The Effects of High Temperature and Low Illumination on Assimilation of Rice Plants and Its Physiological and Morphological Strategies in Response

水稻為熱帶原產之作物，雖然性喜高溫，但在臺灣之氣候條件下仍然會因溫度過高而影響其產量，況且在第二期作還有日照不足的問題。以同化作用之觀點視之，提高水稻之生產能力可以從提高光合作用及減少呼吸消耗兩方面著手。葉片較厚的水稻品種，在強光下其單葉光合速率雖然較高，但在弱光下之光合能力卻較差，而且因光線較不易透過厚葉，厚葉之單位葉面積呼吸消耗量又較多，故隨著葉面積指數（LAl）之增加，其純同化率（NAR）降低之幅度較大，導致其在繁茂狀態下之乾物累積能力降低。氣孔密度較高及氣孔開度較大之品種，會使氣體容易進出葉片，同時促進光合作用及蒸散作用，而蒸散作用又可冷卻葉片，使光合作用不易受到高溫之抑制，呼吸消耗又不因高溫而增加。而蒸散作用需消耗水分，故需注重根的吸水力及稻體之水份通導能力”此外，由於葉片較長者只要不下垂，其冠層（。anoPy）會較高，故單位葉面積分布的空間會較大，使其葉面積密度降低，有利於冠層內空氣之流通及光合作用之進行，而且長而直立之上位葉也較不易被穗遮光。綜合生理及型態方面的考量，較適合於高溫及低光之環境下栽培的水稻品種，可以考慮選育具備高光合作用及低呼吸消耗，氣孔密度較高、氣孔開度較大，根發達，水分吸收、輸導能力強，高溫稔實佳，以及具有長、薄且不易下垂葉的短稈穗重型品種著手。 High temperature and low solar radiation are the climatic characteristics of Taiwan. These environmental conditions would reduce the photosynthesis and increase the respiratory consumption, and are disadvantageous to the productivity of rice plants. It was reported that varieties with lower respiratory rate could decrease the respiratory consumption. Varieties with longer, thinner and erect leaves provides better light and air transmission to canopy. Varieties with higher stomatal density and opening and physiological activity in root system have advantages in photosynthesis and transpiration. For breeding purposes, it is suggested to select the varieties with the aftorementioned physiological and morphological characteristics. Characters such as lower sterility, short cuim, and grester panicle weight are appropriate strategies for rice in response to conditions of high temperature and low illumination