N-transfer between species: effects of legume presence and defoliation
2 ICG-3 (Phytosphäre)
O 1.7 in Funktion von Ökosystemen
15.04.2010, 10:45-11:00, H13
Positive biodiversity-ecosystem process relationships (BD-ESP; e.g. productivity, stability, resistance against invasion/disturbances) are related mainly to two processes: (i) higher total niche occupation and resource use in more diverse communities (niche complementarity theory) and (ii) the occurrence of keystone species which drive the ESP under observation (sampling effects). Nitrogen-fixing legume species contribute to both processes; they increase the realized niche of neighbouring species and are highly productive keystone species. Although lots of research on legume-neighbour interactions was done, most studies focussed on agricultural systems with only two species and neglect aspects of higher biodiversity.We performed a pot experiment with communities (monocultures, 2-, 3-species-mixtures) of three species (one forb, grass and legume species) and a defoliation treatment. We investigated changes in N-transfer between individuals depending on species composition (legume effect) and disturbance (defoliation effect), followed by a 15N-enriched tracer and the potential for up-scaling from pot to field experiments. We found a pronounced composition effect: legume presence but not diversity per se increased the 15N-transfer between species. The profit of legume derived N was higher for the grass than for the forb species. The grass used available N-resources more effectively, especially if both species competed for N (higher total N-accumulation [mg/individual]). Defoliation did not increase N-transfer (due to higher decomposition) but increased internal N-remobilization. Interestingly, defoliation affected N-transfer to neighbours positively in monocultures but negatively in mixtures. In conclusion, we were able to reproduce effects often found in large scale, long-term biodiversity experiments; thus it might be possible to investigate natural species interactions by short-term pot experiments. Effects of defoliation on N-dynamics within the communities were totally unexpected and are worth further investigations for the emerging field of plant species kin recognition.
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