Dynamic variations in the photosynthetic capacity in a leaf's lifetime for five Taiwanese tree species at different successional stages.

摘要

This research investigated the leaf lifespan and dynamic variations in the photosynthetic capacity during the developmental process of a leaf from unfolding, morphological maturity, then to senescence for 5 native broadleaf tree species of Taiwan. Chosen species represent species at different successional stages, including Melanolepis multiglandulosa and Macaranga tanarius (representing early-successional species), Schefflera octophylla (representing a mid-successional species), and Diospyros maritima and D. philippensis (representing late-successional species). For mean leaf lifespans, Mel. multiglandulosa was shortest (107 d), followed by Mac. tanarius (140 d), S. octophylla (236 d), D. maritima (309 d), and D. philippensis (374 d), with significant differences among the 5 species. Patterns of photosynthetic capacity through a leaf's lifetime exhibited a skewed bell-shaped distribution with maximum photosynthetic capacity (A_max) reached either before or after full leaf expansion. A_max values of Mel. multiglandulosa (27.3 micro mol m-2 s-1) and Mac. tanarius (25.4 micro mol m-2 s-1) were reached at 33 and 43 d of leaf age, respectively, which was 1-2 wk before full leaf expansion; A_max values of D. maritima (9.8 micro mol m-2 s-1) and D. philippensis (10.4 micro mol m-2 s-1) were reached at 76 and 106 d of leaf age, respectively, which was 2 and 5 wk after full leaf expansion; A_max values and full leaf expansion occurred at the same time for S. octophylla (17.7 micro mol m-2 s-1). A_max values of both Mel. multiglandulosa and Mac. tanarius were significantly higher than these of S. octophylla, D. maritima, and D. philippensis. Interspecific comparisons revealed significant negative relationships between leaf lifespan and A_max. This relationship, however, was not significant intraspecifically. In each species, the duration when photosynthesis was maintained above 90% of A_max (referred to as a stage of optimal photosynthesis) was approximately 9% of the leaf lifespan. In conclusion, early-successional species possessed a higher photosynthetic capacity and a shorter leaf lifespan, and reached A_max before full leaf expansion, while late-successional species possessed a lower photosynthetic capacity and a longer leaf lifespan, and generally reached Amax after full leaf expansion.