Oral Presentation Freshwater Sciences 2023

Leaf breakdown increases with light availability under some conditions in a Nebraska stream leaf decomposition experiment (#268)

William R Farrell 1 , Jessica R Corman 1 , Steve A Thomas 2 , Kevin A Kuehn 3 , Yawen Guan 1 , Jacob Reiber 1
  1. University of Nebraska-Lincoln, Lincoln, NE, United States
  2. Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama, United States
  3. School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, Hattiesburg, Mississippi, United States

Terrestrial-derived organic material is widely understood to decompose, first, by physical processes like leaching, next, by fungal and bacterial activity, and later, by macroinvertebrate consumption. This sequential pathway fails to incorporate differences in leaf decomposition that may arise in sunlit streams, where leaves offer substrate for stream autotrophs. Previous research examining algal priming report complex effects on breakdown and fungal biomass, necessitating further studies to disentangle the processes that impact leaf decomposition under different levels of algal colonization. To quantify the impact of sunlight on leaf litter breakdown, metabolism, stoichiometry, and fungal and algal biomass on decomposing leaves, we incubated maple leaves under both sunlit and shaded conditions in three anthropogenically impacted Nebraska streams. In one stream, we also manipulated nutrient availability and macroinvertebrate access to differentiate the conditions under which sunlight impacts our response variables. Early results indicate that greater light exposure can increase mass loss by up to 17% at a given collection date and that this increase in breakdown sometimes corresponds with higher levels of fungal biomass (53% more in one sunlit treatment); however, overall breakdown and fungal biomass do not significantly differ by light treatment. These results in concert with inconstant algal biomass in sunlit treatments indicate disturbance of our experimental design by site-specific factors such as sedimentation. Our results suggest that our current understanding of allochthonous decomposition in streams may need to be altered for grassland or other high light stream ecosystems, although inconsistent results highlight the need for further field studies.

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