Vertical Profiles of CO2 Concentration and δ^13C Values in a Subalpine Forest of Taiwan

Abstract

We investigated the vertical gradients in CO2 concentration and stable carbon isotope ratio (δ^13Cco2) of the canopy air within a coniferous-hardwood, Chamaecyparis and Rhododendron dominated, subalpine forest in Taiwan. The stable carbon isotope ratio of vascular plants and a epiphytic bryophyte species (Bazzania fauriana) (δ^13)C(subscript leaf)) from different heights within the forest were also analyzed. Results revealed that CO2 and δ^13Cco(subscript 2) gradients did exist within the forest, with higher CO2 concentrations and more negative δ^13Cco(subscript 2) values in air sampled from the lower canopy. The average vertical gradients in CO2 and δ^13Cco(subscript 2) value of the CO2 of the 12 sampling dates were 28.5±6.1ppm and 1.3±0.3‰, respectively. Seasonal patterns of the relationship between l/[CO2] and the corresponding δ^13C were pronounced, with steady decreases in the slopes and increases in the intercepts found from January to August. A decreasing δ^13C(subscript leaf) with decreasing height was also measured in a bryophyte (ranging from-27.4 to -29.2%o), canopy and understory leaves (ranging from -28.6 to -33.5%o). It was estimated that photosynthetic physiology affected by microclimates within the forest contributed approximately 2.8% of variation of the vertical gradient of vascular plant δ^13C values.