Assessment of nitrogen cycle pathways associated with different major benthic organisms in response to environmental changes

Abstract

Nitrogen (N) cycling in coral reefs is of key importance for these oligotrophic ecosystems, but knowledge about its pathways is limited. While dinitrogen (N2) fixation is comparably well studied, the counteracting denitrification pathway is under-investigated. The present thesis shows that both processes occur reef-wide, and that both N2 fixation and denitrificaiton align at least for coral holobionts. Functional groups associated with high N2 fixation show low denitrification activity, and vice versa, with coral holobionts being major denitrifiers. Further, nitrate availability potentially moderates N2 fixation and denitrification in coral reef substrates with substrate-specific and nitrate concentration-depending thresholds that supress or stimulate both N cycle pathways.