Accumulation of sodium and manganese during litter decomposition of Qinghai spruce (Picea crassifolia) forest in China

Litter decomposition is a key ecological process as a control of nutrient
cycling in forest ecosystems. Forest litter is an important carrier of
element cycles in forest ecosystems. The biogeochemical cycle of elements
is of great significance to plant communities and ecosystem functions. At
present, most of the studies on the litter's major elements only
focus on C, N, and P, but there are few studies on the biogeochemical
cycle of sodium (Na) and manganese (Mn) of forest litter. In this study,
we investigated the concentrations and fluxes of Na and Mn in needle
litter of Qinghai spruce over a 12–month period. Meanwhile, we measured
the release and accumulation dynamics of litter Na and Mn during litter
decomposition at different canopy coverage and elevations over 3.9 years.
The results showed that the annual Na and Mn concentrations were 312.34
and 621.19 mg kg-1, and the annual fluxes of Na and Mn were 236.67 and
343.16 g ha-1 in needle litter, respectively. After 3.9 years of litter
decomposition, Na released 15.6%, and Mn accumulated 93.4% compared to the
initial concentration. The concentration of Na and Mn in needle litter
both accumulated fastest at low canopy coverage. The concentrations of Na
and Mn were different at various elevations, but there was no obvious
regularity. These results illustrated the seasonal characteristics of
litter element return and nutrient cycling during litter decomposition in
typical coniferous forests in the Qilian Mountains and could provide basic
data and a theoretical basis for ecological protection in the Qilian
Mountains.