Global climate change is driving the expansion of mangroves into saltmarsh habitat, which may alter the rate and magnitude of organic matter decomposition and nutrient cycling due to differences in the structural complexity, litter quality, and other ecophysiological traits of foundation species. This work quantified and compared aboveground litter decomposition of the range-expanding mangrove, Avicennia germinans, and resident saltmarsh cordgrass, Spartina alterniflora, and decomposition of a standard substrate belowground, in the saltmarsh and saltmarsh-mangrove ecotone habitat along the Atlantic coast of Florida, USA. Plant and soil fractions were tested for natural abundances of δ13C and δ15N stable isotopes to elucidate soil nutrient sources. Although aboveground decomposition rates differed between marsh and mangrove species due to differences in litter quality, decomposition rates did not vary between saltmarsh and ecotonal habitats. Decay rates were higher for A. germinans leaf litter (0.007 ± 0.0003 k day−1) than for S. alterniflora (0.004 ± 0.0003 k day−1) regardless of habitat, which suggests that increasing inputs of A. germinans litter with encroachment may increase nutrient availability through rapid turnover. Furthermore, belowground decomposition was similar between habitats (0.015 ± 0.0008 k day−1), whereas soil δ13C and δ15N stable isotopes differed significantly. Collectively, these results suggest that mangrove encroachment may not modify the environmental factors driving decomposition, but alterations in foundation plant species may ultimately alter nutrient cycling within habitats through shifts in litter quality.
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This research was funded by the National Aeronautics and Space Administration (NASA) Climate and Biological Response program (NNX11AO94G) and the National Science Foundation (NSF) MacroSystems Biology program (EF1065821). The authors would like to thank Florida State Parks, the Merritt Island National Wildlife Refuge, Guana Tolomato Matanzas National Estuarine Research Reserve, and Canaveral National Seashore for permits and unabridged access to their parks. We also thank K.V. Curtis for laboratory nutrient analysis and T.Z. Osborne, L.J. Duckett, M.H. Lehmann and Z.R. Foltz for field and technical assistance. We sincerely thank the three anonymous reviewers for their edits and suggestions, which greatly improved this manuscript. This is Contribution No. 1144 of the Smithsonian Marine Station.
LTS and ICF designed the study; LTS performed the research; LTS and JAC analyzed the data; RSS contributed additional methods and data; LTS, JAC, RSS and ICF wrote the paper.
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Simpson, L.T., Cherry, J.A., Smith, R.S. et al. Mangrove Encroachment Alters Decomposition Rate in Saltmarsh Through Changes in Litter Quality. Ecosystems 24, 840–854 (2021). https://doi.org/10.1007/s10021-020-00554-z