Study On Photosynthetic Physiology Of Two Ecotypes Of Phalaenopsis Pulcherrima Under Different Light Conditions

Phalaenopsis pulcherrima is a perennial evergreen herb of Phalaenopsis in Orchidaceae.In the natural state,there are two kinds of different ecotypes:red leaf back and green leaf back.Due to the influence of light,its population distribution in the wild habitat is different.In this experiment,the photosynthetic characteristics of leaves,pseudobulbs,flowers,roots and other organs of P.pulcherrima were studied.Three light intensity treatments were set up from the light factors to study the physiological and biochemical characteristics and photosynthetic fluorescence characteristics of P.pulcherrima,to understand the difference of light utilization under different light conditions,and to explore the adaptability of P.pulcherrima under different light conditions,so as to provide a certain theoretical basis for introduction and domestication.This study mainly obtained the following results:（1）The leaves are the main photosynthetic organs of P.pulcherrima,the pseudobulbs and roots are the auxiliary organs for photosynthesis.In contrast,the lip petals have the weakest photosynthetic capacity and contribute less,but their ability to utilize weak light is the largest.（2）The leaf thickness of the red-backed P.pulcherrima did not change significantly under different light treatments.The leaf thickness of the green-backed P.pulcherrima under the T2 light treatment gradually decreased.（3）The chlorophyll a,b and chlorophyll（a+b）contents of two ecotype orchids under low-light treatment T1 showed a rising trend.The chlorophyll a,b and chlorophyll（a+b）contents were the lowest under the highest light treatment T3.（4）The photosynthetic efficiency of the red-backed P.pulcherrima under T2 light intensity treatment is the highest,with P_max reaching 0.412μmol·m^-2·s^-1.The P_max of the green-backed P.pulcherrima decreased with the increase of light intensity in different treatments.P_max,LSP and LCP were the highest under the lowest light T1 treatment,which were 0.415μmol·m^-2·s^-1、263.405μmol·m^-2·s^-1、5.154μmol·m^-2·s^-1.（5）The A_max of the red-backed P.pulcherrima in different light treatments is greater than that of the green-backed,and the A_max of the two ecological types of P.pulcherrima at the CO₂ saturation concentration is higher than that at light saturation.（6）The red-backed P.pulcherrima has a higher actual photochemical efficiency than the green-backed P.pulcherrima.（7）The electron transfer rate of the two ecotypes of P.pulcherrima under the minimum light T1 treatment decreased.The Y（Ⅱ）,ETR,q P,and NPQ curves of the red-backed P.pulcherrima are higher than those of the green-backed P.pulcherrima.（8）The red-backed P.pulcherrima adapts to low light conditions by adjusting the opening of the stomata.Too low light conditions destroy the Rubisco and PEPC functions of its leaves,affect the accumulation of malic acid at night,and reduce the photosynthesis efficiency.The performance of the green-backed P.pulcherrima is exactly the opposite.The leaf stomatal density,stomatal opening,and diurnal accumulation of malic acid all increase as the light intensity of the light treatment decreases,and are not suitable for growth under strong light.Based on the above results,it can be concluded that the type of leaf blade abaxially red grows best under the light intensity of 60μmol·m^-2·s^-1,and the light intensity of 20μmol·m^-2·s^-1 is suitable light intensity for growth of the type of leaf blade abaxially green.