The resorption of nutrients (C, N and P) from senescent leaves of six seagrass species from nine different locations in tropical (Indonesia and Kenya), Mediterranean (Spain) and temperate (The Netherlands) regions has been investigated. Resorption was quantitatively assessed by calculating the difference in nutrient content between the leaves with the highest content, and the oldest leaves. In order to do so, the leaves were classified according to their age. The nutrient contents of leaves of a given age category were calculated by multiplying the measured nutrient concentration in this age category with its corresponding modelled leaf biomass. N- and P-concentrations declined during ageing and senescence of the leaves in all of the investigated situations but two. The decline in concentration varied up to 58% for N and up to 66% for P. The C-concentration declined on three of the investigated occasions and varied up to 24%. Despite a decline in concentration, the leaf C-content did not change, indicating no resorption of carbon. The efficiency of N-resorption from intact seagrass leaves varied between 3.8 and 29% (average: 15%), while the efficiency of phosphorus resorption varied between 0 and 51% (average: 21%). The resorption efficiency was not significantly different in seagrasses with a relatively high and a relatively low nutrient concentration, although within-species comparisons showed that in some cases resorption efficiency was positively related to the nutrient concentration of the leaves. Premature loss of leaves and leaf fragments (by e.g. herbivory) may substantially interfere with the resorption process. In Indonesian seagrasses we estimated that as a result of fragmentation and premature detachment only between 56 and 77% of the physiological resorption potential actually was realised. It is concluded that internal resorption may play a role in the nutrient dynamics of seagrass plants, but that its quantitative importance probably is limited. Nutrient resorption from senescent seagrass leaves may reduce the nutrient requirements for seagrass leaf production by approximately 10% for nitrogen and 15% for phosphorus.
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