土壤温度和水分对长白山3种温带森林土壤呼吸的影响

为了研究土壤温度和土壤含水量对阔叶红松林(山地暗棕壤)、云冷杉暗针叶林(山地棕针叶林土壤)和岳桦林(生草森林土)的土壤呼吸的影响,于2001年9月在长白山进行了土壤实验。利用增加土壤样柱的含水量,将土壤含水量分为9%,、21%、30%、37%和43%5个等级,土壤样品分别在0、5、15、25和35的温度下保持24小时。阔叶红松林土壤在0~35范围内,土壤呼吸速率与温度呈正相关。在一定的含水量范围内(21%~37%),土壤呼吸随含水量的增加而升高,当含水量超出该范围,土壤呼吸速率则随含水量的变化而降低。土壤温度和水分对土壤呼吸作用存在明显的交互作用。不同森林类型土壤呼吸作用强弱存在显著差异,大小顺序为阔叶红松林>岳桦林>云冷杉暗针叶林.红松阔叶林土壤呼吸作用的最佳条件是土壤温度35,含水量37%;云冷杉暗针叶林下的山地棕色针叶土壤呼吸作用的最佳条件是25,21%;岳桦林土壤呼吸作用的最佳条件是35,含水量37%。但是,由于长白山阔叶红松林,云冷杉林和岳桦林处在不同的海拔带上,同期不同森林类型土壤温度各不相同,相差4~5,所以野外所测的同期的山地棕色针叶林土呼吸速率应低于暗棕色森林土呼吸速率,山地生草森林土呼吸速率应高于山地棕色针叶林土的呼吸速率。图2表1参25。     

贡嘎山东坡林地土壤低吸力段持水特性及其影响因素分析

以贡嘎山东坡几种森林类型为例,采集林地原状土以减压法测定土壤低吸力段持水曲线,进行幂函数模拟和计算分形维数。结果表明:该地区针叶混交过熟林、冷杉成熟林林地的土壤在低吸力段,各吸力值含水量高,其持水性能有利于森林水文功能的发挥和林木的生长;而次生林,尤其是次生针叶纯林林地的土壤持水性能差。幂函数对研究区土壤低吸力段的持水曲线模拟较好,新指标—分形维数的计算结果充分反映了土壤低吸力段持水性与土壤的结构、质地、有机质含量等因素的关系,为森林水文生态研究提供了新的方法。     

Water infiltration and hydraulic conductivity in sandy cambisols: impacts of forest transformation on soil hydrological properties

Soil hydrological properties like infiltration capacity and hydraulic conductivity have important consequences for hydrological properties of soils in river catchments and for flood risk prevention. They are dynamic properties due to varying land use management practices. The objective of this study was to characterize the variation of infiltration capacity, hydraulic conductivity and soil organoprofile development on forest sites with comparable geological substrate, soil type and climatic conditions, but different stand ages and tree species in terms of the effects of forest transformation upon soil hydrological properties. The Kahlenberg forest area (50 km northeast of Berlin in the German northeastern lowlands) under investigation contains stands of Scots pine (Pinus sylvestris) and European beech (Fagus sylvatica) of different age structures forming a transformation chronosequence from pure Scots pine stands towards pure European beech stands. The water infiltration capacity and hydraulic conductivity (K) of the investigated sandy-textured soils are low and very few macropores exist. Additionally these pores are marked by poor connectivity and therefore do not have any significant effect on water infiltration rate. Moreover, water infiltration in these soils is impeded by their hydrophobic properties. Along the experimental chronosequence of forest transformation, the thickness of the forest floor layer decreases due to enhanced decomposition and humification intensities. By contrast, the thickness of the humous topsoil increases. Presumably, changes in soil organic matter storage and quality caused by the management practice of forest transformation affect the persistence and degree of water repellency in the soil, which in turn influences the hydraulic properties of the experimental soils. The results indicate clearly that soils play a crucial role for water retention and therefore, in overland flow prevention. There is a need to have more awareness on the intimate link between the land use and soil properties and their possible effects on flooding.     

阔叶红松混交林不同大小林隙土壤含水量的时空异质性

在小兴安岭阔叶红松(Pinus koraiensis)混交林林隙及其周围郁闭林分内,通过网格法布点,于2010年7—9月使用TDR200测定中、小林隙I III层的土壤含水量。运用经典统计学和地统计学方法分析各土层土壤含水量的基本特征及同一林隙各样点土壤含水量的差异性,利用surfer 8.0软件进行克立格空间局部插值,并绘制各土层土壤含水量空间分布图,分析林隙土壤含水量的时空异质性。结果表明:中、小林隙I III土层土壤含水量均呈中等程度变异。随着土层深度的增加,土壤含水量提高,土壤含水量的斑块连接度增大。土壤含水量最大值出现在林隙中心和近中心区域,并呈现出随土层深度增加面积扩大并向中心靠拢的变化趋势;土壤含水量最小值出现在扩展林隙及其郁闭林分内。中、小林隙中心与边缘土壤含水量的差异均为II层较I和III层大。7—9月土壤含水量均值呈单峰型变化,最大值出现在8月,且中林隙土壤含水量较小林隙的大;9月I和II层土壤含水量较8月大幅度减小,但III层与8月相比差异较小。     

2006年特大干旱条件下森林植被对土壤水分的影响

2006年四川发生了百年一遇的特大干旱。于旱期结束末,调查了蓬安县境内两座丘陵-石马寨(栎柏混交林)和碉堡梁(人工柏木林)上、中、下坡林地和林带中耕地及坡脚农田的土壤含水量;调查了四川盆地丘陵区内5个县9个乡镇17个小流域有无农田防护林条件下,稻田开裂起始时间和裂缝宽;以及按照自然地理条件相近、森林覆盖率有较大差异的原则,调查了宣汉县和达县5对乡镇(森林覆盖率高的乡镇森林覆盖率为28.26%～46.85%,平均为37.24%,相对应的低的乡镇森林覆盖率为12.75%～26.74%,平均为18.64%)内不同台地的土壤含水量。结果表明,混交林林地的保水能力强于纯林林地,林地的保水能力强于耕地,农田防护林对水稻具有庇护作用,森林覆盖率高的地区土壤保水能力强于森林覆盖率低的地区土壤。在干旱期末坡上、中、下部位的0～40 cm土层中,栎柏混交林林地的含水量比柏木纯林林地高出3%～7%,林地的土壤含水量比林带中的耕地高出0.7%～2.1%;栎柏混交林带中的耕地含水量比柏木纯林带中的耕地高出3%～6%,石马寨的坡脚农田含水量比碉堡梁的高出5%;在干旱期末不同台地0～40 cm土层中,与森林覆盖率低的地区相比,森林覆盖率高的地区水稻田含水量高3%～7%,二台土高4%～8%,三台土高2%～8%;有农田防护林的农田土壤开裂时间比无农田防护林的推迟5 d～20 d,裂口宽平均窄0.1 cm～3.1 cm。     

土壤水分梯度对阔叶红松林结构的影响

2002年8月,在吉林省白河林业局红石林场(12755E,4230N),沿着一个山坡设置了一个长宽为112m8m、包含14个样方的样带。调查了群落结构、0-10cm和10-20cm的土壤含水量、枯落物现存量及其C、N、P含量,主要树种的叶片和枝条的C、N、P含量。沿着山坡的不同位置土壤含水量的不同导致阔叶红松林的群落结构发生变化。蒙古栎的比例随着土壤含水量的下降而逐渐升高,而其他主要阔叶树种则逐渐减少乃至消失。枯落物的水分变化趋势与土壤一致。在不同坡位枯落物的分解状况不同,干重差异显著。坡下枯落物含量较坡上的丰富,部分原因在于群落结构的变化。水分和养分含量的变化影响了枯落物的成分、降解及其养分的释放,进一步影响了林木的生长速度和林分结构并最终影响整个生态系统。图7表2参14。     

Infiltration characteristics of water in forest soils in the Simian mountains, Chongqing City, southwestern China

Spearman rank-correlation analysis and grey relational grade analysis were used to study infiltration characteristics of water in different forest soils in the Simian mountains, Chongqing City. The results indicate that the soil bulk density, contents of coarse sand, and porosity of macropores were significantly correlated with saturated hydraulic conductivity. Porosity of macropores and contents of coarse sand were positively correlated with soil saturated hydraulic conductivity and soil bulk density negatively. Based on the initial infiltration rate, the stable infiltration rate, time required for infiltration to reach a stable state, and cumulative infiltration, all of which are crucial parameters determining soil infiltration capacity, the results of grey relational grade analysis showed that the grey relational grades of the different forest soils were listed from high to low as broad-leaved forest (0.8031) > Phyllostachys pubescens forest (0.7869) > mixed conifer-broadleaf forest (0.4454) > coniferous forest (0.4039). Broadleaf forest had the best ability to be infiltrated among the four soils studied. The square roots of the coefficients of determination obtained from fitting the Horton infiltration equation, simulated in our study of forest soils, were higher than 0.950.We conclude that soils of broad-leaved forests were the best suited for infiltration processes of forestry in the Simian mountains. __________ Translated from Journal of Soil and Water Conservation, 2008, 22(4): 95–99 [译自: 水土保持学报]     

Effect of vegetation and land use on soil fertility in Wutai Mountains of Shanxi Province

IntroductionSoilpropertiesdependonclimate,vegetationtypes,parentmaterials,landformandsoilderivedage(Bei-jingForestryCoIlege1982).VegetationpIaysasig-nificantroIeintheformationofsoiIparticuIarIyforthepropertiespfSurfBcesoil.PlantsabsorbselectivelynutrientfromsoilandbuiIdtheirbodies.ThenutrientpartofIitterdecomposedgradualIybymicrobeswouldraturntoground-TheroOtsystemOfplantaIsoplaysasignificantroleinsoiIproperties.EffectofpIantsonsoildependonthevegdstiontype,speciescomposi-tion,age,dens…     

湘西南山地主要森林类型土壤养分研究

对湘西南永州市6种主要森林类型(针阔混交林、阔叶林、湿地松林、马尾松林、毛竹林和杉木林)林地的土壤养分进行测定与分析,结果表明:针阔混交林和毛竹林的土壤有机质含量较高;针阔混交林的氮、钾元素含量高,而磷元素含量相对较低;毛竹林的速效磷含量最高;阔叶林钾、磷元素含量较高,氮元素含量相对较低;湿地松和马尾松纯林的土壤有机质...     

Influence of soil temperature and water content on fine-root seasonal growth of European beech natural forest in Southern Alps,Italy

In tree species, fine-root growth is influenced by the interaction between environmental factors such as soil temperature (ST) and soil moisture. Evidences suggest that if soil moisture and nutrient availability are adequate, rates of root growth increase with increasing soil temperature up to an optimum and then decline at supraoptimal temperatures. These optimal conditions vary between different taxa, the native environment and the fine-root diameter sub-classes considered. We investigated the effects of seasonal changes of both ST and soil water content (SWC) on very fine (d < 0.5 mm) and fine-root (0.5 < d < 2 mm) mass (vFRM, FRM) and length (vFRL, FRL) in Italian Southern Alps beech forests (Fagus sylvatica L.). Root samples were collected by soil core method. Turnover rate was higher for the very fine (0.51) than for the fine (0.36) roots. vFRM, FRM, vFRL and FRL displayed a complex seasonal pattern peaking in summer when SWC was around 40 % and ST was around 14 °C. Above this temperature, under almost constant SWC, all above mentioned root traits decreased. vFRM, FRM, vFRL and FRL showed significant second-order polynomial relationship (p < 0.05) with SWC for both diameter classes, with the only exception of SRL. ST showed the same kind of relationship significant only with vFRM and vFRL, the latter within the 12–16 °C smaller range. Interpolation analysis between root mass and length for both diameter classes and investigated soil environmental characteristics (ST and SWC) showed a clear roundish delineation only for vFRM. In conclusion, these findings clarified the occurrence of a bimodal fine-root growth seasonal pattern for our beech forest. The optimal growth ST and SWC ranges were delineated only for very fine roots, giving further evidence on this root category as the more responsiveness to soil environmental changes. Furthermore, F. sylvatica seems to adopt an intensive strategy to cope with decreasing SWC. Finally, fine-root growth, mainly radial type, seems to be driven by SWC, whereas very fine-root growth, mainly longitudinal type, seems to be driven by ST.     

Interactive effects of temperature and precipitation on soil respiration in a temperate maritime pine forest

Soil respiration (SR) was monitored periodically throughout 2001 in a Scots pine (Pinus sylvestris L.) stand located in the Belgian Campine region. As expected for a temperate maritime forest, temperature was the dominant control over SR during most of the year. However, during late spring and summer, when soil water content (SWC) was limiting, SR was insensitive to temperature (Q(10) = 1.24). We observed that during prolonged rain-free periods, when SWC was less than 15% (v/v), SR decreased dramatically (up to 50%) and SWC took over control of SR. During such drought periods, however, rain events sometimes stimulated SR and restored temperature control over SR, even though SWC in the mineral soil was low. We hypothesize that restoration of temperature control occurred only when rain events adequately rewetted the uppermost soil layers, where most of the respiratory activity occurred. To quantify the rewetting capacity of rain events, an index (I(w)) was designed that incorporated rainfall intensity, time elapsed since the last rain event, and atmospheric vapor pressure deficit (a proxy for evaporative water losses). To simulate SR fluxes, a model was developed that included the effects of soil temperature and, under drought and non-rewetting conditions (I(w) and SWC < threshold), an SWC response function. The model explained 95% of the temporal variability in SR observed during summer, whereas the temperature function alone explained only 73% of this variability. Our results revealed that, in addition to temperature and SWC, rain plays a role in determining the total amount of carbon released from soils, even in a maritime climate.     

The influence of land-use change on the organic carbon distribution and microbial respiration in a volcanic soil of the Chilean Patagonia

Land-use changes can modify soil carbon contents. Depending on the rate of soil organic matter (SOM) formation and decomposition, soil-vegetation systems can be a source or sink of CO₂. The objective of this study was to determine the influence of land-use change on SOM distribution, and microbial biomass and respiration in an Andisol of the Chilean Patagonia. Treatments consisted of degraded natural prairie (DNP), thinned and pruned Pinus ponderosa plantations (PPP), and unmanaged second-growth Nothofagus pumilio forest (NPF). The soil was classified as medial, amorphic, mesic Typic Hapludands. Soil microbial respiration and microbial biomass were determined in the laboratory from soil samples taken at 0–5, 5–10, 10–20 and 20–40 cm depths obtained from three pits excavated in each treatment. Physical fractionation of SOM was performed in soil of the upper 40 cm of each treatment to obtain the three following aggregate-size classes: macroaggregates (>212 μm), mesoaggregates (212–53 μm) and microaggregates (<53 μm). Plant C content was 68% higher in PPP than in DNP and 635% higher in NPF than in PPP. Total soil and vegetation C content in both DNP and PPP were less than half of that in NPF. Total SOC at 0–10 cm depth decreased in the order DNP (7.82%) > NPF (6.16%) > PPP (4.41%), showing that land-use practices affected significantly (P < 0.01) SOC stocks. In all treatments, microbial biomass C and respiration were significantly higher (P < 0.05) in the upper 5 cm. Soil microbial respiration was also correlated positively with microbial biomass C and SOC. The different land uses affect the formation of organic matter, SOC and microbial biomass C, which in turn will affect soil microbial respiration. Conversion of DNP to PPP resulted in a 44% decrease of SOC stocks in 0–10 cm mineral soil. The largest amount of SOC was stabilized within the mesoaggregate fraction of the less disturbed system, NPF, followed by PPP. In the long term, formation of stable mesoaggregates in soils protected from erosion can behave as C sinks.     

Soil compaction by grazing livestock in silvopastures as evidenced by changes in soil physical properties

Livestock, pasture, and timber trees are intimately interrelated in silvopastures. Most silvopasture research to date has focused on forage/animal/tree interactions, with less attention paid to animal/soil interactions in silvopastures. While a considerable body of work has been devoted to understanding the effects of livestock trampling on plants and soils in pastures, less has been done for livestock grazing in forests, and even less is available for silvopastures. Three replications of Douglas-fir forest, Douglas-fir/subclover pasture/sheep silvopasture, and subclover/sheep pasture were established in 1989 near Corvallis, Oregon USA. Pastures and silvopastures were grazed each spring during 1990–2001. These plots were sampled in 2002, after 11 years of grazing, and again in 2004 following 2 years without grazing. Soil in the silvopastures had 13% higher bulk density and 7% lower total porosity than those in adjacent forests in 2002. Most of the difference in total porosity was air-filled pores. Average water infiltration rate was 38% less in silvopastures than in forests, however total water stored in the top 6 cm of soil at field capacity was similar. Soil bulk density, total porosity, and air-filled pore space was similar for forests, pastures, and silvopastures after 2 years without livestock grazing. The infiltration rate of silvopasture soils in 2004 had increased to be similar to those of forests in 2002, however, forest soil infiltration rates also increased and continued to be higher than those of silvopastures. Plant production was not sensitive to changes in any of the soil parameters measured. Although livestock grazing did change soil infiltration rates, soil bulk density, and soil porosity, the effects were quickly reversed following cessation of grazing and had little detrimental effect on silvopasture forage or tree production.     

Carbon and nitrogen in forest floor and mineral soil under six common European tree species

The knowledge of tree species effects on soil C and N pools is scarce, particularly for European deciduous tree species. We studied forest floor and mineral soil carbon and nitrogen under six common European tree species in a common garden design replicated at six sites in Denmark. Three decades after planting the six tree species had different profiles in terms of litterfall, forest floor and mineral soil C and N attributes. Three groups were identified: (1) ash, maple and lime, (2) beech and oak, and (3) spruce. There were significant differences in forest floor and soil C and N contents and C/N ratios, also among the five deciduous tree species. The influence of tree species was most pronounced in the forest floor, where C and N contents increased in the order ash = lime = maple < oak = beech ? spruce. Tree species influenced mineral soil only in some of the sampled soil layers within 30 cm depth. Species with low forest floor C and N content had more C and N in the mineral soil. This opposite trend probably offset the differences in forest floor C and N with no significant difference between tree species in C and N contents of the whole soil profile. The effect of tree species on forest floor C and N content was primarily attributed to large differences in turnover rates as indicated by fractional annual loss of forest floor C and N. The C/N ratio of foliar litterfall was a good indicator of forest floor C and N contents, fractional annual loss of forest floor C and N, and mineral soil N status. Forest floor and litterfall C/N ratios were not related, whereas the C/N ratio of mineral soil (0–30 cm) better indicated N status under deciduous species on rich soil. The results suggest that European deciduous tree species differ in C and N sequestration rates within forest floor and mineral soil, respectively, but there is little evidence of major differences in the combined forest floor and mineral soil after three decades.     

Soil–water content and air-filled porosity affect height growth of Scots pine in afforested arable land in Finland

We examined the soil–water content (SWC) and air-filled porosity (AFP) of afforested arable land in situ and related them with tree growth, which was expressed as the total length of 5-year-height growth above 2.5 m stem height. A total of 34 randomly selected sites in western Finland afforested with Scots pine (Pinus sylvestris L.) were sampled and SWC was measured using time domain reflectometry (TDR). Increasing AFP up to 30% and correspondingly decreasing SWC significantly increased tree growth while concentrations of foliar nutrients and contents of soil nutrients had no effect. Increasing organic matter content (OMC) and decreasing bulk density (BD) were accompanied by increasing SWC and decreasing AFP in the 0–10 cm soil layer. SWC values above 70% indicated critical AFP below 10%. It was found that 44% of the studied sites had mean AFP lower than 10%. The results obtained indicate that the afforested Finnish arable land with high soil OMC is commonly characterized by high SWC and low soil aeration, which can limit tree growth.     

中国贡嘎山东坡亚高山针叶林不同林型土壤团聚特征及生态环境效应

Structural properties of forest soils have important hydro-ecological function and can influence the soil water-physical characters and soil erosion.The experimental soil samples were obtained in surface horizon (0-10cm) from different subalpine forest types on east slope of Gongga Mountain in the upriver area of Yangtze River China in May 2002.The soil bulk density,porosity,stable infiltration rate,aggregate distribution and particle-size distribution were analyzed by the routine methods in room,and the features and effects on eco-environment of soil aggregation were studied.The results showed that the structure of soil under mixed mature forest is in the best condition and can clearly enhance the eco-environmental function of soil,and the soil structure under the clear-cutting forest is the worst,the others are ranked between them.The study results can offer a basic guidance for the eco-environmental construction in the upper reaches of Yangtze River.     

Variation in infiltration with landscape position: Implications for forest productivity and surface water quality

Variation of infiltration rates with landscape position influences the amount, distribution, and routing of overland flow. Knowledge of runoff patterns gives land managers the opportunity to affect changes that optimize water use efficiency and reduce the risk of water quality impacts. The objective of this study was to assess the effect of landscape position and associated soil properties on infiltration in a small (147 ha) forest/pasture watershed in the Ozark Highlands. Three previously reported studies measured infiltration rates using double ring, sprinkling, single ring, and tension infiltrometers on soils at varying landscape positions. Although large variation in infiltration rates was observed among measurement techniques, upland and side slope soils (Nixa and Clarksville) had consistently lower infiltration rates compared to the soil in the valley bottom (Razort). A conceptual understanding of watershed runoff is developed from these data that includes infiltration excess runoff from the Nixa and Clarksville soils and saturation excess runoff on the Razort soil. Management of the soil water regime based on this understanding would focus on increasing infiltration in upland soils and maintaining the Razort soil areas in forest. Forest productivity would be enhanced by increasing plant-available water in upland soils and decreasing flooding on the Razort soil. Surface water quality would be improved by reducing the transport of potential water contaminants from animal manure applied to upland pastures.     

The effect of understory removal on microclimate and soil properties in two subtropical lumber plantations

Understory vegetation is an important component in forest ecosystems. However, the effects of understory on soil properties in subtropical forests are not fully understood. We thus conducted an experimental manipulative study in two young fast-growing plantations—Eucalyptus urophylla and Acacia crassicarpa—in southern China, by removing understory vegetation in both plantations, to estimate the effects of understory vegetation on microclimate, soil properties and N mineralization. Our data showed that, after 6 months, understory removal (UR) in both plantations had greatly increased soil surface luminous intensity (90–500 cd) and temperature (0.5–0.8 °C); soil moisture was reduced in the Eucalyptus plantation but not in the Acacia plantation. Understory removal also reduced soil organic matter (SOM), but had little impact on other soil chemical properties, including total phosphorus, C/N, pH, exchangeable cations (K, Ca, Mg), available P, ande extractable NH₄–N and NO₃–N. We found a significant decline of soil N mineralization and nitrification rates in the 0–5 cm soils of UR in both plantations. The decline of SOM in UR may contribute to the lower N transformations rates. This study indicates that a better understanding of understory vegetation effects on soil N cycling would be beneficial to forest management decisions and could provide a critical foundation for advancing management practices.     

Harvest impacts on soil carbon storage in temperate forests

Forest soil carbon (C) storage is a significant component of the global C cycle, and is important for sustaining forest productivity. Although forest management may have substantial impacts on soil C storage, experimental data from forest harvesting studies have not been synthesized recently. To quantify the effects of harvesting on soil C, and to identify sources of variation in soil C responses to harvest, we used meta-analysis to test a database of 432 soil C response ratios drawn from temperate forest harvest studies around the world. Harvesting reduced soil C by an average of 8 ± 3% (95% CI), although numerous sources of variation mediated this significant, overall effect. In particular, we found that C concentrations and C pool sizes responded differently to harvesting, and forest floors were more likely to lose C than mineral soils. Harvesting caused forest floor C storage to decline by a remarkably consistent 30 ± 6%, but losses were significantly smaller in coniferous/mixed stands (−20%) than hardwoods (−36%). Mineral soils showed no significant, overall change in C storage due to harvest, and variation among mineral soils was best explained by soil taxonomy. Alfisols and Spodosols exhibited no significant changes, and Inceptisols and Ultisols lost mineral soil C (−13% and −7%, respectively). However, these C losses were neither permanent nor unavoidable. Controls on variation within orders were not consistent, but included species composition, time, and sampling depth. Temporal patterns and soil C budgets suggest that forest floor C losses probably have a lesser impact on total soil C storage on Alfisols, Inceptisols, and Ultisols than on Spodosols, which store proportionately large amounts of C in forest floors with long C recovery times (50–70 years). Mineral soil C losses on Inceptisols and Ultisols indicate that these orders are vulnerable to significant harvest-induced changes in total soil C storage, but alternative residue management and site preparation techniques, and the passage of time, may mitigate or negate these losses. Key findings of this analysis, including the dependence of forest floor and mineral soil C storage changes on species composition and soil taxonomic order, suggest that further primary research may make it possible to create predictive maps of forest harvesting effects on soil C storage.     

Soil organic matter composition under primary forest,pasture, and secondary forest succession,Región Huetar Norte,Costa Rica

Secondary forests are increasingly wide-spread on neotropical soils. In this study, we investigated if, and how, the establishment of a secondary forest on abandoned pasture affect the quality of soil organic matter (SOM). We approached this by a combination of physical fractionation of soil, where particulate SOM (light fraction and sand-associated SOM) is separated from mineral-bound SOM (silt- and clay-associated SOM), and structural chemical analyses, including measurements of well-decomposable carbohydrates and the more refractory lignin. Particle-size separation revealed that agricultural use of a soil being formerly under primary forest resulted in a depletion of the particulate SOM pool, whereas clay- and silt-bound SOM was less affected. Abandonment of the pasture and growth of a secondary forest raised the C content in all separates to a pre-cultivation level within 18 years, and sand-associated C was even higher as compared to the primary forest. The lignin and carbohydrate signature showed that the land use rarely affected the chemical composition of SOM within the different fractions. This was corroborated by solution ¹³C NMR spectroscopy of the NaOH-soluble SOM. The results suggested that land use primarily influences the C balance across the light fraction and the size separates, with the particulate SOM pool being the most significant SOM component in the context of management impacts on these soils. While the gross chemical composition of SOM within the fractions remained unaffected, some molecular differences indicated a shift in the microbial community and/or activity at transformation of primary forest into pasture and after abandonment of the pasture with growth of secondary forest.