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The role of legumes as a component of biodiversity in a cross-European study of grassland biomass nitrogen


  • E. M. Spehn,

  • M. Scherer-Lorenzen,

  • B. Schmid,

  • A. Hector,

  • M. C. Caldeira,

  • P. G. Dimitrakopoulos,

  • J. A. Finn,

  • A. Jumpponen,

  • G. O'Donnovan,

  • J. S. Pereira,

  • E.-D. Schulze,

  • A. Y. Troumbis,

  • C. Körner

E. M. Spehn, C. Körner, Botanisches Inst., Univ. Basel, Schönbeinstr. 6, CH-4056 Basel, Switzerland ( – M. Scherer-Lorenzen, E.-D. Schulze, Max-Planck-Inst. for Biogeochemistry, Postfach 10 01 64, D-07701 Jena, Germany. – B. Schmid, Inst. für Umweltwissenschaften, Univ. Zürich, Winterthurerstr.190, CH-8057 Zürich, Switzerland. – A. Hector, Natural Environmental Res. Council (NERC) Centre for Population Biology, Imperial College at Silwood Park, Ascot, Berkshire, GB-SL5 7PY, U.K. – M. C. Caldeira, J. S. Pereira, Depto de Engenharia Florestal, Inst, Superior de Agronomia, 1349-017 Lisboa, Portugal. – P. G. Dimitrakopoulos, A. Y. Troumbis, Biodiversity Conservation Lab., Dept of Environmental Studies, Univ. of the Aegean, Karadoni 17, Mytilene, Lesbos, Greece, GR-811 00. – J. A. Finn, Dept of Agriculture, Univ. of Reading, Earley Gate, P.O. Box 236, Reading, Berkshire GB-RG6 6AT, UK. – A. Jumpponen, Div. of Biology, 125 Ackert Hall, Manhattan, KS66506, U.S.A. – G. O'Donnovan, Dept of Environmental Resource Management, University College of Dublin, Belfield, Dublin, Ireland.


To investigate how plant diversity loss affects nitrogen accumulation in above-ground plant biomass and how consistent patterns are across sites of different climatic and soil conditions, we varied the number of plant species and functional groups (grasses, herbs and legumes) in experimental grassland communities across seven European experimental sites (Switzerland, Germany, Ireland, United Kingdom (Silwood Park), Portugal, Sweden and Greece). Nitrogen pools were significantly affected by both plant diversity and community composition. Two years after sowing, nitrogen pools in Germany and Switzerland strongly increased in the presence of legumes. Legume effects on nitrogen pools were less pronounced at the Swedish, Irish and Portuguese site. In Greece and UK there were no legume effects. Nitrogen concentration in total above-ground biomass was quite invariable at 1.66±0.03% across all sites and diversity treatments. Thus, the presence of legumes had a positive effect on nitrogen pools by significantly increasing above-ground biomass, i.e. by increases in vegetation quantity rather than quality. At the German site with the strongest legume effect on nitrogen pools and biomass, nitrogen that was fixed symbiotically by legumes was transferred to the other plant functional groups (grasses and herbs) but varied depending on the particular legume species fixing N and the non-legume species taking it up. Nitrogen-fixation by legumes therefore appeared to be one of the major functional traits of species that influenced nitrogen accumulation and biomass production, although effects varied among sites and legume species. This study demonstrates that the consequences of species loss on the nitrogen budget of plant communities may be more severe if legume species are lost. However, our data indicate that legume species differ in their N2 fixation. Therefore, loss of an efficient N2-fixer (Trifolium in our study) may have a greater influence on the ecosystem function than loss of a less efficient species (Lotus in our study). Furthermore, there is indication that P availability in the soil facilitates the legume effect on biomass production and biomass nitrogen accumulation.