The effect of canopy exchange on input of base cations in a subalpine spruce plantation during the growth season.

Canopy exchange is one of the most important processes involved in the internal transfer of elements in forest ecosystems. However, little information is available on how canopy exchange influences the input of base cations in subalpine forests. Therefore, the concentrations and fluxes of base cations in throughfall and stemflow were investigated from August 2015 to July 2016 (except for the frozen season) in a representative subalpine spruce plantation in the eastern Tibet Plateau. Our results showed that the mean concentrations of K, Ca, Na and Mg were higher in the stemflow than in the throughfall and precipitation. The total input fluxes of K, Ca, Na and Mg in the internal forest were lower than those in the non-forest. Moreover, the results from the canopy budget model indicated that the canopy exchange fluxes of K, Ca and Mg were higher than the dry deposition fluxes, and Ca and Mg were uptaken, whereas K was leached when precipitation passed through the canopy. Therefore, the results suggested that the input of base cations is mainly controlled by canopy exchange during precipitation in subalpine forest ecosystems, and the canopy could alter the sinks and sources of base cations from precipitation.