Seasonal progression of photoprotection responses in different aged savin juniper plants under shade and sun

In savin juniper, age and season can affect photosynthesis, chlorophyll fluorescence and photoprotective pigments. In spring, 2-year-old plants had more lutein than 5-year-olds, but the reverse occurred during summer and autumn. Savin juniper is an endemic evergreen shrub in the Mu Us Desert, where it establishes only with the protection of larger plants. Ultimately, established plants emerge into full sunlight as they grow. To explore how photoprotection responses change during this transition, a pot study was established under field conditions with three sunlight regimes (10%, 50% and 100% light transmittance) and two age cohorts (1- and 4-year-old rooted scions). To avoid potentially confounding effects of differences in leaf form, after one year we measured photosynthesis, chlorophyll fluorescence and foliar pigments of 2- and 5-year-old savin juniper on a monthly basis from April to October. For gas exchange and fluorescence variables, there were no interactions between cohort and sunlight except for intrinsic water-use efficiency in June; however, there were many interactions regarding pigment concentrations and ratios. Generally, 5-year-old plants had higher mean chlorophyll, total carotenoids, and chlorophyll a/b ratios than 2-year-old plants, but lower mean β-carotene/α-carotene ratio, zeaxanthin and lutein. Plants under brighter light had lower mean lutein. There were obvious changes in β-carotene/α-carotene, zeaxanthin and lutein in June, July and August, respectively. Under 100% sunlight, lutein concentration was higher in 2-year-old than 5-year-old plants from April to June, but this pattern reversed from July to October. The effects of age and season, in addition to the prevailing light regime, need to be considered when investigating the role of carotenoids in photoprotection.