Effects of Condensed Tannins on Leaf Processing in Mid-Latitude and Tropical Streams: A Theoretical Approach

Abstract

Differences in the dynamics of allochthonous leaf processing in tropical streams are compared with those at mid-latitudes. Phytochemical differences are linked with transferral of energy in stream ecosystems. Condensed tannins, defensive secondary compounds that remain in leaves after cellular death, are suggested as inhibiting and altering leaf processing microorganisms. Comparisons between condensed tannin concentrations and leaf processing rates in mid-latitude and tropical streams support this view. Although many data are available for leaf processing rates per day in mid-latitude streams, there are few quantitative data on plant secondary compounds. The reverse is true for research in tropical regions. Leaf transfer experiments between Costa Rica and Michigan showed the interpretations based on processing rates per day may mask phytochemical differences in cross-biome studies. Processing rates normalized for temperature as degree days for such studies are preferred, as temperature differences then can be distinguished from biotic differences.