Carbon release from rice roots under paddy rice and maize–paddy rice cropping uri icon

abstract

  • Crop rotations encompassing flooded rice and an upland crop are commonly found in large parts of South and East Asia. However, also rice farmers in Southeast Asia increasingly switch from double-cropping paddy rice to one non-flooded crop-such as maize-in the dry season. We hypothesized that introducing maize (maize-paddy rice, M-MIX) into a double paddy rice (R-WET) cropping system will increase carbon (C) release from rice roots into the rhizosphere and the dissolved soil C pool. To test this hypothesis we assessed the kinetics of C release by the rice plants in a hydroponic greenhouse experiment, and used these data for interpreting their C release in field experiments using C-13 pulse labeling of rice plants. In the greenhouse we observed that rice roots released C-13 labeled dissolved organic carbon (DOC) for 21 days with a mean residence time (MRT) of 19 days after exposure to a (CO2)-C-13 pulse. The MRT of labeled dissolved inorganic carbon (DIC) released from rice roots was only 2 days. In the field (CO2)-C-13 pulse labeling increased the C-13 excess of rhizosphere soil up to 0.7 +/- 0.2 mg C-13 kg(-1) in R-WET and 0.9 +/- 0.3 mg kg(-1) in M-MIX. The C-13 signature of bulk soil remained unaffected. DOC concentrations in R-WET were significantly higher than in M-MIX during the mature grain stage of the rice plants. Nevertheless, the C-13 excess in DOC transiently increased by only 0.5 mu g L-1 after labeling in 13 cm depth in one of three lysimeters previously cropped with maize (M-MIX), while no labeled DOC was detected in 13 cm depth of the R-WET lysimeters and in 60 cm depth of both treatments. In contrast, the C-13 excess of DIC increased by 42.4-93.1 mu g L-1 a few days after labeling with a MRT of 53-66 days in both treatments. Considering the results of the greenhouse experiment, this suggests a rapid mineralization of labeled rhizodeposits in the field and an effective transient storage of CO2 produced by respiration in soil water. (c) 2015 Elsevier B.V. All rights reserved.

publication date

  • 2015
  • 2015
  • 2015