期作間水稻光合成物質供需平衡關係之比較

Abstract

於水稻分蘖盛期至完全成熟止，每週採取水稻分蘗，自上至下依但山立區分葉片、葉鞘與莖，穗部為另一單位，測定全氮與非構造性碳水化合物（TNC）之濃輩與含量，以瞭解水稻之生產潛能與可能之限制因子。 稻株抽穗期之葉片與葉鞘乾重以二期作稍高，但全株乾重則較一期作略低；成熟期一期作之全株與穗乾物量分別較二期作高19.3%與23.0%，顯示較旺盛之光合成能力與有效之乾物質分配。 抽穗時與穀粒有效充實期間之葉片氮素濃度均以二期作點高；就稻株含氮量而言，抽穗時二期作超過一期作達26.2%，成熟時則一期作反較二期作多27.3%，表示第二期作水稻生育後期根吸收活力降低，葉片怏速老化；而且係氮素組成，而非濃度，為影響二期作稻生理的重要原因。水稻抽穗前，葉鞘具有貯存多量碳水化合物功能，但抽穗後隨養份之再分配而喪失貯藏功能。一期作水稻屆成熟時，莖部仍含有30%以上之碳水化合物，二期作則濃度幾近於零。就量之變化而言，抽穗時一期作稻株內非構造性碳水化合物合量較二期作高24.5%，成熟時高44.6%，明顯表示生成量與分配效率差異。上述結果配合一期作較高之穗碳水化合物濃度，可推定一期作之貯蓄(sink)容積為產量隊制因子，二期作則貯蓄與供源(source)並為限制因子。 Rice plants were harvested at a week’s interval from maximum tillering stage to one week after maturity. Amount of dry matter, total nitrogen and total nonstructural carbohydrates (TNC) in the leaf blade, leaf sheath, stem and panicle of rice tillers were analyzed. The purpose was to investigate the balance between supply and demand of N and TNC during grain-filling. At the time of heading, dry weights of leaf blade and leaf sheath were heavier for the second crop rice whereas that of the whole tiller was heavier for the first crop rice. At maturity, dry weights of whole tiller and panicle of the first crop were 19.3% and 23.0%, respectively, higher than those of the second crop, indicating active assimilation and efficient dry matter distribution of the former. Nitrogen concentration of the leaf blade was higher for the second crop during grain-filling. As for the amount of N present in the whole tiller, the second crop rice contained 26.2 % more N at heading but the first crop rice contained 27.3% more N at maturity. The results suggested low absorption ability of the root system and early leaf senescence of the second crop rice during this period. Furthermore, the composition, rather than concen-tration, of N was critical for the physiological activities of the second crop rice. Leaf sheath was able to store carbohydrate before heading. However, such ability was lost after heading with the redistribution of available carbohydrate to panicle. TNC concentration in the stem of the first crop rice was as high as 30% at harvest whereas that of the second crop rice was nil. In terms of TNC amount present in the rice tiller, the first crop rice was 24.5% and 44.6% higher than the second crop rice at heading and maturity, respectively. In other words, differences in the efficiency of photosynthate production and distribution between crops were observed. The above results, along with the higher TNC concentration in the panicle of the first crop rice, indicated that the limiting factor(s)for grain yield was sink size for the first crop and were sink size and source ability for the second crop rice.