Oak Forest Soils Research Articles

Soil organic matter content and composition as influenced by soil management in a semi-arid Mediterranean agro-silvo-pastoral system

The aim of this study was to assess the impact of different long term soil managements on soil organic matter (SOM) quantity and quality in a semi-arid Mediterranean dehesa-like agro-forestry system (North-East of Sardinia, Italy). Seven soil managements were compared: cork oak forest, pasture under oak trees, open pasture, hay crop under oak trees, open hay crop, grass-covered vineyard and tilled vineyard. Analyses include chemical and spectroscopic (FT-IR) characterization of the humic substances (fulvic acids, humic acids and humin) of the A horizons. Lower amounts of total organic C and humic substances were found in the more disturbed soils such as those of the tilled vineyard, while the other soil managements showed a rather similar pattern for many indices of SOM quality (e.g., HA-C/FA-C, fulvic H/C and humic and fulvic C/N ratios) and for spectroscopic characteristics. These results indicated that the impact of soil management on the humic composition was relatively low for these sub-acid (pH ranging from 5.1 to 6.4) sandy soils under Mediterranean type of climate. The relatively small differences between the forest and the grassland land uses also suggested that the periodical light tillage applied to the grassland did not strongly affect SOM accumulation in the topsoil of this land use. In the oak forest soils, a sharp decrease (–77%) of the organic C from the thin A1 to the A2 horizon was observed, which could constrain the resilience of these soils towards disturbance factors, while the grasslands soils, where the organic C sequestration occurred in a thick horizon, may be more resilient.The compared soil managements revealed to be quite conservative, demonstrating that the traditional agro-silvo-pastoral management practices are effective in maintaining relatively good soil quality traits under semi-arid Mediterranean conditions.

Effects of Afforestation with Pines on Collembola Diversity in the Limestone hills of Szárhalom (West Hungary)

Abstract - We investigated the responses of collembolan communities to pine afforestation in an area formerly characterized by a mosaic of autochthonous downy oak woodland and steppe meadows. Study sites were selected in mixed stands of black pine and Scots pine and control samples were taken from downy oak stands and open steppe meadows. A total of 1884 Collembola specimens belonging to 66 species were collected. Three species, namely Protaphorura pannonica (Onychiuridae), Tomocerus mixtus (Tomoceridae) and Isotoma caerulea (Isotomidae) proved to be new to the Hungarian fauna. There are typical Collembola communities which are specific to different habitat types where species of a given composition can only or predominantly be found in that habitat, as well as some basic common species which occur in every habitat. The highest species richness (41) was found in steppe meadows, considerably lower (34) in downy oak forests, reaching the lowest value (25) in pine plantations. Although several forest species present in the oak woodland were completely missing from the pine forests, there was no significant difference between the Collembola diversities of the two forest habitats. The difference became more prominent in collembolan abundance which resulted in less than half of individuals/m2 in pine plantations compared to the soils of downy oak forests, most likely due to the changed soil conditions, especially of humus characteristics, caused by the pine needle litter. Jaccard similarity measure indicated approximately equal similarity (0.24-0.28) for paired comparison, suggesting that a relatively constant 'basic Collembola community' determined by the soil type typical for the area is present; while dissimilarity in communities between sites are partly provided by spatial heterogeneity of open and forest habitats and by the difference of the vegetation type.

Variation Among Phytophthora cinnamomi Isolates from Oak Forest Soils in the Eastern United States.

Phytophthora cinnamomi isolates from geographically diverse oak forest soils in the Mid-Atlantic regions were studied to determine the extent of genotypic, phenotypic, and pathogenic variation. Four microsatellite loci were targeted for genetic analysis. Phenotypic characteristics measured included sexual and asexual spore dimensions and colony growth rate and morphology. Red oak (Quercus rubra) logs were inoculated with selected isolates to determine relative pathogenicity. Microsatellite analysis showed that the genetic variability of P. cinnamomi isolates was low, with two predominant microsatellite fingerprint groups (MFG). Isolates in MFG1 (48% of the total isolates examined) were characterized by DNA fragment lengths of 120 and 122 bp at locus d39, 169 and 170 bp at locus e16, and 254 and 255 bp at locus g13. MFG2 isolates were characterized by marker sizes of 122 and 124 bp at locus d39, 161 and 163 bp at locus e16, and 247 and 248 bp at locus g13. Asexual and sexual spore dimensions varied greatly among isolates but were similar to previously published descriptions. Phenotypic differences were most pronounced when data were grouped by MFG; the most significant were colony morphology and growth rate. Neither characteristic was a reliable predictor of isolate genotype. Differences in growth rates of MFGs were observed, with MFG1 being less tolerant at higher incubation temperatures. No variation in pathogenicity was observed on red oak logs. The low level of phenotypic and genotypic variation of P. cinnamomi suggest that other factors such as climate might play a more important role in its northern distribution and the diseases it causes.

Unravelling Soil Fungal Communities from Different Mediterranean Land-Use Backgrounds

BackgroundFungi strongly influence ecosystem structure and functioning, playing a key role in many ecological services as decomposers, plant mutualists and pathogens. The Mediterranean area is a biodiversity hotspot that is increasingly threatened by intense land use. Therefore, to achieve a balance between conservation and human development, a better understanding of the impact of land use on the underlying fungal communities is needed.Methodology/Principal FindingsWe used parallel pyrosequencing of the nuclear ribosomal ITS regions to characterize the fungal communities in five soils subjected to different anthropogenic impact in a typical Mediterranean landscape: a natural cork-oak forest, a pasture, a managed meadow, and two vineyards. Marked differences in the distribution of taxon assemblages among the different sites and communities were found. Data analyses consistently indicated a sharp distinction of the fungal community of the cork oak forest soil from those described in the other soils. Each soil showed features of the fungal assemblages retrieved which can be easily related to the above-ground settings: ectomycorrhizal phylotypes were numerous in natural sites covered by trees, but were nearly completely missing from the anthropogenic and grass-covered sites; similarly, coprophilous fungi were common in grazed sites.Conclusions/SignificanceData suggest that investigation on the below-ground fungal community may provide useful elements on the above-ground features such as vegetation coverage and agronomic procedures, allowing to assess the cost of anthropogenic land use to hidden diversity in soil. Datasets provided in this study may contribute to future searches for fungal bio-indicators as biodiversity markers of a specific site or a land-use degree.

Influence of climate and litter quality on litter decomposition and nutrient release in sub-tropical forest of Northeast India

Leaf litterfall, litter decomposition and nutrient return through litterfall of three dominant species, i.e. Quercus serrata, Schima wallichi and Lithocarpus dealbata were studied in different months throughout the year to assess the input and release of nutrient in the forest soil of a sub-tropical mixed oak forest of Manipur, northeastern India. Oaks in northeastern region of India are economically important species for the production of Tasar silk. The monthly litterfall ranged from 25.6 g·m−2 (July) to 198.0 g·m−2 (February) and annual litterfall was 1093.8g·m−2 in the forest site. At initial month (on November 3), the concentrations of N and C were the highest in L. dealbata, followed by Q. serrata and lowest in S. wallichi, whereas lignin and cellulose concentrations at initial month were the highest in S. wallichi, followed by Q. serrata and L. dealbata. L. dealbata (k =0.54) exhibited a high rate of litter decomposition, coinciding with high concentrations of N and C and low cellulose in the litter at initial month. However, low rate of litter decomposition in S. wallichi (k = 0.33) coincided with low value of N and C and highest value of lignin and cellulose at initial month. The remaining biomass in different months was positively correlated with the lignin, C, C/N ratio and cellulose, but it negatively correlated with nitrogen concentrations at initial month. The rate of litter decomposition was the highest in rainy summer months, owing to congenial environmental conditions and lowest rate of litter decomposition in cool and dry winter months.

Microbial C, N and P in soils of Mediterranean oak forests: influence of season, canopy cover and soil depth

In Mediterranean ecosystems the effect of aboveground and belowground environmental factors on soil microbial biomass and nutrient immobilization-release cycles may be conditioned by the distinctive seasonal pattern of the Mediterranean-type climates. We studied the effects of season, canopy cover and soil depth on microbial C, N and P in soils of two Mediterranean forests using the fumigation-extraction procedure. Average microbial values recorded were 820 μg C g−1, 115 μg N g−1 and 19 μg P g−1, which accounted for 2.7, 4.7 and 8.8% of the total pools in the surface soil, respectively. Microbial N and P pools were about 10 times higher than the inorganic N and P fractions available for plants. Microbial C values differed between forest sites but in each site they were similar across seasons. Both microbial and inorganic N and P showed maximum values in spring and minimum values in summer, which were positively correlated with soil moisture. Significant differences in soil microbial properties among canopy cover types were observed in the surface soil but only under favourable environmental conditions (spring) and not during summer. Soil depth affected microbial contents which decreased twofold from surface to subsurface soil. Microbial nutrient ratios (C/N, C/P and N/P) varied with seasons and soil depth. Soil moisture regime, which was intimately related to seasonality, emerged as a potential key factor for microbial biomass growth in the studied forests. Our research shows that under a Mediterranean-type climate the interaction among season, vegetation type and structure and soil properties affect microbial nutrient immobilization and thus could influence the biogeochemical cycles of C, N and P in Mediterranean forest ecosystems.

A new mite species of the genus Lasioseius (Acari: Gamasina: Ascidae) from central Europe

Lasioseius minor sp. n. (Acari: Gamasina: Ascidae) is described from the soil of thermophilic oak forest from south-western Slovakia. L. minor sp. n. belongs to the subgenus Crinidens having not reduced number of dorsal setae, separate metapodal platelets, epistomal margin with three well developed branches and only two small smooth pointed dorsal setae.

First Report of Phytophthora cactorum Associated With Beech Decline in Italy.

During 2006 and 2007, declining mature beech trees (Fagus sylvatica) were recorded in two stands in the Natural Park of Monti Cimini in central Italy. Symptoms included crown thinning and the presence of bleeding lesions on the main roots and lower stem. Incidence of decline was approximately 5%. Samples of necrotic bark tissue were collected, cut into 5 mm long segments, plated on PARPNH, and incubated at 20°C (1). Phytophthora isolates were obtained from necrotic tissues of 25% of the sampled declining trees. Colonies were rosaceous on potato dextrose agar (PDA) and homothallic. Papillate, ovoid-to-obpyriform, caducous sporangia (mean 38 × 26.2 μm) were produced in soil extract. Oospores were plerotic (mean diameter of 22 to 32 μm) and antheridia paragynous. Optimum growth temperature was 23 to 25°C, minimum 6 to 8°C and maximum 30 to 33°C. A portion of the internal transcribed spacer sequence has been deposited in the NCBI database (GenBank Accession No. FJ183724). A BLAST search of the NCBI database revealed Phytophthora cactorum, Accession No. EU194384, as the closest match with 100% sequence similarity. Pathogenicity of two isolates, PFE3 and IFB-CAC 38, collected from distressed beech trees was tested using a soil infestation test (10 beech seedlings per isolate and control) and an under the bark inoculation method (10 twigs per isolate and controls, wounded and noninoculated taken from a declining beech tree) (2). After 2 weeks at 20°C, twigs and seedlings inoculated with each isolate developed extensive necrotic lesions around the inoculation sites and the collar, respectively, and P. cactorum could be reisolated from all lesions. Controls showed no symptoms. P. cactorum is widespread in declining beech forests in central Europe (1). In Italy, P. cactorum occurs in soils of chestnut and oak forests and was isolated from collar and root lesions of declining walnut trees (3). To our knowledge, this is the first report of P. cactorum being associated with declining beech trees in Italy.

Relative susceptibility of oaks to seven species of Phytophthora isolated from oak forest soils

SummaryIsolates of Phytophthora cambivora, P. cinnamomi, P. citricola, P. europaea, P. quercetorum and two unidentified species were tested for their pathogenicity to eastern US oak species by root and stem inoculations. Experiments were conducted during two different periods and included 1‐, 2‐ and 20‐year‐old oaks grown under greenhouse and field conditions. Species of Phytophthora were pathogenic in varying degrees to the oak species tested. All species were pathogenic to fine and taproots of at least one oak species. The fine root damage caused by the species of Phytophthora ranged from 9 to 55% when compared to the controls. Roots were more susceptible during the fall inoculation period than the summer. With exception of Phytophthora sp1 and P. quercina‐like, all species of Phytophthora were pathogenic to oak stems with P. cinnamomi and P. citricola being the most aggressive. Quercus montana and Q. rubra were the most susceptible oak species to stem inoculation. Lesion sizes were considerably larger when 20‐year‐old trees were inoculated. Generally, no significant differences in lesion sizes were detected in greenhouse tests when the summer and fall inoculation periods were compared. However, on 2‐year‐old field‐grown seedlings, lesion sizes were considerably smaller or not significantly different from controls during the fall inoculation period, suggesting lower, late season temperatures may restrict lesion development.

Physical and Biological Controls on the In Situ Kinetic Isotope Effect Associated with Oxidation of Atmospheric CH4 in Mineral Soils

The amounts and delta(13)C values of CH4 at subambient concentrations in soil gas were determined along depth profiles in a U.K. grassland (Bronydd Mawr) and woodland (Leigh Woods). The data were used to determine in situ kinetic isotope effects (KIEs) associated with uptake of atmospheric CH4 by high-affinity methanotrophic bacteria that inha bit soil. Three independent calculation approaches yielded similar mean KIEs of 1.0211 +/- 0.0020 (n=18) for Bronydd Mawr and 1.0219 +/- 0.0010 (n=24) for Leigh Woods. Soil methanotrophy KIEs were largely invariant among oak, beech, and pine forest soils of different ages at Leigh Woods but exhibited a statistically significant relationship with methanotroph biomass in individual plots at Bronydd Mawr and Leigh Woods quantified previously by 13C stable isotope probing. This finding, albeit based upon a small data set suggests that 13C and 12C partitioning associated with the global soil sink for atmospheric CH4 may occur in part as a result of biological as well as physical processes. An accurate assessment of the relative importance of each process to the total KIE requires confirmation that significant partitioning of (13)CH4 and (12)CH4 occurs in pore spaces as a result of differences in diffusion rates.

Laccase Gene Composition and Relative Abundance in Oak Forest Soil is not Affected by Short-Term Nitrogen Fertilization

Anthropogenic nitrogen (N) deposition affects a wide range of soil processes including phenol oxidase (PO) activity and soil organic matter dynamics. Depression of phenol oxidase activity in response to N saturation is believed to be mediated by the activity of white-rot basidiomycetes, whose production of extracellular oxidative enzymes can be limited by high N availability. We examined the effect of short-term N deposition on basidiomycete laccase gene diversity and relative abundance in temperate oak forest soil in which significant decreases in phenol oxidase and increased SOM have been recorded in response to experimental N deposition. UniFrac was used to compare the composition of laccase genes between three control- and three nitrogen-fertilized (80 kg(-1) ha(-1) per year) oak forest soils. The relative abundance of laccase genes was determined from qPCR analysis of laccase and basidiomycete ITS gene abundances. Our results indicate that there was no significant shift in the composition of laccase genes between control- and N-fertilized soils, nor was there a significant change in the relative abundance of laccase genes. These data suggest that N deposition effects on mineral soil PO activity do not result from changes in laccase gene diversity of white-rot basidiomycetes but are likely the result of altered microbial abundance or expression in this ecosystem type. Furthermore, laccase gene composition may be tied to factors that structure microbial communities in general, as soil laccase gene communities are more similar to other forest soils than with the corresponding litter.

Phytophthora quercetorum sp. nov., a novel species isolated from eastern and north-central USA oak forest soils

Isolates belonging to an undescribed Phytophthora species were frequently recovered during an oak forest soil survey of Phytophthora species in eastern and north-central USA in 2004. The species was isolated using an oak leaf baiting method from rhizosphere soil samples collected from Quercus rubra, Q. macrocarpa, and Q. phellos. This species is formally described as P. quercetorum. It is homothallic and has aplerotic oogonia and paragynous antheridia. It produces papillate sporangia (occasionally bipapillate) of ovoid-elongated shapes. Its temperature optimum for growth is ca 22.5 °C with the upper limit of ca 32.5 °C. P. quercetorum differs from the morphologically related P. quercina in producing distinct submerged colony-patterns, different growth-temperature requirements, and oogonial shapes and sizes. Phylogenetic analyses using seven nuclear loci supported P. quercetorum as a novel species within clade 4, closely related to P. arecae, P. palmivora, P. megakarya, and P. quercina.

Interannual and interseasonal soil CO 2 efflux and VOC exchange rates in a Mediterranean holm oak forest in response to experimental drought

Climate models predict drier conditions in the next decades in the Mediterranean basin. Given the importance of soil CO 2 efflux in the global carbon balance and the important role of soil monoterpene and volatile organic compounds (VOCs) in soil ecology, we aimed to study the effects of the predicted drought on soil CO 2, monoterpenes and other VOC exchange rates and their seasonal and interannual variations. We decreased soil water availability in a Mediterranean holm oak forest soil by means of an experimental drought system performed since 1999 to the present. Measurements of soil gas exchange were carried out with IRGA, GC and PTR-MS techniques during two annual campaigns of contrasting precipitation. Soil respiration was twice higher the wet year than the dry year (2.27±0.26 and 1.05±0.15, respectively), and varied seasonally from 3.76±0.85 μmol m −2 s −1 in spring, to 0.13±0.01 μmol m −2 s −1 in summer. These results highlight the strong interannual and interseasonal variation in CO 2 efflux in Mediterranean ecosystems. The drought treatment produced a significant soil respiration reduction in drought plots in the wet sampling period. This reduction was even higher in wet springs (43% average reduction). These results show (1) that soil moisture is the main factor driving seasonal and interannual variations in soil respiration and (2) that the response of soil respiration to increased temperature is constrained by soil moisture. The results also show an additional control of soil CO 2 efflux by physiology and phenology of trees and animals. Soil monoterpene exchange rates ranged from −0.01 to 0.004 nmol m −2 s −1, thus the contribution of this Mediterranean holm oak forest soil to the total monoterpenes atmospheric budget seems to be very low. Responses of individual monoterpenes and VOCs to the drought treatment were different depending on the compound. This suggests that the effect of soil moisture reduction in the monoterpenes and VOC exchange rates seems to be dependent on monoterpene and VOC type. In general, soil monoterpene and other VOC exchange rates were not correlated with soil CO 2 efflux. In all cases, only a low proportion of variance was explained by the soil moisture changes, since almost all VOCs increased their emission rates in summer 2005, probably due to the effect of high soil temperature. Results indicate thus that physical and biological processes in soil are controlling soil VOC exchange but further research is needed on how these factors interact to produce the observed VOCs exchange responses.

Growth of ectomycorrhizal mycelia and composition of soil microbial communities in oak forest soils along a nitrogen deposition gradient

Deciduous forests may respond differently from coniferous forests to the anthropogenic deposition of nitrogen (N). Since fungi, especially ectomycorrhizal (EM) fungi, are known to be negatively affected by N deposition, the effects of N deposition on the soil microbial community, total fungal biomass and mycelial growth of EM fungi were studied in oak-dominated deciduous forests along a nitrogen deposition gradient in southern Sweden. In-growth mesh bags were used to estimate the production of mycelia by EM fungi in 19 oak stands in the N deposition gradient, and the results were compared with nitrate leaching data obtained previously. Soil samples from 154 oak forest sites were analysed regarding the content of phospholipid fatty acids (PLFAs). Thirty PLFAs associated with microbes were analysed and the PLFA 18:2omega6,9 was used as an indicator to estimate the total fungal biomass. Higher N deposition (20 kg N ha(-1)y(-1) compared with 10 kg N ha(-1)y(-1)) tended to reduce EM mycelial growth. The total soil fungal biomass was not affected by N deposition or soil pH, while the PLFA 16:1omega5, a biomarker for arbuscular mycorrhizal (AM) fungi, was negatively affected by N deposition, but also positively correlated to soil pH. Other PLFAs positively affected by soil pH were, e.g., i14:0, a15:0, 16:1omega9, a17:0 and 18:1omega7, while some were negatively affected by pH, such as i15:0, 16:1omega7t, 10Me17:0 and cy19:0. In addition, N deposition had an effect on the PLFAs 16:1omega7c and 16:1omega9 (negatively) and cy19:0 (positively). The production of EM mycelia is probably more sensitive to N deposition than total fungal biomass according to the fungal biomarker PLFA 18:2omega6,9. Low amounts of EM mycelia covaried with increased nitrate leaching, suggesting that EM mycelia possibly play an important role in forest soil N retention at increased N input.

Nitric oxide and nitrous oxide emission from Hungarian forest soils; linked with atmospheric N-deposition

Studies of forest nitrogen (N) budgets generally measure inputs from the atmosphere in wet and dry deposition and outputs via hydrologic export. Although denitrification has been shown to be important in many wetland ecosystems, emission of N oxides from forest soils is an important, and often overlooked, component of an ecosystem N budget. During 1 year (2002–03), emissions of nitric oxide (NO) and nitrous oxide (N 2O) were measured from Sessile oak and Norway spruce forest soils in northeast Hungary. Accumulation in small static chambers followed by gas chromatography-mass spectrometry detection was used for the estimation of N 2O emission flux. Because there are rapid chemical reactions of NO and ozone, small dynamic chambers were used for in situ NO flux measurements. Average soil emissions of NO were 1.2 and 2.1 μg N m −2 h −1, and for N 2O were 15 and 20 μg N m −2 h −1, for spruce and oak soils, respectively. Due to the relatively high soil water content, and low C/N ratio in soil, denitrification processes dominate, resulting in an order of magnitude greater N 2O emission rate compared to NO. The previously determined N balance between the atmosphere and the forest ecosystem was re-calculated using these soil emission figures. The total (dry+wet) atmospheric N-deposition to the soil was 1.42 and 1.59 g N m −2 yr −1 for spruce and oak, respectively, while the soil emissions are 0.14 and 0.20 g N m −2 yr −1. Thus, about 10–13% of N compounds deposited to the soil, mostly as NH 3 / NH 4 + and HNO 3 / NO 3 - , were transformed in the soil and emitted back to the atmosphere, mostly as greenhouse gas (N 2O).

CO 2 and N 2O emissions from gleyic soils in the Russian tundra and a German forest during freeze–thaw periods—a microcosm study

Knowledge is scarce on mineralization of soil organic carbon (SOC) in and N 2O emissions from tundra soils in periods of alternate freezing and thawing. Our objectives were to study the CO 2 and N 2O emissions from two silty gleyic soils formed in different climate zones (a gleyic Cryosol located in the Russian tundra, and a stagnic Gleysol located in an oak stand in central Germany) during freeze–thaw events. Soils were adjusted to a matric potential of −0.2 kPa and emissions were measured in 3-h intervals during an incubation period of 50 days including three freeze–thaw cycles. CO 2 emissions from the German oak forest soil were twofold higher than those of the tundra soil. The ratios of the mean CO 2 production rate before the freezing to the mean CO 2 production rate after thawing ranged from 0.63 to 0.73 for the forest soil and from 0.85 to 0.89 for the tundra soil. The specific CO 2-C production rate (CO 2-C/SOC) was 0.16 for the tundra soil and 0.57 for the forest soil. The results indicate that bioavailability of SOC was markedly smaller in the tundra soil than in the forest soil. Large N 2O emissions were found for the German forest soil, but no N 2O emissions were observed for the tundra soil. The main reason for the absence of N 2O emissions was most likely the negligible availability of nitrate for denitrification. There was some indication that the initial increase in mineralization of SOC induced by freezing and thawing differs between soils from various climatic regions, probably mainly due to a differing bioavailability of the SOC and differing releases of nutrients after thawing.

Production of ligninolytic enzymes by litter-decomposing fungi and their ability to decolorize synthetic dyes

Litter-decomposing basidiomycete fungi (LDF) including environmental isolates from oak forest soil were compared with white-rot fungi for ligninolytic enzymes production and decolorization of synthetic dyes Poly B-411, Reactive Black 5, Reactive Orange 16 and Remazol Brilliant Blue R (RBBR). LDF differed significantly in laccase production. Mycena inclinata and Collybia dryophila produced significant amounts of the enzyme during the whole experiment, while the production in Stropharia rugosoannulata started after 3 weeks of cultivation. Soil isolates exhibited detectable though very low laccase activity. The highest activity of Mn-peroxidase was detected in the cultures of C. dryophila with the peak activities over 30 U l −1. In all other strains, Mn-peroxidase activity did not exceed 3 U l −1. The decolorization of 100 mg l −1 dyes after 28 days ranged 80–95% for RBBR, 60–95% for Poly B-411, 58–85% for Reactive Black 5 and 45–82% for Reactive Orange 16. The fastest degradation of Poly B-411 was performed by the strains with high levels of laccase and MnP while the decolorization of other dyes did not depend so strictly on enzyme activities. The highest decolorization of azo dyes was achieved with the LDF C. dryophila, S. rugosoannulata and the soil isolates. The presence of dyes significantly affected enzyme activities in fungal cultures.

Effect of temperature and moisture on rates of carbon mineralization in a Mediterranean oak forest soil under controlled and field conditions

SummaryWe examined the relationship between carbon mineralization (Cmin), moisture and temperature in a Mediterranean forest soil under controlled and field conditions. We studied the following.1 The temperature sensitivity at three soil depths: soil samples were incubated at 4, 10, 20 and 30°C at optimal water content of 60% of water holding capacity (WHC). Values ofCminof the top layer were more than 12 times faster than those measured in deeper layers. We found a temperature sensitivity factor (Q10) of 3.3, 2.7 and 2.2 for the 0–5 cm, 5–10 cm and 10–20 cm layers, respectively.2 The relationship betweenCmin, moisture and temperature (top layer). The sensitivity ofCminto fluctuating moisture depended on temperature. However, theQ10was not significantly affected by soil moisture. We fitted a multiple polynomial model that predictedCminas a multiplicative function of temperature and moisture (R2 > 0.99).3 The response ofCminof soil to rewetting after 1 and 24 hours. In all cases, the response was rapid. The soil incubated at 60% WHC or less responded positively to a sudden increase in water content, with the largest increase in the 20% WHC treatment. The model predictedCminin the field well when rewetting effects were taken into account (R2 > 0.81).These results indicate that sudden changes in soil moisture can lead to increased carbon mineralization during the dry summer. It is necessary to include such responses in models as they may represent a substantial loss of carbon in the overall carbon balance of Mediterranean ecosystems.

A new species of Protoachlya Upadhyay & Khulbe.

Protoachlya nainitalensis isolated from mixed oak forest soil (Quercus leucotrichophora & Q. floribunda) is described herein. The species is characterised by elongated, cylindrical, smooth walled zoosporangia; spherical and smooth walled oogonia with androgynous and rarely diclinous branches of antheridia. A simplified key of the known Protoachlya species has also been established.

The effect of nitrogen deposition on nitrification, carbon and nitrogen mineralisation and litter C:N ratios in oak ( Quercus robur L.) forests

The present study addresses the question why there is a positive relationship between nitrogen deposition and potential net nitrogen mineralisation and nitrification in oak ( Quercus robur L.) forest soils in south Sweden ( Falkengren-Grerup et al., 1998), and how this is related to the carbon mineralisation. We tested three hypotheses based on European studies ( Persson et al., 2000a,b) that postulate lower availability of carbon due to chemical binding of nitrogen to lignin remains and phenolic compounds or a more decomposed, recalcitrant organic matter due to faster initial decomposition rates of fresh litter. This in turn leads to increased net nitrogen mineralisation, and nitrifiers that may adapt to acid soils when ammonium availability increases. We used soils from two regions exposed to a total deposition of 17 and 10 kg N ha −1 per year and incubated the soils in the laboratory separately as well as in mixtures between the regions. To be able to evaluate how the microbial communities and organic matter interacted in the soil mixtures, we divided the observed values of the net carbon and nitrogen mineralisation and nitrification for the soil mixtures by the calculated expected values. C:N ratios of litter, fresh leafs of Deschampsia flexuosa and microbial biomass were also measured. Contrary to the assumptions in the hypothesis, the soil respiration was somewhat higher in soils subjected to high nitrogen deposition. Furthermore, the observed rate of nitrogen mineralisation was higher than expected in the majority of soil mixtures, while observed rates of carbon mineralisation only showed a weak tendency to be higher than expected. All the results taken together indicate that there has been a positive change in litter quality that leads to increased carbon and nitrogen mineralisation. This conclusion is supported by the C:N ratio of oak litter and fresh leaves of Deschampsia flexuosa that was lower in the most nitrogen-exposed sites and which might indicate an increase in decomposability. The observed values of nitrification were significantly higher than the calculated expected values. Thus, the increased net nitrogen mineralisation in the region with high nitrogen deposition seems to allow nitrifiers to adapt to these acid soils when they are no longer limited by ammonium.