Dynamics of Calcium, Magnesium, and Manganese During Litter Decomposition in Alpine Forest Aquatic and Terrestrial Ecosystems

Plant litter decomposition is one of the most important ecosystem processes influencing elemental biogeochemistry across terrestrial and aquatic environments. Calcium (Ca), magnesium (Mg), and manganese (Mn) are essential nutrients, which play a key role in plant energy metabolism, photosynthesis, and membrane transport of plants, and the major source of these nutrients is litter decomposition. Although litter decomposition has been subject to extensive research over the last several decades, the dynamics of Ca, Mg, and Mn in decomposing litter has been poorly assessed. Also, very few decomposition studies have been simultaneously carried out across aquatic and terrestrial ecosystems. Here, we conducted a two-year litterbag experiment across alpine forest aquatic (stream and riparian zone) and terrestrial (forest floor) ecosystems to address the dynamics of Ca, Mg, and Mn during litter decomposition. We found that (1) in general concentrations of Ca, Mg, and Mn all increased (that is, high immobilization) during the period of decomposition; (2) Ca and Mn immobilized in decomposing litter regardless of ecosystem type or litter species identity, while Mg showed release (mineralization) or immobilization depending on litter species identity; (3) a common hierarchy of drivers for Ca, Mg, or Mn release rate was found across all ecosystem types; and (4) Ca, Mg, and Mn concentrations all showed positive relationships with litter decomposition. Our results provide evidence of general patterns of Ca, Mg, and Mn dynamics in decomposing litter and significant positive effects of these nutrients on litter decomposition across terrestrial and aquatic environments associated with a forest ecosystem. We suggest that addressing nutrient dynamics across contrasting environments is crucial for predicting how biogeochemical cycling of different nutrients is modulated by litter mass decomposition.