Journal Article

Nitrogen to phosphorus ratio of plant biomass versus soil solution in a tropical pioneer tree, Ficus insipida

Valerie Garrish, Lucas A. Cernusak, Klaus Winter and Benjamin L. Turner

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 61, issue 13, pages 3735-3748
Published in print August 2010 | ISSN: 0022-0957
Published online June 2010 | e-ISSN: 1460-2431 | DOI: https://dx.doi.org/10.1093/jxb/erq183

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It is commonly assumed that the nitrogen to phosphorus (N:P) ratio of a terrestrial plant reflects the relative availability of N and P in the soil in which the plant grows. Here, this was assessed for a tropical pioneer tree, Ficus insipida. Seedlings were grown in sand and irrigated with nutrient solutions containing N:P ratios ranging from <1 to >100. The experimental design further allowed investigation of physiological responses to N and P availability. Homeostatic control over N:P ratios was stronger in leaves than in stems or roots, suggesting that N:P ratios of stems and roots are more sensitive indicators of the relative availability of N and P at a site than N:P ratios of leaves. The leaf N:P ratio at which the largest plant dry mass and highest photosynthetic rates were achieved was ∼11, whereas the corresponding whole-plant N:P ratio was ∼6. Plant P concentration varied as a function of transpiration rate at constant nutrient solution P concentration, possibly due to transpiration-induced variation in the mass flow of P to root surfaces. The transpiration rate varied in response to nutrient solution N concentration, but not to nutrient solution P concentration, demonstrating nutritional control over transpiration by N but not P. Water-use efficiency varied as a function of N availability, but not as a function of P availability.

Keywords: Carbon isotope ratio; N:P ratio; nutrient supply; transpiration; tropical tree; water-use efficiency

Journal Article.  6560 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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