Effects of defoliation and atmospheric CO2 depletion on nitrate acquisition,and exudation of organic compounds by roots of Festuca rubra |
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Authors: | Paterson Eric Thornton Barry Sim Allan Pratt Shona |
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Institution: | (1) The Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH, Scotland, UK |
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Abstract: | The aim of this study was to investigate the physiological basis of increased root exudation from Festuca rubra, in response to defoliation. The hypothesis, that assimilate supply to roots is a key determinant of the response of root exudation to defoliation was tested by imposing CO2-deplete (< 50 mol mol–1) atmospheres to F. rubra. This was done as a non-destructive means of preventing supply of new assimilate to roots of intact and defoliated plants. F. rubra was grown in axenic sand systems, with defoliation and CO2-depletion treatments applied to plants at 14 and 35 days after planting. Root exudation and NO3
– uptake were quantified throughout, and post-treatment uptake and allocation of N were determined from the distribution of 15N label, supplied as 15NO3
–. Defoliation of F. rubra resulted in significantly (P <0.01) increased root exudation, CO2-depletion did not result in increased exudation from plants of either age. When treatments were applied to F. rubra after 14 days, defoliation and CO2-depletion each reduced NO3
– uptake significantly (P <0.05). However, in older plants, uptake of NO3
– was less sensitive to defoliation and CO2-depletion. The results indicate that increased root exudation following defoliation is not related directly to reduced assimilate supply to roots. This was evident from the lack of effect of CO2-depletion on root exudation, and the absence of correlation between root-C efflux and the rate of NO3
– uptake. The physiological basis of increased exudation following defoliation remains uncertain, but may be dependent on physical damage, either directly or as a consequence of systemic responses to wounding. |
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Keywords: | amino acid exudation CO2-depletion defoliation Festuca rubra nitrate uptake root exudation |
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