Soil physicochemical and microbial drivers of temperature sensitivity of soil organic matter decomposition under boreal forests

Soil organic matter(SOM)in boreal forests is an important carbon sink.The aim of this study was to assess and to detect factors controlling the temperature sensitivity of SOM decomposition.Soils were collected from Scots pine,Norway spruce,silver birch,and mixed forests(O horizon)in northern Finland,and their basal respiration rates at five different temperatures(from 4 to 28℃)were measured.The Q_(10) values,showing the respiration rate changes with a 10℃ increase,were calculated using a Gaussian function and were based on temperature-dependent changes.Several soil physicochemical parameters were measured,and the functional diversity of the soil microbial communities was assessed using the MicroResp?method.The temperature sensitivity of SOM decomposition differed under the studied forest stands.Pine forests had the highest temperature sensitivity for SOM decomposition at the low temperature range(0–12℃).Within this temperature range,the Q_(10) values were positively correlated with the microbial functional diversity index(H'_(mic))and the soil C-to-P ratio.This suggested that the metabolic abilities of the soil microbial communities and the soil nutrient content were important controls of temperature sensitivity in taiga soils.     

Organic matter characteristics and C and N transformations in the humus layer under two tree species, Betula pendula and Picea abies

The aim of this study was to compare the effects of silver birch (Betula pendula Roth) and Norway spruce (Picea abies (L.) Karst.) on soil C and N transformations and on the characteristics of organic matter. Soil samples were taken from the humus layer of a replicated 35-year-old birch-spruce field experiment growing on Vaccinium myrtillus site type in middle-eastern Finland. The soil was a podzol and humus type mor. Soil pH was higher under birch (4.7) than under spruce (4.1). The C-to-N ratio was lower under birch (17) than under spruce (23). Per unit organic matter, microbial biomass C and N, net N mineralization and net nitrification were all higher in birch soil than in spruce soil. The rate of C mineralization (CO₂ production) was, however, the same regardless of tree species. Water-extracts were analyzed for the concentrations of dissolved organic C (DOC) and N (DON) and characterized according to molecular size distribution by ultrafiltration and according to chemical composition using a resin fractionation technique. The concentration of DON, in particular, was higher in birch soil than in spruce soil. The distribution of DOC and DON into different fractions based on molecular size or chemical composition was rather similar in both soils. The concentration of total phenolics, expressed as tannic acid equivalents, was higher in the humus layer under birch than in the humus layer under spruce, because the birch humus layer contained significantly more low-molecular weight (about <0.5 kD) phenolics than the spruce humus layer did. The concentration of proanthocyanidins (condensed tannins) was higher in spruce soil than in birch soil. The concentrations of the five most abundant phenolic acids showed that ferulic and p-coumaric acids were more abundant in spruce soil. Birch soil tended to contain slightly more nonvolatile sesquiterpenes than the spruce soil. The concentration of diterpenes was similar in both soils; but birch soil contained significantly more triterpenes, mainly sterols, than spruce soil did.     

Responses of soil dissolved organic matter to long-term plantations of three coniferous tree species

Tree species have significant effects on the availability and dynamics of soil organic matter. In the present study, the pool sizes of soil dissolved organic matter (DOM), potential mineralizable N (PMN) and bio-available carbon (C) (measured as cumulative CO₂ evolution over 63 days) were compared in soils under three coniferous species — 73 year old slash (Pinus elliottii), hoop (Araucaria cunninghamii) and kauri (Agathis robusta) pines. Results have shown that dissolved organic N (DON) in hot water extracts was 1.5–1.7 times lower in soils under slash pine than under hoop and kauri pines, while soil dissolved organic C (DOC) in hot water extracts tended to be higher under slash pine than hoop and kauri pines but this was not statistically significant. This has led to the higher DOC:DON ratio in soils under slash pine (32) than under hoop and kauri pines (17). Soil DOC and DON in 2 M KCl extracts were not significantly different among the three tree species. The DOC:DON ratio (hot water extracts) was positively and significantly correlated with soil C:N (R² = 0.886, P < 0.01) and surface litter C:N ratios (R² = 0.768, P < 0.01), indicating that DOM was mainly derived from litter materials and soil organic matter through dissolution and decomposition. Soil pH was lower under slash pine (4.5) than under hoop (6.0) and kauri (6.2) pines, and negatively correlated with soil total C, C:N ratio, DOC and DOC:DON ratio (hot water extracts), indicating the soil acidity under slash pine favored the accumulation of soil C. Moreover, the amounts of dissolved inorganic N, PMN and bio-available C were also significantly lower in soils under slash pine than under hoop and kauri pines. It is concluded that changes in the quantity and quality of surface litters and soil pH induced by different tree species largely determined the size and quality of soil DOM, and plantations of hoop and kauri pine trees may be better in maintaining long-term soil N fertility than slash pine plantations.     

有机物料输入稻田提高土壤微生物碳氮及可溶性有机碳氮

土壤微生物量碳、氮和可溶性有机碳、氮是土壤碳、氮库中最活跃的组分,是反应土壤被干扰程度的重要灵敏性指标,通过设置相同有机碳施用量下不同有机物料处理的田间试验,研究了有机物料添加下土壤微生物量碳（soil microbial biomass carbon,MBC）、氮（soil microbial biomass nitrogen,MBN）和可溶性有机碳（dissolved organic carbon,DOC）、氮（dissolved organic nitrogen,DON）的变化特征及相互关系。结果表明化肥和生物碳、玉米秸秆、鲜牛粪或松针配施下土壤微生物量碳、氮和可溶性有机碳、氮显著大于不施肥处理（no fertilization,CK）和单施化肥处理,分别比不施肥处理和单施化肥平均高23.52%和12.66%（MBC）、42.68%和24.02%（MBN）、14.70%和9.99%（DOC）、22.32%和21.79%（DON）。化肥和有机物料配施处理中,化肥+鲜牛粪处理的微生物量碳、氮和可溶性有机碳、氮最高,比CK高26.20%（MBC）、49.54%（MBN）、19.29%（DOC）和32.81%（DON）,其次是化肥+生物碳或化肥+玉米秸秆处理,而化肥+松针处理最低。土壤可溶性有机碳质量分数（308.87 mg/kg）小于微生物量碳（474.71 mg/kg）,而可溶性有机氮质量分数（53.07 mg/kg）要大于微生物量氮（34.79 mg/kg）。与不施肥处理相比,化肥和有机物料配施显著降低MBC/MBN和DOC/DON,降低率分别为24.57%和7.71%。MBC和DOC、MBN和DON随着土壤有机碳（soil organic carbon,SOC）、全氮（total nitrogen,TN）的增加呈显著线性增加。MBC、MBN、DOC、DON、DOC+MBC和DON+MBN之间呈极显著正相关（P<0.01）。从相关程度看,DOC+MBC和DON+MBN较MBC、DOC、MBN、DON更能反映土壤中活性有机碳和氮库的变化,成为评价土壤肥力及质量的更有效指标。结果可为提高洱海流域农田土壤肥力,增强土壤固氮效果,减少土壤中氮素流失,保护洱海水质安全提供科学依据。     

Indices of dissolved organic nitrogen, ammonium and nitrate across productivity gradients of boreal forests

Organic nitrogen (N) uptake, rather than solely inorganic N (DIN), is considered a significant pathway for plant nutrition, especially in arctic, alpine and boreal ecosystems. Assays of plant-available N in these ecosystems might therefore be improved with measures of dissolved organic N (DON). We examined DON and DIN abundance from an in situ 5-week incubation across plant associations that represent the widest range in site potential in southern boreal forests of British Columbia, Canada. The supply of N from forest floors and mineral soils (20 cm depth) was measured separately and then combined (kg ha⁻¹) to facilitate comparisons of sites. DON was the predominant form of extractable N, and was increasingly supplemented, rather than replaced, by NH₄⁺ and NO₃⁻ on productive sites. The amount of DIN produced in the soils was very low, perhaps too small to support forest needs, and the correlation of DIN to asymptotic stand height (a measure of site potential) was significant but nonlinear. The combined amount of DON+DIN was considered a more effective index of plant-available N because it was strongly significant as a linear correlation to stand height and more typical of annual forest N uptake. The relative shift in N forms, from a predominance of DON to progressively greater ratios of DIN:DON, was consistent with the current paradigm of N forms across gradients of N availability, although the actual amounts of DON increased, rather than decreased, with site potential. Based on this, we suggest organic N uptake has the potential to contribute to plant nutrition across the entire productivity gradient of soils in southern boreal forests. Although other N indices were effective in characterizing forest productivity, a combined assay of DON+DIN production could provide new insights into functional differences in plant-available N.     

Effects of dissolved organic matter on permethrin bioavailability to Daphnia species

Synthetic pyrethroids are widely used insecticides in both agricultural and urban environments. Recent studies show frequent appearances of pyrethroid residues in runoff effluents and sediments, which stimulated concerns over the potential ecotoxicological implications. Pyrethroids are known to have two contrasting characteristics, high aquatic toxicity and strong affinity for the solid phase, that may negate the actual toxicity in a multiphased system. This study evaluated the effect of dissolved organic matter (DOM) on the pyrethroid uptake by and acute toxicity to water-column invertebrates using permethrin as a model compound. During the bioassays, the freely dissolved permethrin concentration was simultaneously measured using poly(dimethylsiloxane) (PDMS) fibers as a biomimetic surrogate. The presence of DOM consistently decreased permethrin uptake and increased its LC(50). For instance, compared to the DOM-free treatment, the LC(50) of permethrin to Ceriodaphnia dubia in a pond water containing DOM at 10 mg L(-)(1) increased from 0.56 to 1.03 microg L(-)(1), whereas the bioaccumulation factor by Daphnia magna decreased by 56%. Permethrin accumulation on the PDMS fiber closely mimicked permethrin uptake by D. magna. Statistical analyses suggest that permethrin associated with DOM was completely unavailable to D. magna or C. dubia. The effect of DOM on permethrin bioavailability appeared to depend also on the source of the DOM. These results indicate that the inhibitory role of DOM should be considered in the development of toxicologically relevant water quality limits and in monitoring protocols for permethrin and other pyrethroids in runoff effluents and surface streams that ubiquitously contain DOM.     

Composition of lipophilic compounds and carbohydrates in the accumulated plant litter and soil organic matter in boreal forests

Carbohydrates and lipophilic compounds constitute an important component of litter and soil organic matter in boreal forests, but are still poorly identified. We characterized needle litter and coarse tree litter (cones, seeds, bark and twigs) from coniferous trees (Pinus sylvestris L. and Picea abies Karst.), and moss litter (Pleurozium schreberi, Hylocomnium speldens), fermentation (F) and humus (H) layers in four boreal forest sites in Finland using a combination of sequential fractionation (non‐polar extractions, NPE; water‐soluble extractions, WSE; acid‐soluble fraction, AS) and detailed analyses on the soluble fractions using GC‐MS. Comparisons among the different layers of the soil organic horizon were used to assess which lipophilic compounds and carbohydrates increased in the F and H layers in proportion to their relative abundance in the litter layer and thus might have a large potential to accumulate in soil organic matter. Both concentrations and relative proportions of different compounds varied among the soil layers. Several of the fatty acids (FAs) found in the litter samples were absent in the F and the H layers. Needle and coarse tree litter contained a wide range of di‐ and triterpenes, but in the F and H layers oxidized forms of dehydroabietic acid and sterols were abundant. The large proportion of dehydroabietic acid in the lipophilic fraction in the H layer suggests that it may be poorly degradable by soil microorganisms, probably because of its anti‐microbial function in trees. The composition of the acid‐soluble fraction indicated that the proportion of cellulose in relation to hemicelluloses increased from the litter layer to the F and H layers. Put together, changes in the relative proportions of organic compounds in soluble fractions indicate that selective preservation of compounds, litter input by plant roots and microbial synthesis of compounds all contribute to the accumulation of aliphatic compounds in the H layer of boreal forests.     

Soil organic matter and the extracellular microbial matrix show contrasting responses to C and N availability

An emerging paradigm in soil science suggests microbes can perform ‘N mining’ from recalcitrant soil organic matter (SOM) in conditions of low N availability. However, this requires the production of extracellular structures rich in N (including enzymes and structural components) and thus defies stoichiometric expectation. We set out to extract newly synthesised peptides from the extracellular matrix in soil and compare the amino acid (AA) profiles, N incorporation and AA dynamics in response to labile inputs of contrasting C/N ratio. Glycerol was added both with and without an inorganic source of N (10% ¹⁵N labelled NH₄NO₃) to a soil already containing a large pool of refractory SOM and incubated for 10 days. The resulting total soil peptide (TSP) and extracellular pools were compared using colorimetric methods, gas chromatography, and isotope ratio mass spectrometry. N isotope compositions showed that the extracellular polymeric substance (EPS) contained a greater proportion of products formed de novo than did TSP, with hydrophobic EPS-AAs (leucine, isoleucine, phenylalanine, hydroxyproline and tyrosine) deriving substantially more N from the inorganic source provided. Quantitative comparison between extracts showed that the EPS contained greater relative proportions of alanine, glycine, proline, phenylalanine and tyrosine. The greatest increases in EPS-peptide and EPS-polysaccharide concentrations occurred at the highest C/N ratios. All EPS-AAs responded similarly to treatment whereas the responses of TSP were more complex. The results suggest that extracellular investment of N (as EPS peptides) is a microbial survival mechanism in conditions of low N/high C which, from an evolutionary perspective, must ultimately lead to the tendency for increased N returns to the microbial biomass. A conceptual model is proposed that describes the dynamics of the extracellular matrix in response to the C/N ratio of labile inputs.     

Biochemical properties and biodegradation of dissolved organic matter from soils

Various biologically mediated processes are involved in the turnover of dissolved organic matter (DOM) in soil; however, relatively little is known about the dynamics of either the microbial community or the individual classes of organic molecules during the decomposition of DOM. We examined the net loss of DOC, the mineralisation of C to CO₂ and the degradation of DOC from six different soils by soil microorganisms. We also quantified the changes in the concentrations of protein, carbohydrate and amino acid C during microbial biodegradation. Over a 70-day incubation period at 20°C, the mineralisation of DOC to CO₂ was described by a double exponential model with a labile pool (half-life, 3–8 days) and a stable pool (half-life, 0.4–6 years). However, in nearly all cases, the mass loss of DOC exceeded the C released as CO₂ with significant deviations from the double exponential model. Comparison of mass DOC loss, CO₂ production and microbial cell counts, determined by epifluorescence microscopy, showed that a proportion of the lost DOC mass could be accounted for by microbial assimilation. Carbohydrate and protein C concentrations fluctuated throughout the incubation with a net change of between 3 to 13 and −30 to 22.4% initial DOC, respectively. No amino acid C was detected during the incubation period (level of detection, 0.01 mg C l⁻¹).     

Soluble organic matter and microbial biomass C and N in soils under pasture and arable management and the leaching of organic C,N and nitrate in a lysimeter study

Soluble organic N and C were extracted from soils under long-term kikuyu grass pasture, annual ryegrass pasture and annual maize production using water, 0.5 M K₂SO₄ and 2 M KCl. Quantities extracted with K₂SO₄ were more than double those extracted with water while those extracted with KCl exceeded those using K₂SO₄. Differences in soluble organic C and N between land uses were much more obvious when water rather than salt solutions were used. It was suggested that water extracts give more realistic values than salt solutions. Regardless of the extractant used, the proportion of total N present as soluble N was considerably greater than the equivalent proportion of organic C present as soluble C. While the percentage of soil organic C and total N present in the light fraction and microbial biomass was lower in the kikuyu than ryegrass and maize soils, the equivalent values for water soluble C and N were, in fact, greatest in the kikuyu soil.The leaching of organic C, N and NO₃⁻ from these soils was also measured over a 6-month period in a greenhouse lysimeter study. The soils were either left undisturbed or were disturbed (broken into clods <50 mm diameter) to simulate tillage and stimulate microbial activity. Quantities of organic C and N leached were greater from the kikuyu than other treatments and tended to be greatest from the disturbed kikuyu soil. The percentage of total soil N leached as organic N was considerably greater than that of total organic C leached as soluble C. Leaching of NO₃⁻ was greatest from the disturbed kikuyu soil and least from the undisturbed kikuyu soil. The mean percentage of total soluble N present in organic form in leachates ranged from 17 to 32% confirming the importance of this form of N to leaching losses of N from agricultural soils.     

Changes in properties of soil-derived dissolved organic matter induced by biodegradation

Properties of dissolved organic matter (DOM) determine its biodegradation. In turn, biodegradation changes the properties of the remaining DOM, which may be decisive for the formation of stable organic carbon in soil. To gain information on both mechanisms and controlling factors of DOM biodegradation and the properties of biodegraded DOM, we investigated changes in the composition of 13 different DOM samples extracted from maize straw, forest floors, peats, and agricultural soils during a 90-day incubation using UV absorbance, fluorescence emission spectroscopy, FTIR-spectroscopy, ¹H-NMR spectroscopy, pyrolysis-field ionization mass spectroscopy (Py-FIMS), and ¹³C natural abundance before and after incubation. Changes in the DOM properties were related to the extent of biodegradation determined by the release of CO₂. Increasing UV absorption and humification indices deduced from fluorescence emission spectra, and increasing portions of aromatic H indicated relative enrichment of aromatic compounds during biodegradation. This enrichment significantly correlated with the amount of DOC mineralized suggesting that aromatic compounds were relatively stable and slowly mineralized. ¹³C depletion during the incubation of highly degradable DOM solutions indicated an enrichment of lignin-derived aromatic compounds. Py-FI mass spectra indicated increasing contents of phenols and lignin monomers at the expense of lignin dimers and alkylaromatics during incubation. This partial degradation of higher-molecular, lignin-derived DOM compounds was accompanied by relative increases in the proportions of lower-molecular degradation products and microbial metabolites. Carbohydrates, especially when abundant at high initial contents, seem to be the preferred substrate for microorganisms. However, four independent methods suggested also some microbial production of carbohydrates and peptides during DOM degradation. After incubation, the composition of highly degradable DOM samples became similar to relatively stable DOM samples with respect to aromaticity, carbohydrate content, and thermal stability. We conclude that DOM biodegradation seems to result in organic matter properties being a precondition for the formation of stable carbon. These structural changes induced by DOM biodegradation should also result in stronger DOM sorption to the soil matrix additionally affecting DOM stabilization.     

Decreases in soil moisture and organic matter quality suppress microbial decomposition following a boreal forest fire

Climate warming is projected to increase the frequency and severity of wildfires in boreal forests, and increased wildfire activity may alter the large soil carbon (C) stocks in boreal forests. Changes in boreal soil C stocks that result from increased wildfire activity will be regulated in part by the response of microbial decomposition to fire, but post-fire changes in microbial decomposition are poorly understood. Here, we investigate the response of microbial decomposition to a boreal forest fire in interior Alaska and test the mechanisms that control post-fire changes in microbial decomposition. We used a reciprocal transplant between a recently burned boreal forest stand and a late successional boreal forest stand to test how post-fire changes in abiotic conditions, soil organic matter (SOM) composition, and soil microbial communities influence microbial decomposition. We found that SOM decomposing at the burned site lost 30.9% less mass over two years than SOM decomposing at the unburned site, indicating that post-fire changes in abiotic conditions suppress microbial decomposition. Our results suggest that moisture availability is one abiotic factor that constrains microbial decomposition in recently burned forests. In addition, we observed that burned SOM decomposed more slowly than unburned SOM, but the exact nature of SOM changes in the recently burned stand are unclear. Finally, we found no evidence that post-fire changes in soil microbial community composition significantly affect decomposition. Taken together, our study has demonstrated that boreal forest fires can suppress microbial decomposition due to post-fire changes in abiotic factors and the composition of SOM. Models that predict the consequences of increased wildfires for C storage in boreal forests may increase their predictive power by incorporating the observed negative response of microbial decomposition to boreal wildfires.     

Conservation of beetles in boreal pine forests: the effects of forest age and naturalness on species assemblages

The effort of boreal forest conservation has emphasised the preservation of old-growth forests while the role of young successional stages in maintaining biodiversity has remained largely unstudied. We compared the richness of beetle species and composition of species assemblages between managed and seminatural forests in five stages of forest succession. The sites were in boreal sub-xeric pine-dominated forests in eastern Finland. Seminatural study sites, especially the recently burned sites, were important habitats for threatened and near-threatened species. We propose that young stages of natural succession should be included in the network of protected forest areas. On the other hand, the composition of saproxylic species assemblages in seminatural forests differed from the assemblages in managed forests, indicating also the need to improve the forest management guidelines so that they better address the requirements of species protection. Regeneration methods applied should resemble or mimic the natural disturbances more closely.     

The effect of Siberian tree species on the mineralization rate of soil organic matter

The mineralization of organic matter in the soils under the six main Siberian forest-forming species was studied. The nitrogen mineralization and nitrification were the most affected by the different tree species. The rate of the CO₂ formation was similar in the soils under the different tree species. The factors affecting the variation of the data characterizing the microbiological processes were revealed. The nitrogen mineralization and nitrification correlated with the contents of the soil carbon, nitrogen, and NH₄⁺ and the soil acidity, while the carbon mineralization correlated only with the NH₄⁺ concentration and the C/N ratio.     

Fractionation of dissolved organic matter on the XAD resin

Analytical fractionation conditions on the resin XAD-7H of organic substances from gravitational soil moisture influence the proportion and the yield of the extracted fractions. Increasing the column capacity factor k’ is accompanied by a decreased yield of hydrophobic fraction and the change in its composition. The sorption column capacity factor of k’ = 30 is sufficient for the extraction of all hydrophobic components from a soil solution with a concentration of C_DOM of ～25 mg/L.     

Transformation of dissolved organic matter in soils of the felled areas in fir-spruce forests (Primorskii Krai)

Dissolved organic matter was studied in soils of the felled areas in fir-spruce forests of the southern Sikhote-Alin Ridge. After cutting of the forest, the molecular-mass characteristics of the dissolved organic matter in the soils changed: its molecular structure became simpler, and the degree of aromatic polycondensation and the capacity for the formation of complexes with Fe and Al decreased.     

Long‐term effects of liming on microbial biomass and activity and soil organic matter quality (13C CPMAS NMR) in organic horizons of Norway spruce forests in Southern Germany

Long‐term effects of liming on microbial biomass and activity and soil organic matter (SOM) were investigated in samples from organic horizons (Of/Oh) in spruce forests at Adenau, Höglwald, Idar‐Oberstein, and Schluchsee (Southern Germany) where plots have been manually treated 7 to 13 years ago with dolomitic limestone. At all sites, pH values were markedly increased after liming. The contents of C and N in the organic horizons of the limed plots appeared to be lower with the greatest decrease at Höglwald (Dystric Luvisol) where liming has affected the soil properties for the longest time of all sites. Catalase activity was promoted after liming at Adenau (Cambic Podzol). This was also the case for the Dystric Luvisol where liming resulted also in higher basal respiration. Biomass‐C was higher in samples from the limed plot at Idar‐Oberstein (Dystric Cambisol). The ¹³C CPMAS NMR spectra of organic horizons from the control plots indicate no differences in the gross carbon composition of SOM. Furthermore, spectra from the limed Cambic Podzol, Dystric Cambisol, and Haplic Podzol (Schluchsee) were remarkably similar. However, for the Dystric Luvisol, the lime‐induced promotion of microbial activity resulted in lower O‐alkyl‐C intensity. The observed patterns of microbial biomass and activity were site‐dependent rather than a result of liming. Obviously liming had only small long‐term effects on the humus quality in the organic horizons, as far as detectable by CPMAS NMR spectroscopy. More sensitive techniques like pyrolysis‐GC/MS should be applied to analyze differences in C composition.     

Non-additive effects of mixing different sources of dissolved organic matter on its biodegradation

To examine the potential impact of plant species richness on ecosystems, we studied non-additive effects of different plant litters on the biodegradation rate of dissolved organic matter (DOM) when mixing plant leaf-derived DOM derived from different plant species. A full factorial biodegradation experiment (31 possible singular and multiple combinations of five litter type-derived DOM sources) was conducted using plant litters from the five most abundant plant species in a subtropical watershed ecosystem, from which dissolved organic carbon (DOC) disappearance was measured. Loss of DOC over time was considered biodegradable DOC. We tested whether DOM diversity, measured as source species richness and composition, would affect biodegradation rates. Overall, we found significant non-additive (synergistic) effects of DOM diversity on biodegradation rates of DOM, which were explained both by plant species richness and composition. Across all treatments, a significantly higher biodegradation rate was correlated with the presence of DOM from higher nitrogen (N) containing plant litters; conversely, the presence of lower N decreased these rates. The N content and chemical characteristic of DOM might influence the magnitude of the synergistic effect. Our results suggest that loss of plant litter species diversity would not affect DOC biodegradation rate, provided that at least two species are conserved. However, the variability in DOC biodegradation rate across the treatments decreased with increased DOM diversity at three incubation time points. Our results also indicate that in an ecosystem with low plant biodiversity, loss of key species such as Lophostemon confertus could reduce the synergistic effects on DOC biodegradation rate.     

Potential activities of enzymes involved in N,C, P and S cycling in boreal forest soil under different tree species

The aim of this study was to compare the potential activity of enzymes involved in N, C, P and S cycling in the humus layer under three tree species: silver birch, Norway spruce and Scots pine. For arylsulphatase and protease the highest activities were found under birch, whereas beta-glucosidase activity was highest under pine. Beta-glucosaminidase and acid phosphatase showed similar activities regardless of tree species. Our studies show that soils under these species may differ enzymatically from each other. Enzyme activity studies under different tree species need more attention as the activity of different enzymes influences on soil nutrient availability in boreal forest soil.