Decomposing leaves are an important source of energy and nutrients in many streams. Factors that control the rate of leaf decomposition in streams may vary between tropical and temperate regions. For example, recent studies suggest that bacteria and fungi may be more important to leaf breakdown in tropical streams, while aquatic insects may be more important in temperate streams. The impacts of aquatic insects on leaf decay will be assessed in headwater streams in Puerto Rico and in North Carolina. Microbial communities (bacteria and fungi) will be characterized on decaying leaf material from each site, and the chemical composition of litter will be measured as it decays. This study is part of a larger effort to address fundamental differences in stream ecosystem processes between temperate and tropical regions. Broader impacts of the project will include advancement of the research career of an underrepresented minority scientist, enhancement of collaborations between the Principal Investigator and established researchers at two long term research sites, and mentoring of undergraduate and graduate students by the Principal Investigator.
The breakdown of fallen leaves is a major ecological process in forested streams and believed to be an important energetic resource in these systems. Despite its importance, little is known about the factors driving differences in leaf breakdown rates between tropical and temperate streams. Recent studies suggest that decomposition rates in streams are more tightly linked to invertebrates (e.g., aquatic insects) in temperate regions and to microbial communities (e.g., bacteria and fungi) in the tropics. Furthermore, aquatic invertebrates and microbes have been shown to influence the overall condition of decomposing materials, however these effects can vary between different regions. Understanding the relative influence of major groups (e.g. invertebrates vs. microbes) in driving leaf breakdown rates in stream systems is necessary to understand their role in the functioning of freshwater ecosystems. Broadly speaking, this study addressed fundamental differences in the processing of organic materials and overall differences in energetic pathways between tropical and temperate forested streams. The study was conducted in collaboration with two NSF-funded Long Term Ecological Research (LTER) sites, which will allowed for the use of, and contribution to, existing datasets. The main goal of this study was to assess for differences in leaf litter decomposition rates in common tropical and temperate leaf types. The study examined the relative effects of invertebrate consumers, microbial diversity, and litter quality during different stages of leaf breakdown. The specific aims of the study were to: 1) determine the overall influence of invertebrates on leaf breakdown rates; 2) determine if differences in breakdown are associated to differences in microbial diversity and community composition; 3) assess for differences in leaf nutritional quality over stages of breakdown. The central hypothesis for the study stated that decomposition rates would be mainly driven by differences in microbial community structure which would ultimately influence overall leaf nutritional quality and consumption by invertebrates. The activities associated to the project supported the continued professional development of a member of an under-represented group in the Biological Sciences and the field of Ecology. These activities allowed the Principal Investigator to incorporate new experimental and analytical techniques that are becoming fundamental in the study of ecological communities, particularly for the assessment of microbial community diversity in natural environments. These efforts allowed the research team to continue collaborations with researchers at two of the premier sites of long term research in Ecology. In addition, the research activities allowed the Principal Investigator the opportunity to mentor young scientists (undergraduate and graduate) and of members of groups traditionally under-represented in the sciences, through the development of new research programs at Georgia Southern University. Furthermore, the study contributed new knowledge of an ecosystem processes (e.g., decomposition of organic material) and of biological diversity in a relatively understudied system (e.g., tropical island streams). In addition, the Principal Investigator had the opportunity to encourage, motivate and mentor young minority students to pursue careers in science and research, particularly in the field of Ecology.
