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.     

三种利用类型羊草草地氮总矿化、硝化和无机氮消耗速率的比较研究

采用同位素15N库稀释技术研究了 3种不同利用类型羊草草地土壤氮的总矿化、硝化速率以及无机氮总消耗速率 ,3种类型草地分别为 :保护区 (无人为扰动 )、割草场、过度放牧地。结果表明 :4月份过度放牧场的总矿化速率最高 ,为2 1 .3μg N/ ( g土· d) ,7月份割草场的值最高 ,为 38.5μg N/ ( g土· d) ,9月份保护区最高 ,值为 1 5 .6μg N/ ( g土· d) ,总的来看 ,保护区的总矿化速率高于其它利用类型草地 ,这与土壤有机氮的含量较高有关 ,3种类型草地铵态氮的消耗速率与总矿化速率有类似的趋势。 3种利用类型草地的氮总矿化速率均以 7月份为最高 ,分别为 36 .5、38.5、2 9.8μg N/ ( g土· d)。总硝化速率放牧场最高 ,保护区、割草场、放牧场 7月份的总硝化速率分别为 1 8.6、2 1 .4 5、35 .4 5 μg N/ ( g土·d)。 3种利用类型草地中放牧场的硝态氮含量最高 ,其消耗的速率也高于其它两种利用类型草地     

不同放牧强度对贵州人工草地土壤养分及活性有机碳的影响

研究不同放牧强度下人工草地土壤养分以及有机碳含量的变化,为在西南喀斯特地区建植与检测人工草地提供参考。在贵州省独山县贵州省草业研究所试验示范基地,以2012年10月11日建植的多年生黑麦草:高羊茅:鸭茅:白三叶:紫花苜蓿=3.5:2:2:1:1.5的人工草地0.33 ha,设置禁牧(围栏封育)、中度、重度3个处理,于2015年10月13日开始放牧,61 d后测定不同放牧强度下人工草地土壤营养元素与活性有机碳含量。研究结果表明,放牧显著影响pH值、有机质以及氮、磷、钾等营养元素的含量。土壤有机质含量与pH值在中度放牧的0—10 cm土层中最高,土壤总氮和碱解氮含量随着放牧强度增强而上升,磷元素与钾元素的含量随着放牧强度增强而下降。土壤有机碳、微生物碳及易氧化碳的含量都随着放牧强度增加而降低,并且它们两两显著相关。在贵州喀斯特地区建植人工草地与维护人工草地可适当补充磷肥与钾肥,在草场质量检测中微生物碳和易氧化碳的含量可以作为土壤质量监测的早期指标。     

内蒙古温带草原不同放牧强度和围栏封育对凋落物分解的影响

放牧和围封通过影响植物群落结构和土壤微环境来调控草地生态系统的碳循环。该研究在内蒙古温带草原设置轻度放牧后围封、轻度放牧、重度放牧后围封、重度放牧4种样地,通过测定干旱年(2011年)和湿润年(2012年)地上、地下凋落物产量、质量及其分解速率和土壤养分含量,分析不同放牧强度对凋落物形成和分解的影响,以及围栏封育对生态系统恢复的作用。结果表明:重度放牧地上凋落物产量和分解速率均高于轻度放牧。干旱年轻度放牧样地地下凋落物产量和分解速率高于重度放牧,湿润年相反。短期围封显著提高了凋落物产量,轻度放牧样地围封后地上凋落物分解速率和养分循环加快,而重度放牧样地围封后地上凋落物分解减慢。因此,与重度放牧相比,轻度放牧草地的恢复更适合采用围栏封育措施;而重度放牧草地的恢复可能还需辅以必要的人工措施。降水显著促进地上、地下凋落物形成和分解。地下凋落物的生产和分解受降水年际波动影响较大,重度放牧草地对降水变化的敏感度比轻度放牧草地高。地上凋落物分解速率与凋落物N含量显著正相关,与土壤全N显著负相关,与地上凋落物C:N和木质素:N相关性不大;地下凋落物分解速率与凋落物C、C:N和纤维素含量显著负相关。该研究结果将为不同放牧强度的草地生态系统恢复和碳循环研究提供理论依据。     

放牧对呼伦贝尔草地植物和土壤生态化学计量学特征的影响

放牧通过畜体采食、践踏和排泄物归还影响草地群落组成、植物形态和土壤养分,植物通过改变养分利用策略适应环境变化。通过分析呼伦贝尔草原放牧和围封样地中的群落植物和土壤的碳氮磷养分及化学计量比,探讨放牧对生态系统化学计量学特征和养分循环速率的影响机制。结果如下:(1)群落尺度上,放牧和围封草地植物叶片C、N和P的含量没有显著差异;但是在种群尺度上,放牧草地植物叶片N含量显著高于围封草地;(2)放牧草地土壤全C、全N、有机C、速效P含量,低于围封草地,硝态N含量高于围封草地;土壤全P和铵态N指标没有显著差异;(3)放牧草地植物C∶N比显著低于围封草地,植物残体分解速率较快,提高了生态系统养分循环速率。     

川西亚高山针叶林不同恢复阶段土壤的硝化和反硝化作用

 采用气压过程分离(Barometric process separation, BaPS)技术对川西亚高山针叶林不同恢复 阶段土壤的总硝化和反硝化作用速率进行了测定,结果表明：川西亚高山针叶林不同恢复阶段土壤的总硝化和反硝化速率差异不显著(p<0.05),不同恢复阶段土壤总硝化作用的 Q10值 差异不显著(p<0.05);总硝化作用速率与土壤含水量呈显著正相关(p<0.05),与土 壤pH值、 土壤有机质、全氮及C/N相关不显著;不同恢复阶段土壤反硝化速率均维持在一个较低的水 平,反硝化速率与土壤中的C/N显著正相关(p<0.05),与土壤含水量、pH值、有机质及全氮相关不显著。与反硝化作用相比,硝化作用对亚高山针叶林土壤氮损失的影响可能更大     

放牧对滇西北高原纳帕海沼泽化草甸湿地土壤氮转化的影响

选择位于滇西北高原纳帕海国际重要湿地内的典型沼泽化草甸湿地为研究对象,采用原位土柱室内控制实验法研究了放牧干扰(猪翻拱扰动和牲畜践踏)对沼泽化草甸湿地土壤氮转化的影响。研究结果表明,放牧活动显著提高了沼泽化草甸湿地表层土壤的容重和pH值,降低了土壤含水率、TOC、TN和NH_4~+-N含量,而对NO_3~--N含量影响不显著。放牧干扰下沼泽化草甸湿地土壤的矿化速率和硝化速率均表现为猪翻拱扰动样地(ZG)牲畜践踏样地(JT)对照样地(CK);表现为ZGJTCK。放牧干扰促进了沼泽化草甸湿地土壤的矿化和硝化作用,猪的翻拱活动比牲畜践踏活动对土壤氮矿化和硝化作用的促进作用更显著。放牧干扰下沼泽化草甸湿地土壤的反硝化速率表现为ZGCKJT,猪的翻拱活动促进了土壤N_2O气体的排放,而牲畜践踏活动抑制了土壤N_2O气体的排放。相关性分析表明,受放牧干扰的沼泽化草甸湿地土壤的矿化和硝化速率均与土壤容重、pH呈显著正相关,与土壤含水率、NH_4~+-N、TOC、TN含量呈显著负相关;反硝化速率与TOC含量呈显著负相关。     

晋西北不同年限小叶锦鸡儿灌丛土壤氮矿化和硝化作用

利用PVC管顶盖埋管法研究了晋西北黄土高原区小叶锦鸡儿人工灌丛不同定植年限(5,10,20,30,40a)土壤氮矿化与硝化速率的动态和净矿化与硝化总量。结果表明,⑴小叶锦鸡儿灌丛土壤无机氮主要以NO_-~3-N形式存在,不同生长年限相同月份的土壤硝态氮(NO-3-N)含量分别是铵态氮(NH+4-N)含量的1.5—15.4倍;⑵土壤氮素硝化速率和矿化速率随生长年限延长而加快,30年生时达到高峰,数值达40.2,44.1 mg m~(-2)d~(-1)。从季节性变化看,7—8月份是硝化速率和矿化速率快速增长期,30年生小叶锦鸡儿灌丛土壤硝化速率和矿化速率分别达到86.9,93.1 mg m~(-2)d~(-1),显著高于其它生长年限(P0.05);(3)土壤氮素硝化与矿化总量同样随小叶锦鸡儿生长年限延长而增加,30年生时达到最高,与5年生相比,分别增加了3.7和3.1倍。(4)5—10月份小叶锦鸡儿生长期内,各年限土壤全氮量的2.3%被矿化成无机氮,其中87%最终被转化成NO-3-N形式存在于土体中。     

种植星星草对盐碱草地土壤养分状况的改良作用

对人工种植在碱斑草地上的星星草在不同年份相同生育期的土壤养分状况进行研究,并与天然状况的星星草地在各个生育期的土壤养分相比较,种植星星草后,随着星星草种植年限的增加,0－10cm土壤中;有机质含量和土壤全氮含量呈上升趋势,土壤全磷含量略有增加,土壤全钾含量变化不明显;而土壤全钠含量、全钙含量以及土壤全镁含量都有不同程度的降低。     

土地利用方式和培养温度对土壤氮转化及温室气体排放的影响

在好氧条件下研究土地利用方式(林地、草地)及培养温度(10、15 ℃)对加拿大和中国土壤的硝化作用、氮矿化作用以及N2O和CO2排放的影响.结果表明:草地土壤中的硝化作用和N2O排放量大于林地土壤,中国草地土硝化作用最强.10和15℃下中国草地土硝化速率分别为2.10和2.86 mg N·kg-1·d-1,15 d的N2O累积排放量分别为10.2和15.4μg N2O-N·kg-1.pH是影响土壤硝化作用强度和N2O排放的主要因素,与两者均呈显著正相关.林地土壤的矿化作用和CO2排放量高于草地,中国林地土壤的矿化作用最强,其平均矿化速率在10和15℃时分别为3.08和2.87mgN·kg-1 ·d-1.加拿大林地土壤CO2排放量最高,其15 d的累积排放量在10和15℃时分别为314和370 mg CO2-C·kg-1,土壤有机碳和水溶性有机碳含量分别与有机氮矿化作用和CO2排放量呈显著正相关.温度增加促进草地土壤硝化作用及林地和草地土壤中N2O的排放,也显著促进林地土壤中CO2的排放.     

Net nitrogen mineralization and net nitrification along a tropical forest-to-pasture chronosequence

Soil inorganic nitrogen pools, net mineralization and net nitrification rates were compared during the dry season along a chronosequence of upland (terra firme) forest, 3-, 9- and 20-year-old pastures in the western Brazilian Amazon Basin state of Rondônia to investigate the influence of forest conversion to pasture on soil nitrogen cycles. Surface soil (0 to 10 cm) from forest had larger extractable inorganic nitrogen pools than pasture soils. In the forest, NO ₃ ^– pools equaled or exceeded NH ₄ ⁺ pools, while pasture inorganic N pools consisted almost exclusively of NH ₄ ⁺ . Rates of net N mineralization and net nitrification in seven -day laboratory incubations were higher in the seven - day forest than in the pastures. Net N mineralization rates did not differ significantly among different-aged pastures, but net nitrification rates were significantly lower in the 20-year-old pasture. Higher net N mineralization and net nitrification rates were measured in laboratory and in situ incubations of sieved soil, compared with in situ incubations of intact soil cores. Rates calculated in seven-day incubations were higher than determined by longer incubations. Sieving may increase N mineralization and/or decrease N immobilization compared with intact cores. We concluded that 7-day laboratory incubation of sieved soil was the most useful index for comparing N availability across the chronosequence of forest and pasture sites. High net nitrification rates in forest soils suggest a potential for NO ₃ ^– losses either through leaching or gaseous emissions.     

Net nitrogen mineralization and net nitrification rates in soils following deforestation for pasture across the southwestern Brazilian Amazon Basin landscape

Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO₃ ^?-N and total inorganic N concentrations than pasture soils, but substantial NO₃ ^?-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing.     

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.     

Nitrogen availability in radiata pine plantations on former pasture sites in southern New South Wales

Studies of nitrogen availability were carried out in radiata pine (Pinus radiata D. Don) plantations on former pasture sites in N.S.W. in conjunction with studies of the effects of previous land use on tree form. Sites were selected on previously improved pastures (cleared with introduced legumes) and unimproved pastures (partially cleared without legumes) to form age sequences of stands which had been established for periods of up to fifteen years. Mineral-N pools in soils and forest floor samples were determined monthly for thirteen months and nitrification potentials were determined from periodic laboratory incubations.Nitrate and ammonium pools in 2-, 4-, 6-, 9- and 15-year-old radiata pine stands fluctuated seasonally, peaking in summer and autumn. Maximum total mineral-N concentrations of 20 to 40 g g^–1 soil occurred in the youngest, ex-improved pastures with nitrate-N concentrations of up to 25 g g^–1. In the 15-year-old stands, nitrate-N was only detected during autumn, at less than 5 g g^–1 soil. Net N-mineralization and nitrification potentials were consistently higher in the ex-improved pasture soils compared with the ex-unimproved pastures. N availability decreased with increasing stand age in the ex-improved pasture soils, but the pattern was less clear for the unimproved pasture sites. Suppression of clover by pines and the accumulation of nitrogen in the standing biomass are thought to be the major factors controlling the decline of available N during stand development.     

Soil moisture effects on gross nitrification differ between adjacent grassland and forested soils in central Alberta, Canada

Background and aims

Changes in soil moisture availability seasonally and as a result of climatic variability would influence soil nitrogen (N) cycling in different land use systems. This study aimed to understand mechanisms of soil moisture availability on gross N transformation rates.

Methods

A laboratory incubation experiment was conducted to evaluate the effects of soil moisture content (65 vs. 100% water holding capacity, WHC) on gross N transformation rates using the ¹⁵N tracing technique (calculated by the numerical model FLUAZ) in adjacent grassland and forest soils in central Alberta, Canada.

Results

Gross N mineralization and gross NH ₄ ⁺ immobilization rates were not influenced by soil moisture content for both soils. Gross nitrification rates were greater at 100 than at 65% WHC only in the forest soil. Denitrification rates during the 9 days of incubation were 2.47 and 4.91 mg N kg^-1 soil d^-1 in the grassland and forest soils, respectively, at 100% WHC, but were not different from zero at 65% WHC. In the forest soil, both the ratio of gross nitrification to gross NH ₄ ⁺ immobilization rates (N/IA) and cumulative N₂O emission were lower in the 65 than in the 100% WHC treatment, while in the grassland soil, the N/IA ratio was similar between the two soil moisture content treatments but cumulative N₂O emission was lower at 65% WHC.

Conclusions

The effect of soil moisture content on gross nitrification rates differ between forest and grassland soils and decreasing soil moisture content from 100 to 65% WHC reduced N₂O emissions in both soils.     

Seasonal patterns of ammonium and nitrate uptake in nine temperate forest ecosystems

Summary Seasonal patterns of net N mineralization and nitrification in the 0–10 cm mineral soil of 9 temperate forest sites were analyzed using approximately monthlyin situ soil incubations. Measured nitrification rates in incubated soils were found to be good estimates of nitrification in surrounding forest soils. Monthly net N mineralization rates and pools of ammonium-N in soil fluctuated during the growing season at all sites. Nitrate-N pools in soil were generally smaller than ammonium-N pools and monthly nitrification rates were less variable than net N mineralization rates. Nitrate supplied most of the N taken up annually by vegetation at 8 of the 9 sites. Furthermore, despite the large fluctuations in ammonium-N pools and monthly net N mineralization, nitrate was taken up at relatively uniform rates during the growing season at most sites.     

Seasonal variations in nitrogen mineralization under three land use types in a grassland landscape

Soil nitrogen (N) mineralization is an important component of the N cycling process in ecosystems. In this study, we assessed the seasonal patterns of net soil N mineralization and nitrification using an intact soil core incubation method in the upper 0–10 cm soil layer in three representative land use types. These included a fenced steppe, an abandoned field and a crop field in a grassland landscape of Inner Mongolia, China. The study was conducted from September 2004 to August 2005. Our results demonstrate marked seasonal variations in inorganic N pools, net nitrogen mineralization and net nitrification. Net N mineralization was higher in the crop field than in the fenced steppe and the abandoned field. Daily rates of N mineralization and nitrification during the growing season were approximately twice their corresponding mean annual rates. Accumulative mineralization and nitrification of N during the growing season accounted for about 90 and 85% of that measured for the entire year. Rates of mineralization and nitrification were positively correlated with soil bulk density, but negatively correlated with soil pH. Net N mineralization and nitrification were strongly regulated by land use, precipitation, soil water and temperature.     

Soil–atmosphere exchange of greenhouse gases in a Eucalyptus marginata woodland, a clover-grass pasture, and Pinus radiata and Eucalyptus globulus plantations

Soils provide the largest terrestrial carbon store, the largest atmospheric CO₂ source, the largest terrestrial N₂O source and the largest terrestrial CH₄ sink, as mediated through root and soil microbial processes. A change in land use or management can alter these soil processes such that net greenhouse gas exchange may increase or decrease. We measured soil–atmosphere exchange of CO₂, N₂O and CH₄ in four adjacent land‐use systems (native eucalypt woodland, clover‐grass pasture, Pinus radiata and Eucalyptus globulus plantation) for short, but continuous, periods between October 2005 and June 2006 using an automated trace gas measurement system near Albany in southwest Western Australia. Mean N₂O emission in the pasture was 26.6 μg N m⁻² h⁻¹, significantly greater than in the natural and managed forests (< 2.0 μg N m⁻² h⁻¹). N₂O emission from pasture soil increased after rainfall events (up to 100 μg N m⁻² h⁻¹) and as soil water content increased into winter, whereas no soil water response was detected in the forest systems. Gross nitrification through ¹⁵N isotope dilution in all land‐use systems was small at water holding capacity < 30%, and under optimum soil water conditions gross nitrification ranged between < 0.1 and 1.0 mg N kg⁻¹ h⁻¹, being least in the native woodland/eucalypt plantation < pine plantation < pasture. Forest soils were a constant CH₄ sink, up to −20 μg C m⁻² h⁻¹ in the native woodland. Pasture soil was an occasional CH₄ source, but weak CH₄ sink overall (−3 μg C m⁻² h⁻¹). There were no strong correlations (R < 0.4) between CH₄ flux and soil moisture or temperature. Soil CO₂ emissions (35–55 mg C m⁻² h⁻¹) correlated with soil water content (R < 0.5) in all but the E. globulus plantation. Soil N₂O emissions from improved pastures can be considerable and comparable with intensively managed, irrigated and fertilised dairy pastures. In all land uses, soil N₂O emissions exceeded soil CH₄ uptake on a carbon dioxide equivalent basis. Overall, afforestation of improved pastures (i) decreases soil N₂O emissions and (ii) increases soil CH₄ uptake.     

The Influence of Nutrient Availability on Soil Organic Matter Turnover Estimated by Incubations and Radiocarbon Modeling

We investigated the decomposability of soil organic matter (SOM) along a chronosequence of rainforest sites in Hawaii that form a natural fertility gradient and at two long-term fertilization experiments. To estimate turnover times and pool sizes of organic matter, we used two independent methods: (1) long-term incubations and (2) a three-box soil model constrained by radiocarbon measurements. Turnover times of slow-pool SOM (the intermediate pool between active and passive pools) calculated from incubations ranged from 6 to 20 y in the O horizon and were roughly half as fast in the A horizon. The radiocarbon-based model yielded a similar pattern but slower turnover times. The calculation of the ¹⁴C turnover times is sensitive to the lag time between photosynthesis and incorporation of organic C into SOM in a given horizon. By either method, turnover times at the different sites varied two- or threefold in soils with the same climate and vegetation community. Turnover times were fastest at the sites of highest soil fertility and were correlated with litter decay rates and primary productivity. However, experimental fertilization at the two least-fertile sites had only a small and inconsistent effect on turnover, with N slowing turnover and P slightly speeding it at one site. These results support studies of litter decomposition in suggesting that while plant productivity can respond rapidly to nutrient additions, decomposition may respond much more slowly to added nutrients.