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

Using steady-state photosynthesis–intercellular CO 2 concentration ( A – C i ) response curves to obtain the maximum rates of ribulose-1,5-bisphosphate carboxylase oxygenase carboxylation ( V c max ) 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 CO 2 gradients ([CO 2 ]), 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 c max and J max calculated by steady-state A–C i and RACiR curves overall showed no significant differences across 11 [CO 2 ] 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 [CO 2 ] gradients of R2, R3, R4, R9 and R10 could be applied preferentially for measurements when using the RACiR technique to obtain V c max and J max of evergreen broadleaved species.