Concentration of sugars, phenolic acids, and amino acids in forest soils exposed to elevated atmospheric CO 2 and O 3

Abstract

Concentrations of soluble soil sugars, soluble phenolic acids, and free amino acids were measured in three forest communities at the FACTS-II Aspen FACE Site near Rhinelander, WI, in order to better understand how elevated atmospheric CO 2 and O 3 are influencing soil nutrient availability and cycling. Sugars, phenolic acids, and amino acids are mostly derived from plant and microbial processes, and have the potential to be influenced by changes in carbon inputs. We hypothesized that concentrations in the soil would parallel increases seen in biological activity, due to greater net primary productivity under elevated CO 2 and seasonal patterns of root growth. Chemical analysis of soils revealed marginally significant increases of total soluble sugars and total soluble phenolic acids in the elevated CO 2 treatment (+27 mg kg −1, +0.02 μmol g −1), but there were no significant differences in concentrations due to elevated O 3 or CO 2+O 3. Total free amino acid concentrations were not affected by any of the treatments, but significant shifts in individual amino acids were observed. Elevated CO 2 and the interaction treatment (elevated CO 2+O 3) increased aspartic acid concentrations, while elevated O 3 treatment decreased the concentration of valine. Concentrations of sugars increased throughout the growing season, while phenolic acids were constant and amino acids decreased. The birch–aspen community had the highest concentration of phenolic acids and sugars overall, while maple–aspen had the lowest. These findings suggest that concentrations of soluble sugars, soluble phenolic acids, and free amino acids in the soil are strongly influenced by soil properties, plant and microbial activity, plant community composition, and to a lesser degree, changes in atmospheric CO 2 and O 3.