Soil microbial biomass and activity: the effect of site characteristics in humid temperate forest ecosystems

Microbial biomass, respiratory activity, and in‐situ substrate decomposition were studied in soils from humid temperate forest ecosystems in SW Germany. The sites cover a wide range of abiotic soil and climatic properties. Microbial biomass and respiration were related to both soil dry mass in individual horizons and to the soil volume in the top 25 cm. Soil microbial properties covered the following ranges: soil microbial biomass: 20 µg C g^–1–8.3 mg C g^–1 and 14–249 g C m^–2, respectively; microbial C–to–total organic C ratio: 0.1%–3.6%; soil respiration: 109–963 mg CO₂‐C m^–2 h^–1; metabolic quotient (qCO₂): 1.4–14.7 mg C (g C_mic)^–1 h^–1; daily in‐situ substrate decomposition rate: 0.17%–2.3%. The main abiotic properties affecting concentrations of microbial biomass differed between forest‐floor/organic horizons and mineral horizons. Whereas microbial biomass decreased with increasing soil moisture and altitude in the forest‐floor/organic horizons, it increased with increasing N_tot content and pH value in the mineral horizons. Quantities of microbial biomass in forest soils appear to be mainly controlled by the quality of the soil organic matter (SOM), i.e., by its C : N ratio, the quantity of N_tot, the soil pH, and also showed an optimum relationship with increasing soil moisture conditions. The ratio of C_mic to C_org was a good indicator of SOM quality. The quality of the SOM (C : N ratio) and soil pH appear to be crucial for the incorporation of C into microbial tissue. The data and functional relations between microbial and abiotic variables from this study provide the basis for a valuation scheme for the function of soils to serve as a habitat for microorganisms.     

Adsorption complex,pH relationships in some acid mediterranean forest soil profiles

Acid soils in some mediterranean forests were investigated for the composition of the adsorption complex and the gradients in soil pH. The effective CEC (235–838 mmol_c kg^?1) and base saturation (93–98 %) are highest in ectorganic horizons. In the mineral horizons the effective CEC (23–52 mmol_c kg^?1) and base saturation (11–40 %) are much lower. The exchange complex of mineral horizons consists for 90 (AEh) to 40 percent (Bw2) of organic matter. The effective CEC of the mineral clay fraction is low (60 mmol_c kg^?1 clay). The clear trends in soil pH within the ectorganic layer of deciduous and sclerophyllous oak forests are attributed to vertical spatial separation of nitrogen mineralization (ammonification and strongly impeded nitrification) and nutrient uptake by roots (mainly NH₄). This leads to a high effective CEC in the fermentation layer and acidification of the uppermost part of the mineral soil. In contrast to the situation in temperate forests this process is impeded in mediterranean coniferous forests, where litter decomposition is extremely slow and both proton production and consumption take place in the organic rich mineral horizon.     

Pattern of microbial indicators in forest soils along an European transect

Microbial biomass C and activity were determined in six forest soils along a gradient in physical and chemical climate in Europe. Both parameters were measured microcalorimetrically. The upper 22 cm of the soils were sampled in undisturbed columns (24 cm deep). Measurements were made in homogenized samples of the different surface organic horizons (Ol, Of, Oh) and the mineral horizons (Ah, Aeh, Bv) down to 22 cm.On a mass basis values for both the biomass and the activity showed an exponential decrease with depth in all soils. Expressed on a volume basis these relationships varied with soil pH. in the strongly acidified soils most of the microbial biomass and activity was located in the forest floor. In less acidified soils both parameters were highest in the mineral soil.Further relationships between biomass and activity and between soil chemical properties showed significant positive correlations with exchangeable Ca²⁺, Mg²⁺, Ca/Al and negative correlations with Al³⁺. There were no significant correlations with exchangeable cations in less acidified soils. It was calculated that the microbial biomass is more affected by soil chemistry than activity. The caloric quotient (qW) is a good parameter for determining the ecophysiological state of microorganisms in acidified soils.     

Changes of lignin phenols and neutral sugars in different soil types of a high-elevation forest ecosystem 25 years after forest dieback

Long-term effects of forest disturbance 25 yr ago on lignin and non-cellulosic polysaccharide pools in an unmanaged high-elevation Norway spruce (Picea abies L. [Karst.]) forest were investigated by comparing three dieback sites with three adjacent control sites with non-infested spruce on identical soils. Samples were taken from the forest floor and the mineral soil; one Ah horizon sample per site was physically fractionated into density and particle size fractions. Additionally, changes in the above- and belowground input of lignin and non-cellulosic polysaccharides after forest dieback were quantified. Lignin and its degree of structural alteration in plant and soil samples were assessed by CuO oxidation and subsequent analysis of the lignin phenols. Non-cellulosic polysaccharides were determined after hydrolysis with trifluoroacetic acid (TFA), derivatisation of their neutral sugar monomers by reduction to alditols, and subsequent acetylation. The total plant-derived input of lignin and non-cellulosic polysaccharides to the soil was similar for the dieback and the control sites. The chemical composition of the input has changed considerably after forest dieback, as shown by significantly higher syringyl/vanillyl (S/V) ratios and significantly lower (galactose+mannose)/(arabinose+xylose) (GM/AX) ratios. This indicates a changed plant input and a higher contribution of microbial sugars. Contents of lignin phenols in the forest floor and coarse particle size fractions of the A horizons were significantly smaller at the dieback sites (p<0.01). Moreover, larger acid-to-aldehyde ratios of vanillyl units (Ac/Al)_v indicated an increased degree of lignin phenol alteration. Also contents of neutral sugars were significantly (p<0.01) smaller in the forest floor, but not in the A horizons of the dieback sites. The GM/AX mass ratios as well as the (rhamnose+fucose)/(arabinose+xylose) (RF/AX) ratios in the forest floor and coarse particle size fractions of the mineral topsoil were significantly (p<0.01) larger after forest dieback, indicating a larger relative contribution of microbial sugars. In general, the lignin phenol and neutral sugar pools of all three soil types exhibited similar response patterns to the changed site conditions. Our results demonstrate that the lignin and neutral sugar pools of humic topsoil horizons are highly sensitive to forest disturbances. However, the two compounds show different patterns in the mineral soil, with the major neutral sugar pool being stabilized against changes whereas the lignin phenol pool decreases significantly.     

Substantial net N mineralization during the dormant season in temperate forest soils

In temperate forest soils, N net mineralization has been extensively investigated during the growing season, whereas N cycling during winter was barely addressed. Here, we quantified net ammonification and nitrification during the dormant season by in situ and laboratory incubations in soils of a temperate European beech and a Norway spruce forest. Further, we compared temperature dependency of N net mineralization in in situ field incubations with those from laboratory incubations at controlled temperatures. From November to April, in situ N net mineralization of the organic and upper mineral horizons amounted to 10.9 kg N (ha · 6 months)^–1 in the spruce soil and to 44.3 kg N (ha · 6 months)^–1 in the beech soil, representing 65% (beech) and 26% (spruce) of the annual above ground litterfall. N net mineralization was largest in the Oi/Oe horizon and lowest in the A and EA horizons. Net nitrification in the beech soil [1.5 kg N (ha · 6 months)^–1] was less than in the spruce soil [5.9 kg N (ha · 6 months)^–1]. In the range of soil temperatures observed in the field (0–8°C), the temperature dependency of N net mineralization was generally high for both soils and more pronounced in the laboratory incubations than in the in situ incubations. We suggest that homogenization of laboratory samples increased substrate availability and, thus, enhanced the temperature response of N net mineralization. In temperate forest soils, N net mineralization during the dormant season contributes substantially to the annual N cycling, especially in deciduous sites with large amounts of litterfall immediately before the dormant season. High Q₁₀ values of N net mineralization at low temperatures suggest a huge effect of future increasing winter temperature on the N cycle in temperate forests.     

Microbial responses of forest soil to moderate anthropogenic air pollution

There is a need to introduce soil microbiological methods into long term ecological monitoring programs. For this purpose we studied the impact of moderate anthropogenic air pollution in polluted and less polluted area districts, forest site types Calluna (CT), Vaccinium (VT) and Myrtillus (MT) and the amount of organic matter, measured as carbon content on the soil respiration activity and the ATP content. The main sources of local air pollutants (SO₂ and NO_x) in the polluted area district were from the capital' region and an oil refinery. Humus (F/H-layer) and the underlying 0 to 5 cm mineral soil samples were collected from 193 study plots located in the 5300 km² study area. We found that the soil respiration rate in humus layer samples was lower in the polluted area district compared to the less polluted one (16.0 and 19.5 μL CO₂ h^?1g^?1 dw, respectively), but the difference occurred only in the dry, coarse-textured CT forest site type. The mineral soil respiration rate and the mineral soil and humus layer ATP content were not affected, by the air pollution. Most of the variations of the biological variables were explained primarily by the soil carbon content, secondly by the forest site type and thirdly by the area division.     

Significance of DOM in the translocation of cations and acidity in acid forest soils

We estimated the contribution of dissolved organic matter (DOM) to cation leaching and the translocation of acidity in three acid forest soils. The analysis was based on monitored (2 years) concentrations of dissolved organic carbon (DOC) in the field, measured total acidities of DOM, and measured as well as predicted weighted mean dissociation constants of the organic acids. Although the forest floor solutions were strongly acidic (pH 3.47–4.10), a considerable proportion of the organic acids was dissociated and organic anions represented 22–40% of the total anions in the mineral soil input. The flux of DOM-associated exchangeable protons from the forest floor to the mineral soil ranged from 0.35 (Wülfersreuth) to 3.72 (Hohe Matzen) kmol ha^?1 yr^?1. In the subsoil, this organic acidity may be neutralized by microbial decomposition of the organic acids, but a part of the hydrogen ions may dissociate and contribute to acidification of the soil solution and to weathering processes. Due to the pronounced retention of DOM in the mineral subsoil horizons, the contribution of DOM to the output of cations and acidity from the soil is much lower than in the surface horizons but still significant.?     

Dynamics of mineral components in the forest floor of an acidic beech (Fagus sylvatica L.) forest

Seasonal changes of the mineral components Na, K, Mg, Ca, Mn, Fe, Al, Si and ash were investigated in the L1 horizon of an acidic beech (Fagus sylvatica L.) forest using litterbags (1 mm and 45 μm mesh-size) buried for up to 467 days in the forest floor. The element dynamics in this surface horizon were compared with the concentration and the total amount stored in a complete sequence of horizons (L1, L2, F1, F2 and H) taken from a moder profile in the Solling area. In the 1 mm litterbags with free access of the mesofauna, the concentrations of all cations were increased in comparison to the 45 μm treatment. This increase was highly significant, especially with regard to Fe and Al. The concentrations of these two cations were closely related to Si during the decomposition of fresh leaf litter in the L1 horizon. Si is the dominant element of ash in the litterbags and down the profile. The total amounts stored in the forest floor revealed that the Fe and Al input considerably exceeded the input by litter fall, and dry and wet deposition due to incorporation of mineral soil material. The input of soil material was also indicated by a decrease in the molar Si/Al ratio from 17 to 6 and in the relation of nutrient cations to ash from 30% to 2.5%.     

Changes in forest floor and mineral soil carbon and nitrogen stocks in a boreal forest after clear‐cutting and mechanical site preparation

Significant amounts of organic carbon (C) and nitrogen (N) are accumulated in soil in boreal forests. However, increased concern has been shown regarding the negative impacts of forestry operations on both the C sequestration and N stocks in soil. Changes in the C and N stocks in woody debris, forest floor and mineral soil (0–20 cm) were studied in Eastern Finland for 10 years after stem‐only clear‐cutting followed by soil harrowing. Samples were taken from the uncut forest and from the different microsites formed by the harrowing (ridges, furrows and undisturbed areas). Carbon and N from logging residues were not incorporated into the forest floor or mineral soil stocks to any great extent. After 5 years the C stock above the mineral soil was smaller (< 20%) in the treated area than in the uncut forest and after 10 years it was < 50% smaller. The corresponding N stock was marginally larger (< 5%) after 5 years, but smaller (< 20%) after 10 years. In the mineral soil there were no changes; only the furrows lost C and N when compared with the other microsites, but not when compared with the forest. Harrowing increased the spatial variation in the forest floor C and N stocks. The comparison of the N losses from the soil and logging residues and woody debris with the leaching losses, the amounts utilized by the regenerating vegetation or estimated to be immobilized by the stumps at the same site indicated that N which remained after the clear‐cutting was retained at the site. For a full understanding of the impact of such a disturbance on stocks at a site all significant fluxes and stocks would need to be monitored.     

Assessment of mineral nutrition of cork oak through foliar analysis

Abstract

The changes in the mineral nutrient content of the leaves of an evergreen species, the cork oak (Quercus suber L.), were investigated to assess the possibilities of a diagnosis of the mineral nutrition of this forest species. A comprehensive pattern of change in the leaf contents of N, P, and Ca was then put forward from the data obtained. Among the time intervals that are most favorable to analyses, the end of the vegetative rest period, in January, was investigated more precisely. The variation coefficients of the leaf contents measured tree by tree were determined for a number of nutrients (N, P, K, Ca, Mg, Fe, Cu, Zn, Mn, B, Al, and Cl). The foliar analyses carried out on 7‐ to 10‐month old leaves in stands submitted to various forest management practices led to the characterization of significant differences in P, Ca and Mn leaf contents in relation to the treatments applied.     

Spatial variability of enzyme activities and microbial biomass in the upper layers of Quercus petraea forest soil

Extracellular lignocellulose-degrading enzymes are responsible for the transformation of organic matter in hardwood forest soils. The spatial variability on a 12 × 12 m plot and vertical distribution (0–8 cm) of the ligninolytic enzymes laccase and Mn-peroxidase, the polysaccharide-specific hydrolytic enzymes endoglucanase, endoxylanase, cellobiohydrolase, 1,4-β-glucosidase, 1,4-β-xylosidase and 1,4-β-N-acetylglucosaminidase and the phosphorus-mineralizing acid phosphatase were studied in a Quercus petraea forest soil profile. Activities of all tested enzymes exhibited high spatial variability in the L and H horizons. Acid phosphatase and 1,4-β-N-acetylglucosaminidase exhibited low variability in both horizons, while the variability of Mn-peroxidase activity in the L horizon, and endoxylanase and cellobiohydrolase activities in the H horizon were very high. The L horizon contained 4× more microbial biomass (based on PLFA) and 7× fungal biomass (based on ergosterol content) than the H horizon. The L horizon also contained relatively more fungi-specific and less actinomycete-specific PLFA. There were no significant correlations between enzyme activities and total microbial biomass. In the L horizon cellulose and hemicellulose-degrading enzymes correlated with each other and also with 1,4-β-N-acetylglucosaminidase and acid phosphatase activities. Laccase, Mn-peroxidase and acid phosphatase activities correlated in the H horizon. The soil profile showed a gradient of pH, organic carbon and humic compound content, microbial biomass and enzyme activities, all decreasing with soil depth. Ligninolytic enzymes showed preferential localization in the upper part of the H horizon. Differences in enzyme activities were accompanied by differences in the microbial community composition where the relative amount of fungal biomass decreased and actinomycete biomass increased with soil depth. The results also showed that the vertical gradients occur at a small scale: the upper and lower parts of the H horizon only 1 cm apart were significantly different with respect to seven out of nine activities, microbial biomass content and community composition.     

The heterogeneity of humus profiles and earthworm communities in a virgin beech forest

Thirty sites, encompassing a range of soil and vegetation conditions in the biological reserve of La Tillaie (Fontainebleau Forest, France) were investigated in April 1992. Beech (Fagus sylvatica L.) was the dominant tree species, with several developmental phases forming the forest patchwork. Sessile oak [Quercus petraea (Mattus.) Liebl.] was present but only as old relictual individuals. Gaps in the canopy cover were abundant, mostly caused by wind storms 2 years previously. The next most recent storm was 25 years before, resulting in distinct patches of full-grown trees. Humus profiles were classified and compared with the distribution of earthworm communities, canopy cover, and soil types. Geomorphology was responsible for the main part of the observed variation. Absence of lime in the substrate and direct contact with a sandstone stratum near the ground surface was associated with the absence of earthworms and the appearance of an OH horizon (moder humus). Elsewhere, earthworms were present and humus profiles did not display any OH horizon (mull or mull-like moder humus), but species composition was variable and strongly influenced by the thickness of the superficial sand deposit overlying limestone. On a thick (1 m or more) sandy substrate earthworm communities were dominated by epigeic species together with the anecic Lumbricus terrestris L. The species richness was higher on a shallower sandy substrate (50 cm) where lime was more accessible to tree roots and burrowing animals. The influence of the forest cycle of beech was visible in the latter case (covering most of the area), with an increase in the thickness of the OL and OF horizons and a decrease in endogeic earthworm populations during the phase of intense growth of beech. This fall in burrowing activity was apparent in gaps created by wind storms and fungal diseases within mature stands as early as 2 years after the fall of the trees.     

Repeated freeze–thaw events affect leaching losses of nitrogen and dissolved organic matter in a forest soil

Freezing and thawing may substantially influence the rates of C and N cycling in soils, and soil frost was proposed to induce NO losses with seepage from forest ecosystems. Here, we test the hypothesis that freezing and thawing triggers N and dissolved organic matter (DOM) release from a forest soil after thawing and that low freezing temperatures enhance the effect. Undisturbed soil columns were taken from a soil at a Norway spruce site either comprising only O horizons or O horizons + mineral soil horizons. The columns were subjected to three cycles of freezing and thawing at temperatures of –3°C, –8°C, and –13°C. The control columns were kept at constant +5°C. Following the frost events, the columns were irrigated for 20 d at a rate of 4 mm d^–1. Percolates were analyzed for total N, mineral N, and dissolved organic carbon (DOC). The total amount of mineral N extracted from the O horizons in the control amounted to 8.6 g N m^–2 during the experimental period of 170 d. Frost reduced the amount of mineral N leached from the soil columns with –8°C and –13°C being most effective. In these treatments, only 3.1 and 4.0 g N m^–2 were extracted from the O horizons. Net nitrification was more negatively affected than net ammonification. Severe soil frost increased the release of DOC from the O horizons, but the effect was only observed in the first freeze–thaw cycle. We found no evidence for lysis of microorganisms after soil frost. Our experiment did not confirm the hypothesis that soil frost increases N mineralization after thawing. The total amount of additionally released DOC was rather low in relation to the expected annual fluxes.     

Soil organic matter transformation in Argentinian Hapludolls

Distribution and transformation of SOM in an Argentinian Hapludoll under arable land use and afforested with Pinus radiata was investigated by a combined approach using particle-size fractionation, wet-chemical analysis and ¹³C NMR spectroscopy. The soils showed thick mollic A horizons and had high organic carbon (OC) contents even in the subsoil, clay-sized separates having the highest OC concentrations. Under pine, a thick forest floor was built up. CuO oxidation data indicated low transformation of lignin in the forest floor, but advanced oxidative decomposition in the mineral soil horizon. In contrast, non-cellulosic carbohydrates, appeared to be stabilized in the mineral soil horizon against mineralization. Humic acids extracted from the mineral soil horizons showed an extremely high aromaticity. We assume that this was due to the production of pyrogenic aromatic moieties (black carbon) as a result of frequent fires in this ecosystem. No clear profile differentiation with respect to SOM quality was obtained. Composition of SOM in the mineral soil appeared not yet influenced from land use.     

Humusveränderungen nach Einbringung von Buche und Eiche in Kiefernreinbestände

Humus changes after introduction of beech and oak into Scots‐pine monocultures Medium‐ and long‐term (16 to 83 years) effects of an introduction of broadleaf‐tree species (Common beech [Fagus sylvatica] and European‐Sessile Oak [Quercus robur/petraea]) into mature Scots‐pine (Pinus sylvestris) stands on humus type and chemical properties of the Oh layer (pH value, base saturation, C : N ratio) were studied on 16 sites in Bavaria/Germany. The sites investigated covered a large range with respect to elevation, climate, parent material, and soil type. At most sites, the introduction of beech resulted in a significant change of the soil humus type from biologically inactive humus types to more active ones. The strongest changes occurred on the poorest sites, where forest floors under pure pine were particularly biologically inactive. In most cases, the changes in humus type were accompanied by significant increases in the pH value and the base saturation and significant decreases in the C : N ratio of the Oh layer. However, the latter effect was not noticed at most sites with initial C : N ratios higher than 30. In contrast to beech, the introduction of oak did not result in a systematic change of the humus type, the pH value, or the base saturation of the Oh layer. In spite of the considerable change of humus type under beech to biologically more active types, the introduction of broadleaf trees did not result in a systematic change of the thickness or the mass of the forest floor. A decrease in the mass of the Of layer was compensated by an increase of the Oh‐layer mass. All studied sites considered, the introduction of broadleaf trees into Scots‐pine monocultures resulted on average in an 8% decrease of the total amount of organic carbon (C_org) in the forest floor; the C_org amount in the uppermost 10 cm mineral soil increased by 9%. At 35% of all investigated sites, broadleaf tree introduction resulted in increased (+5% to +18%) topsoil (forest floor and uppermost 10 cm mineral soil) C_org stocks. At 30% of the sites, the stock changes were less than ±5%, and on 35% of all sites, soil C_org stocks decreased by –5% to –36%. The average change in the topsoil C_org stock for all studied sites was –5%. The introduction of beech into Scots‐pine monocultures resulted in an ecologically desired translocation of soil organic matter from the forest floor into the mineral topsoil. It is an effective and sustainable silvicultural measure to restore and revitalize acidified, nutrient‐depleted topsoils with biologically inactive humus types.     

Buried organic horizons represent amino acid reservoirs in boreal forest soils

We examined the composition and concentration of amino acids by soil horizon and depth on the Tanana River floodplain in interior Alaska. Soils from mid-successional stages of balsam poplar and white spruce were separated into successive forest floor (Oe/Oa), buried organic horizons (BOHs), and mineral horizons; and water-extractable amino acid composition and concentration were determined by HPLC. The number, depth, and thickness of BOHs were highly variable across the landscape and among replicates of the same stand type, reflecting differences in terrace age, flood frequency, flood intensity, river channel position, vegetation inputs, and decomposition. BOHs generally had lower pH and bulk density, higher moisture content, and greater concentrations of carbon, nitrogen, and roots than the surrounding mineral horizons. In each horizon of both successional stages, the soil amino acid pool was dominated by glutamic acid, glutamine, alanine, asparagine, aspartic acid, and histidine, which together accounted for approximately 80% of the total amino acids found. Despite the similar overall amino acid composition among the horizons, proportions of glutamine generally increased with depth and were generally greater in the mineral horizons than in the BOHs, suggesting root exudation or fine root turnover as an amino acid source. In both successional stages, amino acid concentrations were nearly always highest in the Oe/Oa horizon and rapidly decreased with depth. BOHs generally had greater amino acid concentrations than the surrounding mineral horizons in both successional stages, but amino acid concentrations in successive BOHs declined with depth in the soil profile, suggesting that although BOHs do remain as biological hot spots and potential nutrient reservoirs as far down as 60 cm depth, their importance declines over time.     

Effects of forest plantations on rainfall redistribution and erosion in the red soil region of Southern China

To evaluate the effects of different forest plantations on rainfall redistribution, we measured throughfall, stemflow, interception loss, surface runoff and soil loss from July 2004 to September 2005 in the three types of forest plantations Eucommia ulmoides, Vernicia fordii and Pinus massoniana. The results showed that differences in throughfall and stemflow between the three forest plantations were significant (p < 0·05). Throughfall was highest in the V.fordii plantation and stemflow was highest in the E.ulmoides plantation. Throughfall plus stemflow below the E.ulmoides canopy was greater than that underneath the other forest types. Moreover, significant spatial variation in throughfall was observed. Throughfall in P.massoniana was 28·0–39·7% higher at a stem distance < 60 cm or 11·5% lower at a stem distance > 120 cm than in the other forests, but the difference was not significant between E.ulmoides and V.fordii. Moreover, the difference in throughfall at stem distances 60–120 cm was not significant between the different forest plantations. For E.ulmoides, throughfall under the peripheral crown part was 16·1% higher than that close to the stem. In contrast to E.ulmoides, P.massoniana had 26·8% lower throughfall under the peripheral crown part than close to the stem. No significant difference was found in throughfall for the various stem distances underneath V.fordii. Stemflow in E.ulmoides was 2–3 times higher than in the other forests (p < 0·01). Interception loss accounted for 19·9% of gross rainfall for E.ulmoides, 20·8% for V.fordii and 27·2% for P.massoniana. Surface runoff and soil loss differed considerably among the three types of forest plantations. Annual runoff and total soil loss were lowest in the P.massoniana forest and highest in the V.fordii forest. This study indicated that P.massoniana, as a reforestation tree species, had the most positive effect on soil and water conservation among the three forest plantations. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

Carbon mineralization rates at different soil depths across a network of European forest sites (FORCAST)

Most of the carbon (C) in terrestrial ecosystems is stored in the mineral soil layers. Thus, the response of the mineral soil to potential increases in temperature is crucial for the prediction of the impact of climate change on terrestrial ecosystems. Samples from three mineral soil layers were collected from eight mature forest sites in the European network CARBOEUROFLUX and were incubated at four temperatures (4, 10, 20 and 30°C) for c. 270 days. Carbon mineralization rates were related to soil and site characteristics. Soil water holding capacity, C content, nitrogen (N) content and organic matter all decreased with soil depth at all sites, with significantly larger amounts of organic matter, C and N in the top 0–5 cm of mineral soil than in the deeper layers. The conifer forest soils had significantly lower pH, higher C/N ratios and carbon contents in the top 5 cm than the broadleaf forest soils. Carbon mineralization rates decreased with soil depth and time at all sites but increased with temperature, with the highest rates measured at 30°C for all sites. Between 50 and 70% of the total C respired after 270 days of incubation came from the top 5 cm. The percentage C loss was small in all cases, ranging from 1 to 10%. A two‐compartment model was fitted to all data to derive the labile/active and slow/recalcitrant fractions, as well as their decomposition constants. Although the labile fraction was small in all cases, we found significantly larger amounts of labile C in the broadleaf forest soils than in the conifer forest soils. No statistically significant differences were found in the temperature sensitivity parameter Q₁₀ among sites, soil layers or between conifer and broadleaf soils. The average Q₁₀ for all soils was 2.98 (± 0.10). We found that despite large differences among sites, C mineralization can be successfully predicted as a combined function of site leaf area index, mean annual temperature and content of labile carbon in the soil (R² = 0.93).     

Changes in the temperature regime of podzolic soils in the course of natural forest restoration after clearcutting

The results of temperature monitoring in podzolic soils under the middle-taiga bilberry spruce forest and secondary mixed forest of the Komi Republic performed in 2008–2014 are presented. The changes in characteristics of soil temperature in the litter horizon and in the mineral horizons at the depths of 20 and 50 cm are outlined. It is shown that soil temperature regimes differ under the native spruce forest, young growth, and middle-aged secondary mixed forest. The soils of secondary phytocenoses are warmed up to a greater depth and are characterized by the higher heat supply. The differences are seen in a number of temperature parameters, such as the accumulated temperatures above 5°C and above 10°C at the depths of 20 and 50 cm. The most significant differences between the studied plots manifest themselves in the values of temperature amplitudes during the warm season. Maximum values of daily temperature amplitudes were obtained on the plot under young growth, whereas the soil under the middle-aged mixed forest was characterized by minimum values of daily temperature amplitudes.