Comparison of soil properties of native forests,Pinus patula plantations and adjacent pastures in the Andean highlands of southern Ecuador: land use history or recent vegetation effects?

In the high Andes of Ecuador scarcity of farmland has led to accelerated deforestation, in particular over the last 40 years. Soil mis‐management has caused the rapid decline of soil fertility and most farmland has been irreversibly transformed into grassland or tree plantations. The present study assessed whether pastures and particularly pine plantations were associated with less soil nutrients. The soils from six sites each of native forests and Pinus patula plantations, and their adjacent pastures were sampled in a geographically large area in the Paute watershed, south Ecuador. Soil analyses showed statistically significant differences for soil cations and effective cation exchange capacity (ECEC) only. ECEC was highest in soils from native forests and their adjacent pastures (6.4 cmol/kg) compared to pine plantations and their pastures (4.2 cmol/kg). Mean soil organic matter and pH were similar in native forests/pastures (39% SOM; pH 5.4) and in plantations/pastures (40% SOM; pH 5). As pasture soils had ECEC concentrations statistically similar to those of their adjacent forest or plantation, they do not form a single homogeneous land use type based on soil nutrients. Therefore, this study cannot conclude that the presence of pines alone has caused soil degradation, but instead that the soil at the site was already degraded before pines were planted. This study proposes the scenario that pine plantations are established in pastures as a last resort, when the soils are already strongly degraded, and more profitable land uses are not available. Farmers are reluctant to use fertile land for tree plantations, and only the planting of well‐known species, such as pines, is officially encouraged.     

Impacts of Plant Community Changes on Soil Carbon Contents in Northeastern Illinois

Land-cover changes not only affect regional climates through alteration in surface energy and water balance, but also affect key ecological processes, such as carbon (C) cycling and sequestration in plant ecosystems. The object of this study was to investigate the effects of land-cover changes on the distribution of soil organic carbon (SOC) contents under four plant community types (deciduous forests, pine forests, mixed pine-deciduous forests, and prairies) in northeastern Illinois, USA. Soil samples were collected from incremental soil depths (0–10, 10–20, 20–30, and 30–50 cm) under the studied plant communities. The results showed that SOC concentration decreased with increases of soil depth in the studied forests and prairies. No significant differences of SOC concentrations were found at the upper soil layers (0–10 cm) among the four plant types. However, SOC concentrations were statistically higher at the lower soil depth (30–40 cm) in prairies than in other three forest types. The SOC storage (0–40 cm soil depth) was reduced in an order prairies (250.6) > mixed pine-deciduous forests (240.7) > pine forests (190.1) > deciduous forests (163.4 Mg/ha). The characteristics of relative short life cycle, restively high turnover rate of roots, and large partition of photosynthetic production allocated to belowground were likely attributed to the higher accumulation of C in soils in tallgrass prairies than in forests. Our data indicated the conversion of native tallgrass prairies to pure forest plantations resulted in a considerable decline of SOC storage. Results suggest that land-cover changes have a significant impact on SOC storage and sequestration in plant ecosystems.     

Effect of wood ash on soil chemistry of a pine stand in Northern Germany

Addition of wood ash to acid soils will affect the soil chemistry of forests in a number of ways which were assessed for a pine stand in northern Germany. A field experiment was carried out in a fifty‐year old pine stand on a sandy Podzol at Fuhrberg (Lüneburger Heide, Lower Saxony/Germany) which involved depositing wood ash (2.4 t ha^—1) on the surface. Soil solution chemistry was investigated monthly at different depths for 24 months. Prior to and 19 months after the ash addition, exchangeable cations and amounts of heavy metals were determined at different depths. Two to four months after addition of wood ash, maximum mean concentrations in the soil solution of Ca were 240 μmol l^—1 at 0 cm (surface of mineral soil) and 100 μmol l^—1 at 100 cm and of K 980 μmol l^—1 and 140 μmol l^—1, respectively. The pH values in soil solutions dropped temporarily by 0.3 units at 0 and 10 cm depth. Nitrate concentrations increased at all depths and maximum mean concentration was 230 μmol l^—1 at 100 cm. Concentrations of Pb and Cr in soil solution did not change significantly (p < 0.05) after ash addition. Concentrations of Cd and Zn increased significantly at some depths but stayed well below the legal limit for drinking water and below the limits given by the German recommendation for soil conservation. Nineteen months after ash addition, the cation exchange capacity (corrected for the release of cations from the ash) of the upper 6 cm of the organic layer was almost doubled and amounts of exchangeable Ca and Mg increased significantly in the upper 8 cm of the organic layer. Amounts of Zn were increased in the entire organic layer, but changes were significant only in the upper 4 cm. The results of this study suggest that ash from untreated wood (using modest additions) may be recommended for amelioration of forest soils.     

Soil microbial attributes along a chronosequence of Scots pine (Pinus sylvestris var. mongolica) plantations in northern China

Soil microorganisms play a key role in soil organic matter dynamics, nutrient cycling, and soil fertility maintenance in forest ecosystems, and they are influenced by stand age and soil depth. However, few studies have simultaneously considered these two factors. In this study, we measured soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), soil basal respiration (SBR) rate, and potential extracellular enzyme activity (EEA) in soil to a depth of 60 cm under 10-, 30-, and 40-year-old Scots pine (Pinus sylvestris var. mongolica) stands (Y10, Y30, and Y40, respectively) in plantations in northern China in 2011. Soil water content (SWC), soil pH, soil organic carbon (SOC), and soil total nitrogen (STN) were also measured to explore their effects on soil microbial indices across different stand ages and soil depths. Our results showed that SMBC, SMBN, and the SBR rate were generally higher for the Y30 stand than for the Y10 and Y40 stands. Potential EEA, except forα-glucosidase, decreased significantly with increasing stand age. Soil organic carbon,STN, SWC, and soil pH explained 67%of the variation in soil microbial attributes among the three stand ages. For the same stand age, soil microbial biomass and the SBR rate decreased with soil depth. Lower microbial biomass, lower SBR rate, and lower EEA for the mature Y40 stand indicate lower substrate availability for soil microorganisms, lower soil quality, and lower microbial adaptability to the environment. Our results suggest that changes in soil quality with stand age should be considered when determining the optimum rotation length of plantations and the best management practices for afforestation programs.     

基于不同林分类型下土壤碳氮储量垂直分布

以辽东大伙房水库周边防护林典型林分针阔混交林(落叶松-油松-刺槐混交林)、油松林、落叶松林、刺槐林为研究对象,对其土壤养分含量进行测定,研究了不同林分土壤剖面上有机碳、全氮、有机碳储量的分布规律。结果表明:随着土层深度的增大,4种林分的土壤有机碳、全氮含量均逐渐降低;4种林分土壤剖面有机碳含量大小顺序为落叶松林(24.16g/kg)刺槐林(23.07g/kg)针阔混交林(16.06g/kg)油松林(15.76g/kg);全氮含量大小顺序为刺槐林(5.23g/kg)落叶松林(4.57g/kg)油松林(3.45g/kg)针阔混交林(2.42g/kg);C/N平均值大小顺序为落叶松林(7.36)针阔混交林(6.51)油松林(4.67)刺槐林(4.57);4个林分0-40cm土层的有机碳储量大小为落叶松林(112.94t/hm~2)刺槐林(107.40t/hm~2)针阔混交林(105.42t/hm~2)油松林(89.89t/hm~2);4种林分土壤pH无明显差别,各土层土壤pH随土层深度增加而增大;4种林分土壤容重由高到低顺序依次为针阔混交林(1.73g/cm~3)油松(1.65g/cm~3)落叶松(1.64g/cm~3)刺槐(1.56g/cm~3)。4个林分土壤有机碳含量与土壤全氮含量互相间均存在极显著正相关关系,土壤有机碳、全氮含量与C/N之间则没有明显相关关系;在针阔混交林中,土壤容重、土壤全氮含量和土壤pH与土壤有机碳之间存在线性数量关系,而其他纯林则没有这种关系。     

Physical,chemical and microbiological soil attributes influence soil greenhouse gases fluxes in Atlantic Forest and pine (Pinus taeda) plantations in Brazil

Forest soils can be sources or sinks of greenhouse gases (GHGs) depending on soil attributes that affect biomass and activity of soil micro-organisms involved in GHGs fluxes. In this work, we tested the hypothesis that soil physical, chemical and microbiological attributes, under different forests ecosystems, affect the soil GHGs [nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄)] fluxes. The study was carried out in two locations in southern Brazil in 2019, with three experimental plots of 900 m² in native forests of the Atlantic Forest biome and in loblolly pine (Pinus taeda) plantations. Air samples released from the soil surface were analysed for concentration and flux of CO₂, N₂O and CH₄. Soil samples were analysed for chemical attributes, density (Ds), soil microporosity (MiPs), soil macroporosity (MaPs), total porosity (TP), water-filled pore space (WFPS), microbial biomass carbon (MB-C), basal respiration (BR), microbial (qMic) and metabolic (qCO₂) quotient and activities of soil urease and β-glucosidase enzymes. The seasons influenced the CO₂ and N₂O emissions, probably because of the changes in seasonal conditions. However, native forests consumed more CH₄ than pine plantations. Meanwhile, the native forests presented soils with lower Ds (average 21.5% lower), more TP (average 12.5% higher) and more moisture (average 33% higher), which improved the microbiological attributes of the soil (20% to 60% more MB-C, 67% higher urease activity and 30% higher β-glucosidase activity) compared with pine plantations. Native forests contributed more intensely to CH₄ consumption than pine plantations because they present better physical, chemical and microbiological soil conditions. Therefore, it is possible that forestry practices that improve soil physical attributes are likely to contribute to increase CH₄ consumption, and to reduce GHGs emissions in forest ecosystems.     

What Characteristics of Soil Fertility Can Improve in Mixed Stands of Scots Pine and European Beech Compared with Monospecific Stands?

According to the current trends in forest management, endeavors are made to adjust the species composition to the site conditions and to increase the biodiversity. Changes in the species composition of forest stands lead to modifications of soil properties and nutrients cycle. The objective of the study was to evaluate the effect of monocultures (beech and pine) and mixed-species stands (pine-beech) on soil properties, particularly accumulation of soil organic carbon. We aim to demonstrate how different vegetation types influence soil properties in surface horizons of soil. The study sites are located in Germany and Poland under different tree stands Pinus sylvestris L., Fagus sylvatica L., and mixed-species stand. Contents of organic carbon and nitrogen, pH, and soil texture were analyzed. The studies conducted confirmed the positive effect of beech and mixed-species stands on acidification of surface soil horizons. We ordered the stands tested according to acidification effect on soils: pine stand > mixed stand > beech stand, which is consistent with previous studies. The most beneficial impact on the accumulation of organic carbon was observed in mixed-species stands in which beech and pine were found. Lower carbon-to-nitrogen (C/N) ratios confirm the high rate of organic matter decomposition and lower C/N ratio was reported in soil under beech stand in comparison to pine stands.     

马尾松纯林改造成针阔混交林后土壤化学性质的变化

在25 a生的马尾松林下分别套种火力楠、闽粤栲、苦槠、格氏栲、青栲和拉氏栲等阔叶树种的1 a生幼苗,16年后形成郁闭的针阔混交异龄林。土壤化学分析结果显示,在马尾松林下套种阔叶树(除青栲外)明显增加了林下表层土壤(0~20 cm)的有机质含量。各林分下土壤全K、全M g、全C a、全N和全P的平均含量分别为11.41,6.64,4.33,1.45,0.46 g/kg,表明土壤K、M g、C a的含量比较丰富,而N和P则相对缺乏,营造混交林在一定程度上增加了土壤N、P含量。所有混交林深层土壤(20~60 cm)的有效N、P含量均大于马尾松纯林,而有效K的含量则相反。混交林下0~20 cm,20~40 cm和40~60 cm土壤的平均pH值分别为4.40,4.61和4.68,而马尾松纯林下各土层的pH值则依次为4.39,4.41及4.42,说明在马尾松林下套种阔叶树在一定程度上降低了20 cm以下土层的活性酸度。套种阔叶树(除苦槠外)后由于降低了土壤交换性酸度,增加了土壤盐基离子浓度,从而明显提高了土壤盐基饱和度。     

丘陵陡坡荒山灌木草丛及其造林地生态系统碳库的分配格局

植被恢复往往有利于提高生态系统的碳储量,但对南方丘陵陡坡荒山灌木草丛造林后如何影响生态系统碳库及其分配格局仍知之甚少。选取江西泰和典型丘陵陡坡(>25°)荒山灌木草丛和马尾松(Pinusmassoniana)造林19年后的林地为对象,开展上、中、下坡0～75cm土壤层和植物体碳储量的对比研究。结果表明,造林地土壤容重低于灌木草丛,土壤石砾含量与土壤碳含量和碳密度呈显著负相关,表明造林有利于改善土壤物理结构;石砾含量影响土壤碳积累。荒山灌木草丛和马尾松林土壤碳含量和碳密度均表现为随土壤加深呈下降的趋势(P<0.05),但上、中、下坡的变异规律不一致,且2种生态系统之间差异不显著。荒山灌木草丛和马尾松生态系统碳储量分别为52.85,111.31t/hm2,均表现为自上、中坡至下坡呈增加的趋势;灌木草丛和马尾松林中的植物体分别占生态系统碳储量的11.2%和59.5%。灌木草丛马尾松造林碳年均增汇3.08t/(hm2.a),林分生物量的积累是造林增汇的直接原因;推断种植耐瘠速生树种是提高困难立地造林碳增汇的有效途径。     

黄土高原北部生长季土壤氮素矿化对植被和地形的响应

氮素矿化是陆地生态系统氮循环的重要过程,对氮素有效性有着重要影响。本文在黄土高原北部六道沟小流域选取退耕年限相近的油松和柠条坡地,用原位培养法测定生长季节(4—10月)不同坡位冠层下和冠层外0~10 cm和10~20 cm土层土壤氮素矿化速率,以确定该区氮素矿化的季节动态特征和主要影响因素。结果表明,研究区生长季土壤矿质氮以铵态氮为主,其含量在0~10 cm和10~20 cm土层分别占矿质氮总量的61%和70%,并随生长季的推移而升高。油松林上坡位和中坡位土壤铵态氮显著高于下坡位土壤,柠条林不同坡位铵态氮差异不显著。土壤硝态氮和矿质氮不受坡位的影响,但与林型和采样位置有关,冠层下硝态氮在油松林与冠层外相近,在柠条林则高于冠层外。生长季土壤氮素矿化在0~10 cm土层由硝化作用引起,在10~20 cm土层则由硝化和铵化作用共同引起。铵化速率在生长季初期较高,中期较低,并受坡位、林型和采样位置的影响。土壤硝化和矿化速率在油松林不受采样位置影响,但是在柠条林则以冠层下较高。硝化和矿化速率在冠层下以下坡位土壤最高,在冠层外则以下坡位土壤最低。柠条林促进了冠层下土壤氮素的硝化和矿化过程,有利于矿质氮的积累;油松林对矿质氮和氮素矿化的影响不受采样位置影响。     

干旱荒漠区人工梭梭林土壤碳氮磷密度与生态化学计量特征

为了阐明人工梭梭林土壤碳氮磷密度及其生态化学计量特征演变规律,以吉兰泰荒漠区不同林龄(3,6,11,16年)人工梭梭林为研究对象,分析0—20,20—40,40—60 cm土层土壤有机碳(SOC)、全氮(TN)、全磷(TP)密度和生态化学计量特征。结果表明:(1)4种林龄人工梭梭林0—60 cm土层SOC、TN含量及其密度随林龄增加而升高,而TP含量及其密度随林龄增加而降低。其中,3,6年梭梭林SOC、TN含量及其密度随土层深度增加而升高,TP含量及其密度则与之相反;11,16年梭梭林SOC、TN、TP含量及其密度随土层深度增加而降低。(2)4种林龄梭梭林土壤C∶N、C∶P、N∶P分别为2.24~9.21,1.59~7.05,0.56~0.81,均属于中等变异水平,且变异系数随林龄和土层深度增加逐渐减小,说明土壤C∶N、C∶P、[JP]N∶P趋于平稳状态。(3)林龄、土层深度及其交互作用显著影响SOC含量、SOC密度、C∶N、C∶P,对TN含量、TP含量、TN密度、TP密度、N∶P无显著影响。(4)土壤孔隙度(STP)与SOC密度呈显著正相关关系(P＜0.05),说明土壤孔隙度增加有助于SOC密度增加,提高土壤肥力。在干旱荒漠区建植梭梭林有利于提高土壤肥力,改善干旱荒漠区土壤环境。     

连续施用不同比例鸡粪氮对水稻土有机质积累及土壤酸化的影响

【目的】土壤酸化是自然过程。随着农业集约化发展,土壤酸化在部分农田呈加速趋势,而施肥是目前农田土壤酸化加速的重要诱因,研究有机肥和化肥对土壤酸化的作用差异及机理,对合理指导施肥及耕地保育有重要的意义。【方法】通过测定不同施肥处理的不同组分有机质含量及酸碱缓冲容量,探明不同施肥处理的酸化影响,从土壤有机质和盐基累积角度对有机-无机肥料不同比例配施条件下土壤酸化特征进行了研究。【结果】① 连续5年在等氮量（N 270 kg/hm2）且有机－无机肥料不同配施比例的处理中,水稻产量以有机肥比例为25%~50%的处理最高,其平均产量比单施化肥处理提高了5.1%,比对照提高44.9%。但处理间无显著性差异;② 土壤各活性有机质及总有机质等指标中仅总有机质含量随鸡粪施用比例的增加而持续增加,不同比例有机无机肥配合施用后,土壤的高活性有机质及低活性有机质均高于CK和纯化肥氮处理,但随着有机肥投入比例的升高,除中活性有机质和水稻产量之间呈显著的正相关外（P=0.0067**）,高活性有机质、活性有机质及总有机质含量与水稻产量之间的相关性不显著（对应的概率值分别为P=0.192,P=0.208,P=0.160）;③ 施肥提高了土壤的碳库管理指数（CPMI）,且其随有机肥施用比例的上升呈增加趋势。增施鸡粪提高土壤的交换性盐基离子（Ca2+、 Mg2+、 K+、 Na+）含量,导致阳离子代换量（CEC）和pH随鸡粪施用比例的提高而升高。供试土壤酸碱缓冲容量为2.07~2.36 cmol/kg,随鸡粪施用比例的上升而增加,其与土壤阳离子代换量及有机质含量呈显著正相关。表明增施鸡粪可使土壤pH及酸碱缓冲容量上升,与鸡粪使土壤盐基累积量及有机质含量的提高有关。【结论】连续有机-无机肥施用下,土壤pH上升和酸碱缓冲容量的提高可能与该试验点下盐基离子和有机质含量随鸡粪施用比例上升有关,但其最终上升幅度及平衡点尚需进一步研究。鸡粪氮替代化肥氮比例为25%~50%时,土壤性质最优,水稻产量最高。     

Organic carbon storage in soils of the Basque Country (Spain): the effect of climate,vegetation type and edaphic variables

This study was performed to identify the environmental factors that control soil organic carbon (SOC) accumulation in the Basque Country (Northern Spain) and to evaluate the impact of land use change on SOC budget in this territory. A total of 30 samples of the organomineral horizon were taken under representative vegetation types including native forest, coniferous plantations, scrub, pasture and cultures. The edaphic variables measured were organic C content, pH, total N, available P, exchangeable H⁺ and Al³⁺, cation exchange capacity (CEC), texture, and carbonates. The substitution of the original forest with a pasture led to a significant increase in organic C content of the topsoil in all cases studied. Temperature was the main climatic factor affecting the organic C levels in soil, being the two variables negatively correlated. The CEC and texture were other key factors controlling the organic C content, which increased with CEC and decreased with total sand. Average organic C content of the organomineral horizon did not differ significantly (P <0.05) with base content of original substrate nor climate type, but it was more sensitive to climate change in the Atlantic soils than in the Mediterranean ones, where edaphic variables such as CEC and texture were important in regulating C sequestration.     

合肥环城公园不同群落类型碳储量

对安徽省合肥市环城公园不同群落类型的碳储量进行了调查分析,结果表明,园林树木生物量碳储量范围为1．38～142．04kg／m^2,平均碳储量为24．97kg／m^2;不同群落类型的碳储量大小依次为：阔叶林〉针阔混交林〉针叶林〉疏林,群落的固碳能力（树木生物量与土壤固碳）顺序同此。表层土壤的有机碳含量变异较大,其变化范围为8．9～35．2g／kg,平均为18．89g／kg。     

土地利用变化对中国西南热带湿润地区土壤磷动态的影响

Land use changes can greatly influence soil phosphorus (P) dynamics, especially when converting native forests to agricultural land. Soils in Xishuangbanna, which is one of southwest China’s tropical areas that maintain fragments of primary forests, were studied to a) evaluate the effect of two common land use changes, conversion of forests to agricultural land or rubber tree plantation, on the dynamics of available P and total P in bulk soils as well as total P in particle size fractions; b) assess the relationship between soil P dynamics and soil organic carbon (SOC); and c) elucidate the relationship between soil P content and soil properties such as pH and texture. Clearing secondary forests with subsequent shifting cultivation and establishment of rubber tree plantation caused significant decreases (P < 0.05) in available P in 0--20 cm soil depths, whereas for total P there was a significant decrease (P < 0.05) when converting to shifting cultivation, rubber tree plantation, or fallow fields at both 0--20 and 20--40 cm depths. Abandonment of fields used for shifting cultivation led to significant increases (P < 0.05) in available P at 20--40 cm depth. In addition, there was a significant positive relationship between soil organic carbon and soil P content. Compared to secondary forests, the ratio of organic carbon to total P in surface soils (0--20 cm) of shifting cultivation and rubber tree plantation was significantly lower (P < 0.05).     

Effect of organic matter on changes in soil zinc fractions found in wetland soils

Abstract

Zinc fractions occurring in five wetland soils as a function of organic matter application and soil redox potential were studied under laboratory conditions. The results indicate that a large portion of native or added Zn is bound to the soil mineral component. Exchangeable and organic complexed Zn and Zn bound to amorphous and crystalline sesquioxides were found to be in dynamic equilibrium. Exchangeable and complexed Zn were positively correlated with both native and/or added organic matter, while Zn bound to the amorphous and crystalline sesquioxides were negatively correlated with added organic matter. As soil redox potential decreased, the amount of exchangeable and organic complexed Zn decreased, while Zn bound to the amorphous and crystalline sesquioxides increased. Zinc fractions examined varied, depending upon soil cation exchange capacity, clay and organic carbon content.     

Effects of Soil-Use Intensity on Selected Properties of Mollisols in Entre Ríos,Argentina

In the province of Entre Ríos (Argentina), land-use changes have been noticeable in recent years, because the portion of land devoted to pasture decreased whereas the proportion and length of crops in the rotation increased. We evaluated soil-use intensity effects on selected physical and chemical properties of a Mollisol in a crop–pasture rotation experiment located in Entre Rios. Treatments included (1) continuous cropping, (2) crop–pasture rotation, (3) pasture, and (4) natural (never-cultivated) land as a reference. Soil samples were analyzed for chemical (pH, carbon and nitrogen contents, extractable phosphorus, cation exchange capacity) and physical (aggregate stability, percolation index, bulk density, pore-size distribution, and specific surface area) properties. Clearing of the native vegetation resulted in a significant reduction of soil organic carbon content and losses of structure stability and soil porosity. No differences were seen in cation exchange capacity between native forest and cultivated land, whereas specific surface area increased with decreased levels of organic carbon content following agricultural use. Although the studied soil properties showed no significant differences when crop–pasture rotation and continuous cropping were compared, the former soil management system is recommended to maintain or promote sustainability.     

Effect of fire on solute release from organic horizons under larch forest in Central Siberian permafrost terrain

To evaluate the effects of forest fire and post-fire stand recovery on the organic layer chemistry and solute release within mound and trough microrelief elements (termed earth hummock microtopography) that mainly distribute permafrost affected area, we chose five fire plots (larch forests burned in 1951, 1981, 1990, 1994 and 2005) paired with adjacent control plots in mature larch forests in Central Siberian permafrost terrain. We determined total carbon, nitrogen and ash content in solid organic soils, and analyzed total carbon, nitrogen, bases and major anions in water extracts. There was a significant correlation between water-extracted organic carbon (WEOC) and total carbon (kg m⁻²) in area basis, implying that the quantity of total carbon was a major factor in WEOC production. WEOC correlated negatively with pH, indicating strong control by organic horizons (organic solute leaching) on soil acidity and base cation dynamics. The sum of water extractable base cations was also correlated significantly to total carbon, indicating that cations can be released through organic matter decomposition. Organic horizons in troughs in burned plots released greater amounts of Ca, Mg and K than those in mounds, probably due to greater content of organic matter as a cation source. Anions including nitrate and phosphate and WEOC also accumulated in trough depressions, due probably to organic matter degradation. The contrasting distribution of solutes between mounds and troughs in burned plots seems to be controlled by organic horizon development via changes in microtopography after forest fires.     

Timber harvesting alters soil carbon mineralization and microbial community structure in coniferous forests

Timber harvesting influences both above and belowground ecosystem nutrient dynamics. Impact of timber harvesting on soil organic matter (SOM) mineralization and microbial community structure was evaluated in two coniferous forest species, ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta). Management of ponderosa pine forests, particularly even-aged stand practices, increased the loss of CO₂-C and hence reduced SOM storage potential. Changes in soil microbial community structure were more pronounced in ponderosa pine uneven-aged and heavy harvest stands and in lodgepole pine even-aged stand as compared to their respective unmanaged stands. Harvesting of trees had a negative impact on SOM mineralization and soil microbial community structure in both coniferous forests, potentially reducing coniferous forest C storage potential.     

不同林龄杉木人工林土壤团聚体及其有机碳变化特征

土壤团聚体作为土壤结构性状的重要指标,对土壤孔隙、持水、保水等状况都有重要影响;土壤团聚体有机碳除了反映土壤固碳状况外,还与团聚体的稳定性能密切相关,研究森林土壤团聚体及其有机碳状况,旨在为合理利用土壤、提高人工林水源涵养功能提供依据。为此,以福建省洋口国有林场不同林龄杉木人工林(幼龄林、中龄林、成熟林)土壤为研究对象,通过野外调查、采样和室内分析,研究不同林龄杉木人工林土壤团聚体及其有机碳变化特征。结果表明:不同林龄杉木人工林对土壤团聚体及其有机碳具有重要影响,成熟林土壤大团聚体含量、团聚体平均重量直径(MWD)、团聚体有机碳含量及贡献率均分别大于幼龄林、中龄林;不同林龄的土壤水稳性团聚体均以大团聚体(粒径0.25 mm)为主,占59.57%～80.97%,粒径0.053 mm的仅占0.80%;土壤团聚体有机碳贡献率也以大团聚为主,其中以2～0.25 mm粒级贡献率最高,达58.43%;另外,土壤有机碳含量与团聚体MWD呈显著正相关,且具有明显的垂直变化特征,即随土层加深而下降。因此,土壤有机碳对团聚体稳定性具有积极作用,不同林龄土壤团聚体稳定性及有机碳变化规律为成熟林幼龄林中龄林。