SOIL NITROGEN MINERALIZATION UNDER NORTHERN HARDWOOD FORESTS ALONG A SULFATE AND NITRATE DEPOSITION GRADIENT IN THE GREAT LAKES REGION

INTRODUCTIoNChangesinsoilNmineralizationratescouIdbeanearlywarningofsoilNavaila-bilityoreventualforestdeclinesinceNisoftenan.importantnutrientforgrowth(Keeneyl98O;Leaetal.l982;Vitouseketal-l982).Nitrogenmineralizationinvolvestwodistinctprocessesfammonification,inwhichNH:isformedfromorganiccom-pounds,andnitrification,theoxidationofNH:toNO3.ManystudiesofatmosphericdepositionimpactsonforestshavetargetedsoilNmineraIizationusingsimulatedaciddepositionundercontrolledlaboratoryconditions(T…     

Nitrogen dynamics across silvicultural canopy gaps in young forests of western Oregon

Silvicultural canopy gaps are emerging as an alternative management tool to accelerate development of complex forest structure in young, even-aged forests of the Pacific Northwest. The effect of gap creation on available nitrogen (N) is of concern to managers because N is often a limiting nutrient in Pacific Northwest forests. We investigated patterns of N availability in the forest floor and upper mineral soil (0–10 cm) across 6–8-year-old silvicultural canopy gaps in three 50–70-year-old Douglas-fir forests spanning a wide range of soil N capital in the Coast Range and Cascade Mountains of western Oregon. We used extractable ammonium (NH₄⁺) and nitrate (NO₃⁻) pools, net N mineralization and nitrification rates, and NH₄⁺ and NO₃⁻ ion exchange resin (IER) concentrations to quantify N availability along north-south transects run through the centers of 0.4 and 0.1 ha gaps. In addition, we measured several factors known to influence N availability, including litterfall, moisture, temperature, and decomposition rates. In general, gap-forest differences in N availability were more pronounced in the mineral soil than in the forest floor. Mineral soil extractable NH₄⁺ and NO₃⁻ pools, net N mineralization and nitrification rates, and NH₄⁺ and NO₃⁻ IER concentrations were all significantly elevated in gaps relative to adjacent forest, and in several cases exhibited significantly greater spatial variability in gaps than forest. Nitrogen availability along the edges of gaps more often resembled levels in the adjacent forest than in gap centers. For the majority of response variables, there were no significant differences between northern and southern transect positions, nor between 0.4 and 0.1 ha gaps. Forest floor and mineral soil gravimetric percent moisture and temperature showed few differences along transects, while litterfall carbon (C) inputs and litterfall C:N ratios in gaps were significantly lower than in the adjacent forest. Reciprocal transfer incubations of mineral soil samples between gap and forest positions revealed that soil originating from gaps had greater net nitrification rates than forest samples, regardless of incubation environment. Overall, our results suggest that increased N availability in 6–8-year-old silvicultural gaps in young western Oregon forests may be due more to the quality and quantity of litterfall inputs resulting from early-seral species colonizing gaps than by changes in temperature and moisture conditions caused by gap creation.     

森林生态系统对大气氮沉降的响应

氮是陆地生态系统中三大营养元素之一,在森林生态系统中被视作主要的限制生长因子。近年来,因工农业的迅猛发展而产生越来越多的含氮化合物,大大增加了氮向全球大气的排放。据研究发现,如果氮的输入已达饱和甚至超过生态系统所能承受的临界负荷,就会带来负面效应。本文主要从以下几方面综述了国内外学者关于大气氮沉降对森林生态系统的影响:1.与大气氮沉降相关的内容,包括1)氮饱和和2)确定氮沉降临界的指示树种;2.国内外的研究进展;3.大气氮对森林生态系统的影响,包括1)导致营养失调,2)对胁迫敏感性的增强,3)加速森林土壤酸化,4)氮淋溶的增加,5)物种多样性的减少和6)氮沉降的评价方法。     

SIMULATION OF SOIL NITROGEN MINERALIZATION AND NITRIFICATION IN TWO NORTHERN HARDWOOD FOREST ECOSYSTEMS

INTRODUCTIoNMeasurementsofNmincralizationinun-fertilizedforestsoilsprovideanindexofavail-ableNfortreegrowth(AuchmoodyandFilipl973,Stonel973,AbereIal.l989,BinklcyandHartl989,MclilIoela/.l993).Histori-cally,tWoapproaches(IaboratoryandinsitlIincubations)havebcenuscdtoestimatetheratCofNmineralization,butneitheriswidelyaccepted(Keeney,l98o).Thegenerallackofagrementamongthemethodsisduetodiffer-encesintheirsensitivitytocnvironmentalfac-torswhichinfluencesoilNmineralization(Raisonetal.l987…     

接种线虫对复垦铜尾矿地碱解氮及氮素矿化的影响

在室内恒温（20℃）控制性培养1个月和2个月后,研究了土壤线虫活动对铜尾矿复垦地土壤碱解氮以及氮素矿化的影响。实验分别设置草、小飞蓬和茅草3种优势植被土下的3个处理：①不接种线虫的对照处理（－Nem ）;②培养盆内接种125条线虫处理（＋125Nem ）;③培养盆内接种250条线虫处理（＋250Nem）,每个处理设置3个重复。实验结果显示：无论是1个月还是2个月为周期的室内培养,在以铜尾矿复垦地土壤为供试土壤中接种线虫处理（＋125Nem ,＋250Nem）的土壤碱解氮含量较相应的对照处理（－Nem）有显著性提高（p＜0．01）。草优势植被土下接种线虫（＋125Nem ,＋250Nem）1个月周期内碱解氮含量分别是对照处理（－N em ）的4．05倍和5．72倍,2个月周期内分别是5．58倍和7．04倍;小飞蓬优势植被土下接种线虫（＋125Nem ,＋250Nem）1个月周期内碱解氮含量分别是对照处理（－Nem）的3．01倍和4．31倍,2个月周期内分别是4．07倍和5．67倍;茅草优势植被土下接种线虫（＋125Nem ,＋250Nem）1个月周期内碱解氮含量分别是对照处理（－N em ）的2．07倍和2．96倍,2个月周期内分别是2．90倍和3．93倍。通过相关数据计算这两个周期内土壤的氮素矿化速率发现,接种线虫后（＋125Nem ,＋250Nem ）,土壤的氮素矿化速率显著高于（p＜0．01）相对应的不接种线虫对照处理（－Nem）,并且在2个月培养期内接种250条线虫处理（＋250Nem）条件下达到最高值。     

Soil nitrogen status of larch plantations in comparison with secondary broad-leaved forest

IntroductionSoildegradationofsouthernChinesefir(CunnhaamialanceolaIe)pIantationshavebeenCon-tinuaIlyreiorted(ShenWeitongl992;Che11BingI1aol992;FangQil992).lnthenortI1eastforestregionsofChina,larch(LarirohensisandLa)`ixgInelinii)planta-tionsmade7opercentoftheman-madeforests,andthechangesinsoilpropertiesundertI1econiferouspIanta-tionshavealsodrawnmuchattentionofmanyforesters.OurobjectivewastoexaminethedifferenceinsoilnitrogenstatusbetweenLarchp1antatiol1sandsecon-darybroad-Ieavedforests(…     

Soil physical and micronutrient changes following clearing of a tropical rainforest

One of the options for achieving an adequate food supply in tropical Africa is by bringing more land into production. This often requires clearing and developing new vegetation areas for agricultural production. In sub-Saharan Africa, large areas of forest are being cleared for cultivation without adequate knowledge as to the consequences of the clearing method employed. This study was therefore initiated to, among other objectives, assess the effects of some forest clearing methods on soil compaction, texture, and micronutrients. Treatments were the following five clearing methods: (1) mechanical (MC), (2) semi-mechanical (SMC), (3) slash and burn (manual) (SB), (4) mechanical – no planting (MCNP), and (5) slash and burn – no planting (SBNP). After clearing, we planted maize and cowpea in every other row during the first year, and planted maize and cassava during the second year in the plots of treatments 1–3. Changes in soil texture, bulk density, and exchangeable Fe, Zn, Mn, and Cu were determined. Soil bulk density increased (with depth) in all treatments from the intitial (0–15cm) level of 1.1gcm^–3 to between 1.27 and 1.39gcm^–3 2 years after clearing, with the highest levels occurring in the MC plots. This indicated that clearing was accompanied by soil compaction. Some changes were noted in soil textural composition, but these were not of practical significance. Exchangeable Mn, Fe, and Cu (0–15cm) decreased markedly after clearing, especially under MC in the first year. Zinc levels changed little during the study period. The decline in micronutrient levels was paralleled by a decline in soil organic carbon.     

Conversion of deciduous forest to silvopasture produces soil properties indicative of rapid transition to improved pasture

Differences in soil properties between forests and pastures have been well documented in the literature, especially under coniferous forests. However, since nearly all of these reports have been time-point comparisons, utilizing long-term paired-sites, properties of transitional states and time of their appearance can only be inferred at present. In this study, a deciduous forest ecosystem was converted to a silvopasture ecosystem by tree thinning, fertilization, and sheep incorporation of seed and forest litter. After 2 years, topsoil (0–15 cm) physico-chemical properties, particularly P fractions, and phosphatases were monitored over the growing season in these ecosystems, and a nearby pasture ecosystem. Initially, before spring vegetative growth, differences were found for pH, exchangeable cations and soil moisture, most of which could be explained by management history. Compared to forest, organic-C (C_o) and organic-N (N_o) concentrations were reduced in silvopasture by 17 and 9%, respectively, indicative of substantial litter decomposition. Most values for all these physico-chemical properties for silvopasture were intermediate between forest and pasture, and generally remained so throughout the growing season. Initial total P (TP_t), organic-P (TP_o) and inorganic-P (TP_i) concentrations were generally as anticipated for the forest and pasture. Silvopasture, however, had 36 and 23% greater TP_o than forest and pasture, respectively, presumably due to fertilizer-P immobilization induced by incorporation of forest litter. Total P components remained essentially constant over the growing season in all ecosystems, with the exception of pasture, likely due to high forage TP_i uptake. Bray I-extractable-organic-P (BrP_o) and bicarbonate-extractable-organic-P (BiP_o) concentrations, although consistently highest in the forest and silvopasture soils, were not reflective of the increase in TP_o under silvopasture. Acid phosphatase (PMEac) activities were highest in spring in all the ecosystems, then gradually declined to typically 25–50% initial activities. Alkaline phosphatase (PMEal) activities showed a broadly-similar pattern, with exception of forest and silvopasture soils, which exhibited low activities throughout the season. For the entire data set, PMEac and PMEal activities were poorly correlated with TP_i, BrP_i, and BiP_i. These results demonstrate that conversion of forest to silvopasture results in soil changes indicative of its rapid transition to pasture and that an increased P_o reservoir results that should be taken into account in fertilizer-P recommendations for temperate silvopastures.     

Soil carbon and physical property changes in Brazilian Coastal Tableland soils with land use following deforestation

The Atlantic Forest has been deforested to the point that only about 7% of the original forest remains. Soil degradation, including loss of soil organic carbon (SOC), has often been associated with deforestation. In extensive areas previously occupied by Atlantic Forest the soil has a naturally compact subsoil horizon called the coeso. This layer challenges root development and plant productivity. The purpose of this study was to investigate soil carbon and selected physical characteristics under the influence of the native forest and post-deforestation agricultural practices. The management regimes were a native forest, a rubber tree plantation, a pasture and annual cropping. Two soil depths were investigated: 0 to 15 cm, corresponding to the A horizon; and 35 to 50 cm, corresponding to the coeso. Management influenced both SOC concentration and soil bulk density; however, SOC content was not significantly changed by any of the post-deforestation land uses. This result supports the annual cropping system that has been adapted by small landholders. Most interesting was the quantity of SOC found in the coeso, which was as much as 50% of the surface horizon.     

土壤硝化和反硝化作用及影响因素研究进展

土壤硝化和反硝化作用是生态系统中氮循环的两个重要环节,是氮素损失的潜在途径,土壤硝化和反硝化作用可向大气中释放温室气体,由此带来环境危害。本文综述了国内外学者对土壤硝化和反硝化作用的研究现状,总结了土壤硝化和反硝化作用的研究方法及其影响因子。土壤硝化和反硝化作用是两个非常复杂的生态学过程,针对研究工作中存在的不足,提出建议:1)改进实验方法、加强对总硝化作用的研究;2)进一步探索森林生态系统中硝化和反硝化作用规律;3)注重对土壤中硝化和反硝化作用微生物学机理的研究。     

Does soil organic matter variation affect the retention of NH4 and NO3 in forest ecosystems?

Human activities have fundamentally changed global nitrogen (N) cycling, leading to elevated N deposition in most parts of the world. The fate of deposited N, whether being retained to sustain plant growth or causing ecosystem N saturation, is critical to the global carbon (C) cycling and local environment. In a short-term laboratory experiment, we used ¹⁵N-labeled NH₄⁺ and NO₃⁻ to study the fate of N inputs in forest soils and what regulates N retention. Soils with a wide range of organic matter content and other attributes were collected from a 70-year-old plantation containing monotypic stands of Norway spruce (Picea abies), red pine (Pinus resinosa), sugar maple (Acer saccharum), and red oak (Quercus rubra), and separated into 0-5 cm and 5-15 cm layers. Nitrogen added to the soil was either immediately extracted (Time 0: T0) with K₂SO₄ solution, or incubated for 7 d (T7) and then extracted. Retention of ¹⁵N into the non-extractable soil pool at T0 was limited; but after the 7-d incubation, between 20 and 70% of the ¹⁵NH₄⁺ was retained. Nitrification transformed on average 50% of the ¹⁵NH₄⁺ into ¹⁵NO₃⁻ during the incubation while retention of ¹⁵NO₃⁻ at T7 remained low (7.40 ± 1.08%). Retention of ¹⁵NH₄⁺ into non-extractable soil at T7 was positively correlated to the percentage of soil organic matter (SOM) (r² = 0.323, P < 0.001), and was significantly higher (P < 0.001) in the high-SOM 0-5 cm layer than in the low-SOM 5-15 cm layer. Conversion of ¹⁵NH₄⁺ to ¹⁵NO₃⁻ during incubation significantly reduced the ¹⁵NH₄⁺ retention (P < 0.001). Our results suggest that the variations of SOM and other soil attributes play strong roles in the retention of newly deposited inorganic N and could affect forest ecosystem responses to chronic N deposition.     

Influence of soil mineralogy and chemistry on site quality within geological regions in Sweden

The relationship between soil properties and forest site quality was investigated. The site quality functions currently used fail in predicting variations within regions and the purpose of this study was to evaluate if the local accuracy in forest resource assessments could benefit from the use of geological and geochemical data. The investigation was conducted in mid-Sweden within two geological regions. The mineralogy of the parent material (C horizon) was estimated using a method for normative mineralogical assessment and the soil chemistry was determined for five soil horizons. The importance of individual minerals for site quality was different within the two geological regions. Functional relations were established between the properties in different soil horizons and site index. The functions between mineralogy and site index were improved by splitting the data according to the geologically different regions. The mineralogy explained 37–61% of the variation in site index, whereas the properties in the upper soil profile (O–B horizon) related more strongly to site index (18–80%). Stronger relations could be established in the mineralogically rich than in the mineralogically poor area.     

Assessment of repeated application of poultry litter on phosphorus and nitrogen dynamics in loblolly pine: Implications for water quality

The Southeastern United States has a robust broiler industry that generates substantial quantities of poultry litter as waste. It has historically been applied to pastures close to poultry production facilities, but pollution of watersheds with litter-derived phosphorus and to a lesser extent nitrogen have led to voluntary and in some areas regulatory restrictions on application rates to pastures. Loblolly pine (Pinus taeda L.) forests are often located in close proximity to broiler production facilities, and these forests often benefit from improved nutrition. Accordingly, loblolly pine forests may serve as alternative land for litter application. However, information on the influence of repeated litter applications on loblolly pine forest N and P dynamics is lacking. Results from three individual ongoing studies were summarized to understand the effects of repeated litter applications, litter application rates, and land use types (loblolly pine forest and pasture) on N and P dynamics in soil and soil water. Each individual study was established at one of three locations in the Western Gulf Coastal Plain region. Annual applications of poultry litter increased soil test P accumulation of surface soils in all three studies, and the magnitude of increase was positively and linearly correlated with application rates and frequencies. In one study that was established at a site with relatively high soil test P concentrations prior to poultry litter application, five annual litter applications of 5 Mg ha⁻¹ and 20 Mg ha⁻¹ also increased soil test P accumulation in subsurface soils to a depth of up to 45 cm. Soil test P accumulations were greater in surface soils of loblolly pine stands than in pastures when both land use types received similar rates of litter application. In one study which monitored N dynamics, lower soil organic N, potential net N mineralization, potential net nitrification, and soil water N was found in loblolly pine stands than pastures after two annual litter applications. However, increases in potential net N mineralization, net nitrification, and soil water N with litter application were more pronounced in loblolly pine than in pasture soils. Loblolly pine plantations can be a viable land use alternative to pastures for poultry litter application, but litter application rate and frequency as well as differences in nutrient cycling dynamics between pine plantations and pastures are important considerations for environmentally sound nutrient management decisions.     

Review of study on mineralization, saturation and cycle of Nitrogen in forest ecosystems

Nitrogen is one of the most important elements that can limit plant growth in forest ecosystems. Studies of nitrogen mineralization, nitrogen saturation and nitrogen cycle in forest ecosystems is very necessary for understanding the productivity of stand, nutrient cycle and turnover of nitrogen of forest ecosystems. Based on comparison and analysis of domestic and international academic references related to studies on nitrogen mineralization, nitrogen saturation and nitrogen cycle in recent 10 years, the current situation and development of the study on these aspects, and the problems existed in current researches were reviewed. At last, some advices were given for future researches.     

Nitrogen additions inhibit nitrification in acidic soils in a subtropical pine plantation: effects of soil pH and compositional shifts in microbial groups

Plantation forests play a pivotal role in carbon sequestration in terrestrial ecosystems, but enhanced nitrogen(N) deposition in these forests may affect plantation productivity by altering soil N cycling. Hence,understanding how simulated N deposition affects the rate and direction of soil N transformation is critically important in predicting responses of plantation productivity in the context of N loading. This study reports the effects of N addition rate(0, 40, and 120 kg N ha^-1 a^-1) and form(NH_4Cl vs. NaNO_3) on net N mineralization and nitrification estimated by in situ soil core incubation and on-soil microbial biomass determined by the phospholipid fatty acid(PLFA) method in a subtropical pine plantation. N additions had no influences on net N mineralization throughout the year. Net nitrification rate was significantly reduced by additions of both NH_4Cl(71.5) and NaNO_3(47.1%) during the active growing season, with the stronger inhibitory effect at high N rates. Soil pH was markedly decreased by 0.16 units by NH_4Cl additions. N inputs significantly decreased the ratio of fungal-to-bacterial PLFAs on average by 0.28(49.1%) in November. Under NH_4Cl additions, nitrification was positively related with fungal biomass and soil pH. Under NaNO_3 additions,nitrification was positively related with all microbial groups except for bacterial biomass. We conclude that simulated N deposition inhibited net nitrification in the acidic soils of a subtropical plantation forest in China,primarily due to accelerated soil acidification and compositional shifts in microbial functional groups. These findings may facilitate a better mechanistic understanding of soil N cycling in the context of N loading.     

华西雨屏区巨桉中龄林土壤呼吸对模拟氮沉降的响应

2009年3月至2009年11月,对华西雨屏区巨桉中龄林进行了模拟氮沉降试验,氮沉降水平分别为对照(0kg N.hm-2.a-1)、低氮(50 kg N.hm-2.a-1)、中氮(150 kgN.hm-2.a-1)和高氮(300 kgN.hm-2.a-1)。每月下旬,采用红外CO2分析法测定土壤呼吸速率,并定量地对各处理施氮(NH4NO3)。结果表明:各处理土壤呼吸速率最大值均出现在7月份,最小值出现在5月份;巨桉林土壤呼吸速率12 h平均值均表现为对照低氮中氮高氮;各处理土壤呼吸速率与10 cm土壤温度呈极显著指数正相关关系;利用温度单因素模型可以解释土壤呼吸速率的大部分;模拟氮沉降使得巨桉中龄林土壤呼吸Q10值增大,表明氮沉降增强了巨桉中龄林土壤呼吸的温度敏感性。     

Effect of Water-table Level on Nitrogen Mineralization in Peat

The effect of drainage on the mineralization of nitrogen inpeat has been investigated using samples from a field experimentin which the water table has been artificially maintained atdifferent levels in five plots for a period of 7 years. Samplescut from the o–10 cm horizon were incubated in the laboratoryat 30 °C for 120 days in a moist condition (aerobic) andalso in a completely waterlogged state (anaerobic). The resultsof anaerobic incubation indicate that lowering the water-tablelevel to 18 cm significantly decreases the amount of nitrogenmineralized but that further lowering of the water level reversesthe position, mineral nitrogen increasing significantly at leastto a water-table depth of 34 cm; the position regarding samplesincubated under aerobic conditions is more complex but can beexplained on the basis of samples containing a mixture of aeratedand non-aerated material.     

退耕造林对土壤氮矿质化的影响

土壤中供林木吸收利用的氮元素主要来自于微生物对有机质的分解,其矿化率常常是林木生长的主要限制因素(Reichet al.,1997)。矿化氮含量常作为土壤供氮能力的一项重要指标(Campbellet al.,1995),由于缺乏田间条件下测定矿化率的有效方法,矿化率和其他生物化学过程间关系的确定受到制约,因此,一直以实验室培养来模仿田间氮矿质化过程,好气性培养法(Stanfordet al.,1972;Bondeet al.,1987;Maimoneetal.,1991;Motavalliet al.,1995)是广泛采用的方法,但缺乏对土壤中氮动态变化的长期研究(Richteret al.,1994a;Leighet al.,1994;Richteret a…     

模拟氮沉降对长白山兴安落叶松林土壤有机碳库的短期影响

以净月潭国家森林公园兴安落叶松林为研究对象,以NH4NO3为原料模拟4个强度的氮沉降,分析土壤总有机碳(TOC)、易氧化有机碳(ROC)、溶解性有机碳(DOC)和微生物量碳(MBC)的动态变化。研究结果表明:低氮沉降量(L,50 kg N yr^-1 ha^-1)提高了TOC、ROC、DOC和MBC浓度,但除MBC外均未达到显著性水平;中氮沉降量(M,100 kg N yr^-1 ha^-1)提高了TOC和DOC浓度,降低了ROC和MBC浓度;高氮沉降量(H,150 kg N yr^-1 ha^-1)提高了ROC和MBC浓度,降低了TOC和DOC浓度。     

生态公益林改造对土壤理化性质的影响

对广东省中山市五桂山、仙逸水库、板芙镇3个林地进行土壤状况调查分析.结果表明:马尾松纯林内种一植阔叶树种对林分改造后,第3年对土壤物理性质影响不大,第5年通气性好,土壤毛管孔隙多有利于水分保持.土壤有机质含量分别是对照地的2.23、1.82倍,全N则为2.05、1.95倍.在经过针阔混交改造后土壤的化学性质得到了明显改善.