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 (Pnsat, near light-saturated net photosynthetic rate measured at 1,200 μmol m−2 s−1 PPFD) to photosystem II efficiency (Fv/Fm) and to photochemical reflectance index [PRI = (R531 − R570)/(R531 + R570)] 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, Pnsat, Fv/Fm 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 −2°C, Pnsat could decrease to ca. 15% of its highest value, which was measured in autumn. At low-elevation site, with the minimum air temperature of 10–12°C in cooler season and almost no seasonal variation of Fv/Fm, Pnsat dropped to ca. 65% of its highest value and PRI decreased ca. 0.02 in winter. Even though seasonal variation of Pnsat 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 Fv/Fm of P. taiwanensis needles was influenced mainly by low temperature at high elevation. Therefore, the correlation of Pnsat − Fv/Fm was lower than that of Pnsat − 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.