马尾松与芒萁鲜叶及凋落物水溶性有机物的溶解特征和光谱学特征

为探讨福建省三明市马尾松人工林淋溶液中水溶性有机物(DOM)的溶解特征和光谱学特征,以马尾松(Pinus massoniana)和芒萁(Dicranopteris dichotoma)鲜叶、未分解层(L层)和半分解层(F层)凋落物为研究对象进行室内淋溶,对淋溶液中的水溶性有机碳(DOC)、水溶性有机氮(DON)与水溶性有机磷(DOP)含量和紫外光谱(SUVA)、荧光光谱指标和红外光谱(FTIR)等特征进行研究。结果表明,在24 h内,随着淋溶时间的延长,DOM含量呈现有波动的上升趋势;芒萁除鲜叶的DOC含量显著高于马尾松外(P0.01),其余DOM含量均小于马尾松。两植物F层DOM的SUVA值和腐殖化指标(HIX)都显著高于鲜叶和L层(P0.05),表明F层的芳香性化合物含量和腐殖化程度越来越高。DOM的同步荧光峰值显示淋溶液中含有类蛋白和类富里酸荧光团。两植物的红外光谱显示有5个相似的吸收谱带,强度最大的吸收来自于H键键合的-OH的伸缩振动,同一植物3种样品之间红外吸收的差异证明从鲜叶-L层-F层凋落物的共轭体系逐渐增大,结构更复杂。因此,随分解进程两植被DOM的化学结构越来越复杂;马尾松较芒萁含有更多的DON和DOP,这一方面为微生物提供了更多的养分,另一方面又增加了底物分解的难度。     

模拟冻融环境下亚高山森林凋落物分解速率及有机碳动态

森林凋落物分解是森林生态系统物质循环的重要环节,季节性冻融交替是影响凋落物分解的重要环境因素之一,但不同林型的凋落物对冻融响应的差异性很少被量化。为了解冻融环境对森林凋落物分解进程的影响,以川西亚高山森林地区阔叶林、针叶林和针阔混交林3种典型林型的凋落物为实验材料,从凋落物基质质量、冻融环境等影响凋落分解的因素着手,采用模拟冻融循环过程（-5-5℃）,研究了冻融循环中3种林型凋落物分解速率和有机碳含量的动态变化。结果发现,3中典型林型凋落物经过不同冻融处理后,其质量损失、质量损失速率均存在显著差异（P<0.05）。混交林凋落物和针叶林凋落物的分解速率呈慢-快-慢的趋势,而阔叶林凋落物的分解速率逐渐减小。在冻融循环处理下,3种林型的凋落物碳绝对含量呈波动下降的趋势,说明微生物固定外源碳和凋落物释放碳间存在动态平衡。相同林型的凋落物在不同冻融处理下,有机碳释放有显著差异（P<0.05）。其中,冻融环境显著（P<0.05）促进了混交林凋落物和针叶林凋落物有机碳的释放,但是对阔叶林凋落物有机碳的释放没有起到促进作用。这表明全球气候变暖情景下,亚高山森林土壤冻融事件频发将加快凋落物的分解,但变化程度受到凋落物质量控制。     

降解剂对森林凋落物可溶性有机碳含量的影响及凋落物降解模式比较研究

森林凋落物是森林生态系统中可溶性有机碳(DOC)的主要来源,在生态系统碳循环过程中起重要作用。以帽儿山地区胡桃楸、兴安落叶松以及胡桃楸-兴安落叶松人工林凋落物为研究对象,通过液体发酵培养将纤维素高效降解真菌Peniophora intranata与Sarocladium strictum制成单一(A菌剂、B菌剂)及混合菌剂(C菌剂),测定野外条件下经降解剂处理的凋落物基质在不同时期的DOC含量,分析降解剂对不同类型森林凋落物DOC动态变化的影响,并比较各凋落物基质降解模式异同。结果表明：(1)凋落物基质DOC含量在降解剂处理后均随降解时间增加呈下降趋势,且下降幅度大小表现为混合基质>胡桃楸基质>落叶松基质;在最初的1个月,各凋落物基质DOC含量均显著高于其他降解时期DOC含量。(2)经混合菌剂处理后的胡桃楸基质DOC含量相较于2种单一菌剂处理后的胡桃楸基质DOC含量低,而经混合菌剂处理后的兴安落叶松基质与胡桃楸-兴安落叶松基质的DOC含量未表现出相同的显著性。(3)经3种菌剂处理后的胡桃楸基质降解模式均相同,经B菌剂与C菌剂处理的落叶松基质降解模式相同,经A菌剂与C菌剂处理...     

凋落物输入对三江平原弃耕农田土壤基础呼吸和活性碳组分的影响

土壤有机碳的积累主要由土壤有机质的输入与输出间的净平衡决定的,植被的恢复和凋落物质的大量输入是土壤恢复的先决条件,凋落物的输入在土壤恢复过程中起着至关重要的作用.通过对不同类型凋落物输入到三江平原弃耕农田后土壤的基础呼吸、溶解有机碳(DOC)和土壤微生物量碳(MBC)的研究表明:相同种类凋落物输入后,输入到土壤总有机碳(TOC)背景值低的凋落物被微生物降解的速率大于TOC背景值高的土壤,TOC较低的土壤能够加快微生物对输入凋落物的分解,不利于有机质的积累;不同类型凋落物的输入使土壤基础呼吸、DOC和MBC等活性组分的生成和降解产生差异,改变了凋落物的降解速率,在三江平原研究的4种主要植被类型中,人工林凋落物最容易降解,小叶章、大豆的降解能力次之,玉米是最难降解的凋落物.     

增温对亚热带常绿阔叶林凋落物溶解性有机质的影响

为了解增温对凋落物分解的影响,依托亚热带常绿阔叶林野外增温试验平台,收集林内凋落物分别布设于对照和增温(+4 ℃)小区中,对增温下凋落物分解过程中可溶性有机质数量和光谱特征的变化进行研究。结果表明,凋落物质量残留率随分解时间的增加显著下降,在0~60 d内快速下降了20.08%~23.32%,在60~210 d内缓慢下降了6.35%~10.98%。凋落物源可溶性有机碳含量随分解时间增加呈现先快后慢的下降趋势,整体降低了94.15%;可溶性有机氮含量则波动式降低了81.82%;可溶性有机质的光谱特征(SUVA₂₅₄、SUVA₂₆₀、SUVA₂₈₀和SUVA₃₇₀)呈增加-下降-增加的趋势。增温未显著影响凋落物质量残留率和可溶性有机质的光谱特征,但可溶性有机碳和有机氮的含量降低了16.72%和25.10%。凋落物分解降低了凋落物质量残留率和可溶性有机碳、有机氮含量,改变了可溶性有机质光谱特征;增温虽然降低了凋落物可溶性有机碳、有机氮含量,但未显著改变凋落物质量残留率和可溶性有机质光谱特征。     

森林凋落物研究进展

对森林凋落物的概念、研究方法及主要研究内容作了阐述,特别就凋落物收集面积和分解袋孔径大小、凋落量时空动态和凋落物分解速率等问题进行了综合分析。目前森林凋落物研究的重要结论有：海拔和纬度因子是通过对光、温、水等生态因子的再分配来影响凋落量,其中主导气候因子是年均温。凋落物的分解与化学组成和环境因子有关,C／N和N含量在凋落物分解过程中起着重要作用。土壤水分是影响凋落物分解主要环境因子之一;土壤微生物对凋落物的影响,前期是通过真菌破碎凋落物表层使内居性动物得以侵入凋落物内部,后期则以细菌降解有机物为主。凋落量、凋落物分解的影响因子,以及凋落物的生态作用等内容应是凋落物研究的重要方向。     

亚热带4种森林凋落物量及其动态特征

通过对枫香林、樟树林、马尾松林、樟树—马尾松混交林4种森林生态系统的凋落物数量及组成进行为期1a的定位研究。结果表明,樟树—马尾松混交林的年凋落总量(4.30 t.hm^-2)＞枫香林(3.66 t.hm^-2)＞马尾松林(3.41 t.hm^-2)＞樟树林(3.26 t.hm^-2)。各组分凋落物中,凋落叶占绝对优势(70%以上),表现为樟树—马尾松混交林(3.09 t.hm^-2)＞枫香林(2.78 t.hm^-2)＞马尾松林(2.46 t.hm^-2)＞樟树林(2.32 t.hm^-2);凋落枝表现为樟树—马尾松混交林(0.73 t.hm^-2)＞樟树林(0.53 t.hm^-2)＞马尾松林(0.30 t.hm^-2)＞枫香林(0.22 t.hm^-2);凋落果表现为马尾松林(0.37 t.hm^-2)＞樟树—马尾松混交林(0.17 t.hm^-2)＞枫香林(0.12 t.hm^-2)＞樟树林(0.09 t.hm^-2);碎屑表现为枫香林(0.55 t.hm^-2)＞樟树林(0.33 t.hm^-2)＞樟树—马尾松混交林(0.31 t.hm^-2)＞马尾松林(0.27 t.hm^-2)。枫香和樟树林年凋落量的最大值分别在10月(1.22 t.hm^-2)和8月(0.58 t.hm^-2),而马尾松林和混交林年凋落量的最大值都在11月(分别为0.77 t.hm^-2和1.23 t.hm^-2)。     

沂蒙山区不同森林类型凋落物量及其动态特征

凋落物在森林养分循环中起重要作用,受森林类型、气候带等因素的影响。本文研究了沂蒙山区黑松(Pinus thunbergii Parl.)人工林、栓皮栎(Quercus variabilis Bl.)人工林和天然次生林的凋落物总量和组分的动态特征。天然次生林年凋落物总量(3368 kg/hm2)高于栓皮栎人工林(3256 kg/hm2)高于黑松人工林(3212 kg/hm2),森林类型间差异不显著。3种森林类型的凋落物月总量呈双峰曲线,最大峰值在10—11月,次峰值在4—5月,最小峰值出现时间不同:黑松人工林为12月,另两种森林类型为7月。针叶凋落量和比例、碎屑凋落量表现为黑松人工林高于天然次生林高于栓皮栎人工林,而阔叶凋落量和比例、果凋落量的比例则相反。枝凋落量在森林类型间无显著差异。线性回归分析表明,凋落物总量月动态受最低和最高气温的影响。针叶凋落量受最低气温、最高气温和最大降水量影响;阔叶凋落量受最低气温影响;枝凋落量受降水量、风速和最大降水量影响;果凋落量受气温、风速和降水量影响。结果阐明了暖温带森林类型对凋落物量及组分动态特征的影响,可为其养分循环特征提供数据支撑。     

紫外-可见分光光度法在药物检验中的应用

紫外可见分光光度法在药品检验中主要用于药品的性状、鉴别、检查和含量测定,具有灵敏度高、样品用量少的优点,实用于微量和痕量物质的分析。检验的过程中,一般采用同批次的空白对照。通常使用1cm的石英洗手池,进行内测试几个点的吸收度。通过核实波长位置,来判断是否符合规定。     

黄土高原不同植物凋落物的分解特性

以黄土高原区典型植物刺槐、小叶杨、沙棘、沙柳、苜蓿和长芒草的凋落物为对象,采用网袋法研究了半干旱区(神木)分解过程中,单种、两种及3种凋落物等质量配比混合后其质量、碳和氮的动态变化.结果表明:在整个分解过程中,不同处理凋落物的质量损失率,全碳、全氮的释放速率以及可溶性有机碳和可溶性总氮的含量均表现为前期大于后期,经过412d的分解,3种凋落物混合后的平均质量损失率高于两种混合凋落物,单种凋落物最低.到分解试验结束时,不同处理凋落物的全碳、全氮平均释放率均表现为单种＞两种混合＞3种混合;而不同处理的可溶性有机碳平均含量表现为两种混合＞单种＞3种混合,但未达到显著水平;可溶性总氮含量则为3种混合＞两种混合＞单种,达到显著水平.凋落物的质量损失率与可溶性有机物,特别是可溶性有机碳具有一定的相关性.从质量损失率来看,小叶杨、沙棘与苜蓿凋落物的组合为最佳组合.建议在黄土高原区退耕还林还草工程建设中,合理增加植物种类多样性,促进土壤改善养分状况.     

Characterization and origin of polar dissolved organic matter from the Great Salt Lake

Polar dissolved organic matter (DOM) was isolated from a surface-water sample from the Great Salt Lake by separating it from colloidal organic matter by membrane dialysis, from less-polar DOM fractions by resin sorbents, and from inorganic salts by a combination of sodium cation exchange followed by precipitation of sodium salts by acetic acid during evaporative concentration. Polar DOM was the most abundant DOM fraction, accounting for 56% of the isolated DOM. Colloidal organic matter was ¹⁴C-age dated to be about 100% modern carbon and all of the DOM fractions were ¹⁴C-age dated to be between 94 and 95% modern carbon. Average structural models of each DOM fraction were derived that incorporated quantitative elemental and infrared, ¹³C-NMR, and electrospray/mass spectrometric data. The polar DOM model consisted of open-chain N-acetyl hydroxy carboxylic acids likely derived from N-acetyl heteropolysaccharides that constituted the colloidal organic matter. The less polar DOM fraction models consisted of aliphatic alicyclic ring structures substituted with carboxyl, hydroxyl, ether, ester, and methyl groups. These ring structures had characteristics similar to terpenoid precursors. All DOM fractions in the Great Salt Lake are derived from algae and bacteria that dominate DOM inputs in this lake.     

Controls on the release of dissolved organic carbon and nitrogen from a deciduous forest floor investigated by manipulations of aboveground litter inputs and water flux

Although dissolved organic matter (DOM) released from the forest floor plays a crucial role in transporting carbon and major nutrients through the soil profile, its formation and responses to changing litter inputs are only partially understood. To gain insights into the controlling mechanisms of DOM release from the forest floor, we investigated responses of the concentrations and fluxes of dissolved organic carbon (DOC) and nitrogen (DON) in forest floor leachates to manipulations of throughfall (TF) flow and aboveground litter inputs (litter removal, litter addition, and glucose addition) at a hardwood stand in Bavaria, Germany. Over the two-year study period, litter manipulations resulted in significant changes in C and N stocks of the uppermost organic horizon (Oi). DOC and DON losses via forest floor leaching represented 8 and 11% of annual litterfall C and N inputs at the control, respectively. The exclusion of aboveground litter inputs caused a slight decrease in DOC release from the Oi horizon but no change in the overall leaching losses of DOC and DON in forest floor leachates. In contrast, the addition of litter or glucose increased the release of DOC and DON either from the Oi or from the lower horizons (Oe + Oa). Net releases of DOC from the Oe + Oa horizons over the entire manipulation period were not related to changes in microbial activity (measured as rates of basal and substrate-induced respiration) but to the original forest floor depths prior to manipulation, pointing to the flux control by the size of source pools rather than a straightforward relationship between microbial activity and DOM production. In response to doubled TF fluxes, net increases in DOM fluxes occurred in the lower forest floor, indicating the presence of substantial pools of potentially soluble organic matter in the Oe + Oa horizons. In contrast to the general assumption of DOM as a leaching product from recent litter, our results suggest that DOM in forest floor leachates is derived from both newly added litter and older organic horizons through complex interactions between microbial production and consumption and hydrologic transport.     

Physicochemical and spectroscopic characteristics of dissolved organic matter extracted from municipal solid waste (MSW) and their influence on the landfill biological stability

For the purpose of evaluating the stability of municipal solid waste (MSW) excavated from a landfill, dissolved organic matter was extracted and characterized by physicochemical and spectroscopic methods. Results showed that dissolved organic carbon concentration, ratio of dissolved organic carbon to dissolved organic nitrogen, and specific ultraviolet absorbance at 254 nm were in the range of 0.383-3.502 g kg⁻¹, 0.388-3.693 and 2.700-4.629 L mg⁻¹ m⁻¹, respectively, indicating the stability of MSW. Results obtained from Fourier transform infrared spectra have demonstrated that the stability of excavated MSW was characterized by disappearance of some easily biodegradable compounds; and the 1635/1406 ratio varied from 0.979 to 1.840 and was higher than that of the matured compost. The excitation-emission matrix spectra have shown that the principal components in excavated MSW comprised humic substances and the MSW was stable by the presence of a peak with wavelength pair of ∼280/420 nm.     

Chemical Characteristics and Origin of Dissolved Organic Matter in the Yukon River

Monthly (or bi-weekly) water samples were collected from the Yukon River, one of the largest rivers in North America, at a station near the US Geological Survey Stevens Village hydrological station, Alaska from May to September 2002, to examine the quantity and quality of dissolved organic matter (DOM) and its seasonal variations. DOM was further size fractionated into high molecular weight (HMW or colloidal, 1 kDa–0.45 μm) and low molecular weight (LMW, <1 kDa) fractions. Dissolved organic carbon (DOC), colored dissolved organic matter (C-DOM) and total dissolved carbohydrate (TCHO) species were measured in the size fractionated DOM samples. Concentrations of DOC were as high as 2830 μmol-C l⁻¹ during the spring breakup in May and decreased significantly to 508–558 μmol-C l⁻¹ during open-water season (June–September). Within the DOC pool, up to 85% was in the colloidal fraction (1 kDa–0.45 μm) in early May. As DOC concentration decreased, this colloidal portion remained high (70–85% of the bulk DOC) throughout the sampling season. Concentrations of TCHO, including monosaccharides (MCHO) and polysaccharides (PCHO), varied from 722 μmol-C l⁻¹ in May to 129 μmol-C l⁻¹ in September, which comprised a fairly constant portion of bulk DOC (24±2%). Within the TCHO pool, the MCHO/TCHO ratio consistently increased from May to September. The C-DOM/DOM ratio and the size fractionated DOM increased from May to September, indicating that DOM draining into the Yukon River contained increased amounts of humified materials, likely related to a greater soil leaching efficiency in summer. The average composition of DOM was 76% pedogenic humic matter and 24% aquagenic CHO. Characteristics of soil-derived humic substances and low chlorophyll-a concentrations support a dominance of terrestrial DOM in Yukon River waters.     

TOC, TON, TOS and TOP in Rainfall, Throughfall, Litter Percolate and Soil Solution of a Montane Rainforest Succession at Mt. Kilimanjaro, Tanzania

Organic nutrients have proven to contribute significantly to nutrient cycling in temperate forest ecosystems. Still, little is known about their relevance in the tropics. In the present study, organic C, N, S and P were analysed in rainfall, throughfall, litter percolate and soil solution of a montane rainforest at Mt. Kilimanjaro, Tanzania. The aim was to determine the amounts of organic nutrients in different water pathways and to assess the influence of forest disturbance on organic nutrients by comparing mature forests, secondary forests and shrub vegetation in clearings. Concentrations of all studied elements increased from rainfall to throughfall and litter percolate and then exhibited a rapid decrease in the mineral soil. Concentrations of organic P were above the detection limit only in the litter percolate. Organic N (ON) as a fraction of total N increased from 50% in rainfall (0.19 mg l⁻¹) to 66% (0.45 mg l⁻¹) in throughfall followed by a decline to 39% in the litter percolate (0.77 mg l⁻¹) of the mature forest. Similarly, proportions of organic S and P amounted to 43 and 34%, respectively, in the litter percolate in mature forest. For ON, this proportion further decreased to less than 10% in the soil solution. The latter was probably attributable to a high sorption capacity of the studied Andisols, which led to overall low organic element concentrations in the soil solution (OC: 1.2 mg l⁻¹, ON: 0.05 mg l⁻¹ at 1 m soil depth) as compared to other temperate and tropical forest ecosystems. Organic element concentrations were higher in litter percolate and soil solution under the clearings, but there were no differences in the relative contribution of these elements. Organic nutrient forms at Mt. Kilimanjaro appeared to be much less susceptible to leaching than their inorganic forms.     

Changes in dissolved lignin-derived phenols, neutral sugars, uronic acids, and amino sugars with depth in forested Haplic Arenosols and Rendzic Leptosols

A major part of the dissolved organic matter produced in the organic layers of forest ecosystems and leached into the mineral soil is retained by the upper subsoil horizons. The retention is selective and thus dissolved organic matter in the subsoils has different composition than dissolved organic matter leached from the forest floor. Here we report on changes in the composition of dissolved organic matter with soil depth based on C-to-N ratios, XAD-8 fractionation, wet-chemical analyses (lignin-derived CuO oxidation products, hydrolysable sugars and amino sugars) and liquid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy. Dissolved organic matter was sampled directly beneath the forest floor using tension-free lysimeters and at 90cm depth by suction cups in Haplic Arenosols under Scots pine (Pinus sylvestris L.) and Rendzic Leptosols under European beech (Fagus sylvatica L.) forest. At both sites, the concentrations of dissolved organic carbon (DOC) decreased but not as strongly as reported for deeply weathered soils. The decrease in DOC was accompanied by strong changes in the composition of dissolved organic matter. The proportion of the XAD-8-adsorbable (hydrophobic) fraction, carboxyl and aromatic C, and the concentrations of lignin-derived phenols decreased whereas the concentrations of sugars, amino sugars, and nitrogen remained either constant or increased. A general feature of the compositional changes within the tested compound classes was that the ratios of neutral to acidic compounds increased with depth. These results indicate that during the transport of dissolved organic matter through the soils, oxidatively degraded lignin-derived compounds were preferentially retained while potentially labile material high in nitrogen and carbohydrates tended to remain dissolved. Despite the studied soils' small capacity to sorb organic matter, the preferential retention of potentially refractory and acidic compounds suggests sorption by the mineral soil matrix rather than biodegradation to govern the retention of dissolved organic matter even in soils with a low sorption capacity.     

Bacterial Degradation of Dissolved Organic Matter from Two Northern Michigan Streams

This study used high-pressure size exclusion chromatography (HPSEC) to measure the changes in molecular weight distributions of dissolved organic matter (DOM) of two Northern Michigan streams following inoculation with bacterial concentrates from the same locations. During the initial 12 h of the experiment, weight average molecular weight (M _w ) of DOM decreased, as high molecular weight components were lost from solution. After 12 h, the M _w of DOM increased, primarily because of a loss of intermediate to lower molecular weight components. Leucine incorporation showed little or no bacterial metabolism during the first 12 h, but metabolism increased substantially after 12 h. The initial loss of high molecular weight components during the period of little or no bacterial metabolism suggests preferential adsorption of these components to the bacterial surfaces, perhaps followed by metabolism. This suggested interpretation is consistent with previous observations of preferential adsorption of higher molecular weight components to viable but non-metabolizing Bacillus subtilis and to mineral surfaces. The latter loss of lower molecular weight components was most likely due to bacterial metabolism of the DOM, which is consistent with previous observations that lower molecular weight components are more biodegradable. The HPSEC technique uses 254 nm wavelength for detection and focuses primarily on humic- and fulvic-type components rather than low molecular weight organic molecules, such as carbohydrates. Thus, results confirmed that humic/fulvic components are biodegradable, but did not address other DOM components.     

Chromophoric dissolved organic matter (CDOM) absorption characteristics in relation to fluorescence in Lake Taihu,China, a large shallow subtropical lake

Absorption measurements from chromophoric dissolved organic matter (CDOM) and their relationships with dissolved organic carbon (DOC) and fluorescence were studied in Lake Taihu, a large, shallow, subtropical lake in China. Absorption spectra of lake water samples were measured from 240 nm to 800 nm. Highest values of a(λ), DOC and F _n (355) occurred near the river inflow to Meiliang Bay and decreased towards the central lake basin. A significant spatial difference was found between Meiliang Bay and the central lake basin in absorption coefficient, DOC-specific absorption coefficient, exponential slope coefficient, DOC concentration and fluorescence value. The spatial distribution of CDOM suggested that a major part of CDOM in the lake was from river input. CDOM absorption coefficients were correlated with DOC over the wavelength range 280–500 nm, and a(355) was also correlated with F _n (355), which showed that CDOM absorption could be inferred from DOC and fluorescence measurement. The coefficient of variation between a(λ) and DOC concentration decreased with increase in wavelength from 240 nm to 800 nm. Furthermore, a significant negative linear relationship was recorded between S value and CDOM absorption coefficient, as well as DOC-specific absorption coefficient. S value and DOC-specific absorption coefficient were used as a proxy for CDOM composition and source. Accurate CDOM absorption measurements are very useful in explaining UV attenuation and in developing, validating remote sensing model of water quality in Lake Taihu.