Testing the allometric scaling of alkaline phosphatase activity to surface/volume ratio in benthic marine macrophytes

Alkaline phosphatase activity (APA), tissue P, N and C were determined for 23 species of benthic marine macrophytes (22 macroalgae, 1 seagrass). In addition, estimates of the surface area/volume ratio (SA:V) of these species were derived from experimental work and from the literature. The tissue nutrient content (especially P) does not explain differences in APA among the species of marine macrophytes. On the contrary, a regression analysis suggested that size-specific variation in APA can be attributed in part to changes in relative surface area among benthic marine macrophytes. The slope of the logarithmically transformed equation relating APA and SA:V was 0.48 (SE=0.16). The slope increased to 0.65 (SE=0.09) when three “anomalous” species, showing high SA:V ratio but negligible APA were not taken into account. The relationship between APA and SA:V suggests an allometric scaling of APA in benthic marine macrophytes. Along with other indicators, the equation might help to indicate to what extent a population of benthic marine macrophytes is limited by phosphorus. The results agree with previous reports on allometric relationships between nutrient uptake (N and P) and SA:V within narrow size-ranges in macroalgae. They also support the hypothesis that there is a general coupling between ecophysiological and morphological properties in aquatic photosynthetic organisms.