温度和湿度对长白山两种林型下土壤氮矿化的影响

在实验室条件下,将不同含水量的两种森林类型的土柱分别置于5,15,25,和35℃条件下培养30d,分析培养前后的NH^ 4-N和NO^-3含量,确定土壤的净矿化速率,结果表明,在温度为5－35℃范围内,N的矿化速率与温度呈正相关,在一定的含水量范围内（0．46－0.54kg.kg^-1),净矿化速率随湿度的增加而升高,当含水量超过该范围,净矿化速率则随含量而降低,温度和湿度对土壤的矿化和硝化过程存在较明显的交互作用,建立了二维的方程（T,θ）来描述温度和湿度对土壤N矿化速率的影响,阔叶红松林土壤N矿化的最佳条件是温度35℃,含水量0.51kg.kg^-1,云冷杉林土壤N矿化的最佳条件是35℃,含水量0.52kg.kg^-1.     

温度和湿度对暖温带落叶阔叶林土壤氮矿化的影响

 更好地了解温度和湿度对土壤氮矿化过程的影响,从而估计森林生态系统土壤有机氮的矿化速率。在实验室条件下,控制土壤的温度与含水量。将不同含水量(0.12、0.20、0.28、0.35、0.40kg·kg-1)的土柱置于5℃、15℃、25℃和35℃条件下培养30d。分析培养前后的NH4+-N和NO3--N含量,确定土壤的净矿化速率和净硝化速率。结果表明：在5～25℃的温度范围内,氮的矿化速率和硝化速率与温度和湿度呈正相关。当温度超过25℃,含水量超过0.20kg·kg-1时,净矿化速率和净硝化速率随着温度和含水量的升高反而降低。温度和湿度对土壤的矿化和硝化过程存在比较明显的交互作用。我们建立了二维的方程(T,θ)来描述温度和湿度对土壤氮矿化速率的影响。暖温带土壤氮矿化的最佳条件是温度22.4℃、含水量0.40kg·kg-1。另外试验过程中,还观察到了比较明显的土壤氨挥发现象。     

不同环境因子对樟子松人工林土壤有机碳矿化的影响

土壤有机碳矿化是土壤向大气释放CO2的最大净输出途径,其与植被的净初级生产力的差值是判断生态系统碳源或碳汇的关键。本研究以科尔沁沙地10年生樟子松人工林生态系统为研究对象,采用室内培养实验方法,测定了不同温度、土壤含水量以及碳、氮添加条件下土壤有机碳矿化的速率。结果表明：土壤有机碳矿化速率随温度和土壤含水量的升高分别呈指数和线性增长,不同的土壤水分条件下土壤有机碳矿化的温度敏感性不同;在土壤含水量最小时（田间持水量的10％）,土壤有机碳矿化的温度敏感性最低;土壤有机碳矿化对水分的敏感性在低温条件下（10℃）显著低于在适温和高温条件下（20℃～30℃）。土壤中有机碳含量的增加显著提高土壤碳矿化速率,氮的添加对土壤有机碳矿化没有显著影响,但随着土壤有机碳含量的增加,土壤氮素含量对土壤碳矿化速率产生影响。     

温度、水分和森林演替对中亚热带丘陵红壤氮素矿化影响的模拟实验

研究了温度、水分和演替阶段及其交互作用对中亚热带丘陵红壤区森林土壤氮素矿化过程及其矿化速率的影响.结果表明：温度和演替阶段对土壤氨化速率影响显著,其中12 ℃<24℃<36 ℃,灌丛林和马尾松(Pinus massoniana)林低于常绿阔叶林(P＜0.05);而水分的影响不显著.水分和演替阶段对土壤硝化速率有显著影响,土壤半饱和含水量高于自然含水量及饱和含水量,且马尾松林高于灌丛林(P＜0.05);而温度的影响不显著.温度、水分和演替阶段对土壤氮净矿化速率的影响均显著,其中12 ℃<24 ℃<36 ℃,土壤半饱和含水量高于自然含水量和饱和含水量,灌丛林<马尾松林<常绿阔叶林(P＜0.05).温度升高有利于提高土壤氨化速率和净矿化速率,温度过高则抑制土壤硝化速率;土壤含水量适中有利于土壤氮素矿化过程;顺行演替将提高土壤供氮能力,且抑制过强的硝化作用.     

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.     

中国森林生态系统的土壤净氮矿化研究

 为了更好地了解温度和湿度对土壤氮矿化过程的影响,从而估计森林生态系统土壤有机氮的矿化速率,在中国7种典型森林生态系统中用PVC管采集森林土壤样品,通过在实验室控制土壤的温度与湿度,将不同湿度的土柱置于不同温度的生化培养箱中培养30 d,分析培养前后的NH+4-N和NO-3-N含量,确定土壤的净矿化速率和净硝化速率。结果表明,温度和湿度与土壤的矿化过程存在比较明显的相关关系（p<0.001）。同时建立了三元的方程来描述温度(t)和湿度(wfps)对土壤氮矿化速率(Rmin)的影响,Rmin=e-7.60+0.07×t+14.74×wfps-10.41×wfps2。利用这个实验模型估算了全国森林生态系统的年氮矿化量,估算结果与野外实测数据基本吻合。     

原始红松林退化演替后土壤氮矿化特征变化

土壤氮矿化是氮素生物地理化学循环的重要环节,表征着土壤的供氮潜力,其变化过程会影响森林生态系统生产力。从小兴安岭典型的原始红松林及其退化形成的次生阔叶林样地采集土壤样品,采用好气室内培养法,研究在不同培养温度(4℃、12℃、20℃、28℃和36℃)和湿度(20%、40%、60%、80%和100%饱和持水量,WHC)下,2种林地土壤氮转化速率的变化。结果表明:与原始红松林相比,次生阔叶林表层土(0—20 cm)的有机质、全碳、全氮、硝态氮、碳/氮比、全磷、速效磷、速效钾、pH值均显著升高,铵态氮显著降低(P0.05)。采用方差分析结果表明:原始红松林表层土壤的净矿化速率、净硝化速率均显著低于次生阔叶林,但净氨化速率的变化则相反;培养温度和湿度及两者的交互作用均对土壤氮转化速率影响显著(P0.001)。原始红松林和次生阔叶林净矿化速率对温度和湿度变化的响应存在一定差异,最适温度和湿度分别为28℃—36℃和60%(WHC)。原始红松林土壤氮矿化温度敏感性指数(Q_(10))显著高于次生阔叶林(P0.05),均值分别为2.08和1.80,Q_(10)与基质质量指数(A)呈负相关,与土壤有机质呈极显著负相关(P0.01)。     

温度对川西亚高山3种森林土壤氮矿化的影响

川西亚高山森林群落土壤氮循环对全球气候变化非常敏感。采用室内培养法,研究川西3个森林群落(天然针叶林、云杉人工林和桦木次生林)土壤有机层和矿质土壤层无机氮含量在两个培养温度(20℃和10℃)下4周内动态变化。结果表明:培养4周后,在20℃培养条件下天然针叶林、云杉人工林和桦木次生林硝态氮含量比在10℃培养条件下分别高出104.32%、52.11%和25.57%;而铵态氮含量仅高出10.18%、24.06%和44.82%。有机层土壤氨化速率、硝化速率和净氮矿化速率大多表现为20℃显著高于10℃;相反,温度对矿质土壤层氮转化速率影响大多不显著。此外,天然林土壤净氨化速率、硝化速率和净氮矿化速率均高于桦木次生林和云杉人工林。实验期间,3个森林群落土壤净硝化速率20℃比10℃高79.03%—128.89%,而净氨化速率仅高37.81%—63.33%。综上所述,温度变化对川西亚高山森林土壤氮矿化具有显著影响,而温度效应因森林类型、土壤层次和氮形态而不同。与矿质土壤层相比,土壤有机层氮矿化对温度变化更为敏感。     

温度和湿度对我国内蒙古羊草草原土壤净氮矿化的影响

土壤氮素的矿化是反映土壤供氮能力的重要因素之一 ,也是目前国内外研究的热点。通过测定内蒙古典型羊草草原自由放牧地土壤净氮矿化量和净氮矿化速率 ,揭示影响草地生态系统土壤氮循环过程的有关机理 ,为草地生态系统建模提供理论依据。在实验室条件下 ,运用恒温恒湿培养箱控制土壤的温度与湿度 ,测定羊草草原长期自由放牧地土壤氮素矿化量的积累。将不同水分含量的土柱分别放在温度为 - 10℃、0℃、5℃、15℃、2 5℃和 35℃的恒温恒湿培养箱中培养 ,培养 1、2、3、5周后取出 ,分析培养前后的 NH 4- N和 NO- 3- N含量 ,以确定土壤净氮矿化 (NH 4- N NO- 3- N)的累积和不同时间段内的矿化速率。结果表明 :不同处理温度和水分之间的差异均达到显著水平 (p<0 .0 0 0 1)。温度和水分之间具有显著的交互作用 (p<0 .0 0 0 1)。随着培养时间的延长 ,矿化氮累积量增加 ,但是矿化速率下降     

大兴安岭北部天然针叶林土壤氮矿化特征

采用顶盖埋管法对大兴安岭地区天然针叶林(樟子松林、樟子松-兴安落叶松混交林和兴安落叶松林)土壤铵态氮(NH~+_4-N)、硝态氮(NO~-_3-N)、净氮矿化速率进行研究,并探索土壤理化性质与氮矿化之间的相关性,为大兴安岭地区森林生态系统土壤养分管理及森林经营提供帮助。结果表明:观测期内(5—10月)3种林型土壤无机氮变化范围为31.51—70.42 mg/kg,以NH~+_4-N形式存在为主,占比达90%以上,且与纯林相比混交林土壤无机氮含量较高。3种林型土壤净氮矿化、净氨化、净硝化速率月变化趋势呈V型,7、8月表现为负值,其他月份为正值。净氮矿化速率变化范围樟子松林为-0.54—1.28 mg kg~(-1) d~(-1)、樟子松-兴安落叶松混交林为-0.13—0.55 mg kg~(-1) d~(-1)、兴安落叶松林为-0.80—1.05 mg kg~(-1) d~(-1)。土壤净氨化过程在土壤氮矿化中占主要地位,占比达60%以上。3种林型土壤净氮矿化、净氨化及净硝化速率垂直差异显著,0—10 cm土层矿化作用明显高于10—20 cm土层(P0.05)。土壤氮矿化速率与土壤含水量、土壤有机碳含量、土壤C/N、枯落物全氮含量和枯落物C/N均存在显著相关性。不同类型的森林土壤及枯落物的质量也存在差异,进而影响土壤氮矿化特征。     

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.     

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.     

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.     

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.