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 (C-T) quality in an agroecosystem. Wheat (Triticum aestivum L.) 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 mu L CO2 L-1; CF air + 150 mu L CO2 L-1; nonfiltered (NF) air + 35 nL O-3 L-1; and NF air + 35 nL O-3 L-1 + 150 mu L CO2 L-1 at two soil moisture levels from 1994 to 1996. The 150 mu L CO2 L-1 addition was 18 h d(-1) and the 35 nL O-3 L-l was 7 h d(-1) from April until late October. In response to treatments, the CT contents did not change significantly; however, particulate, oxidizable, dissolved, humic (C-HA) and fulvic (C-FA) acid, and carbohydrate C pools increased in soils under CO2 enrichment and well-watered conditions but decreased under O-3 stress compared with soils under CF ambient air quality. Tropospheric CO2 enrichment and well-watered condition increased, and O-3, stress decreased the log optical density slope for both C-HA and C-FA fractions more than CF ambient air and restricted moisture treatment. Also, the E-465/E-665 ratios of both C-HA and C-FA fractions were higher for the CO2 enrichment and smaller for the O-3 stress compared With CF ambient air quality, Results suggest that tropospheric CO2 enrichment and well-watered conditions may favor an accumulation of low molecular weight and more aliphatic quality of C and O-3 stress favor high molecular weight and more aromatic quality of C.