Relationships of photosynthetic capacity to PSII efficiency and to photochemical reflectance index of Pinus taiwanensis through different seasons at high and low elevations of sub-tropical Taiwan

We investigated the relationships of photosynthetic capacity (P (nsat), near light-saturated net photosynthetic rate measured at 1,200 mu mol m(-2) s(-1) PPFD) to photosystem II efficiency (F (v)/F (m)) and to photochemical reflectance index [PRI = (R (531) - R (570))/(R (531) + R (570))] of Pinus taiwanensis Hay. needles at high (2,600 m a.s.l) and low-elevation (800 m a.s.l) sites through different seasons. Results indicate that at high-elevation site, P (nsat), F (v)/F (m) and PRI (both measured at predawn) paralleled in general with the air temperature. On the coolest measuring day with the minimum air temperature dropping to -2A degrees C, P (nsat) could decrease to ca. 15% of its highest value, which was measured in autumn. At low-elevation site, with the minimum air temperature of 10-12A degrees C in cooler season and almost no seasonal variation of F (v)/F (m), P (nsat) dropped to ca. 65% of its highest value and PRI decreased ca. 0.02 in winter. Even though seasonal variation of P (nsat) was affected by many factors, it was still closely related to PRI based on statistical analyses using data from both sites, through different seasons. On the contrary, seasonal variation of F (v)/F (m) of P. taiwanensis needles was influenced mainly by low temperature at high elevation. Therefore, the correlation of P (nsat) - F (v)/F (m) was lower than that of P (nsat) - PRI when data combined from both high- and low-elevation sites were analyzed. It is concluded that predawn PRI could be used as an indicator to estimate the seasonal potential of photosynthetic capacity of P. taiwanensis grown at low- and high-elevations of sub-tropical Taiwan.