Soil carbon dioxide flux and rice photosynthesis

Abstract

Abstract Measurement of CO2 concentration in air at 25 em below and 100 em above the canopy of a good rice crop indicated that a severe CO2 deficit occurred around the photosynthetic surface of crop when light intensity was high. Soil CO2 flux as measured by the soda lime method in a closed system ranged from 3.9 to 5.7 g.m-2. day-1 under flooded conditions and from 6.0 to 8,6g.m-2 .day-1 under drained conditions. Cropped soil released more CO2 than bare soil under both flooded and drained conditions. The estimated contribution of soil CO2 to gross photosynthesis was 6%, for the flooded soil and 7% for the drained soil or a contribution of 9 and 12% to net dry matter production. These results together with other information indicate that atmospheric CO2 is the most important source of CO2, in crop photosynthesis, soil CO2 released into atmosphere Is second most important, and soil CO2 absorbed by plant roots is almost negligible.