定位试验地耕层土壤植物寄生线虫空间分布特征

采用经典统计学与地统计学相结合的方法,对中国科学院沈阳生态实验站定位试验地耕层土壤中植物寄生线虫的空间分布特征进行研究。结果表明,在田间尺度下螺旋属（Helicotylenchus）、垫刃属（Tylenchus）是上下两层土壤中植物寄生线虫的优势属,矮化属（Tylenchorchychus）为下层土壤中的优势属,这3个属线虫数量占植物寄生线虫总数的92％。除下层矮化属线虫外,上下两层土壤中植物寄生线虫空间变异为48％-100％,其空间自相关范围为35～91m。克里格插值分析表明,上层土壤中植物寄生线虫总数与螺旋属线虫数量、上下层土壤中垫刃属线虫数量呈现出相似的空间分布格局。这些结果反映了不同属的植物寄生线虫沿水平和垂直方向活动性上的差异;由此可以进一步推测垫刃属和矮化属线虫向下迁移能力强于螺旋属线虫。     

秸秆还田量对植物寄生线虫群落的影响

利用运行11年的中国科学院保护性耕作长期定位试验站,开展了4个不同秸秆还田量处理即秸秆不覆盖还田(NT0)、秸秆33%覆盖还田(NT33)、秸秆67%覆盖还田(NT67)和秸秆100%覆盖还田(NT100)对植物寄生线虫群落影响的研究。本研究共分离鉴定到植物寄生线虫16个属,优势属4个,即巴兹尓属(Basiria)、垫刃属(Tylenchus)、拟盘旋属(Pararotylenchus)和短体属(Pratylenchus)。植物寄生线虫总丰度在0～10 cm土层随着秸秆还田量的增加先增加后减少,在10～20 cm土层随着秸秆还田量的增加变化很小,但两个土层不同秸秆还田量处理间植物寄生线虫总丰度差异均不显著。秸秆还田各个处理中,植物寄生线虫c-p(colonizers-persisters)类群以c-p3类群占优势。秸秆还田导致了0～10 cm土层土壤总有机碳含量增加,植物寄生线虫优势属中巴兹尔属(Basiria)和垫刃属(Tylenchus)的丰度增加,植物寄生线虫c-p2类群的相对丰度增加,以及c-p2和c-p3类群的生物量增加。秸秆还田量的增加并没有增加植物寄生线虫危害的风险。秸秆还田主要是通过影响土壤总有机碳和pH的变化来影响植物寄生线虫c-p类群。     

藏东南急尖长苞冷杉林林隙土壤线虫群落特征

为了解西藏东南部急尖长苞冷杉林林隙土壤线虫群落特征,对林隙、非林隙土壤0~30 cm范围内不同深度土层的线虫群落进行调查,并用线虫个体密度、生物多样性指数和营养类群指数等特征值分析了土壤线虫群落的结构及多样性特点.结果表明： 采用浅盘法分离得到土壤线虫26801 条,隶属于2纲5目40科64属;线虫个体密度平均为3552 条·100 g-1干土,表聚性极强.垫咽属、丝垫刃属为林隙土壤线虫优势属;食细菌性线虫为主要营养类群.土壤有机质的分解兼有真菌分解和细菌分解两种途径.线虫的生物多样性及丰富度与林隙面积有关.土壤线虫群落特征表明,林隙具有异于郁闭林分和林间空地的特性,在环境指示方面具有应用潜力.     

施用化肥对黑土地区线虫群落组成及多样性产生的影响

本文针对玉米生长期内施用化肥对东北黑土地区线虫群落组成及多样性产生的影响进行了研究,共获得14科,16属,其中头叶科（Cephalobidae),小杆科（Rhobditidae) ,真滑刃属（Aphelenchus),垫刃属（Tylenchus)为优势科／优势度指数分析比较了施肥和不施肥试验小区土壤线虫群落多样性分布规律,其中Shannon多样性指数和丰富度指数是评价线虫群薄对化肥投入最敏感的指数。     

川西亚高山/高山森林土壤线虫多样性

为了解青藏高原东缘亚高山/高山森林土壤线虫多样性,于2015年7月以该地区岷江冷杉原始林、混交林和次生林为研究对象,采用淘洗-过筛-蔗糖离心的方法分离土壤线虫,研究了3个海拔森林土壤线虫群落的组成与结构特征.结果表明: 共捕获线虫37950条,隶属于20科27属,平均为4217 条·100 g^-1干土,原始林以丝尾垫刃属为优势属,混交林和次生林以丝尾垫刃属和拟盘旋属为优势属,且优势属个体数量受林型的影响显著.原始林和次生林的优势营养类群为食真菌线虫,混交林则为食细菌线虫.土壤线虫c-p (colonizer-persister)类群c-p 1、c-p 2、 c-p 3和c-p 4数量分别占总数的6.1%、51.1%、30.0%和12.7%.3个海拔森林土壤线虫的自由生活线虫成熟度指数(MI)、总成熟度指数(∑MI)和植物寄生线虫成熟度指数(PPI)随海拔增加而逐渐降低.土壤线虫通路指数(NCR)在混交林高于0.5,在原始林和次生林低于0.5.林型显著影响了土壤线虫成熟度和NCR指数,但林型、土层及二者的交互作用对多样性指数影响不显著.川西亚高山/高山不同森林土壤线虫的组成、营养结构和能流通道存在明显差异,为深入理解土壤线虫在该区森林土壤生态过程中的作用提供了参考.     

稻田不同水分管理方式对土壤线虫群落的影响

在下辽河平原地区就稻田不同水分管理方式对土壤线虫多度、营养类群、群落组成的影响进行了研究．结果表明,0～10cm土层不同水分管理处理的线虫总数在耙耕前和黄熟期显著低于对照,10～20cm土层各时期处理间线虫总数的差异不显著,20～30cm土层线虫总数在耙耕前和黄熟期差异极显著．北方单季稻水田试验共观察到土壤线虫16科22属．绕线属(Plectus)、垫刃属(Tylenchus)、单宫属(Monhystera)是优势属,绕线属和垫刃属对不同的水分管理比较敏感．在耙耕前和黄熟期不同水分管理方式对0～10cm土壤食细菌线虫能够产生显著影响．稻田土壤中食细菌线虫和植物寄生线虫是优势营养类群,而捕食／杂食性线虫的相对多度最低．     

氮磷输入对过度放牧退化草原土壤线虫群落的影响

线虫是陆地生态系统中数量最多的一类无脊椎后生动物,在土壤碎屑食物网中占据多个营养级,并在能量流动和养分循环中发挥重要的生态功能.土壤线虫的群落结构和多样性水平可以反映生态系统功能的变化.多年来,过度放牧等不合理的开发利用导致我国大面积的草原处在不同程度的退化之中,外源性养分输入是维持其养分平衡进而恢复其生态和生产功能的重要措施.本研究以内蒙古锡林郭勒退化草原为对象,就氮磷输入对土壤线虫丰度和群落结构的单独效应和交互效应进行了研究.本研究获得线虫38属,其中垫咽属、滑刃属、索努斯属和盾垫属是该退化草原线虫群落优势属.氮输入降低了土壤线虫总丰度、捕食杂食线虫丰度以及植物寄生线虫丰度,而磷输入提高了土壤线虫总丰度、食真菌线虫丰度、捕食杂食类线虫丰度以及植物寄生线虫丰度,氮输入抑制了磷输入对线虫总丰度、捕食杂食线虫和植物寄生线虫丰度的促进作用.氮磷输入对线虫多样性无影响,可能与不同养分输入下稳定的植物群落多样性有关.氮输入显著提升了退化草原线虫成熟度指数,降低了植物寄生线虫成熟度指数(PPI),并且能缓解磷输入对PPI和瓦斯乐斯卡指数的负面作用,表明氮输入提高退化草地土壤健康程度,促进线虫群落和食物网的稳定性.上述研究结果有助于从土壤生物学角度理解氮磷输入对退化草地恢复的影响机理.     

减施氮肥和控制灌溉对稻田土壤线虫群落的影响

采用2×4双因子完全交互试验设计,研究了常规和控制灌溉条件下氮肥减量施用(常规施氮300 kg N·hm-2、减氮10%、减氮20%和减氮40%)对稻田土壤线虫数量、种类及群落结构的影响。结果表明,8个处理中共观测到16科28属的土壤线虫,分别为食细菌线虫7科12属,食真菌线虫3科4属,植食性线虫3科5属,杂食/捕食性线虫3科7属。其中丝尾垫刃属(Filenchus)为所有处理的优势属,占所有线虫总数的35.4%~47.9%。所有处理中均以食真菌线虫所占比例最高,食细菌线虫次之,然后是植食类线虫,杂食/捕食性线虫数量最少。常规灌溉条件下土壤线虫总数略大于控制灌溉下的线虫总数,但无显著差异;当施氮量减少20%(即降低到240 kg N·hm-2)时,土壤线虫总量有明显的提高,而随着施氮量的进一步降低,线虫总数并没有进一步的变化。     

新疆长期棉花连作对土壤理化性状与线虫群落的影响

土壤线虫群落特征是评价和指示土壤生态系统健康状况的重要依据。本研究选取不同连作年限(5、10、15、20和25年)的棉田为样地,采用高通量测序技术,探究土壤性状和线虫群落对棉田长期连作的响应。结果表明: 棉田连作10～15年后,土壤pH、电导率显著升高,有机碳、全氮、有效磷、有效钾、硝态氮含量和土壤微生物生物量碳(MBC)显著降低。在连作棉田中共鉴定出土壤线虫3纲7目18科25属,其中螺旋属在不同连作年限的棉田土壤中均为优势属;土壤植物寄生类线虫在不同连作年限中均为优势营养类群,呈现先降低后增加的趋势,连作25年较其他连作年限植物寄生类线虫增加9.1%～208.6%,其中螺旋属线虫增加了392%。随着连作年限的增加,矮化属、茎属、Discopersicus、中环属和中轮属等植物寄生类线虫被检出。连作15年的棉田土壤中,土壤线虫丰富度指数和自由生活线虫成熟度指数显著降低,植物寄生线虫成熟度指数/自由生活线虫成熟度指数显著升高,Shannon多样性指数和瓦斯乐斯卡指数最低;有效磷和MBC是影响土壤线虫群落变化的主要环境因子。这说明棉田连作10～15年会发生土壤养分失衡,土壤线虫多样性降低,土壤食物网稳定性变差,棉花致病类植物寄生线虫增加,产生连作障碍。     

大庆油田石油开采对土壤线虫群落的影响

选择大庆油田环境一致的6口油井,研究石油开采干扰对土壤线虫的影响。共鉴定出土壤线虫18科15属。食细菌线虫最多,共15属占总数的49.2%,其次为植物寄生线虫共9属,占30.6%,食真菌线虫4属,占17.6%,杂食/捕食线虫2属,占2.6%。其中优势类群为丝尾垫刃属Filenchus和头叶属Cephalobus,占总数的42.5%。常见类群包括13个属,占总数的51.7%。稀有类群15个属占总数的6.34%。土壤的线虫生活史策略以c-p 2所占比例最大,其次是c-p3和c-p 1类群,受油井开采作业等影响,线虫通过大量繁殖来应对环境的干扰与压力。不同油井线虫总数差异不显著,但所有油井线虫总数比对照明显减少(p<0.001)。不同油井线虫群落结构差异不大,各油井线虫富集指数和结构指数表明所有油井线虫受干扰程度较高,土壤食物网趋于退化。随着采样距离增加,线虫总量差异不显著,但线虫群落的物种数量增加,优势度指数和多样性指数逐渐增加。结果表明油井开采对土壤线虫群落有一定的影响,开采距离对线虫群落结构影响较大。     

Variation in rates of nitrogen fixation in termites: response to dietary nitrogen in the field and laboratory

Abstract. Termites contribute nitrogen to their habitat through the nitrogenase activity of their bacterial symbionts. Previous studies indicate that high levels of dietary nitrogen suppress nitrogen fixation in termites. We examined the effects of dietary nitrogen on fixation rates in termites in both field and laboratory experiments. Ten field cplonies of Reticulitermes were collected and assayed for nitrogenase activity in July 1993, October 1993, January 1994, and April 1994. The nitrogen content of the wood collected with each colony was determined. There was no correlation between termite nitrogen fixation rates and the amount of nitrogen in their food for any of the four collection periods. In laboratory experiments, nitrogen fixation rates decreased when termites were fed filter paper treated with 2% and 5% ammonium nitrate or a 5% mixture of the amino acids proline, tryptophan and leucine, compared to water-treated controls. By contrast, the nitrogenase activity of termites fed filter paper treated with 2% and 5% ammonium phosphate, a mixture of the amino acids histidine, serine and aspartic acid, or 2% and 5% urea did not differ from the controls. However, nitrogenase activity increased when termites were fed with 2% uric acid. No clear association exists between termite nitrogen fixation and the nitrogen content of their food.     

陕西果园主要分布区氮素投入特点及氮负荷风险分析

为了研究果园氮素投入特点及分析氮素负荷特征,加强果园氮素管理、指导果农科学合理施肥。以陕西省果园主要分布区土壤氮素分析、农户投入调查等统计数据为基础,采用盈余法从果树种类和区域角度分析果园生产体系中的氮素输入输出特点及氮素盈余状况。结果表明,陕西果园主要分布区平均化肥氮投入量927.2 kg/hm2,主要来源于尿素和复合肥,其中尿素占调查样本量的40%以上;通过有机肥投入的氮仅为139.4 kg/hm2。94.8%的果园氮素处于盈余,总体平均盈余量为876.3 kg/hm2,其中氮盈余量超过500 kg/hm2的样本占57.5%,盈余量超过1 000 kg/hm2的样本亦占了27.3%。不同果园相比,猕猴桃园氮素投入及盈余量最高,分别为1 432.9、1 186.9 kg/hm2。不同区域果园比较,土壤氮环境负荷以关中灌区果园较高,达1046.1kg/hm2。果园氮素施用与养分盈余量之间存在极显著的正相关。陕西果园氮素的高量投入给土壤环境带来较大的氮素负荷,这对土壤环境和周围水体造成很大威胁。     

Nitrogen yields from undisturbed watersheds in the Americas

Yields of total fixed nitrogen and nitrogen fractions are summarized for thirty-one watersheds in which anthropogenic disturbance of the nitrogen cycle, either through land use or atmospheric deposition, is negligible or slight. These yields are taken as representative of background conditions over a broad range of watershed areas, elevations, and vegetation types. The data set focuses on watersheds of the American tropics, but also includes information on the Gambia River (Africa) and some small watersheds in the Sierra Nevada of California. For the tropical watersheds, total nitrogen yield averages 5.1 kg ha^–1 y^–1. On average, 30% of the total is particulate and 70% is dissolved. Of the dissolved fraction, an average of 50% is organic and 50% is inorganic, of which 20% is ammonium and 80% is nitrate. Yields are substantially lower than previously estimated for background conditions. Yields of all nitrogen fractions are strongly related to runoff, which also explains a large percentage of variance in yield of total nitrogen (r²=0.85). For total nitrogen and nitrogen fractions, yield increases at about two-thirds the rate of runoff; concentration decreases as runoff increases. There is a secondary but significant positive relationship between elevation and yield of DIN. Ratios DON/TDN and PN/TN both are related to watershed area rather than runoff; DON/TDN decreases and PN/TN increases toward higher stream orders. The analysis suggests for tropical watersheds the existence of mechanisms promoting strong homeostasis in the yield of N and its fractions for a given moisture regime, as well as predictable downstream change in proportionate representation N fractions. Yields and concentrations for small tropical watersheds are much larger than for the few temperate ones with which comparisons are possible.     

沉积物氮形态与测定方法研究进展

长期以来,国内外学者对沉积物中氮进行了大量的研究,在氮生物地球化学循环和生态学效应方面取得了重要进展.然而,现有关于氮赋存形态的研究主要集中在总氮和无机氮方面,还不能深入阐明沉积物氮的生物和生态学机制.分析了沉积物和土壤氮赋存形态划分和测定方法的研究进展,研究表明:沉积物氮的形态划分与测定方法基本上还是借鉴了土壤氮的研究方法;无机态氮的研究多集中在可交换态氮方面,对固定铵的研究相对较少;在可交换态氮提取方法上并没有针对沉积物与土壤的差异进行必要的论证和改进,沉积物中可溶态氮对可交换态氮测定的影响还不明确;有机氮的测定方法基本上是经验方法,目前还无针对有机氮生态学效应的分类及测定方法;连续分级浸提方法从生态学效应的角度对沉积物氮的研究进行了有益的探索,为深入揭示氮的生态学机制提供了新的思路,但是此类方法目前还集中在国内学者的相关研究中.     

Time course of N2 fixation in common bean (Phaseolus vulgaris L.)

Field and greenhouse experiments were conducted to assess the nitrogen fixation rates of four cultivars of common bean (Phaseolus vulgaris L.) at different growth stages. The ¹⁵N isotope dilution technique was used to quantify biological nitrogen fixation. In the greenhouse, cultivars M4403 and Kallmet accumulated 301 and 189 mg N plant^–1, respectively, up to 63 days after planting (DAP) of which 57 and 43% was derived from atmosphere. Under field conditions, cultivars Bayocel and Flor de Mayo RMC accumulated in 77 DAP, 147 and 135 kg N ha^–1, respectively, of which approximately one-half was derived from the atmosphere. The rates of N₂ fixation determined at different growth stages increased as the plants developed, and reached a maximum during the reproductive stage both under field and greenhouse conditions. Differences in translocation of N were observed between the cultivars tested, particularly under field conditions. Thus, the fixed N harvest index was 93 and 60 for cultivars Flor de Mayo and Bayocel, respectively. In early stages of growth, the total content of ureides in the plants correlated with the N fixation rates. The findings reported in the present paper can be used to build a strategy for enhancing biological N₂ fixation in common bean.     

Available soil nitrogen in relation to fractions of soil nitrogen and other soil properties

The available N of 27 soils from England and Wales was assessed from the amounts of N taken up over a 6-month period by perennial ryegrass grown in pots under uniform environmental conditions. Relationships between availability and the distribution of soil N amongst various fractions were then examined using multiple regression. The relationship: available soil N (mg kg^–1 dry soil)=(N_min×0.672)+(N_inc×0.840)+(N_mom×0.227)–5.12 was found to account for 91% of the variance in available soil N, where N_min=mineral N, N_inc=N mineralized on incubation and N_mom=N in macro-organic matter. The N mineralized on incubation appeared to be derived largely from sources other than the macro-organic matter because these two fractions were poorly correlated. When availability was expressed in terms of available organic N as % of soil organic N (N_ao) the closest relationship with other soil characteristics was: N_ao=[N_inc×(1.395–0.0347×CN_mom]+[N_mom×0.1416], where CN_mom=CN ratio of the macro-organic matter. This relationship accounted for 81% of the variance in the availability of the soil organic N.The conclusion that the macro-organic matter may contribute substantially to the available N was confirmed by a subsidiary experiment in which the macro-organic fraction was separated from about 20 kg of a grassland soil. The uptake of N by ryegrass was then assessed on two subsamples of this soil, one without the macro-organic matter and the other with this fraction returned: uptake was appreciably increased by the macro-organic matter.     

Challenging the paradigm of nitrogen cycling: no evidence of in situ resource partitioning by coexisting plant species in grasslands of contrasting fertility

In monoculture, certain plant species are able to preferentially utilize different nitrogen (N) forms, both inorganic and organic, including amino acids and peptides, thus forming fundamental niches based on the chemical form of N. Results from field studies, however, are inconsistent: Some showing that coexisting plant species predominantly utilize inorganic N, while others reveal distinct interspecies preferences for different N forms. As a result, the extent to which hypothetical niches are realized in nature remains unclear. Here, we used in situ stable isotope tracer techniques to test the idea, in temperate grassland, that niche partitioning of N based on chemical form is related to plant productivity and the relative availability of organic and inorganic N. We also tested in situ whether grassland plants vary in their ability to compete for, and utilize peptides, which have recently been shown to act as an N source for plants in strongly N-limited ecosystems. We hypothesized that plants would preferentially use NO₃⁻-N and NH₄⁺-N over dissolved organic N in high-productivity grassland where inorganic N availability is high. On the other hand, in low-productivity grasslands, where the availability of dissolved inorganic N is low, and soil availability of dissolved organic N is greater, we predicted that plants would preferentially use N from amino acids and peptides, prior to microbial mineralization. Turves from two well-characterized grasslands of contrasting productivity and soil N availability were injected, in situ, with mixtures of ¹⁵N-labeled inorganic N (NO₃⁻ and NH₄⁺) and ¹³C¹⁵N labeled amino acid (l-alanine) and peptide (l-tri-alanine). In order to measure rapid assimilation of these N forms by soil microbes and plants, the uptake of these substrates was traced within 2.5 hours into the shoots of the most abundant plant species, as well as roots and the soil microbial biomass. We found that, contrary to our hypothesis, the majority of plant species across both grasslands took up most N in the form of NH₄⁺, suggesting that inorganic N is their predominant N source. However, we did find that organic N was a source of N which could be utilized by plant species at both sites, and in the low-productivity grassland, plants were able to capture some tri-alanine-N directly. Although our findings did not support the hypothesis that differences in the availability of inorganic and organic N facilitate resource partitioning in grassland, they do support the emerging view that peptides represent a significant, but until now neglected, component of the terrestrial N cycle.     

黄土丘陵区植被恢复对土壤可溶性氮组分的影响

为探究黄土丘陵地区人工植被恢复对土壤氮素养分累积与有效性的影响,研究分析了植被恢复15年刺槐、柠条、刺槐侧柏混交、刺槐山桃混交以及荒草地土壤可溶性氮组分含量及其垂直分布特征。结果表明,与耕地相比,植被恢复显著提高了0—30 cm土壤可溶性氮组分含量,这也使0—30 cm土壤可溶性氮组分密度显著增加,可溶性有机氮密度增幅表现为柠条(262.2%)刺槐(232.8%)刺槐山桃混交、刺槐侧柏混交(34.5%)荒草地(-21.5%),硝态氮密度整体表现为柠条刺槐刺槐山桃混交荒草地刺槐侧柏混交,增幅为7.9%—182.8%,铵态氮密度以刺槐山桃混交增幅最大(110.3%),荒草地最小为2.6%。可溶性有机氮、硝态氮占全氮的比例以刺槐最高,分别提升了2.4倍和0.6倍,铵态氮占全氮的比例以刺槐山桃混交最高,提升了1.0倍。可溶性氮组分受微生物量碳氮的影响大于有机质和全氮,微生物量氮与可溶性氮组分的相关性优于微生物量碳,硝态氮对土壤有机质、全氮和微生物量碳氮的变化最为敏感。综上,植被恢复能够提高土壤可溶性氮组分含量、密度及其占全氮比例,增加土壤氮的有效性,以刺槐、柠条提升效果最好。     

Challenges of reducing excess nitrogen in Japanese agroecosystems

Fertilizer N use in Japan has decreased by about 30% from 1960 to 2000, while keeping a little increase in cereal yields. This has resulted in a significant increase in apparent nitrogen use efficiency, in particular for rice. On the other hand, national N Icad on the environment associated with the production and consumption of domestic and imported agricultural products has almost tripled during this period, mainly due to the dramatic increase of imports of food and feedstuffs. The environmental problems, including water and air pollution, caused by the excessive loads of N are serious public concerns and there is an urgent need to minimize N losses from agricultural production. In order to meet the necessity for reducing the environmental impacts by excess N, political and technological measures have been taken at regional and country levels. In recent years, the Japanese government has embarked on a series of policies to encourage transition to an environmentally conscious agriculture. Promoting proper material circulation with reducing fertilizer impact and utilizing biomass and livestock wastes is emphasized in these policies. The effectiveness of environmental assessment and planning for reducing regional and national N Icad has been discussed. Implementation of environmentally friendly technologies and management, both conventional and innovational, have been developed and adopted in Japanese agriculture. The effectiveness of conventional technologies in reducing environmental reactive N has been re-evaluated. Innovative technologies, such as use of controlled availability fertilizers and livestock wastes compost pellets, are being investigated and extended.A comprehensive approach that applies political and technological measures with closer cooperation is necessary to control reactive N in the environment.