Abstract
Organic matter processing controls the flow of carbon and nutrients through ecosystems. Heterotrophic metabolism within ponds is supported by both terrestrial leaf litter and autochthonous production. We investigated the potential for the priming of leaf litter decomposition in small ponds using microcosms. We incubated senescent tulip poplar (Liriodendron tulipifera) leaf discs in the dark for 130 days either in contact with eutrophic pond sediments or isolated from sediment contact. Leaves that had been in contact with the sediments were significantly less tough and lost more carbon mass following the incubation than leaves that were not in contact with the sediments, indicating that they were decomposing faster. We calculated a positive priming effect of the sediments of 42% and 77% based on the change in toughness and C mass loss, respectively. We further found that leaf discs that were in contact with the sediments had significantly less fungal biomass, measured as ergosterol mass, and less leaf-derived N in fungal biomass than the leaf discs isolated from the sediments. These results indicate that the presence of the more labile organic matter of the sediments alters the rate of organic matter mineralization and the cycling of nitrogen and carbon.
Highlights
Organic matter processing is a fundamental ecosystem function that regulates the flow of energy and matter through biogeochemical systems (Schlesinger and Bernhardt 2013)
A single leaf disc added to the microcoms had a mean (± 1 SD) AFDM of 0.0035 (± 0.0004) g, so the initial AFDM of 20 leaves added to each microcosm provided approximately 0.071 g of organic matter to the microcosms
The leaves that were in contact with the sediments had lower fungal biomass after 130 days of incubation than the leaves that were not in contact with the sediments despite greater carbon loss from the leaves, the increased carbon mineralization on the leaves in contact with the sediments was not a function of increase in fungal biomass
Summary
Organic matter processing is a fundamental ecosystem function that regulates the flow of energy and matter through biogeochemical systems (Schlesinger and Bernhardt 2013). The availability of energy and inorganic nutrients to an ecosystem is controlled by the mineralization rate of accumulated organic matter by microbial and animal communities (Schlesinger and Bernhardt 2013). There is substantial spatial and temporal variation in the features that combine to affect organic matter mineralization rate in inland waters (i.e., oxygen concentration, temperature, inorganic nutrient concentration, and organic matter quality), making these systems highly dynamic venues of organic matter processing (Hargrave 1969, Granéli and Granéli 1978, del Giorgio and Cole 1998, Wetzel 2001, Berggren et al 2010, Sobek et al 2011, Fortino et al 2014, Gudasz et al 2015). The mixture of autochthonous and allochthonous organic matter sources mean that the organic matter pool of a water body consists of a complex combination of sources, which vary in reactivity and quality (Meyers and Ishiwatari 1993, Finlay and Kendall 2008)
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