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

Previously, we found a significant association between photosystem II efficiency (I broken vertical bar PSII) and photochemical reflectance index (PRI) measured at predawn among different species at different elevations and throughout several seasons. However, this relationship has not been evaluated under varied levels of illumination. Here, we used the Taiwan species Pinus taiwanensis (a conifer distributed at 750-3,000 m a.s.l.), Stranvaesia niitakayamensis (an evergreen tree, 1,700-3,100 m) and two Miscanthus spp. (perennial C-4 Gramineae, coastline-3,200 m) to elucidate the I broken vertical bar PSII-PRI relationship. We studied six levels of photosynthetic photon flux density (PPFD) (0, 200, 400, 800, 1,200 and 2,000 mu mol m(-2) s(-1)) over several growth seasons at high (2,600 m a.s.l.) and low (800 m a.s.l.) elevation sites. In comparing the same species or genus, I broken vertical bar PSII and PRI were closely correlated in darkness or under the same level of PPFD, with data obtained from different seasons and elevations pooled for regression analysis. Because both the intercept and slope of the I broken vertical bar PSII-PRI equation showed a negative curvilinear correlation with PPFD, we could fit an empirical regression model, I broken vertical bar PSII = c + d center dot ln(PPFD) + e center dot[ln(PPFD)](2) + f center dot PRI + g center dot PRI center dot ln(PPFD) + h center dot PRI center dot[ln(PPFD)](2), for multiple regression analysis. Using this model, we found a close correlation between the estimated and measured I broken vertical bar PSII (r (2) = 0.842-0.937, P < 0.001) for all four species examined and for mango (Mangifera indica) measured under both artificial illumination and sunlight (data from Weng et al. 2010). This empirical regression model could simulate both seasonal and diurnal variations of leaf-scale photosynthetic efficiency at high and low elevations