Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid- and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered.

The current changes in our climate will likely have far-reaching consequences for aquatic ecosystems. These changes in the climate, however, do not act alone, and are often accompanied by additional stressors such as eutrophication. Both global warming and eutrophication have been shown to affect the timing and magnitude of phytoplankton blooms. Little is known about the combined effects of rising temperatures and eutrophication on the stoichiometry of entire phytoplankton communities. We exposed a natural phytoplankton spring community to different warming and phosphorus-loading scenarios using a full-factorial design. Our results demonstrate that rising temperatures promote the growth rate of an entire phytoplankton community. Furthermore, both rising temperatures and phosphorus loading stimulated the maximum biomass built up by the phytoplankton community. Rising temperatures led to higher carbon: nutrient stoichiometry of the phytoplankton community under phosphorus-limited conditions. Such a shift towards higher carbon: nutrient ratios, in combination with a higher biomass buildup, suggests a temperature-driven increase in nutrient use efficiency, the phytoplankton community. Importantly, with higher carbon: nutrient stoichiometry, phytoplankton is generally of poorer nutritional value for zooplankton. Thus, although warming may result in higher phytoplankton biomass, this may be accompanied by a stoichiometric mismatch between phytoplankton and their grazers, with possible consequences for the entire aquatic food web.

We studied the occurrence of colony formation within 40 different strains of Scenedesmaceae (Chlorococcales, Chlorophyta) in response to grazing-released infochemicals from the herbivorous zooplankters Brachionus calyciflorus Pallas (Rotifera) and Daphnia magna Strauss (Cladocera). With the exception of two strains, all strains showed similar responses to both B. calyciflorus and D. magna infochemicals, either no response or inducible colony formation. Colony size was found to increase with B. calyciflorus infochemical concentration and could be described by a sigmoid function. The increase in colony size was more pronounced in the Scenedesmus species tested than in Desmodesmus species, which was probably due to higher threshold infochemical concentrations for colony induction in Desmodesmus. Therefore, the adaptivity of colony formation to the herbivory threat only holds above the threshold concentration for colony induction and as long as maximum colony size has not been attained. Taking this into account, our results suggest that inducible colony formation is a common adaptive response of many Scenedesmaceae to the threat of herbivory.

Summary 1. Many host–parasite interaction dynamics show distinct seasonality. Parasite population growth and invasion success are generally explained by host density dependence, while the direct influence of environmental factors on parasite life history traits has been underreported. 2.  In waterbodies, resource availability and environmental conditions change with season (temperature, irradiance and rainfall patterns) and with depth (light, temperature and chemical gradients). Hence, hosts and parasites live in a spatially and temporally variable environment. Such environmental variation leads to structured populations, which in turn have implications for host–parasite interaction dynamics. Nevertheless, time‐series data on the vertical distribution of aquatic hosts and their parasites are rare. 3.  We present a dataset spanning 1.5 years (2008–2010) of weekly sampling in Lake Maarsseveen (the Netherlands) focussing on the dynamics of the diatom Asterionella formosa and its parasite, the chytrid Zygorhizidium planktonicum, at four depths. Environmental variables measured included ice cover, temperature, global irradiance, light extinction, pH, soluble reactive silicate (SRSi), dissolved nitrate and ortho‐phosphate. 4.  We observed four host blooms, two in early spring and one each in summer and autumn. Each host bloom was followed by a time‐lagged parasite epidemic. Blooms and epidemics started in the uppermost water layers and showed a time lag in onset date with increasing depth. 5.  Host abundance was related to SRSi, global irradiance, Schmidt stability and parasite abundance in the upper 10 m, whereas at 15 m only a relationship with parasite abundance prevailed. Parasite abundance was related to host abundance, light extinction, temperature, SRSi, stability and global irradiance within the upper 10 m; again, at 15 m, parasite abundance correlated only with host abundance and disease prevalence. 6.  Host vertical distribution was less aggregated during isothermal conditions than during thermal stratification, when host abundance was higher in the mixed, photic epilimnion and lower in the dark, colder hypolimnion. Parasite vertical distribution was patchy most of the year. Parasite epidemics seemed to reduce host vertical patchiness as they impacted higher density patches in the photic zone more strongly, a result of both higher host abundance and favourable environmental conditions for the parasite. 7.  Seasonal variability and vertical gradients in biotic and abiotic factors expose host and parasite individuals to different environmental conditions even within a single population. Environmental variability affects parasite transmission rates through changes in host abundance and through changes in the strength and outcome of host–parasite interactions.

Abstract. Inducible defenses are dynamic traits that modulate the strength of both plantherbivore and herbivore-carnivore interactions. Surprisingly few studies have considered the relative contributions of induced plant and herbivore defenses to the overall balance of bottom-up and top-down control. Here we compare trophic cascade strengths using replicated two-level and three-level plankton communities in which we systematically varied the presence or absence of induced defenses at the plant and/or herbivore levels. Our results show that a trophic cascade, i.e., significantly higher plant biomass in three-level than in two-level food chains, occurred whenever herbivores were undefended against carnivores. Trophic cascades did not occur when herbivores exhibited an induced defense. This pattern was obtained irrespective of the presence or absence of induced defenses at the plant level. We thus found that herbivore defenses, not plant defenses, had an overriding effect on cascade strength. We discuss these results in relation to variation in cascade strengths in natural communities.