中粒种咖啡光合特性的研究

PHOTOSYNTHESIS OF COFFEA CANEPHORA

自然状态下中粒种咖啡树冠外围向阳叶的光合速率及叶绿素 a/b 值均较树冠内部荫蔽叶大,但叶绿素含量和相等叶面积叶绿素的光谱吸收量却较小。与自然状态相同,人工遮荫叶的光合速率和叶绿素 a/b 值均较不遮荫的同龄叶小,但叶绿素含量和相等叶面积叶绿素的光谱吸收却较大。在低光照强度时,向阳叶和荫敝叶的光合速率部随光照强度的增加而提高,但光照强度超过一定值时,光合速率下降,即发生光抑制。发生光抑制的光照强度,向阳叶大于荫蔽叶。向阳叶光合作用的光饱和点和 DCPIP 光还原活性最大时的光照强度出都大于荫敝叶。呼吸作用和代表光呼吸的乙醇酸氧化酶活性也以树冠外围的向阳叶为大。中粒种咖啡的光合速率对低温敏感,在3万勒克司光照强度和高浓度 CO_2 条件下,光合作用的低温界限约在10℃。但温度高达35℃时,光合速率仍未见下降。

Under field natural conditions,unshade leaves on outer crown of Coffea cane-phora possessed higher photosynthetic rate and chlorophyl a/b ratio but lower chlo-rophyl content and spectrum absorption by chlorophyl in equal unit leaf area thanthose shade leaves on inner crown.This was also true under artificial shading con-dition in which,however,the shaded leaves on outer crown had higher chlorophylcontent and spectrum absorption.At low light intensity,the photosynthetic rate of both the shade and unshadeleaves rose with the increase of light intensity until certain limit when the pho-tosynthetic rate began to go down.The light intensity at which photoinhibitionoccurred was higher in unshade leaves than those shade ones.The light intensity forlight saturation point to appear and for DCPIP photoreduction activity at maximumwas also higher in unshade leaves.Respiration and glyoxalate oxidase activity thatrepresents photorespiration showed the same tendency.The photosynthetic rate of Coffea canephora was very sensitive to low tempera-ture.At the light intensity of 30000 lux and high CO_2 concentration,the low tem-perature limit for photosynthesis was recorded at 10℃.However,when the tempera-ture was as high as 35℃,no evidence of slow-down of photosynthetic rate wasobserved.