Phalaenopsis efficiently acclimate to highlight environment through orchid mycorrhization

Abstract

Phalaenopsis (Phalaenopsis amabilis ‘KC1410’) grow slowly and experience photoinhibition during the daytime. Thus, this study used orchid mycorrhizal (OM) fungus to promote orchid growth hypothetically via increasing the photoacclimation capacity of Phalaenopsis in response to high light (HL). By combining chlorophyll fluorometer and spectral reflectance techniques, the influences of OM colonization on the growth potentials and the photosynthetic performance of HL-grown Phalaenopsis were investigated. OM symbiosis significantly promoted the growth of HL-grown orchids, such as leaf span, fresh weight, and dry weight. Consistent with these observations, OM symbiosis obtained higher value of normalized difference vegetation index (NDVI) and enhanced CO2 uptake rate. This could be attributed to an increase in photosynthetic performance in OM plants. Notably, maximum quantum efficiency of PSII photochemistry (Fv/Fm) was not altered by OM symbiosis, however, the light-adapted fluorescence measurements of PSII operating efficiency (ФPSII) and electron transport rate (ETR) were increased. Nevertheless, OM orchids had higher photochemical quenching (qP) and lower non-photochemical quenching (NPQ). This indicates a relative higher photosynthetic performance and radiation-use efficiency (RUE) in OM plants. The photochemical reflectance index (PRI) as a photoprotection indicator was also enhanced. Based on these results, we proposed that OM symbiosis increases both the photosynthetic performance and the RUE in the HL-acclimated Phalaenopsis, resulting in an advantage to the OM plants to survive the HL stress.