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Earthworm and belowground competition effects on plant productivity in a plant diversity gradient.

Eisenhauer N, Milcu A, Nitschke N, Sabais AC, Scherber C, Scheu S - Oecologia (2009)

Bottom Line: We sampled earthworm subplots and subplots with decreased earthworm density and reduced aboveground competition of phytometer plants by removing the shoot biomass of the resident plant community.Although single plant functional groups benefited from higher earthworm numbers, the effects did not vary with plant species and functional group richness.Moreover, particularly legumes benefited from earthworm presence.

View Article: PubMed Central - PubMed

Affiliation: J.F. Blumenbach Institute of Zoology and Anthropology, Georg August University of Göttingen, Berliner Strasse 28, Göttingen, Germany. eisenhauer@bio.tu-darmstadt.de

ABSTRACT
Diversity is one major factor driving plant productivity in temperate grasslands. Although decomposers like earthworms are known to affect plant productivity, interacting effects of plant diversity and earthworms on plant productivity have been neglected in field studies. We investigated in the field the effects of earthworms on plant productivity, their interaction with plant species and functional group richness, and their effects on belowground plant competition. In the framework of the Jena Experiment we determined plant community productivity (in 2004 and 2007) and performance of two phytometer plant species [Centaurea jacea (herb) and Lolium perenne (grass); in 2007 and 2008] in a plant species (from one to 16) and functional group richness gradient (from one to four). We sampled earthworm subplots and subplots with decreased earthworm density and reduced aboveground competition of phytometer plants by removing the shoot biomass of the resident plant community. Earthworms increased total plant community productivity (+11%), legume shoot biomass (+35%) and shoot biomass of the phytometer C. jacea (+21%). Further, phytometer performance decreased, i.e. belowground competition increased, with increasing plant species and functional group richness. Although single plant functional groups benefited from higher earthworm numbers, the effects did not vary with plant species and functional group richness. The present study indicates that earthworms indeed affect the productivity of semi-natural grasslands irrespective of the diversity of the plant community. Belowground competition increased with increasing plant species diversity. However, belowground competition was modified by earthworms as reflected by increased productivity of the phytometer C. jacea. Moreover, particularly legumes benefited from earthworm presence. Considering also previous studies, we suggest that earthworms and legumes form a loose mutualistic relationship affecting essential ecosystem functions in temperate grasslands, in particular decomposition and plant productivity. Further, earthworms likely alter competitive interactions among plants and the structure of plant communities by beneficially affecting certain plant functional groups.

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Variations in aboveground community biomass as affected by a plant species richness (1, 4, 16) and earthworms [earthworm reduction subplots (−ew) and earthworm subplots (+ew)] and b plant functional group richness (one, two, three, four) and earthworms. Variations in c and d shoot biomass of the phytometer plant species Lolium perenne [g/individual. (ind.)], e and f shoot biomass of the phytometer plant species Centaurea jacea (g/ind.), g and h number of flower heads per Centaurea jacea individual as affected by plant species richness (c, e, g) and plant functional group richness (d, f, h). Bars with different letters vary significantly (Tukey’s HSD test, α < 0.05)
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Fig2: Variations in aboveground community biomass as affected by a plant species richness (1, 4, 16) and earthworms [earthworm reduction subplots (−ew) and earthworm subplots (+ew)] and b plant functional group richness (one, two, three, four) and earthworms. Variations in c and d shoot biomass of the phytometer plant species Lolium perenne [g/individual. (ind.)], e and f shoot biomass of the phytometer plant species Centaurea jacea (g/ind.), g and h number of flower heads per Centaurea jacea individual as affected by plant species richness (c, e, g) and plant functional group richness (d, f, h). Bars with different letters vary significantly (Tukey’s HSD test, α < 0.05)

Mentions: On average, 284.7 g/m² total shoot biomass was harvested in May 2004 and 331.1 g/m² in May 2007. Neither shoot biomass differed between 2004 and 2007 nor were there significant interactions between sampling time and any of the treatments (not shown). Total shoot biomass increased significantly with increasing plant species and functional group richness (Table 2; Fig. 2a, b). Further, total shoot biomass increased significantly in the presence of small herbs (+11%) and legumes (+77%). Moreover, total shoot biomass was increased in earthworm subplots compared to subplots with reduced earthworm density (+11%). The earthworm effect did not depend on plant species and functional group richness, and therefore these interactions were excluded from the statistical model (Table 2; Fig. 2a, b).Table 2


Earthworm and belowground competition effects on plant productivity in a plant diversity gradient.

Eisenhauer N, Milcu A, Nitschke N, Sabais AC, Scherber C, Scheu S - Oecologia (2009)

Variations in aboveground community biomass as affected by a plant species richness (1, 4, 16) and earthworms [earthworm reduction subplots (−ew) and earthworm subplots (+ew)] and b plant functional group richness (one, two, three, four) and earthworms. Variations in c and d shoot biomass of the phytometer plant species Lolium perenne [g/individual. (ind.)], e and f shoot biomass of the phytometer plant species Centaurea jacea (g/ind.), g and h number of flower heads per Centaurea jacea individual as affected by plant species richness (c, e, g) and plant functional group richness (d, f, h). Bars with different letters vary significantly (Tukey’s HSD test, α < 0.05)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2719079&req=5

Fig2: Variations in aboveground community biomass as affected by a plant species richness (1, 4, 16) and earthworms [earthworm reduction subplots (−ew) and earthworm subplots (+ew)] and b plant functional group richness (one, two, three, four) and earthworms. Variations in c and d shoot biomass of the phytometer plant species Lolium perenne [g/individual. (ind.)], e and f shoot biomass of the phytometer plant species Centaurea jacea (g/ind.), g and h number of flower heads per Centaurea jacea individual as affected by plant species richness (c, e, g) and plant functional group richness (d, f, h). Bars with different letters vary significantly (Tukey’s HSD test, α < 0.05)
Mentions: On average, 284.7 g/m² total shoot biomass was harvested in May 2004 and 331.1 g/m² in May 2007. Neither shoot biomass differed between 2004 and 2007 nor were there significant interactions between sampling time and any of the treatments (not shown). Total shoot biomass increased significantly with increasing plant species and functional group richness (Table 2; Fig. 2a, b). Further, total shoot biomass increased significantly in the presence of small herbs (+11%) and legumes (+77%). Moreover, total shoot biomass was increased in earthworm subplots compared to subplots with reduced earthworm density (+11%). The earthworm effect did not depend on plant species and functional group richness, and therefore these interactions were excluded from the statistical model (Table 2; Fig. 2a, b).Table 2

Bottom Line: We sampled earthworm subplots and subplots with decreased earthworm density and reduced aboveground competition of phytometer plants by removing the shoot biomass of the resident plant community.Although single plant functional groups benefited from higher earthworm numbers, the effects did not vary with plant species and functional group richness.Moreover, particularly legumes benefited from earthworm presence.

View Article: PubMed Central - PubMed

Affiliation: J.F. Blumenbach Institute of Zoology and Anthropology, Georg August University of Göttingen, Berliner Strasse 28, Göttingen, Germany. eisenhauer@bio.tu-darmstadt.de

ABSTRACT
Diversity is one major factor driving plant productivity in temperate grasslands. Although decomposers like earthworms are known to affect plant productivity, interacting effects of plant diversity and earthworms on plant productivity have been neglected in field studies. We investigated in the field the effects of earthworms on plant productivity, their interaction with plant species and functional group richness, and their effects on belowground plant competition. In the framework of the Jena Experiment we determined plant community productivity (in 2004 and 2007) and performance of two phytometer plant species [Centaurea jacea (herb) and Lolium perenne (grass); in 2007 and 2008] in a plant species (from one to 16) and functional group richness gradient (from one to four). We sampled earthworm subplots and subplots with decreased earthworm density and reduced aboveground competition of phytometer plants by removing the shoot biomass of the resident plant community. Earthworms increased total plant community productivity (+11%), legume shoot biomass (+35%) and shoot biomass of the phytometer C. jacea (+21%). Further, phytometer performance decreased, i.e. belowground competition increased, with increasing plant species and functional group richness. Although single plant functional groups benefited from higher earthworm numbers, the effects did not vary with plant species and functional group richness. The present study indicates that earthworms indeed affect the productivity of semi-natural grasslands irrespective of the diversity of the plant community. Belowground competition increased with increasing plant species diversity. However, belowground competition was modified by earthworms as reflected by increased productivity of the phytometer C. jacea. Moreover, particularly legumes benefited from earthworm presence. Considering also previous studies, we suggest that earthworms and legumes form a loose mutualistic relationship affecting essential ecosystem functions in temperate grasslands, in particular decomposition and plant productivity. Further, earthworms likely alter competitive interactions among plants and the structure of plant communities by beneficially affecting certain plant functional groups.

Show MeSH