Structure and Function of Rice Root System under FACE Condition

Abstract

The effects of CO2 enrichment on a rice root system was investigated as a part of the Rice-FACE project in 1999, 2000 and 2003. A japonica rice variety, Akitakomachi, (Oryza sativa L.) was grown in irrigated lowland fields. The CO2 concentration in the FACE plots was controlled at 200 μmol/mol above the ambient level. The length and weight of roots were measured at the heading stage. The bleeding rate was measured by using cotton traps as an index of the activity of the whole root system at the heading and the ripening stages. In addition, the bleeding sap was analyzed to determine nitrogen content in 2003. The length and weight of roots were not significantly increased by elevated CO2 except for the root weight in 1999. The specific root length was smaller in the FACE plots than in the ambient plots, suggesting thicker and/or less branching roots under FACE. The bleeding rate per stem was slightly smaller in the FACE than in the ambient plots. The nitrogen content in the bleeding sap at the heading stage was significantly smaller in the FACE plots. These results suggest that physiological activity of roots is not enhanced or somewhat declined by elevated CO2 concentration.