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

Garrish V, Cernusak LA, Winter K, Turner BL - J. Exp. Bot. (2010)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography, McGill University, Montréal, Québec H3A-1B1, Canada.

ABSTRACT
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 approximately 11, whereas the corresponding whole-plant N:P ratio was approximately 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.

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The nitrogen to phosphorus ratio of leaves (A), stems (B), roots (C), and whole plants (D) of Ficus insipida plotted as functions of the nitrogen to phosphorus ratio of the nutrient solutions fed to the plants. Both the x-axis and y-axis are shown on logarithmic scales. The dashed lines represent one-to-one lines.
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fig5: The nitrogen to phosphorus ratio of leaves (A), stems (B), roots (C), and whole plants (D) of Ficus insipida plotted as functions of the nitrogen to phosphorus ratio of the nutrient solutions fed to the plants. Both the x-axis and y-axis are shown on logarithmic scales. The dashed lines represent one-to-one lines.

Mentions: Comparison of the N:P ratio of plant biomass with that of the nutrient solution is shown in Fig. 5. The plot of leaf N:P against nutrient solution N:P suggests that on a logarithmic scale the relationship between the two was approximately linear over most of the range of nutrient solution N:P ratios employed in the study. At the lowest nutrient solution N:P ratio, however, the relationship departed from linearity (Fig. 5A). For the N:P ratio of stem biomass, on the other hand, the relationship to the nutrient solution N:P ratio on a logarithmic scale was linear over the full range of values (Fig. 5B). The relationship between root N:P and nutrient solution N:P followed a similar pattern to that for stem N:P, but with slight departures from linearity at the highest and lowest nutrient solution N:P ratios (Fig. 5C). Given these patterns, geometric mean regressions were fitted to the log–log plots of plant biomass N:P against nutrient solution N:P excluding the lowest nutrient solution N:P treatment. With this treatment excluded, the nutrient solution N:P ratios ranged from 1 to 135. Across this range of nutrient solution N:P, the estimated H, describing the extent of homeostatic control over plant biomass N:P, was 6.3 for leaves, 2.5 for stems, and 2.8 for roots. Thus, regulatory control over N:P stoichiometry was considerably stronger in leaves than in stems or roots. For whole-plant N:P, the relationship to nutrient solution N:P was approximately linear over the full range of nutrient solution N:P (Fig. 5D). The H calculated for whole-plant N:P was 3.1.


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

Garrish V, Cernusak LA, Winter K, Turner BL - J. Exp. Bot. (2010)

The nitrogen to phosphorus ratio of leaves (A), stems (B), roots (C), and whole plants (D) of Ficus insipida plotted as functions of the nitrogen to phosphorus ratio of the nutrient solutions fed to the plants. Both the x-axis and y-axis are shown on logarithmic scales. The dashed lines represent one-to-one lines.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2921206&req=5

fig5: The nitrogen to phosphorus ratio of leaves (A), stems (B), roots (C), and whole plants (D) of Ficus insipida plotted as functions of the nitrogen to phosphorus ratio of the nutrient solutions fed to the plants. Both the x-axis and y-axis are shown on logarithmic scales. The dashed lines represent one-to-one lines.
Mentions: Comparison of the N:P ratio of plant biomass with that of the nutrient solution is shown in Fig. 5. The plot of leaf N:P against nutrient solution N:P suggests that on a logarithmic scale the relationship between the two was approximately linear over most of the range of nutrient solution N:P ratios employed in the study. At the lowest nutrient solution N:P ratio, however, the relationship departed from linearity (Fig. 5A). For the N:P ratio of stem biomass, on the other hand, the relationship to the nutrient solution N:P ratio on a logarithmic scale was linear over the full range of values (Fig. 5B). The relationship between root N:P and nutrient solution N:P followed a similar pattern to that for stem N:P, but with slight departures from linearity at the highest and lowest nutrient solution N:P ratios (Fig. 5C). Given these patterns, geometric mean regressions were fitted to the log–log plots of plant biomass N:P against nutrient solution N:P excluding the lowest nutrient solution N:P treatment. With this treatment excluded, the nutrient solution N:P ratios ranged from 1 to 135. Across this range of nutrient solution N:P, the estimated H, describing the extent of homeostatic control over plant biomass N:P, was 6.3 for leaves, 2.5 for stems, and 2.8 for roots. Thus, regulatory control over N:P stoichiometry was considerably stronger in leaves than in stems or roots. For whole-plant N:P, the relationship to nutrient solution N:P was approximately linear over the full range of nutrient solution N:P (Fig. 5D). The H calculated for whole-plant N:P was 3.1.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography, McGill University, Montréal, Québec H3A-1B1, Canada.

ABSTRACT
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 approximately 11, whereas the corresponding whole-plant N:P ratio was approximately 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.

Show MeSH