Trees increase their P:N ratio with size.

Area of Science:

• Forest Ecology
• Biogeochemistry
• Plant Physiology

Background:

• Phosphorus (P) is a key nutrient that often becomes limiting in aging terrestrial ecosystems.
• Phosphorus resorption efficiency in trees is generally higher than for other elements like nitrogen (N).

Purpose of the Study:

• To test the hypothesis that trees store more P than N as they grow larger.
• To investigate if this P storage is enhanced in slow-growing, late successional trees.

Main Methods:

• Utilized data from the Catalan Forest Inventory (1018 sites) covering diverse forest types.
• Analyzed P and N content in aboveground, foliar, and woody biomass.
• Employed correlation and general linear models (GLM) to assess allometric relationships.

Main Results:

• Aboveground forest P content increases proportionally more with biomass than N content.
• Woody biomass, which has a higher P:N ratio than foliar biomass, increases disproportionately with tree size.
• Wood P:N ratio increases with tree size, and slow-growing species show greater P accumulation in wood.

Conclusions:

• Trees have evolved adaptive mechanisms to store P in biomass, primarily wood, to conserve this vital nutrient.
• This P storage strategy slows nutrient loss from ecosystems and reduces P availability for competitors.
• The trend of increasing P:N ratio with tree size is more pronounced in slow-growing, long-lived species, helping to offset declining soil P availability.