Interception of sulfate deposition from a closed canopy to a forest gap edge canopy in a subalpine dragon spruce plantation

Reducing the threats of sulfate ion (SO42−) deposition to terrestrial ecosystems is a great challenge. The canopy interception effect on SO42− deposition has been well documented, but the interception efficiency of the gap edge remains unknown. Therefore, a subalpine dragon spruce (Picea asperata) plantation was evaluated in the upper reaches of the Yangtze River. The dynamics of the SO42− concentration in the throughfall were investigated from the gap edge to the closed canopy during the rainfall and snowfall periods from August 2015 to July 2016. The annual input of SO42− totaled 2.56 kg/ha through rainfall and 0.69 kg/ha through snowfall. The total annual net interception fluxes (NIFs) of SO42− at the gap edge and in the closed canopy were 1.48 kg/ha and 0.66 kg/ha, respectively, and the net interception ratios (NIRs) accounted for 45.40% and 20.25%, respectively. The NIF and the NIR of SO42− at the gap edge were higher than those in the closed canopy. Therefore, the results suggested that a significant amount of SO42− deposition was intercepted by the tree canopy in the subalpine plantation, with more SO42− deposition at the gap edge than in the closed canopy, which is beneficial for improving the water quality in the upper reaches of the Yangtze River via forest management.