Experiments

Numerous studies in both controlled and natural environments have provided strong evidence of a positive relationship between biodiversity and ecosystem functioning (BEF). Through niche complementarity or facilitation, more diverse communities can support higher levels of ecosystem processes as well as increase their resistance to adverse environmental conditions. Less is known on the importance of multitrophic diversity (e.g. diversity at several trophic levels such as plants and detritivores) for soil functioning. More precisely, we know little on 1) the importance of plant nutrient acquisition strategy through mutualism with mycorrhizae, 2) the importance of soil community complexity, and 3) the interaction between these two trophic levels in modulating soil processes and their response to drought.

In the FunDrought experiment, we manipulate biological communities at two levels. First, with 10 tree species commonly observe in European forest and used in the MyDiv experiment, we set up a treatment of two-species mixtures with 3 levels : Arbuscular Mycorrhizal Fungi (AMF) alone, EctoMycorrhizal Fungi (EMF) alone, or a mixture of both. Second, we recreated soil communities with increasing complexity by sequentially adding microbes and nematodes, mesofauna, macro arthropods, and earthworm, leading to a four level treatment. All the modalities were crossed and replicated five times in 60 units of the iDiv Ecotron. From August 2023 to January 2024, we imposed a first dry phase of 1.5 month at establishment before increasing watering frequency and we monitored dynamically multiple ecosystem response variables (soil respiration, soil fauna feeding rate, tree leaf reflectance, leaf litter decomposition) and analyzed multiple other variables at final harvest (soil carbon fractions, soil nutrient and micronutrient, soil aggregate stability, tree leaf and root traits, fungal communities composition).

Multiple hypotheses will be tested:

1. Increasing oil fauna complexity promotes decomposition rate, primary production, microbial activity and biomass
2. Ecosystem functioning increases in mixed systems (AMF + EMF) because differing mycorrhizal types increase habitat coverage and reduce competition among plants.
3. AMF associated trees are fast-growing with acquisitive traits and are more sensitive to drought compared to EMF trees that are slow-growing with conservative traits.
4. Mycorrhizal identity and mixture effects on soil functioning are stronger in presence of more complex soil fauna communities.
5. Due to differences in leaf litter chemistry (C/N ratio, phenolics content, leaf toughness), litter of AMF trees decomposes faster than litter of EMF trees

How does plant and soil interaction history modify relationships between biodiversity and ecosystem functioning?

Over the last three decades, concern about species loss has motivated many studies that experimentally reduce species richness and examine the consequences for ecosystem functioning. So far, results have shown that there is generally a positive association between plants species richness and ecosystem functioning (BEF). Moreover, the strength of this relationship typically gets stronger over time, which can be seen as enhanced functioning in diverse plots, and reduced functioning in monocultures, In Spring and Summer 2022 the JENATRON experiment will test whether the strengthening BEF relationship over time is driven by soil community assembly, shared plant history, or a combined effect of both factors.

JENATRON will be established in the iDiv Ecotron facility using a plant diversity gradient from 1 to 3 species from the Trait Based Experiment of the Jena Experiment factorially crossed with soil history and plant history. Soil History (+/- SH) will be established by excavating intact monoliths from the Trait Based Experiment (+SH) or from bare ground plots (-SH). Plant History (+/- PH) will be established using two seed sources: seeds harvested from plants growing in the Trait Based Experiment for 12 years (+ PH), and original seed material used to set up the Trait Based Experiment (-PH).

The independent crossing of soil history and plant history for each level of plant species richness results in the following four treatments in each EcoUnit:

1. “with plant history, with soil history”,
2. “without plant history, with soil history”,
3. “with plant history, without soil history”, and
4. “without plant history, without soil history”.

Eleven sub-projects of the Jena Experiment Research Unit will work closely together to investigate the independent and interactive effects of plant history and soil history on BEF relationships. Response variables will be measured from many research areas including microbiology, chemical ecology, phenology, proximal sensing, genomics and food web modelling. If soil or plant history alter BEF relationships, an important implication of the results is that novel communities without shared history could be a poor surrogate for long-term conservation.

Life is not fair. Some areas receive ample resources, while other areas are more depleted. We tested how resource inequity affects model grassland ecosystems, and whether association with mycorrhizal mutualists can facilitate resource distribution and mediate the consequences of inequity. We conceptually subdivided each of 12 EcoUnit landscapes into 25 subplots, and experimentally manipulated the spatial distribution of three macronutrient resources: nitrogen (N), phosphorus (P), and potassium (K). In experimental landscapes where inequity was highest, one of the 25 subplots received all of the NPK resources and 24 of the subplots received no subsidy. In the experimental landscapes where inequity was low, each of the 25 subplots received homogeneous NPK nutrient subsidies. We are currently analyzing the consequences of resource inequity and mycorrhizal associations for distribution of nutrients, as well as magnitude and stability of responses by the plant and soil communities (microbial biomass, respiration, microbial diversity, soil fauna activity).

Lead:
Dr Malte Jochum (contact: malte.jochum@idiv.de)

Overarching research question:
How do simultaneous changes in climate and predator communities affect above-belowground temperate forest communities and ecosystem functioning?

Setting:
Temperate forest soil and litter system, above and belowground; Fagus sylvatica and Quercus petraea trees (2 each) planted in each subunit, predators (see treatments) and two collembola species

Experimental design:
4 predator levels, 3 climate levels, each of the 12 combinations replicated 4 times (48 replicates = Ecotron Subunits)

Treatments:
Climate change (drought) and predator (wolf spider, predatory mite, both, none) treatments

Duration:
04/2021–12/2021

Main collaborating teams and staff involved:

• Helge Bruelheide, Ines Laude (MLU, iDiv)
• François Buscot (UNZ, iDiv), Anna Heintz-Buschart (Univ. Amsterdam)
• Julia Tiede (WWU Münster)
• Nicole van Dam, Henriette Uthe (iDiv, Univ. of Jena)
• Tesfaye Wubet (UFZ, iDiv)
• Ulrich Brose, Benoit Gauzens (iDiv, Univ. of Jena)
• Stefan Scheu, Melanie Pollierer (Univ. Göttingen)
• Olga Ferlian (UL, iDiv)
• Nico Eisenhauer, Jes Hines, Alban Gebler, Lisa Ertel, Anja Zeuner, Conn Heijungs, Merlin Helle (UL, iDiv)

The EcoLux experiment was established in the beginning of 2020 in 12 of the 24 EcoUnits. It tested how the multiple ecosystem responses are influenced by light pollution. The light treatment simulates natural lunar cycles and a range of sky glow intensities.

Or main research question is:
“How do movement patterns of diurnal and nocturnal invertebrates change with increasing light pollution?”

The upper soil layer will be equipped with an RFID sensor network to track tagged invertebrates. The tracking will be conducted over an entire natural moon cycle.

We hypothesise that (1) nocturnal species avoid open space (higher isolation) and show reduced activity as well as speed and encounter rates. In contrast, (2) diurnal species use the open space more intensively (higher connectivity), show increased activity and increased speed along with higher encounter rates.

Additional lines of inquiry include tests of light pollution on plant and soil performance and community composition.

The outcomes of this study will contribute to the elaboration of future light pollution scenarios.

A collaborative experimental study got established in April/May 2019 connecting two iDiv platforms – the iDiv Ecotron and AquaDiva.

The experiment directly addressed the primary aims in AquaDiva towards understanding the links between surface and subsurface, especially how organisms inhabiting the subsurface reflect and influence their physical, ecological, and geochemical environment, and affect water and matter transition. In 6 of the 24 EcoUnits, we investigated these questions in the light of climate change, particularly extreme weather events (drought/heavy rainfalls).

The key questions in EcoXtremes were:

1. How are carbon, soil water, and gas fluxes altered under predicted climate conditions of increasing weather extremes?
2. How do the effects of weather extremes differ in two types of ecosystems – forest vs. grassland?
3. How do these contrasting drought/heavy precipitation events alter the transport mechanisms of organic matter (POM, DOM), nutrients, microorganisms, incl. viruses, inorganic particles and colloids through the soil column?
4. Do we see differences in microbial biomass and activity as well as in the community composition of Nematodes?

Broadly, this experimental design allows us to disentangle carbon, nutrients, microorganisms, and water transport mechanisms across two different factors: (A) precipitation (extreme vs. average) and (B) ecosystem (forest vs. grassland). Furthermore, this study was the first iDiv Ecotron experiment in which intact and undisturbed soil monoliths were excavated using lysimeters.

In April/May 2019 the EcoTrack Experiment was established in 12 of the 24 EcoUnits based on the design of the MyDiv experiment. It aimed at investigating the movement patterns of epigeic macro-invertebrate species – predators and prey – and how they are influenced by the spatial arrangement of tree litter diversity and temperature. The four focal tree species, whose leave litter was used, differ in mycorrhizal interaction partners (ectomycorrhizae versus arbuscular mycorrhizal fungi) and stoichiometry (high versus low C-to-N ratio). The upper soil layer (just below the litter layer) got equipped with RFID sensors to track the animals.

Our hypotheses are:

(A) Movement ecology

1. In heterogeneous habitats, prey predominantly move into patches of high stoichiometric litter quality.
2. In homogeneous, well-mixed habitats prey follow more random movement paths.
3. Predators efficiently track their prey and follow them into the same habitat compartments.
4. Predator aggregation in habitat compartments causes prey movement out of these compartments.
5. The speed of these movements increases with warming.

(B) Biodiversity-ecosystem functioning

1. Small-scale litter mixing will support higher levels of decomposer activity and population sizes that may cascade up to higher predator fitness.

Invertebrates provide a broad set of ecosystem services that regulate the functioning of ecosystems. Recent findings of an almost 75 % decline in flying insect biomass over the past 27 years^[1] motivated a consortium of iDiv scientists to investigate the consequences of aboveground invertebrate loss on ecosystem processes under controlled environmental conditions.

Insect Armageddon was conducted from April to November 2018 and represents the first collaborative study of the iDiv Ecotron, during which the 24 identical experimental EcoUnits ran simultaneously. Nineteen iDiv researchers submitted nine proposals to investigate how the decline in invertebrate biomass in artificial grassland ecosystems affects the biotic interactions between aboveground invertebrates, such as insects, plants, bacteria, and belowground organisms and processes, and thus the associated ecosystem functions and services. Using PhytOakmeters the iDiv Ecotron was linked with the TrophinOak platform.

In April 2018, grassland communities consisting of 12 central European species were established in the EcoUnits. To mimic invertebrate decline, we collected living aboveground invertebrates at two abundance levels (100 % and 25 %) and introduced them to 8 EcoUnits, respectively. Another 8 Units did not receive any fauna and served as a control. To account for the natural seasonal species turnover, invertebrate communities were exchanged regularly at a monthly interval.

In addition to subproject-specific papers, such as on energy fluxes through soil food webs, we will use this diverse dataset to collaborate on overarching syntheses that investigate the responses of the entire ecosystem to invertebrate decline by determining ecosystem multifunctionality.

Reference
[1] Hallmann, C. A., Sorg, M., Jongejans, E., et al. and de Kroon, H. (2017) More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoS One, 12, e0185809.

Earthworms are ecosystem engineers that account for the highest biomass of invertebrates in the soil. Exotic earthworms have significant impact on native ecosystems, with cascading effects on native communities^{[1] [2] [3]}. Canada’s temperate boreal forests, which have been lacking native earthworms since the last ice age, are a good model system for studying the impact of earthworm invasion on native communities and ecosystems.

The Wormotron study, which was conducted from early August 2017 to late January 2018, aimed to investigate the responses of above- and belowground communities to the invasion of earthworms. The main focus was on earthworm effects on the defense of two Poplar tree species against their antagonists, as well as on plant traits of the herbaceous community. In addition, effects of the introduction of exotic earthworms on bacterial and fungal communities, Collembola populations as well as their development and decomposition activity were investigated.

In July 2017, Canadian boreal forest communities were established in twelve of the EcoUnits, consisting of four Canadian native plant species – two grasses (Calamagrostis canadensis, Bromus ciliatus) and two herbs (Aster laevis, Achillea millefolium) – as well as two typical tree species (Populus tremuloides, Populus balsamifera). To half of the chambers, three ecological groups of earthworms (epigeic, endogeic and anecic) were introduced. After six months, the species abundances and biomass of plant-, earthworm-, and Collembola communities were recorded, as well as the above- and belowground functional traits of the trees, grasses and herbs, fungal and herbivore infestation of tree leaves, as well as soil microbial community composition.

References

[1] Crooks, J. A. (2002) Characterizing ecosystem-level consequences of biological invasions: the role of ecosystem engineers. Oikos, 97, 153-166.

[2] Ferlian, O., Eisenhauer, N., Aguirrebengoa, M., et al. and Thakur, M. P. (2018) Invasive earthworms erode soil biodiversity: A meta-analysis. Journal of Animal Ecology, 87, 162-172.

[3] Holdsworth, A. R., Frelich, L. E. and Reich, P. B. (2007) Effects of Earthworm Invasion on Plant Species Richness in Northern Hardwood Forests. Conservation Biology, 21, 997-1008.

The Aphitron study was conducted from early February 2017 to mid-July 2017 and aimed to investigate the ecosystem consequences of above- and belowground interaction network complexity. In this experiment, 12 EcoUnits were split in two fully separated sections (–> 24 independent subunits in total). In each subunit, two lysimeters – isolated from each other belowground, but connected aboveground – were each equipped with two herbs and two grasses, planted in monoculture patches, as well as one broad bean (Vicia faba) as phytometer. Both lysimeters were filled with sterilized soil and subsequently inoculated with bacteria, fungi, and nematodes. One of the two lysimeters was additionally equipped with larger decomposer organisms (earthworms and springtails). A low barrier with hook tape between the lysimeters prevented migration of soil fauna, while allowing aboveground organisms to move freely between plant stands. Besides soil fauna, the presence of herbivores (aphids) as well as the diversity and abundance of predator species (ladybirds) was manipulated.