Nitrification and nitrifying potential of tropical and subtropical soils

Summary Nitrification was measured in five different soils (slate alluvial soil, sandstone shale alluvial soil, sandstone shale and slate alluvial soil, red soil, and Taiwan clay). In these soils different lag periods were recorded before the onset of nitrification. Nitrifying activity was highest in sandstone shale alluvial soil and the lowest in acidic red soil. A part from those in the red soil, the numbers of nitrifying bacteria detected were all higher than numbers reported in temperate soils. However, there were no clear relationships between the numbers of nitrifying bacteria and the rate of nitrification in these soils. When soil cores were incubated for 3 weeks, no NO _inf2 ^sup- or NO _inf3 ^sup- was defected in the slate alluvial soil. This was ascribed to denitrification.     

土样制备和保存方法对亚热带土壤反硝化的影响

比较了两种土样制备和保存方法对厌氧培养1周内土壤反硝化及矿化的动态影响。试验结果表明,强烈风干后并经长期存放过的土样显著促进了NO3--N浓度降低速率和N2O排放速率的提高,其反硝化速率和矿化速率分别较稍微风干后无存放时间(即立即开始培养试验)的土样提高了47.3%和31.0%。强烈风干土有机C矿化作用的增强以及易矿化有效态C含量的提高是促进反硝化作用增强的主要原因。风干程度和存放时间对反硝化的促进程度取决于其对有机质矿化影响的相对大小,对有机质矿化的影响越大,反硝化强度增加的幅度也越大。由试验结果可推测,利用风干土的实验室培养方法测定得到的土壤反硝化势可能会过高估计田间原位测定的反硝化势。     

Production and consumption of N2O during denitrification in subtropical soils of China

Purpose

Nitrous oxide (N₂O) production and reduction rates are dependent on the interactions with each other and it is therefore important to evaluate them within the context of simultaneously operating N₂O emission and reduction. The objective of this study was to quantify the simultaneously occurring N₂O emission and reduction across a range of subtropical soils in China, to gain a mechanistic understanding of potential N₂O dynamics under the denitrification condition and their important drivers, and to evaluate the potential role of the subtropical soils as either sources or sinks of N₂O through denitrification.

Materials and methods

Soils (45, from a range of different land uses and soil parent materials) were collected from the subtropical region of Jiangxi Province, China, and tested for their potential capacity for N₂O emission and N₂O reduction to N₂ during denitrification. N₂O emission and reduction were determined in a closed system under N₂ headspace after the soils were treated with 200?mg?kg^?1 NO ₃ ^? -N and incubation at 30?°C for 28?days. The soil physical and chemical properties, the temporal variations in headspace N₂O concentration, and NO ₃ ^? -N and NH ₄ ⁺ -N concentrations in the soil slurry were measured.

Results and discussion

Variations in N₂O concentration (N) over incubation time (t) were consistent with an equation in which average R ²?=?0.84?±?0.11 (p?<?0.05): $ N = A \times \left( {1 - \exp \left( { - {k_1} \times t} \right)} \right) - B \times \exp \left( {{k_2} \times t} \right) $ , where A is the total N₂O emission during the incubation, B is a constant, and k ₁ and k ₂ are the N₂O emission constant and reduction constants, respectively. The results of the simulation showed that k ₁ was greater than k ₂. The reduced amount of NO ₃ ^? -N in the first 7?days of incubation and the N₂O emission rate (the percentage of A value relative to the amount of NO ₃ ^? -N reduced during the 28-day incubation, R _n) were able to explain 82.9?% (p?<?0.01) of the variation in total N₂O emission (A) during the incubation for the soil samples studied, indicating that the total amount of N₂O emitted was determined predominately by denitrification capacity. Soil organic carbon content and soil nitrogen mineralization are the key factors that determine differences in the amounts of reduced NO ₃ ^? -N among the soil samples. The R _n value decreased with increasing k ₂ (p?<?0.01), indicating that soils with higher N₂O reduction capacity under these incubation conditions would emit less N₂O per unit of denitrified NO ₃ ^? -N than the other soils. Results are valuable in the evaluation of net N₂O emissions in the subtropical soils and the global N budget.

Conclusions

In a closed, anaerobic system, variations in N₂O concentration in the headspace over the incubation time were found to be compatible with a nonlinear equation. Soil organic carbon and the amount of NH ₄ ⁺ -N mineralized from the organic N during the first 7?days of incubation are the key factors that determine differences in the N₂O emission constant (k ₁), the N₂O reduction constant (k ₂), the total N₂O emission during the incubation (A) and the N₂O emission rate (R _n).     

Effects of vegetation regime on denitrification potential in two tropical volcanic soils

Effects of vegetation and nutrient availability on potentail denitrification rates were studied in two volcanic, alluvial-terrace soils in lowland Costa Rica that differ greatly in weathering stage and thus in availability of P and base cations. Potential denitrification rates were significantly higher in plots where vegetation had been left undisturbed than in plots where all vegetation had been removed continuously, and were higher on the less fertile of the two soils. The potential denitrification rates were correlated strongly with respiration rates, levels of mineralizable N, microbial biomass, and moisture content, and moderately well with concentrations of extractable NH _inf4 ^sup+ , Kjeldahl N, and total C. In all plots, denitrification rates were stimulated by the removal of O₂ and by the addition of glucose but not by the addition of water or NO _inf3 ^sup- .This is Paper 2772 of the Forest Research Laboratory, Oregon State University     

Simulation of the dynamics of different forms of radiocesium in soils of terrestrial ecosystems

A refined imitational model of the seasonal dynamics of radiocesium in soils of forest ecosystems is suggested. This model has been used to predict the dynamics of biologically available and unavailable forms of radiocesium in an artificially contaminated sandy soddy-podzolic soil of an oak ecosystem for a period of 50 years.     

Citric acid enhances the mobilization of organic phosphorus in subtropical and tropical forest soils

Low-molecular-weight organic acids are considered to be effective in the release of inorganic phosphorus (P) but their effectiveness to mobilize organic P is not well understood. The aim of this study was to examine the role of three common organic acids (maleic, oxalic, and citric acids) in mobilizing organic P in forest soils. Soil samples tested in this study were collected from either native or plantation forests in subtropical and tropical Australia with 16–87% of soil total P being in organic form. At a concentration of 10 mM organic acid kg^?1 soil, all three organic acids did not enhance the release of inorganic P as compared with water, whereas the three organic acids displayed different capacities in mobilizing organic P. Citric acid significantly enhanced the solubilization of organic P by 34.7% as compared with water; whereas no significant differences were observed in the mobilization of organic P among maleic acid, oxalic acids, and water. The amount of organic P solubilized by citric acid was not correlated with soil pH but increased with increasing soil organic P as the values were below 200 mg kg.^?1 The possible mechanisms of the effective mobilization of organic P by citric acid were discussed. Our results implied that organic P might play an important role in P nutrition of plants in subtropical and tropical forests due to its substantial proportion in soil P and the effective mobilization by organic acids.     

Available organic nitrogen in temperate, subtropical, and tropical soils extracted with different solutions

Extraction of organic N by chemical solutions has been used to assess the amount of available N in soil. We tested the efficiency of several solutions in extracting organic N from tropical, subtropical and temperate soils. A conventional 0.067 M phosphate buffer successfully extracted organic N from all 23 soils examined. High-performance size exclusion chromatograms showed a single peak at about 7,800 Da for all phosphate buffer extracts irrespective of soil types. The peak area correlated with the organic N concentration of extracts. Tropical soils had lower retention of organic N than other soils according to the conventional and sequential extraction with phosphate buffer. Organic N extracted with sulfuric acid was significantly (P < 0.001) correlated with the amount of extracted Fe, suggesting that Fe might play a role in the retention of organic N in soil.     

Forms and buffering potential of aluminum in tropical and subtropical acid soils cultivated with Pinus taeda L

Purpose

Several interactions between Al and the solid phase of soil influence Al buffering in soil solution. This work evaluated soils cultivated with Pinus taeda L. to determine Al forms in organic and mineral horizons using various extraction methods and to relate acidity with clay mineralogy.

Materials and methods

Organic and mineral horizons of 10 soil profiles (up to 2.1 m deep) in southern Brazil were sampled. Organic horizons were separated into fresh, aged, and fermented/humified litter. The following Al extraction methods were utilized: 0.5 mol L^?1 pH 2.8 CuCl₂–Al complexed in organic matter; 1.0 mol L^?1 KCl–exchangeable Al; water–Al soluble in soil solution; HF concentrated?+?HNO₃ concentrated?+?H₂O₂ 30% (v/v)–total Al. Six sequential extractions were carried out to isolate different forms of amorphous minerals that can buffer Al on soil solution: 0.05 and 0.1 mol L^?1 sodium pyrophosphate; 0.1 and 0.2 mol L^?1 ammonium oxalate; 0.25 and 0.5 mol L^?1 NaOH. Samples of clay were also analyzed by XRD.

Results and discussion

There was a clear effect of litter age on increasing total Al concentration. In the aged litter and fermented and/or humified litter, levels of total Al were 1.4 to 3.8 and 1.5 to 7.8 times greater than in fresh litter, respectively. The CuCl₂ method had higher Al extraction capacity than the KCl method for litter. The lowest Al–pyrophosphate values were observed in the Oxisol, which also had a predominance of gibbsite and the lowest levels of Al–KCl and Al–CuCl₂. There was an inverse relationship between degree of soil weathering and soluble and exchangeable Al in soils. Available Al increased with higher Si proportion in minerals of the clay fraction (2:1?>?1:1?>?0:1).

Conclusions

The worst scenario was soils with the combination of high soluble and exchangeable Al levels and high concentrations of amorphous forms of Al minerals. The best predictors of Al accumulation in the youngest litter horizon were extractions of amorphous minerals with pyrophosphate and NaOH. These extractors are normally used to predict the level of Al buffering in soils. Organic matter had less influence on Al dynamics in soils.

     

Nitrate reduction and denitrification in flooded soils

It has been well known that the utilization rate of ammonium sulfate fertilizer by lowland rice was as low as 40 percent of the applied ammonium. This low utilization rate was due to nitrogen loss from the paddy field. There are problems as to whether the loss of nitrogen from the flooded soil was caused by the nitrification of ammonium nitrogen and its subsequent denitrification, by the evaporation of ammonium, or by the leaching of ammonium-nitrogen with percolated water. Shioiri and his associatesll clarified that this loss of nitrogen resulted largely from denitrification through nitrate reduction in 1942. After the paddy soil is flooded with water, the oxygen in furrow slice is consumed by aerobic microorganisms, and then the soil becomes reductive. Conversely the oxigen is supplied to the soil through the water from the air, and from various kinds of algae and duckweeds, which produce oxygen through photosynthesis. At the early stage the reduction by oxygen consumption is superior to the oxidation by oxygen supply, the furrow slice is reductive, and is bluish gray in color due to the presence of certain ferrous compounds. After months flooding, the oxygen supply becomes superior to oxygen consumption and the uppermost layer of furrow slice becomes brown in color due to the presence of ferric compounds. This layer corresponds to an “oxidised layer” where microorganisms live aerobically. In this oxidized layer the nitrifying bacteria converts ammonium nitrogen into nitrate nitrogen which is percolated into the reduced layer, and lost through denitrification. A large amount of ammonium sulfate fertilizer is then dressed at the uppermost layer, after flooding, the loss of nitrogen through denitrification is serious.     

Microclimate and moisture dynamics of wood decomposing in terrestrial ecosystems

The theoretical relationship between microclimate, temperature and moisture in decaying branchwood is considered and methods of expressing moisture content discussed. Field measurements were obtained over a 1-yr period. The annual pattern of branch temperature and moisture contents consisted of a cold wet winter period when branch moisture contents are at or above saturation, low temperatures and high rainfall prevent drying. When temperatures rise in spring the trend is for branches to begin gradually to dry. During the summer months moisture contents are not constant and vary considerably from day to day with fairly rapid drying following periods of wetting. Moisture contents only rarely fell below the fibre saturation point. With the approach of autumn and winter the overall trend is for a gradual increase in moisture content but with periods of slow drying occurring whilst temperatures are still high enough to allow this.     

Monitoring terrestrial ecosystems by analysis of nutrient export

Current methodology for environmental impact assessment relies heavily on population parameters to detect ecological effects of perturbation. We believe that recent advances in ecosystem analysis permit the identification of monitoring points that reflect changes in the total system. Focusing on mechanisms of ecosystem homeostasis, we suggest soil nutrient loss as a sensitive, holistic measure of ecological effects. In three separate studies, attempts were made to detect the effects of toxic substances by monitoring relevant population parameters. In each case, disturbance could be detected in nutrient cycling, but no significant change was evident in the population/community parameters. These results indicate that indices of total ecosystem function may be feasible.     

Nitrous oxide production and denitrification in Scottish arable soils

Nitrous oxide (N₂O) emissions and concentrations in the soil atmosphere were measured at a number of sites of differing soil type in south-east Scotland between 1985 and 1988. Concentrations followed log-normal distributions and were significantly affected by soil type, tillage treatment, and nitrate application rate. The shape of the profiles suggested significant consumption in the upper 5 cm, making calculations of emission rates using Fick's Law unsatisfactory. Emission rates measured using closed flux chambers were at least one order of magnitude smaller from heavier-textured arable soils than from lighter ones. Denitrification fluxes measured by field application of the acetylene inhibition technique were lowest in a clay loam, and highest in an alluvial sandy loam; this was attributed to a failure to achieve a satisfactory distribution of acetylene in the heavier soil. Denitrification rates in soil cores generally exceeded measured surface fluxes; incubation at decreased oxygen concentrations typical of those measured in the field produced a further significant increase. Core incubation should be used as an alternative to in situ field measurement only if the oxygen concentration in the incubation vessels is adjusted to mimic that in the field; otherwise denitrification rates may be significantly underestimated.     

Anaerobic methane oxidation in soils and water ecosystems

The process of anaerobic methane oxidation has been studied for over 30 years on the example of bottom marine sediments and fresh water ecosystems. This paper presents a review of the results of these investigations. It is also demonstrated that this process can proceed not only in submerged but also in drained peat and automorphic sod-podzol soils. The latter soils continue to absorb methane after anaerobic conditions are created and an inhibitor of methane monooxygenase (acetylene) is introduced. Oxidated compounds (nitrates, sulphates) are stimulatory to gas absorption; deoxidated nitrogen compounds (ammonium chloride) do not produce significant changes. Incubation with the addition of nitrates and sulphates in an atmosphere of argon and methane results in an increase in the fraction and abundance of archaea in the soil. This is in agreement with the data obtained for aquatic inhabits.     

Parameters of the productivity of soil algae in terrestrial ecosystems

A review is presented of the recent state of the problem of soil algae productivity in terrestrial ecosystems on the basis of literature data and our own research. It is shown that the organic matter accumulated by soil algae is highly mobile. The following parameters were analyzed: the biological production, the time of the biomass turnover, and the rate of the algal organic matter renewal in the soil. The average monthly production of algae ranged from 0.9 to 765 g/m², the rate of the organic matter renewal ranged from 0.03 to 25.5 g/m² per day, and the time of the algal biomass renewal ranged from 0.1 to 7 days.     

Nitrogen isotope discrimination in denitrification of nitrate in soils

Nitrogen isotope discrimination during denitrification in soils of nitrate containing natural concentrations of ¹⁴N and ¹⁵N was studied by determining the amount and the ¹⁵N content of nitrate-N and (nitrate + nitrite)-N in nitrate-treated soils incubated under anaerobic conditions (He atmosphere) for various times after treatment with glucose to promote denitrification. Analyses performed showed that the nitrate-N lost on incubation of these soils could largely be accounted for as products of denitrification (nitrite, NO. N₂O and N₂).The studies reported show that marked discrimination between ¹⁴N and ¹⁵N occurs during denitrification of nitrate in soils and that significant N isotope effects occur both in reduction of nitrate to nitrite and in reduction of nitrite to gaseous forms of N. They also indicate that the overall N isotope effect during denitrification of nitrate in soil will depend upon the tendency of the soil to accumulate nitrite under conditions that induce denitrification.It is concluded that discrimination between ¹⁴N and ¹⁵N during denitrification in soils of nitrate containing natural concentrations of these isotopes is of sufficient magnitude to invalidate the use of N isotope-ratio analyses for assessment of the contributions of soil and fertilizer N to nitrate in surface or ground waters or to nitrous oxide in the atmosphere.     

Uncertainty analysis of critical loads for terrestrial ecosystems in Russia

The goal of this study is to give a comprehensive and quantitative estimation of the uncertainty of computed in different scale nitrogen (N) and sulphur (S) critical loads (CL) values for terrestrial ecosystems of the Northern Asia, European part and the North-Western regions of Russia. The CL values are used to set goals for future deposition rates of acidifying compounds so that the environment is protected. In this research CL values for terrestrial ecosystems are determined using the expert-modelling geoinformation system (EM GIS) approach. UNCSAM software package is used as the tool for uncertainty analysis. The analysis presented here focuses on the estimation and effect of the input source uncertainties and sensitivities on the CL values in various regions under study. In spite of the region, nitrogen uptake by vegetation, nitrogen leaching from terrestrial ecosystems and the difference between deposition and uptake by plants of base cations (BC) are the most influential factors for all terrestrial ecosystems of Russia.     

气候变暖对陆地生态系统的影响

人类活动引起的温室效应导致全球气候变暖,气候变暖对全球生态环境的影响越来越受到人们的关注.作为人类赖以生存的环境主体,陆地生态系统对气候变暖将做出何种响应,更是人们关注的重点.植物物候的变化可以直观地反映某些气候变化,尤其是气候变暖.气候变暖影响植物的生长节律,进而引起植物与环境关系的改变及生态系统物质循环(如水和碳的循环)的改变.不同种类植物对气候变化的差异响应,会使植物间和动植物间的竞争与依赖关系发生深刻的变化,如北半球中高纬度地区植被生长季延长、植物提早开花、昆虫提早出现、鸟类提早产蛋以及冰川退缩、永冻土带融化、江河湖泊结冰推迟而融化提早等.本文主要从陆地生态系统的分布和演替两方面着眼,以植物和动物作为考察对象,系统论述了森林、草原、荒漠、湿地及农田等陆地生态系统在气候变暖背景下产生的变化,并从微观和宏观尺度上提出陆地生态系统变化的生态学机制,最后在技术和政策层面给出若干对策.     

亚热带丘岗区生态系统水分平衡及农业反应

通过对自然集雨区水分动态10年定位观测研究,初步明确了我国亚热带丘岗区生态系统水资源的分布特征与水平衡状况。该区域雨水丰沛,总量可维持系统水分平衡,但其时空变化大,加之蒸发变化与之错位和土壤持蓄水分性能差等因素作用,导致系统水分盈亏现象发生,水分“高盈期”的湿害和“亏缺期”的伏旱严重制约了丘岗区农业的发展。强化工程、农艺措施调控能力,提高农业水资源管理水平,是促进我国亚热带丘岗区农业持续稳定发展的技术保障。     

Atmospheric deposition in maritime environments and its impact on terrestrial ecosystems

Seasalts are the dominant chemical constituents of precipitation in maritime regions. Dry deposition of these salts is also an important process and consequently, canopy interception by forest ecosystems greatly augments wet deposition. The separation of seasalt from non-seasalt sulphur is usually accomplished by reference to the concentration ratio of other major component ions of seawater, such as sodium-, chloride-, or magnesium-to sulphate. Biogenic sulphur, from the oceans or from terrestrial ecosystems is sometimes of importance in maritime regions. Seasalts, which dominate atmospheric deposition in maritime regions can induce short-term acidification in surface waters as a result of ion-exchange reactions following storm events. The results of one large storm in western Ireland in 1991 and the recovery process in a peat soil were clearly discernible in soil water analysis. The seasalt impact on acid mineral soils can be seen in the exchangeable sodium levels and the degree of base saturation of these soils.