How light and nutrients affect the relationship between autotrophic and heterotrophic biomass in a tropical black water periphyton community Rafael D. Guariento • Luciana S. Carneiro • Adriano Caliman • Reinaldo Luiz Bozelli • Francisco A. Esteves Received: 2 April 2011 / Accepted: 21 September 2011 / Published online: 5 October 2011 Ó Springer Science+Business Media B.V. 2011 Abstract This study examines how nutrients and light affect the relationship between autotrophic biomass and non-autotrophic periphyton organic mat- ter in a tropical black water lake biofilm community. We hypothesized that there is no positive correlation between autotrophic and non-autotrophic organic matter in the periphytic community of a black water humic lake, where non-algal components of periphy- ton can rely on carbon sources external to the periphyton matrix and where nutrient availability is low. Second, we sought to test our hypothesis that non- autotrophic periphyton organic matter will benefit from nutrient enhancement in a lake where the availability of DOC is high. We performed a field experiment using in situ lake mesocosms to manipu- late nutrient concentrations and light availability in a 2 9 2 factorial design. Control treatments (no nutrient added) and nutrient treatments (N ? P) were com- pared in different light conditions: high light (near surface water) and low light (near bottom). No positive correlation was found between autotrophic biomass and non-autotrophic periphyton organic matter, but a negative correlation was observed in high nutrient and light conditions. The low C:P and N:P ratios revealed that the non-autotrophic organic matter mostly com- prised a heterotrophic microbial biofilm. High levels of light and nutrients together caused significant changes in periphyton community properties. The non-autotrophic periphyton organic matter was nega- tively affected by nutrient addition, whereas auto- trophic biomass was positively affected, especially in high light conditions. Our results strongly suggest that non-autotrophic periphyton organic matter in a humic lake is primarily comprised of a bacterial biofilm that directly competes for nutrients with autotrophs in the periphytic community. We also observed no effect of nutrient addition on periphyton growing in light- limited conditions. These results suggest that hetero- trophic periphytic organisms might experience carbon limitation despite the high availability, but usually low quality, of dissolved carbon in the water column of humic lakes. Handling Editor: Piet Spaak. R. D. Guariento (&)  L. S. Carneiro  A. Caliman  R. L. Bozelli  F. A. Esteves Departamento de Ecologia, Instituto de Biologia, Pre ´dio do CCS, Universidade Federal do Rio de Janeiro, CP 68020, Ilha do Funda ˜o, Rio de Janeiro, RJ CEP 21941-590, Brazil e-mail: dettogni@gmail.com L. S. Carneiro  A. Caliman Departamento de Bota ˆnica, Ecologia e Zoologia, Centro de Biocie ˆncias, Universidade Federal do Rio Grande do Norte, Natal, Rio Grande do Norte, RN CEP 59078-900, Brazil F. A. Esteves Nu ´cleo em Ecologia e Desenvolvimento So ´cio-Ambiental de Macae ´, NUPEM, Universidade Federal do Rio de Janeiro, Av. Rotary Club, s/n, Sa ˜o Jose ´ do Barreto, CP 119331, Macae ´, RJ, Brazil 123 Aquat Ecol (2011) 45:561–569 DOI 10.1007/s10452-011-9377-5