Medium-term response of the natural grassland soil biota to multiwalled carbon nanotube contamination.

Although the soil environment can potentially be exposed to contamination by carbon nanotubes (CNT), its impact on soil biology is poorly understood. In this study, we investigated the effect of the multiwalled CNT (MWCNT) contamination on different groups of soil organisms (microbial, micro- and mesofaunal communities) as well as the soil enzyme activity. The experimental mesocosms included the intact soil cores that were collected from a natural grassland. The MWCNTs that were pristine (pCNTs) and functionalised (fCNTs) at a concentration of 500 µg g-1 of soil were applied in the form of water suspensions to the surface of the mesocosms, while ensuring the soil was not mixed after the treatment. Soil samples were taken at 3, 6, and 15 weeks after CNT application. The CNT soil contamination highlighted differences in the community dynamics within the studied groups when compared to the control (non-contaminated soil). Among the faunal groups, nematodes were found to be more sensitive to the CNT impact than mites. The most pronounced response of the nematodes was observed in the subsoil at week 6, when their numbers were 3- (pCNTs) and 4-fold (fCNTs) higher than the control mesocosms. Both types of CNTs influenced the relative abundance of the bacterial- and hyphal-feeding nematodes, where pCNTs significantly and negatively affected the predatory nematodes. Moreover, CNTs temporarily, but significantly, decreased the diversity of the nematode communities. In addition, the values of the nematode Structure Index confirmed a strong transitional disturbance effect of CNTs in the soil food web, while the Channel Index in the pCNTs indicated an increasing share of fungi in the decomposition pathway. Hence, we can infer that although the impact of CNTs seems to be temporary, the shifts in the soil community abundance and structure that it induced may have long-term consequences for soil functioning, including nutrient cycling.

A systemic overreaction to years versus decades of warming in a subarctic grassland ecosystem.

Temperature governs most biotic processes, yet we know little about how warming affects whole ecosystems. Here we examined the responses of 128 components of a subarctic grassland to either 5-8 or >50 years of soil warming. Warming of >50 years drove the ecosystem to a new steady state possessing a distinct biotic composition and reduced species richness, biomass and soil organic matter. However, the warmed state was preceded by an overreaction to warming, which was related to organism physiology and was evident after 5-8 years. Ignoring this overreaction yielded errors of >100% for 83 variables when predicting their responses to a realistic warming scenario of 1 °C over 50 years, although some, including soil carbon content, remained stable after 5-8 years. This study challenges long-term ecosystem predictions made from short-term observations, and provides a framework for characterization of ecosystem responses to sustained climate change.

Temporal patterns of energy equivalence in temperate soil invertebrates.

The question whether total population energy use is invariant to species body size (the energy equivalence hypothesis) is central to metabolic ecology and continues to be controversial. While recent comparative field work and meta-analyses pointed to systematic deviations of the underlying allometric scaling laws from predictions of metabolic theory none of these studies included the variability of metabolic scaling in ecological time. Here we used extensive data on the invertebrate soil fauna of Kampinos National Park (Poland) obtained from six consecutive quantitative sampling seasons to show that phylogenetically corrected species density-body weight and population energy use-body weight relationships across all soil fauna species and within trophic groups and body weight classes were highly variable in time. On average, population energy use tended to increase with species body weight in decomposers and phytophages, but not in predators. Despite these trends, our data do not exclude the possibility that energy equivalence marks the central tendency of energy use in the edaphon. Our results highlight the need for long-term studies on energy use to unequivocally assess predictions of metabolic theory.