Submergence of Rice. II. Adverse Effects of Low CO₂ Concentrations

Abstract

Submergence of rice in water at low CO₂ concentrations was studied in phytotron experiments using plants in the 3rd to 4th leaf stage. Cultivars known to differ in tolerance to complete submergence were adversely affected by the same mechanisms but to a different degree. Submergence for 4-12 days either reduced dry weight production of the whole plant by 6 to 10 fold or even resulted in a loss of dry weight. Nevertheless, the emerging leaf elongated, and both ethanol insoluble material and protein content increased with time. These increases were associated with translocation of dry matter and nitrogen from expanded to expanding leaves.

Submergence also reduced concentrations of soluble sugars and starch in all plant parts by 4 to 12 fold. In contrast, concentrations of potassium and free amino acids in shoots were either the same or, in the case of the emerging leaf, higher than in plants which were not submerged. These results indicate (i) these solutes were not limiting growth and (ii) the tissues retained their semipermeability to these solutes during submergence.

Insufficient capacity of root metabolism in submerged plants was indicated by low rates of respiration, which persisted in the presence of glucose, and by a low ability to consume ethanol.

A model is presented on the adverse effects of submergence of rice which considers possible interactions between CO₂, low O₂ and high ethylene concentrations.