Effects of elevated CO sub(2) and O sub(3) on leaf litter phenolics and subsequent performance of litter-feeding soil macrofauna

摘要

Two field-growing silver birch (Betula pendula Roth) clones (clone 4 and 80) were exposed to elevated CO sub(2) and O sub(3) for three growing seasons (1999-2001). The phenolic compounds of naturally abscised leaf litter were analyzed in order to determine the possible CO sub(2)- and O sub(3)-induced changes in the litter quality. The potential litter-mediated CO sub(2) and O sub(3) effects on litter-feeding soil macrofauna (detritivore) performance were assessed in microcosm experiments, i.e., the relative growth rates (RGR) of Lumbricus terrestris and Porcellio scaber, the relative consumption rates (RCR) of P. scaber, and mortality of the test animals were measured. The leaf litter grown under elevated CO sub(2) had increased concentrations (weight per mass unit) and contents (weight per leaf) of phenolic acids, flavonol glycosides, condensed tannins and total measured phenolics. Elevated O sub(3) increased the concentrations of 3,4'-dihydroxypropiophenone 3- beta -d-glucoside (DHPPG) and flavonoid aglycones but only under ambient CO sub(2). However, elevated O sub(3) effects on the content of some low-molecular-weight phenolic (LMWP) compounds (i.e. phenolic acids, DHPPG, flavonoid aglycones) and total LMWP changed over time emphasizing the importance of conducting long-term (>3 years) exposure studies. In general, RGR of young L. terrestris was affected by the litter quality changes induced by elevated CO sub(2) and O sub(3), as the animal growth rates were reduced when they were fed with CO sub(2)- and O sub(3)-exposed leaf litter of clone 80 in Experiment 1. P. scaber RCR or RGR responses to CO sub(2)- and O sub(3)-induced changes in litter quality were more variable and inconsistent, and neither were there any litter-mediated CO sub(2) and O sub(3 )effects on animal mortality in these microcosm experiments. In conclusion, elevated CO sub(2) has the potential to alter silver birch leaf litter quality, but the possible O sub(3) effects on phenolic compounds and litter-mediated CO sub(2) and O sub(3) effects on detritivores are more difficult to validate.