Chin J Plan Ecolo ›› 2003, Vol. 27 ›› Issue (5): 617-623.DOI: 10.17521/cjpe.2003.0089

• Research Articles • Previous Articles     Next Articles

Photosynthetic Induction in Seedlings of Six Tropical Rainforest Tree Species

CAI Zhi-Quan, CAO Kun-Fang, ZHENG Li   

  • Published:2003-05-10
  • Contact: YU Hua and Bee-Lian ONG

Abstract:

In order to investigate the differences in capacity of sunfleck utilization between species with different ecological characteristics, the photosynthetic characteristics and photosynthetic induction responses were examined with LI-6400 portable photosynthesis system in seedlings of six tropical rainforest species acclimated in simulated understory light environment for more than one and a half years. The species studied were Mallotus macrostachys, a pioneer species, Pometia tomentosa, Shorea chinensis, Barringtonia pendala, Linociera insignis, Lasianthus hookeri, four canopy species and an extremely shade-tolerant understory shrub. After leaves were shaded in darkness for 3 h, photosynthetic induction was measured under optimum temperature ((26±1.2) ℃) and humidity (75%±5%) and normal ambient CO2 ((400±0.5) μmol CO2·mol-1 air) in the morning. The time courses of induction varied from a sigmoidal to a hyperbolic increase in net photosynthesis. The time required to reach 90% of maximum net photosynthetic rate differed among species, and was short (4.4-12.5 min), which was consistent with induction times reported in other tropical shade-tolerant species. Seedlings of M. macrostachys and L. hookeri were induced two to three times more quickly than the other four canopy species. The response of attaining maximal stomatal conductance significantly lagged behind the increase in net photosynthetic rate during the induction course. When fully induced leaves were shaded in darkness for 20 min, loss of induction was moderate in all species. Among these species, seedlings of M. macrostachys had a relatively rapid induction loss, which was due to rapid loss of stomatal conductance and biochemical factors. The loss of B. pendala was mainly due to biochemical limitation as stomatal conductance decreased only slowly. Seedlings of L. hookeri showed the slowest loss of induction as a result of maintaining higher relative stomatal conductance and maximum carboxylation capacity. Thus this effective utilization of sunflecks is likely to be a critical determinant of growth and generation for understory species.