Season-Long Experimental Drought Alters Fungal Community Composition but Not Diversity in a Grassland Soil.

Using terrestrial model ecosystems (TMEs), we investigated how reduced moisture conditions impact soil fungal communities from a temperate grassland over the course of an entire season. Starting at about 65% of the soil's maximum water holding capacity (WHCmax), TME soils were adjusted to three moisture levels for 15 weeks: 70% WHCmax, approximating starting conditions, 50% WHCmax, and 30% WHCmax, representing reduced moisture conditions. Diversity and abundances of soil fungi at the start and at the end of the experiment were characterized using Illumina meta-barcoding. Community diversity at the end of the experiment did not differ between experimental moisture levels and was comparable to diversity measures from the field. However, fungal communities did change compositionally in both abundances and presence/absence of species. Analyzing class-level and individual contributions of fungi to these changes revealed that only a minor portion reacted significantly, indicating that most compositional change was likely driven by many consistent small-scale shifts in presence/absences or abundances. Together, our results show that prolonged reduction in soil moisture conditions will trigger compositional changes in soil fungal communities but not necessarily change overall diversity. We highlight the cumulative contribution of minor but consistent changes among community members, as opposed to significant responses of individual species. We also detected a strong general experimental effect on soil fungi that are moved from the field to experimental TMEs, suggesting the importance of acclimatization effects in these communities under laboratory conditions.

A TME study with the fungicide pyrimethanil combined with different moisture regimes: effects on enchytraeids.

Today's ecosystems are influenced by different factors that could evolve into stressors. Effects of pesticides, especially in agricultural areas, may interact with environmental factors, such as soil moisture fluctuation caused by global climate change. In this contribution, two semi-field studies conducted in Germany and Portugal with terrestrial model ecosystems are presented. Their aim was to assess the effects of the fungicide pyrimethanil under different soil moisture levels on Enchytraeidae. In Portugal a no observed effect concentration design was chosen, using two concentration levels: the maximum application rate (MAR) according to the safe use registration within the European Union and five times the MAR (1.82 and 9.09 mg/kg dry soil, respectively). Both concentrations did neither affect the total enchytraeid abundance nor single populations. In Germany an ECx design (effect concentration) was conducted, using 11 concentrations. In general, 14 EC50 values for different combinations of single species, moisture level and sampling date were determined. The strongest effects were found in dry soil, particularly for Fridericia connata (EC50: 3.48 mg/kg dry soil after 8 weeks of exposure). The advantages and challenges of these test designs are discussed with regard to the registration process of pesticides in the European Union. In any case, enchytraeids are suitable test organisms in such higher tier studies for the combined evaluation of chemical and climatic stressors due to their usually high diversity and abundances and their close contact with the soil solution.

Interactive effects of λ-cyhalothrin, soil moisture, and temperature on Folsomia candida and Sinella curviseta (Collembola).

The authors investigated whether and how 2 environmental factors could influence the toxicity of a pyrethroid to 2 representatives of an important group of soil organisms. The impacts of different temperatures (20 °C and 26 °C) and soil moisture levels (30%, 50%, and 70% of water holding capacity) were investigated in combination with the insecticide λ-cyhalothrin on the reproduction success of Folsomia candida and Sinella curviseta in a full factorial design. Testing was based on the standard collembolan reproduction test (Organisation for Economic Co-operation and Development, guideline 232) following an effect concentration design. The results showed an effect of environmental and chemical factors on the number of juveniles of these animals. Particularly in dry soil, the reproduction of both species was reduced, while higher soil moisture levels influenced the number of juveniles positively compared with the middle soil moisture level. In general, however, higher soil moisture led to increased sensitivity to λ-cyhalothrin. In both organisms, temperature affected the toxicity of the pesticide but in different directions: high temperature led to higher toxicity in F. candida but to lower toxicity in S. curviseta.

Development of an embryo toxicity test with the pond snail Lymnaea stagnalis using the model substance tributyltin and common solvents.

The development of a chronic mollusc toxicity test is a current work item on the agenda of the OECD. The freshwater pond snail Lymnaea stagnalis is one of the candidate snail species for such a test. This paper presents a 21-day chronic toxicity test with L. stagnalis, focussing on embryonic development. Eggs were collected from freshly laid egg masses and exposed individually until hatching. The endpoints were hatching success and mean hatching time. Tributyltin (TBT), added as TBT-chloride, was chosen as model substance. The selected exposure concentrations ranged from 0.03 to 10 µg TBT/L (all as nominal values) and induced the full range of responses. The embryos were sensitive to TBT (the NOEC for mean hatching time was 0.03 µg TBT/L and the NOEC for hatching success was 0.1 µg TBT/L). In addition, data on maximum limit concentrations of seven common solvents, recommended in OECD aquatic toxicity testing guidelines, are presented. Among the results, further findings as average embryonic growth and mean hatching time of control groups are provided. In conclusion, the test presented here could easily be standardised and is considered useful as a potential trigger to judge if further studies, e.g. a (partial) life-cycle study with molluscs, should be conducted.