The iDiv Ecotron—A flexible research platform for multitrophic biodiversity research

Abstract

Across the globe, ecological communities are confronted with multiple global environmental change drivers, and they are responding in complex ways ranging from behavioral, physiological, and morphological changes within populations to changes in community composition and food web structure with consequences for ecosystem functioning. A better understanding of global change-induced alterations of multitrophic biodiversity and the ecosystem-level responses in terrestrial ecosystems requires holistic and integrative experimental approaches to manipulate and study complex communities and processes above and below the ground. We argue that mesocosm experiments fill a critical gap in this context, especially when based on ecological theory and coupled with microcosm experiments, field experiments, and observational studies of macroecological patterns. We describe the design and specifications of a novel terrestrial mesocosm facility, the iDiv Ecotron. It was developed to allow the setup and maintenance of complex communities and the manipulation of several abiotic factors in a near-natural way, while simultaneously measuring multiple ecosystem functions. To demonstrate the capabilities of the facility, we provide a case study. This study shows that changes in aboveground multitrophic interactions caused by decreased predator densities can have cascading effects on the composition of belowground communities. The iDiv Ecotrons technical features, which allow for the assembly of an endless spectrum of ecosystem components, create the opportunity for collaboration among researchers with an equally broad spectrum of expertise. In the last part, we outline some of such components that will be implemented in future ecological experiments to be realized in the iDiv Ecotron.

Full text

15174
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Ecology and Evolution. 2021;11:15174–15190.www.ecolevol.org
Received: 17 March 2021
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Revised: 31 Aug ust 2021
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Accepted: 6 September 2021
DOI: 10.1002 /ece3.8198
RESEARCH ARTICLE
The iDiv Ecotron— A flexible research platform for multitrophic
biodiversity research
Anja Schmidt1,2,3 | Jes Hines2,3 | Manfred Türke2,3 | François Buscot1,2 |
Martin Schädler1,2 | Alexandra Weigelt2,3 | Alban Gebler2,3 | Stefan Klotz1 |
Tao Liu4 | Sascha Reth5 | Stefan Trogisch2,6 | Jacques Roy7 | Christian Wirth2,3 |
Nico Eisenhauer2,3
This is an op en access arti cle under the ter ms of the Creat ive Commo ns Attri bution License, which pe rmits use, dis tribution and reproduction in any medium,
provide d the original wor k is properly cited.
© 2021 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.
1Helmholtz Centre for Env ironmental
Research – UFZ, Halle (Saale), Germany
2German Centre for Integr ative Biodiver sity
Research (iDiv) Halle- Jena- Leipzig, Leipzig,
Germany
3Leipzig University, Leipzig , Germany
4Key Laborator y of Vegetation Restoration
and Management of D egraded Ecosystems,
South China Botanical Garden, Chine se
Academy of Sciences, Guangzhou, China
5Umwelt- Geräte- Technik GmbH – UG T,
Müncheberg, Germany
6Martin Luther Univer sity Halle- Wittenberg,
Halle (Saale), Germany
7French National Ce ntre for S cientific
Research – CNRS, Paris, Fra nce
Correspondence
Anja Schmidt, D epar tment of Community
Ecology, Helmholtz Centre for
Environmental Research – UFZ, Th eodor-
Lieser- Str. 4, 06120 Halle (Saale), G ermany.
Email: a.schmidt@ufz.de
Funding information
Deutsche Forschungsgemeinschaft,
Grant/Award Number: DFG- FZT 118 and
202548816
Abstract
Across the globe, ecological communities are confronted with multiple global envi-
ronmental change drivers, and they are responding in complex ways ranging from
behavioral, physiological, and morphological changes within populations to changes
in community composition and food web structure with consequences for ecosys-
tem funct ioning. A better un der standing of globa l change- induced alteratio ns of mul-
titrophic biodiversity and the ecosystem- level responses in terrestrial ecosystems
requires holistic and integrative experimental approaches to manipulate and study
complex communities and processes above and below the ground. We argue that
mesocosm experiments fill a critical gap in this context, especially when based on
ecological theory and coupled with microcosm experiments, field experiments, and
observational studies of macroecological patterns. We describe the design and speci-
fications of a novel terrestrial mesocosm facility, the iDiv Ecotron. It was developed
to allow the setup and maintenance of complex communities and the manipulation of
several abiotic factors in a near- natural way, while simultaneously measuring multiple
ecosystem functions. To demonstrate the capabilities of the facility, we provide a
case study. This study shows that changes in aboveground multitrophic interactions
caused by decreased predator densities can have cascading effects on the composi-
tion of belowground communities. The iDiv Ecotrons technical features, which allow
for the assembly of an endless spectrum of ecosystem components, create the op-
portunity for collaboration among researchers with an equally broad spectrum of
expertise. In the last part, we outline some of such components that will be imple-
mented in future ecological experiments to be realized in the iDiv Ecotron.
KEYWORDS
biodiversity and ecosystem functioning, biotic interactions, climate chambers, food webs,
lysimeters, mesocosms

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1 | INTRODUCTION
Ecosystems are threatened by a multitude of environmental change
drivers (Díaz et al., 2019; Maxwell et al., 2016; Murphy & Romanuk,
2014; Newbold et al., 2015; Pereira et al., 2012). Over the last few
decades, there has been an explosion of studies examining changes
in ecological communities and environmental conditions (Hines
et al., 2019; Liu et al., 2011; Stork & Astrin, 2014). The desire to
draw generalizable conclusions from these studies led to a period
of synthesis, during which information from individual studies was
compiled allowing for quantitative evaluation of the variation in eco-
logical changes across systems (Gurevitch et al., 1992; Halpern et al.,
2020; Hillebrand et al., 2020). Such comprehensive and quantitative
synthesis studies enabled researchers to identify generalizable pat-
terns in biodiversity (Calatayud et al., 2020), trends in biodiversity
change (Blowes et al., 2019; Dornelas et al., 2014), and relationships
between biodiversity and ecosystem functioning (e.g., Cardinale
et al., 2012; Gessner et al., 2010; Lefcheck et al., 2015; Soliveres
et al., 2016). These high- impact synthesis studies can also serve as a
roadmap for designing future experiments, as they help to identify
important knowledge gaps which need to be filled in order to better
understand the func tioning of ecosystems and predict the conse-
quences of climate change.
We have limited empirical evidence for at least three key aspects
of environmental changes in ecosystems and communities that draw
a roadmap for future research. First, there are limited numbers of
ecosystem response variables that have been consistently studied
across systems. For example, the most commonly reported response
variables are primary production and decomposition (Cardinale
et al., 2006; Schmidt, Auge, et al., 2015; Schmidt, John, et al., 2015).
However, the few existing multitrophic biodiversity studies indicate
that the interactions of higher trophic levels may be particularly im-
portant for multiple ecosystem functions (Hines, van der Putten,
et al., 2015; Lefcheck et al., 2015; Naeem et al., 1994; Soliveres et al.,
2016) and that especially these species might be very vulnerable to
environmental changes (Hines, Eisenhauer, et al., 2015; Voigt et al.,
2003). Second, studies tend to investigate limited types of mecha-
nisms and processes underlying changes in biodiversity, ecosystem
functioning, and the relationship between the two (Hillebrand et al.,
2020). That is, while there is strong emphasis on the effects of global
change drivers on changes in species richness (Tilman & Downing,
1994; Harpole et al., 2016; Seabloom et al., 2021, but see Dornelas
et al., 2014; Vellend et al., 2013), there is less known about the eco-
system consequences of changes in behavior (Cordero- Rivera, 2017;
Wilson et al., 2020) and community composition (Hillebrand et al.,
2018; Spaak et al., 2017) of species that persist in communities. Third,
although ecosystems are confronted with complex cocktails of global
change drivers (Bowler et al., 2020), so far only a limited number of
their types and combinations have been studied in realistic experi-
ments (Rineau et al., 2019; Rillig et al., 2019, but see Schädler et al.,
2019; Korell et al., 2020). Especially with regard to climate change,
understanding interactions between different environmental vari-
ables such as temperature and precipitation, land use or biodiversity
on ecosystem functioning is essential to make predictions for future
ecosystem developments and the potential consequences for soci-
ety (Roy et al., 2017). To address our current knowledge gaps, we
need experiments which can simultaneously manipulate and mea-
sure different global change drivers (Vanderkelen et al., 2020) and
investigate their impacts on a wide range of functional groups and
trophic levels of organisms (De Boeck et al., 2020; Komatsu et al.,
2019; Korell et al., 2020). Combining such “meta- scale” studies with
laboratory and field studies, especially large- scale climate change
experiments (like Schädler et al., 2019), provides the opportunity to
understand the complex patterns of biodiversity– ecosystem func-
tion relationships and their responses to environmental changes as
well as the underlying processes that operate across organizational
levels of life (cell- individual- population- community- ecosystem;
Ferlian et al., 2018).
Here, we introduce the iDiv Ecotron plat form (iDiv stands for
the German Centre for Integrative Biodiversit y Research Halle- Jena-
Leipzig in Germany). This platform is a highly flexible experimental
infrastructure that was specifically designed to perform multitrophic
biodiversity experiments in terrestrial ecosystems (Eisenhauer &
Türke, 2018). In the following sections, we describe the iDiv Ecotron
specifications and functioning, we highlight a case study experiment
as an application possibility, and we provide an outlook on the po-
tential contributions of future ecotron experiments. The concept of
the iDiv Ecotron was to create a facility which allows the setup and
maintenance of complex communities and manipulation of several
abiotic factors in a near- natural way, while simultaneously measur-
ing multiple ecosystem functions. Environmental conditions, such as
humidity, nutrient supply, light, and precipitation, can be fully con-
trolled and monitored (for details see Appendix 1), which allows the
iDiv Ecotron to be used for the simulation of multiple abiotic sce-
narios together with scenarios of above- belowground community
change. The iDiv Ecotron offers the possibility to study a wide range
of ecosystem responses, including above- belowground interactions
of plants, microbes, and inver tebrates. The platform can accommo-
date stand- alone experiments and also provides complementary in-
formation to small- and large- scale experiments (lab- ecotron- field).
Therefore, the iDiv Ecotron links investigations at multiple experi-
mental and spatial scales and ser ves as a key component for collab-
orations between researchers from different disciplines to conduct
interdisciplinary studies on the drivers of, and relationship between,
biodiversity and ecosystem functioning. Consequently, this platform
is likely to provide novel insights into ecosystem responses to global
change.
2 | SETUP AND DESIGN OF THE iDiv
ECOTRON
Based on some first facilities that were built in Germany
(ExpoSCREEN Munich, Payer et al., 1987), England (Imperial College
ecotron in Silwood Park; Lawton, 1996; Law ton et al., 1993) and
the United States (Desert Institute EcoCELLs in Reno, Nevada,

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Griffin et al., 1996) in the 1980s and 1990s, highly sophisticated
experimental infrastructures, so- called “ecotrons,” star ted to get
established worldwide in the early century, reflecting the urgent
need for such infrastructures accompanied by the rapid evolution
in digital technology and electronics (e.g., Ecotron in Montpellier,
France, Milcu et al., 2014; IleDeFrance Ecotron EcoLabs in Saint-
Pierre- lès- Nemours, France, Verdier et al., 2014; Ecotron in Hasselt,
Belgium; Biotron in Lincoln, New Zealand). These t ypes of facilities
started to go beyond single trophic levels (mainly plants), like the
so- called “phytotrons” that were emerging in the 1950s and 1960s
(e.g., the Duke University, https://biolo gy.duke.edu/facil ities/ phyto
tron; or the North Carolina State, https://phyto tron.ncsu.edu/; see
Roy et al., 2021 “supinfo- 0 003”). The idea behind an ecotron is to
combine the precision, specificity, and complete control of single
independent and response variables of laboratory experiments and
the realism and large- scale community- and environment- related as-
pects of field studies. Roy et al. (2021) define an ecotron as an “…
experimental facility comprising a set of replicated enclosures de-
signed to host ecosystems samples, enabling realistic simulation of
above- and belowground environmental conditions, while simultane-
ously and automatically measuring ecosystem processes. Therefore,
ecotrons provide continuous information on ecosystem functioning
(fluxes of energy and matter).” The Silwood Park Ecotron in particu-
lar has focused research on multitrophic interactions (see Lawton,
1996; Lawton et al., 1993). The iDiv Ecotron continues the tradi-
tion of aboveground– belowground work by creating a facility capa-
ble of housing a multitude of above- and belowground organisms
from various trophic groups in a large number of single independ-
ent chambers (unlike other indoor facilities, such as ExpoSCREEN in
Munich, Germany, or the Montpellier Ecotron mesocosms in France;
see Roy et al., 2021) while being completely independent from ex-
ternal weather conditions (unlike, for example, the Hasselt Ecotron
in Belgium).
A review with detailed descriptions and comparisons of a vari-
ety of current ecotrons worldwide can be found in Roy et al. (2021).
However, the breadth of ecotrons compared in Roy et al. (2021) pre-
vents an in- depth examination of any one facility. With the goal of
inspiring collaborative proposals to use the research platform, and
to provide a reference for the design and specification of the facil-
ity for future research, we provide an in- depth description of the
iDiv Ecotron here. The iDiv Ecotron is located in a climate- controlled
and blacked out hall on an area of 485 m2 at the research station
of the Helmholtz Centre for Environmental Research— UFZ in Bad
Lauchstädt (Saxony- Anhalt, 51°22′60N, 11°50′60E, 118 m a.s.l.),
Germany. The indoor research facility houses 24 identical experi-
mental units (hereaf ter EcoUnits, see Figure 1), each of which can
contain one to four ecosystems, separated above- or belowground,
or both. In this way, up to 96 subunits with various biotic and abiotic
variables to be manipulated and measured independently can be set
up. The iDiv Ecotron concept was developed in cooperation with
numerous scientists and technicians from iDiv, including strong par-
ticipation by the UFZ, national and international collaborators, and
the companies “EMC – Gesellschaft zur Erfassung und Bewertung
von Umweltdaten mbH,” and “Umwelt- Geräte- Technik GmbH (UGT),
Müncheberg.”
EcoUnits are experimental chambers with the outer dimensions
of 1.55 m × 1.55 m × 3.20 m (L × W × H), comprising a lower par t,
which can be filled with soil (belowground part), an upper par t (abo-
veground part), and a technical section on the top. The frame of the
chamber is constructed of aluminum construction profiles providing
stability and flexibility.
The belowground part contains a container with internal dimen-
sions of 1.24 m × 1.24 m × 0.80 m (L × W × H) made of welded
PE- HD and a steel bottom. It can be filled with up to 1.23 m3 of soil,
or alternatively equipped with four steel cylinders (lysimeters) mea-
suring 0.50 m × 0.80 m (D × H), each of which can hold 0.16 m3 of
soil. The container as well as the lysimeters feature pluggable open-
ings in three different depths (9.5, 21.5, and 43.5 cm), where sen-
sors for soil temperature, soil moisture, and water potential can be
inserted. Additional larger openings in the same depths as those for
FIGURE 1 Illustration of an EcoUnit;
(a) construction drawing with corner
cutout to visualize the technical interior
features; (b) EcoUnit with earth- filled
lower part, upper part equipped with
illustrative vegetation
(a) (b)

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the sensors offer the opportunity to install minirhizotrons (acr ylic
glass tubes) for horizontal monitoring of root development using a
portable root scanner (see Möller et al., 2019).
Besides manually filling the lysimeters with soil, they can be used
to excavate intact soil monoliths, including aboveground vegetation,
directly from the field. This enables precise investigations of almost
undisturbed soil systems, preserving their structure and stratification
as well as their faunal and microbial soil communities. Both the lysim-
eters and the containers provide a living space of sufficient size to es-
tablish and study belowground organisms and processes. To achieve
a near- natural soil temperature gradient with temperature decreasing
from the surface to deeper soil depths, the bottom of the soil con-
tainer was fitted with a coil that circulates a cooling medium. This
system can be regulated individually for each EcoUnit and automated
with the data from the above- and belowground temperature sensors.
To allow pore water sampling and near- natural drainage of water
from the soil system, four suction systems are installed at the bot-
tom of the soil container or one in each lysimeter. Each suction sys-
tem consists of a suction cup ring with 8 suction cups, a pump, a
control module, and two glass bottles. By applying negative pressure
(max. −60 kPa), the suction systems continuously extract and col-
lect pore water. When one bottle is filled, the control unit of each
suction system automatically switches to the alternate bottle and
empties the first one. To quantify the volume of water sampled, the
system counts the number of bottle changes. This enables a contin-
uous supply of soil water for chemical analyses and an automated
recording of the total amount of collec ted water. Simultaneously,
the negative pressure applied at the bottom of the lysimeter lowers
the water potential from there up and reduces “unnatural” high plant
transpiration. When the soil column is cut over the course of the
monolit h ext ra ction, the water poten ti al at th e cu t level becomes ze-
ro— it is brought to atmospheric pressure, which eases and therefore
increases the extraction of water by plants. Here, the suction system
can be used to apply the pressure that corresponds to the natural
in situ water potential at that depth. This allows for these ecosys-
tems to further approximate natural conditions (Groh et al., 2016).
Opti on ally, si ng le suct ion cup s can als o be inst all ed in thr ee diff erent
depths (9.5, 21.5, and 43.5 cm) by using the pluggable openings.
The aboveground part, with internal dimensions of 1.46 m × 1.46
m × 1.50 m (L × W × H), provides sufficient space for communities
of large herbs or tree saplings (see Figure 2) including their complex
multitrophic interaction networks. In each quarter, a video camera can
be installed (for details on the camera system, see Appendix 1), for ex-
ample, for monitoring vegetation development over time (Ulrich et al.,
2020) or insect behavior, such as movement patterns, flower visitation
of pollinators, and habitat use. By using infrared lights, the cameras
can also operate in darkness.
The aboveground part is further equipped with an irrigation
system consisting of a flow meter and four electromagnetic valves
with fixed nozzles. By sequentially processing the opening times
of the valves, each quarter of an EcoUnit can be automatically pro-
vided with individual volumes of water at programmable times. All
irrigation systems are supplied with deionized water from a central
reverse osmosis system. To compensate for the flow resistance
caused by different lengths of supply hoses to each EcoUnit, the
water pressure at the water treatment plant is increased to approx.
4 bar (400 kPa) and then reduced to a constant level of about 2 bar
(200 kPa).
Ambient air temperature is maintained centrally in the Ecotron
hall, but the air flow rate of each subunit can be regulated individually.
Climatic conditions are recorded by combined humidity and tempera-
ture sensors installed in each quarter of an EcoUnit, usually placed at a
height of 40 cm above soil surface. Conditions are continuously com-
pared with those of the hall and, as needed, automatically adjusted by
increasing or decreasing the fan speed of the ventilation system. All
four quarters of the EcoUnit can be regulated individually.
Further, the top part of the EcoUnits is equipped with a diffuser
holding 4 LED lamps adjustable in color and intensity. The light sys-
tem provides three individually dimmable color channels (400– 405,
460– 475, 625– 720 nm) as well as a dimmable white channel (5000 K
+ 30 00 K), and a binar y (ON/OFF) infrared channel (840– 850 nm).
For the overall luminance as well as for each color channel, the inten-
sity can be set from 0% to 100% individually, determining the gen-
eral light color. This can be done either manually or automated in an
hourly resolution with an automatically linear transition between the
settings. In this way, the relative propor tion of different wavelengths
within the light spectrum can be modified (e.g., a higher proportion
of red light at dawn and dusk). The maximum photosynthetic ac tive
radiation (PAR) 5 cm above the standard soil surface can reach about
400 μmol s−1 m
−2 on average (detailed information on the hetero-
geneity of illumination can be found in Appendix 2). Two electrical
cabinets provide the power supply for the lamps and a local control
unit for all sensors and actuators.
Control commands and settings of all manipulable environmen-
tal parameters are stored in a central database and get transmitted
to each EcoUnit via a network. In turn, the execution confirmations
as well as the timest amped sensor data of each EcoUnit are logged
in the same database. This asynchronous communication between
EcoUnits and database server provides a high operational reliabil-
ity and independence of network's capacity bottlenecks. A simple
graphical user interface eases the handling of database entries.
3 | CASE STUDY– EFFECTS OF
ABOVEGROUND PREDATORS ON
ABOVEGROUND– BELOWGROUND
INTERACTIONS AND ECOSYSTEM
FUNCTIONS
3.1 | Rationale
Aboveground– belowground interactions are known to determine
the functioning of terrestrial ecosystems (Scheu, 2001; Wardle
et al., 2004). Previous work has shown that aboveground inverte-
brate predators can induce trophic cascades that “trickle- down”
to affect soil food webs and a broad range of ecosystem functions

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(Wardle et al., 2005). Here, we present a case study conducted in
the iDiv Ecotron to test how plant communit y composition may af-
fect such trickle- down effects. Further, as plant- mediated effects
of aboveground predators may additionally depend on the activity
of soil ecosystem engineers, which structure the environment for
(Bro wn , 1995; Eise nha uer, 2010) and the re sou rce sup ply of so il fo od
webs (Eisenhauer, 2010; Schwarzmuller et al., 2015), we investigated
the effects of soil fauna on multitrophic diversity and ecosystem
functions. The unique functionality of the iDiv Ecotron enabled us
to study potential cascading effects of aboveground predators on
herbivores, plants, and soil food webs, and how these effects are
modulated by decomposer communities in the soil. Specifically, we
tested (1) if the target plant biomass would be lower in the presence
of herbivores, an effect that would be alleviated by the presence and
higher density of predators (e.g., Wardle et al., 2005). We further
hypothesized (2) that the identity of the neighboring plant commu-
nity will affect the biomass of the target plant with biomass being
higher in a community with herb species compared to grass species
due to elevated competition for soil resources in the presence of
grasses (Eisenhauer & Scheu, 2008). Moreover, we expected (3) the
presence of decomposers (earthworms and Collembola) to affect the
tritrophic interactions aboveground, as decomposition and minerali-
zation processes in soil can significantly alter the performance of the
target plant (van Groenigen et al., 2014; Scheu, 2003) as well as the
competition with the surrounding vegetation (Eisenhauer & Scheu,
2008; Sabais et al., 2012). Finally, we hypothesized (4) that there will
FIGURE 2 Grassland (upper picture) and tree saplings (bottom
picture) planted in EcoUnits of the iDiv Ecotron
FIGURE 3 Experimental setup of the case study

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be trickle- down effects of aboveground predators on soil nematode
density and species richness due to altered resource supply and
that soil food web responses to these trickle- down effects will be
modulated by earthworm presence as they significantly change the
structure of the environment for and resource supply of other soil
organisms (Brown, 1995; Eisenhauer, 2010).
3.2 | Methods
Experimental setup and data analyses
In six EcoUnits in a lysimeter configuration, a tritrophic system got
established comprising a target plant (Vicia faba L.), its host- specific
aphid (Acyrthosiphon pisum Harris), and a predator exclusively feed-
ing on aphids (Coccinella septempunctata Linnaeus; details on initial
densities can be found in Appendix 3). We further included a soil
fauna treatment (with and without soil fauna) to test whether preda-
tor effects are modulated by the presence of macro- and meso-
de comp o sers in the so i l; an d a “pl a nt ne igh bor ” trea t ment to te st pl ant
responses in different competitive environments and to increase
variation for reproducibility purposes (Milcu et al., 2018). Concisely,
we established an experimental setup with three treatment factors
comprising aboveground invertebrates, belowground invertebrates, and
surrounding vegetation (see Figure 3). Each treatment combination
was replicated three times. While soil compartments were all fully
isolated one from another (four per EcoUnit), the aboveground com-
partments allowed for an exchange of inver tebrates between lysim-
eter pairs with an acr ylic glass barrier of 15 cm height preventing the
migration of soil invertebrates between lysimeters. In this way, there
were two independent experimental units in each of the six EcoUnits
resulting in twelve independent “Sub- units” and 24 “Sub- sub- units” in
total (more details on the experimental setup and environmental con-
ditions ca n be fou nd in Ap pendi x 4). The expe ri ment ran for 124 days,
from February 03, 2017, to June 06, 2017.
A general linear mixed model (GLMM) type III sum of squares
(procedure MIXED, SAS 9.2) was used to analyze dry weight (g) of
the focal plant (Vicia faba), nematode density, nematode species
richness (all three recorded during the harvest at the end of the ex-
periment), maximum numbers of aphids (peak number of individu-
als counted in one assessment during the experiment), and days of
aphid infestation (number of days beans were infested with aphids;
details can be found in Appendix 5) in relation to the fixed factors
aboveground invertebrates, belowground invertebrates, and surround-
ing vegetation. The factor “Sub- unit” nested in “Sub- sub- unit” was
considered random. Post hoc Tukey's HSD tests were carried out to
reveal significant differences between the respective factor levels
within factors.
Details on treatment factors:
1. Aboveground invertebrates: The treatment was established to test
whether predator effects depend on their density (4 levels: all
aboveground invertebrates absent [Control], only aboveground
herbivores present [Herbivores only], aboveground herbivores
present with aboveground predators in low density [Coccinella
low], aboveground herbivores present with aboveground pred-
ators in high density [Coccinella high]).
2. Belowground invertebrates: To half of the lysimeters ear thworms
and Collembola were added to test if predator performance is
modulated by the presence of macro- and meso- decomposers
in the soil (2 levels: earthworms and Collembola present [with soil
fauna] versus earthworms and Collembola absent [no soil fauna]);
soil invertebrate species list and initial densities can be found in
Appendix 5).
3. Surrounding vegetation: the focal plants (Vicia faba L) were each
surrounded by a herb or grass monoculture (4 levels: Bellis peren-
nis L., Centaurea jacea L., Festuca pratensis Huds., Holcus lanatus L.;
details on plants can be found in Appendix 7).
3.3 | Results
The target plant (for brevity “bean” in the following) dry weight
differed significantly depending on the neighboring plant species
(F3,48 = 5.16, p < .01; Figure 4, Table A3) and the aboveground in-
vertebrate treatments (F3,48 = 6.48, p < .001; Figure 4, Table A3),
whereas it did not dif fer among belowground invertebrate treat-
ments as well as with any of the two- or three- way interactions of
the three variables tested. Bean dry weight was lowest in patches
with B. perennis and H. lanatus, whereas it was significantly higher in
C. jacea patches (Figure 4). Fur thermore, bean dr y weight was highest
in the aboveground invertebrate “Control” and the “Coccinella high”
treatments, whereas it was lowest in the “Herbivores only” treatment.
The maximum number of aphids and number of days of aphid in-
festation differed significantly between the aboveground invertebrate
treatments (F1,24 = 8.24, p = .01; Figure 4, Table A3; and F3,48 = 63.19,
p < .001, respectively; Table A3). Further, the maximum number of
aphids showed significant differences in the interaction between
plant neighbor species and belowground invertebrates (F3,24 = 5.82,
p = <.01; Figure 4, Table A3). In general, numbers of aphids were
higher in the “Coccinella low” treatment compared to the “Coccinella
high” treatment. Depending on the plant neighbor identity, maximum
number of aphids slightly decreased (B. perennis and F. pratensis) or
increased (C. jacea and H. lanatus) with the presence of belowground
invertebrates, but effects were not statistically significant.
Nematode densities differed significantly only between plant
neighbor species (F3,48 = 2.86, p = .05; Table A3). Highest numbers
were found in patches where C. jacea was planted and lowest numbers
in plots with F. pratensis (significant differences were found only be-
tween these two). For nematode species richness, only the interaction
between plant neighbor species and the aboveground invertebrate
treatment was significant (F9,48 = 2.21, p = .04; Figure 4, Table A3).
Although the post hoc Tukey's HSD test showed no significant differ-
ences between factor levels, nematode species richness was lowest in
the “Herbivores only” treatment in the presence of F. pratensis, while
it was highest in the “Control” treatment in the presence of C. jacea.

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3.4 | Discussion
In contrast to our expectations, beans did not generally benefit from
growing in her b commu ni ties, while bein g su ppres sed by more dom i-
nant nitrophilous grasses (Eisenhauer & Scheu, 20 08). We observed
opp osing effects for the two gr ass spe cies an d for the two herb spe-
cies on bean biomass. Among the four neighboring plant species, H.
lanatus produced by far the highest amount of aboveground plant
biomass (139.5 g) at the end of the experiment compared to the
other three species (F. pratensis: 92.1 g, C. jacea: 51.1 g, B. peren-
nis: 5.3 g), and, as graminoid species typically produce a dense and
large root system, we speculate that also root biomass was highest
(not assessed in this study). Thus, both enhanced aboveground light
competition and belowground competition for resources may have
contributed to an overall advantage in resource acquisition over the
bean, causing low bean biomass. Indeed, it has been often confirmed
that grasses are stronger competitors compared to herbaceous spe-
cies (Del- Val & Crawley, 2005; Tilman, 1982). Moreover, another
potential explanation for the patterns found in our study may be
that in patches of low biomass, for example, in B. perennis patches,
the habitat structure for predators was comparably low leading to
a migration to more favorable habitat structures. This effect may
have cascaded to lower trophic levels increasing abundances of
herbivores and decreasing plant performance (Romero & Koricheva,
2011). The importance of such non- trophic interactions based on
habitat structure has been often highlighted (Kalinkat et al., 2013;
Majdi et al., 2014).
Our results confirm the often found tritrophic relationships be-
tween predators, herbivores, and primary producers, where pred-
ators, in our case ladybirds, exert a top- down control on aphid
abundances which, in turn, have a top- down effect on the bean
(Romero & Kor icheva, 2011). Surprisingly, the effects of plant neigh-
bor species on aphid abundances were opposing for communities
without and with belowground inver tebrates. These findings high-
light the significance of aboveground– belowground interactions and
show that decomposers can influence aboveground multitrophic
interactions by altering the competition between plants (Wardle
et al., 20 04). Moreover, we found that trickle- down effects of
FIGURE 4 Effects of (a) aboveground
invertebrate treatment (control,
herbivores only, Coccinella low, Coccinella
high; details in Appendix 3) as well
as (b) the interaction of belowground
invertebrate presence (with/+ soil fauna,
without/- soil fauna) and bean plant
neighbor species identity (Bellis perennis
L., Centaurea jacea L., Festuca pratensis
Huds., Holcus lanatus L.) on the maximum
number of aphids; (c) aboveground
invertebrate treatment and (d) bean
plant neighbor species identity on bean
dry weight; and (e) the interaction of
aboveground invertebrate treatment
and bean plant neighbor species identity
on the species richness of nematodes.
*p = .05; **p < .01; ***p < .001. For
detailed results see Table A3

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aboveground invertebrates on soil food webs (here represented by
soil nematode species richness) depend on plant community compo-
sition. This finding suggests that the competitive environment of a
focal plant can alter its effects on soil community composition, po-
tentially through changes in the amount and quality of plant- derived
resources entering the soil (Hooper et al., 200 0).
Taken together, our study shows distinct interaction effects be-
tween aboveground and belowground invertebrate communities on
multitrophic interactions and community composition in the sub-
compartments. These changes are likely to alter how communities
function, which may have subsequent feedback effects on nutri-
ent cycling and community composition. The results of our study
highlight the need for infrastructures that allow to manipulate food
webs of high complexity, which can hardly be realized experimen-
tally under field or simplified laboratory conditions (Beyers & Odum,
1993 ), and at the sam e time, tak ing adv an tage of measuri ng and con-
trolling a large fraction of other non- targeted parameters including
environmental conditions.
4 | OUTLOOK
Over the last several decades, ecologists have written thousands
of papers about changes in climate and biological communities. Yet,
some important knowledge gaps remain. Here, we discuss the rel-
evance of mesocosm research as an underappreciated scale of in-
quiry. The utility of mesocosm/Ecotron experiments is not limited to
terrestrial systems, and similar rationale has been used to promote
independent aquatic mesocosm facilities (e.g., Hines et al., 2013), as
well as consortia of aquatic facilities (e.g., Mesoaqua, https://cordis.
europa.eu/proje ct/id/22822 4/repor ting; Aquacosm, https://www.
a q u a c o s m . e u / p r o j e c t - i n f o r m a t i o n / ) . H o w e v e r , w e f o c u s o n t e r r e s -
trial systems here, because we further develop this line of reasoning
by describing three opportunities where the iDiv Ecotron is particu-
larly well suited to address challenges limiting an integrative under-
standing of biodiversity and ecosystem functioning.
Mesoecology is an important and often overlooked scale in
environmental change research (Stewart et al., 2013). While mac-
roecological studies provide more realistic abiotic and biotic con-
text for investigating ecosystem processes, complex communities
and environmental conditions can only be controlled, and causality
of patterns inferred, to a very limited extent, and of ten with very
few replicates (Eisenhauer & Türke, 2018; Lawton et al., 1993). On
the other hand, laboratory microcosm studies can fully control and
alter external factors and allow for high replication (Benton et al.,
2007). However, laboratory studies are often limited to investigat-
ing single mechanisms and processes under artificial and simplified
environmental conditions (Lawton et al., 1993). They are prone to
experimental artifacts caused by the simplification of complex in-
teractions which may bias results and induce misleading conclusions
(Carpenter, 1996, 1999; Milcu et al., 2018; Roy et al., 2021; Schindler,
1998). The iDiv Ecotron provides an important middle ground, es-
pecially with the possibility of extracting and implementing up to
96 intac t soil monoliths which allows for precise investigations of
almost undisturbed soil systems, while preserving their structure
and stratification as well as their faunal and microbial soil commu-
nities. Mesocosm experiments close the gap between small- and
large- scale studies and they allow scientists working together across
levels of organization from cells to ecosystems to test basic and ap-
plied ecological questions. However, attempts to do so will profit
from including a few key aspects of research that serve as future
opportunities.
Opportunity 1: Multitrophic diversity change
Although many studies have evaluated responses of plant species
to environmental variation, ecologists have yet to demonstrate the
collective importance of these responses for the full complement
of plants’ interaction partners above and below the ground. This is
particularly important because not all taxa that interact with plants
perceive environmental variation at the same scale (Heinen et al.,
2018; Veen et al., 2019). Therefore, although it has been shown
that diversity can beget diversity, and patterns in plant diversity can
parallel patterns of soil diversity and aboveground consumer diver-
sity (Eisenhauer et al., 2013; Scherber et al., 2010), these patterns
may be mismatched (Cameron et al., 2019) and/or further decou-
pled by environmental change drivers (Bardgett & Wardle, 2010;
Thakur, 2020). Future iDiv Ecotron experiments will evaluate differ-
ences in spatial and temporal response to drivers that may explain
mismatches in above- and belowground biodiversity (Eisenhauer &
Türke, 2018). The iDiv Ecotron allows for simultaneous manipula-
tion of aboveground and belowground biodiversit y, with particular
emphasis on belowground sub- systems through the use of intact
soil cores, the examination of roots via rhizotrons, and large enough
spatial scale to examine differences in patterns of aboveground and
belowground diversity. Rigorously testing factors that influence
aboveground– belowground relationships is critical, because they
form key pathways by which environmental variation influences
communit y assembly, biodiversity effects on ecosystem functioning,
and the impacts of environmental change on community dynamics.
To develop effective plans to conserve biodiversity, we need meso-
scale empirical studies that test the mechanisms underlying effects
of environmental drivers on aboveground– belowground biodiversity
and ecosystem functioning.
Opportunity 2: Beyond presence/absence—
Behavioral and chemical mechanisms of plants and
animal interactions
Traditionally, experimental examinations of food web interactions
have been conducted by stocking simplified communities into mi-
crocosms or field plots and quantif ying the outcome of the inter-
actions by counting the presence and abundance of species af ter
a designated time period. It is likely that phenotypic changes (e.g.,

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changes in behavior, chemistry, or morphology) ser ve as precur-
sors to the numerical changes in communit y composition that are
typically quantified, or that phenotypic changes can drive major
changes in ecosystem functioning on their own (Matthews et al.,
2011; Turcotte & Levine, 2016). Yet, phenot ypic responses are
more often evaluated in highly simplified communities with lim-
ited emphasis on interaction complexity. We see considerable
potential for iDiv Ecotron studies to extend highly simplified labo-
ratory experiments showing effects of environmental drivers on
phenotypic responses (e.g., behavioral, morphological, and physi-
ological change). Changes in local foraging and behavior/activit y
patterns may be an important mechanism underlying changes
in biodiversity– ecosystem function relationships (Jeltsch et al.,
2013). The iDiv Ecotron can be fit with a landscape of sensors for
detecting movement of animals tagged with RFID chips. Repulsed
(or aggregated) animal activity patterns can point to the impor-
tance of non- trophic and trait- mediated interactions (e.g., fear).
Such behavioral changes are not limited to animals. For exam-
ple, behavior changes of plants emission of plant volatiles can be
turned off and on depending on plant interaction partners. Plant
volatiles play key roles in plant defense against aboveground and
belowground herbivores, plant competition, and plant communica-
tion (Pierik et al., 2014). Yet, research of plant volatiles is often
conducted on isolated plant s or pairs of plants. These aspects of
phenotypic changes (animal movement, plant volatiles) are diffi-
cult to assess in field conditions where signals may be detected by
ecological communities but not my scientific instruments due to
difficulties relocating animals in larger more complex landscapes,
or buffering effects of wind. Future iDiv Ecotron experiment s will
examine the role of aboveground– belowground plant and animal
behavior in complex communities.
Opportunity 3: Multiple drivers of environmental
heterogeneity and environmental change
We have only begun to identify the full array of environmental
changes confronting ecosystems today (Bowler et al., 2020). The
iDiv Ecotron allows for independent manipulation of several abi-
otic factors (e.g. precipitation, light, nutrients, and temperature) in
gradient- based or factorial combinations. Non- additive, synergistic,
or unexpected responses may be detected from heretofore untested
combinations of environmental change drivers. There is also much
potential to use the iDiv Ecotron to examine the influence of minor
or extreme levels of drivers and to detect non- linear relationships
between drivers and ecosystem responses (De Boeck et al., 2015;
Damgaard et al., 2018). Therefore, the iDiv Ecotron is an ideal tool
to complement environmental change experiments where ecological
responses are evaluated over longer time periods or greater spatial
scales, but at the cost of examining a reduced number of scenarios
(e.g., Schädler et al., 2019). Future studies may therefore be consid-
ered as a step toward precision and mechanistic understanding sup-
plementing other laboratory or field studies.
In conclusion, the iDiv Ecotron provides a flexible collaborative
research platform that operates at an intermediate scale, connect-
ing simplistic microcosm experiments and real- world heterogeneity.
Their size allows for evaluation of naturally complex aboveground–
belowground interactions, often overlooked mechanisms (e.g., be-
havior, plant volatiles), as well as a broad range of environmental
drivers. Therefore, this robust experimental facility can help to fill
several critical knowledge gaps identified in synthesis studies. The
iDiv Ecotron will be used to assemble, disassemble, and reassemble
ecological communities in rigorous tests of basic and applied eco-
logical questions. We start with an empty box with strong technical
capabilities to control environmental conditions, endless possible
combinations of species, and an open call to potential collaborators:
What would you do if you could rebuild the world?
ACKNOWLEDGMENTS
Numerous scientific and technical staff from iDiv and UFZ were in-
volved in the conceptualization of the iDiv Ecotron. Special thanks
to the participants of the first sDiv Ecotron workshop in 2013, to all
iDiv scientists who provided valuable input for the Ecotron concept
by participating in surveys, and to the other members of the Ecotron
Board, Ulrich Brose, Stanley Harpole, and Reinart Feldmann. All au-
thors acknowledge funding by the German Centre for Integrative
Biodiversity Research (iDiv) Halle- Jena- Leipzig funded by the
German Research Foundation (DFG- FZT 118, 202548816). We
thank Oliver Bednorz, Konrad Kirsch, Ines Merbach, and all other
employees of the Bad Lauchstädt Experimental Research Station of
the Helmholtz Centre for Environmental Research— UFZ for support
on- site. Finally, we acknowledge the members of the Experimental
Interaction Ecolog y group and all student helpers for their support
during field and lab work. Open Access funding enabled and organ-
ized by Projekt DEAL.
CONFLICT OF INTEREST
The authors declare no conflicts of interest s.
AUTHOR CONTRIBUTIONS
Anja Schmidt: Data curation (lead); Formal analysis (lead);
Investigation (equal); Visualization (lead); Writing- original draft
(lead); Writing- review & editing (lead). Jes Hines: Validation (equal);
Writing- original draft (equal); Writing- review & editing (equal).
Manfred Türke: Conceptualization (equal); Data curation (lead);
Investigation (equal); Methodology (lead); Project administration
(lead); Supervision (lead); Writing- review & editing (equal). François
Buscot: Conceptualization (equal); Funding acquisition (equal);
Investigation (equal); Validation (equal); Writing- review & editing
(equal). Martin Schädler: Conceptualization (equal); Funding acquisi-
tion (equal); Investigation (equal); Validation (equal); Writing- review
& editing (equal). Alexandra Weigelt: Conceptualization (equal);
Funding acquisition (equal); Investigation (equal); Validation (equal);
Writing- review & editing (equal). Alban Gebler: Conceptualization
(equal); Investigation (equal); Software (equal); Writing- review & ed-
iting (equal). Stefan Klotz: Conceptualization (equal); Methodology

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SCHMIDT eT a l.
(equal); Writing- review & editing (equal). Tao Li u : Investigation
(equal); Methodology (equal); Writing- review & editing (equal).
Sascha Reth: Conceptualization (equal); Software (equal); Writing-
review & editing (equal). Jacques Roy: Conceptualization (equal);
Methodology (equal); Writing- review & editing (equal). Stefan
Trogisch: Conceptualization (equal); Methodology (equal); Writing-
review & editing (equal). Christian Wirth: Conceptualization
(equal); Methodology (equal); Writing- review & editing (equal). Nico
Eisenhauer: Conceptualization (lead); Funding acquisition (lead);
Investigation (equal); Methodology (equal); Project administration
(lead); Resources (equal); Supervision (equal); Validation (equal);
Writing- review & editing (equal).
DATA AVAIL AB ILI T Y STAT EME N T
All underlying data are available from the iDiv Data Repository.
h t t p s : / / d o i . o r g / 1 0 . 2 5 8 2 9 / i d i v . 3 4 9 6 - 8 - 5 6 9 5 .
ORCID
Anja Schmidt https://orcid.org/0000-0001-5339-219X
Jes Hines https://orcid.org/0000-0002-9129-5179
Manfred Türke https://orcid.org/0000-0002-8957-5454
François Buscot https://orcid.org/0000-0002-2364-0006
Martin Schädler https://orcid.org/0000-0001-9700-0311
Alexandra Weigelt https://orcid.org/0000-0001-6242-603X
Stefan Klotz https://orcid.org/0000-0003-4355-6415
Stefan Trogisch https://orcid.org/0000-0002-1426-1012
Jacques Roy https://orcid.org/0000-0003-2275-9870
Nico Eisenhauer https://orcid.org/0000-0002-0371-6720
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APPENDIX 1
TABLE A1 Abiotic parameters of an EcoUnit, control, and data storage options; combined temperature/humidit y sensors: MEL A FE09,
Galltec Meß- und Regeltechnik GmbH Bondorf, Germany; integrated flow meter: FCH- midi- PO M 97478976, B.I.O.- TECH e.K. Vilshofen, Germany;
temperature/moisture sensors belowground: SMT100 , TRUEBNER GmbH Neustadt, Germany; observation cameras: YUC- Hi82 M, Yudor
Technology Co, Ltd Tao Yuan City 324, Taiwa n
Parameter Controlling User inter face Sensing
Air temperature Via adjustable ambient temperature of hall GUI 4 combined temperature/humidity sensors
Air humidity Indirect only by air temperature and air flow
rate
– 4 combined temperature/humidity sensors
Air flow rate By blower speed GUI Manually by air velocimeter
Lighting timing 1- h setting resolution with automatically
calculated intermediate dim steps for each
channel
GUI Logging of execution confirmation only
LIGHT intensity Nominal 1% set ting resolution with internal
mapping to neares t dim step
GUI Logging of execution confirmation only
Light color mix 4 dim channels (UV, blue, red, NIR); 1 non dim
channel (FIR)
GUI Logging of execution confirmation only
Irrigation volume 50 ml setting resolution GUI Integrated flow meter
Irrigation timing 1- h setting resolution GUI Logging of execution confirmation only
Soil temperature By cooling at the bottom down to ~10°C with
resulting temperature gradient to soil
surface
GUI Up to 12 combined temperature/moisture
sensors in three levels belowground
Soil moisture Indirect only by change of irrigation volume,
soil water removal, and the manipulation of
evaporation rate by air flow rate
– Up to 12 combined temperature/moisture
sensors in three levels belowground
Suction low pressure 1 kPa setting resolution with low pressure down
to −60 kPa below ambient air pressure
GUI Each suc tion system includes an integrated
pressure sensor
Video observation Orientation of vision and operation mode
manually only
Camera's web GUI Observation camera
Still pictures By external script with access to video stream
of running cams
Camera's web GUI
+ Linux shell
Observation camera

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APPENDIX 2
APPENDIX 3
ABOVEGROUND INVERTEBRATES
To test for effects of aboveground invertebrates on tritrophic interac-
tions and nematode communities, we implemented different combi-
nat ions of her bi vore and pred ator specie s pr es en ce and absence. We
used the pea aphid Acyrthosiphon pisum Harr is as aboveg ro und herb i-
vore feeding specifically on the broad bean Vicia faba L. Eight matur e
individuals were added to each replicate of respective treatments
between April 27 and May 3. We used adult beetles of the seven-
spot ladybird (Coccinella septempunctata Linnaeus) as specialized
aphid predators which were added in two different densities (two
or four individuals) on May 10 to respective treatments. In total, we
tested four aboveground treatments: control (no invertebrates), her-
bivores only (with aphids, without ladybirds), Coccinella low (with
aphids, with two individuals of C. septempunctata), and Coccinella
high (with aphids, with four individuals of C. septempunctata).
APPENDIX 4
DETAILS ON THE EXPERIMENTAL SETUP
The 24 Lysimeters were filled with steam- sterilized top soil (pur-
chased at Bauzentrum Farys GmbH, Laucha). For sterilization, the
soil was subjected to water steam at approx. 100°C for 30 min. Such
sterilization leads to a heavy release of nutrients due to the death of
soil organisms (Alphei & Scheu, 1993; Trevors, 1996), which is why
the soil was thoroughly rinsed with tap water afterward (Jager et al.,
1970). The soil was inoculated with nematode and microbial com-
munities on February 2, 2017, marking the start of the experiment.
Live soil organisms were extracted from top soil of an experimental
grassland site (Jena Experiment, Roscher et al., 2004). We added
four independent samples of soil wash solution (extracted from
100 g of soil each, fil tered through a 125- µm sieve) to each lysimeter
on February 3. In addition, we added three independent inoculates
of nematode solution between Februar y 2 and March 10, which
were previously live- extracted from 20 g wet soil each, following the
modified Baermann funnel method (Cesarz et al., 2019; for det ails
on nematode communities in the Jena Experiment, see Eisenhauer
et al., 2011; Cesarz et al., 2017). To exclude that unintended addi-
tions of nematodes might have confounded the controlled inocula-
tion, soil samples from the sterilized soil filled into lysimeters were
extracted with the same method and yielded no live nematodes. The
following environmental parameters were set in the EcoUnits: light/
dar k cycle 16/8 h (max illumina tion at day, gradual chan ge), tempera-
ture 21°C at day and 17°C at night (gradual change over the course
of 3 h), irrigation of 400 ml on each lysimeter area daily at 4 am, soil
temperature set to 17°C in 43.5 cm soil depth.
APPENDIX 5
MEASUREMENTS
Numbers of aphids on each bean were counted every 7 days. For
analyses, we used the peak number of all assessments during
the experiment (hereafter called “maximum number of aphids”).
Furthermore, we recorded the number of days beans were infested
with aphids by counting live aphids on each bean individual from first
discovery until last discovery; last discovery could either be the end
of the experiment or the time a bean got in a bad status and was not
a suitable host for aphids anymore.
All beans were harvested 49 days after their transplantation by taking
5- cm- diameter soil cores to a depth of 10 cm with beans in their center.
The soil was sieved through a 2- mm sieve, bean roots were extracted
and both were stored at 4°C until further processing. After the removal
of aphids the bean aboveground parts were dried at 45°C for 3 days and
FIGURE A1 (a) Total light intensity (μmol/m2 s), 5 cm above the
standard soil surface, at 36 locations within an EcoUnit, averaged
over 24 EcoUnits, and (b) normalized deviations of light intensit y at
the 36 spots within an EcoUnit; normalization based on the highest
measured average value of total light intensity (shown in (a)),
highest value is set to 1. Five cm above the standard soil surface.
Distance luminaire to backlighting layer 160 mm; outside corners
are not included in calculations due to high edge effects inevitably
created by the construction itself

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weighed. Nematodes were extracted from the previous stored soil fol-
lowing a modified Baermann technique with an extraction time of 48 h
(Cesarz et al., 2019). Extracted nematodes were transferred to formalin
(4%) and counted to obtain the total density of nematodes (given as
number of individuals per 100 g dry soil). Subsequently, 100 individuals
were randomly selected and identified to genus level following (Bongers
& Bongers, 1998) or separated into morphospecies where not possible.
Nematode species richness was calculated as (S−1)/lnN, where S is the
number of total genera in the community, and N is the number of identi-
fied individuals of nematodes in the community.
APPENDIX 6
SOIL INVERTEBR ATES
The steam- sterilized soil (Dietrich et al., 2020) got inoculated with
micr oor ga nis ms and ne matod es (see Appe ndi x 4) . To te st for in te rac-
tions bet ween the aboveground tritrophic system and belowground
invertebrate presence (meso- /macro- fauna), we added the follow-
ing soil invertebrates to one of the t wo lysimeters in each replicate:
15 juvenile anecic earthworms (Lumbricus terrestris Linnaeus, mean
weight 4.4 g) and 20 individuals each of two Collembola species
(Folsomia candida Willem, Protaphorura armata Tullberg). Collembola
populations have been shown to develop rapidly in the experimental
soil until the carrying capacity of the system is reached (Eisenhauer
et al., 2011). Fifty grams of commercial grassland litter was provided
as substrate to both lysimeters (bunny® Frischgras- Heu). Since hay
is a natural product, its grain properties var y according to season.
Typically, in Table A2 shown groups of plants are included.
APPENDIX 7
PLANTS
Nineteen 23- day- old seedlings each of two herbaceous (Bellis
perennis L., Centaurea jacea L.) and two grass species (Festuca
pratensis Huds., Holcus lanatus L.) were transplanted in regular dis-
tances of 5 cm and within monoculture quarters into each lysim-
eter on February 16 to mimic a simplified grassland community.
In the center of each monoculture quarter, a single individual of
an 8- day- old broad bean seedling (Vicia faba L., variety “Dreifach
Weiße,” Bruno Nebelung GmbH) was transplanted on April 19,
representing the specific host plant of aboveground herbivores.
Consequently, there were four host plant individuals per lysimeter
and thus eight individuals per replicate.
TABLE A2 Species list of the commercial grassland litter from
bunny® Frischgras- Heu provided as substrate to both lysimeters
English name Latin name
Timothy ( grass) Phleum pratense
Meadow fescue Festuca pratensis
Meadow fox tail Alopecurus pratensis
Ryegrass Lolium sp.
Red fescue Festuca rubra agg.
Kentucky bluegrass Poa pratensis
Bent grass Agrostis sp.
Cat grass Dactylis glomerata
Common dandelion Taraxacum of ficinale
Common silverweed Potentilla anserina
Mouse- ear chickweed Cerastium sp.
Yarrows Achillea sp.
Ribwort plantain Plantago lanceolata
White clover Trifolium repens
Red clover Trifolium pratense
Common bird's- foot trefoil Lotus corniculatus

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APPENDIX 8
Results of GLMM
TABLE A3 Effects of aboveground (AG) and belowground (BG) invertebrates and bean plant neighbor species identity as well as their interactions on five response variables using GLMM
type III sum of squares analyses
Grouping variable
Response variable
Bean dr y weight Nematode density Nematode sp. richness Max. no. of aphids Days aphid infestation
df F p df F p df F p df F p df F p
AG invertebrates 3, 48 6.48 <.001 3, 48 0.16 .92 3, 48 0 . 51 .67 1, 24 8.24 .01 3, 48 63.19 <.001
BG invertebrates 1, 48 0.26 . 61 1, 48 1.01 .32 1, 48 1.99 .16 1, 24 0.22 .64 1, 48 0.20 .65
AG invertebrates*BG invertebrates 3, 48 1.37 .26 3, 48 0.84 .48 3, 48 0.12 .95 1, 24 0.25 .62 3, 48 1.25 .30
Neighbor species 3, 48 5.16 <.01 3, 48 2.86 .05 3, 48 1.62 .20 3, 24 1.42 .26 3, 48 0.36 .78
Neighbor species*AG invertebrates 9, 48 0.22 .99 9, 48 1.40 .22 9, 48 2.21 .04 3, 24 0.44 .73 9, 48 0.87 .56
Neighbor species*BG inver tebrates 3, 48 0.30 .82 3, 48 1.25 .30 3, 48 0.62 .61 3, 24 5.82 <.01 3, 48 1.58 .21
Neighbor species*AG invertebrates*BG
invertebrates
9, 48 0.92 . 52 9, 48 0 .76 .65 9, 48 0.86 .56 3, 24 0.24 .87 9, 48 0.30 .97
Note: Significant effects ( p < .05) are indicated in bold font.
Abbreviations: max. no. of aphids, maximum number of aphids; sp. Richness, species richness.