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Base cation depletion due to soil acidification is a major environmental problem which can disrupt proper ecosystem functioning. We investigated nine mesic broad-leaved forests growing on Devonian sediments of the Rhenish Shield (Germany) and investigated the effect of coarse woody debris (CWD). The forests grow on soils originating from different parent material (graywacke, slates, dolostone) with upper soil pH-values ranging from 3.0 to 7.0. We analyzed soil chemistry, soil microbial parameters and the density of litter-dwelling detritivores (snails, slugs, woodlice and millipedes) to assess the influence of both acidification and CWD. The forests were classified according to their (Ca + Mg + K)/Al molar ratios into groups with ratios of either 2+ and Mg 2+ availability and an improved (Ca + Mg + K)/Al molar ratio. The presence of CWD also enhanced soil microbial biomass, the density of detritivores and species richness of snails, slugs and millipedes. Consequently, coarse woody debris influences nutrient fluxes and decreases the acidification-related risk of tree damage.

In many afforested reclamation sites as well as in commercial forests naturally settled shrubs or trees (“non-target species”; NTS) are cut down to improve the growth of the target trees (TT). In afforested oak plantations ( Quercus robur ) of the Rhineland (Germany) the NTS broom ( Cytisus scoparius ) and birch ( Betula pendula ) can occur in high densities during the first decades of succession. Hazel ( Corylus avellana ) is a common shrub in the understory of commercial oak forests ( Quercus petraea ). We studied the influence of these NTS on selected physical, chemical and biotic soil properties in cultures of oak (TT). Soil samples taken under single oak trees were compared with samples taken under broom and birch at afforested reclamation sites of different age (2, 9, 13 years) and with samples taken under hazel in an 80-year-old oak forest. At initial stages of succession (2 years) all of the investigated soil properties indicated a higher soil quality under broom than under oak. However, the advantage of broom was less evident in a later stage of succession (9 years). Birch (13 years) and hazel (80 years) only improved soil chemical properties. The soil pH and the content of Mg 2+ were significantly higher under birch, the contents of Ca 2+ , Mg 2+ and PO 4 3− were significantly higher under hazel than under oak ( p =0.05). The results demonstrate that the selected NTS improve soil quality in afforested and commercial oak forests. This effect is pronounced under the influence of broom at initial stages of soil development.

We studied the soil properties of 18-year-old plantations beneath the crowns of the native sessile oak ( Quercus petraea ) and of the introduced red oak ( Quercus rubra ) growing on reclaimed lignite open-cast mines. The soil properties of both plantations, which are growing on either highly fertile (loess deposits, silty loam) or on low fertile (mixture of loess and sand deposits, clayed sand) soil, were measured and compared with values taken from 2-year-old Quercus robur plantations. In plantations of Q. petraea we generally found higher values of total carbon (C org ) and total nitrogen (N tot ) in the upper soil, although the amount of organic matter in the O-horizon did not significantly differ. Soils of Q. petraea plantations also exhibited higher values for microbial and faunal life. For example, microbial activity, the respiratory quotient ( q CO 2 ) and C-mineralization were about twice as high as for the Q. rubra plantations. Collembola and mites (Oribatei), both belonging to the soil mesofauna, reached higher densities in the Q. petraea plantations. When growing on highly fertile soils, the amount of soil nutrients (K + , Ca 2+ , Mg 2+ , and PO 4 3− P) did not differ between the two plantations. However, when oak trees grew on the less-fertile soil, the amount of soil nutrients was significantly lower beneath red oak. The amount of soil nutrients beneath red oak was even lower than beneath 2-year-old Q. robur plantations; the soil properties of which are almost at the beginning stage of succession. The results suggest that nutrient depletion beneath red oak when compared to sessile oak is caused both by increased immobilization into woody biomass, and by increased recalcitrance of organic matter.

Summary 1In laboratory microcosms, we investigated the influence of diversity of both leaf litter and detritivores on decomposition processes. Either woodlice or earthworms, or a combination of woodlice and earthworms, fed on leaf litter of either oak or alder, or oak and alder for 8 weeks. Mass loss of leaf litter, soil microbial respiration and soil nutrient concentrations were determined every 2 weeks. 2For four out of seven decomposition parameters, the joint effects of woodlice and earthworms were stronger than the sum of single-species effects when they had fed on alder litter. When feeding on oak litter, however, woodlice and earthworms together revealed lower decomposition rates than predicted from their single effects. Joint effects of detritivores on decomposition of mixed litter were always lower than predicted from the sum of their effects. 3In mixed-litter assays, we obtained intermediate values of decomposition parameters, indicating that doubling the species richness of leaf litter from one to two species did not promote decomposition processes. Effects of mixing litter were, thus, mostly additive; essentially only when earthworms fed on mixed litter we observed, mostly positive, non-additive effects of diverse litter. 4Our findings provide evidence for a potential effect on ecosystem functioning through joint action of detritivores even at low species diversity, while litter diversity seems to be less significant. On high-quality litter, isopods and earthworms are not functionally redundant but act synergistically on litter decomposition. The effects of detritivore diversity on ecosystem processes, however, are context-specific and depend on the quality and diversity of the available food sources, and on species-specific characteristics of the detritivores.

Different explanations have been proposed for why terrestrial isopods prefer, and gain from, feeding on microbially inoculated food materials. In the present study, no-choice feeding experiments are used to test three contrasting, but not mutually exclusive, hypotheses. (1) The digestion and nutritional utilization of microbial cells enhance the nutritive value of leaf litter; (2) extracellular digestive enzymes of microbial origin promote digestion of leaf litter; (3) leaf litter-colonizing microbiota serve as indicators for easily digestible leaf litter of high nutritive value. Predictions derived from these hypotheses are compared with the results of a study with experimentally manipulated leaf litter, serving as food sources for the common woodlouse Porcellio scaber. Leaf litter-colonizing microbiota increased consumption of leaf litter by isopods and contributed somewhat to biomass gain of isopods, but not to the assimilation of ingested food. Thus, the present results coincide with predictions derived from hypothesis (3) suggesting that leaf litter-colonizing microbiota stimulate consumption by indicating high food quality. Their positive effects on assimilation and growth, however, are context-specific, being stronger in case of high-quality food than in case of low-quality food.

In feeding experiments, leaf litter of different tree species and isopod feces derived from these leaf litter materials were offered to the common woodlouse, Porcellio scaber . Consumption indices were used to elucidate the nutritional significance of coprophagy. Consumption rates of P. scaber clearly differed between feeding assays with alder ( Alnus glutinosa ) litter and those with isopod feces derived from alder. Differences between feeding assays depended on microbial activity of the food sources when oak ( Quercus robur ) litter or isopod feces derived from oak were offered. Further, microbiota increased the digestibility of oak material, but did not change digestibility of alder litter and reduced digestibility of feces derived from alder. Thus, the significance of litter- or feces-colonizing microbiota decreased with increasing nutritive value of the leaf litter. Inoculated feces derived from oak provided better growth than any other oak-derived food. In contrast, isopods grew better on alder litter than on alder-derived feces. In sum, we found little evidence to support the notion that P. scaber gains from coprophagy. We reject the hypothesis that coprophagy meets a need for nutrients that, due to digestive incapabilities, cannot be satisfied by feeding on leaf litter alone. The hypothesis that microbial colonizers render feces attractive as a source of microbial enzymes or nutrients is only partly corroborated. P. scaber gains from coprophagy through microbial activity or biomass only if leaf litter quality is low.

In microcosms containing soil from a mixed deciduous forest, we examined the nutrient release from feces of phytophagous insects through coprophagous behavior of saprophagous soil animals during 12 weeks of decomposition. The decomposition of feces of Operophthera fagata (Lepidoptera: Geometridae) fed on beech (Fagus sylvatica) released more cations (Ca2+, Mg2+, K+) into the soil than the decomposition of beech litter, whether or not woodlice, Porcellio scaber and Oniscus asellus (Isopoda: Oniscidea), were present. Similarly, the C/N ratio of the soil was lower in assays with feces than in those with leaf litter. Coprophagy by isopods resulted in decreased C/N ratio of the soil. Respiratory activity of soil microbiota was greater when woodlice degraded Operophthera feces than when they degraded beech litter for 12 weeks. The present study provides evidence for nutrient release from the feces of phytophagous insects into the soil through the feeding activity of coprophagous soil animals.

Herbivorous beetles were sampled in central Slovakia and in the Tatra Mountains of northern Slovakia from seven different Salix species which are partly characterized by smooth leaves containing phenolic glycosides and partly by hairy leaves containing tannins. The collection included about 8000 individuals representing 129 species. Of the 129 species, 77 species are able to use the willows as hosts; the remaining 52 ‘tourist’ species comprise less than 3% of the collected individuals. The data on species richness and abundance did not generally support the ‘feeding specialization’ hypothesis. The proportion of specialized (= monophagous and oligophagous) beetles feeding on willows of both morphological and biochemical groups was in the same range. Host plants of the two groups could support high diversity and high evenness values, even when leaf characteristics and plant chemicals largely influenced species assemblage. The region in which the willow trees grow had a considerable impact on host plant use. Generalist beetle species predominated in central Slovakia. By contrast, in the Tatra Mountains, specialist feeders which are able to use phenolic glycosides to their advantage were predominant. The number of species and the total density of individuals collected from willows containing phenolic glycosides (S. fragilis and S. purpurea) did not usually vary between the two regions. In contrast, fewer species and individuals were found in the Tatra Mountains when they settled on willow species containing tannins (S. caprea and S. cinerea). Also, the phylogenetic status of host plants affected species assemblages. In central Slovakia willow species of the subgenus Vetrix (S. purpurea, S. caprea and S. cinerea) generally showed a higher beetle diversity (Hs) than species of the subgenus Salix (S. fragilis, S. alba and S. triandra), although both subgenera comprise species of both morphological and biochemical groups. Furthermore, when the analysis was restricted to beetles of central Slovakia, which should be most adapted to their host plants (i.e. catkin feeders and phyllophages in the adult and larval stage), the phylogenetic status was found to be more important than any single leaf character measured.

In microcosm experiments Porcellio scaber increased litter disappearance of oak and alder litter. Alder litter disappeared at more than twice the rate of oak litter. Soil texture did not influence the disappearance of oak litter; however, disappearance of alder litter was enhanced on silt rather than on sand. P. scaber enhanced microbial communities (i.e. microbial respiration and microbial biomass) on both silt and sand when feeding on either alder or oak. Overall, microbial respiration increased 10-fold when isopods fed on oak litter on sand and 20-fold when isopods fed on alder litter on sand. On silt, the initially high microbial respiration remained constant when isopods fed on oak and doubled when they fed on alder litter. In all treatments without P. scaber there was a decrease in microbial respiration over the 12-week experimental period. The availability of macronutrients (Corg, Ntot, P, K, Mg, Ca) in the topsoil was increased when P. scaber fed on alder litter but less pronounced when P. scaber fed on oak litter. Using sand as a substrate, there was an apparent increase only for Corg, Mg and Ca; on silt, increases in Corg, Ntot and P were measured. Under field conditions the contribution of P. scaber to nutrient fluxes will be higher on sand than on silt.

This paper is focused on diapause and polyphenism of development of Lagria hirta L. and tries to unravel its mechanism of life-history adaptation. Lagria hirta, distributed widely in Europe, has a strictly univoltine life cycle. The results showed that larval diapause and moulting polymorphism were the deciding factors that made L. hirta maintain its univoltinism and keep a flexible relation between seasonal changes and life-history phases. In the laboratory, larvae of this species were not able to pupate if kept at constant temperatures of 5 °, 10 °, 15 °, 20°, 25 ° or 30 °C combined with a photoperiod of either LD (L16:D8) or SD (L8:L16). Pupation only occurred if larvae were reared at 15 °-25 °C when intervened by a three-month chilling at 5 °C in stages L 3 , L 4 , L 5 or L 6 . A chilling treatment was shown to be obligatory for the termination of its larval diapause and had an accelerating and synchronizing effect on larval development. Larval diapause of L. hirta was characterized by no pupation and more moulting in advanced instars, longer duration of each single stage, and moulting desynchronization. Larval development was found to be variable with respect to the total number of instars: most larvae underwent a total of seven or eight moults; some larvae might even moult once or twice more, but they seldom pupated. It seemed that the choice for the 7-instar or the 8-instar development did not directly relate to any of the external conditions, such as temperature, photoperiod, and stages with chilling treatment. This polyphenism was observed in the same group under identical conditions and even in a single egg clutch. In L. hirta, overwintering in different stages of L 3 -L 6 . and choosing the 7- or 8-instar pathway of development are two features that increase the plasticity and flexibility in coordinating its life cycle with seasonal change, that varies unpredictably from year to year.

In the common woodlouse Porcellio scaber different parts of the gut were observed with respect to microbial counts, cellulose activity, and degradation of cellulose. Cellulose is mainly digested in the anterior part of the hindgut, as was indicated by the distribution of cellulolytic activity and the decrease of cellulose content inside the gut. The cellulases woodlice utilize for the degradation of litter are mainly produced by endosymbiotic bacteria in the hepatopancreas rather than by microorganisms ingested with the food. Microorganisms ingested with the litter are digested in the anterior part of the hindgut and may provide an important food source. In the posterior hindgut, bacterial proliferation ensures microbial colonization of feces.

Population parameters (mortality of females, reproductive success, longevity of juveniles) of the common woodlouse, Porcellio scaber (Isopoda, Oniscidea), were examined with respect to the influence of varying leaf litter attributes: pH level, microbial cellulase activity, microbial dehydrogenase activity, protein content, nitrogen content, water content, tannin content, total phenol content and toughness of the leaves. These attributes were combined by using Principal Component Analysis. We obtained three Principal Components (PC) that were defined as “acidification,”“microorganisms” and “tree species.” The PCs explained 85% of the variance of leaf litter attributes. The PC “acidification” mainly influenced the mortality of females (P