoundment with adjacent nonflooded marsh. The spring-flooded marsh had net N mineralization rates up to 4 times greater than nonflooded marsh. Total growing season net N mineralization was 124 kg N ha^–1 in the spring-flooded marsh compared with 62 kg N ha^–1 in the nonflooded marsh. Summer water level drawdown in the spring-flooded marsh decreased net N mineralization rates. Net nitrification rates increased in the nonflooded marsh following a lowering of the water table during mid summer. Growing season net nitrification was 33 kg N ha^–1 in the nonflooded marsh but < 1 kg N ha^–1 in the spring-flooded marsh. Added NO₃ ^–1 induced nitrate reductase (NRA) activity in whitetop grown in pot culture. Field-collected plants showed higher NRA in the nonflooded marsh. Nitrate comprised 40% of total plant N uptake in the nonflooded marsh but <1% of total N uptake in the spring-flooded marsh. Higher plant N demand caused by higher whitetop production in the spring-flooded marsh approximately balanced greater net N mineralization. A close association between the presence of spring flooding and net N mineralization and net nitrification rates indicated that modifications to prairie marshes that change the pattern of spring inundation will lead to rapid and significant changes in marsh N cycling patterns.     

火烧对草地土壤氮总矿化、硝化及无机氮消耗速率的影响

采用同位素^15N库稀释技术结合扰动较小的管型取样法,测定了羊草草地火烧区与未烧区不同季节土壤氮的总矿化速率、总硝化速率、无机氮消耗速率．结果表明,火烧地的氮总矿化与硝化速率在牧草返青后的4、5月份均高于未烧地,7月份差异不显著,到生长季末的9月份又低于未烧地;火烧地NH^4-N的消耗速率7月份以前均高于未烧地,9月份低于未烧地,N03^--N的消耗4、5份火烧地要高于未烧地,7、9月份又低于未烧地;火烧地土壤NH4^ -N含量在4、5和7月份均高于未烧地,9月份基本没有差别,而N03^--N在4、5月份无大差别,7、9月份高于未烧地．     

Net nitrogen mineralization,nitrification and CO2 production in alternating moisture conditions in an unfertilized low-humus sandy soil from the Sahel

In this study the rates of net mineralization, net immobilization and net nitrification have been quantified under laboratory conditions in a sandy low-humus soil from a semi-arid region, in absence of plant growth. Incubation experiments were carried out under constant humidity and under alternating wet and dry conditions to simulate field conditions during the rainy season. The ammonium and nitrate content of the incubates were determined and their CO₂ production measured.The rate of net mineralization at field capacity was 0.6 kg N ha^–1d^–1 during the first 40 days and decreased to 0.06 kg N ha^–1d^–1 after 400 days. This rate was twice as high on wet days under alternating wet and dry conditions. The rate of net nitrification during alternating wet and dry conditions was also higher (1.9 kg N ha^–1d^–1) than at constant field capacity (1.3 kg N ha^–1d^–1) until the ammonium was almost completely depleted. These rates of net mineralization and net nitrification are in agreement with field observations.Net immobilization did not occur in the experiments, unless glucose was added to the soil.The data on CO₂ production and net mineralization showed that the C/N ratio of the degraded material was around 9 or below. It is much lower than the ratio of total carbon over total nitrogen in the soil. This indicates that microorganisms and compounds high in nitrogen were mineralized. Certainly after about 30 days the only growth taking place is based on turnover of material of the microbial biomass itself.A decrease in the amount of inorganic nitrogen was observed upon drying of the soil, while it returned to the original content after rewetting. It is postulated that this might be due to temporary uptake of nitrogen in an inorganic form in microorganisms as part of their osmoregulation.     

湖南省4种森林群落土壤氮的矿化作用

2007年7月,用树脂芯原位测定土壤无机氮含量的方法,对湖南杉木、马尾松、樟树和枫香4种森林群落的土壤氮矿化进行了研究.研究结果表明,经过28d培养,4种森林群落土壤中NH+4-N含量分别下降了31.4%～50.5%,NO-3-N含量增加了8.2～17.3倍,氮矿化主要表现为硝化作用;氮矿化速率由大到小依次为樟树(0.05mg·kg-1·d-1)>马尾松(0.04 mg·kg-1·d-1)>枫香(-0.12 mg·kg-1·d-1)>杉木(-0.15 mg·kg-1·d-1).在4个森林群落的土壤中,NH+4-N是无机氮的主要存在形式,表现为在杉木群落中占78.42%、在马尾松中占79.17%、在樟树中占71.14%和枫香中占79.22%,而且NH+4-N的变化可以解释氮矿化量变化的96.1%～98.8%.土壤氮矿化速率与0～15 cm土壤的C/N、pH值呈显著性正相关,但与凋落物量和0～30 cm 土壤中细根生物量相关性不显著.     

硝化抑制剂DCD、 DMPP对褐土氮总矿化速率和硝化速率的影响

采用15N库稀释-原位培养法研究了硝化抑制剂DCD、DMPP对华北盐碱性褐土氮总矿化速率和硝化速率的影响.试验在山西省运城市种植玉米的盐碱性土壤上进行,设单施尿素、尿素+DCD、尿素+DMPP 3个处理.结果表明:施肥后2周,DCD、DMPP分别使氮总矿化速率和氮总硝化速率减少了25.5％、7.3％和60.3％、59.1％,DCD对氮总矿化速率的影响显著高于DMPP,两者对氮总硝化速率的影响无显著差异;而在施肥后7周,不同硝化抑制剂对氮总硝化速率的影响存在差异.施肥后2周,3个处理的土壤氮总矿化速率和硝化速率分别是施肥前的7.2 ～10.0倍和5.5 ～21.5倍;NH4+和NO3-消耗速率分别是施肥前的9.1 ～12.2倍和5.1 ～8.4倍,这是由氮肥对土壤的激发效应所致.硝化抑制剂使氮肥更多地以NH4+形式保持在土壤中,减少了NO3-的积累.土壤氮总矿化速率和总硝化速率受硝化抑制剂的抑制是N2O减排的主要原因.     

Manure composition affects net transformation of nitrogen from dairy manures

The plant available nitrogen (PAN) content of dairy manure is commonly calculated using concentration and availability coefficients for organic nitrogen (N) and ammonium N (NH₄), but the carbon (C) fraction of the manure also influences the availability of N over time. We evaluated the interactive effect of manure C and N from nine dairy manures during a 176 days aerobic incubation. All of the manures had appreciable NH₄ content, and varied widely in fibrous C. The incubation was conducted using sandy loam (coarse-loamy, mixed, frigid, Typic Haplorthod) and silt loam (fine, illitic, non-acid, frigid, Aeric Epiaquepts) soils at 25°C and 60% water-filled pore space. There were clear differences in nitrate (NO₃) accumulation over time, including manures that resulted in net nitrification and net immobilization. For both soils, the rate of nitrification at 7 and 56 days after application, and the amount of NO₃ accumulated at the end of the incubation (176 days) were strongly correlated (r = –0.88) with C: NH₄ and also to the ratio of neutral detergent fiber (NDF):NH₄ (r = –0.90). The addition of manure C also resulted in significant net immobilization, compared to addition of mineral N fertilizer alone. These studies demonstrate that increased understanding of manure C and N interactions may lead to improved prediction of manure PAN.     

森林土壤氮素转换及其对氮沉降的响应

近几十年人类活动向大气中排放的含氮化合物激增 ,并引起大气氮沉降也成比例增加。目前 ,氮沉降的增加使一些森林生态系统结构和功能发生改变 ,甚至衰退。近 2 0 a欧洲和北美有关氮沉降及其对森林生态系统的影响方面的研究较多 ,而我国少有涉及。森林土壤氮素转换是森林生态系统氮素循环的一个重要的组成部分 ,而矿化、硝化和反硝化作用是其核心过程 ,氮沉降作为驱动因子势必改变森林土壤氮素转换速度、方向和通量。根据国外近 2 0 a有关研究 ,首先介绍了森林土壤氮素转换过程和强度 ,论述森林土壤氮素在生态系统氮素循环中的作用 ,然后在此基础上 ,介绍了氮沉降对森林土壤氮素循环的研究途径 ,探讨了氮沉降对森林土壤氮素矿化、硝化和反硝化作用的影响及其机理     

Soil nitrogen mineralization in a coastal fynbos succession

Patterns of net nitrogen mineralization and nitrification in 0–7.5 cm deep mineral soils of different stages (seral ages 1, 6 and 20 years) of a post-fire coastal fynbos succession were assayed using laboratory andin situ incubations. No evidence of increasing allelopathic inhibition of nitrification with successional development was found as NO₃−N was the predominant product at all seral stages and the NO₃−N∶NH₄−N ratio remained constant. Rather the results of field incubations of soils beneathProtea repens stands of different successional ages showed that increased mineralization and nitrification appeared to be associated with increased soil total N content rather than with successional age. Further, the incubation of soilsin situ during the dry summer months showed that NO₃−N production appears to be closely related to temperature and soil moisture content, both of which are variables that vary throughout succession due to the changing structure of the vegetation.     

Geostatistical analysis of soil properties in a secondary tropical dry forest,St. Lucia,West Indies

Spatial variability of soil properties directly influences forest growth. However, spatial variation in soil properties has not been studied within tropical dry forests. As such, it is unclear whether soil properties, like moisture and N availability, display spatial variation at scales similar to that of other ecosystems. To gain insight into this variation, we established a 56 × 56 m sampling grid in tropical dry forest on the Caribbean island of St. Lucia. Samples collected at 4-m intervals were analyzed for forest floor mass, soil texture, pH, organic C, net N mineralization, net nitrification and available P. Geostatistical procedures were used to determine spatial autocorrelation of the aforementioned properties and processes. Semivariogram parameters were used in a block kriging procedure to produce spatial maps of soil properties. At the scale of our study, most soil properties exhibited spatial autocorrelation at distances of 24 m or less. Varying degrees of similarity were found between patterns of forest floor mass, organic C, net N mineralization, net nitrification and available P. No similarity was found between soil texture or pH and other properties. Fine-scale spatial patterns of net N mineralization and net nitrification are likely driven by overstory litter inputs, rather than variation in soil texture and water availability.     

Temperature-dependent nitrogen transformations in acid oak-beech forest litter in the Netherlands

Laboratory incubation experiments have been carried out to quantify net nitrogen mineralization and nitrification in oak-beech litter at temperatures ranging from 0 to 30°C. Net mineralization was linearly proportional to temperature. Nitrification was inhibited at 0,5 and 30°C. As compared with soils under cultivation, there is only restricted knowledge of nitrification kinetics in acid forest litters, especially when temperature is considered. With these litter types, one should be cautious applying high incubation temperatures, which seldomly occur under field conditions.     

长白山两种主要林型下土壤氮矿化速率与温度的关系

在实验室条件下,控制土壤的温度与含水量,测定长白山两种森林类型,阔叶红松林和云冷杉林土壤的氮净矿化速率。将含水量适度和饱和的原样土柱置于5℃、15℃、25℃和35℃恒温箱中培养30d。分析培养前后的NH^ 4-N和NO^-3-N含量,确定土壤有机氮的矿化速率。结果表明,对于不同的土壤和不同的含水量,土壤的净的净矿化速率与温度呈正相关;而净硝化速率在低温段与温度正相关,在高温段则呈负相关,而且整个培养期硝态氮的变化不大。建立两种森林类型土壤氮净矿化速率与温度的一次线性和指数回归方程,发现指数回归效果较好,用回归方程模拟两种森林类型土壤的年矿化量分别为111．8kg/(hm^2.a)和57．4kg/(hm^2.a),与实测值1217．36kg(hm^2.a)和47．41kg/(hm^2.a)很接近。