Decomposition and Products of Wheat and Rice Straw from a FACE Experiment Under Flooded Conditions

Abstract

ABSTRACT Winter wheat and rice straw produced under ambient and elevated CO 2 in a China rice-wheat rotation free-air CO 2 enrichment (FACE) experiment was mixed with a paddy soil at a rate of 10 g kg −1 (air-dried), and the mixture was incubated under flooded conditions at 25 °C to examine the differences in decomposition as well as the products of crop residues produced under elevated CO 2 . Results showed that the C/N ratio and the amount of soluble fraction in the amended rice straw grown under elevated CO 2 (FR) were 9.8% and 73.1% greater, and the cellulose and lignin were 16.0% and 9.9% lesser than those of the amended rice straw grown under ambient CO 2 (AR), respectively. Compared with those of the AR treatment, the CO 2 -C and CH 4 -C emissions in the FR treatment for 25 d were increased by 7.9% and 25.0%, respectively; a higher ratio of CH 4 to CO 2 emissions induced by straw in the FR treatment was also observed. In contrast, in the treatments with winter wheat straw, the CO 2 -C and CH 4 -C emissions, the ratio of straw-induced CH 4 to CO 2 emissions, and the straw composition were not significantly affected by elevated CO 2 , except for an 8.0% decrease in total N and a 9.7% increase in C/N ratio in the wheat straw grown under elevated CO 2 . Correlation analysis showed that the net CO 2 -C and CH 4 -C emission from straw and the ratio of straw-induced CH 4 to CO 2 emissions were all exponentially related to the amount of soluble fraction in the amended straw ( P 0.05). These indicated that under flooded conditions, the turnover and CH 4 emission from crop straw incorporated into soil were dependent on the effect of elevated CO 2 on straw composition, and varied with crop species. Incorporation of rice straw grown under elevated CO 2 would stimulate CH 4 emission from flooded rice fields, whereas winter wheat straw grown under elevated CO 2 had no effect on CH 4 emission.