Microbial enzyme activities in leaf litter, humus and mineral soil layers of European forests

The rationale of the study was to investigate microbial activity in different soil horizons in European forests. Hence, activities of chitinase and cellulase, microbial biomass carbon (C_mic) and basal respiration were measured in litter, fragmentation, humus and mineral soil layers collected several times from various beech and spruce forests. Sites were selected to form a gradient in N availability. Analyses were also performed on beech litter from a litterbag transplant experiment. Furthermore, microbiological parameters were measured in horizons of beech and spruce chronosequence sites with different stand age in order to investigate the influence of forest rotation, and hence changes in soil organic matter (SOM) dynamics, on microbial activity. Finally in horizons of one beech forest, the seasonal variation of selected microbiological parameters was measured more intensively. β-Glucosaminidase and cellobiohydrolase activities were measured using fluorogenic 4-methylumbelliferyl substrates to estimate chitinase and cellulase activities, respectively. On a spatial scale, chitinase and cellulase activities, C_mic determined by substrate induced respiration, and basal respiration ranged from 144 to 1924 and 6-177 nmol 4-MU g⁻¹ org-C h⁻¹, 8-48 mg C g⁻¹ org-C and 11-149 μg CO₂-C g⁻¹ org-C h⁻¹, respectively; in general values were significantly lower in layers of humus and mineral soil than of litter. Chitinase activity, C_mic and basal respiration from humus and mineral soil layers, together, correlated positively, while none correlated with cellulase activity. Similarly in the litter layer, no correlations were found between the microbiological parameters. On a seasonal scale, a time lag between a burst in basal respiration rate and activities of both enzymes were observed. In general, activities of cellulase and chitinase, C_mic and basal respiration, did not change with stand age, except in the humus layer in the spruce chronosequence, where C_mic decreased with stand age. In the litter layer, cellulase activity was significantly and positively related to the C:N ratio, while only a tendency for chitinase activity was shown, indicating that enzyme activities decreased with increasing N availability. In accordance, the enzyme activities and C_mic decreased significantly with increasing chronic N deposition in the humus layer, while basal respiration only tended to decrease with increasing N deposition. In contrast, enzyme activities in beech litter from litterbags after 2 years of incubation were generally higher at sites with higher N deposition. The results show different layer-specific responses of enzyme activities to changes in N availability, indicating different impacts of N availability on decomposition of SOM and stage of litter decomposition.     

Responses of co-occurring populations of Dendrobaena octaedra (Lumbricidae) and Cognettia sphagnetorum (Enchytraeidae) to soil pH, moisture and resource addition

Dendrobaena octaedra (Lumbricidae) and Cognettia sphagnetorum (Enchytraeidae) are the two most dominating soil invertebrates in terms of biomass in boreal coniferous forest soils. A microcosm experiment was set up in order to study the influence of pH, moisture and resource addition on D. octaedra and C. sphagnetorum when both species are simultaneously present. Two kinds of coniferous forest humus were used as substrate, pine stand humus (pH 4.2), and spruce stand humus (pH 4.6); in the third treatment the pine stand humus was adjusted with slaked lime (CaOH₂) to the same initial pH as the spruce stand humus. Each substrate was adjusted to water contents of 25%, 42.5% and 60% of WHC (referred to as ‘dry’, ‘moist’ and ‘wet’). In the second part of the experiment, spruce needle litter and birch leaf litter were separately added into the pine stand humus (‘moist’, unlimed) and compared with a control without litter. The microcosms were plastic jars with 75 g (d.m.) of humus, into which 4 specimens of D. octaedra and 70 specimens of C. sphagnetorum were added. D. octaedra showed the highest biomass and C. sphagnetorum the lowest biomass in the spruce stand humus with higher pH. Moisture did not affect earthworms, while C. sphagnetorum thrived best at the highest moisture. Addition of both kinds of litter increased the numbers and biomass of D. octaedra, while on C. sphagnetorum resource addition had little effect. The results help to explain the abundance of these two species in coniferous forests differing in soil acidity, moisture and fertility.     

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.     

Does moder development along a pure beech (Fagus sylvatica L.) chronosequence result from changes in litter production or in decomposition rates?

The development of temperate deciduous and conifers forests stands usually results in accumulation of forest floor organic matter and a shift from mull to moder humus forms. It has been suggested that an increase in nutrient uptake by trees during their rapid growth phase leads to topsoil acidification, decrease in earthworm density and thereby a decrease in litter turnover. The focus of this paper was to examine if the mull-moder shift with forest ageing results from higher leaf litter production and/or lower litter decay rates. The objectives of this research were to determine (1) changes in macro-morphological properties of humus forms, leaf litter production, litter decay rates, soil nutrients content and pH along a 130-year pure beech (Fagus sylvatica L.) chronosequence in Normandy (Northwest France), (2) if humus form varied from mull to moder with increasing stand age, and (3) if a shift from mull to moder resulted from increased litter production, decreased litter decay rates, or both. Annual litter production did not change significantly along the chronosequence (mean 2.41 t ha⁻¹). In contrast, litter decay rates decreased significantly during the rapid growth phase of trees. In consequence, the litter turnover time (1/k) was lower in the youngest stands (20 months) compared to the oldest ones (31 months). Even in the absence of a significant pattern of variation, litter production was positively correlated with the thickness of the OF (Oi) horizon. In contrast, litter decay was strongly negatively correlated with maximum thickness of the OH (Oa) horizon, suggesting that the appearance of the humification layer was mainly due to a decrease in litter decay rate. We did not find significant changes in the main properties of the organo-mineral horizon, suggesting that soil nutrient availability may not directly affect litter dynamics. We concluded that moder development along the chronosequence resulted in decreasing litter decay rates during the aggradation phase while litter production was stable. Further studies are required to identify the ecological factors responsible for moder development along forest ageing.     

Nitrification mineralisation and inorganic-N uptakein evergreen forests of the central Himalayas

Nitrogen mineralisation and available nitrogen (NO₃^– + NH₄⁺) in two evergreen forests species, viz. Quercus leucotrichophora and Pinus roxburghii, were examined. The plant available N ranged from 7.7–35.8 μg·g^–1·m^–1 with maximum values in March and minimum in November. The trend for N-mineralisation was opposite to that of the size of the available N-pool. N-Mineralisation rates ranged from 1.7–30.3 μg·g^–1·m^–1 within an annual cycle. Inorganic-N uptake was calculated for each incubated period, and for an entire year showed that in an oak forest site, nitrate-N was the dominant form of mineral nitrogen taken up by plants from soil. However, in a chir pine forest, nitrate-N and ammonium-N are equally taken up by plants from the soil. In both oak and pine forest sites, the nitrate-N uptake was maximum in the month of July and ranged between 2.4–11 μg·g^–1·m^–1 in the pine forest site and from 0–25 μg·g^–1·m^–1 in the oak forest site. In addition, ammonium-N varied from 0–12 μg·g^–1·m^–1 in the pine forest site and from 1–20 μg·g^–1·m^–1 in the oak forest site. N-Mineralisation was greater in N-rich forests and was moisture (soil) dependent and inversely related to bulk density.     

Enchytraeid and earthworm communities along a pollution gradient near Olkusz (southern Poland)

The effect of heavy metal pollution on Oligochaeta (Enchytraeidae and Lumbricidae) populations was studied along a pollution gradient in vicinity of Olkusz (southern Poland). The study sites, which differed in metal concentrations in the humus layer, were established in mixed-pine forests 3.5 km, 2.5 km, 3.9 km, 7.9 km and 31.9 km (reference site) from the source of pollution (zinc smelter). Enchytraeid and earthworm population density and species composition were determined from soil sampled four times from the study sites. Enchytraeidae populations consisted of nine genera and 18 species. The dominating enchytraeid species in all study sites was Cognettia sphagnetorum (approx. 90%), except for the most polluted site, where Enchytraeus, Fridericia and Henlea were the most common species diversity and heterogeneity were the highest in the most polluted site. The highest mean densities were found in the reference site (16,333 individuals m^?2) and lowest in the most polluted site (3932 individuals m^?2). Earthworm populations consisted of three epigeic species, and the most abundant one was Dendrobaena octaedra. Earthworms densities in all sites sampled were low. The concentrations of Zn, Pb and Cd in: humus layer, and in enchytraeids and earthworms, were the highest for the most polluted site and decreased with distance from pollution source. Density of Enchytraeidae and body loads of metals in Enchytraeidae and Lumbricidae can be employed for biomonitoring.     

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.     

The Enchytraeidae of spruce forest plots of different exposure and acid deposition in a German mountain range

Enchytraeidae were studied at spruce forest sites (Harz, Germany) differing in their exposure and soil acidity affected by acid deposition. Total density ranged between 38 000 and 59 000 ind. m^–2 and biomass between 0.5 and 1 g m^–2 d.m. (annual means). Of the seven species recorded, Cognettia sphagnetorum, Marionina clavata, and Achaeta camerani were dominant. The site affected most by acidification had the highest densities and lowest species number. Population dynamics and vertical distributions were affected by climate. Field and laboratory data provide evidence for sexual reproduction in C. sphagnetorum. Substrate preference experiments showed this species to prefer spruce litter from the O_L-Horizon to that from the O_H-Horizon, and spruce litter to beech litter.     

Lumbricus terrestris L. distribution within an experimental humus mosaic in a mountain spruce forest

 An experiment was designed at a mountain site to study the distribution of adult Lumbricus terrestris in relation to a small-scale mosaic of humus forms representative of different stages of a spruce forest ecosystem. Good agreement was found between distribution in the mosaic and that in the field. ANOVA tests demonstrated the strong influence of humus form on earthworm abundance when comparing a vermimull (high earthworm burrowing activity) taken from a spruce regeneration site (61.8 individuals m^–2) with a leptomoder (no earthworm burrowing activity) taken from a 60-year-old spruce stand (6.2 individuals m^–2). Other humus forms were intermediate (mean density 34.6 individuals m^–2). The same pattern was found with individual biomass, but with lower significance. Main differences observed in the experimental design were attributed to the immediate carrying density of the humus forms. A distinction was made between humus profiles built up with or without spruce cover. In the latter case (regeneration site and bilberry heath), the immediate carrying capacity indicated by the experimental approach overestimated the field density by a factor of 4. Under spruce this overestimate was even higher (approximately 10 times too high in an adult spruce stand (160 years old) and 30 times too high under moss cover). The increase in density due to experimental conditions was not determined for leptomoder humus accumulated under the actively growing spruce stand (60 years old) since the earthworm density was near zero in both cases. Relationships between humus form and earthworm populations are discussed. Received: 9 June 1997     

Restoration of shrub communities elevates organic carbon in arid soils of northwestern China

Artificial restoration by shrub plantation in semi-arid sandy land can increase carbon sequestration. However, little information is available on the carbon flux input to soil resulted from fine roots turnover and leaf fallen during restoration. The present study relying on the ingrowth core and sequential core methods investigated the fine-root dynamics and fine-root production of three shrub stands (dominated by Artemisia halodendron, Caragana microphylla and Salix gordejevii respectively) which have different life-forms and root architectures. The soil carbon and nitrogen stock was also estimated in the restoration, and the relative contribution of carbon input related to fine root mortality and leaf fallen was assessed. The mean standing live and dead fine-root biomass in A. halodendron stand at the primary restoration were significantly less than in C. microphylla stand at moderate restoration and S. gordejevii stand in lowland. Consistent with leaf production, fine root production showed a positive correlation with soil water content and followed the order of A. halodendron < C. microphylla < S. gordejevii. In contrast, the fine-root turnover rate was quicker in primary restoration phase (2.12 year⁻¹) than in moderate restoration phase (1.55 year⁻¹) and lowland (1.28 year⁻¹). The annual carbon and nitrogen inputs via fine root mortality and leaf fallen increased from 74.78 g C m⁻² year⁻¹ and 1.25 g N m⁻² year⁻¹ in A. halodendron stand to 189.66 g C m⁻² year⁻¹ and 1.67 g N m⁻² year⁻¹ in S. gordejevii stand. Although the share of the fine roots of A. halodendron seized a relatively smaller proportion in the net primary production compared with those in C. microphylla and S. gordejevii, the relative contribution of carbon input related to fine roots mortality in primary restoration phase was higher than in the other two shrub stands. The present study proved that the carbon input to soil by fine-root mortality considerably contributed to the restoration of soil carbon and nitrogen stock in semi-arid degraded lands.     

Spatial variability of O layer thickness and humus forms under different pine beech–forest transformation stages in NE Germany

Spatial variability of humus layer (O layer) thicknesses can have important impacts upon soil water dynamics, nutrient storage and availability, as well as plant growth. The purpose of the present study was to elucidate the impact of forest‐transformation practices on the spatial variability of O layer thicknesses. The study focused on the Kahlenberg forest area (NE Germany) with stands of Scots pine (Pinus sylvestris) and European beech (Fagus sylvatica) of different age structures that form a transformation chronosequence from pure Scots pine stands towards pure European beech stands. Topsoil profiles including both, the O layer and the uppermost humic mineral soil horizon were excavated at intervals of 0.4 m along 15–20 m long transects, and spatial variability of O layer thicknesses was quantified by variogram analysis. The correlation lengths of total O layer thickness increased in the sequence consisting of pure pine stand (3.1 m) → older mixed stand (3.7 m) → pure beech stand (4.5 m), with the exception of the younger mixed stand, for which no correlation lengths of total O layer thickness could be determined. The degree of spatial correlation, i.e., the percentage of the total variance which can be described by variograms, was highest for the two monospecies stands, whereas this percentage was distinctly lower for the two mixed stands. A similar minimum for the two mixed stands was observed for the correlation lengths of the Oh horizon. These results suggest that the spatial structures of forest‐transformation stands may be interpreted in terms of a disturbance (in the form of the underplanting of beech trees). After this disturbance, the forest ecosystem requires at least 100 y to again reach relative equilibrium. These findings are in line with the results of other soil‐related investigations at these sites.     

Is the soil microbial community related to the basal area of trees in a Scots pine stand?

The main energy sources of soil microorganisms are litter fall, root litter and exudation. The amount on these carbon inputs vary according to basal area of the forest stand. We hypothesized that soil microbes utilizing these soil carbon sources relate to the basal area of trees. We measured the amount of soil microbial biomass, soil respiration and microbial community structure as determined by phospholipid fatty acid (PLFA) profiles in the humus layer (FH) of an even-aged stand of Scots pine (Pinus sylvestris L.) with four different basal area levels ranging from 19.9 m² ha⁻¹ in the study plot Kasper 1 to 35.7 m² ha⁻¹ in Kasper 4. Increasing trend in basal respiration, total PLFAs and fungal-to-bacterial ratio was observed from Kasper 1 to Kasper 3 (basal area 29.2 m² ha⁻¹). The soil microbial community structure in Kasper 3 differed from that of the other study plots.     

Evapotranspiration and water use efficiency in different-aged Pacific Northwest Douglas-fir stands

We used the eddy-covariance technique to measure evapotranspiration (E) and gross primary production (GPP) in a chronosequence of three coastal Douglas-fir (Pseudotsuga menziesii) stands (7, 19 and 58 years old in 2007, hereafter referred to as HDF00, HDF88 and DF49, respectively) since 1998. Here, we focus on the controls on canopy conductance (g_c), E, GPP and water use efficiency (WUE) and the effect of interannual climate variability at the intermediate-aged stand (DF49) and then analyze the effects of stand age following clearcut harvesting on these characteristics. Daytime dry-foliage Priestley–Taylor α and g_c at DF49 were 0.4–0.8 and 2–6 mm s^?1, respectively, and were linearly correlated (R² = 0.65). Low values of α and g_c at DF49 as well at the other two stands suggested stomatal limitation to transpiration. Monthly E, however, showed strong positive linear correlations to monthly net radiation (R² = 0.94), air temperature (R² = 0.77), and daytime vapour pressure deficit (R² = 0.76). During July–September, monthly E (mm) was linearly correlated to monthly mean soil water content (θ, m³ m^?3) in the 0–60 cm layer (E = 453θ ? 21, R² = 0.69), and GPP was similarly affected. Annual E and GPP of DF49 for the period 1998–2007 varied from 370 to 430 mm and from 1950 to 2390 g C m^?2, respectively. After clearcut harvesting, E dropped to about 70% of that for DF49 while ecosystem evapotranspiration was fully recovered when stand age was ～12 years. This contrasted to GPP, which varied hyperbolically with stand age. Monthly GPP showed a strong positive linear relationship with E irrespective of the stand age. While annual WUE of HDF00 and HDF88 varied with age from 0.5 to 4.1 g C m^?2 kg^?1 and from 2.8 to 4.4 g C m^?2 kg^?1, respectively, it was quite conservative at ～5.3 g C m^?2 kg^?1 for DF49. N-fertilization had little first-year response on E and WUE. This study not only provides important results for a more detailed validation of process-based models but also helps in predicting the influences of climate change and forest management on water vapour and CO₂ fluxes in Douglas-fir forests.     

Controls of temporal and spatial variability of methane uptake in soils of a temperate deciduous forest with different abundance of European beech (Fagus sylvatica L.)

Aerated forest soils are a significant sink for atmospheric methane (CH₄). Soil properties, local climate and tree species can affect the soil CH₄ sink. A two-year field study was conducted in a deciduous mixed forest in the Hainich National Park in Germany to quantify the sink strength of this forest for atmospheric CH₄ and to determine the key factors that control the seasonal, annual and spatial variability of CH₄ uptake by soils in this forest. Net exchange of CH₄ was measured using closed chambers on 18 plots in three stands exhibiting different beech (Fagus sylvatica L.) abundance and which differed in soil acidity, soil texture, and organic layer thickness. The annual CH₄ uptake ranged from 2.0 to 3.4 kg CH₄-C ha⁻¹. The variation of CH₄ uptake over time could be explained to a large extent (R² = 0.71, P < 0.001) by changes in soil moisture in the upper 5 cm of the mineral soil. Differences of the annual CH₄ uptake between sites were primarily caused by the spatial variability of the soil clay content at a depth of 0-5 cm (R² = 0.5, P < 0.01). The CH₄ uptake during the main growing period (May-September) increased considerably with decreasing precipitation rate. Low CH₄ uptake activity during winter was further reduced by periods with soil frost and snow cover. There was no evidence of a significant effect of soil acidity, soil nutrient availability, thickness of the humus layer or abundance of beech on net-CH₄ uptake in soils in this deciduous forest. The results show that detailed information on the spatial distribution of the clay content in the upper mineral soil is necessary for a reliable larger scale estimate of the CH₄ sink strength in this mixed deciduous forest. The results suggest that climate change will result in increasing CH₄ uptake rates in this region because of the trend to drier summers and warmer winters.     

Succession of soil nematodes in pine forests on coal-mining sands near Cottbus,Germany

The succession of soil nematodes from initial planting with Pinus sylvestris seedling to about 30-year-old pine plantations on coal mining sands in the Lusatian lignite-mining district near Cottbus (Germany) was studied and compared with the nematode fauna of a 40-year-old semi-natural pine forest on naturally formed sandy soil. The initial stage was primarily characterised by a very low abundance (20×10³ individuals/m²), which increased over a period of two years to values common in older pine plantations (500–600×10³ individuals/m²). In the semi-natural forest the mean abundance of nematodes was about 1300×10³ individuals/m². Populations of Tardigrada, Rotifera and Enchytraeidae also increased with stand age. Nematode biomass increased from 49 to 543 mg m⁻² in pine plantations and slightly decreased in the semi-natural forest to 301 mg m⁻² over the period of investigation. The early colonisation of the initial stage was by bacterivorous (Acrobeloides) and fungal feeding (Aphelenchoides) nematodes, but the communities diversified as succession progressed with bacterivorous nematodes of the genera Plectus, Wilsonema and Metateratocephalus, root-fungal feeding Filenchus, omnivorous Aporcelaimellus and Eudorylaimus, and predacious Prionchulus becoming abundant. The abundance of plant-parasitic nematodes was very low. The greatest number of nematode genera was found in the semi-natural forest.     

The occurrence of terrestrial algae on two beech sites on a Cambisol

The occurrence of terrestrial algae on two beech sites was determined qualitatively and quantitatively in the litter, organic and mineral layer. Both sites are beech stands of different age and the soil type is a Cambisol. On the site with young beech the maximal value determined was 1.0 · 10⁸ algae g^?1 dw in the litter layer. With increasing soil depth the number of algae decreased on both sites, and at the young beech stand site no algae were found in the mineral soil. Chlorophyceae were the dominant algae group and at the young beech stand Bacillariophyceae were present.     

Response of soil respiration to precipitation during the dry season in two typical forest stands in the forest-grassland transition zone of the Loess Plateau

Forest ecosystems on the Loess Plateau are receiving increasing attention for their special importance in carbon fixation and conservation of soil and water in the region. Soil respiration was investigated in two typical forest stands of the forest-grassland transition zone in the region, an exotic black locust (Robinia pseudoacacia) plantation and an indigenous oak (Quercus liaotungensis) forest, in response to rain events (27.7 mm in May 2009 and 19 mm in May 2010) during the early summer dry season. In both ecosystems, precipitation significantly increased soil moisture, decreased soil temperature, and accelerated soil respiration. The peak values of soil respiration were 4.8 and 4.4 μmol CO₂ m⁻² s⁻¹ in the oak plot and the black locust plot, respectively. In the dry period after rainfall, the soil moisture and respiration rate gradually decreased and the soil temperature increased. Soil respiration rate in black locust stand was consistently less than that in oak stand, being consistent with the differences in C, N contents and fine root mass on the forest floor and in soil between the two stands. However, root respiration (R_r) per unit fine root mass and microbial respiration (R_m) per unit the amount of soil organic matter were higher in black locust stand than in oak stand. Respiration by root rhizosphere in black locust stand was the dominant component resulting in total respiration changes, whereas respiration by roots and soil microbes contributed equally in oak stand. Soil respiration in the black locust plantation showed higher sensitivity to precipitation than that in the oak forest.     

云南省森林土壤腐殖质组分特征及影响因素

云南省森林生态系统在全球碳循环及平衡中具有不可替代的作用,但其森林土壤腐殖质组分特征及其影响因素尚不十分清楚。基于云南省不同林区采集的88个表层土样,通过描述性统计和回归分析量化了海拔、土壤类型、坡向和坡度、年均温和年降水量对土壤腐殖质组分分布影响的相对重要性,探讨云南省森林土壤腐殖质组分分布特征。结果表明:云南省森林土壤表层有机碳含量为8.40～199.73 g·kg~(–1),平均含量为51.37 g·kg~(–1),土壤可提取腐殖质碳含量为2.54～84.02 g·kg~(–1),平均含量为24.52 g·kg~(–1);胡富比均值小于1,土壤腐殖质聚合度较低;土壤腐殖质组分分布特征总体表现为滇西北、滇东北部较高,滇中、滇南部较低;土壤类型、海拔、年均温是影响云南省森林土壤腐殖质组分含量的主导因子,各因素的贡献程度总体呈现为土壤类型最高,其次是年均温、海拔,这说明土壤类型对森林表层土壤腐殖质的积累起重要作用。     

Endemic Collembola, privileged bioindicators of forest management

Our study compared the soil collembolan community at three semi-natural sites (a beech forest, a beech–fir forest and a fir stand) and three managed sites (Norway spruce, beech–fir and fir). Collembola were extracted from a total of 60 samples with a Berlese–Tullgren funnel, counted and identified to species level. A total of 7187 specimens, representing 51 species and 37 genera, were collected. There were significant differences between managed and natural forests (t-test, P=0.000). The communities and their population densities were significantly lower in the managed site: 51 species with 708,498 ind m⁻² in the semi-natural forests to 36 species and 306,042 ind m⁻² in the managed stands. The endemic component suffered a particularly severe decrease in species richness and abundance (57% and 71% lower in the managed forests, respectively). These species with narrow distribution and small local populations are doubly vulnerable to alterations of environmental conditions. They are very sensitive to loss of their natural habitat owing to human intervention and thus represent useful indicators of tolerance to environmental stress. We highlight the need to take endemic species into consideration in studies on the conservation of biodiversity because they are most at risk of extinction. Semi-natural forests are refuges for endemic species and should be protected.     

Does forest type and vegetation patchiness influence horizontal distribution of soil Collembola in two neighbouring forest sites?

The influence of forest type and heterogeneity of understory vegetation on the horizontal distribution of soil living Collembola was studied in two neighbouring mountain forest sites—a 180-year old beech forest and a 70-year old natural spruce forest. Four homogenous patches with different understory vegetation were chosen within each forest site and sampled 12 times between 1997 and 1998. A total of 56 collembolan species were identified, 51 in the beech forest and 48 in the spruce site. Twenty-three species were rare—they were recorded with low constancy and density. Although both forest sites differed in soil type, humus form and soil chemical parameters, the species composition of their collembolan communities was quite similar (77% shared species). Nevertheless, soil collembolan communities of both forest sites were clearly delimited on both qualitative (presence–absence) and quantitative (in density of individual species) levels as well as in terms of total collembolan density. Mean collembolan density reached 26 650–44 030 ind/m² in the beech patches compared to 44 470–68 050 ind/m² found in the spruce patches. Considerably higher densities of several species in one forest site may indicate more suitable habitat. In spite of similar species composition and minor differences in qualitative parameters among different vegetation patches within one forest site, there was clear variation in density of individual species, particularly between patches with and without herb vegetation. This could reflect different microclimatic conditions, additional litter supply from herbs or indirect interactions of Collembola with their roots.