Inter‐Annual Variability of the Effects of Elevated CO 2 and Temperature on Litter Quantity and Quality of Rice ( Oryza sativa L.) Residues
Abstract
ABSTRACT Rice ( Oryza sativa L.) straw and roots are the primary sources of soil organic carbon (SOC) of paddies; however, variations in the quantity and quality of these residues under climate change remains unclear. This study investigated the changes in the rice residue biomass and the carbon‐to‐nitrogen ratio (C/N) under elevated [CO 2 ] (e[CO 2 ]) and air temperature (e T air ) for 2 years with naturally varying weather conditions. Rice was cultivated under different [CO 2 ]– T air for 2019–2020, with longer sunshine hours and solar radiation ( R solar ) during rice growing period in 2019 (675 h and 2079 MJ m −2 , respectively) than in 2020 (589 h and 1929 MJ m −2 , respectively). Rice biomass (grains, straw and roots), C gain and N uptake were measured, and C/N was determined. Compared to the ambient conditions, e[CO 2 ]–e T air consistently increased straw and roots biomass for both years by 38.7% and 137.2% in 2019 and by 46.0% and 76.2% in 2020, respectively. However, under e[CO 2 ]–e T air , C/N increased in 2019 (by 14.5%–31.6%), but decreased in 2020 (by 10.0%–12.2%) compared to ambient conditions. Comparing both years, straw and roots biomass were lower in 2020 than in 2019 by 19%–31% and by 31%–58%, respectively, with decreased C/N in 2020 by up to 32%. These results indicate that e[CO 2 ]–e T air coupled with lower R solar produces lower‐quantity rice residues with high quality (i.e., a lower C/N) compared to those with higher R solar , thus potentially reducing SOC accrual compared to higher R solar conditions.