Hintergrundbild mit Feldern
 

Design



We investigate the processes and relationships in a typical european mesophilic grassland ecosystem (assembled from grasses, herbs, and legumes) and measure a range of key community characteristics, species traits and processes in more than 600 research plots (ranging from plant diversity, biomass to rates of soil respiration) since the beginning of the experiment in 2002. A main aim of the Jena Experiment is that a number of research groups are able to study ecosystem processes on the same plots, and over a time-scale of more than two years. Emphasis on particular effects of species is therefore reflected in a different experimental designs in large as well as small plots. The experiment consists of a number of sub-experiments, the main experiment (species range 1-60 species in large plots), the dominance experiment (species range from 1-9 species, only dominant species) and the trait-based experiment (started in 2011). For details of the experiments see the paper by Christiane Roscher et al. (2004)

Main Experiment

To avoid a strong increase in the similarity of species mixtures with increasing plant species richness, a large species pool including 60 species in our main experiment was selected. Plant species mixtures with levels of 1, 2, 4, 8, 16 and 60 were varied independently and also replicated in our experimental design. Our experiment uses technology to measure climate and soil parameters, to manipulate experimental design and experimental plots reproduces different management strategies (e.g. through weeding in spring and summer, invasion experiments, fertilization). Since 2002 the experiment yielded time-series data on a wide range of ecosystem processes in different subplots, ranging from productivity, C-storage, and N-cycling to herbivory, pollination and decomposition. For all plant species investigated, a large number of demographic, morphological and physiological variables are compiled.

subplot2012




Trait Based Experiment

In 2010 we set-up a trait-based experiment to investigate species interactions and to understand mechanistic functioning of our experimental ecosystem using specific species information (i.e. plant height, leaf area, rooting depth, root length density, phenology). The trait based experiment focuses on a gradient in species diversity as well as functional diversity. The design uses three different species pools. For each pool species diversity is expressed as a different number of species in different plots. Within the gradient in plant species richness plots differ in their functional diversity- the trait space which is covered by the several plant species mixtures. In other words species pools have a gradient from very similar plant traits to species with completely different plant traits.

trait experiment



Our statistical design therefore realized different hierarchical levels of combination: (i) different species richness levels ranging from monocultures, 2, 3, 4 and 8 species mixtures, (ii) three different pools with different trait combinations focused on spatial resource use (e.g. root characteristics), temporal resource use (e.g. plant phenology), or on both together. Regarding defined plant traits, species within each species pool were divided into four different sectors, whereas species within the same sector are very similar and species from different sectors very dissimilar. Functional diversity is defined as the number of sectors covered by a specific species mixture from high number of sectors as being functional diverse to single sectors being functional low diverse. In total, 138 plots (3.5mx3.5m) were set up and in order to maintain different soil characteristics randomly arranged in three blocks with an equal number of plots in each block. All possible combinations result in 8 monocultures, 16 two species, 12 three-species, 9 four species and 1 eight-species mixtures. Experimental plots were mown and weeded to maintain the target composition.

Ecotron

This artificial environment simulates natural conditions allowing experimental control over parameters like temperature, soil humidity, gas exchange: We have a cooperation with the ECOTRON facility in Montpellier/France: as a controlled environmental facility for the investigation of ecosystem processes. Here we can manipulate and study meso-environmental conditions of a number of physical factors comparing it with results from our field site. We therfor excavated soil cores in 2011 from the field site to a depth of 2.20m that are transported to Montpellier and recreated in a chamber.


Ecotron


Monocultures and Dominance Experiment

Monocultures
All 60 species that were sown in our main experiment are grown in replicated monocultures on small-area plots. Monocultures of each species are a pre-requisite in the study of overyielding, for the a-posteriori separation of sampling and complementarity effects at the species level. Additionally the monocultures provide a basis for measuring species specific traits as a prerequisite for the identification of key traits.

Dominance Experiment
In the main experiment, species are chosen randomly from a large species pool, and the design does not allow for the separation of effects of individual species from effects of diversity. The dominance experiment was especially designed to disentangle the effects of species richness per se and the presence/absence of particular single dominant species or particular pairs of dominant species.

Small Replicates (abondoned in 2007)
To assess within-mixture variability and its dependence on diversity, all species mixtures from 1-16 species and the 60-species mixtures are identically replicated on small plots (=82 plots). Control plots (bare ground, free succession and succession with mowing) are also present (=12 plots). The replicates of the main experiment have been used to study effects of evenness and density of plant species.


small


Other

We integrate information from greenhouse tests, mesocosm studies (cf. Ecotron) and field experimentation at multiple sites. Combined with data mining, and modelling our integrative approach is intended to provide insights in ecosystem functioning.