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 infuences the input of base cations in subalpine forests. Therefore, the concentrations and fuxes of base cations in throughfall and stemfow 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 stemfow than in the throughfall and precipitation. The total input fuxes 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 fuxes of K, Ca and Mg were higher than the dry deposition fuxes, 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.
