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Plant and Soil

, Volume 311, Issue 1–2, pp 141–149 | Cite as

Legume defoliation affects rhizosphere decomposers, but not the uptake of organic matter N by a neighbouring grass

  • S. SajEmail author
  • J. Mikola
  • F. Ekelund
Regular Article

Abstract

Legume–grass interactions have a great influence on grassland primary production and it was recently shown how defoliation of a legume can increase the transfer of fixed N to a neighbouring grass. It has also been shown that defoliation of a plant can increase soil microbial activity and lead to better soil N availability in the rhizosphere of the defoliated plant. We combined these two perspectives and tested whether defoliation of a legume (Lotus corniculatus) can enhance N nutrition of the neighbouring grass (Holcus lanatus) by increasing growth of soil decomposer biota and the availability of soil organic matter N for grass uptake. We grew mixtures of L. corniculatus and H. lanatus in grassland soil that included 15N-labelled L. corniculatus litter. In half of the systems, we subjected L. corniculatus to a defoliation treatment mimicking insect larvae feeding. At destructive harvests 1, 3, 9 and 30 days after the last defoliation event, we determined how L. corniculatus defoliation affected decomposer microbes, protozoa and nematodes and whether these changes among decomposers created a feedback on the growth and 15N uptake of the neighbouring H. lanatus. Defoliation reduced the growth and litter-N uptake, but increased shoot N concentration of L. corniculatus. Of the soil variables measured, defoliation doubled the number of bacterial-feeding protozoa, but did not affect the abundance of decomposer microbes and bacterial- and fungal-feeding nematodes. Defoliation did not have statistically significant effects on H. lanatus shoot growth, shoot N concentration or litter-N uptake. Our results demonstrate how defoliation-induced changes in legume ecophysiology can affect the growth of decomposers in soil. However, these effects did not appear to lead to a significant change in the availability of soil organic N to the neighbouring grass. It seems that when positive effects of legume defoliation on grass N nutrition are found in grassland ecosystems, these are more likely to be explained by direct transfer of fixed N rather than changes in the availability of soil organic matter N.

Keywords

Decomposer Grass Legume Litter Nitrogen Soil feedback 

Notes

Acknowledgments

This study is a part of the EU-funded project “Biotic interactions in the rhizosphere as structuring forces for plant communities” (BIORHIZ). We thank I. Popovici for identifying the nematodes and the two anonymous reviewers for their constructive comments.

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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  1. 1.Department of Biological and Environmental ScienceUniversity of JyväskyläJyväskyläFinland
  2. 2.Terrestrial Ecology, Biological InstituteUniversity of CopenhagenCopenhagenDenmark
  3. 3.Department of Ecological and Environmental SciencesUniversity of HelsinkiLahtiFinland

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