Concentrations of exchangeable bases and cation exchange capacity in soils of cropland, grazing and forest in the Bale Mountains, Ethiopia

Conversion of native forest ecosystem to cropland has considerably degraded the soil nutrient levels in the Bale Mountains, south-eastern highlands of Ethiopia. This study investigated the effects of land use change through conversion of native forest to cropland and/or grazing land on soil pH (H₂O), base cations (Ca²⁺, Mg²⁺, K⁺, Na⁺), CEC and percentage base saturation (PBS) in three adjacent land-use types: cropland, grazing land and native forest. A total of 108 soil samples (3 replications × 3 land-use types × 4 profiles × 3 soil depth layers, 0–0.2, 0.2–0.4 and 0.4–1.0 m) were collected for laboratory analyses. Results showed that soil pH, Na⁺ and K⁺, CEC, and PBS varied significantly with respect to land use and soil depth while Ca²⁺and Mg²⁺ varied with soil depth (ρ < 0.05). Conversion of native forest ecosystem to cropland during a 15-year period significantly increased soil pH and PBS while reducing Na⁺ and K⁺. The CEC in the cropland was reduced by 37.7% (2.6% per annum) compared to the native forest, which could be attributed to the decline in organic matter concentrations. If such rapid declines in soil nutrient concentrations continue unabated, the soils will reach at the point of no return within a few decades. Although the effect of grazing on most of the properties was found to be minimal, adapting the number of stock to the carrying capacity of the land and thereby enhancing the natural regeneration, combined with proper cropland management practices could help restoring soil nutrients for sustainable agricultural production and ecosystem functions.     

Coarse woody debris dynamics in a post-fire jack pine chronosequence and its relation with site productivity

The long-term relationships between coarse woody debris (CWD) dynamics, soil characteristics and site productivity have, so far, received little attention. The objectives of the study were to describe CWD dynamics along a post-fire chronosequence (43–86 years after fire) in jack pine (Pinus banksiana Lamb.) stands, assess the importance of buried CWD in terms of soil available water holding capacity (AWHC), and investigate relationships between CWD, AWHC, nutrient retention and site productivity.

Twelve jack pine stands on sandy, mesic sites of glaciolacustrine origin were surveyed. Buried wood volume within the forest floor varied between 1 and 57 m³ ha⁻¹ (4–92% of total site CWD volume) and showed no relationship with time. Downed log mass accumulation followed a “U shaped” successional pattern with time since fire. Buried wood AWHC was negligible compared with that of the 0–20 cm mineral soil layer. The most productive sites were characterised by higher forest floor dry weight, effective CEC and water holding capacity in the mineral soil. Path analyses of relationships between organic matter content, CWD and forest floor CEC showed that CEC was conditioned by forest floor organic matter and buried wood content.     

Nutrient retranslocation from the fine roots of <Emphasis Type="Italic">Fraxinus mandshurica</Emphasis> and <Emphasis Type="Italic">Larix olgensis</Emphasis> in northeastern China

Nutrient retranslocation in trees is important in nutrient budgets and energy flows in forest ecosystems. We investigated nutrient retranslocation in the fine roots of a Manchurian Ash (Fraxinus mandshurica) and a Larch (Larix olgensis) plantation in northeastern China. Nutrient retranslocation in the fine roots was investigated using three methods, specifically, nutrient concentration, the ratio of Ca to other elements (Ca/other elements ratio) and nutrient content. The method based on nutrient content proved most suitable when investigating nutrient retranslocation from fine roots of the two species. The nutrient-content-based method showed that there were retranslocations of N, P, K and Mg from the fine roots of Manchurian Ash, with retranslocation efficiencies of 13, 25, 65, and 38 %, respectively, whereas there were no Ca retranslocations. There were retranslocations of N, P, K, Ca and Mg from the fine roots of Larch, with retranslocation efficiencies of 31, 40, 52, 23 and 25 %, respectively.     

Forest floor contribution to phosphorus nutrition: experimental data

? Although accumulation of decomposing litter temporarily removes nutrients from active circulation, it creates a medium that is more suitable for nutrient uptake where soil conditions are unfavorable.

? A pot experiment was conducted using labeling of isotopically exchangeable phosphate ions of the soil and applying the dilution principle to accurately assess the contribution of the forest floor to P nutrition of maritime pine seedlings (Pinus pinaster Aït.). Three-week-old maritime pine seedlings were planted in pots containing either mineral soil (MS) or mineral soil covered with a forest floor layer (MS+FF).

? After 130 d, P uptake was still insignificant in the MS treatment while the P content of the seedlings in the MS+FF treatment increased tenfold with respect to the initial P content. In the latter treatment, the forest floor contributed 99.1% of the P supply to pine seedlings.

? The higher P uptake from the forest floor than from the mineral soil may be explained by its lower ability to retain inorganic P, which enabled a higher concentration of inorganic P to be maintained in solution.

     

Soil aggregation may be a relevant indicator of nutrient cation availability

Key message

Aggregation was studied in two acidic forest soils (NE France) to investigate the potential link between available Ca and Mg content and soil aggregate size distribution and properties. Clay content influenced the aggregation status while clay mineralogy influenced aggregate stability and dynamics. Aggregation status and reactivity of soil components contributed to the difference of exchangeable Ca and Mg content in topsoil between the two sites.

Context

Though nutrient fluxes are important to define forest soil chemical fertility, the quantification of nutrient reservoirs in the soils and their availability to tree uptake is essential. A thorough understanding of nutrient availability requires an investigation of nutrient location and distribution in the soil solid phase.

Aims

The general aim was to investigate the potential link between available Ca and Mg content and soil aggregate size distribution and their properties (chemical, physical, mineralogical).

Methods

Soil aggregates were separated according to three size classes (200–2000 μm; 50–200 μm; <?50 μm) in two forest soils of the Lorraine plateau (France), both classified as Luvisols ruptic. The physical, chemical, and mineralogical properties were measured for each aggregate class.

Results

We showed that the relative abundance of an intermediate aggregate class [200–50 μm] was relevant to explain the difference of exchangeable Ca and Mg between sites. These aggregates were the poorest in organic and reactive mineral components and were unstable, which may mitigate the retention of Ca and Mg by ion-exchange.

Conclusion

This study highlights the role of aggregation and reactivity of soil components as relevant determinants of cation availability to tree uptake in soils.

     

秦岭南坡中山地带华北落叶松人工林对土壤的影响

秦岭南坡中山地带华北落叶松人工林对土壤的影响雷瑞德，党坤良，张硕新，谭芳林（西北林学院森林资源保护系杨陵７１２１００）关键词华北落叶松，土壤养分状况，阳离子交换量，酶活华北落叶松（Ｌａｒｉｘｐｒｉｎｃｉｐｉｓ－ｒｕｐｐｒｅｃｈｃｉｉＭａｒｙｒ．）天然...     

On the activation energy of diffusion of water in wood

Summary The diffusion equation for water in wood is expanded in terms of temperature and moisture gradient on the assumption that the driving force for the diffusion of water in wood is the partial pressure of water vapour. An analytic expression is then developed for the activation energy of diffusion in terms of enthalpy and entropy changes associated with the sorption process. The expression is compared with another published curve and some similarity was observed.Symbols C water concentration, kg/m³ - D diffusion coefficient for water vapour in wood with vapour pressure as the driving potential, kg/ms Pa - D_c diffusion coefficient for water vapour in wood with water concentration as the driving potential, m²/s - D_c a constant value of D_c, m²/s - E activation energy of diffusion, J/kg - F flow density, kg/m² s - f h/l - h specific enthalpy, J/kg - L l/R T - l latent heat of vapourization of free water, J/kg - l_s latent heat of vapourization of sorbed water, J/kg - p partial pressure of water vapour, Pa - p_s pressure of water vapour at saturation, Pa - R specifc gas constant for water, J/kg K - r relative humidity - s specific entropy, J/kg K - w dry basis moisture content - x length coordinate, m - a constant temperature equal to 6,800 K - -/ln r - _w density of wood (dry mass/moisture volume) at a given moisture content, kg/m³ - s/R - L style as 2 lines above - free water relative to sorbed water The author is grateful to the Editorial Board in relation to the use of (4)     

The thermodynamics of sorption with reference to klinki pine

Summary An investigation into the bonding energy relationships for water in wood indicates that as the temperature increases at constant total moisture content, water moves from within the chemical structure to the adsorption surface. The analysis is evaluated for the wood Araucaria klinkii Lauterb and it is indicated that at 25 °C, less water is held in the chemical structure during adsorption than during desorption.Symbols A amplitude of liquid surface profile - A₀ amplitude of solid surface profile - a mean radius of curvature of liquid surface (bubble radius), Å - a₀ mean radius of curvature of solid surface, Å - a_c a constant value of a, Å - F a function of temperature - f capisorption energy fraction - G a function of - g specific Gibbs free energy of saturated water vapour relative to unsaturated water vapour at the same temperature, J/kg - g_c specific Gibbs free energy associated with capisorption, J/kg - g_p specific Gibbs free energy associated with physisorption, J/kg - h change in specific enthalpy of liquid water as it is desorbed, J/kg - l latent heat of vaporisation of free water, J/kg - m wave number/m - p_s pressure of water vapour at saturation, Pa - R specific gas constant for water vapour, J/kg K - r relative humidity - s change in specific entropy of liquid water as it is desorbed, J/kg K - T temperature, K - w dry basis moisture content - x ln p_s/p_s25 - y In r - z length coordinate, m - , , constant coefficients - change in mean height of liquid surface, Å - ₀ a constant length, Å - constant - distance from solid to liquid vapour interface measured normal to solid surface, Å - ₀ a constant value of , Å     

巨尾桉林地土壤化学性质变化分析

通过对福建省长泰县一块巨尾桉林地18 a经营前后土壤各种养分指标的比较,揭示桉树林地长期经营对土壤肥力的影响,结果表明：土壤有机质、养分全量及交换性钙、镁、碱解氮等都有不同程度提高,而速效钾、pH值和速效磷等有所降低,分析认为杂交桉主要靠杂交优势而非靠消耗地力获得增产,杂交桉林地养分循环良好,土壤有机质增加,土壤供肥潜力提高;现有速效钾、pH值为林地正常值,18 a前测定的为炼山造林后的样品数据,草木灰（K2CO3）渗入土壤所致,速效磷降低为杂交桉对其需求量较大所致;建议在桉树人工林经营过程中应注意补充磷肥和钙肥。     

Effects of forest cover types and environmental factors on soil respiration dynamics in a coastal sand dune of subtropical China

Trees on sand dunes are more sensitive to environmental changes because sandy soils have extremely low water holding capacity and nutrient availability. We investigated the dynamics of soil respiration(Rs) for secondary natural Litsea forest and plantations of casuarina,pine, acacia and eucalyptus. Results show that significant diurnal variations of Rsoccurred in autumn for the eucalyptus species and in summer for the pine species, with higher mean soil respiration at night. However, significant seasonal variations of Rswere found in all five forest stands. Rschanged exponentially with soil temperatures at the 10-cm depth; the models explain 43.3–77.0% of Rs variations. Positive relationships between seasonal Rsand soil moisture varied with stands. The correlations were significant only in the secondary forest, and the eucalyptus and pine plantations. The temperature sensitivity parameter(Q10 value) of Rsranged from 1.64 in casuarina plantation to 2.32 the in secondary forest; annual Rswas highest in the secondary forest and lowest in the pine plantation. The results indicate that soil temperatures and moisture are the primary environmental controls of soil respiration and mainly act through a direct influence on roots and microbial activity. Differences in root biomass, quality of litter,and soil properties(pH, total N, available P, and exchangeable Mg) were also significant factors.     

On movement of water through wood — The diffusion coefficient

Summary It is demonstrated that there can be only one driving potential for the movement of water through wood and this will be a function of wood state. On the assumption that the driving potential is the partial pressure of water vapour, a theoretical expression is derived for the diffusion coefficient. Such expression is fitted to diffusion coefficients for Scots pine and a remarkably good fit is obtained.Symbols a reciprocal mean radius of curvature of a capillary meniscus; also taken to be the radius of the corresponding exposed liquid surface, m - b spacing between flow paths in the cell wall, m - D diffusion coefficient for water in wood with vapour pressure as the driving potential, kg/ms Pa - D_a diffusion coefficient for water vapour through air, kg/ms Pa - D diffusion coefficient for water in wood with the driving potential - D diffusion coefficient for water in wood with the driving potential - D₀ diffusion coefficient for water in wood with vapour pressure as the driving potential, which is associated with leakage paths through the wood, kg/ms Pa - D_f diffusion coefficient for water in wood with vapour pressure as the driving potential, corresponding to fibre saturation and with no leakage paths, kg/ms Pa - D_c diffusion coefficient for water in wood with vapour pressure as the driving potential, which is associated with the constriction of the vapour flow as it approaches the cell wall, kg/ms Pa - D diffusion coefficient for water in wood with moisture content as the driving potential, kg/ms - diffusivity for water vapour in air, m²/s - F flux of water, kg/m² s - p partial pressure of water vapour, Pa - R specific gas constant for water, J/kg K - r fractional relative humidity - T temperature, K - x length coordinate in direction of flow, m - the dimensionless ratio D_f/D_c evaluated at r=1/e - arbitrary driving potential for movement of water in wood - cell spacing in the direction of water flux, m - density of liquid water, kg/m³ - coefficient of surface tension, N/m - arbitrary driving potential for movement of water in wood - fractional moisture content     

马尾松两种林型土壤养分特征及其与凋落物质量的关系

【目的】研究土壤养分和地被层凋落物养分含量的差异,为马尾松人工林营林措施及地力维持提供科学依据。【方法】以鼎湖山两种典型林型(马尾松纯林和马尾松-黧蒴混交林)为研究对象,对比分析0~60 cm土层的土壤养分含量及地被层凋落物养分含量的差异,探索凋落物质量如何影响土壤养分。【结果】1)林型对土壤有机质、全氮和硫酸根含量有显著影响(P<0.05),对土壤全磷、交换性K+、Ca2+和Mg2+有极显著影响(P<0.01),混交林土壤养分含量(除硝态氮含量和交换性H+含量以外)均高于纯林。2)相同林型不同土层间土壤养分含量差异极显著(P<0.01),其中,土壤有机质和全氮含量随土层的加深而递减,且主要聚集在0~10 cm土层,表聚效应十分明显。3)纯林凋落物有机碳、全氮、C/N和全磷等含量高于混交林;相同林型不同分解层凋落物有机碳、全钙和全镁含量有显著差异(P<0.05),均表现为未分解层>半分解层>腐殖质层。4)土壤养分与地被层凋落物质量的RDA分析表明,0~10 cm土层土壤养分与腐殖质层有机碳呈极显著负相关(P<0.01),与腐殖质层C/N呈显著负相关(P<0.05);在10~20 cm土层,土壤养分与腐殖质层有机碳呈极显著负相关(P<0.05)。【结论】纯林的土壤养分低于混交林的主要原因是纯林凋落物具有较高的C/N和有机碳含量。     

Influences of stand composition and age on forest floor processes and chemistry in pure and mixed stands of Douglas-fir and paper birch in interior British Columbia

The influence of stand composition and age on forest floor chemical properties, nitrogen availability, and microbial activity was examined in mixed and pure stands of Douglas-fir (Pseudotsuga menziesii) and paper birch (Betula papyrifera). Decomposition of Douglas-fir and birch litter over two years as well as annual litter input was also measured. Mixed and pure stands of each species aged 10–25, 50–65 and >85 years old were selected in the Interior Cedar Hemlock (ICH) zone of southern interior British Columbia. Significantly more total N was mineralized in the forest floor of pure birch compare to that of pure Douglas-fir stands while forest floor of mixed species stands had intermediate N mineralization values. When sampling times were pooled forest floor N mineralization was lowest in the young stands compared to the older stands. Stand composition did not significantly affect litter decomposition were found in litter decomposition, microbial respiration and biomass. Stand age, however, did affect these parameters significantly. More birch litter mass was lost in young stands than in their older counterparts while the opposite trend was observed for fir litter. Generally, lower basal respiration, microbial biomass and C_mic/C_org was found in young compared to older stands. Concentrations and contents of forest floor total N and exchangeable K and Mg, and pH under pure birch were consistently higher compared to pure Douglas-fir. While forest floor total C, available P contents, exchangeable K and Mg concentrations were lowest in young stands, no differences were observed for total N and exchangeable Ca. All litter nutrient concentrations and contents were highest in pure birch stands. No clear trends could be discerned in litter nutrient concentration data among stand ages, although when converted to nutrient contents, there was a general increase with stand age. Both stand type and age had significant effects on forest floor properties and processes suggesting that stand age is another factor to evaluate when assessing the influence of forest composition on forest floor processes and chemistry. In terms of the effect of mixture, the data indicated that the maintenance of paper birch in mixed stands in these forest may have some effect on nutrient availability and status.     

The effect of red wood ant (<Emphasis Type="Italic">Formica rufa</Emphasis> group) mounds on root biomass,density, and nutrient concentrations in boreal managed forests

Red wood ants (Formica rufa group, RWAs) are common insects in boreal forests in Fennoscandia, and they build large, long-lived mounds as their nests. RWA mounds are enriched with carbon and nutrients, but little information is available about how they affect root distribution and the nutrient uptake of trees. In this study, we investigated the biomass, biomass density, nutrient concentrations, and amounts of fine (<2 mm) and coarse (>2 mm) roots in RWA mounds, and compared them with those of surrounding forest soil in mixed coniferous stands of different age classes in Finland. Neither fine nor coarse root biomasses differed significantly between the aboveground parts of the mounds and the organic layer of the soil. Root biomass density was lower in mounds than in the organic layer. However, fine root biomass and biomass density were higher in the belowground parts of mounds than in the surrounding mineral soil. Macroelement (N, Ca, K, P, S, Mg) and Zn and Cu concentrations in roots in the mounds were significantly higher than those in the organic layer. Root biomass and biomass density did not differ between stands of different age classes. The results of this study indicate that RWA mounds increase heterogeneity in root distribution in forest ecosystems, and also increase the availability of nutrients for plants that extend their roots inside RWA mounds.     

Effect of six years of nitrogen additions on soil chemistry in a subtropical <Emphasis Type="Italic">Pleioblastus amarus</Emphasis> forest,Southwest China

Soil chemistry influences plant health and carbon storage in forest ecosystems. Increasing nitrogen (N) deposition has potential effect on soil chemistry. We studied N deposition effects on soil chemistry in subtropical Pleioblastus amarus bamboo forest ecosystems. An experiment with four N treatment levels (0, 50, 150, and 300 kg N ha^?1 a^?1, applied monthly, expressed as CK, LN, MN, HN, respectively) in three replicates. After 6 years of N additions, soil base cations, acid-forming cations, exchangeable acidity (EA), organic carbon fractions and nitrogen components were measured in all four seasons. The mean soil pH values in CK, LN, MN and HN were 4.71, 4.62, 4.71, and 4.40, respectively, with a significant difference between CK and HN. Nitrogen additions significantly increased soil exchangeable Al³⁺, EA, and Al/Ca, and exchangeable Al³⁺ in HN increased by 70% compared to CK. Soil base cations (Ca²⁺, Mg²⁺, K⁺, and Na⁺) did not respond to N additions. Nitrogen treatments significantly increased soil NO₃^?–N but had little effect on soil total nitrogen, particulate organic nitrogen, or NH₄⁺–N. Nitrogen additions did not affect soil total organic carbon, extractable dissolved organic carbon, incorporated organic carbon, or particulate organic carbon. This study suggests that increasing N deposition could increase soil NO₃^?–N, reduce soil pH, and increase mobilization of Al³⁺. These changes induced by N deposition can impede root grow and function, further may influence soil carbon storage and nutrient cycles in the future.     

Using model scenarios to predict and evaluate forest-management impacts on soil base saturation at landscape level

Silviculture, forest conversion and technical tools of ecosystem management, such as forest liming, display their effects at the landscape level. Therefore their planning and control should take place at the same scale. The primary objective of this work was to assess soil chemical properties and their changes in relationship to ecosystem management, especially forest conversion and forest liming. We calculated scenario models, based on regression analysis, which allow such an examination in the context of understanding landscape processes which can be expected to operate in the sampling region. Stepwise multiple linear regression analysis was used to predict soil chemical attributes (base saturation, pH, C/N content and stock, exchangeable stocks of Ca and Mg) as indicators of site stability or off-site effects of forest ecosystems such as effects on clean drinking water from forested watersheds. Because of space limitations, in this paper only the modelling results of base saturation are presented. Base saturation was used as an integrative example for other soil chemical properties. The transformation of measurements to the regional scale, i.e., the regionalization, was calculated for the forested parts of two test regions in the Black Forest on the basis of measured chemical properties of 90–150 soil profiles per test region. The models have a spatial resolution of 50×50 m, which is a spatial scale relevant for forestry practice and forest management. Topographic variables (e.g., elevation, aspect, slope gradient, and slope length), the stratigraphic classification of the geologic substrate, stand characteristics from forest inventory data, and finally technical information about forest liming were the auxiliary variables (secondary site properties) that provided indirect information about base saturation and were available for the whole forested area of the test regions. Base saturation could be predicted with an accuracy of ~50–70% (in terms of the multiple R²) by using these properties as predictor variables in multiple linear regression analyses. The explained proportion of variance was unexpectedly high considering the high geomorphological heterogeneity of the two test regions. Based upon the regionalization models, it was possible to establish scenarios showing the landscape-related effects on base saturation that may be achieved by forest conversion towards a higher proportion of forests with broad-leaved mixed stands and by forest liming. These scenarios allow the interactions between several influencing factors and management strategies and the impacts on the target variable to be synoptically judged. Thus the presented regionalization models achieve the role of decision support tools for the planning of forest management at the landscape level. They allow an assessment of the environmental effects of forest management strategies in terms of site sustainability or preservation of water resources in forested catchments.     

Comparison of P and cation cycling in two contrasting seasonally dry forest ecosystems

Context

Interactions of N and P cycles and those of other macro-elements in forests are scarcely known.

Aim

This study compares the P cycle in two very different forest ecosystems where soil P availability is low (tropical dry forest in Mexico and Mediterranean forest in Spain) in relation to Ca, K, and Mg cycles.

Methods

Compiled data belonging to these two forest sites are discussed, comparing the P and base cation budgets and exploring relationships among P and base cation cycles.

Results

Broad differences between input and output of base cations were observed. Analysis of the P budget indicates P retention inside both forest ecosystems. The tropical dry forest has higher nutrient contents than those found in the Mediterranean temperate forest. Chemical composition of forest leaves and litters, and base cation?CP ratios varied according to soil P availability and cation concentrations. However, P resorption is higher in the tropical dry forest than in the temperate one.

Conclusion

This study reveals the existence of P retention at the ecosystem level in both forests, but suggested P limitation at the Mediterranean forest seems to be stronger than that occurring at the tropical forest.     

Variations of plant and soil 87Sr/86Sr along the slope of a tropical inselberg

? From the summit downslope a granitic inselberg in French Guiana, soils and vegetation evolve from bare granite covered by cyanobacteria, to a savannah-type vegetation on thin patchy sandy accumulations, then to a low forest on shallow young soils and to a high forest on deep highly weathered ultisols.

? We have used element budgets and Sr isotopic variations in soils and plants to investigate the mineral nutrient supply sources of the different plant communities.

? Granite and atmospheric deposition have ⁸⁷Sr/⁸⁶Sr ratios of 1.3 and 0.71, respectively. The ⁸⁷Sr/⁸⁶Sr ratio of cyanobacteria (0.72) suggests granite weathering by cyanobacteria crusts. The ⁸⁷Sr/⁸⁶Sr ratio of the savannah-type vegetation is 0.73 and varies between 0.75 and 0.76 in the low and high forest leaf litter regardless of soil depth, age and degree of impoverishment.

? These almost constant ratio suggest that forest Sr comes from rainwater and from the summit of this inselberg, where it is released and redistributed along the slope, by surface flow, lateral redistribution of litter, and mineral particles. However, because of its very low content in the rock and soils, Ca is supplied to plants by atmospheric deposition.

     

Charge characteristics of soil organic matter fractions in a Ferric Lixisol under some multipurpose trees

Soil organic matter (SOM) has a key role in maintaining soil fertility in weathered soils in the tropics. This study was conducted to determine the contribution of different SOM fractions to the cation exchange capacity (CEC) of a tropical soil as influenced by organic matter inputs of different biochemical composition. Soil samples were collected from a 16-yr old arboretum established on a Ferric Lixisol, under five multipurpose tree species: Leucaena leucocephala, Dactyladenia barteri, Afzelia africana, Pterocarpus santalinoides, and Treculia africana. Fractions were obtained by wet sieving and sedimentation after dispersion with Na₂CO₃. Fractions larger than 0.053 mm were separated into mineral and organic components by flotation on water. Relationships between CEC and pH were determined using the silverthioureum-method. For all treatments the organic fractions had the highest CEC, expressed on a dry matter basis, and the CEC of the fractions smaller than 0.053 mm was inversely related to their particle size: clay (< 0.002 mm) > fine silt (0.002–0.02 mm) > coarse silt (0.02–0.053 mm). A positive correlation (significant at the 0.01 probability level) existed between the slope of the fitted CEC-pH relationships and the organic C concentrations of the whole soil and both silt fractions. The clay and fine silt fractions were responsible for 85 to 90% of the CEC of the soil. Organic inputs with a high C/N and lignin/N ratio produced fine and coarse silt sized SOM fractions with the highest charge density. Therefore, inputs of slowly decomposing organic residues seem to be promising for increasing the CEC of highly weathered soils.This revised version was published online in November 2005 with corrections to the Cover Date.     

Estimation of the biomass of fine roots and mycorrhizal fungi: a case study in a Japanese red pine (Pinus densiflora) stand

As part of a study on soil carbon flow in forest ecosystems, the biomass of fine roots (2.0mm in diameter) and root-associated fungi, including ectomycorrhizal fungi, were estimated in the summer season in 1998 at a Pinus densiflora (Japanese red pine) stand in western Japan. Fine roots of pine were classified into three categories: class I roots (0.5–2.0mm in diameter), long class II roots (long roots with diameter 0.5mm; II_L), and short class II roots (short roots with diameter 0.5mm; II_S). Total biomass of fine roots (I + II_L + II_S) at this stand was estimated to be 91.0gm^–2, about 23% of which was class II roots (II_L + II_S). Ergosterol, which is a component of fungal membranes, was analyzed to estimate the biomass of root-associated fungi in roots. In the upper soil layers (from the surface to 13.4cm in depth), ergosterol contents in the class I, II_L and II_S roots were in the ranges 43.1–82.2, 126.1–196.3 and 271.2–321.0µgg^–1 root DW, respectively. The ergosterol content was converted to fungal biomass using the median (minimum–maximum) value of ergosterol concentration reported for ectomycorrhizal fungi. Root-associated fungal biomass in this stand was estimated to be 2.0 (0.5–9.6) gm^–2. The data suggest the biomass of ectomycorrhizal fungi in the P. densiflora stand is small compared with that in other forest ecosystems.