N and P colimitation of N2-fixing and N-supplied fynbos legumes from the Cape Floristic Region |
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Authors: | Pravin M. Maistry Michael D. Cramer Samson BM. Chimphango |
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Affiliation: | 1. Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa 2. School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Perth, WA, 6009, Australia
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Abstract: | Background and aims Legume species in the fynbos vegetation of the Cape Floristic Region, that fix N2 in soils with low P, may have evolved for enhanced acquisition and efficient use of P. It was hypothesized that N2-fixing and combined-N supplied (N-supplied) A. linearis, P. calyptrata and C. genistoides are adapted to low P and would be relatively unresponsive to increased P of 100 μM. Methods 18 legume species were evaluated for their nodulation response to low P availability. The N X P interaction was then examined in A. linearis, P. calyptrata and C. genistoides reliant on either N2-fixation or 300 μM N (NH4NO3), and receiving 0.1, 1.0, 10 and 100 μM P (NaH2PO4). Results In the species selection experiment, A. linearis, P. calyptrata and C. genistoides, with the greatest nodule fresh weight (FW) and nodule FW to root FW ratio, were the most prolific nodulating species. In the N X P experiment, with low P supply, the biomass of N2-fixing P. calyptrata and C. genistoides was consistently greater than that of N-supplied plants. In contrast, with high P supply of 100 μM P, all N-supplied plants accumulated more biomass than the corresponding N2-fixing plants. High P-use efficiency, poor down-regulation of P uptake and P storage was evident in A. linearis and P. calyptrata. Conclusion The growth response to P and the significant N X P interactions indicate that N2-fixing and N-supplied plants were not adapted to low P, but rather colimited by both N and P. |
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