Abstract: Plant litter and sediments play a crucial role in the storage and migration of nutrients in forest headwater streams, and can significantly impact material cycling in downstream waters. We examined the spatial and temporal dynamics of calcium (Ca) and magnesium (Mg) concentrations and storage in plant litter and sediments of a subtropical forest headwater stream from March 2021 to February 2022 in the upper reaches of Minjiang River, Sanming, Fujian. Results showed that: (1) The maximum concentrations of Ca and Mg in plant litter were 15557.72 and 970.98 mg·kg^-1 in December and October, respectively. The highest concentrations of sediment Ca and Mg were 1840.61 and 576.74 mg·kg^-1 in August and May, respectively. (2) The highest storage of plant litter Ca and Mg was observed in April, with average values of 1.27 and 0.09 g·m^-2, respectively, while those of sediment Ca and Mg occurred in August and May, with average values of 130.76 and 46.77 g·m^-2, respectively. (3) The largest storage of plant litter Ca and Mg occurred in the source reach, whereas that of sediments occurred in a sampling site with confluence at the middle-lower reaches of the stream. (4) Stream physical and chemical properties, particularly discharge, water temperature, monthly rainfall, rainfall frequency, and dissolved oxygen, significantly affected the storage and concentrations of Ca and Mg in plant litter and sediments. These results will help to better understand the role of forest headwater streams in nutrient storage and fluxes in subtropical forests.

Key words: nutrient cycle, stream characteristics, inflow of tributary, calcium, magnesium