Effects of shading on photosynthesis characteristics of Photinia x frasery and Aucuba japonica var. variegata

This paper studied the effects of different shading (light transmittance 20%, 40%, 60%, and 100%) on the photosynthesis characteristics of two ornamental foliage plants Photinia x frasery and Aucuba japonica var. variegata. After shading for six weeks, the net photosynthesis rates of two plants measured ex situ under natural light enhanced, compared to those measured in situ, and, with the increase of shading degree, the net photosynthetic rates had an increasing trend, with the maximum being 9.7 micromol x m(-2) x s(-1) for Photinia x frasery and 8.3 micromol x m(-2) x s(-1) for Aucuba japonica var. variegata. In the meantime, the transpiration rates of the two plants increased significantly. Shading increased the chlorophyll a, b, and a+b contents and the chlorophyll/carotenoids ratio, decreased the chlorophyll a/b, but less affected the carotenoids content. The phenotypic plasticity index (PPI) of net photosynthesis rate and transpiration rate of Photinia x frasery and Aucuba japonica var. variegate was 2.08 and 3.21, and 0.55 and 1.60, respectively. The chlorophyll and carotenoids contents of the two plants were relatively stable, indicating the minor influence of external environment factors on pigments. Aucuba japonica var. variegata had a higher shading tolerance than Photinia x frasery.