4个林龄白桦次生林降雨中氮化学性质研究

通过对凉水国家级自然保护区内4个林龄白桦次生林林外降雨、穿透雨、树干茎流和枯透水中的NH+4-N、NO-3-N、TN进行测定,以研究4个林龄之间氮化学性质的差异。结果表明:各元素含量在林外降雨中随季节变化较大,其平均含量(以mg/L计)排列顺序为TNNH+4-NNO-3-N;穿透雨中无机N、TN含量均在28 a白桦次生林中最低,树干茎流中NH+4-N含量在28 a中最低,NO-3-N、TN含量在41 a白桦次生林中最低,枯透水中NH+4-N、TN含量在28 a白桦次生林中最低,而NO-3-N含量在41 a中最低。     

都市农业村域地下水非点源氮污染及其风险评估

以上海市南汇区新场镇果园村为研究区域,连续监测了该村域地下水中的总氮和"三氮"含量变化。结果表明:该村域地下水中的"三氮"主要以NO3--N形态存在,平均浓度范围为1.43～13.71 mg/L;地下水氮污染与土地利用类型有关,居民区地下水中NH4+-N污染最为严重,平均浓度范围为0.074～0.457 mg/L;河道旁地下水中NH4+-N污染较轻;果园旁和河道旁地下水总氮污染程度相当,平均浓度范围分别为33.67～62.57 mg/L,33.05～65.04 mg/L。均比居民区地下水污染严重。同时研究发现,该村域地下水中的总氮和"三氮"含量也受降雨强度和降雨时间的影响。同时,采用模糊综合评价法评价了该区域地下水氮污染的环境风险。     

控制排水和施氮量对旱地土壤氮素运移转化的影响

为了研究控制排水和氮肥共同作用对旱地土壤氮素运移转化的影响,在湖北荆州丫角排灌试验站进行微区对照试验,以控制水位水平(30、50、100cm)和3个施氮水平(H:68.25/145.6kg/hm2;C:52.5/112kg/hm2,L:36.75/78.4kg/hm2,前面数值是施磷酸二铵量,后面为施硫酸钾复合肥量)为试验变量,组合成H30、H50、H100、C30、C50、C100、L30、L50、L100等9个处理测定了土壤剖面分层NO3-N、NH4+-N含量。对观测结果进行分析表明,常规施氮水平下,自由排水处理各土层NO3-N含量最高、50处理各土层NO3-N含量最低;低施氮水平下30处理NH4+-N含量最高;同一水位处理高施氮水平NH4+-N含量最低。同一施氮水平下,控制水位30cm的NH+4-N含量大于50cm的NH+4-N含量大于100cm的NH+4-N含量。同一施氮水平下实行控制排水可以增加氮素稳定性;实行控制水位处理时,不需增加或减少施氮量、常规施氮条件下氮素稳定性保持最高;而在自由排水时,减少施氮量,能够增加耕层土壤氮素稳定性。     

农村污水加入对模拟稻田生态系统中氮、磷的影响

在温室内,以中性紫色水稻土为基质,水稻(Oryza sativa)为植被构建了模拟稻田生态系统用以处理农村污水,研究了外源污水(TN 15.0mg/L,其中NH4+-N 13.5mg/L,NO3--N 1.5mg/L;TP 2.0mg/L)加入4种系统后,土壤和田面水中各种形态氮、磷、pH等的动态变化。结果表明,外源污水加入后3d土壤中NH4+-N、NO3--N、pH均达到峰值,其中NH4+-N 29.4～46.5mg/kg,NO3--N 12.3～21.4mg/kg,pH 7.9～9.1,完全施肥处理显著高于减量施肥处理,垄作与平作之间差异不显著。7d后NH4+-N、NO3--N、pH显著降低,处理之间差异不显著。外源污水加入后3d,土壤中NH4+-N增加了5.76～9.70g/m2,显著高于田面水中NH4+-N的损失量1.15～1.34g/m2,田面水和土壤中NO3--N分别上升了0.64～0.91g/m2和2.02～4.12g/m2。表明田面水中NH4+-N的减少可能对土壤中NH4+-N的升高有一定的贡献,而田面水中NO3--N的增加量可能来自土壤。土壤中碱解氮和Olsen-P浓度均在污水加入后1d达到峰值,完全施肥处理显著高于减量施肥处理,垄作与平作之间差异不显著。土壤中TN和TP在试验期间有下降的趋势,但是差异不显著。相同施肥条件下,垄作较平作能够获得更高的生物产量,意味着能够带走更多的氮、磷。     

三江平原典型小叶章湿地土壤中硝态氮和铵态氮的空间分布格局

运用地统计学方法对三江平原典型小叶章湿地土壤中硝态氮(NO3-N)和铵态氮(NH4+-N)的空间分布格局进行了研究.结果表明,湿地土壤不同土层NO3--N和NH4+-N含量的变异性差异较大,但均表现为N073-NH4+-N,原因主要与其物理运移特性的差异有关.两种土壤在不同土层或相同土层中的NO3-N和NH4+-N含量差异均达到极显著水平(P<0.01);湿地土壤不同土层NO3--N和NH4+-N的含量分布具有明显空间结构,符合不同变异函数理论模型,结构因素对空间异质性起主导作用,随机因素的影响相对较少.微地貌特征是导致其空间异质性的一个重要随机因素,水分条件和土壤类型则是两个重要结构因素;湿地土壤不同土层NO3-N和NH4+-N含量的空间变异性均以向洼地中心倾斜方向最大.研究发现,水分条件是导致NO3-N含量在地势较低处形成低值区的主要原因,于湿交替则是导致NH4+-N含量在地势较低处形成高值区的重要原因.     

增设回流提高厌氧氨氧化反应器脱氮效能

采用2套上流式反应器接种厌氧氨氧化污泥,研究了高基质浓度下增设回流对厌氧氨氧化反应器脱氮性能影响.研究结果表明,增设出水回流的反应器1经过116 d的运行,进水NH4+-N和NO2--N质量浓度由初始100、130 mg/L达到602、782 mg/L时,出水质量浓度仅增加到44、60 mg/L,氮容积去除负荷最高达到7.87 kg/(m3·d).NO2--N与NH4+-N的转化比维持在1.303,NO3--N生成量与NH4+-N转化量之比维持在0.24.无回流的反应器2经过67 d运行,进水NH4+-N和NO2--N质量浓度由最初100、130 mg/L分别增加到456和600 mg/L,相应出水质量浓度达到174和253 mg/L,氮容积去除负荷最高达到4.31 kg/(m3·d).NO2--N与NH4+-N的转化比维持在1.298左右, NO3--N生成量与NH4+-N转化量之比维持在0.21.说明回流对进入反应器的基质具有较强稀释作用,有助于避免高基质浓度对厌氧氨氧化活性的影响,同时对厌氧氨氧化反应过程中氮素转化比不产生影响.增设出水回流后的反应器1污泥粒径主要分布在1.25~2 mm之间,而反应器2污泥粒径主要分布在0.9~1.6 mm.说明在反应器运行过程中增设回流有助于反应器内液体上升流速的增加,颗粒污泥具有良好的流态,能够更好地与底物接触,有利于微生物增长.     

镉污染下不同类型水稻土氮素供应特征及其影响因素

污染条件下的土壤氮素供应影响了作物生产和植物生态修复。采用温室盆栽试验,研究了两种剂量镉污染下我国21种水稻土无机氮的供应特征和影响因素。结果表明：淹水10天后,不同水稻土土壤溶液无机态氮含量变幅为1.42 ~ 70.40 mg/L （(平均值为16.76 mg/L）),其中NH4+-N和NO3--N分别占62.5% 和33.7%;与施肥对照相比,镉污染降低了大多数水稻土土壤溶液无机态氮的含量,平均降幅为58.4%,主要是由土壤溶液NH4+-N含量下降所致;土壤溶液NO3--N含量受镉污染的影响程度则因土壤类型而异。基于典范对应分析的偏因子分析（(VPA）)表明镉污染对水稻土土壤溶液无机氮含量的影响最大,其次是土壤类型,施肥影响最小,三类因子单独作用的影响比例分别为40.38%、6.51% 和0.05%。镉污染下,pH、CEC和土壤质地显著影响水稻土无机氮供应,其中土壤pH是镉污染条件下影响NH4+-N含量变化的首要因子。     

添加硝化抑制剂DMPP对红壤水稻土硝化作用及微生物群落功能多样性的影响

通过室内培育试验,研究了不同施氮水平下添加硝化抑制剂(DMPP)处理对红壤水稻土NH4+-N、NO3–-N含量、微生物生物量碳及微生物群落功能多样性的影响。结果表明:56天培养期内,不同处理的NH4+-N含量总体呈下降趋势,而NO3–-N含量呈上升趋势。随施氮水平提高,培养期内NH4+-N平均含量从0 mg/kg处理的24.10 mg/kg增加到400 mg/kg处理的412.10 mg/kg,NO3–-N平均含量从0 mg/kg处理的41.88 mg/kg增加到400 mg/kg处理的99.83 mg/kg。添加DMPP显著抑制硝化作用进行,抑制效果随施氮量增加而提高,400 mg/kg施氮水平下,添加DMPP硝化率和硝化速率比不添加DMPP处理分别下降了29.0%和44.3%,下降幅度远大于其他施氮水平处理。施氮水平也影响土壤微生物生物量碳和微生物群落功能多样性。施氮量从0 mg/kg增加到400 mg/kg,土壤微生物生物量碳下降了12.5%,AWCD值下降了78.4%,Shannon指数下降了22.3%;与不添加DMPP处理相比,添加DMPP处理的土壤微生物生物量、AWCD值、Shannon指数分别提高了2.1%、23.9%、7.8%,尤其在400 mg/kg施氮水平下,提高的幅度更加明显。     

施用铵态氮对森林土壤硝态氮和铵态氮的影响

对取自武夷山的红壤、黄壤、黄壤性草甸土分别在对照(CK,N 0 mg/kg)、低氮(LN,N 50 mg/kg)、高氮(HN,N 100 mg/kg)3种氮(N)水平处理下开展培养实验,研究施加NH4+-N对森林土壤N转化的短期影响.结果表明,添加NH4+-N可显著(p＜0.05)降低土壤NO3--N含量4.5％～25.7％,但LN与HN处理差异不显著,NO3--N降低可能与NO3--N反硝化和异氧还原有关;然而,黄壤性草甸土NO3--N没有降低.与培养前比较,在第56天红壤NO3--N含量显著增加5倍左右;桐木关黄壤增加40％左右,而黄冈山25 km黄壤仅在CK处理下增加16％,但是黄壤性草甸土显著降低;结果显示LN与HN处理土壤NO3--N含量变化幅度小于CK.与CK相比,LN和HN处理红壤NH4+-N分别显著(p＜0.05)升高24.1％ ～ 96.5％和68.7％～114.1％,且随培养进行没有累积,可能与微生物固N有关;桐木关NH4+-N分别升高17.6％ ～ 39.6％和37.6％～95.8％ (p＜0.05),LN处理黄冈山25 km黄壤NH4+-N只有第7天升高17.8％ (p＜0.05),HN处理第7、14、28、42天显著升高17.5％～48.6％(p＜0.05).LN处理黄壤性草甸土的NH4+-N在前3周显著降低11.6％～28.5％ (p＜0.01); HN处理在第7天和14天分别降低10.8％(p＜0.01)和7.5％,但是在第28～56天显著增加17.6％～20.4％(p=0.002).随着培养进行,CK处理红壤NH4+-N逐渐降低,桐木关黄壤、黄冈山25 km黄壤和黄壤性草甸土升高;LN和HN处理黄壤和黄壤性草甸土NH4+-N逐渐升高.可见,不同海拔土壤类型对NH4+-N添加响应存在差异.     

成都平原菌渣还田下稻田田面水氮磷动态变化特征

为合理利用菌渣,以化肥施氮量为基准,设置1,1.5,2,2.5倍氮量的菌渣还田处理,采用田间定位监测并结合室内分析实验,以期通过研究稻田田面水中氮素和磷素的动态变化探明菌渣还田下面源污染风险。结果表明:与化肥处理相比,菌渣还田处理显著降低田面水TN、DTN、DON、PN和NH4+-N含量,显著提高NO3--N/TN比例(P0.05);其田面水TN、DTN和NO3--N含量在施肥后均呈下降趋势,NH4+-N含量则表现为"先增后减",施肥后第5d达最大值,其中TN、DTN和NH4+-N含量变化均可用指数降低模型Y=C0×ekt(k0)拟合,NO3--N含量变化可用倒数模型Y=C0+k/x拟合;受田面水中氮含量等因素的影响,其TP、DTP和PP含量均显著降低(P0.05),TP和DTP含量表现为"先降后升再降"。总体来看,较化肥处理,菌渣还田不会延长田面水氮磷素流失风险期,同时显著降低田面水NH4+-N含量,缩短NH4+-N流失风险期,但等氮量还田会显著降低水稻产量及糙米氮含量(P0.05),超过2倍氮量还田会增加NO3--N流失风险。综合环境风险与粮食生产,应以1.5倍氮量还田为宜。     

地中海生态系统中可溶性有机N研究

Dissolved organic nitrogen (DON) in soils has recently gained increasing interest because it may be both a direct N source for plants and the dominant available N form in nutrient-poor soils, however, its prevalence in Mediterranean ecosystems remains unclear. The aims of this study were to i) estimate soil DON in a wide set of Mediterranean ecosystems and compare this levels with those for other ecosystems; ii) describe temporal changes in DON and dissolved inorganic nitrogen (DIN) forms (NH4+ and NO3? ), and characterize spatial heterogeneity within plant communities; and iii) study the relative proportion of soil DON and DIN forms as a test of Schimel and Bennett’s hypothesis that the prevalence of different N forms follows a gradient of nutrient availability. The study was carried out in eleven plant communities chosen to represent a wide spectrum of Mediterranean vegetation types, ranging from early to late successional status. DON concentrations in the studied Mediterranean plant communities (0-18.2 mg N kg-1) were consistently lower than those found in the literature for other ecosystems. We found high temporal and spatial variability in soil DON for all plant communities. As predicted by the Schimel and Bennett model for nutrient-poor ecosystems, DON dominance over ammonium and nitrate was observed for most plant communities in winter and spring soil samples. However, mineral-N dominated over DON in summer and autumn. Thus, soil water content may have an important effect on DON versus mineral N dominance in Mediterranean ecosystems.     

不同松栎混交林土壤溶解性有机碳氮的差异分析

为揭示北亚热带地区不同林分类型的土壤活性碳氮分布特征,在驻马店市南部山区选取4处具有代表性的松栎人工混交林为研究对象,对其0-20 cm土壤的溶解性有机碳（DOC）,溶解性有机氮（DON）等组分进行研究。结果表明:4种林型土壤DOC的含量为麻栎纯林 > 湿地松麻栎混交林 > 火炬松麻栎混交林 > 马尾松麻栎混交林,DON的含量为马尾松麻栎混交林 > 麻栎纯林 > 湿地松麻栎混交林 > 火炬松麻栎混交林,不同林分类型间整体上差异性显著（p<0.05）;在垂直剖面上,4种林型土壤DOC和DON均随土层深度的增加而显著性下降（p<0.05）。4种林分类型DOC/SOC,DON/TN,DOC/DON分别以麻栎纯林、马尾松麻栎混交林、麻栎纯林最高,在垂直空间分布上,差异性整体上不显著。土壤DOC和DON与土壤含水率、土壤硬度、速效钾、全氮均呈显著（p<0.05）或极显著（p<0.01）相关性。     

Different effect of drying on the fluxes of dissolved organic carbon and nitrogen from a Norway spruce forest floor

The forest floor represents the major source of dissolved organic carbon (DOC) and nitrogen (DON) in forest soils. The release mechanisms of DOC and DON from forest floors and their environmental controls as well as the dynamics of concentrations and fluxes are still poorly understood. We investigated the effect of drying and rewetting on the release of DOC and DON from a Norway spruce forest floor. Undisturbed soil columns of 17 cm diameter and 15—20 cm height were taken with 7 replicates from the forest floor of a mature Norway spruce (Picea abies [L.] Karst.) site and established at 10°C in the laboratory. Columns were exposed to different periods of drying (3, 5, 10, 20 days). Each drying period was followed by a rewetting for 5 days at an irrigation rate of 10 mm d^—1 with a natural throughfall solution. The percolates from the forest floor were collected daily and analyzed for DOC, total N, NH₄, NO₃, pH, electrical conductivity and major ions. Drying for 10 and 20 days decreased the water content of the Oi horizon from 280% dry weight to about 30%. The water content of the Oe and the Oa horizon only changed from about 300% to 200%. The fluxes of DOC from the forest floor were moderately effected by drying and rewetting with an increase after 3 and 5 days of drying, but a decrease after 10 and 20 days. On the contrary, the drying for 10 and 20 days resulted in a drastic increase of the DON fluxes and a subsequent decrease of the DOC/DON ratios in the forest floor percolates from about 50 to 3.3. These results suggest that the mechanisms for DOC release in forest floors differ from those for DON and that drying and rewetting cause temporal variations in the DOC/DON ratios in forest floor percolates.     

Release of dissolved organic carbon and nitrogen from forest floors in relation to solid phase properties,respiration and N-mineralization

Dissolved organic carbon (DOC) and nitrogen (DON) are important components of the carbon and nitrogen turnover in soils. Little is known about the controls on the release of DOC and DON from forest floors, especially about the influence of solid phase properties. We investigated the spatial variation of the release of DOC and DON from Oe and Oa forest floor samples at a regional scale. Samples were taken from 12 different Norway spruce sites with varying solid phase properties, including C/N ratio, pH, different fractions of extractable carbon and exchangeable cations. Most of these solid phase properties are available for large forested areas of Europe in high spatial resolution. The samples were incubated at water holding capacity for eight weeks at 15°C and then extracted with an artificial throughfall solution to measure DOC and DON release. The rates of soil respiration and N-mineralization were determined to estimate soil microbial activity. The release of DOC and DON from Oe samples was two- to threefold higher than from Oa samples. The amounts released differed by one order of magnitude among the sites. The DOC/DON ratios in the percolates of the Oa samples were much higher as compared to the solid phase C/N, indicating different release rates of DOC and DON. In contrast, the DOC/DON ratios of the Oe percolates were in the range of the C/N ratios of the solid phase. The release of DOC and DON from Oe samples was not statistically correlated to any of the measured solid phase parameters, but to N-mineralization. The DOC and DON release from the Oa samples was positively related only to pH and soil respiration. Overall it was not possible to explain the large spatial variation of DOC and DON release by the measured solid phase properties with satisfying accuracy.     

Contribution of dissolved organic nitrogen to N leaching from four German agricultural soils

Dissolved organic nitrogen (DON) substantially contributes to N leaching from forest ecosystems. However, little is known about the role of DON for N leaching from agricultural soils. Therefore, the aim of our study was to quantify the contribution of DON to total N leaching from four agricultural soils. Concentrations and fluxes of DON and mineral N were monitored at two cropped sites (Plaggic Anthrosols) and two fallow plots (Plaggic Anthrosol and Gleyic Podzol) from November 1999 till May 2001 by means of glass suction plates. The experimental sites were located near the city of Münster, NW Germany. Median DON concentrations in 90 cm depth were 2.3 mg l^—1 and 2.0 mg l^—1 at the cropped sites and 1.6 mg l^—1 and 1.3 mg l^—1 at the fallow sites. There was only a slight (Anthrosols) or no (Gleyic Podzol) decrease in median DON concentrations with increasing depth. Total N seepage was between 19 kg N ha^—1 yr^—1 and 46 kg N ha^—1 yr^—1 at the fallow sites and 16—159 kg N ha^—1 yr^—1 at the cropped sites. For the fallow plots, DON seepage contributed 10—21 % to the total N flux (4—5 kg DON ha^—1 yr^—1), at the cropped sites DON seepage was 6—21 % of the total N flux (6—10 kg DON ha^—1 yr^—1). Thus, even in highly fertilized agricultural soils, DON is a considerable N carrier in seepage that should be considered in detailed soil N budgets.     

上海郊区园艺土壤氮素的生物形成动态变化

Dissolved organic nitrogen (DON) represents a significant pool of soluble nitrogen (N) in soil ecosystems. Soil samples under three different horticultural management practices were collected from the Xiaxiyang Organic Vegetable and Fruit Farm, Shanghai, China, to investigate the dynamics of N speciation during 2 months of aerobic incubation, to compare the effects of different soils on the mineralization of ¹⁴C-labeled amino acids and peptides, and to determine which of the pathways in the decomposition and subsequent ammonification and nitrification of organic N represented a significant blockage in soil N supply. The dynamics of N speciation was found to be significantly affected by mineralization and immobilization. DON, total free amino acids, and NH₄⁺-N were maintained at very low levels and did not accumulate, whereas NO₃^--N gradually accumulated in these soils. The conversion of insoluble organic N to low-molecular-weight (LMW) DON represented a main constraint to N supply, while conversions of LMW DON to NH₄⁺-N and NH₄⁺-N to NO₃^--N did not. Free amino acids and peptides were rapidly mineralized in the soils by the microbial community and consequently did not accumulate in soil. Turnover rates of the additional amino acids and peptides were soil-dependent and generally followed the order of organic soil > transitional soil > conventional soil. The turnover of high-molecular-weight DON was very slow and represented the major DON loss. Further studies are needed to investigate the pathways and bottlenecks of organic N degradation.     

Indices of dissolved organic nitrogen, ammonium and nitrate across productivity gradients of boreal forests

Organic nitrogen (N) uptake, rather than solely inorganic N (DIN), is considered a significant pathway for plant nutrition, especially in arctic, alpine and boreal ecosystems. Assays of plant-available N in these ecosystems might therefore be improved with measures of dissolved organic N (DON). We examined DON and DIN abundance from an in situ 5-week incubation across plant associations that represent the widest range in site potential in southern boreal forests of British Columbia, Canada. The supply of N from forest floors and mineral soils (20 cm depth) was measured separately and then combined (kg ha⁻¹) to facilitate comparisons of sites. DON was the predominant form of extractable N, and was increasingly supplemented, rather than replaced, by NH₄⁺ and NO₃⁻ on productive sites. The amount of DIN produced in the soils was very low, perhaps too small to support forest needs, and the correlation of DIN to asymptotic stand height (a measure of site potential) was significant but nonlinear. The combined amount of DON+DIN was considered a more effective index of plant-available N because it was strongly significant as a linear correlation to stand height and more typical of annual forest N uptake. The relative shift in N forms, from a predominance of DON to progressively greater ratios of DIN:DON, was consistent with the current paradigm of N forms across gradients of N availability, although the actual amounts of DON increased, rather than decreased, with site potential. Based on this, we suggest organic N uptake has the potential to contribute to plant nutrition across the entire productivity gradient of soils in southern boreal forests. Although other N indices were effective in characterizing forest productivity, a combined assay of DON+DIN production could provide new insights into functional differences in plant-available N.     

华南花岗岩侵蚀区不同植被类型坡面土壤有机碳分布和团聚体稳定性

植物是影响土壤有机碳含量和土壤团聚体稳定性的重要因素。选取华南典型花岗岩侵蚀区荒草地、桉树林、湿地松林和木荷林4种植被类型径流小区的土壤为研究对象,分析测定不同坡位、不同土层深度的土壤有机碳特性和团聚体稳定性等指标,评价不同植被类型对土壤养分的分布特性以及团聚体稳定性差异,明确花岗岩侵蚀退化区较为理想的生态恢复措施,旨在为合理利用土壤、重建坡面植被和改善土壤结构提供科学依据。结果表明:土壤总有机碳(TOC)、全氮(TN)和溶解性有机碳(DOC)含量随土层加深逐渐降低,而林地小区土壤碳氮比(C/N)则相反,荒草地碳氮元素的坡面变异系数(CV)显著高于其他3种林地,其中桉树林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低40%,56.18%,68.5%和25.81%;湿地松林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低62.73%,33.71%,46.46%,58.06%;木荷林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低41.82%,38.2%,51.18%,48.39%,表明林地较荒草地更有利于土壤碳氮在坡面的均质化和有机质的积累。荒草地和木荷林地0.25 mm粒径以上的团聚体在上、中坡位的质量分数显著高于其他植被类型,而林下植被生物量较高的木荷林地的平均质量直径(MWD)和几何平均直径(GMD)显著高于其他植被类型。其中木荷小区水稳性团聚体平均质量直径(MWD)较荒草地、桉树和湿地松分别高20.10%,19.58%,23.20%;几何平均直径(GMD)较荒草地、桉树和湿地松分别高20.00%,19.54%,22.23%,表明在花岗岩侵蚀区林地空间结构较好的林草模式有利于土壤有机碳的积累和土壤结构的稳定。     

Dissolved Organic Nitrogen Concentrations and Ratios of Dissolved Organic Carbon to Dissolved Organic Nitrogen in Throughfall and Soil Waters in Norway Spruce and Scots Pine Forest Stands Throughout Norway

Dissolved organic nitrogen (DON) plays an important ecological role in forest ecosystems, and its concentration is related to that of dissolved organic carbon (DOC). We investigated DON concentrations and ratios of DOC to DON in throughfall and soil waters in 16 Norway spruce and two Scots pine forest stands sampled at weekly intervals between 1996 and 2006. The stands are all included in the ICP Forests Level II monitoring program and are located throughout Norway. DON concentrations were significantly and positively related to DOC concentrations in throughfall (r ²?=?0.72, p?<?0.0001) and soil water at 5, 15, and 40 cm (r ²?=?0.86, 0.32, and 0.84 and p?<?0.0001, 0.04, and <0.0001, respectively). At most sites, the annual median DOC/DON ratio in throughfall ranged from 20.3 to 55.5, which is lower than values in soil water, which ranged from 24.5 to 81.3, gradually decreasing with soil depth. DON concentrations varied seasonally in throughfall at many plots and in soil water at 5-cm depth at one plot only, with higher values in the growing season, but there was no noticeable seasonality at greater depth. The ratios of DOC/DON in soil water were significantly positively related to the C/N ratio in soil at the same depth. Above-ground litter input was the main factor having a significant, negative relationship to DOC/DON in soil water at all depths studied. This might reflect the effect of site conditions on both DOC/DON ratios and litter quantity.     

Dissolved organic carbon and nitrogen in precipitation,throughfall, soil solution,and stream water of the tropical highlands in northern Thailand

Dissolved organic matter (DOM) is important for the cycling and transport of carbon (C) and nitrogen (N) in soil. In temperate forest soils, dissolved organic N (DON) partly escapes mineralization and is mobile, promoting loss of N via leaching. Little information is available comparing DOC and DON dynamics under tropical conditions. Here, mineralization is more rapid, and the demand of the vegetation for nutrients is larger, thus, leaching of DON could be small. We studied concentrations of DOC and DON during the rainy seasons 1998–2001 in precipitation, canopy throughfall, pore water in the mineral soil at 5, 15, 30, and 80 cm depth, and stream water under different land‐use systems representative of the highlands of northern Thailand. In addition, we determined the distribution of organic C (OC) and N (ON) between two operationally defined fractions of DOM. Samples were collected in small water catchments including a cultivated cabbage field, a pine plantation, a secondary forest, and a primary forest. The mean concentrations of DOC and DON in bulk precipitation were 1.7 ± 0.2 and 0.2 ± 0.1 mg L^–1, respectively, dominated by the hydrophilic fraction. The throughfall of the three forest sites became enriched up to three times in DOC in the hydrophobic fraction, but not in DON. Maximum concentrations of DOC and DON (7.9–13.9 mg C L^–1 and 0.9–1.2 mg N L^–1, respectively) were found in samples from lysimeters at 5 cm soil depth. Hydrophobic OC and hydrophilic ON compounds were released from the O layer and the upper mineral soil. Concentrations of OC and ON in mineral‐soil solutions under the cabbage cultivation were elevated when compared with those under the forests. Similar to most temperate soils, the concentrations in the soil solution decreased with soil depth. The reduction of OC with depth was mainly due to the decrease of hydrophobic compounds. The changes in OC indicated the release of hydrophobic compounds poor in N in the forest canopy and the organic layers. These substances were removed from solution during passage through the mineral soil. In contrast, organic N related more to labile microbial‐derived hydrophilic compounds. At least at the cabbage‐cultivation site, mineralization seemed to contribute largely to the decrease of DOC and DON with depth, possibly because of increased microbial activity stimulated by the inorganic‐N fertilization. Similar concentrations and compositions of OC and ON in subsoils and streams draining the forested catchments suggest soil control on stream DOM. The contribution of DON to total dissolved N in those streams ranged between 50% and 73%, underscoring the importance of DOM for the leaching of nutrients from forested areas. In summary, OC and ON showed differences in their dynamics in forest as well as in agricultural ecosystems. This was mainly due to the differing distribution of OC and ON between the more immobile hydrophobic and the more easily degradable hydrophilic fraction.