JenaTron - An Experimental Approach to Study the Effects of Plant History and Soil History on Grassland Ecosystem Functioning

Our study explores whether the relationship between plant diversity and ecosystem functioning is influenced by plant history, soil history or a combination of the two. We examine how long-term community-specific histories in plants and soils shape these relationships. We use experimental semi-natural grasslands in a controlled Ecotron facility.

Recent research highlights how the positive relationship between plant diversity and ecosystem functioning strengthens over time. Long-term experiments show that higher biodiversity enhances, for instance, resource use, beneficial soil organisms, natural pest control and ecosystem resilience. The key factors expected to influence such biodiversity effects are plant and soil history.

New experimental facilities emerged, known as Ecotrons, designed to replicate natural ecosystems under controlled conditions. These facilities feature multiple enclosures for studying complex ecosystem processes, multi-traffic interactions and ecosystem functions. Ecotrons allow precise control over environmental conditions and enable the monitoring of both above and below ground ecosystems in independent mesocosm chambers.

Our protocol offers us the unique opportunity to study intact soil modulates under controlled environmental conditions, to orthogonally cross plants and soils with different plant community-specific history and to study their effects on multiple ecosystem functions along a plant diversity gradient, which is difficult to achieve under field conditions. To begin, gently remove the upper five centimeters of soil from the selected plots using a mini excavator to equalize conditions across soil history treatments. Set up the monolith extraction device at the plot to start the soil monolith excavation.

Next, switch on the monolith extraction device and allow the cutting system to rotate around the outer cylinder wall to cut a notch in the soil, while the extraction device simultaneously presses the steel cylinder into the soil. In parallel, using a mini digger, excavate a pit at the side of the steel cylinder. Once the steel cylinder is fully embedded in the soil, mount a temporary bottom plate and use the monolith extraction device to lift the cylinder out of the excavation pit.

Dismantle the extraction device and the cutting system from the steel cylinder. Then mount a temporary top plate onto the cylinder. Lift the monolith using a suspension attached to the mini digger and turn it upside down.

Next, dismount the bottom plate from the steel cylinder. Using a trowel, remove approximately five centimeters of the soil layer from the bottom of the steel cylinder. Embed a ring of water suction probes, consisting of eight candles connected with polyvinyl chloride hoses, into quartz powder.

Moisten the powder with demineralized water and refill the bottom of the steel cylinder with soil again. Connect the polyvinyl chloride end piece of the water suction probe ring to the bottom plate. Bolt the bottom plate securely to the steel cylinder.

Turn the steel cylinder upright using the suspension on the mini excavator. Label the cylinder individually. Seal the openings in its walls with adhesive tape and wrap it in plastic foil for protection during transportation.

After unpacking, cut precisely fitting holes for the sensors horizontally in the soil monolith with a customized steel blade, using the openings in the cylinder wall at three different depths. Place the soil sensors into the prepared holes and use a wooden log to position them correctly. Bolt the openings with custom-made seal plugs.

Carefully lift the technical and upper part of each EcoUnit from the lower part. Transport the lower part to the steel cylinders containing the intact soil monoliths equipped with soil sensors. Next, lift four soil monoliths into the lower container of each of the 24 EcoUnits.

Lead the cables of the soil sensors through the openings in the ground container. Use the forklift to transport the container equipped with the four soil monoliths into a 24-meter-by-24-meter hall. Carefully place the technical and upper parts of each EcoUnit back onto the lower part.

Finally, arrange all 24 EcoUnits in three rows, each consisting of two groups of four EcoUnits, forming a total of six blocks. After collecting soil from each of the selected plots at the Jena Experiment Field Site, sieve each plot-specific soil through a four-millimeter mesh. Heat the sand in a drying oven at 200 degrees Celsius for four hours to remove unwanted biota.

After heating, mix plot-specific soil and quartz sand in a three-to-one ratio. Using a plastic shovel, fill the soil-sand mixture into multi-pot plates. Label each multi-pot plate individually.

Place the plates in a greenhouse with a day-night cycle of 16 hours at 18 degrees Celsius and eight hours at 12 degrees Celsius. maintaining 60 to 70%relative humidity. After watering plates on demand and keeping them bare for two weeks to allow soil seed banks to germinate, weed all plates twice to remove unwanted seedlings.

Pretreat ranunculus acris seeds in petri dishes on filter paper moistened with a gibberellic acid solution for 24 hours to break dormancy. The next day, transfer ranunculus acris seeds to filter paper moistened with demineralized water until germination. Once the seeds reach the radical stage, use spring-steel tweezers to prick the seedlings into the plot-specific soil-sand substrate in the prepared multi-pot plates.

Sow all species except ranunculus acris directly into the plot-specific soil-sand substrate in multi-pot plates. Water all plant individuals with deionized water. Incubate the plates in the greenhouse until transport to the iDiv Ecotron.

After opening the EcoUnit, for the planting campaign, use a custom-made planting stencil to mark the exact position of each plant on the soil monoliths. Assign different colored plastic toothpicks for marking, with each color representing a specific plant species. Remove the stencil after marking.

Plant the pre-grown plants on all soil monoliths within one week using bulb planters with a four centimeter diameter. Turn on the lights and set the lighting regime to a 16-hour day and eight-hour night cycle. Simulate dusk by dimming the lights from 100%to 75%intensity over one hour, then to 0%intensity over the next hour.

Simulate dawn by reversing this dimming pattern. Treatment-specific differences in plant community height and color were observed after a three-week establishment phase of the JenaTron experiment and plants grown from seeds without plant history exhibited earlier flowering onset compared to those with community-specific plant history. Vegetative plant height measurements in the iDiv Ecotron were strongly correlated with those from the Jena experiment field plots, confirming consistency in plant development.