Light and irrigation effects on chlorophyll fluorescence depend on seedling provenance in Magnolia pugana endemic of Mexico

Abstract

In riparian forests, light and water are two important factors for plant acclimation to different environments. We evaluated the effect of different light and irrigation regimes on the effective quantum yield of photosystem II (фPSII), the maximum quantum efficiency of photosystem II (Fv/Fm), and the electron transfer rate (ETR) of Magnolia pugana seedlings that come from wild and cultivated plants, under greenhouse conditions. Rapid light curves (RLCs) were performed to obtain the maximum apparent electron transport rate and the saturating photosynthetic photon flux density for PSII. Effective quantum yield of PSII was higher at afternoon for cultivated and wild provenances, but in the latter decreased in longest water deficit treatment at noon. The combined water deficit and high light stress in the morning decreased фPSII; however, фPSII recovered in the afternoon, suggesting dynamic photoinhibition. Furthermore, фPSII of wild and cultivated seedlings in all irrigation levels showed dynamic photoinhibition as well. The electron transfer rate was higher for seedlings grown under high light than in shade. ETR results suggest that wild seedlings showed greater tolerance to water deficit conditions than cultivated ones. Rapid light curves indicate that photosystem II of M. pugana seedlings grown in high light conditions requires higher light intensities to reach saturation. In conclusion, wild and cultivated populations of Magnolia pugana seedlings showed photochemical adjustments to tolerate water deficit and light stress. This study offers new insights into the physiology of endangered plants and valuable guidance for conservation efforts designed at protecting in situ and ex situ wild Magnolia species.