Application of the rapid leaf A-C_i response (RACiR) technique: examples from evergreen broadleaved species

Using steady-state photosynthesis-intercellular CO₂ concentration (A-C_i) response curves to obtain the maximum rates of ribulose-1,5-bisphosphate carboxylase oxygenase carboxylation (V_cmax) and electron transport (J_max) is time-consuming and labour-intensive. Instead, the rapid A-C_i response (RACiR) technique provides a potential, high-efficiency method. However, efficient parameter settings of RACiR technique for evergreen broadleaved species remain unclear. Here, we used Li-COR LI-6800 to obtain the optimum parameter settings of RACiR curves for evergreen broadleaved trees and shrubs. We set 11 groups of CO₂ gradients ([CO₂]), i.e. R1 (400-1500 ppm), R2 (400-200-800 ppm), R3 (420-20-620 ppm), R4 (420-20-820 ppm), R5 (420-20-1020 ppm), R6 (420-20-1220 ppm), R7 (420-20-1520 ppm), R8 (420-20-1820 ppm), R9 (450-50-650 ppm), R10 (650-50 ppm) and R11 (650-50-650 ppm), and then compared the differences between steady-state A-C_i and RACiR curves. We found that V_cmax and J_max calculated by steady-state A-C_i and RACiR curves overall showed no significant differences across 11 [CO₂] gradients (P > 0.05). For the studied evergreens, the efficiency and accuracy of R2, R3, R4, R9 and R10 were higher than the others. Hence, we recommend that the [CO₂] gradients of R2, R3, R4, R9 and R10 could be applied preferentially for measurements when using the RACiR technique to obtain V_cmax and J_max of evergreen broadleaved species.