Summary1. Studying the effects of climate or weather extremes such as drought and heat waves on biodiversity and ecosystem functions is one of the most important facets of climate change research. In particular, primary production is amounting to the common currency in field experiments world-wide. Rarely, however, are multiple ecosystem functions measured in a single study in order to address general patterns across different categories of responses and to analyse effects of climate extremes on various ecosystem functions. 2. We set up a long-term field experiment, where we applied recurrent severe drought events annually for five consecutive years to constructed grassland communities in central Europe. The 32 response parameters studied were closely related to ecosystem functions such as primary production, nutrient cycling, carbon fixation, water regulation and community stability. 3. Surprisingly, in the face of severe drought, above-and below-ground primary production of plants remained stable across all years of the drought manipulation.4. Yet, severe drought significantly reduced below-ground performance of microbes in soil indicated by reduced soil respiration, microbial biomass and cellulose decomposition rates as well as mycorrhization rates. Furthermore, drought reduced leaf water potential, leaf gas exchange and leaf protein content, while increasing maximum uptake capacity, leaf carbon isotope signature and leaf carbohydrate content. With regard to community stability, drought induced complementary plantplant interactions and shifts in flower phenology, and decreased invasibility of plant communities and primary consumer abundance. 5. Synthesis. Our results provide the first field-based experimental evidence that climate extremes initiate plant physiological processes, which may serve to regulate ecosystem productivity. Journal of Ecology 2011Ecology , 99, 689-702 doi: 10.1111Ecology /j.1365Ecology -2745Ecology .2011 of synergisms or decoupling of biogeochemical processes, and of fundamental response dynamics to drought at the ecosystem level including potential tipping points and thresholds of regime shift. Future work is needed to elucidate the role of biodiversity and of biotic interactions in modulating ecosystem response to climate extremes.

Climate change will increase the recurrence of extreme weather events such as drought and heavy rainfall. Evidence suggests that extreme weather events pose threats to ecosystem functioning, particularly to nutrient cycling and biomass production. These ecosystem functions depend strongly on belowground biotic processes, including the activity and interactions among plants, soil fauna, and microorganisms. Here, experimental grassland and heath communities of three phytodiversity levels were exposed either to a simulated single drought or to a heavy rainfall event. Both weather manipulations were repeated for two consecutive years. The magnitude of manipulations imitated the local 100-year extreme weather event. Heavy rainfall events increased below-ground plant biomass and stimulated soil enzyme activities as well as decomposition rates for both plant communities. In contrast, extreme drought did not reduce below-ground plant biomass and root length, soil enzyme activities, and cellulose decomposition rate. The low responsiveness of the measured ecosystem properties in face of the applied weather manipulations rendered the detection of significant interactions between weather events and phytodiversity impossible. Our data indicate on the one hand the close interaction between below ground plant parameters and microbial turnover processes in soil; on the other hand it shows that the plant-soil system can buffer against extreme drought events, at last for the period of investigation.

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In autumn 2005 the artificial catchment Chicken Creek was completed in an open-cast lignite mine in Lusatia, Germany. The 6 ha area has been constructed as a two-layer system consisting of a clay aquiclude and a sandy aquifer at the top. After construction the site was left to an unrestricted and unmanaged succession. A comprehensive environmental monitoring program started immediately after the site was completed. Time series of essential environmental parameters were recorded with high temporal and spatial resolution. This paper presents selected time series of the past sixyear ecosystem development. Important changes registered in this period allow for the definition of distinctive phases of the still ongoing initial ecosystem evolution. A primary, short but pronounced geo-phasecharacterized by surface runoff, excessive erosion and sedimentation as well as very rapid immigration of biotawas followed by a hydrological dominated phase with processes such as groundwater recharge. At the end of the study period biotic processes became more evident. It can be concluded that the artificial catchment offers unique opportunities for Manuscript Click here to download Manuscript: Elmer_etal_EES_080213_revision.docx Click here to view linked References 2 interdisciplinary research on the establishment of an ecological system with rapidly growing complexity. The highly dynamic development of the Chicken Creek catchment provides the possibility to observe manifold changes within short time and to detect feedbacks and their modifications between different ecosystem compartments.

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In initial ecosystems concentrations of all macro- and micronutrients can be considered as extremely low. Plant litter therefore strongly influences the development of a degraders' food web and is an important source for C and N input into soil in such ecosystems. In the present study, a ¹³C litter decomposition field experiment was performed for 30 weeks in initial soils from a post-mining area near the city of Cottbus (Germany). Two of this regions' dominant but contrasting pioneering plant species (<i>Lotus corniculatus</i> L. and <i>Calamagrostis epigejos</i> L.) were chosen to investigate the effects of litter quality on the litter decomposing microbial food web in initially nutrient-poor substrates. The results clearly indicate the importance of litter quality, mainly the amount of N stored in the litter material and its bioavailability for the degradation process and the development of microbial communities in the detritusphere and bulk soil. Whereas the degradation process of the <i>L. corniculatus</i> litter which had a low C/N ratio was fast and most pronounced changes in the microbial community structure were observed 1–4 weeks after litter addition, the degradation of the <i>C. epigejos</i> litter material was slow and microbial community changes mainly occurred at between 4 and 30 weeks after litter addition to the soil. However for both litter materials a clear indication for the importance of fungi for the degradation process was observed both on the abundance level as well as on the level of ¹³C incorporation (activity)

In initial ecosystems, concentrations of all macro- and micronutrients can be considered as extremely low. Plant litter therefore strongly influences the development of a degrader's food web and is an important source for C and N input into soil in such ecosystems. In the present study, a ¹³C litter decomposition field experiment was performed for 30 weeks in initial soils from a post-mining area near the city of Cottbus (Germany). Two of this region's dominant but contrasting pioneering plant species (Lotus corniculatus L. and Calamagrostis epigejos L.) were chosen to investigate the effects of litter quality on the litter decomposing microbial food web in initially nutrient-poor substrates. The results clearly indicate the importance of litter quality, as indicated by its N content, its bioavailability for the degradation process and the development of microbial communities in the detritusphere and soil. The degradation of the L. corniculatus litter, which had a low C / N ratio, was fast and showed pronounced changes in the microbial community structure 1–4 weeks after litter addition. The degradation of the C. epigejos litter material was slow and microbial community changes mainly occurred between 4 and 30 weeks after litter addition to the soil. However, for both litter materials a clear indication of the importance of fungi for the degradation process was observed both in terms of fungal abundance and activity (¹³C incorporation activity

Testate amoebae play an important role at the very first beginning of succession on land. We used litterbags buried into four different soils to study the early colonization (which occurred within less than 55 days) and establishment of testate amoebae. The litterbag cellulose exposed at the youngest mining site poor in nitrogen and phosphorus was colonized firstly in high abundances, whereas the substrate introduced into the reference sites of undisturbed soil was colonized slowly and in low densities. Besides the (expected) small-sized r-strategists (e.g., Euglypha rotunda, Tracheleuglypha dentata, and Trinema lineare), large-sized K-strategists (e.g., Centropyxis spp., Phryganella acropodia) occurred in remarkably high densities on all sites. Species that colonized the cellulose in high densities (e.g., P. acropodia and T. dentata) were found extremely rarely in the adjacent source substrate and vice versa, stressing the importance of the target substrate quality. In the course of the experiment, the influencing environmental factors became more complex, as shown by redundancy analysis (RDA). Concerning the amoebal community, there was a change from variability to stability, as visualized by cluster analysis. Adjacent litterbags within an investigation site revealed amoebal species and abundances with an increasing similarity during exposition time, whereas the litterbags between the four investigation sites were colonized differently. These observations point to a stochastic (variable) beginning of community assembly, changing to a more deterministic (stable) course. No species replacement has been observed, which is an essential part of most successional theories. Thus, the more flexible concept of "community assembly" should be considered instead of "succession" for protozoa. The stochastic beginning of community assembly and the lack of species replacement are explained by a neutral community model.