Nitrogen to phosphorus ratio of plant biomass versus soil solution in a tropical pioneer tree, Ficus insipida
Journal Publication ResearchOnline@JCUAbstract
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.
Journal
Journal of Experimental Botany
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Volume
61
ISBN/ISSN
1460-2431
Edition
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Issue
13
Pages Count
14
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Publisher
Oxford University Press
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EISSN
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DOI
10.1093/jxb/erq183