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

Dep. of Natural Resource Sciences and Landscape Architecture, Univ. of Maryland, College Park, MD 20742;

A. A. Ali

Dep. of Botany, Zagazig Univ., Zagazig, Egypt.

^* Corresponding author (cm48{at}umail.umd.edu).

ABSTRACT

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 µL CO₂ L^–1; CF air + 150 µL CO₂ L^–1; nonfiltered (NF) air + 35 nL O₃ L^–1; and NF air + 35 nL O₃ L^–1 + 150 µL CO₂ L^–1 at two soil moisture levels from 1994 to 1996. The 150 µL CO₂ L^–1 addition was 18 h d^–1 and the 35 nL O₃ L^–1 was 7 h d^–1 from April until late October. In response to treatments, the Cr contents did not change significantly; however, participate, 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 O₃ stress compared with soils under CF ambient air quality. Tropospheric CO₂ enrichment and well-watered condition increased, and O₃ 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 E₄₆₅/E₆₆₅ ratios of both C_HA and C_FA fractions were higher for the CO₂ enrichment and smaller for the O₃ 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 O₃ stress favor high molecular weight and more aromatic quality of C.