Seasonal dynamics of decomposition of coniferous leaf litter in a forest plantation (Pinus merkusii) in Central Java, Indonesia.

Decomposition of coniferous litter was studied from March 1990 until March 1991 in a pine forest plantation (Pinus merkusii) in two 0.2 ha plots, at altitudes of 600 and 800 m on the southwest slope of Mount Merapi (2911 m), Central Java. Stratified litterbag sets were used to compare the influences of seasonality and degradation stage on the decomposition of pine litter. The variables used in monitoring the decomposition processes were weight loss, carbon and nitrogen contents and enzyme activity of the litter microflora. At each site the litterbags containing pine needles from L and F layers were randomly distributed in the L and F layers, respectively. After 1 year the weight loss in the litterbags in the upper plot was 32% in the L and 53% in the F layer. Weight loss in the lower plot was 60% in the L and 42% in the F layer. Temperature and moisture were not responsible for these differences in weight loss. Carbon content of litter in both plots decreased during a year from 49 to 35-37% in the L layer and from 38 to 28-31% in the F layer. Net immobilization of N took place in the L layer and net mobilization in the F layer. Dehydrogenase activity was positively correlated with N content and was highest when the critical N % was reached. Decomposition rate was influenced by moisture, but the chemical composition of the litter seemed to be even more important in determining the decay rate of the L layer

Analysis of bioassays with time-varying concentrations.

In the analysis of ecotoxicological bioassays the concentration of the test compounds is assumed to be constant. In many situations this assumption is questionable, as various processes may cause a substantial decline in the concentration during exposure. This leads to difficulties in the estimation of parameters that characterise the toxicity of the test compound. As a solution to this problem, time-varying concentrations are often replaced by their mean values for the estimation of toxicity parameters. However, Monte-Carlo simulations show that this approach results in biased estimates of the toxicity parameters. As an alternative approach, we propose models to estimate one important toxicity parameter, the no effect concentration, in situations where the concentration of the compound varies in time. These models are extensions of the DEBtox model (Kooijman and Bedaux, 1996) which is based on biological assumptions about toxicokinetics and toxic effects. We also propose a new approach for the estimation of toxicity parameters for strongly accumulating non-metabolisable compounds. This approach does not require any kinetics assumption. Computer simulation and experimental data confirm the relevance of the different proposals. © Elsevier Science Ltd. All rights reserved

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

Quantitative Relationship between Phytochelatin Accumulation and Growth Inhibition during Prolonged Exposure to Cadmium in Silene vulgaris.

Phytochelatins (PCs) are known to detoxify heavy metals in plants. This study aimed to investigate the possibility of using PCs as a biomarker for chronic Cd toxicity in Silene vulgaris. For this purpose, the effects of Cd on growth rate, related to plant weight, and the PC concentrations were recorded throughout the bigger part of the vegetative phase. The lowest concentrations of Cd used, 1 and 2 μM, inhibited plant growth rates by 30 and 50%, respectively, independent of the weight of the exposed plants. Above an exposure concentration of 2 μM Cd, the toxic effect increased with plant weight. At 3.5 μM Cd, the plant growth rates were inhibited up to 90%. Further increases of the exposure concentration did not produce additional inhibition. Root PC concentrations correlated with growth inhibition only at the lower Cd concentrations, i.e. up to 2 μM Cd. Above this concentration the correlation was lost