Gap edge canopy buffering of throughfall deposition in a subalpine natural forest

Base cation loads are rarely considered in forest gap edge canopies, but they can play critical roles in capturing or buffering atmospheric deposition in forests with frequent gap disturbances, such as subalpine forests. We selected an expanded gap edge canopy and a closed canopy in a subalpine natural forest on the eastern Tibetan Plateau. The throughfall deposition and canopy exchange processes of common base cations (K+, Ca2+, Na+, and Mg2+) were continuously studied over two years. The results showed that the enrichment ratio and fluxes had lower levels of base cations in the gap-edge canopy than in the closed canopy, which indicated that base cations were concentrated more in the closed canopy than in the gap-edge canopy. Although Ca2+ in the gap-edge canopy showed a higher net throughfall flux, the annual net throughfall fluxes of K+, Na+ and Mg2+ within the gap-edge canopy were 1.83, 6.75 and 2.95 times lower than those in the closed canopy, respectively. Moreover, dry deposition fluxes of base cations significantly decreased in the gap edge canopy compared to those in the closed canopy, and the decreasing tendency was more significant during the snowy season than during the rainy season. Overall, these results suggest that the amount of base cations in subalpine natural forest ecosystems may be overestimated when the throughfall deposition of ions in gap edge canopies is ignored.