Distribution characteristics of dissolved organic carbon in annular wetland soil-water solutions through soil profiles in the Sanjiang Plain,Northeast China

Overwhelming evidence reveals that concentrations of dissolved organic carbon （DOC） have increased in streams which brings negative environmental impacts. DOC in stream flow is mainly originated from soil-water solutions of watershed. Wetlands prove to be the most sensitive areas as an important DOC reserve between terrestrial and fluvial biogeosystems. This reported study was focused on the distribution characteristics and the controlling factors of DOC in soil-water solutions of annular wetland, i.e., a dishing wetland and a forest wetland together, in the Sanjiang Plain, Northeast China. The results indicate that DOC concentrations in soilwater solutions decreased and then increased with increasing soil depth in the annular wetland. In the upper soil layers of 0-10 cm and 10-20 cm, DOC concentrations in soil-water solutions linearly increased from edge to center of the annular wetland （R^2 = 0.3122 and R^2 = 0.443）. The distribution variations were intimately linked to DOC production and utilization and DOC transport processes in annular wetland soil-water solutions. The concentrations of total organic carbon （TOC）, total carbon （TC） and Fe（II）, DOC mobility and continuous vertical and lateral flow affectext the distribution variations of DOC in soil-water solutions. The correlation coefficients between DOC concentrations and TOC, TC and Fe（II） were 0.974, 0.813 and 0.753 respectively. These distribution characteristics suggested a systematic response of the distribution variations of DOC in annular wetland soil-water solutions to the geometry of closed depressions on a scale of small catchments. However, the DOC in soil pore water of the annular wetland may be the potential source of DOC to stream flow on watershed scale. These observations also implied the fragmentation of wetland landscape could bring the spatial-temporal variations of DOC distribution and exports, which would bring negative environmental impacts in watersheds of the Sanjiang Plain.

Key Physical Factors Affecting Spatial-temporal Variation of Labile Organic Carbon Fractions by Biochar Driven in Mollisols Region of Northeast China

Biochar is widely used to improve soil physical properties and carbon sequestration. However, few studies focuse on the impact of maize stalk biochar on labile organic carbon(LOC) pool and the relationship between physical properties and LOC fractions. A field positioning experiment was performed in Mollisols region of Northeast China to evaluate the influence of maize stalk biochar on the spatial distribution and temporal changes of physical properties and LOC fractions. Maize stalk biochar treatments included C1(1.5 kg·hm^(-2)), C2(3 kg·hm^(-2)), C3(15 kg·hm^(-2)), C4(30 kg·hm^(-2)), and CK(0). The results showed that maize stalk biochar increased soil water contents(SWC) and soil porosity(SP), but reduced bulk density(BD). Maize stalk biochar reduced dissolved organic carbon(DOC) contents in the 0-20 cm soil layer, ranging from 0.25 g·kg^(-1) to 0.31 g·kg^(-1) in harvest period, while increased in the 20-40 cm soil layer. In addition, the application of biochar had a significant impact on the spatial distribution and temporal change of SWC, BD, SP, DOC, hot-water extractable carbon(HWC), acid hydrolyzed organic carbon(AHC Ⅰ, Ⅱ), and readily oxidized organic carbon(ROC). High amounts of maize stalk biochar up-regulated the contents of soil organic carbon SOC, HWC, AHC Ⅰ, AHC Ⅱ, and ROC. In addition, SWC and SP were the key physical factors to affect LOC fractions. In conclusions, maize stalk biochar could improve physical properties, and then influence LOC fractions, and maize stalk biochar could be used as an organic amendment for restoring degraded soils governed by their rates of addition.

Labile and stabile soil organic carbon fractions in surface horizons of mountain soils–relationships with vegetation and altitude

Global and local climate changes could disturb carbon sequestration and carbon stocks in forest soils. Thus, it is important to characterize the stability of soil organic matter and the dynamics of soil organic carbon(SOC) fractions in forest ecosystems. This study had two aims:(1) to evaluate the effects of altitude and vegetation on the content of labile and stabile forms of organic carbon in the mountain soils; and(2) to assess the impact of the properties of soil organic matter on the SOC pools under changing environmental conditions. The studies were conducted in the Karkonosze Mountains(SW Poland, Central Europe). The content of the most labile fraction of carbon(dissolved organic carbon,DOC) decreases with altitude, but the content of fulvic acids(FA), clearly increases in the zone above 1000 m asl, while the stabile fraction(humins, nonhydrolyzing carbon) significantly decreases. A higher contribution of stabile forms was found in soils under coniferous forests(Norway spruce), while a smaller-under deciduous forests(European beech) and on grasslands. The expected climate change and the ongoing land use transformations in the zone above1000 m asl may lead to a substantial increase in the stable humus fraction(mainly of a non-hydrolyzing carbon) and an increase in the SOC pools, even if humus acids are characterized by a lower maturity and greater mobility favorable to soil podzolization.In the lower zone(below 1000 m asl), a decrease in the most stable humus forms can be expected,accompanied by an increase of DOC contribution,which will result in a reduction in SOC pools. Overall,the expected prevailing(spatial) effect is a decreasing contribution of the most stable humus fractions,which will be associated with a reduction in the SOC pools in medium-high mountains of temperate zone of Central Europe.

Effects of Carbon and Nitrogen Additions on Soil Microbial Biomass Carbon and Enzyme Activities Under Rice Straw Returning

The effects of different amounts of carbon and nitrogen sources on the soil microbial biomass carbon,dissolved organic carbon and related enzyme activities were studied by the simulation experiment of rice straw returning to the field,and the mechanism of the decomposition of rice straw returning to the field was discussed.Completely randomized experiment of the two factors of the three levels was designed,and a total of nine treatments of indoor soil incubation tests were conducted.Full amount of rice straw was applied to the soil in this simulation experiment and different amounts of brown sugar and urea were added in the three levels of 0(no carbon source and nitrogen source),1(low levels of carbon and nitrogen sources)and 2(high levels of carbon and nitrogen sources),respectively.The results showed that the addition of different amounts of carbon and nitrogen sources to the rice straw could increase the soil carbon content.Compared with T0N0,the microbial biomass carbon of T2N2 was increased significantly by 170.48%;the dissolved organic carbon content of T1N2 was significantly increased by 58.14%and the free humic acid carbon contents of T0N2,T1N1 and T2N0 were significantly increased by 56.16%and 45.55%and 47.80%,respectively;however,there were no significant differences among those of treatments at later incubation periods.The addition of different carbon and nitrogen sources could promote the soil enzyme activities.During the incubation period,all of the soil enzyme activities of adding sugar and urea were higher than those of T0N0 treatment.Therefore,the addition of different amounts of carbon and nitrogen sources to rice straw returning could improve soil microbial biomass carbon content,dissolved organic carbon and soil enzyme activities.

极端降雨条件下淹水对农田土壤有机碳、可溶性有机碳的影响

随着气候变化的日益加剧,极端降雨事件的发生更为频繁,但目前针对极端暴雨对土壤有机碳(SOC)及其不同组分的影响还需更深入地研究。本研究以河南省“7.20”极端降雨事件为契机,选择暴雨事件发生后未淹水(CK)、淹水不超过1个月(Y1)及淹水超过2个月(Y2)3种不同淹水时长的农田为研究对象,探讨了极端暴雨事件对0~100 cm土层深度内SOC、可溶性有机碳(DOC)的影响及其主要影响因素。研究结果发现:1)极端暴雨事件发生后,农田SOC与DOC随淹水时长的变化呈现不同的变化规律,SOC表现为淹水农田整体高于未淹水农田,且40 cm以下土层增加比例高于40 cm以上土层。0~100 cm土层内SOC含量CK为3.41~14.25 g∙kg^(-1),Y1为5.45~18.11 g∙kg^(-1),Y2为4.68~15.15 g∙kg^(-1),随着淹水时长的增加,SOC呈先增加后降低的趋势;0~100 cm土层内DOC含量CK为414.19~580.39 mg∙kg^(-1),Y1为327.99~874.19 mg∙kg^(-1),Y2为242.34~301.93 mg∙kg^(-1);随着淹水时长的增加,DOC在0~40 cm土层表现为先增加后降低的趋势,40 cm以下土层则表现为逐渐降低的趋势,其中40~60 cm和80~100 cm土层DOC含量CK显著高于Y2。2)极端暴雨事件后,不同淹水时长下农田SOC和DOC垂直剖面上的分布规律存在差异:随着土层深度的增加,SOC均呈降低趋势;DOC在CK处理表现为先升高后降低,其中10~20 cm土层DOC含量最高,Y1的DOC整体表现为随土层深度的增加而降低,Y2的DOC在0~100 cm土层内变化趋势不明显。3)土壤水分能够显著影响SOC及DOC/SOC,但与DOC之间未见显著回归关系,土壤总碳、总磷、总氮等养分含量对SOC、DOC及DOC/SOC存在显著的影响,pH和电导率变化与SOC和DOC的分布未见显著相关性。

配施紫云英对不同类型水稻土溶解性有机碳氮淋溶及损失的影响

为探讨配施紫云英对不同类型稻田土壤溶解性有机碳(Dissolved organic carbon,DOC)和溶解性有机氮(Dissolved organic nitrogen,DON)含量的影响程度,阐明稻田土壤DOC和DON的淋溶特性,本研究以亚热带3种典型水稻土(黄泥田、灰黄泥田和灰泥田)为研究对象,通过田间试验,探讨等氮磷钾条件下单施化肥(CK)和紫云英配施化肥(cmv)处理对不同水稻土DOC和DON的动态变化、淋溶特性及损失的影响。结果表明,不同土壤类型水稻土DOC和DON的淋溶特性有所不同。3种供试水稻土中,灰泥田水稻土DOC淋溶损失量最大,其CK处理DOC淋溶损失量较灰黄泥田和黄泥田分别显著提高24.09%和72.15%,cmv处理淋溶损失量较灰黄泥田和黄泥田分别显著提高16.53%和40.55%;而黄泥田水稻土DON淋溶损失量最大,其CK处理淋溶损失量较灰黄泥田和灰泥田分别显著提高18.93%和37.01%,cmv处理3种不同类型水稻土DON淋溶损失量无显著差异。配施紫云英可显著降低水稻土DON的淋溶损失量,每季水稻中cmv处理黄泥田、灰黄泥田和灰泥田DON淋溶损失量较CK处理分别降低了24.67%、14.88%和13.54%;黄泥田cmv处理DOC较CK处理提高了19.19%,而灰黄泥田和灰泥田2种施肥处理无显著差异。供试稻田中DOC和DON在土层间的淋溶具有一定的延迟性,且DOC的延迟时间大于DON。灰色关联分析表明,在土壤性质中有机质是影响水稻土DOC淋溶损失的重要因素,孔隙度是DON淋溶损失的重要影响因素。不同类型水稻土DON的淋失早于DOC,且DON在黄泥田中淋溶损失较高,而DOC在灰泥田中淋溶损失较高;在等氮磷钾的条件下,配施紫云英可减少水稻土DON的淋溶损失,而低肥力水稻土DOC的淋溶损失量有所增加。

不同母质发育水稻土N_(2)O消耗潜力及环境影响因素

土壤是N_(2)O的源和汇,在淹水和厌氧条件下具有消耗N_(2)O的能力。稻田土壤长期处于淹水状态,为N_(2)O的消耗提供了有利的环境,从而减少了N_(2)O排放。目前,有关稻田土壤N_(2)O排放的相关研究已有很多,但关于稻田表层土壤N_(2)O的消耗能力及其与环境因素之间的关系研究较少。研究采集了第四纪红壤母质发育的壤土、湖积物砂土发育的砂质壤土、冲积土发育的粉砂质黏壤土3类土壤的各3个表层(0~5 cm)水稻土,风干后将其回填至具有5 cm深土柱的培养装置内,在土柱底部添加N_(2)O和添加氦气(He,对照)两个处理,于28℃下恒温淹水厌氧培养96 h。培养期间监测各土壤N_(2)O、N_(2)的动态变化,以及培养前后土壤养分的变化,量化N_(2)O消耗量和N2增量,以期揭示稻田表层土壤N_(2)O的消耗能力及其与环境因素之间的关系。结果表明,土壤剖面积累的N_(2)O有95.01%~99.92%被稻田表层土壤吸收,其中被还原为N2的N_(2)O量占总消耗量的64.50%~83.64%,表明淹水厌氧状态下,不同的水稻土均具有很强的N_(2)O吸收和消耗能力。研究还发现,3类土壤N_(2)O的消耗存在一定差异,其中影响砂质壤土N_(2)O消耗的主要环境因子为土壤砂粒含量,且两者之间存在显著的线性相关关系(R^(2)=0.964,P=0.000);土壤黏粒、粉砂粒、pH是粉砂质黏壤土N_(2)O消耗的主要环境影响因素,其中土壤黏粒与其消耗量呈显著线性相关(P<0.05);土壤速效钾和铵态氮增加量是影响壤土N_(2)O消耗的主要环境因子,其消耗量与速效钾之间在0.01水平上显著正相关。这些结果表明,土壤可溶性有机碳、土壤质地、土壤速效钾等是影响稻田土壤N_(2)O消耗的重要环境因子,且不同土壤N_(2)O消耗的环境影响因子存在差异,这将为调节土壤N_(2)O排放提供重要参考。

微塑料对稻田土壤温室气体排放和微生物群落的影响

微塑料因在土壤环境中广泛存在及其潜在的生态风险而受到越来越多的关注。微塑料的赋存会改变土壤理化性质,并对土壤微生物群落及其驱动的生物地球化学过程产生影响,而相关研究尚处于起步阶段。可生物降解塑料作为传统塑料的替代品,越来越多地应用于农业活动,并释放到土壤中。然而,可生物降解微塑料对土壤微生物特性产生影响的研究鲜有报道。基于此,本试验以我国三江平原水稻田土壤为研究对象,选取了2种常见的微塑料为试验材料,分别为传统型微塑料聚丙烯(Polypropylene,PP)和可降解微塑料聚乳酸(Polylactic acid,PLA),进行了为期41d的微宇宙培养实验,旨在分析不同浓度与类型的微塑料对土壤可溶性有机碳(Dissolved Organic Carbon,DOC)含量及官能团特征、温室气体排放以及微生物群落结构的差异性影响。结果表明,传统型微塑料PP与可降解微塑料PLA添加均对土壤理化性质与微生物群落产生显著影响。其中,微塑料添加大体上增加了土壤DOC含量,PLA的促进作用较为明显,且增加含量与微塑料添加量呈正相关;PP和PLA均影响土壤DOC分子结构,削弱了土壤团聚化程度并促进了大分子量DOC化合物的生成;微塑料的添加促进土壤CH_(4)排放,而有效抑制了土壤CO_(2)排放;微塑料显著改变了土壤细菌和真菌群落的丰富度与多样性。相关分析结果表明,土壤CO_(2)累计排放量与芳香族化合物结构及疏水性等官能团特征、变形菌门(Proteobacteria)与放线菌门(Actinobacteria)均呈显著正相关关系。以上结果表明,微塑料添加改变了土壤DOC含量及官能团特征与微生物环境,进而影响土壤温室气体排放。本研究为今后微塑料对土壤地球化学和微生物特性的影响研究提供了科学的思路,同时也有助于评估微塑料对土壤生态系统的生态风险。

武夷山西坡退耕还林对土壤溶解性有机质含量和生物降解性的影响

[目的]揭示典型人工林土壤溶解性有机质(DOM)含量和生物降解性及其影响因素,为评估武夷山西坡退耕还林工程的生态服务功能提供科学支撑。[方法]选取江西省武夷山西坡杉木林、枫香林、枫香-木荷混交林和弃耕地,调查了0—10 cm和10—30 cm土壤溶解性有机碳(DOC)、溶解性全氮(DTN)和溶解性全磷(DTP)浓度以及DOM芳香化程度,分析了土壤DOM生物降解性及其影响因素。[结果](1)退耕还林对土壤DOM含量的影响趋势取决于造林树种,但退耕还林地土壤DOC∶DTP和DTN∶DTP均高于弃耕地;(2)在0—10 cm中,枫香林土壤DOM的芳香族碳含量高于弃耕地,在10—30 cm中,杉木林土壤DOM的芳香族碳含量则低于弃耕地;(3)枫香林和混交林0—10 cm土壤DOM生物降解性均低于弃耕地,而杉木林10—30 cm土壤DOM生物降解性则高于弃耕地;(4)土壤DOM生物降解性与DOC∶DTN∶DTP化学计量比无显著相关,但与芳香族碳含量存在显著负相关关系,即碳质量调控土壤DOM生物降解性。[结论]树种决定着武夷山西坡退耕还林地土壤DOM数量和芳香化程度,而且碳质量是驱动退耕还林后土壤DOM生物降解性变化的主要因素。这些研究结果有助于理解和评估亚热带地区退耕还林工程的土壤碳汇功能。

Effect of experimental warming on soil respiration under conventional tillage and no-tillage farmland in the North China Plain

Understanding the response of soil respiration to global warming in agro-ecosystem is crucial for simulating terrestrial carbon （C） cycle. We conducted an infrared warming experiment under conventional tillage （CT） and no-tillage （NT） farmland for winter wheat and summer maize rotation system in North China Plain （NCP）. Treatments include CT with and without warming （CTW and CTN）, NT with and without warming （NTW and NTN）. The results indicated that warming had no sig- nificant effect on soil moisture in irrigated farmland of NCP （P〉0.05）. The elevated average soil temperature of 1.1-116℃ in crop growing periods could increase annual soil CO2 emission by 10.3% in CT filed （P〉0.05）, but significantly increase it by 12.7% in NT field （P〈0.05）, respectively. The disturbances such as plowing, irrigation and precipitation resulted in the obvious soil CO2 emission peaks, which contributed 36.6-40.8% of annual soil cumulative CO2 emission. Warming would enhance these soil CO2 emission peaks; it might be associated with the warming-induced increase of autotrophic respiration and heterotrophic respiration. Compared with un-warming treatments, dissolved organic carbon （DOC） and soil microbial biomass carbon （MBC） in warming treatments were significantly increased by 11.6-23.4 and 12.9-23.6%, respectively, indicating that the positive responses of DOC and MBC to warming in both of two tillage systems. Our study highlights that climate warming may have positive effects on soil C release in NCP in association with response of labile C substrate to warming.

Soil Acidification Stimulates the Emission of Ethylene from Temperate Forest Soils

Soil acidification via acid precipitation is recognized to have detrimental impacts on forest ecosystems, which is in part associated with the function of ethylene released from the soil. However, the impacts of acidification on the cycling of ethylene in forest soils have not been fully taken into consideration in global change studies. Forest topsoils （0-5 cm） under four temperate forest stands were sampled to study the effects of a pH change on the emissions of ethylene and carbon dioxide from the soils and concentrations of dissolved organic carbon （DOC） released into the soils. Increasing acidification or alkalinization of forest soils could increase concentrations of DOC released into the soils under anoxic and oxic conditions. The ethylene emission from these forest topsoils could significantly increase with a decreasing pH, when the soils were acidified experimentally to a pH〈4.0, and it increased with an increasing concentration of DOC released into the soils, which was different from the carbon dioxide emission from the soils. Hence, the short-term stimulating responses of ethylene emission to a decreasing pH in such forest soils resulted from the increase in the DOC concentration due to acidification rather than carbon mineralization. The results would promote one to study the effects of soil acidification on the cycling of ethylene under different forest stands, particularly under degraded forest stands with heavy acid depositions.

Short-term Effects of Nitrogen Deposition on Soil Physical and Chemical Properties of Tibetan Forest-Grassland Landscape Boundary

[Objective] The paper was to study the effects of nitrogen deposition on soil nutrients and soil dissolved organic carbon in forest-grassland landscape in Linzhi, Tibet, and to provide scientific basis and basic data for understanding and assessing the effect of atmospheric nitrogen deposition on soil nutrients and soil dissolved organic carbon. [Method] From July 2014 to August 2015, in situ nitrogen deposition （CK0 kg· hm^2/a, LN25 kg·hm^2/a, MN 50 kg·hm^2/a, HN 150 kg· hm^2/a） was simulated in the forestgrassland boundary of Zhuqudeng village, Bujiu Township, LinzhiCounty, Tibet. The soil samples were collected for analyzing nutrient and dissolved contents in the soil layer of 0-20 and 20-40 cm. The effects ofdifferent nitrogen deposition levels on soil nutrients and dissolved organic carbon （DOC） were studied. [Result] Nitrogen deposition had significantimpacts on soil organic matter, total N, total P, total K, available N, available P, available K, exchangeable Ca, exchangeable Mg, pH, and DOC（P〈0.05）. （2） With the deepening of nitrogen deposition from CK, LN, MN to HN in the 0-20 cm boundary soil, the contents of organic matter, total N,total P, available P, exchangeable Ca, exchangeable Mg and DOC kept decreasing, and the content of total K and available N increased continuously. The pH increased in LN treatment and decreased in HN treatment, while the available K content was decreased in LN and HN treatment, butincreased in MN treatment. （3） The contents of organic matter, total N, total P, available N, available P, exchangeable Ca, exchangeable Mg andDOC all decreased at the soil layer of 20-40 cm under the same nitrogen deposition. The pH increased in LN treatment, but decreased in HN treatment; the content of total K decreased in LN treatment and increased in MN and HN treatments; the content of available K decreased in LN andHN treatments, but increased in MN treatment. （4） With the deepening of boundary soil layer （0-20 to 20-40 cm）, the organic matter, total N, totalP, available P, available K, exchangeable Ca, exchangeable Mg, DOC showed the same response to simulated nitrogen deposition, while the available N and total K responded differently. [Conclusion] Different levels of N deposition had certain impact on soil nutrient, and the variation of soilnutrients was not the same at different levels.

Removal and transformation of organic matter during soil-aquifer treatment

This study investigated the removal and transformation of organic matter through laboratory-scale soil-aquifer treatment (SAT) soil columns over a 110-day period. Reductions in total organic carbon (TOC), dissolved organic carbon (DOC), biodegradable dissolved organic carbon (BDOC), nonbiodegradable dissolved organic carbon (NBDOC) and absorbance of ul-traviolet light at 254 nm (UV-254) averaged 71.46%, 68.05%, 99.31%, 33.27% and 38.96% across the soil columns, respectively. DOC/TOC ratios increased slightly with depth while BDOC/DOC ratios showed a converse trend. DOC exiting the soil-column system contained only a very small biodegradable fraction. SAT decreased the concentration of DOC present in feed water but increased its aromaticity, as indicated by specific ultraviolet light absorbance (SUVA), which increased by 50%～115% across the soil columns, indicating preferential removal of non-aromatic DOC during SAT. Overall, laboratory-scale SAT reduced triha-lomethane formation potential (THMFP), although specific THMFP increased. THMFP reduction was dominated by removal in chloroform. All samples exhibited a common general relationship with respect to weight: chloroform>dichlorobromomethane >dibromochloromethane>bromoform.

Litter Decomposition and Soluble Carbon, Nitrogen, and Phosphorus Release in a Forest Ecosystem

Litter is an important source of easily mineralizable C, N, and P for microbial metabolism in forest ecosystems;however, its decomposition is dependent upon a variety of biotic and abiotic factors, including litter chemical composition and plant specie, soil properties, and climate. We investigated C, N, and P mineralization patterns of pine litter, oak and a mixture of various species commonly found in wetland landscape position. Litter species were incubated (alone and with soils) under laboratory conditions in the dark for 120 days. Samples were leached weekly and the leachates were analyzed for pH, E4:E6 ratio, dissolved organic carbon (DOC), total N, NO3, NH4, soluble reactive P, and total P. CO2 effluxes during the 120-d incubation period were measure using NaOH traps. Carbon loss was calculated as the sum of DOC and CO2 effluxes. Results indicated that patterns of C and N release varied with litter species and soil type. Mix species treatment resulted in larger DOC and N pulses compared to pine and oak treatments. The majority of the DOC, N, and P leached was retained by the soils. When litters were added to the soils, a greater proportion of the C was lost as CO2, while litter incubated alone lost more C as DOC. This result demonstrated the importance of the soil microbial community affecting the patterns of litter mineralization. Total N concentration and C:N ratio of the litter species were significantly correlated to C loss.

湿地土壤活性有机碳研究进展

本研究对湿地土壤活性有机碳的生物地球化学循环过程、测量方法、影响因素进行系统梳理,并从研究的不足之处提出了未来的研究方向,主要结论包括:(1)湿地土壤活性有机碳的研究还相对较少,对于活性炭的测量还不是那么全面,应该按照活性炭分组逐级进行,对于同一湿地进行深入分析。(2)国内外关于湿地土壤活性有机碳的研究主要集中在滨海湿地,对于高寒和干旱区湿地的研究还相对较少,应加强干旱、高寒区湿地土壤活性有机碳的研究,填补湿地研究的不足。(3)对于湿地土壤活性有机碳的研究多采用室内模拟配演实验,应该在实验地建立湿地土壤活性有机碳长期观测点,以便能够观测到最真实状态下湿地土壤活性有机碳的变化。

武夷山国家公园马尾松林改为茶园后影响表层土壤碳含量的林缘效应

【目的】探究马尾松林改为茶园的土地利用/覆盖变化对土壤碳含量的影响,明确林缘形成对森林土壤碳含量的作用,为准确估算森林土壤碳储量和固碳功能提供科学依据。【方法】在武夷山国家公园选择马尾松纯林转为茶园的典型地点,研究马尾松林内不同林距(距“林—茶”接壤边缘1、20和50 m)及接壤茶园内4处位置的表层土壤(0~20 cm)总有机碳(TOC)、可溶性有机碳(DOC)和微生物生物量碳(MBC)含量变化及影响因素。【结果】马尾松林改为茶园16~28年后,土壤TOC、DOC和MBC含量分别比原马尾松林下降了57.1%、48.8%和16.9%。在马尾松林内至林缘方向上,TOC和DOC含量呈下降趋势,而MBC含量无显著差异(P>0.1),为TOC含量均值在林距50 m、20 m、1 m和毗邻茶园处依次为31.08、30.67、22.26和13.25 g·kg^(-1),DOC含量均值依次为269.7、259.8、226.5和135.5 mg·kg^(-1)。TOC和DOC含量与解释变量(土壤理化性质、土地利用/覆被类型和林缘年龄)的逐步回归方程拟合优度好,自变量分别解释了各自变异的87.7%和76.6%;但MBC的拟合效果很差。其中,土地利用/覆被类型和土壤氮组分含量对TOC和DOC产生不同程度的作用;而林缘年龄仅对DOC含量产生影响。【结论】马尾松林改为茶园的土地利用/覆盖变化使土壤碳含量下降(TOC和DOC最为明显),且随离开林缘的距离增加而降低。因此,需要考虑土壤碳含量的林缘效应,以降低景观尺度的森林土壤碳库和碳汇估算中的不确定性。

土壤矿质结合态有机碳形成及稳定机制的研究进展

随着分子生物学的发展,微生物的作用改变了科学界对土壤有机碳(SOC)形成和固持的认知。土壤微生物残体与矿物结合形成矿质结合态有机碳(mineral-associated organic carbon,MAOC)加深了对SOC固存的理解。MAOC是以土壤微生物残体C为主的SOC组分,主要由分子量相对较低且可识别的微生物残体与矿物表面结合而成。由于MAOC对草地和农田生态系统土壤C库的贡献超过50%,且周转时间较长(百年—千年尺度),研究其形成过程和稳定机制已成为碳中和背景下土壤碳汇的焦点。现阶段的研究明确指出,MAOC的形成和稳定不仅与微生物残体C密切相关,还与土壤矿物有着非常紧密的联系。基于此,聚焦土壤微生物“碳泵”调控SOC形成这一前沿科学问题,围绕土壤微生物残体贡献MAOC形成这一科学构架进行概述,旨在揭示不同来源LMW—DC(溶解态低分子量C底物)对MAOC形成的贡献,探讨土壤矿物对LMW—DC选择性吸附机理,探究MAOC贡献稳定C库的影响因素。并对该研究领域未来的发展进行展望,以期能从分子水平出发,探究不同生态系统、土壤类型及土层深度微生物的调控差异,为土壤有机碳固持的研究提供理论参考,为丰富土壤C源/汇功能提供科学依据。

杉木和米槠人工林土壤可溶性碳组分动态及其对凋落叶输入的响应

可溶性碳组分是土壤有机碳库中最活跃的部分,作为土壤碳周转初期变化的敏感指标,其含量受到凋落叶等植物残体输入、森林类型及季节性水热变化的共同调节。采用土壤原位培养法,以亚热带米槠(Castanopsis carlesii)人工林与杉木(Cunninghamia lanceolata)人工林为对象,分析生长季内土壤可溶性碳(DOC)与热水溶性碳(HWSC)含量动态变化及其对凋落叶输入的响应趋势。结果表明,凋落叶输入、森林类型和培养月份均极显著影响土壤可溶性碳组分含量(p<0.001)。杉木人工林土壤DOC与HWSC含量整体较高,分别高出米槠人工林15.09%和13.06%,但后者的土壤可溶性有机质芳香化程度更高。经过1个生长季的培养,2种人工林土壤DOC与HWSC含量均明显增加。凋落叶增加生长季米槠人工林土壤DOC与HWSC的含量,但对杉木人工林的影响具有季节差异。研究结果表明杉木人工林土壤DOC与HWSC含量更高,但凋落叶输入促进米槠人工林DOC与HWSC含量,更易于随淋溶过程流失。

海南东寨港流域土壤-溪流连续体溶解态黑碳分子特征及其界面转化机制

研究不同土地利用背景下土壤-溪流连续体溶解态黑碳(DBC)分子特征及其界面转化规律对调控溪流温室气体排放具有重要的指导意义。以海南东寨港3个典型热带流域为研究区,对流域内3种土地利用类型(农田、林地、湿地)的土壤、溪流进行监测,通过超滤技术、苯多羧酸法与傅里叶变换离子回旋共振质谱技术(FT-ICR-MS)对DBC粒径分布、结构组成进行表征,进一步揭示不同土地利用背景下土壤-溪流界面中DBC转化机制。结果表明,从土壤到溪流环境DBC质量浓度逐渐变小;土壤DBC平均质量浓度、DBC/DOC比值大小顺序为湿地>农田>林地,而在溪流中湿地最低,分别为0.14 mg·L^(-1)、6.61%;林地、农田、湿地的土壤DBC分别主要分布在>10 kDa、<10 kDa、<1 kDa的粒径中,质量浓度范围为1.21—4.01 mg·L^(-1),所有溪流DBC在不同粒径中的分布更为均匀;所有土壤与溪流的DBC稠环结构以B4CAs和B5CAs为主,其中农田溪流B4CAs占比超过60%;DBC中CHO化合物的占比最高为73.56%,土壤DBC的CHOS/CHONS化合物在湿地中占比最高为21.84%,但在溪流DBC中湿地占比最低为6.73%;不同地类土壤-溪流界面中DBC含量平均损失率大小顺序为农田>林地>湿地,而林地、农田、湿地水土界面中具有最大损失率的DBC组分分别为>0.2μm、1—10 kDa、<1 kDa,而农田溪流中B3CAs、B4CAs和B5CAs平均损失率显著高于地类溪流。土壤-溪流界面的DBC转化主要受分子特征的影响,其次为界面环境理化性质与微生物组成,流域内不同土地利用方式通过改变土壤-溪流界面输入性DBC结构组成与界面环境因子共同影响DBC的界面转化过程。