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

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.

Water and nutrient cycling regulation functions in forest ecosystems: a comparison between native forests and exotic fast-growing tree species plantations in tropical highlands

“…Both types of native forests showed greater efficiency in hydrological and hydrochemical regulation in these high Andean lands than what was found in both coniferous plantations, as they not only captured extra water input, but also enriched water with nutrients from the canopy (Dezzeo and Chacón 2006, Liu and others 2016, Tan and others 2018). In terms of nutrient mass, and considering our proposed “per unit occupation” metric, both native forests were very effective on transferring nutrients to the soil via net precipitation.…”

“…Changes in the chemical composition of water that reaches the forest floor (as throughfall-Th) are generally the result of the interaction of incoming precipitation (Pi) with the canopy (Scheer 2011). Nutrients from precipitation that reach the canopy change as the result of two processes that include the washing of dry deposition accumulated on the canopy, and canopy exchange through nutrient leaching and direct uptake from the canopy (Tan and others 2018). When comparing nutrient concentrations of the Pi with those of the Th, using the concentration ratio metric (Cr in Figure 3), a general pattern of enrichment was found for K and N when passing the canopy (Cr>1), similar to patterns found in long-term studies (Heartsill-Scalley and others 2007).…”

“…Canopy exchange and washing of the dry deposition represent important nutrient transfer processes within forest ecosystems (Tan and others 2018). Consequently, Np (Th + Sf) has been recognized as an important flow path in the internal dynamics of nutrients worldwide (Macinnis-Ng and others 2012).…”

“…Numerous studies have shown the influence of the forest canopies on water and nutrient fluxes to and into soil, modifying the amount and quality of partitioned rainfall (Tan and others 2018). In Andean montane forests, rainfall partitioning (into throughfall, stemflow and interception) and nutrient concentrations in rainfall determine key aspects of nutrient cycling and plant nutrition (Macinnis-Ng and others 2012).…”

“…Specifically, two considerations regarding the nature and functioning of these forests make them strategic ecosystems of great fragility for the sustainability of ecosystem services: (1) their spatial location in the headwaters with strong anthropic pressure (Ramírez and others 2014), and (2) the extremely nutrient-poor soils on which they are established (Peláez-Silva and others 2018). Therefore, needed are assessments of the potential effects in both the water balance and water chemistry to better assess the effects of native forest transformations into other vegetation cover types (Tan and others 2018).…”