Abstract
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.
Highlights
Precipitation often acts as a primary transporting agent and solvent; element cycles in forests are always closely linked to the hydrological process[1]
The elements from precipitation that travel through the canopy are changed by two processes: (i) the washing of the dry deposition accumulated on the canopy, and (ii) the canopy exchange process through the leaching and uptake from the canopy[2]
Those studies did not focus on the role of canopy exchange processes in forest ecosystems, and research on hydrology in subalpine forests is scarce
Summary
Precipitation often acts as a primary transporting agent and solvent; element cycles in forests are always closely linked to the hydrological process[1]. Stemflow delivers water to the ground via branches and tree stems[5,6], and base cations are transported greater distances by stemflow than throughfall Both types of water fluxes are important pathways in the internal element dynamics of forests and are essential to the growth of a forest community[7,8,9]. Many studies have evaluated the differences in the hydrology and chemical processes between throughfall and stemflow of different forests in different regions in China[12,21,22] Those studies did not focus on the role of canopy exchange processes in forest ecosystems, and research on hydrology in subalpine forests is scarce. This research can help understand how the coniferous forest canopy can alter the elements of precipitation processes and provide basic data for subsequent research in alpine forest ecosystems
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