Effects of artificial acidification and liming on the activity of digestive enzymes in Cognettia sphagnetorum (Vejdovsky´, 1878) (Annelida, Enchytraeidae)

The effects of simulated acid rain and acidification, combined with liming, on amylolytic, laminarinolytic and xylanolytic activity in whole body homogenates of enchytraeids Cognettia sphagnetorum were studied under field conditions. Simulated acid rain (pH 2.5) and simulated acid rain with subsequent liming (CaCO₃) were applied to experimental plots in a mixed forest soil. The pH of the soil was lowered by acid treatment (4.3), while the pH increased after liming (6.3) in comparison with the control (4.5). Acidification of soil caused a decrease in enchytraeid body mass and amylolytic activity. In acidified plots after liming, amylolytic activity and laminarinolytic activity increased, while live body mass decreased. The enzymatic activity of enchytraeids depended on season and also indirectly on individual mean mass. Received: 12 February 1996     

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     

Estimates of the Enchytraeidae (Oligochaeta,Annelida) contribution to energy flow in the soil system of an acid beech wood forest

Summary The data introduced here are part of a project lasting from 1976 to 1985 in an acid beech wood forest in the northern part of the Black Forst in Southern Germany. With Enchytraeidae (Oligochaeta) as an example, attempts were made to determine the part played by the mesofauna in the soil system. Parameters such as respiration, production, and consumption were estimated using abundance and biomass data as a basis. The results show that not only the Enchytraeidae but even single species like Cognettia sphagnetorum or Mesenchytraeus glandulosus contribute a measurable amount to the energy flow of the soil ecosystem. The respiration of the whole population, for example, corresponds to 3.4% of the total energy input via leaf litter, and consumption amounts to 8.1% of the total litter including twigs. It seems that the Enchytraeidae contribute around 60% of the total soil animal respiration in this acid beech wood, and thus play an important role in soil renewal.     

Effects of Key deer herbivory on forest communities in the lower Florida Keys

Ungulate herbivory can have strong impacts on plant communities, but these impacts are rarely considered in recovery plans of endangered species. This study examined the effects of the endangered Key deer (Odocoileus virginianus clavium) on its environment in the lower Florida Keys. The Key deer population has increased to over 700 deer from approximately 50 deer in the 1950s; however, approximately 75% of the population resides on only a few islands (Big Pine, No Name, Big Munson) where Key deer herbivory on forest communities may be substantial. Effects of deer herbivory on plant densities were estimated on these islands using vegetation quadrats in hardwood hammock, buttonwood transition, and mangrove wetlands and compared to nine other islands with intermediate or low deer densities. On islands with high deer density, densities of preferred woody plant species <1.2 m tall (within Key deer reach) were significantly lower than islands with lower deer densities, while densities of some nonpreferred species were significantly higher. Deer exclosures established in hardwood hammock on a high-density deer island revealed a mean increase in abundance/height of preferred woody species inside exclosures, while nonpreferred species significantly increased in open plots. We conclude that on high deer density islands, highly preferred plant species might eventually fail to regenerate and unpalatable plant species may become dominant. Careful criteria need to be developed to maintain Key deer numbers above an endangered species status yet below levels that are destructive to local forest species.     

Influence of Cognettia sphagnetorum (Oligochaeta: Enchytraeidae) on nitrogen mineralization in homogenized mor humus

Summary The influence of the enchytraeid species Cognettia sphagnetorum on N mineralization in homogenized mor humus was examined in a laboratory study. The mor humus was incubated in containers (150 ml) for 8 months at various temperatures and with different moisture levels. Two series were used, one with C. sphagnetorum and one without. The presence of enchytraeids in the cultures increased the level of NH₄ ⁺ and NO₃ ^- by about 18% compared with the cultures without enchytraeids. Almost 40% of this difference was explained by the decomposition of dead enchytraeids. Temperature and soil moisture were the most important factors controlling the mineralization rate. The optimum moisture for N mineralization was between pF 1.6 and 1.1.Dedicated to the late Prof. Dr. W. Kühnelt     

Secondary succession of terrestrial isopod,centipede, and millipede communities in grasslands under restoration

The aim of this study was to investigate the impact of restoration management on the composition of a macro-invertebrate community in a formerly, nutrient-poor grassland. Four grassland plots were selected that were last fertilised 7, 11, 24 or 29 years before sampling in 1996. In the same plots it was observed that nutrient impoverishment as a restoration tool resulted in a decrease in primary production and a directional shift in vegetation composition after cessation of fertiliser application. Terrestrial isopods, millipedes, and centipedes were sampled with pitfall traps in the four plots. The directional shift observed in vegetation composition before this study was not accompanied by a directional change in macro-invertebrate composition. Both the field poorest in nutrients and the one richest in nutrients showed the lowest density and species richness, while the species composition was similar across intermediate succession stages. By far the most specimens and species were caught in the field that had not received fertilisers for 24 years. Succession theory could only partly explain the observed results. Canonical correspondence analysis of the data revealed that only a small part of the pattern could be explained by the nutrient status of the grasslands. The C accumulation due to secondary succession of plants was hypothesised to influence the densities and diversity of macro-invertebrate communities in these grasslands.     

Response of ectomycorrhizal communities to past Roman occupation in an oak forest

The impact of past Roman occupation on the composition of ectomycorrhizal (ECM) communities was analysed in 12 Roman settlements in an oak forest in Central France. At each Roman settlement, soils and ECM roots were sampled from two plots (600 m² each), one plot close to the remains of the buildings (<100 m), supposed to be impacted by ancient Roman agriculture, and the second plot 250-500 m away from the remains of the buildings, supposed to be less intensively influenced by previous cultivation. Soils were analysed and ECM fungal taxa were identified by morphotyping and sequencing the rDNA ITS region. The soil properties were significantly affected by the past Roman occupation, in terms of nutrient availability, especially for P, N and Mg. The enhancement of soil nutrient levels by past Roman land-use had significantly modified alpha diversity and species composition of ECM communities. Among the 67 determined ECM morphotypes, 40 were shared by the occupied and non-occupied plots, 17 were found only in the occupied plots and 10 only in the non-occupied plots. Six morphotypes were significantly more frequent near the antique remnants. Our study showed, for the first time, that ectomycorrhizal communities are impacted by previous Roman land-use, even after nearly two thousand years of forest state.     

南亚热带森林演替过程土壤水分、有机质和交换性阳离子的变化格局

Information on the distribution patterns of soil water content （SWC）, soil organic matter （SOM）, and soil exchangeable cations （SEC） is important for managing forest ecosystems in a sustainable manner. This study investigated how SWC, SOM, and SEC were influenced in forests along a successional gradient, including a regional climax （monsoon evergreen broad-leaved forest, or MEBF）, a transitional forest （coniferous and broad-leaved mixed forest, or MF）, and a pioneer forest （coniferous Masson pine （Pinus rnassoniana） forest, or MPF） of the Dinghushan Biosphere Reserve in the subtropical region of southern China. SWC, SOM, and SEC excluding Ca^2＋ were found to increase in the soil during forest succession, being highest in the top soil layer （0 to 15 cm depth） except for Na^＋. The differences between soil layers were largest in MF. This finding also suggested that the nutrients were enriched in the topsoil when they became increasingly scarce in the soil. There were no significant differences （P = 0.05） among SWC, SOM, and SEC. A linear, positive correlation was found between SWC and SOM. The correlation between SOM and cation exchange capacity （CEC） was statistically significant, which agreed with the theory that the most important factor determining SEC is SOM. The ratio of K^＋ to Na^＋ in the topsoil was about a half of that in the plants of each forest. MF had the lowest exchangeable Ca^2＋ concentration among the three forests and Ca^2＋：K^＋ in MPF was two times higher than that in MF. Understanding the changes of SWC, SOM, and CEC during forest succession would be of great help in protecting all three forests in southern China.     

Pollution-induced tolerance of soil bacterial communities in meadow and forest ecosystems polluted with heavy metals

Pollution-induced community tolerance (PICT) allows finding a cause–effect relationship between pollution and adverse changes in a community. In our previous study we found that functional diversity of bacterial communities decreased significantly with increasing metal concentration, in both forest humus and meadow topsoil. Thus, the aim of the present study was to test whether tolerance of soil bacterial communities had increased as an effect of long-term metal pollution. Bacterial tolerance was tested with the use of the Biolog^® ECO plates in soils originating from the most polluted and the least polluted sites from three forest and five meadow transects located near smelters in Avonmouth (England), Clydach (Wales), and Głogów and Olkusz (Poland). We found that tolerance of bacterial communities was significantly increased in polluted meadow soils when compared to control meadow soils. On the contrary, no increase in tolerance was detected in polluted forest humus.     

Parasitoids (Hymenoptera, Ichneumonoidea) of Saproxylic beetles are affected by forest successional stage and dead wood characteristics in boreal spruce forest

The habitat requirements and effects of forest management on insects belonging to higher trophic levels are relatively unknown in forest ecosystems. We tested the effect of forest successional stage and dead wood characteristics on the saproxylic parasitoid (Hymenoptera, Ichneumonoidea) assemblage in boreal spruce-dominated forests in northern Sweden. Within each of nine areas, we selected three sites with different management histories: (1) a clear-cut (2) a mature managed forest and (3) an old-growth forest. Parasitoids were collected in 2003 using eclector traps mounted on fresh logs, which were either untreated (control), burned, inoculated with fungi, or naturally shaded, and on artificially-created snags.Both forest type and dead wood characteristics had a significant effect on parasitoid assemblages. Grouped idiobionts and some species, such as Bracon obscurator and Ontsira antica, preferred clear-cuts, while others, such as Cosmophorus regius (Hym., Braconidae) and other koinobionts, were associated with older successional forest stages. No single dead wood substrate was sufficient to support the entire community of parasitoids in any forest type, even when the regular host was present. In particular, snags hosted a different assemblage of species from other types of dead wood, with parasitoids of Tetropium spp. such as Rhimphoctona spp. (Hym., Ichneumonidae) and Helconidea dentator (Hym., Braconidae) being abundant. These results indicate that a diversity of dead wood habitats is necessary to support complete assemblages of beetle-associated parasitoids from early successional stages of dead wood and that parasitoids may be more sensitive to habitat change than their hosts.     

Cryptic diversity in the well-studied terrestrial worm Cognettia sphagnetorum (Clitellata: Enchytraeidae)

The terrestrial worm Cognettia sphagnetorum has been used as a model in several studies focusing on research areas such as climate change as well as forest and soil ecology; it has also been shown to play a key role in the decomposition of organic matter and nutrient cycling. Cognettia is an enchytraeid genus commonly found in acidic terrestrial habitats, such as coniferous forests and bogs. In this study, the diversity of the genus, with particular focus on the morphospecies C. sphagnetorum in northern Europe, is assessed using four molecular markers, the mitochondrial COI (cytochrome c oxidase subunit I) and16S (16S ribosomal RNA), and the nuclear H3 (Histone 3) and ITS (Internal Transcribed Spacer). The datasets were first delimited into Molecular Operational Units (MOTUs) and the existence of global barcoding-gaps was tested. Single gene-trees were then estimated for all genes using Bayesian Inference, and a species tree was estimated with all markers combined using the multi-species coalescence. The results show that in northern Europe the genus consists of at least eight MOTUs supported by all genes except H3. Four of these MOTUs were within the morphotaxon C. sphagnetorum and two within Cognettia glandulosa. C. sphagnetorum s.l. was found to be non-monophyletic in all gene-trees, as well as in the species tree. As the MOTUs were well separated and non-monophyly was observed within C. sphagnetorum s.l., we conclude that the MOTUs are best treated as separate species. Given that cryptic diversity was found in this genus, we recommend that material of Cognettia used in future studies should be identified using molecular barcodes.     

The impacts of forest clearance on lizard, small mammal and bird communities in the arid spiny forest, southern Madagascar

Madagascar is a global biodiversity hotspot threatened by forest loss, degradation and fragmentation, all of which are detrimental to the future survival of forest-dwelling organisms. For conservation purposes it is essential to determine how species respond to habitat disturbance, specifically deforestation. In this study we investigated the impacts of deforestation on three vertebrate communities, lizards, small mammals and birds, in an area of spiny forest subjected to anthropogenic forest clearance. Spiny forest has high levels of endemism, but conservation in this unique ecosystem is hindered by the lack of research. We undertook standardised trapping, time-constrained and timed species searches to assess species richness, species abundance and community composition of lizards, small mammals and birds in six areas of ‘forest’ and six ‘cleared’ areas. From surveys and opportunistic sightings we recorded a total of 70 species of birds, 14 species of mammals and 38 species of reptiles and amphibians. We found forest clearing to have a negative effect on species richness and community structure of all groups and identified loss of canopy cover as a driving factor behind this. However, the response and sensitivity to clearing varied between groups and species. Lizards (50%) and small mammals (40%) had the greatest decline in species richness in response to clearing as compared to birds (26%), although birds showed the greatest shift in community structure. The community in cleared areas contained more generalist and introduced species that have wider geographic ranges and habitat preferences, than those unique to the spiny forest. We found the first suite of species to suffer from forest clearance were those of high conservation priority due to their restricted geographic range. Our findings are discussed in relation to future spiny forest conservation and management.     

Limits to the bioindication potential of Collembola in environmental impact analysis: a case study of forest soil-liming and fertilization

We tested the suitability of the collembolan community as a bioindicator for assessing the effects of forest soil-liming and fertilization on the belowground decomposer community. Our investigation was based on a 5-year survey that took place in a German oak-hornbeam and spruce forest in which amelioration measures took place in 1988, 1994 and 1995, with chemical parameters and Collembola being sampled between 1993 and 1997. To address these questions, we applied new methods which have not yet, to our knowledge, been used in biomonitoring studies on forest soils. We used a time-lag analysis for the detection of directional change and a regression-tree induction to show the relationship between Collembola and soil factors. Soil parameters changed considerably after the onset of liming and fertilization. However, no change was detected in community composition over time, nor was there a relationship between Collembola and soil parameters that would make possible the development of a model with at least a moderate predictive success. Taking into account the effort invested in this study (5-year sampling period, identification of 35,000 Collembola, 99 species, 1,170 chemical analyses), we question the suitability of collembolan communities as a bioindicator for forest disturbance.     

Involvement of Enchytraeidae (Oligochaeta) in soil structure evolution in agricultural fields

Summary The effects of enchytraeid activity on soil structure were recorded in a field study on population dynamics in agro-ecosystems and in a field experiment, using artificially compounded soil cores. It was established that 21–35% of the enchytraeid population contained mineral grains. The estimated transport of mineral material in the upper 0.4 m amounted to 0.001–0.01% of the bulk soil per year. In experimental cores with enchytraeids present, the air permeability, volume of pores in the size class corresponding to the enchytraeid body width, and the proportion of aggregates corresponding to the size of their fecal pellets were higher than in cores without enchytraeids.Dedicated to the late Prof. Dr. W. Kühnelt Communication no. 15 of the Dutch programme on soil ecology of arable farming systems     

石灰岩山地淡竹林演替序列土壤养分及其与群落特征的关系

为探寻石灰岩山地淡竹林演替序列土壤养分变化及其与群落特征的关系,采用空间代替时间方法,对竹纯林、混交林和阔叶林3个演替阶段的土壤养分、群落物种组成和多样性进行了研究,结果表明:(1)竹纯林向混交林、阔叶林演替的过程中,有机质、速效氮、速效磷含量、pH和电导率均呈"V"形变化,阔叶林土壤养分含量最高;(2)混交林阔叶树比例介于26%~73%之间,不同阔叶树比例的混交林土壤养分含量有差异,但养分含量与阔叶树比例没有显著相关关系;(3)由竹纯林演替到混交林,有机质含量和电导率的降低量分别与群落物种替代速率、草本层均匀度的变化呈显著负相关和正相关;从混交林演替到阔叶林,有机质、速效氮和速效磷含量的增量随着木本植物多样性的增加、草本植物多样性的降低而增加。分析认为,淡竹林演替序列土壤养分的"V"形变化是喀斯特地区自然演替序列较为特殊的规律,它与演替过程的群落特征变化具有密切联系。今后以混交林为关键阶段,整合土壤微生物和土壤酶的研究将有助于深入揭示淡竹林演替序列土壤养分变化规律的形成机制。     

Response of soil properties and yam yield to Chromolaena odorata (Asteraceae) and Tithonia diversifolia (Asteraceae) mulches

Plant materials differ in their chemical composition, rate of decomposition and suitability as mulch materials. Experiments were conducted during 2006–2007 and 2007–2008 cropping seasons for early yam cultivation at Owo in the forest–savanna transition zone of southwest Nigeria to study the effect of Chromolaena odorata and Tithonia diversifolia mulches applied at 0.0, 5.0, 7.5, 10.0 and 12.5 t ha^?1 on soil chemical properties, leaf nutrient composition, growth and tuber yield of white yam (Dioscorea rotundata Poir). Both C. odorata and T. diversifolia mulches reduced soil bulk density and temperature; increased concentrations of soil organic matter (SOM), total N, available P, exchangeable K, Ca and Mg, leaf N, P, K, Ca and Mg; enhanced growth and yield of yam compared with control. The values of SOM, total N and available P and leaf N and P concentrations increased with increasing mulch rate. C. odorata mulch and T. diversifolia mulch applied at 10.0 and 7.5 t ha^?1, respectively, was found to be suitable for yam production. T. diversifolia mulch compared with C. odorata mulch produced higher values of soil chemical properties, leaf nutrient concentrations, growth and yield of yam. T. diversifolia mulch produced 19% and 18% higher tuber yield compared with C. odorata mulch during 2006–2007 and 2007–2008 cropping seasons, respectively.     

Arbuscular mycorrhizal fungal communities in changing environments: The effects of seasonality and anthropogenic disturbance in a seasonal dry forest

The landscape of Mexican seasonal dry forests is affected by various periodic (long and drastic drought) and random (elimination of the forest coverage for agricultural purposes) disturbance events. The community of arbuscular mycorrhizal fungi (AMF) responds to these changes, sporulating and reducing its activity during the dry season, and slowly reestablishing itself following abandonment of cultivated fields. To determine the dynamics of the AMF community in response to natural phenomena and anthropogenic disturbances, we collected soil samples during the wet and dry seasons from plots with different time periods since abandonment of agricultural activity, categorized as early (less than 5 years), middle (11–23 years), and late (over 30 years) age plots. From each plot, AMF spores were isolated and identified in order to estimate abundance, richness and diversity. In addition, the number of infective propagules and value of mycorrhizal inoculum potential were calculated for each plot. Twenty-three species were recorded, for which Glomeraceae and Acaulosporaceae were the most commonly represented families. Significant differences were found in AMF species richness among plots and seasons and the diversity index of AMF was higher than 1.0 in most cases. There were no significant differences in spore abundance. Viable propagules were observed in all soil samples, with fluctuations relating mainly to time since abandonment. Overall, seasonality has a strong influence on AMF diversity but not on AMF infectivity, while time since abandonment had a more important impact.