The role of rice plants in regulating mechanisms of methane missions

 Rice plants play a pivotal role in different levels of the methane (CH₄) budget of rice fields. CH₄ production in rice fields largely depends on plant-borne material that can be either decaying tissue or root exudates. The quantity and quality of root exudates is affected by mechanical impedance, presence of toxic elements, nutrient deficiencies, water status of growing medium, and nitrogenase activity in the rhizosphere. CH₄ oxidation in rice fields is localized in the rhizosphere where the concentration gradients of CH₄ and oxygen overlap. CH₄ oxidation capacity is a function of the downward transport of oxygen through the aerenchyma, which, in turn, also acts as a conduit for CH₄ from the soil to the atmosphere. The decisive step in the passage of CH₄ through rice plant is the transition from root to stem. However, rice plants show an enormous variety of morphological and physiological properties, including differences in root exudation and gas transfer capacity. Comparative studies on different cultivars are deemed crucial for accomplishing a better understanding of the mechanisms of CH₄ consumption in the rhizosphere and CH₄ transport through the rice plant as well as the interaction of these processes. The results of such studies are considered tools for devising mitigation options. Received: 7 April 1999