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Experimental evaluation of herbivory on live plant seedlings by the earthworm Lumbricus terrestris L. in the presence and absence of soil surface litter.

Kirchberger J, Eisenhauer N, Weisser WW, Türke M - PLoS ONE (2015)

Bottom Line: Lumbricus terrestris preferred to consume legume litter over litter of the other plant functional groups.Pulling live plants into earthworm burrows might induce microbial decomposition of leaves to make them suitable for later consumption.Herbivory on plants beyond the initial seedling stage may only play a minor role in earthworm nutrition and has limited potential to influence plant growth.

View Article: PubMed Central - PubMed

Affiliation: Terrestrial Ecology Research Group, Department of Ecology and Ecosystem Management, Technische Universität München, Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising, Germany.

ABSTRACT

Background: Recent studies suggested that the earthworm Lumbricus terrestris might act as a seedling predator by ingesting emerging seedlings, and individuals were observed damaging fresh leaves of various plant species in the field. To evaluate the significance of herbivore behavior of L. terrestris for plant and earthworm performance we exposed 23- to 33-days-old seedlings of six plant species to earthworms in two microcosm experiments. Plants belonged to the three functional groups grasses, non-leguminous herbs, and legumes. Leaf damage, leaf mortality, the number of leaves as well as mortality and growth of seedlings were followed over a period of up to 26 days. In a subset of replicates 0.1 g of soil surface litter of each of the six plant species was provided and consumption was estimated regularly to determine potential feeding preferences of earthworms.

Results: There was no difference in seedling growth, the number of live seedlings and dead leaves between treatments with or without worms. Fresh leaves were damaged eight times during the experiment, most likely by L. terrestris, with two direct observations of earthworms tearing off leaf parts. Another nine leaves were partly pulled into earthworm burrows. Lumbricus terrestris preferred to consume legume litter over litter of the other plant functional groups. Earthworms that consumed litter lost less weight than individuals that were provided with soil and live plants only, indicating that live plants are not a suitable substitute for litter in earthworm nutrition.

Conclusion: Our results demonstrate that L. terrestris damages live plants; however, this behavior occurs only rarely. Pulling live plants into earthworm burrows might induce microbial decomposition of leaves to make them suitable for later consumption. Herbivory on plants beyond the initial seedling stage may only play a minor role in earthworm nutrition and has limited potential to influence plant growth.

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Schematic example of a microcosm (view from above).The six plant species were randomly arranged. Plant litter was placed on the soil surface next to the live plants of the same species in the respective treatments in the seedling mortality experiment.
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pone.0123465.g001: Schematic example of a microcosm (view from above).The six plant species were randomly arranged. Plant litter was placed on the soil surface next to the live plants of the same species in the respective treatments in the seedling mortality experiment.

Mentions: Microcosms were built from rigid polyvinyl chloride tubes with a volume of 4.42 liter (diameter 15 cm, height 25 cm). Tubes were filled with soil up to the top. To prevent earthworms from escaping, the bottom of the tubes was closed with fly screen (mesh size 1.3 × 1.3 mm), and robust plastic foil was wrapped around the top (height of the plastic fence: 19 cm), which prevents earthworms from escaping the microcosms aboveground [17]. Thus, microcosms had not to be covered by a lid. Microcosms were set up in a greenhouse with regulated air exchange with the outside air and with automatic shading to prevent severe heating. On July 4, 2013 after weighing individuals of L. terrestris (accuracy 0.01 g), earthworms were transferred to microcosms of the respective treatments. Worms had four (herbivory experiment) or eight days (seedling mortality experiment) to adapt to the new environment before plants were added. Plastic pots with plants (diameter 3.5 cm, height 8 cm) were lowered almost entirely into the soil of each microcosm (Fig 1). Plants were isolated from the soil of the microcosm to exclude effects of earthworms on plant growth through changes in soil structure and nutrient availability. Control treatments without worms were arranged in between the earthworm treatments in order to balance microclimatic differences in the greenhouse chamber. Each microcosm was watered daily with about 4 l of tap water (less water was added if the soil was still wet) and plant pots with approximately 100 ml of water each. An excess of water could easily drain from microcosms as bottoms were only closed by fly screen. The average temperature on the soil surface of the microcosms was 26.3°C, ranging between 17 and 32°C. On July 22, 2013 microcosms were transferred to another greenhouse with facility for cooling because the average temperature increased to 28°C, a temperature which is lethal for L. terrestris. The average temperature in the new environment was 16.3°C, ranging between 14 and 22.5°C. At the end of the experiments, the soil of all microcosms was removed from tubes and examined for individuals of L. terrestris.


Experimental evaluation of herbivory on live plant seedlings by the earthworm Lumbricus terrestris L. in the presence and absence of soil surface litter.

Kirchberger J, Eisenhauer N, Weisser WW, Türke M - PLoS ONE (2015)

Schematic example of a microcosm (view from above).The six plant species were randomly arranged. Plant litter was placed on the soil surface next to the live plants of the same species in the respective treatments in the seedling mortality experiment.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401770&req=5

pone.0123465.g001: Schematic example of a microcosm (view from above).The six plant species were randomly arranged. Plant litter was placed on the soil surface next to the live plants of the same species in the respective treatments in the seedling mortality experiment.
Mentions: Microcosms were built from rigid polyvinyl chloride tubes with a volume of 4.42 liter (diameter 15 cm, height 25 cm). Tubes were filled with soil up to the top. To prevent earthworms from escaping, the bottom of the tubes was closed with fly screen (mesh size 1.3 × 1.3 mm), and robust plastic foil was wrapped around the top (height of the plastic fence: 19 cm), which prevents earthworms from escaping the microcosms aboveground [17]. Thus, microcosms had not to be covered by a lid. Microcosms were set up in a greenhouse with regulated air exchange with the outside air and with automatic shading to prevent severe heating. On July 4, 2013 after weighing individuals of L. terrestris (accuracy 0.01 g), earthworms were transferred to microcosms of the respective treatments. Worms had four (herbivory experiment) or eight days (seedling mortality experiment) to adapt to the new environment before plants were added. Plastic pots with plants (diameter 3.5 cm, height 8 cm) were lowered almost entirely into the soil of each microcosm (Fig 1). Plants were isolated from the soil of the microcosm to exclude effects of earthworms on plant growth through changes in soil structure and nutrient availability. Control treatments without worms were arranged in between the earthworm treatments in order to balance microclimatic differences in the greenhouse chamber. Each microcosm was watered daily with about 4 l of tap water (less water was added if the soil was still wet) and plant pots with approximately 100 ml of water each. An excess of water could easily drain from microcosms as bottoms were only closed by fly screen. The average temperature on the soil surface of the microcosms was 26.3°C, ranging between 17 and 32°C. On July 22, 2013 microcosms were transferred to another greenhouse with facility for cooling because the average temperature increased to 28°C, a temperature which is lethal for L. terrestris. The average temperature in the new environment was 16.3°C, ranging between 14 and 22.5°C. At the end of the experiments, the soil of all microcosms was removed from tubes and examined for individuals of L. terrestris.

Bottom Line: Lumbricus terrestris preferred to consume legume litter over litter of the other plant functional groups.Pulling live plants into earthworm burrows might induce microbial decomposition of leaves to make them suitable for later consumption.Herbivory on plants beyond the initial seedling stage may only play a minor role in earthworm nutrition and has limited potential to influence plant growth.

View Article: PubMed Central - PubMed

Affiliation: Terrestrial Ecology Research Group, Department of Ecology and Ecosystem Management, Technische Universität München, Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising, Germany.

ABSTRACT

Background: Recent studies suggested that the earthworm Lumbricus terrestris might act as a seedling predator by ingesting emerging seedlings, and individuals were observed damaging fresh leaves of various plant species in the field. To evaluate the significance of herbivore behavior of L. terrestris for plant and earthworm performance we exposed 23- to 33-days-old seedlings of six plant species to earthworms in two microcosm experiments. Plants belonged to the three functional groups grasses, non-leguminous herbs, and legumes. Leaf damage, leaf mortality, the number of leaves as well as mortality and growth of seedlings were followed over a period of up to 26 days. In a subset of replicates 0.1 g of soil surface litter of each of the six plant species was provided and consumption was estimated regularly to determine potential feeding preferences of earthworms.

Results: There was no difference in seedling growth, the number of live seedlings and dead leaves between treatments with or without worms. Fresh leaves were damaged eight times during the experiment, most likely by L. terrestris, with two direct observations of earthworms tearing off leaf parts. Another nine leaves were partly pulled into earthworm burrows. Lumbricus terrestris preferred to consume legume litter over litter of the other plant functional groups. Earthworms that consumed litter lost less weight than individuals that were provided with soil and live plants only, indicating that live plants are not a suitable substitute for litter in earthworm nutrition.

Conclusion: Our results demonstrate that L. terrestris damages live plants; however, this behavior occurs only rarely. Pulling live plants into earthworm burrows might induce microbial decomposition of leaves to make them suitable for later consumption. Herbivory on plants beyond the initial seedling stage may only play a minor role in earthworm nutrition and has limited potential to influence plant growth.

Show MeSH
Related in: MedlinePlus