Carbon allocation in ectomycorrhizal plants at limited and optimal N supply: an attempt at unraveling conflicting theories |
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Authors: | Ana Corr��a R��diger Hampp Elisabeth Magel Maria-Am��lia Martins-Lou??o |
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Affiliation: | (1) Universidade de Lisboa, Faculdade de Ci?ncias, Centro de Biologia Aplicada, Campo Grande C2. Piso 4, 1749-016 Lisbon, Portugal;(2) Departamento de Microbiolog?a del Suelo y Sistemas Simbi?ticos, Estaci?n Experimental del Zaid?n, CSIC, Profesor Albareda 1, 18008 Granada, Spain;(3) Physiological Ecology of Plants, University of T?bingen, Auf der Morgenstelle 1, 72076 T?bingen, Germany;(4) Department of Wood Science / Wood Biology, University of Hamburg, Leuschnerstr. 91, 21031 Hamburg, Germany |
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Abstract: | With regard to mycorrhiza, conflicting theories try to explain how the balance between fungal demand for carbohydrates and
the plant’s needs for nutrients varies, resulting in conflicting predictions. In order to evaluate current concepts, we investigated
some metabolic parameters, which are indicative for plant carbon allocation in response to mycorrhization at limited and optimal
N supply. Pinus pinaster seedlings were inoculated with living or dead (control) cultures of Pisolithus tinctorius, supplied with ammonium at 4 (limiting) or 7% d−1 (non-limiting) N relative addition rate (RARN), and followed development for 29 days. Mycorrhizal colonization of roots was quantified by the determination of ergosterol.
A series of enzymes (sucrose and trehalose metabolism, anaplerosis) and metabolites (soluble carbohydrate, including trehalose;
fructose 2,6 bisphosphate, free amino acids) relevant in the C/N exchange between symbionts, and in the carbon allocation
and sink strength within the plant were assayed for 2-day-intervals for up to 14 days, and at 5-day-intervals for the rest
of the experiment. The first 10 days reflected the establishment of mycorrhizal interaction, and the carbon allocation to
the root was higher in M plants independent of N supply. Following this period, carbon allocation became N-related, higher
at low, and lower at high N supply. The belowground C investment of M plants was dependent on N availability, but not on N
gain. Finally, increased belowground C allocation was accompanied by a shift from plant to fungal metabolism. |
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