氮肥使用量對大豆(高雄選10號)和毛豆(高雄3號)碳氮代謝之影響

Abstract

本研究以大豆品種高雄選10號（Glycine max (L.) Merr.cv. Kaohsuing Sel. 10）及毛 豆品種高雄三號（Glycine max (L.)Merr. cv. Kaohsuing 3）為材料，以尿素為氮源，進 行不同氮肥量處理，分別 在開花期及種子充實期進行採樣、分析，探討不同氮肥量處理對大豆及毛 豆碳、氮代謝之影響。 實驗結果顯示，氮肥量處理在品種之間及生育時期之間，有不同程度的影 響。增施氮肥處理，對大豆葉片CO2同化速率之影響程度大於毛豆。增施 氮肥處理，導致大豆和毛豆葉片呼 吸率降低。呼吸作用可產生能量及碳 架，以供其他生化反應之進行，而增施氮肥，導致呼吸率降低，將減少碳 架之供應，不利於其他生化反應。 從乾物分配於葉片、莖及莢果的比率，來探討光合成產物分配之情形，發 現加倍氮肥量及三倍氮肥量處理，可降低大豆乾物分配於葉片和莖的比率 ，增加乾物分配於莢果的比率，而四倍氮肥量處理之分配情形與不施氮肥 處理者相若；對毛豆而言，氮肥量處理並不影響其分配於葉片、莖及莢果 的比率。然而五種不同氮肥量處理，對大豆和毛豆之收穫指數並無明顯影 響，推測其與光合成產物不能充分轉流至莢果有關。 在開花期和種子充實期，大豆和毛豆葉片之麩胺酸脫氫還原酵素活性遠高 於醯胺麩胺酸合成酵素活性；但增加氮肥量處理，可提高大豆和毛豆之醯 胺麩胺酸合成酵素活性，卻未能提高麩胺酸脫氫還原酵素活性，故大豆和 毛豆在高氮環境下，主要是以醯胺麩胺酸合成酵素路徑來代謝銨鹽。另外 ，大豆和毛豆在開花期、種子充實期，植株內之glutamate含量遠高於 glutamine，顯示麩胺酸還原酵素可能亦參與代謝銨鹽。開花期和種子充 實期之大豆、毛豆 植株中含量最高之胺基酸為asparagine，醯胺類胺基 酸（glutamine及asparagine）可經由 簡單之轉胺作用合成其他種類之胺 基酸，不需要消耗太多能量，可能有利於正在發育之莢果利用。大豆種子 含大量蛋白質約33.1~49.2 %，因此，在種子充實時，葉片中之 asparagine 轉運至種子後有利於合成蛋白質。 增施氮肥可提高大豆和毛豆之光合成速率，但對氮代謝並無促進之效果， 且葉片內含大量的氮素，無法充分將氮素完全轉移至莢果，故氮素同化作 用及產量間的關係並不單純。有待進一步探討氮素累積於葉片中與種子生 長間之關係，以明瞭本省栽培大豆和毛豆之氮素利用效率是否為限制種子 乾物質生產的因子。

Our research focused on soybean cultivar Kaohsuing Sel. 10(Glycine max (L.) Merr. cv. Kaohsuing Sel. 10) and vegetable soybean cultivar Kaohsuing 3 (Glycine max (L.) Merr. cv. Kaohsuing 3). We treated the samples with different amounts of nitrogen fertilization using urea as a nitrogen source, and analyzed its effects on the carbon and nitrogen metabolism of the leaves during the flowering stage and seed filling period. The experimental results showed that there were different levels of influence of nitrogen treatment to different cultivars and their growth stages.The effectsof the addition of nitrogen treatment affected leaf CO2 assimilatory rates more on the soybean than the vegetable soybean. The addition of nitrogen led to a decrease of respiratory rate of both soybean and vegetable soybean leaves,which resulted in discrepancy of carbon skeleton and thus the consequential biochemical reactions. In addition,the yield was affected by assimilate translocation and distribution. Twofold and threefold nitrogen treatments raised the ratio of assimilates partitioning to the soybean pod while there were no obvious effects of which to the assimilates partitioning in vegetable soybean.But, there were noobvious effects on the harvest index,perhaps being attributed to of both soybeanand vegetable soybean under different amounts of nitrogen fertilization.It mightbe the failure of efficient translocation of assimilates to pods. During the flowering and seed filling stages, the glutamate dehydrogenase activity of soybean and vegetable soybean leaves was higher than the glutamine synthetase activity. The addition of nitrogen fertilization increased the glutamine synthetase activity and yet it was unable to increase the glutamate dehydrogenase,therefore under the high nitrogen situation, soybean and vegetablesoybean used glutamine synthetase pathway to metabolise ammonium in leaves.Otherthan this, during the flowering and seed filling stages, the glutamate contents were higher than glutamine inside the soybean and vegetable soybean leaves.Whichindicated that glutamate dehydrogenase took part in metabolising the ammonium. During the flowering and seed filling stages, asparagine, the highest quantityamino acid could be used to synthesize other amino acids through transamination without consuming too much energies. This was beneficial to the developing pods.Soybean seeds contain a large amount of protein (about 33.1% to 49.2%),therefore, during the seed filling stage, it was beneficial to protein synthesis as the asparagine contained in the soybean leaves to transport to the seeds. We found that addition of nitrogen fertilization raised the photosynthetic rate in both soybean and vegetable soybean and yet it had little effects in the nitrogen assimilation and thus was unable to translocate the ample nitrogen contained in the leaves to the pods. Therefore, there was no trivial correlationbetween the nitrogen assimilation and the yields. Further studies about the correlation of seed growth and the nitrogen content in the leaves must be done in order to understand that whether the assimilation and partioning efficiency of soybean and vegetable soybean is a restrictive factor to the seed growth.