Experiments and gradient studies – University of Copenhagen

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Experiments and gradient studies

Phytometer initiative

A central goal in ecosystem ecology is disentangling co-occurring drivers of ecosystem processes such as decomposition rates and biomass production. Standardized common metrics can isolate these drivers to provide background rates of these processes in model systems. The Bayreuth Phytometer is a common metric being developed for plant community ecology that uses a standardized plant community-substrate unit alongside the same plant community grown in local soils to determine relative influences of climate and soils in driving biomass production. In 2017 these phytometers will be exposed across Europe as part of the ClimMani COST action network of climate change research. Teabags are being added to this year’s phytometers and will be harvested and reweighed after one year of exposure. By linking the TeaComposition initiative with the Bayreuth Phytometer, we can compare decomposition rates in standardized substrate phytometers to local soil substrate phytometers to better understand the relative roles of local soils in breaking down organic matter. Furthermore, we can see climatically driven background rates of decomposition in the standardized substrate phytometers which will initially be uncolonized by local soil fauna. Finally, this will allow researchers to link the fundamental process of litter decomposition across sites and within their own experimental setups using the common background of the phytometers.

Number of sites: 18
Contact: Peter Wilfahrt (peter.wilfahrt@uni-bayreuth.de)

PastForward – (ERC project)

The decomposition of plant and leaf litter is a central process in the functioning of forest ecosystems, forming a link between abiotic conditions and many other biotic processes. Litter decomposition is, however, a complex process that is potentially altered by multiple global changes such as climate warming, and nitrogen (N) deposition. Environmental changes could have occurred on a local scale as well: the legacy of past (agricultural) land use can still affect present soil composition and dynamics through elevation of nutrient stocks, and particularly Phosphorus (P). These environmental changes can potentially interact with the effects of current forest management, where a more intensive management implies a higher light availability.

We designed a multi-factor mesocosm experiment to disentangle interactive effects of warming (T) , N addition (N), increased light availability (L) and land-use legacy on model herb layer communities and their ecosystem functions. Forest soil was collected from eight European regions across a latitudinal gradient, ranging from Southern Estonia to central France. In each region, we collected soil from three post-agricultural (recent) and three ancient forests that were occurring in the same landscape. The herb layer communities growing on these soils were selected for their differences in plant functional traits, reflecting their affinity with either ancient or post-agricultural forests.

In this field experiment, we test the hypothesis that litter (replaced by green tea and rooibos tea) decomposition rates are increased in the experimental treatments where resources and growth conditions are elevated. . Therefore, we buried 1728 tea bags in 384 experimental units according to the design below.

Design
8 regions × (3 ancient + 3 recent forests) × 2 T × 2 L × 2 N × (2 green tea bag + 2 rooibos tea) + 192 extra tea bags on soil with highest contrast in past land use)

Figure 1 The 8 European regions considered in the multi-factor experiment. EST= Southern Estonia, SW = Southern Sweden, BR= Bremen (Germany), PR = Prignitz (Germany), VL = Vlaanderen (Belgium), CH= Chimay (Belgium), AM = Amiens (France), OR = Orléans (France)

Figure 2 One experimental unit of 43x 28 cm,holding twenty plants in a 7 x 8 cm grid. Four tea –bags were planted in each mesocosm (2 rooibos tea + 2 green tea). On 64 soil samples from Sweden (SW) and Flanders (VL), we planted two additional tea bags for earlier collection.

Number of sites: NN
Contact: Kris Verheyen (Kris.Verheyen@UGent.be)

SADE experiment

Litter decomposition in relation to disturbance and experimentally increased plant diversity

Within the framework of the Biodiversity Exploratories (http://www.biodiversity-exploratories.de/1/home/) project in Germany, the groups of Markus Fischer (University Bern) and Norbert Hölzel (University Münster) and colleagues have installed a large-scale plant diversity experiment (http://www.biodiversity-exploratories.de/1/projects/derzeit-gefoerdert/pflanzen/sade/) in temperate grassland ecosystems.

The Experiment
At in total 73 agriculturally used grasslands within the three study regions we conduct a seed addition and disturbance experiment (called SADE) where seeding with a regional seed mixture and sward disturbance are combined along a land-use intensity gradient. This gradient reaches from unfertilized sheep pastures and single-cut grasslands over mesic fertilized semi-natural grasslands up to highly fertilized, frequently mown and/or heavily grazed grasslands. The main aims of the experiment are to address questions of ecosystem resilience and of effects of increased plant diversity and how both may change ecosystem functioning, such as litter decomposition within the TeaComposition project.

Sward disturbance down to 10 cm depth is done to open the existing vegetation

Design
At each grassland, the experiment consists of four 7 m × 7 m plots at which the factors “disturbance” and “seed addition” are studied. To separate combined and individual effects of the two factors, not only the combination of but also the separate application of both treatments as well as an untreated control plot is necessary. The disturbance of the topsoil was done by rotary cultivation or harrowing down to 10 cm soil depth and aims at temporarily setting back the current vegetation and creating open patches for germination. Seeding is done using regionally produced seed mixtures of native grassland plants. Each plot within one of the three study regions will be treated with the same high-diversity combination of grasses, herbs and legumes. As basis for the species mixture, we used a set of vegetation records from earlier years. Due to differences in regional species pools, seed mixtures differed among regions, ranging from 47 to 66 species. Even during the first year, a significant increase in plant diversity could be observed. Further details and first results of the experiment can be found in Klaus et al. (2017).

All experimental plots are regularly managed, for example by sheep herding

Klaus VH, Schäfer D, Kleinebecker T, Fischer M, Prati D, Hölzel N (in press) Enriching plant diversity in grasslands by large-scale experimental sward disturbance and seed addition along gradients of land-use intensity. Journal of Plant Ecology: rtw062 [doi:10.1093/jpe/rtw062]

Number of sites: NN
Contact: Valentin H. Klaus (v.klaus@uni-muenster.de)

CLIMOSEQUENCE Approach

To investigate the long-term litter decomposition initiative across 9 zonobiomes in alpine ecosystems and its key drivers under present and future climate scenarios using a climosequence approach. Climosequence are sequences of soil whose variations are caused by climate and associated vegetation. All other parameters (parent material, soil type, exposition etc.) are kept similar so that observed changes can be attributed to the local climate and vegetation.

An example of a climosequence with site selections criteria

Number of sites: 9
Contact: Ika Djukic (ika.djukic@umweltbundesamt.at)

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