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Schlagwörter:
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Zusammenfassung:
Aims The stress-gradient-hypothesis predicts that interactions among organisms shift from competition to facilitation
as environmental stress increases. Whether the
strength of mutualism will increase among symbiotically
associated organisms when partners are forced into
resource limitation remains unknown. Plants exchange
photosynthetic carbohydrates (plant C) for nutrients in
mycorrhizal symbiosis but how this exchange varies
with plant C limitation is not fully understood.
Methods We investigated the influence of plant C availability
and of arbuscular mycorrhizal fungi (AMF) on
plant nitrogen (N) uptake and resource allocation using
13C and 15N labeling. We grew Plantago lanceolata
with and without AMF Rhizophagus irregularis under
ambient (400 ppm, AC) and low (100 ppm, LC) atmospheric [CO2] and physically restricted plant root but not mycorrhizal access to soil N. Results We found that plants grown under LC used
AMF to obtain the same amount of N as those grown
under AC, but the amount of newly fixed C correlated
with the acquisition of N only under LC. The LC plants
allocated more of their C to aboveground tissues.
Conclusions Overall our results suggest a more beneficial
role of symbiosis under C limitation. The tight
reciprocal control on N transfer and C allocation under C limited conditions supports the stress-gradient hypothesis of mutualistic symbiotic functioning.
