Pretreatment artefacts associated with the removal of calcareous epiphytes from seagrass leaves

Abstract

Experimental removal of calcareous epiphytes from seagrass leaves using varying dilutions of acetic acid, hydrochloric acid and phosphoric acid, significantly altered the carbon (C), nitrogen (N) and phosphorus (P) contents of seagrass tissue. In addition to dissolution of the carbonate, the acid treatments caused leaching and weak digestion of the leaf material, resulting in the loss of certain organic compounds; this was positively correlated with the concentrations of the acids applied. Removal of calcareous epiphytes from seagrass leaves using diluted acids prior to measurements, such as recommended in handbooks, is therefore strongly advised against. An alternative pretreatment procedure for the determination of organic C, N and P in seagrass leaves rich in calcareous epiphytic growth is proposed and tested. This new methodology involves the in situ acidification of untreated powdered leaf tissue (including microepiphytes) within silver cups prior to analysis of the C and N contents. Comparison with results from non-acidified samples yields information on inorganic C contents (from the epiphytic carbonate) and its contribution as CaCO 3 to the dry weight of the sample, which is used to correct the results obtained for organic C, N and P (and other elements).