Faunal stage-dependent altering of soil nitrogen availability in a temperate forest

Functional traits of organisms often depend on their developmental stages during growth. However, whether the ecological functions of organisms change at different developmental stages remains poorly understood, especially for soil animals. The train millipede, Parafontaria laminata, which has a synchronised life cycle, often dominates in soil invertebrate communities in central Japan. Because adults of this species are litter-feeders and larvae are soil-feeders, we hypothesised that the train millipede assumes a different role in of the cycling of nitrogen (N) depending on its developmental stage. To determine the effects of P. laminata on N retention or loss in temperate forest soil, millipede density was manipulated in two mesocosm experiments using adult and larval millipedes. We found strong evidence that the effects of P. laminata on N dynamics differ between millipede developmental stages. Larvae enhanced N leaching, which was significantly higher in the high-density treatment than in treatments without millipedes (control). In contrast, adults did not affect N leaching, although high and intermediate adult density significantly increased soil N content compared to control and low-density treatments. Our results suggest that soil-feeding larvae promote soil N mineralisation, whereas litter-feeding adults inhibit N mineralisation, potentially sustaining N levels in the soil for at least the duration of our experimental period. Because natural populations of P. laminata exhibit high abundance and a synchronised life cycle at the landscape level, the soil-to-litter feeding shift that depends on P. laminata's developmental stage-of may cause large temporal variation in N dynamics in forest ecosystems compared to macrofauna-free systems.     

Exploitation of litter and soil by the train millipede Parafontaria laminata (Diplopoda: Xystodesmidae) in larch plantation forests in Japan

Swarms of the train millipede (Parafontaria laminata) are known to occur every 8 years; during the swarms, adults emerging from the soil have an extremely high density in natural and plantation forests in central Japan. Their influence on organic layer accumulation on forest floors was investigated under field conditions in plantation larch forests in central Japan, before and after the adult swarming period of 2000. In addition, the adult millipede feeding preference and the amount of food consumed were observed in the laboratory. The field density of adults ranged from 11 to 311 individuals m⁻² in October 2000; the highest biomass was 28.6±16.4 g dry wt m⁻². Reduction of the forest floor organic layer was density- dependent when the population consisted of 7th instar larvae; however, the adult population did not consume in a density-dependent manner. Higher levels of geophagy were observed in high-density treatments in the laboratory. We hypothesized that the geophagy of the millipedes was partly supported by the naturally high organic matter content of Andosol, and that soil consumption would sustain an extremely high biomass in a temperate conifer forest soil.     

Digestion and residue stabilization of bacterial and fungal cells,protein, peptidoglycan,and chitin by the geophagous earthworm Metaphire guillelmi

Microbial biomass is an important source of soil organic matter, which plays crucial roles in the maintenance of soil fertility and food security. However, the mineralization and transformation of microbial biomass by the dominant soil macrofauna earthworms are still unclear. We performed feeding trials with the geophagous earthworm Metaphire guillelmi using ¹⁴C-labelled bacteria (Escherichia coli and Bacillus megaterium) cells, fungal (Penicillium chrysogenum) cells, protein, peptidoglycan, and chitin. The mineralization rate of the microbial cells and cell components was significantly 1.2–4.0-fold higher in soil with the presence of M. guillelmi for seven days than in earthworm-free soil and 1–11-fold higher than in fresh earthworm cast material. When the earthworms were removed from the soil, the mineralization of the residual carbon of the microbial biomass was significantly lower than that in the earthworm-free soil, indicating that M. guillelmi affects the mineralization of the biomass in soil in two aspects: first stimulation and then reduction, which were attributed to the passage of the microbial biomass through the earthworm gut, and that the microorganisms in the cast could play only minor roles in the stimulated mineralization and residual stabilization of microbial biomass. Large amounts (8–29%) of radiolabel of the tested microbial biomass were assimilated in the earthworm tissue. Accumulation of fungal cells (11%) and cell wall component chitin (29%) in the tissue was significantly higher than that of bacterial cells (8%) and cell wall component peptidoglycan (15%). Feeding trails with ¹⁴C-lablled microbial cells and cell components provided direct evidence that microbial biomass is a food source for geophagous earthworm and fungal biomass is likely a more important food source for earthworms than bacterial biomass. Findings of this study have important implications for the roles of geophagous earthworms in the fate of microbial biomass in soil.     

The biochemical transformation of oak (Quercus robur) leaf litter consumed by the pill millipede (Glomeris marginata)

Soil macrofauna play an essential role in the initial comminution and degradation of organic matter entering the soil environment and yet the chemical effects of digestion on leaf litter are poorly understood at the molecular level. This study was undertaken to assess the selective chemical transformations that saprophagous soil invertebrates mediate in consumed leaf litter. A number of pill millipedes (Glomeris marginata) were fed oak leaves (Quercus robur) after which the biomolecular compositions (lipids and macromolecular components) of the leaves and millipede faeces were compared using a series of wet chemical techniques and subsequent analysis by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). It was found that the concentrations of short chain (<C₂₀) n-alkanoic acids, sterols and triacylglycerols reduced dramatically in the millipede faeces relative to the leaf litter. Hydrolysable carbohydrates and proteins both decreased in concentration in the faeces, whereas similar yields of phenolic components were observed for the cupric oxidation products of lignin, although the oxygenated functionalities were affected by passage through the millipede gut, yielding a more highly condensed state for lignin. This shows that the chemical composition of fresh organic matter entering the soil is directly controlled by invertebrates feeding upon the leaf litter and as such that they are key contributors to the early stages of diagenesis in terrestrial soils.     

Consistent effects of eastern subterranean termites (Reticulitermes flavipes) on properties of a temperate forest soil

Termites inhabit a large portion of land covered by temperate forests. Climate warming and urbanization will likely extend their range and increase their densities in these ecosystems but, compared to their tropical counterparts, little is known about their effects on soil properties and processes. If temperate termites have the strong ecosystem engineering effects of tropical termites, then knowledge of their ecology and impacts will be vital for predicting how temperate systems respond to environmental change. We investigated how feeding and tunneling by the eastern subterranean termite, Reticulitermes flavipes, affected wood decomposition and soil properties under decaying wood. Twelve laboratory microcosms filled with mineral soil and with wood blocks of four common temperate tree species, received R. flavipes soldiers and workers at field densities, with an additional five termite-free microcosms serving as controls. After 25 weeks, the effects of termites on wood mass loss, and on carbon and nitrogen dynamics, differed across tree species, yet their effects on soil properties were consistent regardless of wood type. Microbially-available carbon in soil was 20% higher with termites and soil moisture content 20% lower. Soil pH was more acid with termites and their effects on soil microbial biomass were positive but non-significant. These soil responses were consistent regardless of the wood species, suggesting that termite effects on soil are dictated largely by their activity within the soil matrix and not by their feeding rate on specific wood substrates. These results are among the first to quantify the effects of temperate forest termite activity on soil properties, demonstrating the potential for these termites to shape biogeochemical cycling and plant communities through their alteration of the soil environment.     

Effects of root and litter exclusion on soil CO2 efflux and microbial biomass in wet tropical forests

We examined the effects of root and litter exclusion on the rate of soil CO₂ efflux and microbial biomass at a soil depth of 25 cm in a secondary forest (dominated by Tabebuia heterophylla) and a pine (Pinus caribaea) plantation in the Luquillo Experimental Forest in Puerto Rico. The experimental plots were initially established in 1990, when root, forest floor mass and new litterfall were excluded for 7 y since then. Soil respiration was significantly reduced in the litter and root exclusion plots in both the secondary forest and the pine plantation compared with the control. Root exclusion had a greater effect on soil CO₂ efflux than the litter exclusion in the plantation, whereas a reversed pattern was observed in the secondary forest. The reduction of microbial biomass in the root exclusion plot was greater in the secondary forest (59%) than in the plantation (31%), while there was no difference of the reduction in the litter exclusion plots between these forests. Our results suggest that above-ground input and roots (root litter and exudates) differentially affect soil CO₂ efflux under different vegetation types.     

Dynamics and stratification of functional groups of micro- and mesoarthropods in the organic layer of a Scots pine forest

This paper addresses the abundance, biomass and microstratification of functional groups of micro- and mesoarthropods inhabiting the organic layers of a Scots pine forest (Pinus sylvestris L.). An experiment using stratified litterbags, containing organic material of four degradation stages, i.e., freshly fallen litter, litter, fragmented litter and humus, was performed over a period of 2.5 years. Statistical data analysis revealed that each organic layer had a different, characteristic species composition that changed with time following successive degradation stages. Species of Acari, Araneae and Collembola were assigned to different functional groups based on taxonomy, microstratification, food type or feeding mode. The abundance and biomass carbon of functional groups were dependent on the organic layer and most functional groups showed a particular preference for one of the upper organic layers. Temporal and spatial differences in density and biomass carbon of functional groups could partly be related to fluctuations in the soil climate, although effects of trophic interactions could not be ruled out. A general decline in abundance and biomass, especially in populations of fungal feeders, during the last year of the study could not be explained by a reduction in litterbag volume, changed litter chemistry or soil climate, but was attributed to an indirect effect of a remarkable increase in soil coverage by wavy hair grass, Deschampsia flexuosa (L.). The analysis demonstrated that species diversity, microhabitat specification, soil fauna succession, and degradation stages of organic material are interrelated. The results obtained indicate that both the chemistry of organic matter and decomposition rates have an important effect on trophic relationships and community structure. Received: 26 June 1997     

Effects of long-term litter manipulation on soil carbon,nitrogen, and phosphorus in a temperate deciduous forest

Changes in above-ground litterfall can influence below-ground biogeochemical processes in forests. In order to examine how above-ground litter inputs affect soil carbon (C), nitrogen (N) and phosphorus (P) in a temperate deciduous forest, we studied a 14-year-old small-scale litter manipulation experiment that included control, litter exclusion, and doubled litter addition at a mature Fagus sylvatica L. site. Total organic C (TOC), total N (TN) and total P (TP), total organic P (TOP), bioavailable inorganic P (Pi), microbial C, N and P, soil respiration and fine root biomass were analyzed in the A and in two B horizons. Our results showed that litter manipulation had no significant effect on TOC in the mineral soil. Litter addition increased the bioavailable Pi in the A horizon but had no significant effect on N in the mineral soil. Litter exclusion decreased TN and TP in the B horizon to a depth of 10 cm. In the A horizon of the litter exclusion treatment, TP, TOP and bioavailable Pi were increased, which is most likely due to the higher root biomass in this treatment. The high fine root biomass seems to have counteracted the effects of the excluded aboveground litter. In conclusion, our study indicates that aboveground litter is not an important source for C in the mineral soil and that P recycling from root litter might be more important than from above-ground litter.     

Consumption of introduced oak litter by native decomposers (Glomeridae,Diplopoda)

In view of the predicted climate change in Central Europe, preventive forestry adaptation strategies are currently being developed in Germany to maintain stable forest ecosystems with high biodiversity. Mediterranean, drought-tolerant oak species such as Quercus pubescens, Quercus frainetto and Quercus ilex are being evaluated as future forest trees for German forest sites which are becoming increasingly dry. The present study represents first investigations concerning the influence of these introduced species on local soil-biological processes, especially primary leaf litter decomposition. The feeding activity of native Glomeris marginata was observed with the Mediterranean leaf litter in comparison to litter of local Quercus robur and Fagus sylvatica under laboratory conditions. In the experiments the introduced litter was readily fed upon by local millipede populations. The results furthermore show that the introduced litter is consumed at equal or even higher rates than the litter of native tree species. Leaf litter of the introduced tree species seems to have no or possibly even a positive influence on the feeding activity of G. marginata.     

退耕还林地在植被恢复初期碳储量及分配格局研究

利用标准样方法研究了川西最主要的两种退耕还林植被(苦竹林和桦木林)在恢复初期生态系统碳储量、碳素密度以及空间分配特征.结果表明:(1)苦竹不同器官碳素密度为0.348 5～0.518 6 gC/g,桦木不同器官碳素密度为0.451 9～0.513 7 gC/g;(2)苦竹林林下枯落物的碳素密度为0.341 7 gC/g,桦木林林下枯落物的碳素密度为0.395 3 gC/g;(3)不同植物器官的碳储量分配与各器官的生物量显著相关.苦竹林分中竹秆生物量占48.87%,其碳储量占53.06%;桦木林树干生物量占57.25%,其碳储量占57.27%;(4)两种森林生态系统碳储量的空间分布格局表现为以土壤碳储量最大,占64.19%～82.59%,其次是乔木层,占21.93%～33.90%,最小是桔落物层,占0.27%～1.91%;(5)在退耕还林初期,植被恢复后土壤各层碳素密度小于对照的各层土壤碳素密度,土壤有机碳储量减少;(6)退耕地转变为森林后,成为大气CO2的一个重要碳汇.     

Decomposition and macroinvertebrates in experimental litter along a secondary chronosequence of tropical montane forest

This paper presents the results of a decomposition experiment performed in a secondary chronosequence of tropical montane cloud forest in Mexico. The experiment was designed to explore whether the age of the forest influences the decomposition process and macroinvertebrate community independently of the quality of the decomposition resources. Fresh Pinus chiapensis needles and Persea americana leaves were set to decompose in each of four successional stages (15, 45, 75 and 100 years old). Results do not support the hypothesis that decomposition rate declines with increasing nutrient deficiency as forest succession proceeds. However, the chemical composition in decomposing leaves differed between successional stages. Higher availability of Ca in the 15-year-old forest appears to promote a positive feedback in the release of this nutrient from Persea americana leaves. Additionally, in old forests, a soil community that is more capable of breaking down recalcitrant material (acid detergent lignin) appears to have developed compared to early successional stages. The diversity of macroinvertebrates and abundance of predatory (Aranea and Diplura), detrivorous (Diplopoda) and geophagous (Enchytaeidae) taxa were different between boxes placed in different successional stages. We conclude that the decomposition and associated biota differ between successional stages. Apart from differences in litter quality, other factors associated with the age of the forest, such as small differences in soil temperature and long-lasting effects of disturbance, may also play influential roles.     

竹生物质炭和竹凋落物对毛竹林土壤营养元素和酶活性的影响

以广西壮族自治区桂林市华江乡内广泛分布的毛竹林土壤为研究对象,以竹生物质炭和竹凋落物作为外源碳,设置对照（CK）、低添加量生物质炭（1% BC）、高添加量生物质炭（2% BC）、低添加量凋落物（1% L）、高添加量凋落物（2% L）5个处理,进行为期两个月的室内培养试验,研究不同外源碳添加对毛竹林土壤营养元素和酶活性的影响。结果表明：与对照相比,竹生物质炭和竹凋落物添加均显著提高了土壤pH;竹生物质炭添加显著降低了而竹凋落物添加显著提高了土壤铵态氮（NH₄⁺-N）含量（P<0.05）,且高添加量（2% BC和2% L）的降低或提高作用更明显;不同外源碳添加均显著提高了土壤硝态氮（NO₃^–-N）含量,且凋落物添加的提高作用更明显;不同外源碳添加均显著提高了土壤有效磷（AP）含量,且高添加量的提高作用更明显;竹生物质炭添加对土壤可溶性有机碳（DOC）含量没有显著影响,但降低了土壤可溶性氮（DN）含量,而竹凋落物添加显著提高了土壤DOC和DN含量;不同外源碳添加对土壤微生物生物量碳（MBC）和氮含量（MBN）均没有显著影响,但降低了土壤蔗糖酶和脲酶活性。相关性分析表明,土壤pH、NH₄⁺-N、NO₃^–-N、DOC和DN是影响竹林土壤酶活性的关键性因子。     

Compartmentalization of the soil animal food web as indicated by dual analysis of stable isotope ratios (N/N and C/C)

The soil animal food web has become a focus of recent ecological research but trophic relationships still remain enigmatic for many taxa. Analysis of stable isotope ratios of N and C provides a powerful tool for disentangling food web structure. In this study, animals, roots, soil and litter material from a temperate deciduous forest were analysed. The combined measurement of δ¹⁵N and δ¹³C provided insights into the compartmentalization of the soil animal food web. Leaf litter feeders were separated from animals relying mainly on recent belowground carbon resources and from animals feeding on older carbon. The trophic pathway of leaf litter-feeding species appears to be a dead end, presumably because leaf litter feeders (mainly diplopods and oribatid mites) are unavailable to predators due to large size and/or strong sclerotization. Endogeic earthworms that rely on older carbon also appear to exist in predator-free space. The data suggest that the largest trophic compartment constitutes of ectomycorrhizal feeders and their predators. Additionally, there is a smaller trophic compartment consisting of predators likely feeding on enchytraeids and potentially nematodes.     

Alterations in forest detritus inputs influence soil carbon concentration and soil respiration in a Central-European deciduous forest

In a Quercetum petraeae–cerris forest in northeastern Hungary, we examined effects of litter input alterations on the quantity and quality soil carbon stocks and soil CO₂ emissions. Treatments at the Síkfőkút DIRT (Detritus Input and Removal Treatments) experimental site include adding (by doubling) of either leaf litter (DL) or wood (DW) (including branches, twigs, bark), and removing all aboveground litter (NL), all root inputs by trenching (NR), or removing all litter inputs (NI). Within 4 years we saw a significant decrease in soil carbon (C) concentrations in the upper 15 cm for root exclusion plots. Decreases in C for the litter exclusion treatments appeared later, and were smaller than declines in root exclusion plots, highlighting the role of root detritus in the formation of soil organic matter in this forest. By year 8 of the experiment, surface soil C concentrations were lower than Control plots by 32% in NI, 23% in NR and 19% in NL. Increases in soil C in litter addition treatments were less than C losses from litter exclusion treatments, with surface C increasing by 12% in DL and 6% in DW. Detritus additions and removals had significant effects on soil microclimate, with decreases in seasonal variations in soil temperature (between summer and winter) in Double Litter plots but enhanced seasonal variation in detritus exclusion plots. Carbon dioxide (CO₂) emissions were most influenced by detritus input quantity and soil organic matter concentration when soils were warm and moist. Clearly changes in detritus inputs from altered forest productivity, as well as altered litter impacts on soil microclimate, must be included in models of soil carbon fluxes and pools with expected future changes in climate.     

Litter breakdown by the Seychelles giant millipede and the conservation of soil processes on Cousine Island, Seychelles

The Seychelles giant millipede, Seychelleptus seychellarum, is abundant on Cousine Island, Seychelles (ca. 4.4 ind m⁻²), where there are no alien invasive mammals as predators. This study of its feeding behaviour and activity pattern showed that its dietary range is wide, feeding mostly on leaf litter and fallen fruit. There were quantitative differences in the feeding behaviour and activity patterns of both sexes and immatures. Its ingestion rate for its size was relatively low, but its role in litter breakdown was substantial. It ingested 4.55% of the litter standing crop, and 17.19% of the daily litter fall every 24 h. Total faecal production was 2.90% of the total litter standing crop and 10.96% of the daily litter fall. This has a highly significant effect on Cousine Island which, being small and granitic, depends on nutrient cycling to maintain its ecological integrity, especially when seabirds are absent and not contributing to soil nutrient input. As this Seychelles endemic millipede has been extirpated from several islands, its continued conservation on the islands where it still occurs is not simply about conserving an endemic species, but also about maintaining intact a tropical ecosystem, with a keystone species.     

Edaphic macroarthropod communities in fast-growing plantations of Eucalyptus grandis Hill ex Maid (Myrtaceae) and Acacia mangium Wild (Leguminosae) in Brazil

This study compares the edaphic macroarthropod communities from experimental plantations of Acacia mangium and Eucalyptus grandis, both 7 years old, and from the primary forest, all located on the table-land region in the state of Espírito Santo (Brazil). Most of the taxonomic groups analyzed reach densities as high, or higher, in the plantations as in the primary forest. Four points however differentiate the communities of both plantations from that of the forest: the absence of Diplura and Pseudoscorpionida; the lower relative abundance of ants; the dominance of some non-social arthropods; and the concentration of a great percentage of macroarthropods in the litter layers. All these features seem to reflect a higher complexity in the decomposition subsystem of the primary forest, which is expected since it is a natural ecosystem. Regarding agroecosystems, the community under A. mangium shows a lower seasonal variation of total densities and a higher density of Blattaria, Isopoda, Coleopteran larvae and Lepidopteran larvae. These differences are apparently a consequence of the greater quantity of leaf litter, rich in nutrients, accumulated on the soil in this plantation. Therefore, both plantations create a propitious environment for macroarthropod communities. But A. mangium seems to provide better conditions to the soil communities, and thus it seems to be an important alternative to conciliate the wood production and the recuperation of edaphic communities in areas surrounding the remnants of the Atlantic forest.     

Lipid composition of Collembola and their food resources in deciduous forest stands—Implications for feeding strategies

The lipid composition of Collembola and their potential food resources was assessed in three deciduous forest stands, in order to gain insight into food web linkages under field conditions. Fatty acids (FAs) previously assigned as trophic markers in laboratory experiments were used to investigate feeding strategies in situ. As potential food sources soil microbiota and plant debris were characterised by their phospholipid fatty acid (PLFA) composition. Both the amount and the pattern of PLFAs differed between sites and soil depth, in particular the bacterial and plant marker FAs in the upper soil layer. Thus, the availability of resources for micro-detritivores varied due to forest and soil layer. The lipid composition of vital and senescent beech leaves was predominantly influenced by metabolic status and represented a quite homogenous FA resource across forest stands. Comparing Folsomia quadrioculata, Lepidocyrtus lignorum, Neanura muscorum and Pogonognathellus longicornis between the different forests revealed FA profiles to be predominantly affected by site, suggesting a diet shift depending on resources at hand. However, species-specific differences in individual FAs occurred, likely related to feeding strategy and physiological activity. Lipids of Collembola comprised low amounts of bacterial marker FAs, and bacterial consumption may occur to some extent, particularly on Gram-positives. The marker FA for predatory feeding, 20:1ω9, was found in several species, although in low amounts. This contradicts known feeding habits and caution is advisable in using 20:1ω9 as trophic marker. Overall, as indicated by high proportions of oleic (18:1ω9) or linoleic (18:2ω6,9) acid, most species were either plant litter or fungal feeders, with some transitions. The ratio 18:1ω9/18:2ω6,9 is proposed as a tool to distinguish between these two major feeding strategies in Collembola.     

Resource dynamics in an early-successional plant community are influenced by insect exclusion

The exclusion of insects from terrestrial ecosystems may change productivity, diversity and composition of plant communities and thereby nutrient dynamics. In an early-successional plant community we reduced densities of above- and below-ground insects in a factorial design using insecticides. Beside measuring vegetation dynamics we investigated the effects of insect exclusion on above- and below-ground plant biomass, below-ground C and N storage by plants, litter quality, decomposition rate, soil water content, soil C:N ratio, nutrient availability and soil microbial activity and biomass.The application of soil insecticide had only minor effects on above- and below-ground biomass of the plant community but increased carbon content in root biomass and total carbon and nitrogen storage in roots. In one of the three investigated plant species (Cirsium arvense), application of soil insecticide decreased nitrogen concentration of leaves (−12%). Since C. arvense responded positively to soil insecticide application, this effect may be due to drought stress caused by root herbivory. Decomposition rate was slightly increased by the application of above-ground insecticide, possibly due to an impact on epigeic predators. The application of soil insecticide caused a slightly increased availability of soil water and an increased availability of mineralised nitrogen (+30%) in the second season. We explain these effects by phenological differences between the plant communities, which developed on the experimental plots. Microbial biomass and activity were not influenced by insecticide application, but were correlated to above-ground plant biomass of the previous year. Overall, we conclude that the particular traits of the involved plant species, e.g. their phenology, are the key to understand the resource dynamics in the soil.     

Limitations of faunal effects on soil carbon flow: density dependence, biotic regulation and mutual inhibition

Soil animals are known to stimulate soil microbial activity and thereby to accelerate decomposition of soil organic matter. In this paper, we investigate potential limitations of soil animal effects on soil carbon flow by analysing how animal effects relate to the density of four major faunal groups. Specifically, we analyse the extent to which faunal effects are subject to biotic regulation or to mutual inhibition between groups under different levels of resource supply.In an extensive laboratory experiment, 96 microcosms established in three consecutive blocks were inoculated with nematodes, enchytraeids, microarthropods, and lumbricids. Each faunal group was inoculated in three densities, including combinations of groups. Introduced animal densities were within the natural range of densities in fallow soil. Bare agricultural soil and soil covered with maize litter were used as substrates. The microcosms were kept under constant conditions at 12 °C and 50% water holding capacity for 8 weeks. Soil CO₂ evolution was measured daily by means of gas chromatography.Animal effects were on an average relatively stronger in bare soil (+95% CO₂; R²=0.76) than in soil with litter (+14% CO₂; R²=0.40), where organic matter decomposition was seven times more intense. Higher animal densities generally led to accelerated decomposition up to three times that of the controls. However, beyond a specific density, decomposition rates stopped increasing or even declined, depending on the faunal group. In addition, animal effects were limited by mutual inhibition between groups in bare soil where effects were strong, while stimulatory interactions were prominent in the litter treatments where effects were generally weak.We interpret the limitation of soil faunal effects on soil carbon flow in terms of incomplete habitat exploitation and biotic regulation. Under conditions of substrate homogeneity, such as in the bare soil treatments, animal effects were stronger, but they were limited by overexploitation. Under conditions of substrate heterogeneity, such as in the litter treatments, animal effects were limited by incomplete habitat utilisation. We assume that complementary habitat colonisation by different faunal groups in the litter treatments gave rise to positive diversity effects, but that these effects did not compensate for reduced overall habitat utilisation. We infer that a knowledge of faunal resource utilisation and of mutual inhibition of faunal groups can be exploited for ecological soil management towards stabilisation of soil organic matter.     

Litter N-content influences soil millipede abundance,species richness and feeding preferences in a semi-evergreen dry forest of Guadeloupe (Lesser Antilles)

Despite the impact of soil millipedes on litter fragmentation in tropical forests, there have been few studies dealing with factors determining their habitat preference in these ecosystems. In a natural secondary dry forest of Guadeloupe on Leptosol, two complementary studies were carried out in order to test the hypothesis that litter N-content strongly influences millipede distribution. Millipede abundance and species richness were described in the field under two tree species, Bursera simaruba and Pisonia subcordata, and were related to the chemical characteristics of their foliage. In addition, a laboratory experiment was done in order to assess millipede feeding preferences regarding the chemical characteristics of leaves from various species. Millipede abundance and species richness were significantly higher under P. subcordata than under B. simaruba, probably due to the higher N content of P. subcordata leaves. Moreover, millipedes fed preferentially on N-rich leaves. The present study confirms that there was a close correlation between the preferred food, its chemical composition and the local distribution of millipede populations.