Carbon dioxide emissions of soils under pure and mixed stands of beech and spruce, affected by decomposing foliage litter mixtures

Soil respiration is the largest terrestrial source of CO₂ to the atmosphere. In forests, roughly half of the soil respiration is autotrophic (mainly root respiration) while the remainder is heterotrophic, originating from decomposition of soil organic matter. Decomposition is an important process for cycling of nutrients in forest ecosystems. Hence, tree species induced changes may have a great impact on atmospheric CO₂ concentrations. Since studies on the combined effects of beech-spruce mixtures are very rare, we firstly measured CO₂ emission rates in three adjacent stands of pure spruce (Picea abies), mixed spruce-beech and pure beech (Fagus sylvatica) on three base-rich sites (Flysch) and three base-poor sites (Molasse; yielding a total of 18 stands) during two summer periods using the closed chamber method. CO₂ emissions were higher on the well-aerated sandy soils on Molasse than on the clayey soils on Flysch, characterized by frequent water logging. Mean CO₂ effluxes increased from spruce (41) over the mixed (55) to the beech (59) stands on Molasse, while tree species effects were lower on Flysch (30-35, mixed > beech = spruce; all data in mg CO₂-C m⁻² h⁻¹). Secondly, we studied decomposition after fourfold litter manipulations at the 6 mixed species stands: the O_i - and O_e horizons were removed and replaced by additions of beech -, spruce - and mixed litter of the adjacent pure stands of known chemical quality and one zero addition (blank) in open rings (20 cm inner diameter), which were covered with meshes to exclude fresh litter fall. Mass loss within two years amounted to 61-68% on Flysch and 36-44% on Molasse, indicating non-additive mixed species effects (mixed litter showed highest mass loss). However, base cation release showed a linear response, increasing from the spruce - over the mixed - to the beech litter. The differences in N release (immobilization) resulted in a characteristic converging trend in C/N ratios for all litter compositions on both bedrocks during decomposition. In the summers 2006 and 2007 we measured CO₂ efflux from these manipulated areas (a closed chamber fits exactly over such a ring) as field indicator of the microbial activity. Net fluxes (subtracting the so-called blank values) are considered an indicator of litter induced changes only and increased on both bedrocks from the spruce - over the mixed - to the beech litter. According to these measurements, decomposing litter contributed between 22-32% (Flysch) and 11-28% (Molasse) to total soil respiration, strengthening its role within the global carbon cycle.     

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

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

The excretion of ammonium by enchytraeids (Cognettia sphagnetorum)

Enchytraeids are involved both directly and indirectly in decomposition processes and nitrogen mineralization in soil. Their influence is especially important in nitrogen poor ecosystems such as heathland where the enchytraeid species, Cognettia sphagnetorum, is often abundant and playing a significant role in the N-cycling. The objective of this study was to quantify NH₄⁺-N excretion of C. sphagnetorum at different temperatures. The results were combined with investigations of population dynamics during one year to estimate annual NH₄⁺-N excretion of the population of C. sphagnetorum in a dry Danish heath soil. C. sphagnetorum significantly increased its NH₄⁺-N excretion rate with increasing temperature. At 5 °C about 0.5 μg NH₄⁺-N mg dry weight⁻¹ day⁻¹ was excreted increasing to about 3.3 μg NH₄⁺-N mg dry weight⁻¹ day⁻¹ at 20 °C. Average enchytraeid biomass in the field was 2.5-3.5 g dry weight m⁻² during cool and wet periods. Dry and warm conditions in May and June, 2008, had a drastic and long-term negative impact on the enchytraeid community. The excretion of NH₄⁺-N by enchytraeids was therefore highest during the cool and moist months despite low temperatures (October 2007-May 2008) and amounted to about 2 mg NH₄⁺-N m⁻² day⁻¹ during this period. The estimated annual NH₄⁺-N excretion of the enchytraeid community was approximately 0.3 g N m⁻² year⁻¹. The results of the present study and the method described for estimation of N-excretion can increase our understanding of enchytraeids’ role in nitrogen mineralization.     

Dynamics and stratification of Enchytraeidae in the organic layer of a Scots pine forest

In a Dutch Scots pine forest an experiment was conducted to quantify the role of soil biota in the functioning of the soil ecosystem, and the effects of enhanced nitrogen deposition. For this, the site was sampled at 8-week intervals during 2.5 years. This paper reports on the population dynamics of enchytraeids in the field and in stratified litterbags. Mean yearly abundance of the enchytraeid community in the field was 47 600 m^–2, or 0.70 g (dry weight) m^–2. The community consisted mainly of three species: Cognettia sphagnetorum, Marionina clavata and Achaeta eiseni, of which C. sphagnetorum was dominant. The enchytraeid populations showed a marked stratification in the same sequence. Freshly fallen pine needles were colonized by C. sphagnetorum, while other species followed much later. It was found that data from the litterbags were reasonably comparable with field data, when expressed per gram of dry substrate, but less so when expressed per square metre. Multiple regression analysis of the data showed that the population dynamics in the litter layer could largely be explained by temperature and moisture fluctuations; in deeper layers other factors, such as the stage of decomposition, were probably more important. Received: 26 June 1997     

Litter- and ecosystem-driven decomposition under elevated CO2 and enhanced N deposition in a Sphagnum peatland

Peatlands represent massive global C pools and sinks. Carbon accumulation depends on the ratio between net primary production and decomposition, both of which can change under projected increases of atmospheric CO₂ and N deposition. The decomposition of litter is influenced by 1) the quality of the litter, and 2) the microenvironmental conditions in which the litter decomposes. This study aims at experimentally testing the effects of these two drivers in the context of global change. We studied the in situ litter decomposition from three common peatland species (Eriophorum vaginatum, Polytrichum strictum and Sphagnum fallax) collected after one year of litter production under pre-treatment conditions (elevated CO₂: 560 ppm or enhanced N: 3 g m⁻² y⁻¹ NH₄NO₃) and decomposed the following year under treatment conditions (same as pre-treatment). By considering the cross-effects between pre-treatments and treatments, we distinguished between the effects on mass loss of 1) the pre-treatment-induced litter quality and 2) the treatment conditions under which the litters were decomposing. The combination between CO₂ pre-treatment and CO₂ treatment reduced Polytrichum decomposition by −24% and this can be explained by litter quality-driven decomposition changes brought by the pre-treatment. CO₂ pre-treatment reduced Eriophorum litter quality, although this was not sufficient to predict decomposition. The N addition pre-treatment reduced the decomposition of Eriophorum, due to enhanced lignin and soluble phenols concentrations in the initial litter, and reduced litter-driven losses of starch and enhanced litter-driven losses of soluble phenols. While decomposition indices based on initial litter quality provide a broad explanation of quantitative and qualitative decomposition, they can only be taken as first approximations. Indeed, the microbial ATP activity, the litter N loss and resulting litter quality, were strongly altered irrespective of the compounds' initial concentration and by means of processes that occurred independently of the initial litter-qualitative changes. The experimental design was valuable to assess litter- and ecosystem-driven decomposition pathways simultaneously or independently. The ability to separate these two drivers makes it possible to attest the presence of litter-qualitative changes even without any litter biochemical determinations, and shows the screening potential of this approach for future experiments dealing with multiple plant species.     

Foliar exchange of mercury vapor: Evidence for a compensation point

Historical studies for crop and weed species documented elemental Hg vapor (Hg°) deposition to foliage, but they used Hg° concentrations that were orders of magnitude higher than levels now known to occur under background conditions, possibly creating artificially high gradients between the atmosphere and landscape surfaces. Measurements of Hg° exchange with white oak (Quercus alba L.), red maple (Acer rubrum L.), Norway spruce (Picea abies L.), and yellow-poplar (Liriodendron tulipifera L.) foliage were conducted in an open gas exchange system that allows for simultaneous measurements of CO₂, H₂O and Hg° exchange under controlled environmental conditions. When Hg° concentrations were held at 0.5 to 1.5 ng m^?3, red maple (Acer rubrum L.), Norway spruce (Picea abies L.), yellow-poplar (Liriodendron tulipifera L.), and white oak (Quercus alba L.) foliage exhibited mean Hg° emissions of 5.5, 1.7, 2.7, and 5.3 ng m^?2 h^?1, respectively. At Hg° concentrations between 9 and 20 ng m^?3 little net exchange of Hg° was observed. However at concentrations between 50 and 70 ng m^?3 the Hg° was deposited to foliage at rates between 22 and 38 ng m^?2 h^?1. These data suggest that dry foliar surfaces in terrestrial forest landscapes may be a dynamic exchange surface that can function as a source or sink dependent on the magnitude of current Hg° concentrations. These data provide evidence of species-specific compensation concentrations (or compensation points) for Hg° deposition to seedling foliage in the 10–25 ng m^?3 range.     

Deciduous woodland exposed to elevated atmospheric CO2 has species-specific impacts on anecic earthworms

Elevated atmospheric CO₂ induced reductions in litter quality can adversely affect earthworms. However, this understanding is based on laboratory rather than field research and relates to single earthworm and tree species. Here earthworm populations were investigated under Alnus glutinosa, Betula pendula, and Fagus sylvatica in a Free Air Carbon dioxide Enrichment field experiment. Litters from this experiment were also fed to Lumbricus terrestris L. at two rates with live weight change and cast properties assessed. Elevated CO₂ (580 ppmv) reduced litter N (−12%) with a corresponding increase in C:N ratio, especially for A. glutinosa. In the field, elevated CO₂ caused a shift in overall population composition, mainly characterised by reduced anecic biomass (–25%); endogeic and epigeic species were less affected. CO₂ effects on total biomass were most pronounced for A. glutinosa (e.g. field total biomass −47% vs. −11% overall). Growth of L. terrestris was lower when fed elevated CO₂ litter (−18%), although increased inputs of A. glutinosa litter mitigated this effect. In mesocosms, fresh cast respiration was lower (−14%) for elevated CO₂ litter, an effect more pronounced for A. glutinosa (−24%). When normalised for C content, elevated CO₂ effects on cast respiration were again negative and most marked for A. glutinosa litter. Litter N concentration, and possibly ease of litter mineralisation were factors affecting litter resource quality Litter N and P concentrations varied with A. glutinosa > B. pendula > F. sylvatica; F. sylvatica had the highest cellulose content. Field earthworm biomass was higher under A. glutinosa compared with B. pendula and F. sylvatica (+17 and +70%, respectively); live weight increased with A. glutinosa litter in the feeding trial almost three times more than for B. pendula, whereas it decreased for F. sylvatica. Cast respiration was highest for A. glutinosa, intermediate for B. pendula (ca. −36%) and lowest for F. sylvatica (ca. −78%). Earthworm responses to elevated CO₂ were complex, being characteristic of individual tree and earthworm species; responses were more adverse for trees with higher quality litter and for anecic earthworms.     

Changes in the earthworm community of an acidophilous lowland beech forest during a stand rotation

The study examines humus profile development during a chronosequence consisting of four beech forest growth stages, and particularly the role of some components of soil fauna (lumbricid oligochaetes) on humus morphogenesis. An experimental site was set up in a lowland beech forest (Fougères state forest, eastern Brittany, France) to carry out a chronosequence analysis. This lowland beech forest is acidophilous, managed as an even-aged beech stand. The dominant tree species is beech (Fagus sylvatica L.). Samples were taken twice a year, from autumn 1997 to spring 2000 inclusive. Earthworms were caught after watering with formalin solutions. Only five species were found: three epigeic (litter-dwellers): Dendrobaena octaedra, D. rubida tenuis, Eisenia eiseni; one epi-anecic (litter/soil-dweller): Lumbricus rubellus; one endogeic (soil-dweller): Allolobophora caliginosa. D. octaedra is dominant in the four plots at densities ranging from 41 ind·m^–2 (88 % of total earthworm population) to 12.4 ind·m^–2 (99 % of total). Species richness and abundance are low in accordance with a moder humus form typical of acid soil conditions. Results are discussed according to plot heterogeneity, stand age, seasonal variations and functional diversity.     

Nitrous oxide emissions from a bermudagrass pasture: Interseeded winter rye and poultry litter

Adequate use of manure in grasslands may constitute an economical means of manure disposal and an abundant source of nutrients for plants; however, excessive nitrogen (N) additions to these soils could create new environmental risks such as increasing nitrous oxide (N₂O) emissions. These potentially adverse effects in grasslands may be mitigated by improved management practices. In pasture systems, the combined effects of poultry litter applications and interseeded rye (Secale cereale L.) on N₂O emissions are still not well established. This study was conducted to estimate the magnitude of soil surface N₂O fluxes as affected by interseeded winter rye forage, annually spring-applied composted turkey litter as well as by weather and soil parameters. Fluxes were measured by vented chambers during 2 yr in a bermudagrass (Cynodon dactylon [L.] Pers.) pasture in moderately well-drained Tonti gravelly silt loam (fine-loamy, active, mesic Typic Fragiudault) located in northwestern Arkansas, USA. During the 60 d following turkey litter applications, N₂O fluxes were frequently well correlated with soil nitrate (NO₃⁻; r: up to 0.82, P's < 0.05) implying substrate stimulation on soil N₂O production. Likewise, rainfall patterns strongly influenced N₂O fluxes. Large rainfalls of 91 and 32 mm occurred within 6 d prior to the maximum N₂O flux means (263 and 290 μg N m⁻² h⁻¹, respectively). Treatment effects on N₂O emissions were significant only in spring periods following manure addition, particularly in the second year of our study. In the spring of 2000, additions of composted turkey litter resulted in 1.5-fold increase in seasonal cumulative N₂O emissions (P = 0.04) which was directly associated to a numerically greater soil NO₃⁻. In the spring of 2001, soils planted to rye exhibited a pronounced significant effect on mitigating N₂O emissions (30 vs. 112 mg N m⁻²; P = 0.04). During the winter and early spring, rye growth also decreased quantities of both soil NO₃⁻ and water-filled pore space (WFPS) partly accounting for the lower N₂O emissions in these fields. These results suggest that because poultry litter additions increased and interseeded rye diminished N₂O emissions, the combined implementation of both management practices can produce environmental benefits while sustaining productivity in temperate pasture systems.     

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.     

Can field populations of the enchytraeid,Cognettia sphagnetorum,adapt to increased drought stress?

The ability to evolve increased drought tolerance in response to climate change was investigated in the enchytraeid, Cognettia sphagnetorum. Populations exposed to reduced precipitation or increased night time temperature for more than six years were collected in mixed Calluna/grass heathland at the Mols Laboratory, Denmark. The level of prolonged drought and increased temperature corresponded to a predicted climate change scenario and has been applied since 1999. In autumn 2005, enchytraeids were sampled in 3 cm intervals down to 9 cm depth and total number, biomass, diversity and soil organic matter were determined. The drought treatment resulted in a significant reduction of the density and biomass of enchytraeids, as well as changes in the species composition. In total, five different genera were found at the site in all three treatments (control, temperature and drought). C. sphagnetorum was the dominant species, especially in the upper 0–3 cm, and was clearly affected by the drought treatment. C. sphagnetorum from all plots were cultured in the laboratory to rear second or third generation adults. Results showed that populations of drought treated plots had not developed an increased drought resistance compared to populations of control or warming plots even after several years of a putative severe selection. Lack of adaptive potential in C. sphagnetorum suggests that more frequent periods with drought in the future will have a very strong negative influence on enchytraeid density, biomass and diversity.     

Overgrazing and soil carbon dynamics in the western Chaco of Argentina

Very little is known about the effect of overgrazing on carbon loss from soil in semi-arid savannas and woodlands of South America. Soil carbon parameters were measured in a 10,000 ha restoration project in the western Chaco of Argentina (24°43′S and 63°17′W). Three situations were compared: highly restored (HRS), moderately restored (MRS) and highly degraded (HDS). Soil and litter samples were recovered in the dry and wet seasons. SOC and CO₂–C values decreased from the HRS (7.0 kg m⁻² and 130 g m⁻²) to the HDS (1.5 kg m⁻² and 46 g m⁻²) whereas the C mineralization rate increased toward the less restored sites (0.96–2.29). Surface-litter C was similar in both sites under restoration (260 and 229 g m⁻²), being non-existent at the HDS. Leaves from woody species dominated surface-litter in the HRS, whereas grass material was predominant in the MRS. During the wet season, the SOC decreased, whereas both CO₂–C and C mineralization rate increased. The magnitude of the between-season differences was highest at the HDS (62% in SOC, 55% in CO₂, and 80% in C mineralization rate). We estimated that C loss since introduction of cattle into the forest was 58 Mg ha⁻¹, reaching a total of 2×10¹⁵ g at for the entire Chaco. These values are higher than those caused by the conversion of savannas and other ecosystems into agriculture or cultivated pastures. The amount of C fixed in the highly restored site (275 g ha⁻¹ per year) indicates that the Chaco soils have a significant potential as atmospheric carbon sinks.     

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

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

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

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

Accounting for variability in soil microbial communities of temperate upland grassland ecosystems

This study aimed to determine the factors which regulate soil microbial community organisation and function in temperate upland grassland ecosystems. Soil microbial biomass (C_mic), activity (respiration and potential carbon utilisation) and community structure (phospholipid fatty acid (PLFA) analysis, culturing and community level physiological profiles (CLPP) (Biolog^®)) were measured across a gradient of three upland grassland types; Festuca–Agrostis–Galium grassland (unimproved grassland, National Vegetation Classification (NVC) — U4a); Festuca–Agrostis–Galium grassland, Holcus–Trifolium sub-community (semi-improved grassland, NVC — U4b); Lolium–Cynosurus grassland (improved grassland, NVC — MG6) at three sites in different biogeographic areas of the UK over a period of 1 year. Variation in C_mic was mainly due to grassland type and site (accounting for 55% variance, v, in the data). C_mic was significantly (P<0.001) high in the unimproved grassland at Torridon (237.4 g C m⁻² cf. 81.2 g C m⁻² in semi- and 63.8 g C m⁻² in improved grasslands) and Sourhope (114.6 g C m⁻² cf. in 44.8 g C m⁻² semi- and 68.3 g C m⁻² in improved grasslands) and semi-improved grassland at Abergwyngregyn (76.0 g C m⁻² cf. 41.7 g C m⁻² in un- and 58.3 g C m⁻² in improved grasslands). C_mic showed little temporal variation (v=3.7%). Soil microbial activity, measured as basal respiration was also mainly affected by grassland type and site (n=32%). In contrast to C_mic, respiration was significantly (P<0.001) high in the improved grassland at Sourhope (263.4 l h⁻¹m⁻² cf. 79.6 l h⁻¹m⁻² in semi- and 203.9 l h⁻¹m⁻² unimproved grasslands) and Abergwyngregyn (198.8 l h⁻¹m⁻² cf. 173.7 l h⁻¹m⁻² in semi- and 88.2 l h⁻¹m⁻² unimproved grasslands). Microbial activity, measured as potential carbon utilisation, agreed with the respiration measurements and was significantly (P<0.001) high in the improved grassland at all three sites (A₅₉₀ 0.14 cf. 0.09 in semi- and 0.07 in unimproved grassland). However, date of sampling also had a significant (P<0.001) impact on C utilisation potential (v=24.7%) with samples from April 1997 having highest activity at all three sites. Variation in microbial community structure was due, predominantly, to grassland type (average v=23.6% for bacterial and fungal numbers and PLFA) and date of sampling (average v=39.7% for bacterial and fungal numbers and PLFA). Numbers of culturable bacteria and bacterial PLFA were significantly (P<0.001) high in the improved grassland at all three sites. Fungal populations were significantly (P<0.01) high in the unimproved grassland at Sourhope and Abergwyngregyn. The results demonstrate a shift in soil microbial community structure from one favouring fungi to one favouring bacteria as grassland improvement increased. Numbers of bacteria and fungi were also significantly (P<0.001) higher in August than any other sampling date. Canonical variate analysis (CVA) of the carbon utilisation data significantly (P<0.05) differentiated microbial communities from the three grassland types, mainly due to greater utilisation of sugars and citric acid in the improved grasslands compared to greater utilisation of carboxylic acids, phenolics and neutral amino acids in the unimproved grasslands, possibly reflecting substrate availability in these grasslands. Differences in C_mic, activity and community structure between grassland types were robust over time. In addition, broad scale measures of microbial growth and activity (C_mic and respiration) showed little temporal variation compared to measures of soil microbial community structure, which varied quantitatively with respect to environmental variables (temperature, moisture) and plant productivity, hence substrate supply.     

Inter- and intra-specific interactions of Lumbricus rubellus (Hoffmeister, 1843) and Octolasion lacteum (Örley, 1881) (Lumbricidae) and the implication for C cycling

Earthworms are important engineering species of many terrestrial ecosystems as they play a significant role in regulating C turnover. The effects of earthworms on moderating C decomposition processes differ across species and with interactions between species, which is not fully understood. We carried out an experiment to study the interactions of Lumbricus rubellus and Octolasion lacteum, and their effects on soil respiration. Laboratory mesocosms were set up using tulip poplar (Liriodendron tulipifera) leaf litter and varying densities of earthworms in single and combined species treatments. CO₂ efflux rate was used as an indicator of C decomposition rates, and measured with CO₂ sensors every five days over one month. L. rubellus induced higher leaf consumption rate and higher CO₂ efflux than O. lacteum; meanwhile O. lacteum grew more than L. rubellus. Both litter consumption rate and growth rate of earthworms decreased with increasing earthworm density. Soil CO₂ efflux increased with increasing earthworm density (from ∼1-2 μg CO₂ g⁻¹ hr⁻¹ with no earthworms to ∼ 4 μg CO₂ g⁻¹ hr⁻¹ with 8 earthworms). Combining the two species had a synergistic effect on leaf litter consumption, and neutralizing effects on soil respiration. The data suggest that the strength of intra- and inter-specific interactions among earthworm ecological groups varies at different absolute and relative densities, leading to altered leaf litter decomposition and C cycling.     

Distribution pattern of woodlice (Isopoda) and millipedes (Diplopoda) in four primeval forests of the Western Carpathians (Central Slovakia)

We collected 1605 isopod individuals (eight species) and 671 diplopod individuals (17 species) in four primeval forests of the Western Carpathians, Central Slovakia, by leaf litter extraction. The forests are of different temperate deciduous forest types varying in tree species, aspect, elevation and soil characteristics. The oak forests, established on southwest oriented slopes at an elevation of 280-600 m, were characterized by Hyloniscus riparius, Porcellium conspersum, Enantiulus nanus and Ophioiulus pilosus. The beech forests, established on northeast oriented slopes at an elevation of 700-1100 m, were characterised by Ligidium hypnorum, Trachysphaera costata and Polyzonium germanicum. A remarkable increase of the total number of species and individuals occurred in both forest types adjacent to coarse woody debris (CWD). Woodlice density close to CWD was between 200 and 630 individuals m⁻² (35-130 individuals m⁻² distant from CWD); millipede density close to CWD ranged from 60 to 230 individuals m⁻² (15-75 individuals m⁻² distant from CWD). Species richness of both taxa close to CWD varied from 13 to 16 species m⁻² (7-12 species m⁻² distant from CWD). Thus, CWD has a significant influence on saprophages. However, structural components such as CWD and the amount of leaf litter did not significantly alter species assemblages. Species at sites distant from CWD were a subset of species at sites close to CWD. According to a canonical correspondence analysis (CCA), ‘forest type’ and ‘elevation within a slope’, as well as chemistry of the upper soil layer, i.e. ‘acidification’ and ‘nutrition’, strongly influenced species assemblages.     

Comparison of the eddy covariance and automated closed chamber methods for evaluating nocturnal CO2 exchange in a Japanese cypress forest

Underestimation of nocturnal CO₂ respiration using the eddy covariance method under calm conditions remains an unsolved problem at many flux observation sites in forests. To evaluate nocturnal CO₂ exchange in a Japanese cypress forest, we observed CO₂ flux above the canopy (F_c), changes in CO₂ storage in the canopy (S_t) and soil, and trunk and foliar respiration for 2 years (2003–2004). We scaled these chamber data to the soil, trunk, and foliar respiration per unit of ground area (F_s, F_t, F_f, respectively) and used the relationships of F_s, F_t, and F_f with air or soil temperature for comparison with canopy-scale CO₂ exchange measurements (=F_c + S_t). The annual average F_s, F_t, and F_f were 714 g C m⁻² year⁻¹, 170 g C m⁻² year⁻¹, and 575 g C m⁻² year⁻¹, respectively. At small friction velocity (u_*), nocturnal F_c + S_t was smaller than F_s + F_t + F_f estimated using the chamber method, whereas the two values were almost the same at large u_*. We replaced F_c + S_t measured during calm nocturnal periods with a value simulated using a temperature response function derived during well-mixed nocturnal periods. With this correction, the estimated net ecosystem exchange (NEE) from F_c + S_t data ranged from −713 g C m⁻² year⁻¹ to −412 g C m⁻² year⁻¹ in 2003 and from −883 g C m⁻² year⁻¹ to −603 g C m⁻² year⁻¹ in 2004, depending on the u_* threshold. When we replaced all nocturnal F_c + S_t data with F_s + F_t + F_f estimated using the chamber method, NEE was −506 g C m⁻² year⁻¹ and −682 g C m⁻² year⁻¹ for 2003 and 2004, respectively.     

Microbial biomass and activity in soil and litter underPinus sylvestris, Picea abies andBetula pendula at originally similar field afforestation sites

Microbial biomass C and N, and activities related to C and N cycles, were compared in needle and leaf litter, and in the uppermost 10 cm of soil under the litter layer in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) stands, planted on originally similar field afforestation sites 23–24 years ago. The ground vegetation was differentiated under different tree species, consisting of grasses and herbs under birch and pine, and mosses or no vegetation with a thick layer of needles under spruce. The C:N ratio of the soils was 13–21 and the soil pH_{CaCl 2} 3.8–5.2. Both showed little variation under different tree species. Microbial biomass C and N, C mineralization, net ammonification, reduction) did not differ significantly in soil under different tree species either. Birch leaf litter had a higher pH_{CaCl 2} (5.9) than spruce and pine needle litter (pH 5.0 and 4.8, respectively). The C:N ratio of spruce needles was 30, and was considerably higher in pine needles (69) and birch leaves (54). Birch leaves tended to have the highest microbial biomass C and C mineralization. Spruce needles appeared to have the highest microbial biomass N and net formation of mineral N, whereas formation of mineral N in pine needles and birch leaves was negligible. Microbial biomass C and N were of the same order of magnitude in the soil and litter samples but C mineralization was tenfold higher in the litter samples.     

Are enchytraeid worms (Oligochaeta) sensitive indicators of ammonia-N impacts on an ombrotrophic bog?

Enchytraeid worms (Oligochaeta) are the dominant mesofauna in wet acidic habitats. They have key roles in biogeochemical cycling, and can be used as biological indicators. Here we report the response of these worms to in situ ammonia-N (NH₃-N) deposition on an ombrotrophic bog. Three years of NH₃-N fumigation from an automated release system has created a gradient of NH₃-N concentrations downwind of the release pipe ranging from 83 μg m⁻³ (near source) to 4.5 μg m⁻³ NH₃-N (60 m from release pipe); the ambient NH₃-N concentration is 0.56 μg m⁻³ NH₃-N. Peat pH and mineral N content have increased near the ammonia release pipe. We hypothesised that enhanced N deposition at the site would have improved litter quality and thus, enchytraeid distribution would be increased along the transect compared to ambient. However, neither litter quality nor enchytraeid abundance and diversity were affected by NH₃-N despite increases in peat pH and mineral N. This suggests that three years of ammonia fumigation was not enough time for plant matter exposed to ammonia to become incorporated into the peat litter layer. Enchytraeids appear not to be sensitive indicators of NH₃ fumigation because there was no effect below-ground of peat chemistry on litter quality.