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The role of earthworms for plant performance and ecosystem functioning in a plant diversity gradient

Milcu, Alexandru (2006)
The role of earthworms for plant performance and ecosystem functioning in a plant diversity gradient.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

The role of earthworms for plant performance and ecosystem functioning in a plant diversity gradient was investigated as part of the “Jena Biodiversity Experiment”. Concomitantly effects of the plant diversity on earthworms, springtails, microorganisms and decomposition were studied. Two greenhouse experiments and one field experiment were conducted. The first greenhouse experiment focused on the responses of three decomposer groups (earthworms, springtails and microorganisms) to manipulations in plant species diversity (1, 2, 4, 8), plant functional group diversity (1, 2, 3, 4) and functional group identity (grasses, legumes, small herbs, tall herbs) in a microcosm experiment. Also, the response of the plant community to the four decomposer treatments (control, earthworms, springtails and combined) was investigated. The use of 15N labelled litter allowed tracking of nutrient fluxes from dead organic matter into plants and animals. We hypothesised (1) that an increase in plant species and functional group diversity will beneficially affect earthworms and microorganisms, and accelerate decomposition processes, (2) that plant species and functional groups will differentially respond to earthworms and springtails in the rhizosphere. As hypothesised, earthworm performance (biomass and 15N incorporation) increased with increasing plant species and functional group diversity. Presence of legumes also beneficially affected earthworm performance. The mechanism of the beneficial effect of increasing plant species diversity differed between the earthworm functional groups. For anecic species (Lumbricus terrestris) the effect of plant diversity was mainly due to the presence of legumes; nitrogen rich legume litter being preferred by this species. The endogeic species also benefited from increased plant diversity, but via belowground effects of plant diversity based on rhizodeposits. Increasing plant species and functional group diversity also affected microorganisms in soil. Respiration rates decreased with increasing plant species and functional group diversity, but correlated with root biomass. Identity of plant functional groups was also important; legumes increased and grasses decreased microbial respiration. Microbial biomass, however, was little responsive to changes in plant diversity. Plant performance (biomass, N tissue concentration, 15N) was strongly affected by the decomposer treatments and plant diversity. Increasing plant species and plant functional group diversity increased total number and total weight of seeds. Shoot biomass increased with increasing plant species diversity and, even more pronounced, with plant functional group diversity. The increased shoot biomass with increasing plant species and functional group diversity remained significant when calculated without legume biomass. Increasing plant species diversity but not plant functional group diversity, decreased root biomass. Plant functional group diversity but not plant species diversity, increased total plant biomass. Plant functional group identity mattered; grasses benefited most from the presence of earthworms. Decomposers strongly increased shoot biomass, being at a maximum in the earthworm only treatment. Root biomass decreased in presence of collembolans, and even stronger in presence of earthworms; however, it increased when both animal groups were present. In treatments with decomposers, total N tissue concentration and 15N enrichment of three focal species was increased. In the second greenhouse experiment the effect of the anecic earthworm L. terrestris on plant seedling recruitment and aggregation was investigated by varying the number of plant functional groups (grass, legumes, herbs), seed size (small and large), plant species diversity (1, 3, 6) and plant functional group diversity (1, 3). L. terrestris strongly affected the recruitment of plant seedlings depending on seed size and plant functional group. Furthermore, earthworms increased microhabitat heterogeneity. Seed translocation, surface cast deposition and formation of burrows presumably act as intermediate disturbances favouring the formation of a more diverse plant community. In the field experiment similar hypothesis as in the first greenhouse experiment were investigated. Manipulations of the density of earthworms (reduced and increased) and springtails (reduced and natural) were established. In addition, decomposition of litter as affected by plant species (1, 4, 16) and functional group diversity (1, 2, 3), decomposers and litter functional group identity was investigated. Consistent with the microcosm experiment earthworm performance (biomass) was increased with increasing plant species diversity. Microbial respiration increased with increasing plant species diversity and was correlated with root biomass. Soil texture and presence of legumes but not plant diversity affected the community composition of earthworms. Decomposition of litter was primarily affected by local abiotic conditions (block effects) and less by the plant diversity gradient. As expected, litter decomposition was strongly affected by the identity of plant functional groups; legume litter decomposed faster than grass and herb litter. Earthworms and increasing plant functional group diversity increased the decomposition of legume litter. The increase in earthworm density with increasing plant diversity accelerated the decomposition and mineralization of nitrogen rich organic matter; therefore, earthworms may have contributed to higher plant productivity in particular in treatments with high plant species and functional group diversity. The effects of earthworms on plant performance were more distinct in the greenhouse experiments than in the field. After two years from the establishment of the plant communities in the field we did not find significant effects of earthworms on plant performance (biomass) or plant community composition (plant species diversity or cover). Overall, the results document that there is a strong interdependence between plant diversity and the functioning of the decomposers and vice versa. The results suggest that increasing plant diversity has beneficial effects on decomposer performance. Legumes represent a key plant functional group that strongly affects the decomposition processes at least in part via beneficial effects on soil decomposer invertebrates, such as earthworms. The results also show that plant performance is beneficially affected by decomposers and that some decomposers, such as anecic earthworms, are promoting plant diversity.

Typ des Eintrags: Dissertation
Erschienen: 2006
Autor(en): Milcu, Alexandru
Art des Eintrags: Erstveröffentlichung
Titel: The role of earthworms for plant performance and ecosystem functioning in a plant diversity gradient
Sprache: Englisch
Referenten: Schwabe-Kratochwil, Prof.Dr Angelica ; Thiel, Prof.Dr. Gerhardt ; Ebhardt, Prof.Dr. Götz
Berater: Scheu, Prof.Dr. Stefan
Publikationsjahr: 13 Januar 2006
Ort: Darmstadt
Verlag: Technische Universität
Datum der mündlichen Prüfung: 12 Juli 2005
URL / URN: urn:nbn:de:tuda-tuprints-6386
Kurzbeschreibung (Abstract):

The role of earthworms for plant performance and ecosystem functioning in a plant diversity gradient was investigated as part of the “Jena Biodiversity Experiment”. Concomitantly effects of the plant diversity on earthworms, springtails, microorganisms and decomposition were studied. Two greenhouse experiments and one field experiment were conducted. The first greenhouse experiment focused on the responses of three decomposer groups (earthworms, springtails and microorganisms) to manipulations in plant species diversity (1, 2, 4, 8), plant functional group diversity (1, 2, 3, 4) and functional group identity (grasses, legumes, small herbs, tall herbs) in a microcosm experiment. Also, the response of the plant community to the four decomposer treatments (control, earthworms, springtails and combined) was investigated. The use of 15N labelled litter allowed tracking of nutrient fluxes from dead organic matter into plants and animals. We hypothesised (1) that an increase in plant species and functional group diversity will beneficially affect earthworms and microorganisms, and accelerate decomposition processes, (2) that plant species and functional groups will differentially respond to earthworms and springtails in the rhizosphere. As hypothesised, earthworm performance (biomass and 15N incorporation) increased with increasing plant species and functional group diversity. Presence of legumes also beneficially affected earthworm performance. The mechanism of the beneficial effect of increasing plant species diversity differed between the earthworm functional groups. For anecic species (Lumbricus terrestris) the effect of plant diversity was mainly due to the presence of legumes; nitrogen rich legume litter being preferred by this species. The endogeic species also benefited from increased plant diversity, but via belowground effects of plant diversity based on rhizodeposits. Increasing plant species and functional group diversity also affected microorganisms in soil. Respiration rates decreased with increasing plant species and functional group diversity, but correlated with root biomass. Identity of plant functional groups was also important; legumes increased and grasses decreased microbial respiration. Microbial biomass, however, was little responsive to changes in plant diversity. Plant performance (biomass, N tissue concentration, 15N) was strongly affected by the decomposer treatments and plant diversity. Increasing plant species and plant functional group diversity increased total number and total weight of seeds. Shoot biomass increased with increasing plant species diversity and, even more pronounced, with plant functional group diversity. The increased shoot biomass with increasing plant species and functional group diversity remained significant when calculated without legume biomass. Increasing plant species diversity but not plant functional group diversity, decreased root biomass. Plant functional group diversity but not plant species diversity, increased total plant biomass. Plant functional group identity mattered; grasses benefited most from the presence of earthworms. Decomposers strongly increased shoot biomass, being at a maximum in the earthworm only treatment. Root biomass decreased in presence of collembolans, and even stronger in presence of earthworms; however, it increased when both animal groups were present. In treatments with decomposers, total N tissue concentration and 15N enrichment of three focal species was increased. In the second greenhouse experiment the effect of the anecic earthworm L. terrestris on plant seedling recruitment and aggregation was investigated by varying the number of plant functional groups (grass, legumes, herbs), seed size (small and large), plant species diversity (1, 3, 6) and plant functional group diversity (1, 3). L. terrestris strongly affected the recruitment of plant seedlings depending on seed size and plant functional group. Furthermore, earthworms increased microhabitat heterogeneity. Seed translocation, surface cast deposition and formation of burrows presumably act as intermediate disturbances favouring the formation of a more diverse plant community. In the field experiment similar hypothesis as in the first greenhouse experiment were investigated. Manipulations of the density of earthworms (reduced and increased) and springtails (reduced and natural) were established. In addition, decomposition of litter as affected by plant species (1, 4, 16) and functional group diversity (1, 2, 3), decomposers and litter functional group identity was investigated. Consistent with the microcosm experiment earthworm performance (biomass) was increased with increasing plant species diversity. Microbial respiration increased with increasing plant species diversity and was correlated with root biomass. Soil texture and presence of legumes but not plant diversity affected the community composition of earthworms. Decomposition of litter was primarily affected by local abiotic conditions (block effects) and less by the plant diversity gradient. As expected, litter decomposition was strongly affected by the identity of plant functional groups; legume litter decomposed faster than grass and herb litter. Earthworms and increasing plant functional group diversity increased the decomposition of legume litter. The increase in earthworm density with increasing plant diversity accelerated the decomposition and mineralization of nitrogen rich organic matter; therefore, earthworms may have contributed to higher plant productivity in particular in treatments with high plant species and functional group diversity. The effects of earthworms on plant performance were more distinct in the greenhouse experiments than in the field. After two years from the establishment of the plant communities in the field we did not find significant effects of earthworms on plant performance (biomass) or plant community composition (plant species diversity or cover). Overall, the results document that there is a strong interdependence between plant diversity and the functioning of the decomposers and vice versa. The results suggest that increasing plant diversity has beneficial effects on decomposer performance. Legumes represent a key plant functional group that strongly affects the decomposition processes at least in part via beneficial effects on soil decomposer invertebrates, such as earthworms. The results also show that plant performance is beneficially affected by decomposers and that some decomposers, such as anecic earthworms, are promoting plant diversity.

Alternatives oder übersetztes Abstract:
Alternatives AbstractSprache

Im Rahmen des „Jena Biodiversitäts Experiments“ wurde der Einfluss von Regenwürmern auf Pflanzen und Ökosystemprozesse in einem Gradienten zunehmender Pflanzendiversität untersucht. Außerdem wurde der Einfluss der Pflanzendiversität auf Regenwürmer, Springschwänze, Mikroorganismen und Zersetzungsprozesse untersucht. Dazu wurden ein Freilandversuch und zwei Gewächshausversuche durchgeführt. In dem ersten Labor-Mikrokosmosversuch wurde der Einfluss der Diversität von Pflanzen (1, 2, 4, 8 Arten), von funktionellen Pflanzengrupen (1, 2, 3, 4 funktionelle Gruppen) sowie der Identität der Pflanzengruppen (Gräser, Leguminosen, große und kleine Kräuter) auf drei Zersetzergruppen (Regenwürmer, Springschwänze, Mikroorganismen) untersucht. Weiterhin wurde die Reaktion der Pflanzengemeinschaft auf die Präsenz von zwei tierischen Zersetzergruppen (Regenwürmer, Springschwänze) untersucht. Für diesen Versuch wurde 15N markierte Streu benutzt, um die Nährstoffflüsse nachvollziehen zu können. Folgende Hypothesen wurden geprüft: (1) Regenwürmer, Mikroorganismen und Zersetzungsprozesse profitieren von bzw. werden beschleunigt durch zunehmende Diversität von Pflanzenarten und funktionellen Pflanzengruppen. (2) Die Wirkung von Regenwürmern und Springschwänzen in der Rhizosphäre auf die Artenzusammensetzung und Produktivität von Pflanzengemeinschaften hängt von der Pflanzendiversität ab. Entsprechend Hypothese (1) nahm die Biomasse und 15N-Aufnahme von Regenwürmern mit zunehmender Pflanzendiversität und mit der Zunahme funktioneller Pflanzengruppen zu. Vor allem die Anwesenheit von Leguminosen beeinflusste die Regenwurmbiomasse stark positiv. Die Effekte zunehmender Pflanzendiversität wirkten sich auf die verschiedenen funktionellen Gruppen der Regenwürmer unterschiedlich aus. Die anözische Regenwurmart Lumbricus terrestris wurde vor allem von der Präsenz stickstoffreicher Leguminosen positiv beeinflusst. Die endogäischen Arten profitierten ebenfalls von der zunehmenden Diversität von Pflanzen, jedoch verursacht durch unterirdische Effekte, vermutlich basierend auf Wurzelexsudaten. Eine zunehmende Diversität von Pflanzenarten sowie von funktionellen Pflanzengruppen beeinflusste auch Mikroorganismen im Boden. Die mikrobielle Respiration nahm mit zunehmender Diversität von Pflanzenarten und von funktionellen Pflanzengruppen zu. Die Respirationsraten der Mikroorganismen waren mit der Wurzelbiomasse korreliert. Leguminosen erhöhten die mikrobielle Respiration, während die Präsenz von Gräsern sie reduzierte. Generell reagierte die mikrobielle Biomasse jedoch nur wenig auf Änderungen der Pflanzendiversität. Entsprechend Hypothese (2) wurde der 14N- und 15N-Gehalt von Pflanzen durch die Anwesenheit verschiedener Zersetzergruppen signifikant beeinflusst. Mit zunehmender Diversität von Pflanzenarten und funktionellen Pflanzengruppen nahmen die Sprossbiomasse und die Anzahl und das Gewicht von Pflanzensamen zu. Die Sprossbiomasse nahm sogar dann mit zunehmender Pflanzendiversität zu, wenn die Biomasse der Leguminosen unberüchsicktigt blieb. Zunehmende Diversität von funktionellen Pflanzengruppen, jedoch nicht die Zunahme der Artendiversität, führte zu einer Zunahme der gesamten Pflanzenbiomasse. Die Präsenz der Zersetzer führte zu einer Zunahme der Sprossbiomasse, mit einem Maximum in den Varianten mit Regenwürmern. Die Wurzelbiomasse nahm in Anwesenheit von Collembolen und Regenwürmern ab. In Varianten mit Zersetzern nahmen der Stickstoff-Gehalt des Pflanzengewebes und die 15N-Gehalte zu. In dem zweiten Gewächshaus-Mikrokosmosversuch wurde der Einfluss der anözischen Regenwurmart L. terrestris auf die Keimungsrate und die Aggregation von Pflanzensamen untersucht indem die Anzahl von funktionellen Pflanzengruppen (Gräser, Leguminosen, Kräuter), die Samengröße (klein und groß), die Artendiversität der Samen (1, 3, 6) und deren Zugehörigkeit zu funktionellen Pflanzengruppen (1, 3) variiert wurde. L. terrestris beeinflusste die Keimungsrate in Abhängigkeit von der Samengröße und der Zugehörigkeit der Samen zu funktionellen Pflanzengruppen. Zusätzlich führten Regenwürmer zu heterogeneren Mikrohabitaten und förderten dadurch eine diversere Pflanzengemeinschaft. In dem Freilandexperiment wurde eine ähnliche Fragestellung wie in dem ersten Gewächshausexperiment untersucht. Die Siedlungsdichte von Regenwürmern (erhöht und reduziert) und der Springschwänze (reduziert und unbeeinflusst) wurde verändert. Außerdem wurde die Streuabbaurate in unterschiedlich diversen Pflanzengemeinschaften (1, 4, 16 Arten bzw. 1, 2, 3 funktionelle Pflanzengruppen) untersucht. Wie in dem Mikrokosmos-Experiment stieg mit zunehmender Pflanzendiversität die Biomasse der Regenwürmer. Die mikrobielle Respirationsrate nahm bei erhöhter Pflanzendiversität zu und korrelierte mit der Wurzelbiomasse. Die Bodenbeschaffenheit und das Vorhandensein von Leguminosen, jedoch nicht die Pflanzendiversität, veränderte die Regenwurmgemeinschaft. Die Zersetzungsrate der Streu wurde hauptsächlich durch lokale abiotische Faktoren (Block-Effekt) und weniger durch Pflanzendiversität beeinflusst. Wie erwartet hing die Streuabbaurate von der Streuart ab; Leguminosenstreu wurde schneller abgebaut als Gras- und Kräuterstreu. Regenwürmer und eine erhöhte Diversität funktioneller Pflanzengruppen beschleunigten die Zersetzung und Mineralisierung von stickstoffreicher Leguminosenstreu. Vermutlich tragen Regenwürmer vor allem in diversen Pflanzengemeinschaften zu erhöhter Produktivität bei. Der Einfluss der Regenwürmer auf die Pflanzen war im Gewächshausexperiment deutlicher als im Feldversuch. Zwei Jahre nach der Etablierung der Pflanzen im Freiland konnten keine signifikanten Zusammenhänge zwischen Regenwurmdichte und Pflanzenbiomasse oder Pflanzenzusammensetzung festgestellt werden. Insgesamt zeigen die Ergebnisse eine starke gegenseitige Abhängigkeit von Pflanzendiversität und Zersetzeraktivität. Vor allem Leguminosen sind eine wichtige funktionelle Pflanzengruppe, die die Zersetzer im Boden stark positiv beeinflussen. Tierische Zersetzer fördern generell das Pflanzenwachstum und manche Zersetzer, wie z.B. anözische Regenwürmer, erhöhen auch die pflanzliche Diversität.

Deutsch
Sachgruppe der Dewey Dezimalklassifikatin (DDC): 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
Fachbereich(e)/-gebiet(e): 10 Fachbereich Biologie
Hinterlegungsdatum: 17 Okt 2008 09:22
Letzte Änderung: 30 Jul 2017 21:18
PPN:
Referenten: Schwabe-Kratochwil, Prof.Dr Angelica ; Thiel, Prof.Dr. Gerhardt ; Ebhardt, Prof.Dr. Götz
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: 12 Juli 2005
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