Department of Botany, University of Hawaii, 3190 Maile Way, 96822, Honolulu, Hawaii, USA.
Photosynth Res. 1984 Dec;5(4):325-34. doi: 10.1007/BF00034977.
The effect of irradiance on the rate of net photosynthesis was measured for mature leaves of coffee grown under five levels of radiation from 100% to 5% daylight. The rate of light-saturated photosynthesis per unit leaf area (PNmax) increased from 2 μmol CO2 m(-2) s(-1) under 5% daylight to 4.4 μmol CO2 m(-2) s(-1) under 100% daylight. The photon flux density (PAR, photosynthetically active radiation) needed for 50% saturation of photosynthesis, as well as the light compensation point, also increased with increasing levels of irradiation during growth. The quantum efficiency of photosynthesis (α), measured by the initial slope of the photosynthetic response to increasing irradiance, was greater under shaded growth conditions. The rate of dark respiration was greatest for plants grown in full daylight. On the basis of the increase in the quantal efficiency of photosynthesis and the low light compensation point when grown under shaded conditions, coffee shows high shade adaptation. Plants adjusted to shade by an increased ability to utilize short-term increases in irradiance above the level of the growth irradiance (measured by the difference between photosynthesis at the growth irradiance, PNg, and PNmax).
光照对净光合速率的影响是在五种辐射水平下对生长于咖啡成熟叶片进行的，辐射范围从 100%自然光到 5%自然光。单位叶面积的光饱和光合作用速率（PNmax）从 5%自然光下的 2 μmol CO2 m(-2) s(-1)增加到 100%自然光下的 4.4 μmol CO2 m(-2) s(-1)。光合作用的 50%饱和所需的光子通量密度（PAR，光合作用有效辐射）以及光补偿点也随着生长期间辐射水平的增加而增加。通过增加光照强度来测量光合作用的量子效率（α），在遮荫生长条件下更大。在全日照下生长的植物呼吸速率最大。基于光合作用量子效率的增加和在遮荫条件下生长时的低光补偿点，咖啡表现出对遮荫的高度适应。植物通过增加利用生长光照强度以上的短期光照强度增加的能力来适应遮荫（通过生长光照强度下的光合作用（PNg）和 PNmax 之间的差异来衡量）。
