Effects of vegetation and slope aspect on water budget in the hill and gully region of the Loess Plateau of China

Precipitation, throughfall, stemflow and soil water content were measured, and interception, transpiration, evaporation, runoff, deep percolation and soil water recharge were estimated in the natural Liaotung Oak (Quercus liaotungensis) and regrown Black Locust (Robinia pseudoacacia) forestlands in the hill and gully region of the China Loess Plateau. Four stands (south- and north-facing slopes) of two forests were studied between May 27, 2006 and October 31, 2007. Hydrological fluxes were calculated using a coupled water and heat flow model called CoupModel. Throughfall, stemflow and soil water content were used to calibrate the model. The simulations indicated that, interception, vegetation transpiration and soil water evaporation were the main components of water consumption in the 4 stands, accounting for about 90% of the precipitation. The simulated interception and vegetation transpiration in the south-facing slope (154 and 327 mm in regrown forestland and 173 and 338 mm in natural forestland) were lower than those in the north-facing slope (219 and 344 mm in regrown forestland and 203 and 342 mm in natural forestland). Soil water evaporation in the south-facing slope (416 mm in regrown forestland and 373 mm in natural forestland) was larger than that in the north-facing slope (325 mm in regrown forestland and 330 mm in natural forestland) in the same vegetation stands. This was mainly due to greater vegetation density in the north-facing slope than in the south-facing slope. For the regrown forestlands, the simulated soil water recharge was larger under north-facing slope stands (90 mm) than under south-facing slope stands (76 mm), and the natural forestland in the north-facing slope had the largest soil water recharge (104 mm). The results indicated that vegetation species and slope aspects significantly influenced the water balance budget in the soil–vegetation–atmosphere system. The water budget differences among the 4 stands indicate that care is required for properly selecting regrown tree-species. Soil and water conservation measures must be applied scientifically when converting farmland to forest in the Loess Plateau of China, especially on the south-facing slopes.     

中国北方森林坡向对土壤细菌和从枝菌根真菌群落的影响（英文）

The effects of slope aspects on soil biogeochemical properties and plant communities in forested environments have been studied extensively;however,slope aspect influence on soil microbial communities remains largely unexamined,despite the central role of soil biota in ecosystem functioning.In this study,the communities of both soil bacteria and arbuscular mycorrhizal fungi(AMF)were investigated using tagged pyrosequencing for three types of slope aspects(south-facing aspect,north-facing aspect and flat area)in a boreal forest of the Greater Khingan Mountains,China.The bacterial and AMF community composition differed with slope aspects.Bacterial diversity was the lowest on the north-facing aspect,and AMF diversity was the lowest on the flat area.Aspects also had a significant impact on soil pH and available phosphorus(P) and shrubby biomass.Soil pH and understory shrub biomass were significantly correlated with bacterial communities,and soil available P and shrub biomass showed significant correlations with AMF communities.Our results suggested that slope aspects affected bacterial and AMF communities,mediated by aspect-induced changes in plant community and soil chemical properties(e.g.,pH and available P),which improved the knowledge on the effects of forest slope aspects on aboveground and belowground communities.     

中国北方森林坡向对土壤细菌和从枝菌根真菌群落的影响

The effects of slope aspects on soil biogeochemical properties and plant communities in forested environments have been studied extensively; however, slope aspect influence on soil microbial communities remains largely unexamined, despite the central role of soil biota in ecosystem functioning. In this study, the communities of both soil bacteria and arbuscular mycorrhizal fungi (AMF) were investigated using tagged pyrosequencing for three types of slope aspects (south-facing aspect, north-facing aspect and flat area) in a boreal forest of the Greater Khingan Mountains, China. The bacterial and AMF community composition differed with slope aspects. Bacterial diversity was the lowest on the north-facing aspect, and AMF diversity was the lowest on the flat area. Aspects also had a significant impact on soil pH and available phosphorus (P) and shrubby biomass. Soil pH and understory shrub biomass were significantly correlated with bacterial communities, and soil available P and shrub biomass showed significant correlations with AMF communities. Our results suggested that slope aspects affected bacterial and AMF communities, mediated by aspect-induced changes in plant community and soil chemical properties (e.g., pH and available P), which improved the knowledge on the effects of forest slope aspects on aboveground and belowground communities.     

Management strategies to increase stand structural diversity and enhance biodiversity in coastal rainforests of Alaska

Coastal rainforests of southeast Alaska have relatively simple species composition but complex structures with high diversity of tree ages, sizes and forest canopy layers, and an abundant understory plant community. Wildlife and fisheries resources also play an important role in the ecological functioning of forest and aquatic systems. Clearcutting has greatly altered these forest ecosystems with significant decreases in structural diversity of forest stands and greatly reduced wildlife habitat. This paper synthesizes information on management options in older forests that have never been actively managed, and in younger forests to increase diversity of stand structures and their associated effects on biodiversity. Light to moderate levels of partial cutting in old-growth forests can maintain the original diversity of overstory stand structures and understory plant communities. In younger forests that develop after clearcutting, mixed alder-conifer stands provide more heterogeneous structures and significantly higher understory biomass than in pure conifer forests. Research has shown that red alder increases diversity and abundance of understory plants, and provides forage for deer and small mammals. Results also show a clear linkage between alder and improved invertebrate diversity in aquatic systems. A combination of light partial cutting in older forests along with inclusion of red alder in conifer-dominated forests could provide the greatest amount of diversity and maintain the complex stand structures that are an important component of these forest ecosystems.     

The Collembola community of pure and mixed stands of beech (Fagus sylvatica) and spruce (Picea abies) of different age

The idea of establishing mixed forests that are better adapted to site conditions than spruce monocultures has attracted increasing attention of forest owners and governmental institutions over the last decades. Currently, beech is being replanted and an increasing proportion of German forests are mixed stands. Focusing on the reaction of the soil fauna to forest conversion, this study investigates the response of the Collembola community to replacement of beech by spruce or by mixed stands of beech and spruce. Stands of different age were investigated in a factorial design with the factors stand type (beech, spruce and mixed stands) and stand age (30 and 120 years). Collembola communities did not differ strongly between stand types and stand age and were dominated by Folsomia quadrioculata and Mesaphorura species (e.g. Mesaphorura macrochaeta). Moreover, neither total abundance of Collembola nor densities of the fungal feeding euedaphic Onychiurinae and Tullbergiinae significantly responded to stand type and stand age. The density of the epedaphic and partly herbivorous groups Symphypleona/Neelipleona and Entomobryidae in the 120-year-old stands significantly exceeded that in the 30-year-old stands; presumably, this was due to the well developed herb layer in the 120-year-old stands with more open canopies. Canonical correspondence analysis (CCA) of the Collembola community of the L/F horizon also indicated that most of the epigeic species were associated with the 120-year-old stands. Moreover, the diversity of Collembola significantly increased with forest age which likely reflects increased amount and diversity of food resources in the 120-year-old stands. The density of the hygrophilous species Fo. quadrioculata was significantly higher in the spruce than in the beech stands; probably this was due to the higher water content in litter of the spruce stands. Moreover, the results of the CCAs indicated that soil pH is an important structuring force for the Collembola communities. Overall, the results suggest that stand type and forest age impact Collembola communities, presumably via changes in the amount and quality of food resources, such as living plant and herb litter materials. The pronounced changes which occurred with forest age likely were related to the development of more dense and diverse herb layer in mature forests which provides additional food resources in particular for epedaphic species. On the other hand, dominant species/functional groups of Collembola, such as hemiedaphic species, appear to depend predominantly on abiotic factors, most importantly soil pH and soil water content.     

Soil fauna abundance and diversity in a secondary semi-evergreen forest in Guadeloupe (Lesser Antilles): influence of soil type and dominant tree species

The importance of secondary tropical forests regarding the maintenance of soil fauna abundance and diversity is poorly known. The aims of this study were (1) to describe soil fauna abundance and diversity and (2) to assess the determinants of soil fauna abundance and diversity in two stands of a tropical semi-evergreen secondary forest. Soil macrofauna and microarthropod abundance and soil macrofauna diversity were described at two sites developed on different soils and with different site histories: (1) a natural secondary stand (natural forest) under two dominant tree species, Pisonia subcordata and Bursera simaruba, and (2) a planted secondary forest (planted forest) under three tree species, B. simaruba, Swietenia macrophylla, and Tabebuia heterophylla. The effects of both soil and main tree species’ litter quality were assessed to explain soil fauna abundance and diversity. The abundance of soil macrofauna was significantly higher in the soil under the planted forest, and soil fauna communities were contrasted between the two sites. In the planted forest, a soil-dwelling macrofauna community developed (mainly consisting of the anecic earthworm Polypheretima elongata). In the natural forest, soil macrofauna and microarthropod communities were located at the soil surface. The effect of plant litter quality varied according to each dominant tree species and was superimposed to soil effect. The lowest macrofauna abundance was associated with B. simaruba in the natural forest. T. heterophylla supported a much greater macrofauna community than the two other tree species studied at the same soil, and it appears likely that this is due to the palatability of its leaves compared with the other trees (low lignin, tannins, soluble phenols).     

Evidence that plant diversity and site productivity confer stability to forest floor microbial biomass

The ability of soil microbial communities to withstand punctual disturbance or chronic stress is important for the stability of ecosystem processes. Factors controlling microbial community composition or soil resource availability should be regarded as potential determinants of this stability. Here, we explored the effects of three stand types (jack pine, aspen and mixed-wood) and two geologic parent materials (clay and till), on the stability of the microbial biomass in the forest floor. We hypothesised that microbial communities in mixed-wood stands or on the clay soil would show greater resistance to, and resilience from, a dry-wet disturbance, and a higher tolerance to incremental additions of HCl or Cu, than microbial communities in mono-specific stands or on the till soil. We also surveyed the understory vegetation, and measured chemical properties and microbial phospholipid fatty acid profiles in the forest floor, so as to gain insights into the factors regulating microbial stability. Microbial resistance to disturbance was found to be higher in mixed-wood than in mono-specific stands. Microbial communities from mixed-wood stands also showed a high tolerance to HCl and Cu stress over both geologic parent materials, as opposed to those in mono-specific stands that showed a high tolerance to stress on only one type of parent material. Some forest floor properties in mixed-wood stands (e.g. Ca on clay, mineralisable N and C/N ratio on till) were more similar to the more productive aspen, than to jack pine stands. Other properties (understory plant communities, pH, actinomycete and arbuscular mycorrhizae) of mixed-wood stands were transitional between those in aspen and jack pine stands, suggesting that both tree species contribute in structuring the forest floor microbial pool in mixed-wood stands. We put forward that this may provide a more diverse capability to resist disturbance and tolerate stress than in mono-specific stands. We found no effect of stand type on microbial resilience to disturbance, but resilience was higher on clay than on till plots. This could be due to a higher fungal/bacterial ratio on till plots, as slower fungal growth rates may hinder resilience, or to lower carbon and nutrient availability limiting the growth rate of resistant microbial cells. We conclude that plant diversity and site productivity are important drivers of forest floor microbial stability in the southern boreal forest of eastern Canada.     

Edaphic interslope and valley bottom differences at “Evolution Canyon”, Lower Nahal Oren, Mount Carmel, Israel

The opposite slopes of lower Nahal Oren, Mount Carmel, Israel, designated “Evolution Canyon”, display physical and biotic contrasts, although both are cut in Upper Cenomanian calcareous limestone. The three-fold greater solar radiation makes the south-facing slope warmer, drier and more variable than the north-facing slope and valley bottom. Consequently, biodiversity is greater. Microclimate (mesic–xeric) is a major force driving adaptive evolution, and causing soil divergence. The soils on both slopes are Terra Rossas in the Israeli classification system (Rhodoxeralfs in US taxonomy). However, selected properties (pH, humus content, NH₄–N content, cation exchange capacity and others) display greater interslope than intraslope differences. The north-facing Terra Rossas have a dark-coloured A1 humic horizon, which is better developed than in south-facing Terra Rossas. Differences in soil morphology, moisture regime and microfabric between the north- and south-facing soils suggest that they belong to different taxonomic classes. These differences probably result in part from the forested ecosystem of the north-facing slope versus the savanna-like ecosystem of the opposite slope.     

Chaotic or deterministic development of nematode populations in pine forest humus incubated in the laboratory

Humus material from an old stand of Scots pine and from an open area clearcut 13–15 years ago was incubated in the laboratory. The incubations were started in different years and the differences in nematode faunal development between the years were compared with site characteristics. In all incubations there was an increase in total nematode abundance. The total number and diversity of nematodes were higher in humus from the forest than from the clearing. The results indicated that biotic control mechanisms were much weaker in the humus from the clearcut area, where a strong dominance of Acrobeloides nanus occurred in most incubations. The differences in faunal development between years were rather large. A certain pattern of unpredictability indicated that the nematode fauna was a rather labile component of the community of soil organisms in a pine forest soil.     

Variation of soil microbial biomass C and hydrolytic enzyme activities in a rangeland ecosystem: are slope aspect and position effective?

This study was conducted to investigate the effects of slope aspect and position on microbial biomass C (MBC) and some hydrolytic enzyme activities involved in soil N, P, and S cycles in a rangeland ecosystem of west central Iran. Soil samples were collected from three slope positions (summit, backslope, and footslope) of contiguous north- and south-facing slopes. Results indicated higher silt and clay content, soil organic C (SOC), total N (TN), and C/N ratio on the north-facing slope. Furthermore, MBC, alkaline phosphomonoesterase (ALP), acid phosphomonoesterase (ACP), arylsulfatase (ARS), urease (URS), L-asparaginase (LAS), and L-glutaminase (LGL) activities were greater by 46.1, 65.9, 58.6, 59.6, 52.6, 62.8, and 65.7%, respectively, on the north-facing slope compared to the south-facing one. Higher ratios of enzyme activities to MBC were observed on the north-facing slope. In contrast, per cent of inorganic N and microbial quotient were greater on the south-facing slope. The activity of ALP, ACP, ARS along with SOC, TN, and MBC values decreased from summit to footslope. Overall, our findings indicate that north-facing slope and summit position support greater microbial biomass and hydrolytic diversity.     

Humus macro-morphology and soil microbial community changes along a 130-yr-old Fagus sylvatica chronosequence

We aimed to characterize humus macro-morphology and the associated soil microbial community within the unmodified litter (OL), the fragmented and humified layers (FH) and the organo-mineral (A) layer along a beech (Fagus sylvatica L.) forest chronosequence with four stand age-classes (15-, 65-, 95-, 130-yr-old) in Normandy, France. Humus macro-morphology was described with 36 quantitative and semi-quantitative variables. We measured microbial biomass N (N_mic), microbial N quotient (N_mic-to-N_t), fungal ergosterol, bacterial and fungal DNA using 16S and 18S rDNA real-time qPCR and evaluated the potential metabolic profile of heterotrophic bacteria within each soil layer and stand age-class. The log-transform ergosterol/fungal DNA ratio (EFR index) was used as an indicator related to active fungal biomass and the fungal/bacterial (F/B) ratio was calculated from qPCR results. There was a shift from mull (mainly dysmull) to moder humus forms along the chronosequence. While the N_mic did not change significantly, the N_mic-to-N_t decreased along the chronosequence in the OL layer. Ergosterol content increased in FH and A layers and the F/B ratio increased in the FH layer with increasing beech forest age. The EFR index was significantly higher in the OL and A layers of the oldest stands, whereas the highest EFR index in the FH layer occurred in the 15-yr-old stands. The functional diversity of heterotrophic bacteria was greater within OL and FH layers of 130-yr-old stands, but highest in the A layer of 15-yr-old stands while the Average Well Color Development remained stable for all soil layers. We found significant correlations between macro-morphology and microbial variables, especially between FH-based morphology and fungal biomass. Our main results are that beech forest maturation is accompanied by (1) an increase in fungal biomass in the FH layers and, (2) an increase in heterotrophic bacteria functional diversity in the organic layers. We have identified key macro-morphology variables that are good predictors of the structural and functional profile of the soil microbial community during beech forest development.     

The Collembola community of a Central European forest: Influence of tree species composition

The present study investigates the response of the Collembola community to replacement of beech by spruce or by mixed stands of beech and spruce in the Solling mountains (Germany). The study was carried out in three beech (Fagus sylvatica), spruce (Picea abies) and mixed stands of beech and spruce arranged in three blocks. The density, diversity and community structure of Collembola as well as microbial and abiotic parameters in the organic layers and mineral soil of the three spruce, three beech and three mixed stands were investigated. Major results are: (i) Collembola communities did not differ strongly between stand types and were dominated by Folsomia quadrioculata and Mesaphorura species, (ii) neither total abundance of Collembola nor densities of the hemiedaphic species F. quadrioculata, Parisotoma notabilis and Isotomiella minor significantly responded to stand type, (iii) in the mixed stands the fungal biomass was increased leading to high densities of fungal feeding Collembola (e.g. Mesaphorura sp.) and high species numbers of Collembola, (iv) the density of the epedaphic and partly herbivorous group Entomobryidae/Tomoceridae in the spruce stands exceeded that in the mixed and beech stands; presumably this was due to the higher diversity of the ground vegetation in the spruce stands. Canonical correspondence analysis (CCA) of the collembolan communities of L/F and H/Ah horizons also indicated that most of the epedaphic species were associated with the spruce stands. Moreover, results of the CCA indicated that soil pH is an important structuring force for collembolan communities. Overall, results suggest that stand type impact collembolan communities, presumably via changes in the amount and quality of food resources, such as fungal biomass and living plant material. However, differences in collembolan community structure between the investigated stand types were moderate supporting earlier findings that Collembola generally respond little to changes in the vegetation structure.     

Functional diversity of microbial communities in the mixed boreal plain forest of central Canada

This study was designed to examine whether or not specific tree species (Picea glauca, Picea mariana, Pinus banksiana, Populus tremuloides), their post-fire stand age, or their position in a successional pathway had any significant effect on the functional diversity of associated soil microbial communities in a typical mixed boreal forest ecosystem (Duck Mountain Provincial Forest, Manitoba, Canada). Multivariate analyses designed to identify significant biotic and/or abiotic variables associated with patterns of organic substrate utilization (assessed using the BIOLOG™ System) revealed the overall similarity in substrate utilization by the soil microbial communities. The five clusters identified differed mainly by their substrate-utilization value rather than by specific substrate utilization. Variability in community functional diversity was not strongly associated to tree species or post-fire stand age; however, redundancy analysis indicated a stronger association between substrate utilization and successional pathway and soil pH. For example, microbial communities associated with the relatively high pH soils of the P. tremuloides-P. glauca successional pathway, exhibited a greater degree of substrate utilization than those associated with the P. banksiana-P. mariana successional pathway and more acidic soils. Differences in functional diversity specific to tree species were not observed and this may have reflected the mixed nature of the forest stands and of their heterogeneous forest floor. In a densely treed, mixed boreal forest ecosystem, great overlap in tree and understory species occur making it difficult to assign a definitive microbial community to any particular tree species. The presence of P. tremuloides in all stand types and post fire stand ages has probably contributed to the large amount of overlap in utilization profiles among soil samples.     

Invertebrate communities (Annelida and epigeic fauna) in three types of Estonian cultivated soils

The abundance and diversity of invertebrate communities (annelids and epigeic fauna) in three types of cultivated soils were studied. Soil biota communities in the three most widespread soil types in Estonia (Calcaric Regosols, Calcaric Cambisols and Stagnic Luvisols) are influenced by environmental conditions, the factors connected to soil texture including moisture, organic matter content and pH being the most essential, and by the intensity of agricultural practice. Potentially high biological activity and low intensity of agricultural human activity of Calcaric Regosols occurs in parameters of communities of organisms not sensitive to soil which dries off, i.e. epigeic fauna living on the soil surface and preferring dry and warm habitat; temporarily dried off soil is not a suitable habitat for Oligochaeta. Both groups of Oligochaeta (earthworms, enchytraeids) appear to prefer Calcaric Cambisols where soil moisture conditions are more stable. The abundance of invertebrate communities is the highest and the diversity is the lowest in Stagnic Luvisols. Some trends occurred in community characteristics along the soil surface following a hypothetical gradient; the number of carabids per trap and diversity of spiders decreased from the edge to the centre of the field. The results presented here on spatial variability in distribution of soil organisms are preliminary.     

The microbial communities of aspen and spruce forest floors are resistant to changes in litter inputs and microclimate

Previous studies have shown that forest floors from stands dominated by trembling aspen (ASPEN; Populus tremuloides Michx.) tend to support a greater microbial biomass with a different microbial community structure than forest floors from stands dominated by white spruce (SPRUCE; Picea glauca (Moench) Voss). A reciprocal transfer experiment, in concert with coarse and fine mesh bags that allowed or excluded fine root in-growth, was used to examine how the composition of these forest floor microbial communities respond to changes in belowground inputs from fine roots, aboveground inputs (e.g. from litter and through-fall) and soil microclimatic conditions over 1 year. Neither the microbial biomass nor the microbial community structure (assessed using phospholipid fatty acid analyses and substrate-induced respiration techniques) of forest floors of ASPEN or SPRUCE origin were altered by reciprocal transfer to SPRUCE or ASPEN stands, with or without fine root inputs. Despite the lack of changes in microbial community structure, the stand type during incubation had a strong effect on forest floor moisture content and concentrations of nitrate, while mesh size had a significant effect on forest floor pH and the abundance of mesofauna. Thus, changes in microbial community structure did not co-occur with changes in other characteristics of these forest floors. The resistance of the forest floor microbial communities to change may be a function of the high C contents of these soils. Further treatment effects may have been detected if the study had been extended beyond 1 year. Reciprocal transfer studies using coarse and fine mesh bags allow transferred soils to respond to fluctuations in microclimate, organic inputs and soil biota and, therefore, hold considerable promise for studies examining the influence of disturbances on soil properties.     

Differential effect of arbuscular mycorrhizal fungal communities from ecosystems along management gradient on the growth of forest understorey plant species

Arbuscular mycorrhizal fungi (AMF) are important functional components of ecosystems. Although there is accumulating knowledge about AMF diversity in different ecosystems, the effect of forest management on diversity and functional characteristics of AMF communities has not been addressed. Here, we used soil inoculum representing three different AM fungal communities (from a young forest stand, an old forest stand and an arable field) in a greenhouse experiment to investigate their effect on the growth of three plant species with contrasting local distributions - Geum rivale, Trifolium pratense and Hypericum maculatum. AM fungal communities in plant roots were analysed using the terminal restriction fragment length polymorphism (T-RFLP) method. The effect of natural AMF communities from the old and young forest on the growth of studied plant species was similar. However, the AMF community from the contrasting arable ecosystems increased H. maculatum root and shoot biomass compared with forest inocula and T. pratense root biomass compared to sterile control. According to ordination analysis AMF inocula from old and young forest resulted in similar root AMF communities whilst plants grown with AM fungi from arable field hosted a different AMF community from those grown with old forest inocula. AMF richness in plant roots was not related to the origin of AMF inoculum. G. rivale hosted a significantly different AM fungal community to that of T. pratense and H. maculatum. We conclude that although the composition of AM fungal communities in intensively managed stands differed from that of old stands, the ecosystem can still offer the ‘symbiotic service’ necessary for the restoration of a characteristic old growth understorey plant community.     

Bilanzierung jährlicher Elementflüsse in Waldökosystemen im Solling

Balances of annual element fluxes within forest ecosystems in the Solling region Based on measurements of element fluxes the annual changes of element storage within the compartments ?Stand”?, ?Humus layer”? and ?Mineral soil”? are calculated for a beech and a spruce stand. In spite of high rates of N-deposition insufficient N supply especially for the beech stand is obvious. The H⁺ buffering capacity of the stands is very limited and is greater for the spruce than for the beech stand. The accumulation of C, N, P and Ca within the humus layer of both stands seems to be due to far reaching changes of decomposition conditions caused by acid precipitation. The mineral soil reacts as a sink for H⁺ and S and as a source for Ca, Mg, Mn and Al. From the cation-anion-balance for the changes of element storage the annual H⁺-production within the mineral soil was calculated. The sum of H⁺ ions produced ecosystem internal within the humus layer and the mineral soil ist greater for spruce than for beech. For the spruce stand the total H⁺-load from deposition and from internal sources is about twice as big as the one of the beech stand.     

Factors affecting the nutrient status of forest sites in a mountain watershed in Nepal

Soil and foliage samples were collected from 136 sample sites in forested areas of the Dhulikhel Watershed, Nepal. Analyses showed that the soils have small values for pH, base saturation, total nitrogen, carbon and available phosphorus. Sample sites were stratified on the basis of aspect and elevation, soil type, forest type and management and the strata were compared to determine the influence of site factors on forest soil fertility. Soils on south-facing slopes at low elevation contained significantly less total nitrogen and organic carbon compared with soils from north-facing slopes at high elevation. Foliage of both sal (Shorea robusta Gaertn.) and chir pine (Pinus roxburghii Sargent) growing on red soils (Rhodustults and Haplustults) contained significantly less phosphorus compared with non-red soils (Ustochrepts and Dystrochrepts). Soils under stands of sal have the poorest soil fertility levels in comparison with chir pine and hardwood sites. The continuous removal of base-rich litter from sal sites may account for the poor fertility conditions. Soil fertility levels are greater on sites which have been protected from biomass removal for at least 15 years relative to sites which have come under protection in the past 7 years.     

Effect of north and south exposure on weathering rates and clay mineral formation in Alpine soils

A comparison was made between two soil climosequences on north- and south-facing slopes in northern Italy to determine the influence of slope aspect on soil processes. The climosequences span an elevational gradient ranging from moderate (1200 m a.s.l.) to high alpine (2420 m a.s.l.) climate zones on surfaces having an age of about 15 000 years. The soils were investigated with respect to organic C, oxalate and dithionite extractable Fe, Al and Si, elemental losses (Ca, Mg, K, Na, Fe, Al, Si, Mn) and clay minerals. The stocks of soil org. C as well as of oxalate-extractable Fe and Al was greatest in the subalpine zone near the timberline. There are no clear differences in organic C content between the soils on north- and south-facing sites. Fe-oxalate and to a lesser extent Al_o-stocks were, however, greater on north-facing sites, indicating that weathering is greater there. Eluviation and illuviation of Al and Fe within the soil profile, typical for podzolisation, was more distinctly expressed on the N slopes. The probability of ITM (Imogolite-type-material) formation in the soil seemed to be greater on south-facing sites. On the north-facing sites, element leaching was most intense in the subalpine zone close to the timberline while on the south-facing sites this was only the case for the base cations. The N slopes exhibited higher leaching of elements which generally indicates a higher weathering intensity. On south-facing sites, typical podzolisation processes were measurable only above 2000 m a.s.l. The development of smectites is also a reflection of the weathering intensity; smectite was discernible in the surface horizon at all sites on N slopes but the highest amount was detected in the sub-alpine climate zone. For the south-facing sites only in the alpine climate zone could smectite be detected. Higher temperatures and an increased number of freeze-thaw cycles on south-facing slopes should theoretically enhance rates of chemical weathering. This could, however, not be confirmed with our measurements. The degree of chemical weathering increases from the south- to the north-facing sites that are characterised by lower temperatures, lower evapotranspiration and consequently by a higher humidity. Although precipitation in Alpine regions is abundant, the availability and flux of water through the soil is the prime factor in weathering intensity.     

吉林省东部低山丘陵区4种林分类型林地的土壤肥力分析

根据吉林省东部低山丘陵区汪清林业局金仓林场中4种主要林分类型(长白落叶松天然林、长白落叶松人工林、天然针阔混交林和天然阔叶混交林)的土壤肥力调查数据,分析和比较了4种林分类型林地的土壤物理和化学性质,并采用主成分分析评价了其土壤肥力状况。(1)随土壤深度增加,土壤容重和土壤pH值增大,而土壤含水量、阳离子交换量和养分含量减少,但其在不同林分下的变化程度不同;(2)林分类型对部分土壤化学性质(如土壤CEC、有机质、全氮和速效钾)影响显著。其中,天然针阔混交林的土壤含水量、土壤pH值、阳离子交换量、有机质含量及全氮、磷、钾含量均为最高;(3)采用主成分分析法对不同林分类型的林地土壤肥力状况进行了评价,结果发现土壤肥力状况为:天然针阔混交林>长白落叶松天然林>长白落叶松人工林>天然阔叶混交林。建议在经营现有的林分时,考虑近自然育林,及时进行林下补植更新,并营造针阔混交林,以改善该区林地土壤的肥力状况。