Effects of Elevated CO2 and Temperature on Condensed Tannin Concentrations in Silver Birch Tree Leaves
Huttunen, L., Aphalo, P.J., Lehto, T., Niemela, P., Kuokkanen, K. and Kellomaki, S. 2009. Effects of elevated temperature, elevated CO2 and fertilization on quality and subsequent decomposition of silver birch leaf litter. Soil Biology & Biochemistry 41: 2414-2421.
In the present study, Huttunen et al. (2009) grew, from seed, well-watered silver birch (Betula pendula) plants in small containers filled with peat that were supplied with nitrogen (N) at low, moderate and high rates equivalent to 0, 150 or 500 kg N per hectare per year, respectively, and maintained within climate-controlled closed-top chambers located out-of-doors at the University of Joensuu in Finland at either ambient or elevated air temperature (T or T + 2°C) at either ambient or elevated air CO2 concentrations (360 or 720 ppm) from mid-June 1999 to the end of the 2000 growing season, after which they harvested their leaves and determined their insoluble condensed tannin concentrations.
As best as can be estimated from the graphical presentations of Huttunen et al.'s results, the doubling of the atmospheric CO2 concentration they imposed on the tree seedlings led to the following increases in insoluble condensed tannin concentrations: 52% (low N), 17% (moderate N), 99% (high N) under the ambient air temperature regime, and 61% (low N), 67% (moderate N), 20% (high N) under the elevated air temperature regime. With all air temperature and soil nitrogen treatments showing CO2-induced increases in insoluble condensed tannin concentrations in silver birch leaves, it can be expected that this phenomenon would help to protect the trees' foliage from predation by voracious insect herbivores, as well as reduce methane emissions from ruminants that might nibble on birch-tree foliage produced in CO2-enriched air.