Seasonal and year to year variation in performance of Gordonia acuminata seedlings in different light environments

Abstract

The effects of light environment on temporal growth and allocation patterns in the subtropical Chinese evergreen tree Gordonia acuminata, a gap-dependent species, were studied during its first 2 years of growth. Seedlings were grown in full sun (S100), 55% of full sun (S5S), 33% of full sun (S33), and 18% of full sun (S18). During the 1st year, plant size and leaf dynamics were monitored nondestructively. The best growth was at S33. Growth rates fluctuated more from season to season in treatments of higher relative light exposure, largely owing to sun-imposed inhibition of growth in summer. Leaf size was to a large extent ontogenetically determined. Additionally, a size reduction with increasing light exposure was shown for individual leaves that had expanded during a given ontogenetic phase. In the 2nd year relative growth was best at S55 (first 6 months) and in full sun (second 6 months), successively, which resulted in S55 plants outgrowing the initially bigger S33 plants. Self-shading and smaller relative investment in leaf area were associated with a reduction of sun-imposed inhibition and thus with enhanced growth in sun in the 2nd year. The large seasonal and year to year variation in growth response to relative light exposure may have important consequences for the success of young Gordonia plants in gaps of different sizes or formed in different seasons. Key words: broad-leaved evergreen seedlings, gaps, growth, morphology, ontogeny, seasons, subtropical China.