Characteristics of photosynthesis and light energy partitioning in Amorphophallus xiei grown along a light-intensity gradient.

Abstract

The objective of the present study was to examine the adaptation strategy of Amorphophallus xiei, a shade-demanding species, grown under different levels of light intensity. The responses of leaf to photosynthetic active radiation, CO2 and simulated sunflecks were analyzed in A. xiei grown under 100% (high light), 32.6% (moderate light) and 5.98% (low light) of full sun. Meanwhile, chlorophyll a fluorescence parameter and light energy partitioning were also recorded and calculated in the above-mentioned responsive process. The results showed that in most cases, the maximum photosynthetic rate (Pmax), dark respiration rate, apparent quantum yield and carboxylation efficiency in A. xiei significantly decreased with increasing the light level, however, the light compensation point, CO2 compensation point significantly increased. The photosynthetic induction was quicker in individuals grown under moderate light (P<0.05), and the initial stomatal conductance (gs-i) during dark adaptation increased significantly with increasing the light level. There was a ne-gative correlation between gs-i and the time required to reach 30%, 50% and 90% of Pmax during the process of photosynthetic induction. Moreover, the values of actual photochemical efficiency of PS2 (ΔF/Fm') in the light, phototochemical quenching of chlorophyll fluorescence (qP) and photosynthetic electron transport rate (ETR) were higher and non-photochemical quenching (NPQ) recorded in photosynthetic induction was also higher in individuals grown under high light, nevertheless, the maximum photochemical efficiency of PS2 in the light (Fv'/Fm') was higher in individuals grown under low light. The proportion of light energy allocated to non-photochemical quenching (ФNPQ) was lower in individuals grown under high light, and, correspondingly, it was higher in ones grown under low light. The results obtained here suggested that, when exposed to high light stress, moderate- and low-light-grown A. xiei would activate the mechanism of energy dissipation to protect itself from injury. Correspondingly, high-light-grown individuals would employ the strategy of increasing heat dissipation and forming quenching complex to cope with high light stress, which, however, might be one of reasons for the sensitivity of A. xiei to high light environment.