Subsidy or Stress? How Sodium Levels Impact Decomposer Communities and Decomposition Rates

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Sodium (Na) in moderate amounts is essential to invertebrates for osmoregulation, nerve function, and decomposition of organic matter. Previous research suggests that increasing the amount of NaCl will increase the amount of decomposers, and therefore decomposition, in terrestrial ecosystems where Na is in shortfall. However, the amount of Na decomposers need to perform optimally before too much Na causes stress may vary across the landscape due to availability. Ruston, LA has Na levels that are likely around slight shortfall to optimal amounts. We hypothesized that in Ruston the amount of detritivores, decomposition, and food chain length would increase up to 5% added sodium before dropping again due to sodium induced stress. To test this, 20- 0.25 x 0.25m2 plots were set up in Ruston, with artificial litter containing 0%, 1%, 5%, and 10% NaCl solutions. Filter paper was placed on each plot for one month to test initial differences in decomposition. After three months, we collected all the organic matter from the plots, and extracted invertebrates using Berlese funnels. There was a 2.3-fold increase in decomposition on the 1% NaCl solution than controls, and the 5% and 10% had decomposition rates similar to the controls. This suggests that small amounts of NaCl help detritivores decompose organic matter, while high amounts may eventually cause stress and lower decomposition rates. Climate change and human activity are increasing NaCl globally. Our results suggest that decomposition rates will increase in environments with Na shortfalls but not where Na is already high.