Atmospheric CO2 and soil extracellular enzyme activity: a meta-analysis and CO2 gradient experiment
Kelley, A. M., Fay, P. A., Polley, H. W., Gill, R. A. and Jackson, R. B. 2011. Ecosphere. 2: Article 96
Abstract
Rising atmospheric CO2 concentrations can alter carbon and nutrient cycling and microbial
processes in terrestrial ecosystems. One of the primary ways microbes interact with soil organic matter is
through the production of extracellular enzymes, which break down complex organic molecules and
release nutrients into the soil. We conducted a meta-analysis of 34 studies that examined responses in
microbial enzyme activity to elevated CO2. We also conducted a field study of soil enzyme activity in a
tallgrass-prairie ecosystem growing in sandy loam (lower organic matter content) and clayey soils (higher
organic matter content) exposed to a continuous gradient of 250 to 500 ppm CO2. Of the 10 enzyme groups
examined in the meta-analysis, including those degrading starch, β-glucan, cellulose, xylan/hemicellulose,
lignin, organic P, and organic N, only the activity of one enzyme that degrades the C- and N-containing
building blocks of chitin (N-acetyl-glucosaminidase) increased consistently at elevated CO2 by an average
of 12.6% (p < 0.05), especially in field studies and in woody ecosystems. In our field study, increasing CO2
from subambient to elevated concentrations reduced the activity of leucine aminopeptidase by 32% in the
black clay soil during the peak of the growing season, while β1,4-N-acetyl-glucosaminidase increased by
44% near the end of the season, indicating increased N limitation with increasing CO2. In the sandy loam
soil, alkaline phosphatase activity increased by 42% with CO2 enrichment at the end of the growing season,
suggesting CO2-induced phosphorus limitation in these soils. Additionally, a 53% decrease in the
carbon cycling enzymes cellobiohydrolase, α-glucosidase, and xylosidase activity with increased CO2 was
found in July. Our field study shows that soil type can strongly influence how microbial functioning may
change with rising CO2 concentrations and that microbial responses associated with C-, N-, and P-cycling
are likely to change--and may already have changed--with increasing CO2 under some soil types and
conditions. Our meta-analysis revealed that, despite variable enzyme activities with CO2, chitinase activity
increased consistently with CO2 across ecosystems.
Key Words
α-glucosidase, cellobiohydrolase, elevated CO2, grassland, leucine aminopeptidase, N-acetyl-glucosaminidase; phosphatase, soil texture, xylosidase
