The effects of long-term, partial shading on growth and photosynthesis in Pinus radiata D. Don trees

摘要

Two 8-year-old Pinus radiata trees growing in a dry-land plantation forest were subjected to a partial shading treatment for 2 years in order to investigate the responses of photosynthesis and tree growth to a long-term reduction in illuminated leaf area. The lower 60% of the crown of shaded trees was surrounded by 50% neutral density shade cloth. This reduced radiation absorption by 13% for the trees as a whole compared to the control trees during the first year, while modelled annual whole-canopy photosynthesis was 9% lower, and was strongly regulated by seasonal soil water availability, temperature and irradiance. The shaded trees responded by increasing carbon partitioning to the branches, at the expense of the stem, As a result, basal area growth of the shaded trees was almost 50% lower than that for control trees.