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。     

牦牛排泄物输入对滇西北高寒泥炭沼泽湿地土壤氮转化的影响

牦牛放牧对滇西北高寒湿地土壤环境产生严重影响，改变土壤氮的迁移转化过程，影响湿地生态系统初级生产。然而，关于牦牛排泄物输入对滇西北高寒泥炭沼泽湿地土壤氮转化过程的影响尚不清楚。本研究以滇西北高原典型泥炭沼泽湿地为对象，采用原位土芯室内控制实验方法，研究牦牛排泄物输入对泥炭沼泽湿地土壤氮转化的影响。结果表明，粪便和尿液输入初期促进土壤铵态氮(NH₄⁺-N)积累，但整个培养期则表现为消耗NH₄⁺-N,积累硝态氮(NO₃^--N),表明该过程以硝化作用为主。粪便和尿液输入提高土壤脲酶活性(P<0.05),降低反硝化酶活性(P<0.05)。粪便输入提高过氧化氢酶活性(P<0.05)和N-乙酰氨基葡萄糖苷酶活性(P<0.05),尿液输入降低N-乙酰氨基葡萄糖苷酶活性(P<0.05)。粪便输入对土壤的矿化和硝化作用无显著性影响，尿液输入对土壤硝化作用影响显著。粪便输入抑制土壤反硝化作用，而尿液输入促进反硝化作用。牦牛排泄物输入通过影响泥炭沼...     

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     

牲畜排泄物返还对草地土壤氮转化和氧化亚氮(N2O)排放的影响研究进展

牲畜排泄物返还被认为是对草地的一种天然的施肥措施,也是草地养分归还的一种重要途径,对于维持土壤肥力和植被生产力具有十分重要的生态学意义。论述了放牧牲畜粪便和尿液自身降解及其氮素变化、粪尿返还对草地土壤氮转化和氧化亚氮(N₂O)排放的作用机制及影响效应,指出排泄物氮输入使粪尿斑块成为草地土壤氮转化和N₂O排放的活跃点,且不同排泄物类型、土壤理化特性和气候条件等使土壤氮素矿化、固持、硝化及反硝化等关键过程具有复杂性和差异性,进而导致不同类型草地生态系统N₂O排放对牲畜排泄物返还的响应不尽相同。建议未来在全球气候变化背景下,应加强草地牲畜排泄物-植被-土壤体系氮素生物地球化学循环过程的系统研究,进一步加深天然草地关键氮素转化过程和N₂O排放的微生物作用机制方面的认识,从而有助于为优化放牧牲畜排泄物的管理模式、制定科学合理的草地土壤养分调控策略和维持草地生态系统可持续发展提供科学有效的理论指导。     

覆盖措施对雷竹林地土壤硝化和反硝化作用的影响

为探讨林地覆盖对雷竹林土壤硝化和反硝化作用的影响,以不覆盖雷竹林为对照,测定了林地覆盖期间(覆盖后30、60、90 d)雷竹林土壤基本理化性质,并用气压分离过程技术(Ba PS)测定了土壤硝化速率和反硝化速率。结果表明:覆盖措施和覆盖时间对雷竹林土壤硝化和反硝化作用均有显著影响,而且两者存在明显的交互作用;覆盖能促进雷竹林土壤反硝化作用,但长时间覆盖会抑制雷竹林土壤硝化作用;覆盖总体上会降低雷竹林土壤硝化速率、反硝化速率与土壤理化性质的相关性程度,并使土壤硝化和反硝化作用的主要环境影响因子趋于多样化和复杂化;覆盖雷竹林土壤硝化速率的主要环境影响因子是土壤含水量、p H值、铵态氮含量和总孔隙度,反硝化速率的主要环境影响因子是土壤p H值、含水量和总孔隙度。林地覆盖会显著影响雷竹林土壤的氮循环过程,可能会增加土壤氮素损失。     

CO_2浓度升高对水体硝化、反硝化作用的影响研究进展

大气CO_2浓度升高潜移默化地影响着水体生态系统的碳循环过程.然而,该过程如何影响与其耦合的氮循环过程仍不明确.水体硝化、反硝化过程作为水体氮循环的重要环节,必然会对大气CO_2浓度升高产生一系列的响应.本文总结了国内外关于大气CO_2浓度升高对水体理化性质、硝化作用、反硝化作用及N形态转化影响方面的研究工作,发现大气CO_2浓度升高会降低水体的p H,增加水中CO_2和HCO_3^-含量,但对富营养化与寡营养化水体中硝化、反硝化作用的影响具有明显差异.大气CO_2浓度升高抑制寡营养化水体的硝化作用和反硝化作用,降低N2_O的释放通量,抑制富营养化水体的硝化作用,但当水体pH在7～9时,可能促进反硝化作用,增加N2_O的释放通量,最终可能导致水体中NH_4^+的积累及NO_3^-浓度的降低,影响水体中微生物的多样性.在此基础上提出目前相关研究存在的瓶颈问题及值得深入探讨的科学问题,为进一步深入理解温室效应背景下全球CO_2浓度升高对水体生态系统N循环的影响提供参考.     

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.     

重度放牧对欧亚温带草原东缘生态样带土壤氮矿化及其温度敏感性的影响

以欧亚温带草原东缘生态样带为平台,以样带上未放牧和重度放牧配对样地为研究对象,开展重度放牧对欧亚温带典型草原土壤氮矿化及其温度敏感性的影响研究。结果表明:(1)在室内培养条件下,土壤氮积累量和土壤净氮矿化速率呈现出干燥度指数较大的样点显著大于干燥度指数最低的样点(P0.05)。在相对湿润的样点,土壤氮素矿化周转速率较快;(2)重度放牧对不同样点土壤氮积累量和土壤氮矿化速率的影响是不同的。在干燥度指数较高样点,重度放牧样地土壤铵态氮减少量和速率较未放牧样地低(P0.05),重度放牧显著降低了土壤硝态氮积累量、无机氮积累量、硝化速率、净氮矿化速率(P0.05);在干燥度指数较低样点,重度放牧样地土壤铵态氮减少量和速率较未放牧样地高(P0.05),重度放牧对土壤硝态氮积累量、无机氮积累量、硝化速率、净氮矿化速率影响不大(P0.05);(3)土壤氮矿化作用温度敏感性(Q_(10))变化范围在1.61—2.06,重度放牧对Q_(10)无显著影响。随着纬度的升高,Q_(10)呈升高趋势。Q_(10)与基质质量指数以及表观活化能与基质质量指数均呈显著的负相关关系(P0.05);(4)土壤硝态氮积累量、无机氮积累量、硝化速率、净氮矿化速率对重度放牧的响应比与干燥度指数呈极显著负相关(P0.01),重度放牧对欧亚温带典型草原土壤氮矿化的影响受气候条件(温度和降水)的调控。     

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.     

乙炔抑制法在硝化与反硝化过程中的应用

硝化和反硝化作用在土壤氮素循环中扮演重要作用,由于硝化和反硝化作用一方面能够导致土壤中氮素的损失,另一方面能够产生温室气体-N2O,所以硝化和反硝化作用的研究备受关注.乙炔抑制法能同时测定硝化和反硝化作用,在硝化和反硝化作用中有着重要的应用.该文主要论述了乙炔抑制法的研究进展;以及对应用乙炔气体时存在的一些问题进行了综述.     

放牧对牧草光合作用、呼吸作用和氮、碳吸收与转运的影响

研究放牧对草地植物生理活动的影响,对于揭示草地放牧演替的生理机制有重要意义.大量研究表明,家畜放牧对牧草光合作用、呼吸作用以及C和N吸收与转运的影响,可以分为生理伤害和生理恢复2个阶段.放牧通过改变草地冠层结构影响牧草光合作用,净光合作用速率短期内迅速下降,随着叶面积指数增加又逐渐上升,呼吸作用有相似的变化趋势.牧草放牧后再生长所需的C和N最初主要来自根系和留茬中的贮藏物质,此后随着牧草生长恢复逐渐由同化作用供给,C代谢与土壤N水平负相关.放牧后牧草生理活动变化与牧草遗传特性、种间竞争、家畜放牧特征、非生物环境等因素密切相关.     

Nitrogen cycling in low input legume-based agriculture,with emphasis on legume/grass pastures

Low input legume-based agriculture exists in a continuum between subsistence farming and intensive arable and pastoral systems. This review covers this range, but with most emphasis on temperate legume/grass pastures under grazing by livestock. Key determinants of nitrogen (N) flows in grazed legume/grass pastures are: inputs of N from symbiotic N₂ fixation which are constrained through self-regulation via grass/legume interactions; large quantities of N cycling through grazing animals with localised return in excreta; low direct conversion of pasture N into produce (typically 5–20%) but with N recycling under intensive grazing the farm efficiency of product N: fixed N can be up to 50%; and regulation of N flows by mineralisation/immobilisation reactions. Pastoral systems reliant solely on fixed N are capable of moderate-high production with modest N losses e.g. average denitrification and leaching losses from grazed pastures of 6 and 23 kg N ha^–1 yr^–1. Methods for improving efficiency of N cycling in legume-based cropping and legume/grass pasture systems are discussed. In legume/arable rotations, the utilisation of fixed N by crops is influenced greatly by the timing of management practices for synchrony of N supply via mineralisation and crop N uptake. In legume/grass pastures, the spatial return of excreta and the uptake of excreta N by pastures can potentially be improved through dietary manipulation and management strategies. Plant species selection and plant constituent modification also offer the potential to increase N efficiency through greater conversion into animal produce, improved N uptake from soil and manipulation of mineralisation/immobilisation/nitrification reactions.     

Nitrogen accumulation in Kaolin wastes in Cornwall

Summary Nitrogen accumulation and nitrogen mineralisation rates were measured in a series of waste heaps, produced by the china clay mining industry, which had been reclaimed at different times with a sward ofAgrostis tenuis, Festuca rubra, andTrifolium repens. The best swards tended to have high ammonification rates and rapid N turnover (which is represented by a nitrogen turnover index) —nitrification rates or nitrogen accumulation were not such good predictors of sward quality. Ammonification increased with pH and with organic nitrogen accumulation whereas N turnover was not related to these factors. Nitrification levels were generally low and it was concluded that nitrification was not important to sward health. Organic nitrogen increased with age in all swards, ammonification in certain types only and nitrification not at all. Levels of all are well short of those in adjacent grazing land. Rates of turnover had however a tendency to decline towards those in the grazings owing probably to the build up of resistant humus. The proportion of the total nitrogen which is in the biomass (30%) is also higher than in adjacent grazings (6%). Rapid nitrogen cycling is thus needed to maintain productivity and greenness, and the disadvantages of this are discussed. The adequacy of nitrogen cycle development to date is considered, and possible future strategies outlined.     

Do non-ruminant wildlife pose a risk of paratuberculosis to domestic livestock and vice versa in Scotland?

Paratuberculosis (Johne's disease) was long considered only a disease of ruminants. Recently non-ruminant wildlife species have been shown to harbor Mycobacterium avium subsp. paratuberculosis, the causative organism of paratuberculosis. We review the known non-ruminant wildlife host range of M. avium subsp. paratuberculosis and consider their role in the epidemiology of paratuberculosis in domestic ruminant livestock. Mycobacterium avium subsp. paratuberculosis has been isolated from lagomorph, canid, mustelid, corvid, and murid species. In agricultural environments domestic ruminants may contact wildlife and/or their excreta when grazing or feeding on farm-stored feed contaminated with wildlife feces, opening up the possibility of inter-species transmission. Of the wildlife species known to harbor M. avium subsp. paratuberculosis in Scotland, the rabbit is likely to pose the greatest risk to grazing livestock. Paratuberculosis in domestic ruminants is a notoriously difficult disease to control; the participation of non-ruminant wildlife in the epidemiology of the disease may partially account for this difficulty.     

放牧对草地土壤氮素循环关键过程的影响与机制研究进展

放牧是人类管理利用草地生态系统的最主要途径之一.食草动物的采食、践踏、卧息和排泄物归还等干扰不仅会改变草地地上植物群落,也会对土壤养分循环产生显著的影响.随着人类活动的加剧,放牧强度和频率也在逐渐增加,从而对草地土壤氮素循环关键过程产生重要影响.放牧主要通过改变土壤的物理性质、土壤氮库以及微生物的组成和结构,进而影响氮素在土壤中的迁移与转化.适度放牧会促进土壤氮素的矿化过程和硝化过程,加快氮素的周转,有利于植物吸收可利用氮素,而对于反硝化的影响与草地的水热条件和土壤类型等密切相关.目前,关于放牧强度对土壤氮素循环关键过程影响的研究结果不一致,其影响机制尚不明晰,尤其对于不同类型的草原仍存在较大的差异.本研究在大量查阅国内外已有研究结果的基础上,论述了放牧对土壤氮素循环关键过程的影响效应,总结了放牧对土壤氮素循环的影响机制,指出了目前研究过程中存在的不足,并对未来研究中值得重点关注和深入研究的科学问题进行了探讨与展望,为进一步理解放牧对草地土壤氮素循环的影响提供参考.     

基于分子生态学网络探究西藏草地放牧对土壤微生物群落的影响

【目的】揭示西藏地区放牧对在功能基因层面上的微生物相互作用的影响。【方法】利用最近发明的网络工具(基于随机矩阵理论的分子生态学网络)分别在对照和放牧条件下分析基因芯片中碳循环和氮循环基因。【结果】碳和氮循环基因网络在对照和放牧条件下都具有无标度、小世界、模块性和层次性的拓扑学特征。放牧条件下的网络关键基因(模块枢纽和连通者)与对照显著不同。放牧导致网络变得小而紧密,暗示环境压力的存在。地上植物生物量与微生物基因网络显著相关(P=0.001),证实了研究样地地上植物与地下微生物紧密相连。【结论】放牧显著改变了西藏草地在功能基因层面上的微生物相互作用关系。     

放牧强度对高寒嵩草草甸土壤养分特性的影响

植物-土壤系统是草地生态和生产服务价值实现的基础,放牧是草地植物群落演替的重要因素。植物、土壤亚系统对放牧的敏感性是评价草地稳定性和提高草地恢复力的重要依据。以不同放牧强度下的高寒嵩草(Kobresia)草甸为研究对象,探讨土壤养分特征对放牧强度的响应及作用位点,结果表明:改变放牧强度可以明显改变植物群落数量特征,但没有明显改变土壤层次分类特征,说明土壤养分特征对一定范围内放牧强度具有自我稳定维持功能;但放牧干扰强度不同时,土壤剖面过渡层养分含量存在差异,说明长期放牧强度的差异会对土壤剖面养分性质产生影响,且这种影响起源于土壤剖面过渡层。在放牧高寒嵩草草甸植物-土壤系统中土壤剖面养分特征较植物群落数量特征更稳定;土壤剖面过渡层养分特征是土壤亚系统中对放牧的敏感因素;而放牧引起土壤剖面养分特征的改变主要表现在各过渡层上,并构成土壤发生层迁移的风险,因此推测,更为持久和更高强度的放牧干扰将最终改变土壤剖面特征及养分性质。     

Islands of Fertility: A Byproduct of Grazing?

Empirical work in arid shrubland systems has documented a distinct spatial pattern of soil nutrient distribution, with higher concentrations of nutrients under shrub canopies compared to bare ground interspaces between shrubs. This “fertile island” pattern is considered characteristic of arid ecosystems. However, recent work at a desertified shrubland site reported no island of fertility pattern for nitrogen inside a long-term grazing exclosure despite a strong fertile island pattern outside the exclosure, leading to a hypothesis that the pattern may be associated with grazing. In this paper we examine this hypothesis in two ways. First, we collected soil nitrogen data inside and outside two long-term livestock exclosures. Second, we examined published work on the fertile island pattern for nitrogen, phosphorus and carbon, and its association with livestock grazing. At the field sites, there was a strong fertile island pattern for soil nitrogen in the grazed area outside each exclosure but no fertile island pattern in the ungrazed area inside the fence. From the literature, we identified 49 studies, which represent 99 cases that examine differences in soil nutrients under and between shrubs (that is, tests of the fertile island pattern). In 92 cases, fertile islands were present for at least one of the nutrients. All cases where livestock grazing was present exhibited fertile island patterns for nitrogen and most did so for carbon and phosphorus. In contrast, fertile islands were less consistent where livestock grazing was absent; all nine cases that had been ungrazed for more than 30 years did not exhibit fertile islands for nitrogen. Our empirical data and literature review suggest that the fertile island pattern may be an artifact of grazing rather than an inherent property of arid shrublands. Further, we suggest that the grazing history of a site needs to be explicitly considered when documenting spatial patterns of soil nutrients in arid systems. This has significant implications for our understanding of soil nutrient dynamics in arid systems, the management of rangelands, and the potential for reversal of desertification.     

Impact of rapid urbanization on the floral diversity and agriculture land of district Dir,Pakistan

In the World urbanization is a serious problem especially in developing countries which creates serious environmental problems like climatic and ecological changes in the ecosystem. The present paper aims to explain urbanization that causes loss of agriculture lands, biodiversity, soil erosions and grazing in District Dir. Urbanization decreased species richness such as Salix alba and Populus alba in the last few years in the local area. Soil of local area was divided into three different zones and was tested for soil texture and mineral percentage. Zone I soil showed sandy loamy texture with a pH of 8.3, Nitrogen 0.012%, Phosphorus 5.0% and organic matter was 0.74 (ppm). Zone II soil was loamy sand in texture with pH 8.1, Nitrogen 0.011%, Phosphorus 6.2%, and organic matter was 0.24 (ppm) while Zone III soil texture was silty clay loam with a pH of 8.1, Nitrogen 0.032%, Phosphorus 11.3%, and organic matter was 0.60 (ppm). The current work concludes that urbanizations affect natural biodiversity and agriculture lands, and that soil erosion and watering-points trampled by livestock is one of the significant problems in district Dir, and that the main degrading factor is the overexploitation of vegetation for fuel-wood and livestock grazing.