Tropospheric Carbon Dioxide or Ozone Enrichments and Moisture Effects on Soil Organic Carbon Quality

Carbon, as an active component of organic matter, has considerable effects on soil quality and productivity. The objective of this study was to examine the effect of climate change variables on soil organic C (CT) quality in an agroecosystem. Wheat (Triticum aestivumL.) and soybean [Glycine max(L.) Merr] plants were grown in 3 m in diam. open‐top field chambers and exposed to charcoal‐filtered (CF) air at 350 µL CO2L−1; CF air + 150 µL CO2L−1; nonfiltered (NF) air + 35 nL O3L−1; and NF air + 35 nL O3L−1+ 150 µL CO2L−1at two soil moisture levels from 1994 to 1996. The 150 µL CO2L−1addition was 18 h d−1and the 35 nL O3L−1was 7 h d−1from April until late October. In response to treatments, the Cr contents did not change significantly; however, participate, oxidizable, dissolved, humic (CHA) and fulvic (CFA) acid, and carbohydrate C pools increased in soils under CO2enrichment and well‐watered conditions but decreased under O3stress compared with soils under CF ambient air quality. Tropospheric CO2enrichment and well‐watered condition increased, and O3stress decreased the log optical density slope for both CHAand CFAfractions more than CF ambient air and restricted moisture treatment. Also, the E465/E665ratios of both CHAand CFAfractions were higher for the CO2enrichment and smaller for the O3stress compared with CF ambient air quality. Results suggest that tropospheric CO2enrichment and well‐watered conditions may favor an accumulation of low molecular weight and more aliphatic quality of C and O3stress favor high molecular weight and more aromatic quality of C.