The Effect of N Deposition on Nitrous Oxide and Nitric Oxide Emissions from Temperate Forest Soils

Long-term and short-term N deposition effects on N₂O and NO emissions from forest soils were compared. Long-term NH₃ deposition (> 20 years) from a poultry farm to a downwind woodland (decreasing from 73 to 18 kg N ha^-1 y^-1, 30 to 110 m downwind of the farm) resulted in the re-emission of 6% and 14% of NH₃-N deposited as N₂O-N and NO-N, respectively. However, when in short-term (2-3 years) field experiments the atmospheric N deposition to mature conifer plantations was raised by fumigation with NH₃ to 15 kg N ha^-1 y^-1 or by acid mist to 48 and 96 kg N ha^-1 y^-1 the N deposited was immobilised. In the acid mist experiment more than 2 years of acid mist (48 and 96 kg N ha-1 y^-1) were required to significantly increase N₂O emissions from -0.3 μg N₂O-N m^-2 h^-1 (control) to 0.5 and 5.7 μg N₂O-N m^-2 h^-1, respectively. This suggests, that N deposition simulation studies in soil ecosystems, which have previously not been exposed to high rates of N (by deposition or fertilisation), need to be long-term. Also, measurements of N₂O and/or NO may be a non-destructive, quick indicator of the N status of the soil.     

Retention and Leaching of Elevated N Deposition in a Forest Ecosystem with Gleysols

The responses of nitrogen transformations and nitrate (NO_{_3} ^-) leaching to experimentally increased N deposition were studied in forested sub-catchments (1500 m²) with Gleysols in Central Switzerland. The aim was toinvestigate whether the increase in NO₃ ^- leaching,due to elevated N deposition, was hydrologically driven orresulted from N saturation of the forest ecosystem.Three years of continuous N addition at a rate of 30 kgNH₄NO₃-N ha^-1 yr^-1 had no effects on bulksoil N, on microbial biomass N, on K₂SO₄-extractableN concentrations in the soil, and on net nitrification rates.In contrast, N losses from the ecosystem through denitrification and NO₃ ^- leaching increased significantly. Nitrate leaching was 4 kg N ha^-1yr^-1at an ambient N deposition of 18 kg N ha^-1 yr^-1.Leaching of NO₃ ^- at elevated N deposition was 8 kg Nha^-1 yr^-1. Highest NO₃ ^- leaching occurredduring snowmelt. Ammonium was effectively retained within theuppermost centimetres of the soil as shown by the absence ofNH₄ ⁺ in the soil solution collected with microsuction cups. Quantifying the N fluxes indicated that 80% ofthe added N were retained in the forest ecosystem.Discharge and NO₃ ^- concentrations of the outflow from the sub-catchments responded to rainfall within 30 min. The water chemistry of the sub-catchment outflow showed thatduring storms, a large part of the runoff from this Gleysol derived from precipitation and from water which had interactedonly with the topsoil. This suggests a dominance of near-surface flow and/or preferential transport through this soil. The contact time of the water with the soil matrix wassufficient to retain NH₄ ⁺, but insufficient for a complete retention of NO₃ ^-. At this site with soilsclose to water saturation, the increase in NO₃ ^- leaching by 4 kg N ha^-1 yr^-1 through elevated N inputsappeared to be due to the bypassing of the soil and the rootsystem rather than to a soil-internal N surplus.     

Effects of Nitrogen Deposition on Nitrous Oxide Emissions from the Forest Floor

Increasing nitrogen deposition due to human activity might have a serious impact on ecosystem functions such as the nitrogen transformations conducted by microbes. We therefore focused on nitrous oxide (N₂O) production as an indicator of soil microbial activity. The rates of N₂O emission from the forest floor were measured every two weeks in two forest stands in the central part of Japan: a red pine stand at Kannondai and a deciduous stand at Yasato. Nitrogen deposition rates by throughfall were 30.6 kg N ha^?1 y^?1 at Kannondai and 15.7 at Yasato. The rates of N₂O emission ranged from 0.5 to 14.2 µg N m^?2 h^?1 (mean 4.5) at Kannondai and from 0.2 to 7.0 µg N m^?2 h^?1 (mean 2.3) at Yasato. The N₂O emission rate showed significant positive relationships with soil temperature and nitrogen deposition during the preceding two weeks. The annual emission rates of N₂O were 0.38 kg N ha^?1 y^?1 at Kannondai and 0.20 at Yasato. As a the annual nitrogen deposition, these rates were 1.23% at Kannondai and 1.27% at Yasato.     

高氮和NO2-对中亚热带森林土壤N2O和NO产生的影响

利用15N同位素标记方法,研究在两种水分条件即60%和90% WHC下,添加硝酸盐(NH4NO3, 300mgN kg-1)和亚硝酸盐(NaNO2, 1mgN kg-1)对中亚热带天然森林土壤N2O和NO产生过程及途径的影响。结果表明,在含水量为60% WHC的情况下,高氮输入显著抑制了N2O和NO的产生(p<0.01);但当含水量增为90% WHC后,实验9h内抑制N2O产生,之后转为促进。所有未灭菌处理在添加NO2-后高氮抑制均立即解除并大量产生N2O和NO,与对照成显著差异(p<0.01)。在60% WHC条件下,这种情况维持时间较短(21h),但如果含水量高(90% WHC)这种情况会持续很长时间(2wk以上),说明水分有效性的提高和外源NO2-在高氮抑制解除中起到重要作用。本实验中N2O主要来源于土壤反硝化过程,而且加入未标记NO2-后导致杂合的N2O(14N15NO)分子在实验21h内迅速增加,表明这种森林土壤的反硝化过程可能主要是通过真菌的“共脱氮”来实现,其贡献率可多达80%以上。Spearman等级相关分析表明未灭菌土壤NO的产生速率与N2O产生速率成显著正相关性(p<0.05),土壤含水量越低二者相关性越高。灭菌土壤添加NO2-能比未灭菌土壤产生更多的NO,但却几乎不产生N2O,表明酸性土壤的化学反硝化对NO的贡献要大于N2O。     

Soil Zinc Transformations as Affected by Applied Zinc and Organic Materials

Information on soil zinc (Zn) distribution is essential for understanding its chemical reactions and bioavailability. An experiment was conducted to evaluate the effect of wheat straw, cow manure, and vermicompost applied with Zn rates on Zn distribution in a calcareous soil. A sequential extraction scheme was used to fractionate Zn into soluble and exchangeable, bound to carbonate, organically bound, bound to manganese (Mn) oxide, bound to amorphous iron (Fe) oxide, bound to crystalline Fe oxide, and residual forms. In untreated soil, Zn was mainly in the residual fraction. Increasing rates of applied Zn increased all forms of Zn. Carbonate and residual forms showed the greatest increase. Organic materials application increased all fractions, except Mn-oxide form, and this increase was more pronounced for the organically bound form. Concentration of soluble, exchangeable, and organically bound forms was greatest in cow manure–amended samples as compared to other organic materials, suggesting that cow manure contained more bioavailable Zn than other organic materials.     

Formation and Deposition of Ozone in a Red Pine Forest

Concentrations of ozone and nitrogen oxides, together with air temperature and solar radiation intensity, were measured at several heights on a tower standing through the canopy of a red pine forest in summer and in autumn. In the summer observation, the diurnal variation patterns of ozone concentration both above and below the canopy were all similar and parallel to the solar radiation intensity. Using the data collected immediately above the canopy, deviation from the Leighton relationship and variations of concentration sums [O₃] + [NO] and [NO₂] + [NO] were examined, and as a result, it was supposedthat ozone was photochemically formed there in the daytime, probably because hydrocarbons emitted from pine trees broke the photostationary state among ozone and nitrogen oxides. The vertical temperature profile exhibited an inversion at the leaf-layer, which must have hindered vertical mixing of the air and made the trunk space more or less isolated from the upper atmosphere. These observations led to an idea that the similarity of the ozone variation pattern at every height was caused by the photochemical formation that proceeded simultaneously above and below the canopy rather than by vertical transport. Such situations of ozone formation were supported by observation of two maximums in the ozone vertical profile, one immediately above the canopy and another in the trunk space. Another feature of the ozone profile was a deep minimum in the leaf layer, which indicated ozone deposition onto leaf surfaces. This study thus revealed concurrence of ozone formation and deposition, and left two potentially important implications worthy of further investigation: (1) a forest is not always a sink but can be a source of ozone in sunlit conditions, and (2) deposition of ozone to trees can take place not only from outside but also from inside of a forest. In the autumn observation, however, the ozone formation was barely recognizable above the canopy and no longer found in the trunk space; in addition, the ozone concentration minimum in the leaf layer disappeared, suggesting that the deposition or removal was dependent on temperature.     

Consequences of N Deposition to Forest Ecosystems - Recent Results and Future Research Needs

Wet and dry deposition of atmospheric nitrogen (N) compounds into forest ecosystems and their effect on physical, chemical and microbial processes in the soil has attracted considerable attention for many years. Still the consequences of atmospheric N deposition on N metabolism of trees and its interaction with soil microbial processes has only recently been studied. Atmospheric N deposited to the leaves is thought to enter the general N metabolism of the leaves, but the processes involved, the interaction with different metabolic pathways, and the connection between injury by atmospheric N and its metabolic conversion are largely unknown. Laboratory and field experiments have shown that N of atmospheric NO₂ and NH₃, deposited to the leaves of trees, is subject to long-distance transport in the phloem to the roots. This allocation can result in considerable decline of N uptake by the roots. Apparently, the flux of N from the soil into the roots can be down-regulated to an extent that equals N influx into the leaves. This down-regulation is not mediated by generally enhanced amino-N contents, but by elevated levels of particular amino acids. Field experiments confirm these results from laboratory studies: Nitrate (NO₃) uptake by the roots of trees at a field sites exposed to high loads of atmospheric N is negligible, provided concentrations of Gln in the roots are high. At the ecosystem level, consequences of reduced N uptake by the roots of trees exposed to high loads of atmospheric N are (1) an increased availability of N for soil microbial processes, (2) enhanced emission of gaseous N-oxides from the soil, and (3) elevated leaching of NO₃ into the ground water. How recent forest management practices aimed at transforming uniform monocultures to more structured species-rich forests will interact with these processes remains to be seen. Possible implications of these forest management practices on N metabolism in trees and N conversion in the soil are discussed particularly in relation to atmospheric N deposition.     

N Mineralization as Affected by Long-Term N Fertilization and Its Relationship with Crop N Uptake.

A field experiment established in 1997 was conducted to study the effect of long-term N fertilizer application on N mineralization in a paddy soil determined using a laboratory anaerobic incubation followed with a field incubation and to measure the relationship between in situ N mineralization and crop N uptake. To estimate N mineralization in the laboratory, soil samples were collected from plots with N application at different rates for six years and were incubated. Soils treated with fertilizer N mineralized more N than unfertilized soils and mineralization increased with N application rates. Also, the fraction of total N mineralized increased with increasing N fertilizer application. These findings meant that a substantial portion of previously applied N could be recovered slowly over time in subsequent crops. The field incubation of the plot receiving no fertilizer N showed that the NH4^＋-N concentration varied greatly during the rice-growing season and seasonal changes of N mineralization were due more to accumulation of NH4^＋-N than NO3^-N. Hice N uptake increased up to a maximum of 82 kg N ha^-1 during the season. The close agreement found between in situ N mineralization and rice N uptake suggested that the measurement of in situ N mineralization could provide useful recommendations for adequate fertilizer N application.     

Simulation of Increased Nitrogen Deposition to a Montane Forest Ecosystem: Partitioning of the Added 15N

Nitrogen (N) was added over two years to a spruce-dominated (Picea abies) montane forest at Alptal, central Switzerland. A solution of ammonium nitrate (NH₄NO₂) was frequently sprinkled on the forest floor (1500 m²) to simulate an additional input of 30 kg N ha^-1 yr^-1 over the ambient 12 kg bulk inorganic N deposition. The added nitrogen was labelled with ¹⁵NH₄ ¹⁵NO₃ during the first year. Results are compared to a control plot. Neither the trees nor the ground vegetation showed any increase in their N content. Only 4.1% of N in the ground vegetation came from the N addition. Current-year needles contained 11 mg N g^-1 dry weight, of which only 2% was from labelled N; older needles had approximately half as much ¹⁵N. The uptake from the treatment was therefore very small. Redistribution of N also took place in the trunks: 1 to 2-year-old wood contained 0.7% labelled N, tree rings dating back 3 to 14 years contained 0.4%. Altogether, the above-ground vegetation took up 12% of the labelled N. Most ¹⁵N was recovered in the soil: 13% in litter and roots, 63% in the sieved soil. Nitrate leaching accounted for 10%. Factors thought to be influencing N uptake are discussed in relation to plant use of N and soil conditions.     

六盘山林下地被物分布特征

对六盘山不同植被的地被物分布特征进行研究发现,华北落叶松、白桦和油松林下草本植物物种丰富。辽东栎林枯落物叶片宽厚肥大,分解后枯落物较为松软,厚度最大,枯落物总储量仅次于华北落叶松。不同森林植被枯落物中,针叶枯落物所占比例最大。未分解层储量／厚度比值小于半分解层,9月份针叶林枯落物储量／厚度比值最大。天然次生林辽东栎林植被结构复杂,尽管不断有枯落物补充,枯落物却能迅速破碎分解,一方面能够迅速补充土壤养分含量,另一方面能够在地表形成更为疏松的枯落物层,因此7—9月份辽东栎林枯落物变化较大。     

Soil C/N Ratio as Affected by Climate: An Ecological Factor of Forest NO3 − Leaching

The soil nitrogen cycle was investigated for several watershed forests of which stream waters have distinctively different nitrate (NO₃ ^?) concentrations. In a watershed with stream water NO₃ ^? of more than 100 µM, soil NO₃ ^? content increased even beneath the rooting zone, revealing "nitrogen saturation" status. A laboratory soil experiment demonstrated that the proportion of net NO₃ ^? production to CO₂ production was largely regulated by a soil C/N ratio, suggesting a key parameter for NO₃ ^? abundance. In the respective watershed soils, little nitrogen was actually present as NO₃ ^? above a soil C/N ratio of 20. The annual mean soil temperature recorded at the sites was correlated with a shift in the C/N ratio in watershed soils (a soil C/N ratio increase of 0.5 per 1°C decrease) along the stream NO₃ ^? gradient of 30 fold. The results suggest that soil microbial metabolisms affected by C/N ratio may be a direct agent regulating NO₃ ^? leaching from watersheds under the influence of an atmospheric nitrogen load and climate.     

Long-Term Soil Reaction Changes in a Temperate Beech Forest Subject to Past Alkaline Pollution

Changes in deposition exert effects on forests. Some evidence for a slow recovery of strongly alkalised forest soils after a reduction in alkaline pollution exists, but the recovery rate is little known. The objective of this study was to estimate temporal soil reaction changes. For this purpose, measurements of soil reaction under a beech forest near magnesite works in Central Slovakia were taken in 1991 and 2006, following the alkaline pollution reduction in 1992. As a result, the mean active soil reaction decreased from pH 7.8 to 6.6. Beyond the range of beech stemflow, which amplifies water and acid pollution inputs into soils locally, soil reaction dropped from pH 7.8 to 6.8. The effect of stemflow on local exchangeable reaction minima was detected even before the pollution reduction. The logarithmic function fitted on the pH data indicates considerable differences between neutralisation rates within and outside the stemflow zone.     

Effect of Simulated N Deposition on Soil Exchangeable Cations in Three Forest Types of Subtropical China

The effects of simulated nitrogen (N) deposition on soil exchangeable cations were studied in three forest types of subtropical China.Four N treatments with three replications were designed for the monsoon evergreen broadleaf forest (mature forest):control (0 kg N ha-1 year-1),low N (50 kg N ha-1 year-1),medium N (100 kg N ha-1 year-1) and high N (150 kg N ha-1 ycar-1),and only three treatments (i.e.,control,low N,medium N) were established for the pine and mixed forests.Nitrogen had been applied continuously for 26 months before the measurement.The mature forest responded more rapidly and intensively to N additions than the pine and mixed forests,and exhibited some significant negative symptoms,e.g.,soil acidification,Al mobilization and leaching of base cations from soil.The pine and mixed forests responded slowly to N additions and exhibited no significant response of soil cations.Response of soil exchangeable cations to N deposition varied in the forests of subtropical China,depending on soil N status and land-nse history.     

Input of Atmospheric Particles into Forest Stands by Dry Deposition

In this study the dry input of atmospheric particles into a forest stand is quantified. A wash-off-method using the natural leaf surfaces as collectors of the dry deposition was chosen. The direct on-site-measurement on living branches were achieved in a spruce stand (Picea abies (L.) Karst) at Solling, Germany. The ion exchange processes occurring on natural branches can reliably be quantified through immediate sequential washings. In order to calculate also the gas dry deposition of those trace elements which occur in both particle and gas phases, a resistance model was used. From these results the deposition velocity of particulate aerosol components into the forest stand was calculated. Dry particle deposition constitutes an important part of the total matter input into the forest ecosystem. Just the nitrogen input into Solling only by dry deposition (from particle-, mist-, and gas-deposition) with about 30 kg N ha^?1 a^?1 already exceeds the critical load of 20 kg N ha^?1 a^?1 by far, and this is without even considering the additional load by wet deposition which amounts to 15 kg ha^?1 a^?1. These findings are of greatest ecological importance, as the damage to the stability of the forest ecosystem caused by increased nitrogen input is considerable. Only a quick and drastic reduction of sulphur and nitrogen emissions could stop the further increase of the nutritient imbalance and the progressing acidification of this ecosystem.     

Soil Quality Indicators as Affected by Shallow Tillage in a Vineyard Grown in a Semiarid Mediterranean Environment

Within the Mediterranean basin, soil tillage enhances the mineralisation of soil organic matter. We assessed the short‐term impact of shallow tillage [field cultivator (FC), rotary tiller (RT) and spading machine (SM)] on some soil quality indicators [bulk density, water‐stable aggregates, total and labile organic C pools (microbial biomass and extractable organic C), soil respiration and related eco‐physiological indexes] in a Sicilian vineyard. Also no tillage was included. We hypothesized that (i) RT and FC worsened soil quality indicators more than SM, and (ii) within the same tillage system, labile C pools, soil respiration and eco‐physiological indexes will respond more efficiently than chemical and physical soil properties since the tillage starts. The experiment started at March 2009, and each tillage type was applied three times per year (March or April, May and June), with soil tilled up to 15‐cm depth. Soil was sampled (0–15 and 15–30‐cm depth) in March 2009, April 2010, May 2012 and June 2014. SM was very effective in preserving soil organic matter pool and in improving any monitored soil quality indicator, similarly to no tillage. By contrast, RT was the most deleterious machine as it worsened most investigated indicators. Such deleterious effects were due to drastic disruption of soil aggregates and consequent exposition of protected soil organic matter to further microbial mineralization. Labile organic C pools and microbial quotients were the most responsive soil parameters for assessing the impact of shallow tillage on soil quality, even in the short term (<5 years). Copyright © 2016 John Wiley & Sons, Ltd.     

Atmospheric Deposition of Acidifying Components to a Japanese Cedar Forest

One-year field measurements were conducted in a Japanese cedar (Cryptomeria japonica) forest, located in Gunma Prefecture, Japan. On the basis of the meteorological and atmospheric concentration data, the dry deposition of SO₂, HNO₃, NO₂ and HCl was estimated using the inferential method. The annual dry deposition of H⁺ was estimated at 721 eq ha^?1yr^?1, which was 40% larger than the measured annual wet deposition of H⁺ (514 eq ha^?1yr^?1). Therefore, dry deposition is an important pathway for the atmospheric input of H⁺ to the forest in the study site. The contribution of each gas to the dry deposition of H⁺ was as follows: SO₂, 25%; HNO₃, 32%; NO₂, 10%; and HCl, 33%. The extremely high contribution of HCl appeared to be caused by the high emission intensity of HCl due to waste incineration in the site region. The differences between estimated deposition and throughfall and stemflow measurements indicated that about 80% of the total deposition of H⁺ was taken up by the canopy.     

Soil Quality of a Mature Alley Cropping Agroforestry System in Temperate North America

Long-term effects of alley cropping on soils in the temperate zone are not widely known. Management, landscape, and soil depth effects on soil physical and biological properties were examined in a silver maple (Acer saccharinum L.) no-till corn (Zea mays L.)- soybean (Glycine max L.) rotation established in 1990 in northeast Missouri. Soils from crop alleys and tree rows were collected along transects traversing upper to lower landscape positions at three depths. Fluorescein diacetate hydrolase (FDA), β-glucosidase, β-glucosaminidase, and dehydrogenase activities were measured. Soil bulk density, aggregate stability, carbon (C), nitrogen N), and enzyme activities decreased with soil depth in alley and tree rows except for glucosaminidase. Soil physical and biological parameters did not differ significantly between alley and tree row. Landscape position effects were not significant for management or depth. Tree establishment improves soil quality in the crop alley as the system matures with improvements extended throughout the soil profile.     

施肥和耕作方式对棕壤微生物生物量碳氮的影响

以辽宁省昌图县主要粮食产区为研究对象,分析施肥(化肥、玉米秸秆和有机肥)和耕作方式(旋耕、深松和隔行深松)对棕壤微生物生物量碳、氮(SMB-C、-N)的影响。结果显示,与对照处理相比,施用化肥处理SMB-C、-N分别下降14.3%和13.3%,秸秆回田处理下降12.3%和12.2%,而施用有机肥则显著提高SMB-C、-N,幅度分别为31.7%和38.6%。说明施用化肥明显降低土壤微生物生物量,配施秸秆在短时期内无法缓解化肥施用对微生物生物量的抑制作用,而有机肥却能迅速缓解抑制作用,提高土壤微生物生物量。深松(行行)和隔行深松作为保护性土壤耕作方式,与常规耕作(NPK处理)相比,显著提高了SMB-C、-N,其中深松提高幅度为56.8%和77.0%,隔行深松则为27.7%和36.1%。试验伊始,有机肥处理SMB-C/SOC(土壤有机碳)最高,达到1.57,至实验结束,深松处理最高,为2.15,其次为隔行深松处理。有机肥处理SMB-N/TN(土壤全氮)受年际影响上下波动,深松和隔行深松处理呈现先下降后上升的态势。深松和隔行深松能有效保存土壤养分含量,特别是活性碳、氮库,是土壤肥力贫瘠地区推荐的土壤耕作方式,从人力和机械消耗角度而言,隔行深松更有利于我国农业可持续发展。     

森林采伐对林地表层土壤主要特征及其生态过程的影响

森林采伐是森林经营过程中的一类常见作业,而森林重要生态过程都离不开林地表层(土壤及覆盖物),为此,理解和把握森林采伐对林地表层的影响对于合理经营和管理森林生态系统,实现生态系统的可持续发展等具有重要意义。本文在简单回顾了采伐对森林组成、结构及其功能的影响基础上;介绍了森林采伐对林地表层温度、湿度、土壤结构、pH值、养分(C、N、P、S)等理化特性的影响;分析了土壤生物对森林采伐的反馈过程;阐述了森林采伐对林地水文、C、N转化等生态过程的作用。最后,从研究方法、研究目标和研究内容三个方面提出森林采伐影响林地表层研究的发展趋势,指出森林采伐的边缘效应和空间异质性;森林采伐后土壤生物的响应;森林采伐后的水、C、N转化和循环等生态过程及其耦合作用是目前及今后研究的三大热点。