Comparison of parameters estimated from A/C i and A/C c curve analysis

The parameters estimated from traditional A/C (i) curve analysis are dependent upon some underlying assumptions that substomatal CO2 concentration (C (i)) equals the chloroplast CO2 concentration (C (c)) and the C (i) value at which the A/C (i) curve switches between Rubisco- and electron transport-limited portions of the curve (C (i)-t) is set to a constant. However, the assumptions reduced the accuracy of parameter estimation significantly without taking the influence of C (i)-t value and mesophyll conductance (g (m)) on parameters into account. Based on the analysis of Larix gmelinii's A/C (i) curves, it showed the C (i)-t value varied significantly, ranging from 24 Pa to 72 Pa and averaging 38 Pa. t-test demonstrated there were significant differences in parameters respectively estimated from A/C (i) and A/C (c) curve analysis (p < 0.01). Compared with the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (V-cmax), the maximum electron transport rate (J(max)) and J(max)/V-cmax estimated from A/C (c) curve analysis which considers the effects of g (m) limit and simultaneously fits parameters with the whole A/C (c) curve, mean V-cmax estimated from A/C (i) curve analysis (V-cmax-C (i)) was underestimated by 37.49%; mean Jmax estimated from A/C (i) curve analysis (J(max)-C (i)) was overestimated by 17.8% and (J(max)-C (i))/(V-cmax-C (i)) was overestimated by 24.2%. However, there was a significant linear relationship between V-cmax estimated from A/C (i) curve analysis and V-cmax estimated from A/C (c) curve analysis, so was it J(max) (p < 0.05).