A reciprocal decomposition experiment of Scots pine needles 19 yr after wood ash fertilization

Scots pine (Pinus sylvestris) needle litter originating from control plots and plots that had received a wood ash fertilization (3 t ha⁻¹) 19 yr earlier were allowed to decompose in a reciprocal experimental design to detect the effects of ash fertilization and needle litter origin on the decomposition rate. The experimental design was repeated in two Scots pine forest stands of different fertility and the litterbags were harvested after 4 and 16 months. Ash fertilization resulted in a higher needle litter decomposition rate but the needle origin did not influence the results. Stand fertility correlated positively to the decomposition rate.     

Litter type, but not plant cover, regulates initial litter decomposition and fungal community structure in a recolonising cutover peatland

Cutover peatlands are often rapidly colonised by pioneer plant species, which have the potential to affect key ecosystem processes such as carbon (C) turnover. The aim of this study was to investigate how plant cover and litter type affect fungal community structure and litter decomposition in a cutover peatland. Intact cores containing Eriophorum vaginatum, Eriophorum angustifolium, Calluna vulgaris and bare soil were removed and a mesh bag with litter from only one of each of these species or fragments of the moss Sphagnum auriculatum was added to each core in a factorial design. The presence or absence of live plants, regardless of the species, had no effect on mass loss, C, nitrogen (N) or phosphorus (P) concentrations of the litter following 12 months of incubation. However, there was a very strong effect of litter type on mass loss and concentrations of C, N and P between most combinations of litter. Similarly, plant species did not affect fungal community structure but litter type had a strong effect, with significant differences between most pairs of litter types. The data suggest that labile C inputs via rhizodeposition from a range of plant functional types that have colonised cutover bogs for 10-15 years have little direct effect on nutrient turnover from plant litter and in shaping litter fungal community structure. In contrast, the chemistry of the litter they produce has much stronger and varied effects on decomposition and fungal community composition. Thus it appears that there is distinct niche differentiation between the fungal communities involved in turnover of litter versus rhizodeposits in the early phases of plant succession on regenerating cutover peatlands.     

Ant-mediated effects on spruce litter decomposition, solution chemistry, and microbial activity

Forest management practices often generate clear-cut patches, which may be colonized by ants not present in the same densities in mature forests. In addition to the associated changes in abiotic conditions ants can initiate processes, which do not occur in old-growth stands. Here, we analyse the effects of ants and aphid honeydew on litter solution of Norway spruce, microbial enzyme activities, and needle decomposition in a field and greenhouse experiment during summer 2003. In the field, low ant densities had relatively little effects on litter solution 30 cm away from a tree trunk, but significantly increased organic carbon concentrations and decreased inorganic nitrogen concentrations next to a trunk where ants tend to build their nests. In a greenhouse experiment, the addition of ants to lysimeters containing spruce litter significantly increased dissolved organic carbon (DOC), dissolved organic nitrogen (DON), NH₄-N, NO₃-N and K concentrations in litter solutions compared to the control treatment, while the simulation of aphid infestation (addition of honeydew) significantly increased DOC as a direct result of honeydew leaching, and decreased inorganic N concentrations in leachates. The presence of ants resulted in a changed composition of dissolved organic matter (DOM) with more aromatic and complex compounds, and microbial enzyme activity was significantly higher in litter extracts from the ant treatment compared to the honeydew and control treatment. However, mass loss, litter %C and %N were not affected by ants or honeydew. Our results suggest that ants have a distinct and immediate effect on solution composition and microbial activity in the litter layer indicating accelerated litter decay whereas the effect of honeydew was insignificant.     

Fungal colonization as affected by litter depth and decomposition stage of needle litter

The present study was designated to evaluate the relative effects of litter depth and decomposition stage of needles on fungal colonization of needle litter in field experiments. The experiment was carried out in coniferous temperate forests in central Japan. Needle litter of Chamaecyparis obtusa and Pinus pentaphylla var. himekomatsu at two decomposition stages (recently dead and partly decomposed) were placed into the organic layer at two depths (on the surface of and beneath the litter layer). Fungal colonization of needles after 1 year was examined in terms of hyphal abundance and frequency of fungal species. Total and live hyphal length on needles were affected by the litter depth and (or) the decomposition stage of needles. Length of darkly pigmented hyphae on needles was 1.7-2.6 times greater beneath the litter layer than on the litter surface regardless of the decomposition stage of needles. Length of clamp-bearing hyphae in Pinus pentaphylla was 5.0-5.2 times greater in partly decomposed needles than in recently dead needles regardless of the litter depth. Frequencies of Pestalotiopsis spp. and Cladosporium cladosporioides were higher on recently dead needles than on partly decomposed needles and (or) were higher on the litter surface than beneath the litter layer. Frequencies of Trichoderma, Penicillium, and Umbelopsis species generally were higher on partly decomposed needles than on recently dead needles and were higher beneath the litter layer than on the surface.     

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

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

The responses of leaf litter invertebrates to environmental gradients along road edges in subtropical island forests

Knowledge of how roads affect forest biodiversity can be improved by measuring the responses of indicator species to complex environmental gradients caused by these infrastructures. We studied litter invertebrate species responses to road edges in laurel and pine forests in Tenerife, Canary Islands. We sampled invertebrates from litter and assessed the environmental variation related to road proximity. We also assessed the effect of relevant environmental predictors on a diverse array of potential indicator species. We applied canonical ordination and non-parametric regression (Lowess) to classify invertebrate species responses to roads and their associated gradients. Three types of responses to road edge proximity were defined for the most common invertebrate taxa: edge-preferring or edge specialists, interior-preferring or edge-avoiders, and edge-indifferent or neutral species. Those species appearing most frequently and with higher population density between 1 and 20 m from the edge (commonly peaking at 10 m from the road) were categorized as edge-preferring. We classified taxa attaining peak population densities at or beyond 60 m from the edge (and most commonly 100 m) as interior species. Edge-neutral species were those without an evident pattern of stabilization in abundance along the gradient and with peaks in abundance at varying distance intervals. These edge litter communities contain a high native and endemic diversity but also a significant density of alien fauna. The specific patterns of penetration of road edge effects on invertebrate species should be seen as having a pervasive and cumulative impact considering the exceptionally large number of roads in these forests and the high population densities of alien invertebrates. Future management plans for forest conservation on the Canary Islands should include the highly altered but valuable litter communities along road edges.     

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.     

Impacts of extreme winter warming events on litter decomposition in a sub-Arctic heathland

Arctic climate change is expected to lead to a greater frequency of extreme winter warming events. During these events, temperatures rapidly increase to well above 0 °C for a number of days, which can lead to snow melt at the landscape scale, loss of insulating snow cover and warming of soils. However, upon return of cold ambient temperatures, soils can freeze deeper and may experience more freeze-thaw cycles due to the absence of a buffering snow layer. Such loss of snow cover and changes in soil temperatures may be critical for litter decomposition since a stable soil microclimate during winter (facilitated by snow cover) allows activity of soil organisms. Indeed, a substantial part of fresh litter decomposition may occur in winter. However, the impacts of extreme winter warming events on soil processes such as decomposition have never before been investigated. With this study we quantify the impacts of winter warming events on fresh litter decomposition using field simulations and lab studies.Winter warming events were simulated in sub-Arctic heathland using infrared heating lamps and soil warming cables during March (typically the period of maximum snow depth) in three consecutive years of 2007, 2008, and 2009. During the winters of 2008 and 2009, simulations were also run in January (typically a period of shallow snow cover) on separate plots. The lab study included soil cores with and without fresh litter subjected to winter-warming simulations in climate chambers.Litter decomposition of common plant species was unaffected by winter warming events simulated either in the lab (litter of Betula pubescens ssp. czerepanovii), or field (litter of Vaccinium vitis-idaea, and B. pubescens ssp. czerepanovii) with the exception of Vaccinium myrtillus (a common deciduous dwarf shrub) that showed less mass loss in response to winter warming events. Soil CO₂ efflux measured in the lab study was (as expected) highly responsive to winter warming events but surprisingly fresh litter decomposition was not. Most fresh litter mass loss in the lab occurred during the first 3-4 weeks (simulating the period after litter fall).In contrast to past understanding, this suggests that winter decomposition of fresh litter is almost non-existent and observations of substantial mass loss across the cold season seen here and in other studies may result from leaching in autumn, prior to the onset of “true” winter. Further, our findings surprisingly suggest that extreme winter warming events do not affect fresh litter decomposition.     

Mass loss and nutrient release during litter decay in peatland: The role of microbial adaptability to litter chemistry

In peatlands the reduced decomposition rate of plant litter is the fundamental mechanism making these peat-accumulating ecosystems effective carbon sinks. A better knowledge of litter decomposition and nutrient cycling is thus crucial to improve our predictions of the effects of anthropogenic perturbation on the capacity of peatlands to continue to behave as carbon sinks. We investigated patterns of plant litter decomposition and nutrient release along a minerotrophic-ombrotrophic gradient in a bog on the south-eastern Alps of Italy. We determined mass loss as well as P, N, K, and C release of seven vascular plant species and four moss species after 1 year in both native and transplanted habitats. Hence, differences in litter decay were supposed to reflect the degree of adaptability of microbial communities to litter quality. Polyphenols/nutrient and C/nutrient quotients appeared as the main parameters accounting for decomposition rates of Sphagnum litter. In particular, litter of minerotrophic Sphagnum species decomposed always faster than litter of ombrotrophic Sphagnum species, both in native and transplanted habitats. Decomposition rates of vascular plant litter in native habitats were always higher than the corresponding mass loss rates of Sphagnum litter. Minerotrophic forbs showed the fastest decomposition both in native and transplanted habitats in accordance with low C/P and C/N litter quotients. On the other hand, C/P quotient seems to play a primary role also in controlling decomposition of graminoids. Decomposition of deciduous and evergreen shrubs was negatively related to their high lignin content. Nitrogen release from Sphagnum litter was primarily controlled by C/N quotient, so that minerotrophic Sphagnum litter released more N than ombrotrophic Sphagnum litter. Overall, we observed slower N release from litter of ombrotrophic vascular plant species compared to minerotrophic vascular plant species. No single chemical parameter could predict the variability associated with different functional groups. The release of K was very high compared to all the other nutrients and rather similar between ombrotrophic and minerotrophic litter types. In Sphagnum litter, a higher C/P quotient was associated with a slower P mineralisation, whereas a faster P release from vascular plant litter seems primarily associated with lower C/P and polyphenols/P quotients.     

Dominant effects of litter substrate quality on the difference between leaf and root decomposition process above- and belowground

Initial decomposition rates, changes in organic chemical components (acid-insoluble fraction, holocellulose, polyphenols, soluble carbohydrates) and nutrient dynamics (K, Mg, Ca, P, N) were examined for fine roots and leaves of Japanese cypress (Chamaecyparis obtusa). Litterbag experiments designed to evaluate the relative effects of litter type and position of litter supply in the soil were carried out, considering that root and leaf litter typically occupy different locations and have different substrate qualities. Litterbags of roots and leaves were placed at two positions (on the soil surface and in the humus layer), and collected every 3 months over one year. The mass loss rate and N release were slower during root decomposition in the humus layer than during leaf decomposition on the soil surface. These differences between root and leaf decomposition were mainly caused by the litter type, and the effect of the position on decomposition was relatively small. Root litter was less influenced by position related effects, such as differences in humidity, than leaf litter, and this recalcitrant trait to environmental effects may be responsible for the slower mass loss rate and N release in root decomposition. The results of the present study suggest that fine roots are persistent in the soil and serve an important role in N retention in forest ecosystems because of their litter substrate quality.     

Rhizosphere activity, grass species and N availability effects on the soil C and N cycles

We examined whether grass species and soil nitrogen (N) availability could enhance Carbon (C) and N turnover during root litter decay in grassland. Three species with increasing competitiveness (Festuca ovina, Dactylis glomerata and Lolium perenne) were grown at two N fertiliser levels in an undisturbed grassland soil, in which soil organic fractions derived for the last 9 years from Lolium root litter which was ¹³C-depleted. During the subsequent experimental year, the C turnover was calculated using the respective δ¹³C values of the old and new C in the root phytomass, in two Particulate Organic Matter (POM) fractions above 200 μm and in the lightest part of the aggregated soil fraction between 50 and 200 μm. Soil N availability was monitored during the regrowth periods with ion exchange resins (IER). The C decay rates of each particle size fraction were calculated with a simple mechanistic model of C dynamics. The N mineralisation immobilisation turnover (MIT) was characterised by dilution of ¹⁵N-labelled fertiliser in the N harvestThe C:N ratio and the residence time of C in the fractions decreased with particle size. The presence of a grass rhizosphere increased the decay rate of old C. Accumulation of new C in particle size fractions increased with species competitiveness and with N supply. Species competitiveness increased C turnover in the aggregated fraction, as a result of greater accumulation of new C and faster decay of old C. Fertiliser N increased N turnover and C mineralisation in the SOM. Species competitiveness decreased soil -N exchanged with the IER and increased dissolved organic C (DOC) content. The nature of the current rhizosphere is thus an important factor driving C and N transformations of the old root litter, in relation with grass species strategy. Plant competitiveness may stimulate the C and N turnover in the more evolved SOM fractions in a similar way to the mineral N supply.     

Effects of elevated temperature, elevated CO2 and fertilization on quality and subsequent decomposition of silver birch leaf litter

We examined the quality and decomposition of naturally abscised leaves of silver birch (Betula pendula) seedlings subjected to three different levels of fertilization under ambient and elevated levels of temperature and CO₂. At the end of the second growing season, the chemical composition of the litter collected from the seedlings was analyzed. Whole-leaf samples from pooled litter from each of the four replicates from each treatment were put in mesh bags and transferred to ambient climate in the field. The remaining mass of litter was measured by sampling bags in May and October throughout the four-year incubation period. Fertilization with all nutrients decreased the initial carbon and tannin contents of litter, and increased the proportion of the fast-decomposing fraction, but still fertilization slowed down the decomposition of this fraction. Initially, the estimated proportion of the fast-decomposing fraction was smallest in elevated CO₂ + temperature, and largest in ambient climate. During decomposition, elevated growth-temperature slowed down decomposition of the fast fraction under ambient CO₂ but increased it under elevated CO₂. The changes in litter decomposition rates found over four years were not very large. However, we conclude that the interactions of different factors lead to different results than if the factors had been studied separately, and future studies should take interactions into account.     

Fumigation-extraction and substrate-induced respiration derived microbial biomass C,and respiration rate in limed soil of Scots pine sapling stands

The effect of liming on microbial biomass C and respiration activity was studied in four liming experiments on young pine plantations. One of the experimental sites had been limed and planted 12 years before, two 5 years before, and one a year before soil sampling. The youngest experimental site was also treated with ash fertilizer. Liming raised the pH_KCl of the humus layer by 1.5 units or less. Microbial biomass was measured using the fumigation-extraction and substrate-induced respiration methods. Liming did not significantly affect microbial biomass C, except in the experiment which had been limed 11 years ago, where there was a slight biomass increase. Basal respiration, which was measured by the evolution of CO₂, increased in the limed soils, except for the youngest experiment, where there was no effect. Ash fertilization raised the soil pH_KCl by about 0.5 unit, but did not influence microbial biomass C or basal respiration. Fumigation-extraction and substrate-induced respiration derived microbial biomass C values were correlated positively with each other (r=0.65), but substrate-induced respiration gave approximately 1.3 times higher results. In addition, the effect of storing the soil samples at +6 and -18°C was evaluated. The effects were variable but, generally, the substrate-induced respiration derived microbial biomass C decreased, and the fumigation-extraction derived microbial biomass C and basal respiration decreased or were not affected by storage.     

Modelling decomposition of standard plant material along an altitudinal gradient: A re-analysis of data of Coûteaux et al. (2002)

We explored an alternative method to analyse data of Coûteaux et al. [2002, Soil Biology and Biochemistry 34, 69-78] on the decomposition of a standard organic material in six soils along an altitudinal gradient in the Venezuelan Andes (65-3968 m a.s.l.). Coûteaux et al., fitted separate two-component decomposition models to data of the individual sites, allowing the initial size of the labile and the resistant component to differ between sites. This procedure led them to conclude that the initial size of the resistant component and its decomposition rate depend on temperature while decomposition rate of the labile component does not, which seems biologically unlikely and at variance with literature. As an alternative we fitted a single two-component model to the whole data set, using identical initial component sizes for all sites. We found no statistical ground for using variable initial component sizes. It appeared that the data does not allow a conclusion on the effect of temperature on the decomposition of the labile component. We also investigated alternatives for the values of Q₁₀ and T_opt that were used by Coûteaux et al., and found that temperature explains a larger part of the differences in decomposition rate among sites when using a Q₁₀ value of 3.75 instead of 2.2 and a T_opt value of 27 °C instead of 25 °C. We discuss the arguments used in model selection and the consequences for predictions of long-term accumulation of soil carbon. Our analysis suggests an even stronger positive feedback between global warming and soil carbon emission than the analysis by Coûteaux et al.     

Wood-ash fertilization and fire treatments in a Scots pine forest stand: Effects on the organic layer,microbial biomass,and microbial activity

We studied the reactions of humus layer (F/H) microbial respiratory activity, microbial biomass C, and the fungal biomass, measured as the soil ergosterol content, to the application of three levels of wood ash (1000, 2500, and 5000 kg ha^-1) and to fire treatment in a Scots pine (Pinus sylvestris L.) stand. Physicochemical measurements (pH, organic matter content, extractable and total C content, NH ₄ ⁺ and total N content, cation-exchange capacity, base saturation) showed similarity between the fire-treated plots and those treated with the lowest dose of wood ash (1000 kg ha^-1). The ash application did not change the level of microbial biomass C or fungal ergosterol when compared to the control, being around 7500 and 350 g g^-1 organic matter for the biomass C and ergosterol, respectively. The fire treatment lowered the values of both biomass measurements to about half that of the control values. The fire treatment caused a sevenfold fall in the respiration rate of fieldmoist soil to 1.8 l h^-1 g^-1 organic matter compared to the values of the control or ash treatments. However, in the same soils adjusted to a water-holding capacity of 60%, the differences between the fire treatment and the control were diminished, and the ash-fertilized plots were characterized by a higher respiration rate compared to the control plots. The glucose-induced respiration reacted in the same way as the water-adjusted soil respiration. The metabolic quotient, qCO₂, gradually increased from the control level with increasing applications of ash, reaching a maximum in the fire treatment. Nitrification was not observed in the treatment plots.     

Controls over pathways of carbon efflux from soils along climate and black spruce productivity gradients in interior Alaska

Small changes in C cycling in boreal forests can change the sign of their C balance, so it is important to gain an understanding of the factors controlling small exports like water-soluble organic carbon (WSOC) fluxes from the soils in these systems. To examine this, we estimated WSOC fluxes based on measured concentrations along four replicate gradients in upland black spruce (Picea mariana [Mill.] BSP) productivity and soil temperature in interior Alaska and compared them to concurrent rates of soil CO₂ efflux. Concentrations of WSOC in organic and mineral horizons ranged from 4.9 to 22.7 g C m⁻² and from 1.4 to 8.4 g C m⁻², respectively. Annual WSOC fluxes (4.5-12.0 g C m⁻² y⁻¹) increased with annual soil CO₂ effluxes (365-739 g C m⁻² y⁻¹) across all sites (R²=0.55, p=0.02), with higher fluxes occurring in warmer, more productive stands. Although annual WSOC flux was relatively small compared to total soil CO₂ efflux across all sites (<3%), its relative contribution was highest in warmer, more productive stands which harbored less soil organic carbon. The proportions of relatively bioavailable organic fractions (hydrophilic organic matter and low molecular weight acids) were highest in WSOC in colder, low-productivity stands whereas the more degraded products of microbial activity (fulvic acids) were highest in warmer, more productive stands. These data suggest that WSOC mineralization may be a mechanism for increased soil C loss if the climate warms and therefore should be accounted for in order to accurately determine the sensitivity of boreal soil organic C balance to climate change.     

The invasion of two native Eucalypt forests by Pinus radiata in the Blue Mountains, New South Wales, Australia

Invasions of Pinus species are a major environmental concern in South Africa and New Zealand where pines are beginning to dominate native grasslands and shrublands. Pines are widely cultivated in Australia with almost a million hectares growing in large plantations. Plantations are commonly bordered by native Eucalypt vegetation resulting in a high potential for invasion and providing an opportunity to study pine invasion processes within forest environments.In order to determine if Pinus radiata equally invades different dry Eucalypt woodland vegetation types, two areas in the upper Blue Mountains in New South Wales, Australia were surveyed. Similar levels of invasion were observed in both Eucalypt forest types. An average pine abundance of 55 individuals for the Eucalyptus oreades and Eucalyptus sieberi vegetation type and 49 individuals for the Eucalyptus mannifera and Eucalyptus dives vegetation type was recorded in 20 m by 20 m plots located 50 m from the plantation boundary. To characterise the spatial distribution of the pines, transects were placed perpendicular to the plantation edge. As expected pine numbers diminished with distance from the plantation, however, large reproductive pine trees were found up to 4 km from the seed source signifying long distance dispersal.Investigation of wildling pine response to fire suggests that it may not always be an appropriate management tool. Fire stimulated seed release from cones and resulted in high recruitment of seedlings around reproductive pines which were large enough to survive the burn. Infrequent fires at intervals greater than time to maturity will lead to increased pine densities and further spread into the native vegetation.     

The effect of disturbance by Phellinus weirii on decomposition and nutrient mineralization in a Tsuga mertensiana forest

Summary Microbial biomass in the upper 7 cm of soil and needle decomposition on the forest floor were measured seasonally for 10 months in a mountain hemlock (Tsuga mertensiana) old-growth forest and in a regrowth forest after Phellinus weirii, a root-rot pathogen infection, had caused disturbance. The microbial biomass was higher in the old-growth forest soil than in the regrowth forest soil. However, T. mertensiana needle decomposition rates were higher in the regrowth than in the old-growth forest. Total N, Ca, Fe, Cu, and Zn concentrations in needles increased during the 1st year of decomposition in both the old and the regrowth forests, but P, K, Mg, Mn, and B concentrations decreased. N, P, K, Mg, Cu, and Zn concentrations were lower in regrowth than in old-growth decomposing needles. During mineralization, needles in the regrowth forests released more N, P, and K as a result of higher needle decomposition rates. Our results suggest that higher needle decomposition rates increased the mineralization of N, P, and K, which may lead to increased soil fertility and faster tree growth rates in the regrowth forest.     

Fungal communities associated with the decomposition of a common leaf litter (Quercus leucotrichophora A. Camus) along an elevational transect in the Central Himalaya

Summary We studied the fungal communities associated with decomposing common leaf litter (Quercus leucotrichophora A. Camus) placed in five forests of Central Himalaya between the elevations of 330 and 2150 m. During the initial period of decay, conciding with the rainy season, a progressive increase in fungal counts and species diversity was observed in all forest sites. The sal forest site had a greater weight loss and supported the largest fungal densities, whereas the pine forest had a lower weight loss and the smallest fungal densities. Deuteromycetes were the dominant group in all the forest sites. Most of the species isolated during the annual cycle of the forest sites were of the accidental type. Species diversity and fungal counts on the common leaf litter were markedly affected by the environmental changes brought about by the native leaf litter. This effect was most obvious in the chir pine forest site where the leaf litter of the native dominant species was distinctly more resistant to decay than those of the other sites, making the soil environment of the site markedly different from that of other sites. The pattern of fungal-species changes with progressive decay of the substrate was similar to that suggested by the tolerance model of Connel and Slatyer.     

Effects of seasonal and diurnal temperature fluctuations on population dynamics of two epigeic earthworm species in forest soil

Temperature fluctuations are a fundamental entity of the soil environment in the temperate zone and show fast (diurnal) and slow (seasonal) dynamics. However, responses of soil ecosystem engineers, such as earthworms, to annual temperature dynamics are virtually unknown. We studied growth, mortality and cocoon production of epigeic earthworm species (Lumbricus rubellus and Dendrobaena octaedra) exposed to temperature fluctuations in root-free soil of a mid-European beech-oak forest. Both earthworm species (3 + 3 individuals of each species) were kept in microcosms containing soil stratified into L, F + H and A_h horizons. In the field, earthworm responses to smoothing of diurnal temperature fluctuations were studied, simulating possible global change. In the laboratory, earthworm responses to seasonal (±5 °C of the annual mean) and diurnal temperature fluctuations (±5 °C of the seasonal levels) were analyzed in a two-factorial design. Both experiments lasted 12 months to differentiate between seasonal and diurnal responses. In the third experiment overwintering success of both earthworm species was investigated by comparing effects of constant temperature regime (+2 °C), and daily or weekly temperature fluctuations (2 °C ± 5 °C).Temperature regime strongly affected population performance of the earthworms studied. In the field, smoothed temperature fluctuations beneficially affected population development of both earthworm species (higher biomass, faster maturity and reproduction, lower mortality). Consequently, density of both species increased faster at smoothed than at ambient temperature conditions. In the laboratory, responses of L. rubellus and D. octaedra to temperature treatments differed; however, in general, earthworms benefited from the absence of diurnal fluctuations. Total earthworm numbers were at a maximum at constant temperature and lowest in the treatment with both diurnal and seasonal temperature fluctuations. However, after one year L. rubellus tended to dominate irrespective of the temperature regime. In the overwintering experiment L. rubellus sensitively responded to even short-term winter frost and went extinct after one week of frost whereas D. octaedra much better tolerated frost conditions. Earthworms of both species which survived frosts were characterized by a significant body weight decrease during the period of frosts and fast recovery in spring suggesting a different pattern of individual resource expenditure as compared with constant +2 °C winter regime. Contrasting trends in the population dynamics of L. rubellus and D. octaedra during the frost-free period and during winter suggest that in the long-term temperature fluctuations contribute to the coexistence of decomposer species of similar trophic position in the forest litter. The results are discussed in context of consequences of climate change for the functioning of soil systems.