Temperature response and photoinhibition investigated by chlorophyll fluorescence measurements for four distinct species of dipterocarp trees

Abstract

The effects of strong light in combination with elevated temperatures on the photosynthetic system were examined in 4 dipterocarp tree species with ecologically different habitats. The 4 dipterocarp tree species were: Shorea platyclados originated from upper dipterocarp forests, Shorea parvifolia– lowland and hill dipterocarp forests, Shorea assamica– lowland dipterocarp forests, and Dipterocarpus oblongifolius– riparian fringes. S. platyclados and D. oblongifolius have higher growth and survival rates in open sites than S. parvifolia and S. assamica. Tolerance of high temperature among the species was assessed by determining the critical temperatures (Tc) at which the minimal fluorescence (Fo) began to rise sharply. This was measured by exposing plants to an increasing temperature of about 1°C min−1. The intrinsic thermotolerance of the thylakoid membrane appears to be the highest for D. oblongifolius (Tc=46.4°C), intermediate for S. platyclados (45.7°C), and lowest for S. parvifolia and S. assamica (45.2 and 45.3°C, respectively). The temperature‐dependent efficiency of PSII electron transport (ΔF/F′m), photochemical quenching (qP), and the efficiency of light capture of open PSII (F′v/F′m) were measured at the photosynthetic steady state at least 10 min after the light exposure (180 μmol m−2 s−1 PFD). Stable temperature responses of ΔF/F′m and qP were observed in S. platyclados and D. oblongifolius, while those in S. parvifolia and S. assamica were more temperature‐dependent and severely affected at 45°C. Little difference was observed in temperature‐dependent F′v/F′m among species. Photoinhibitory light exposure (1600 μmol m−2 s−1 PFD) for 2 h at 40°C had little effect on the recovery kinetics from photoinhibition of S. platyclados and D. oblongifolius compared with those at 35°C. In contrast, the recovery from photoinhibition was retarded in S. parvifolia and S. assamica. These findings suggest that even at 40°C, a temperature below Tc, an exposure to strong light exacerbated photoinhibition in S. parvifolia and S. assamica corresponding to the closure of PSII reaction centers, as indicated by the decrease in qP at this temperature. Thus, S. platyclados and D. oblongifolius, which occur at uplands and riparian fringes with frequent disturbances, are suggested to have higher photosynthetic tolerance to elevated temperatures contributing to a circumvention of photoinhibition.