How the deadwood of different tree species in various stages of decomposition affected nutrient dynamics?

Purpose

The aim of the study was to estimate how the deadwood of different tree species in various stages of decomposition affected nutrient dynamics.

Materials and methods

The deadwood of eight species (common alder, common aspen, common ash, silver fir, pedunculate oak, Norway spruce, common hornbeam and silver birch) was selected. Three logs from each species in the third, fourth and fifth decay classes were chosen for analysis. Wood in the third decay class was characterised by larger hard fragments, fragmented bark and no branches; in the fourth decay class, it was characterised by small pieces and a fragmented bark; and in the fifth decay class, it was characterised by a soft texture and no bark. The investigation was carried out in the Czarna Rózga Reserve in Central Poland. Tension lysimeters were installed under each log in the humus horizon. The water samples collected from tension lysimeters were chemically analysed in the laboratory. The water chemistry was analysed by means of ion chromatography using a DIONEX ICS 5000 unit.

Results and discussion

The leachate obtained from different tree species contained different ion concentrations. The high similarity of the concentration of total anions and statistically significant differences in the content of total cations were determined in the leachate from the wood of coniferous and deciduous species. The concentration of the cations increases with the advancement of the decomposition level. A general linear model analysis demonstrates that wood species and the decomposition classes are of equal importance in defining the ion composition of the filtrate leaching from deadwood.

Conclusions

Wood at the highest decomposition stage releases more ions to the surface soil layers than wood at the lower decay class. An exception from the rule is the wood of birch, which in the III decay class releases more ions than in its higher decay classes. When comparing the ionic composition of leachate released from wood of coniferous and deciduous tree species, the latter are characterised by higher cation concentrations in comparison with coniferous species. Among the deciduous species, wood of such species as ash, hornbeam, aspen, birch and alder has the most favourable effects on the soil surface horizons through its supply with ionic substances. The ash wood releases high amounts of calcium, hornbeam wood releases magnesium and sodium, and aspen releases calcium, potassium and nitrate anion. From the analysed coniferous species, fir wood has a more favourable effect in terms of ion release to soil than spruce wood.

     

Amounts and degradability of dissolved organic carbon from foliar litter at different decomposition stages

Litter is one of the main sources of dissolved organic carbon (DOC) in forest soils and litter decomposition is an important control of carbon storage and DOC dynamics. The aim of our study was to evaluate (i) effects of tree species on DOC production and (ii) relationships between litter decomposition and the amount and quality of DOC. Five different types of leaves and needles were exposed in litterbags at two neighboring forest sites. Within 12 months we sampled the litterbags five times and leached aliquots of field moist litter in the laboratory. In the collected litter percolates we measured DOC concentrations and recorded UV and fluorescence spectra in order to estimate the aromaticity and complexity of the organic molecules. Furthermore, we investigated the biodegradability of DOC from fresh and decomposed litter during 6 weeks incubations. Fresh sycamore maple litter released the largest amounts of DOC reaching about 6.2% of litter C after applying precipitation of 94 mm. We leached 3.9, 1.6, 1.0 and 3.3% carbon from fresh mountain ash, beech, spruce and pine litter, respectively. In the initial phase of litter decomposition significantly decreasing DOC amounts were released with increasing litter mass loss. However, after mass loss exceeds 20% DOC production from needle litter tended to increase. UV and fluorescence spectra of percolates from pine and spruce litter indicated an increasing degree of aromaticity and complexity with increasing mass loss as often described for decomposing litter. However, for deciduous litter the relationship was less obvious. We assume that during litter decomposition the source of produced DOC in coniferous litter tended toward a larger contribution from lignin-derived compounds. Biodegradability of DOC from fresh litter was very high, ranging from 30 to 95% mineralized C. DOC from degraded litter was on average 34% less mineralizable than DOC from fresh litter. Taking into account the large DOC production from decomposed needles we can assume there is an important role for DOC in the accumulation of organic matter in soils during litter decomposition particularly in coniferous forests.     

西藏原始暗针叶林凋落物有机碳释放特征与土壤有机碳库关系研究

结合野外凋落物分解袋法和室内分析试验,对藏东南2种典型暗针叶林—急尖长苞冷杉(Abies georgei var.Smithii)和林芝云杉(Picea likiangensis var.linzhiensis)凋落物的分解和有机碳释放特征进行研究,分析了2种亚高山暗针叶林凋落物有机碳释放速率与土壤有机碳及其组分之间的关系。结果表明:藏东南2种原始暗针叶林凋落物分解均呈现出雨季分解快(4—9月)、旱季分解慢(10—翌年3月),前期分解快(3—9月)、后期分解慢(10—翌年2月)的特征,且冷杉(PLLF)分解速率大于云杉(AGSF),Olson指数衰减模型能够较好地模拟2种暗针叶林凋落物的分解,冷杉(PLLF)和云杉(AGSF)凋落物半分解时间为2.11,2.52年;分解95%时间为8.96,10.84年;2种暗针叶林凋落物中有机碳含量表现出先上升后下降,再平稳降低的趋势,而2种暗针叶林凋落物中有机碳释放速率表现出先短暂富集再释放的模式;2种暗针叶林土壤总有机碳(TOC)及其活性组分(MBC、POC、LOC)含量都具有明显的表聚性(p<0.01),且同一土壤层次内TOC、MBC、POC、LOC互相之间均呈极显著正相关关系(p<0.01);2种暗针叶林凋落物分解进程中有机碳的释放速率与表层土(0—10 cm)中TOC、MBC、POC、LOC含量、10—20 cm土层中的TOC、MBC含量以及20—40 cm土层中MBC含量之间呈现显著的正相关(p<0.05)。     

不同复垦年限煤矸山重构土壤有机碳及其组分差异

土壤有机碳含量是土壤肥力状况的重要标志之一,其活性组分对田间管理措施反映敏感。因此,分析煤矸山复垦重构土壤有机碳含量及其组分差异对于揭示土壤碳库变化、指导复垦地田间管理措施的实施有重要意义。本研究以山西省霍州曹村煤矸山复垦后5a(R-5a)、7a(R-7a)和9a(R-9a)的果园为对象,通过与当地原地貌果园(CK)对比,分析了3种复垦样地土壤总有机碳(TOC)及其组分可溶性有机碳(DOC)、微生物生物量碳(MBC)、轻组有机碳(LFOC)和重组有机碳(HFOC)的差异,以及与土壤环境因子间的关系。结果表明:①随复垦年限的增加,3种复垦样地土壤TOC、LFOC和HFOC含量均呈先增后减趋势,DOC含量呈增加趋势,MBC含量呈先减后增趋势;但与CK相比,3种复垦样地土壤TOC、DOC、MBC、LFOC和HFOC含量均明显偏低。②DOC/TOC和MBC/TOC在R-7a样地中最低,LFOC/TOC随复垦年限的增加呈增加趋势,HFOC/TOC呈减少趋势,表明土壤中更多的有机碳从稳定态转变为活性态。③土壤全氮、全磷、碱解氮、碳氮比、黏粒含量、pH和含水量均不同程度影响有机碳含量,其中全氮、全磷、黏粒含量和土壤pH为关键因子。     

The contribution of fresh litter to dissolved organic carbon leached from a coniferous forest floor

The relative contributions of litter and humified organic matter as the source of dissolved organic carbon (DOC) leached from organic layers of forest soils are poorly understood. In the present investigation, ¹³C labelled spruce litter was used to study the role of recent litter in the leaching of DOC from a coniferous forest floor in southern Sweden, while litterbags were used to quantify the total loss of C from the labelled litter. The labelled litter applied on bare lysimeters released considerable amounts of DOC during the first weeks, but the concentration of DOC originating from labelled litter decreased gradually from 176 mg litre⁻¹ during the first sampling period in May to 5 mg litre⁻¹ in the last sampling period in October. Only a moderate flush of DOC from the labelled litter occurred under the Oe and Oa horizons, with concentrations of 20 and 6 mg litre⁻¹ from labelled litter, equal to 19 and 9% of the total DOC flux, respectively, during the first sampling period. Total flux of DOC from labelled litter from May to September was 16 g m⁻², whereas only 2.2 and 0.9 g m⁻² were captured under the Oe and Oa horizons, respectively. The almost complete loss of new DOC implies that DOC leached from the Oe and Oa horizons consists not of recent litter‐derived carbon, but of DOC produced in these two horizons themselves. Water‐extractable organic carbon from labelled litter left in litterbags in the field for 4 months consisted of about one‐third native carbon from external sources at the experimental site and two‐thirds of the labelled litter. In contrast, the ¹³C content of the bulk litter from the litterbags was not changed by the incubation in the field. We suggest that the soluble native carbon in water extracts originated from throughfall DOC that had been assimilated by microorganisms in the litterbags.     

Characterization of dissolved organic matter in decomposing Norway spruce and silver birch litter

Dissolved organic matter (DOM) plays an important role in transport, storage and cycling of carbon (C) and nitrogen (N) in forest soils where litter is one of the main sources. The aim was to study the amount and characteristics of DOM leached from freshly fallen litters of silver birch (Betula pendula Roth.), Norway spruce (Picea abies (L.) Karst.) and their mixture during decomposition. DOM was collected after irrigation on eight occasions during 252 days incubation in the laboratory at about 18°C, including one freeze‐thaw cycle. During the incubation about 33–35% of C from birch and spruce litter and 40% of C from their mixture was lost. The total cumulative flux of dissolved organic carbon (DOC) from the mixture of litters was approximately 40% larger than that from single litters. The flux of DOC, DON, phenolic compounds and proteins followed a two‐stage pattern during decomposition. In the first stage the initially large fluxes decreased gradually. In the second stage, after freezing and thawing, the fluxes tended to increase again. Mixing birch and spruce litters and a freeze‐thaw cycle seems to increase the decomposition of litter and result in the increased flux of DOC, DON and phenolic compounds. The flux of hemicelluloses and the degradability of DOM were large at the first leaching occasion and decreased during the incubation. Birch had a 40% larger total flux of easily degradable DOM than spruce, supporting the previous consistent signs of greater microbial biomass and activities related to C and N cycling in soil under birch than under spruce. It is known that recalcitrant DOM might be stabilized whereas labile DOM may promote microbial activity and nutrient cycling. We conclude that the storage and cycling of C and N is affected by both tree species and degradation stage of litter in forest soils.     

Linking the abundance of aspen with soil faunal communities and rates of belowground processes within single stands of mixed aspen–black spruce

The occurrence of aspen (Populus tremuloides Michx.) patches within stands dominated by black spruce (Picea mariana Mill. BSP) has been shown to increase litter decomposition and nutrient cycling rates by improving soil physical and chemical properties. It is well known, however, that these processes are also influenced by the structure of the soil biota, but this factor has received less attention. In this study, relationships between forest floor properties and soil invertebrates were studied along black spruce–trembling aspen gradients in three stands of the eastern boreal forest of Canada. The forest floor layer of 36 plots differing in aspen basal area was sampled and analyzed to determine physical and chemical properties, the rates of decomposition of standard substrates, net N mineralization, as well as microbial basal respiration and metabolic quotient. Soil invertebrates were also collected using funnel-extraction and pitfall trapping methods. Based on redundancy analyses, we found that forest floor properties, the abundance and composition of soil invertebrates, and the rates of belowground processes changed along the spruce–aspen gradient. The increase in aspen basal area was associated with a reduction in forest floor thickness, moisture content and microbial biomass, and with an increase in the concentration of nutrients. It was also accompanied by changes in soil faunal communities, as soil invertebrates were associated with specific soil properties. In general, macroinvertebrates (i.e., Lumbricidae, Formicidae, Carabidae, Staphylinidae and Gastropoda) were related to the nutrient-rich forest floor associated with aspen, whereas microarthropods and Enchytraeidae tended to be negatively related to aspen basal area. According to mixed linear models, decomposition rates of standard substrates and net ammonification significantly increased along the spruce–aspen gradient. Given the functional significance of macroinvertebrates in soils, these results suggest that aspen favours the elaboration of a macrofaunal community, which in turn accelerates the rate of soil processes by having either direct or indirect influence on microbial activity. Moreover, this study shows that the changes in soil processes and in the biodiversity of soil organisms related to the presence of mixed stands can operate only in the immediate surroundings of a given tree species. Therefore, coarse-scale tree species mixing in a forest stand may have a different effect on soil biodiversity and soil processes than fine-scale mixing.     

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。     

乌梁素海和岱海上覆水中碳的形态分布及其制约机制

以乌梁素海和岱海2个不同类型湖泊上覆水中TIC、DIC、TOC、DOC的地球化学特征为基础,分析和探讨了2个湖泊上覆水的水化学特征和TIC、DIC、TOC、DOC的空间分布格局及其制约机制。结果表明,乌梁素海和岱海湖泊的水化学特征均属蒸发-浓缩类型,湖泊水体离子组分特征受控于流域的蒸发-浓缩作用及蒸发盐岩的风化作用;岱海TIC、DIC、TOC、DOC的含量范围分别为（0.93-1.16）×10^4、（0.78-0.90）×10^4、（0.07-0.63）×10^4、（0.07-0.48）×10^4 μmol·L^-1,乌梁素海TIC、DIC、TOC、DOC的含量范围分别为（0.18-1.00）×10^4、（0.03-0.81）×10^4、（0.10-0.51）×10^4、（0.04-0.32）×10^4 μmol·L^-1,2个湖泊上覆水中TIC和DIC含量的差异性是湖泊富营养化类型、自然地理区划、水文地质背景及水量收支方式等因素综合作用的结果;岱海上覆水中DIC、TIC、DOC、TOC受N、P、Si等3种营养盐的共同影响,乌梁素海上覆水中DIC、TIC、DOC、TOC主要受N的影响。     

土壤溶解性有机碳四种测定方法的对比和转换

针对土壤溶解性有机碳(DOC)不同测定方法之间可比性较差的问题,应用TOC仪法、容量法、紫外分光光度法和比色法分别测定了中亚热带丘陵山地6个土属共46个新鲜土壤样品的DOC含量。结果表明:参照TOC仪法测得的DOC数据,容量法一致性地低估20%~67%;比色法测定DOC含量较低的底土时(200 mg/kg)仅低估7%~27%,但在分析DOC含量较高的表土(600 mg/kg)时最不敏感,低估达53%~93%;紫外分光光度法在DOC含量较高时也存在一定的低估,但在DOC含量较低时高估65%~189%。4种方法测得的DOC数据均呈极显著正相关关系(P0.01)。统计分析获得的线性或指数方程可应用于将容量法、紫外分光光度法和比色法的测定结果向TOC仪法的数据转换,而且有必要针对表土和底土使用不同的转换方程或参数,这些经验转换方程的建立有助于增强不同研究结果之间DOC数据的可比性,也有利于推动土壤DOC测定标准的完善。     

控制条件下水肥耦合对黄泥田还田秸秆腐解及土壤碳转化的影响

【目的】研究秸秆还田后不同水温和肥剂管理措施下土壤碳素转化特征。【方法】以华中双季稻区低产水稻土黄泥田为供试材料,模拟早稻和晚稻秸秆还田的田间环境,在实验室控制条件下,开展了两种温度环境中(15℃、35℃)不同水分(40%和100%最大田间持水量,即40%WHC、100%WHC)、配施氮肥类型(尿素、猪粪即U、M)、以及促腐菌剂添加对秸秆腐解效果及其过程中土壤碳素转化影响的研究。对水稻秸秆腐解过程中土壤CO2释放量、以及土壤可溶性有机碳(DOC)和总有机碳(TOC)含量在105天培养周期内变化特征进行动态监测分析。【结果】两种温度环境中整个培养周期内,各处理的CO2释放速率和释放总量通常表现为100%WHC-M100%WHC-U40%WHC-M40%WHC-U,即猪粪优于尿素的规律,而不论配施何种氮肥都存在100%WHC40%WHC(P0.01)的现象,同时40%WHC条件下辅施菌剂可显著提升CO2释放量;与此相反,两种温度环境下DOC含量都表现为40%WHC-M40%WHC-U100%WHC-M100%WHC-U(后两者差异小),即40%WHC条件下DOC含量显著高于100%WHC(P0.05),且配施猪粪处理优于配施尿素处理,但这两种氮肥处理间差异随培养时间延长而减小;以CO2-C释放量计算0 7 d、0 28 d、0 105 d内物料分解率,结果表明,35℃时100%WHC-U的处理中物料分解最快,15℃时40%WHC-M的处理中物料分解最慢。与之对应,105 d内TOC含量和净增量则在35℃时100%WHC-U的处理中最小(P0.01),而在15℃时40%WHC-M的处理中最大(P0.01);TOC的净增量和净损失量在相同温度条件下,尤其试验前期不同水分(P0.01)、氮素(P0.05)间均存在显著差异,且促腐菌剂添加普遍减小TOC含量;培养周期内所有处理的CO2释放速率与DOC含量间存在显著相关(P0.05)。【结论】水分状况对碳素的转化存在极大影响,其次是氮肥类型,且氮肥的影响作用随秸秆还田时间的延长而减弱;高湿条件更利于促进秸秆腐解,但导致土壤DOC含量较低,TOC的固持量也较少,而配施猪粪则可促进土壤DOC含量的提升及TOC的固持;促腐菌剂添加可促进秸秆腐解,但由于40%WHC条件下显著激发了CO2的释放而不利于土壤固碳。因此在华中低产黄泥田双季轮作稻区,早稻还田时由于气温高周期短,建议保持100%WHC、辅施适量尿素、并配合添加秸秆腐解菌剂,侧重秸秆快腐;而晚稻还田时气温低周期长,建议保持40%WHC并辅施缓效猪粪,侧重土壤固碳。     

Amounts of carbon mineralised and leached as DOC during decomposition of Norway spruce needles and fine roots

Changes in climate or forest management practices leading to increased litter production will most likely cause increased leaching rates of dissolved organic carbon (DOC) from the O horizon. The rhizosphere is often assumed to have a large carbon flux associated with root turnover and exudation. However, little has been done to quantify the amount of DOC originating from root litter. We studied decomposition of fine root and needle litter of Norway spruce (Picea abies) through a combined incubation and leaching experiment in the laboratory using five different litter types: fresh needle litter, aged needles from the litter layer, fresh and dead roots from mineral soil samples, and seven-year-old roots from a previous litterbag study. After respiration measurements, the samples were percolated with artificial throughfall water and DOC and UV absorbance were measured in the leachate. Mineralisation of dissolved organic matter in the leachate and sorption of DOC to ferrihydrite were determined as a measure of DOC ability to be stabilised by iron (hydr)oxide surfaces.The mineralisation rate and DOC production rate of root samples were always lower than that of needle samples. However, root and needle derived dissolved organic matter (DOM) were similar in terms of aromaticity, as indicated by their specific UV absorbance, and ability to be sorbed by ferrihydrite. For seven-year-old roots, a significantly higher fraction of carbon was lost as DOC (30%) than for younger roots (20%). Furthermore, DOM from old roots bound more strongly to ferrihydrite and is mineralised at a lower rate than DOC from younger roots, suggesting that roots at late stages of decomposition, although a small fraction of total litter, significantly contribute to carbon build-up in mineral soils. The slower decomposition rate of roots compared with needles must be taken into account when modelling litter decomposition.     

黄土区不同类型土壤微生物量碳、氮和可溶性有机碳、氮的含量及其关系

研究了黄土高原南部地区不同土壤类型及不同利用方式下土壤微生物摄碳、氮和可溶性有机碳、氮的含量。结果表明：不同土地利用方式下，土壤微生物量碳、氮和可溶性有机碳、氮含量均为林地〉农田，其中林地枯枝落叶层〉林地O～20cm土层。农田土壤微生物量碳、氮的含量均为红油土〉黑垆土〉淋溶褐土；农田土壤中可溶性有机碳含量为淋溶褐土〉红油土〉黑垆土，而可溶性有机氮含量则为黑垆土〉红油土〉淋溶褐土。方差分析表明，不同土壤类型土壤微生物量氮含量之间的差异达显著水平，而不同土壤类型间土壤微生物量碳、可溶性有机碳、氯含量之间的差异未达显著水平。土壤微生物量碳、氮占土壤有机碳和全氮的比例明显高于可溶性有机碳、氮占土壤有机碳和全氮的比例。相关分析发现，土壤微生物量碳与可溶性有机碳之间以及土壤微生物量氮与可溶性有机氮之间的相关性达显著或极显著水平，说明土壤微生物量碳、氮和土壤可溶性有机碳、氮之间有密切联系。     

庐山不同林分类型土壤活性有机碳及其组分与土壤酶的相关性

土壤活性有机碳直接参与土壤生物化学转化过程,影响土壤酶活性,对土壤养分有效化作用明显。以庐山3种不同林分类型下土壤为研究对象,通过对不同林分下土壤活性有机碳及其组分与土壤酶活性状况进行相关分析。结果表明:（1）3种林分类型下WSOC和DOC平均含量排序均为阔叶林 > 针阔混交林 > 针叶林,而ROC由大到小依次为针阔混交林 > 阔叶林 > 针叶林;针阔混交林下MBC平均含量较高,针叶林下MBC平均含量较低。（2）3种林分类型下土壤蔗糖酶活性排序为针阔混交林 > 阔叶林 > 针叶林;纤维素酶和酸性磷酸酶活性的大小顺序为针叶林 > 针阔混交林 > 阔叶林;针阔混交林下脲酶活性最低,阔叶林最高;针阔混交林下多酚氧化酶活性最高,阔叶林最低;过氧化氢酶活性高低序列为阔叶林 > 针阔混交林 > 针叶林。（3）3种林分类型下土壤蔗糖酶、纤维素酶等水解酶与土壤活性有机碳各组分的相关性较好,多酚氧化酶、过氧化氢酶等氧化酶与土壤活性有机碳各组分之间没有表现出明显的相关性。     

Carbon pools and fluxes of 25-year old coniferous and deciduous stands in middle Siberia

Between 72 and 88% of carbon (C) loss in forest litter decomposition returns to the atmosphere in the form of carbon dioxide. The share of water-soluble organic products does not exceed 3–4%. Between 8% under spruce and 25% under aspen and pine of the total C loss from litter organic matter goes to the formation of humus. Decomposition intensity of the dead organic matter on the soil surface is close to annual litterfall income (except under cedar). The specific rate of decomposition processes among the coniferous litters is minimum for cedar (167 mgC g^?1yr^?1) and maximum for larch (249 mg C g^?1 yr^?1). The specific rate of decomposition of organic residues under aspen and birch canopies are 344 and 362 mg C g^?1yr^?1.     

红壤稻田土壤溶解有机碳含量动态及其生物降解特征

本通过田间采样分析和室内培育试验,研究了不同利用年限的3种红壤水田土壤中溶解有机C(DOC)的含量动态和生物降解特征。结果表明：土壤DOC的含量随土壤深度而降低,二具有显负相关性。0-30cm土壤DOC的含量及其占总C比例随土壤有机C含量的升高而增大。DOC的季节变化明显,主要与气候因素有关：降雨和灌水可显提高DOC的含量,是落干时含量的1．44-2．50倍。淋溶试验结果表明,从试验开始,淋滤液中DOC的浓度呈增加趋势,至2l天时达到最大,其后又趋下降。在49天的培养期内,DOC的分解速率为3l％-58％,其中低分子量组分能在数天内降解掉。不同土壤间DOC的分解速率有明显差异。     

土地利用方式对土壤活性有机碳含量影响的初步研究

以我国川中丘陵区紫色土为背景,研究了5种不同土地利用方式对土壤活性有机碳(可溶性有机碳和微生物量碳)含量的影响,分析了可溶性有机碳(DOC)、微生物量碳(MBC)、总有机碳(TOC)的关系。结果表明,土地利用方式对土壤活性有机碳有显著影响。DOC含量呈现菜地>果园>水田>林地>旱地的趋势;MBC含量为水田>果园>菜地>林地>旱地。有机物质的输入量、种植制度和土壤管理措施是差异存在的重要原因。菜地、旱地、林地、果园和水田的DOC/TOC均值分别为0.58%、0.28%、0.19%、0.57%和0.28%,其相应的MBC/TOC均值分别为3.57%、3.09%、2.38%、2.67%和3.42%。经相关性分析,5种土地利用方式DOC、MBC含量与TOC之间的差异性达到了显著或极显著水平。     

Land use effects on the dynamics of soil C, N and microbes in the water-wind erosion crisscross region of the northern Loess Plateau, China

The water-wind erosion crisscross region of the northern Loess Plateau in China is under constant pressure from severe erosion due to its windy and dry climate and intensive human activities. Identifying sustainable land use patterns is key to maintaining ecosystem sustainability in the area. Our aim was to appraise the impacts of different land use regimes on the dynamics of soil total organic C(TOC), total N(TN), and microbes in a typical watershed in the northern Loess Plateau to identify sui...     

黄土高原半干旱区不同土地利用下的土壤有机碳、碳组分和土壤营养

Cropland (CP), native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L. ) (ST), and branchytamarisk (Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China. Total organic carbon (TOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), total N (TN), nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N), ammonium nitrogen (NH₄⁺-N), total P, and available P (AP) were measured. The results showed that SOC in NG, ST and BT were 12.7%, 27.7% and 34.8% higher than that of the cropland, respectively. LFOC, light fraction (LF) dry matter, ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland. Cropland had the highest TN, the sum of NO₃^--N and NO₂^--N, TP and AP due to the use of chemical fertilizers. TOC significantly correlated with LFOC, HFOC and C/N. LFOC significantly correlated with dry matter of the LF and C/N. TN, the sum of NO₃^--N and NO₂^--N and AP were significantly negatively correlated with TOC and LFOC. Therefore, land use conversion from cropland to shrub land, or maybe grassland, contributed to SOC sequestration and improved soil nutrients stabilization.     

Dissolved soil organic nitrogen and carbon in a Norway spruce stand and an adjacent clear-cut

 The aims of this study were to characterize dissolved soil organic N (DON) and C (DOC) in a coniferous stand and an adjacent clear-cut, and to evaluate the importance of DON in N leaching. The study was carried out in a Norway spruce stand and a clear-cutting treatment in the same forest stand. Concentrations of DON in soil solution were monitored for 5 years after clear-cutting with gravity lysimeters. In the Norway spruce stand DON comprised 62–83% of the total N in soil solution over the 5-year period. The concentrations of DON in the clear-cut were higher than in the forest stand, but the proportion of total N was lower. To characterize dissolved organic matter, soil samples were aerobically incubated for 6 weeks in the laboratory, and the quantity, molecular size distribution and chemical nature of both DON and DOC were determined from water extracts made before and after the incubation. In the soil samples from the Norway spruce stand, C-rich compounds with a high C/N ratio and large molecular size were formed. In contrast, after the incubation the major carriers of DON in soil samples from the clear-cut were N-rich organic compounds with a low C/N ratio and a small molecular size. The distribution of different chemical fractions of DOC in soil did not differ much whether recovered from the Norway spruce stand or the clear-cut. It was (from highest to lowest concentration): hydrophobic acids>hydrophilic acids>phenols>hydrophilic neutrals. A major part of DON was also carried by these fractions. During incubation the concentration of N-containing hydrophilic acids increased, especially in the soil from the clearcut. In soil samples from the Norway spruce stand, the rate of net N mineralization was low and no NO₃ was formed, whilst the rate of net N mineralization was high and net nitrification was intensive in soil from the clear-cut. Received: 12 June 2000