Parameterization and testing of a biochemically based photosynthesis model for walnut (Juglans regia) trees and seedlings.

摘要

The biochemically based leaf photosynthesis model proposed by Farquhar et al. [see Planta (1980) 149, 78-90] and the stomatal conductance model proposed by Jarvis [see Philos. Trans. R. Soc. Lond B. Biol. Sci. (1976) 273, 593-610] were parameterizedfor walnuts (Juglans regia). Responses of photosynthesis to CO2 and irradiance were used to determine the key parameters of the photosynthesis model. Concurrently, stomatal conductance responses to leaf irradiance (Q), leaf temperature (T1), water vapour pressure deficit at the leaf surface (D), and air CO2 concentration at the leaf surface (Cs) were used to parameterize the stomatal conductance model. To test the generality of the model parameters, measurements were made on leaves from a 20-year-old tree growing in the field at Plauzat, France, and from sunlit and shaded greenhouse-grown seedlings. The three key parameters of the photosynthesis model (maximum carboxylation rate Vcmax, electron transport capacity Jmax, and dark respiration rate Rd) and the key parameter of the conductance model (reference stomatal conductance, gsref) were linearly correlated with the amount of leaf nitrogen per unit leaf area. Unique relationships could be used to describe nitrogen effects on these parameters for leaves from both the tree and the seedlings. The data allowed separation of the effects of increasing total photosynthetic apparatus per unit leaf area from the effects of partitioning nitrogen among different pools of this apparatus for foliage acclimatization to leaf irradiance. Strong correlations were found between stomatal conductance gs and Q, D and Cs, whereas the relationship between gs and Tl was weak. Based on these parameterizations, the model adequately predicted leaf photosynthesis and stomatal conductance when tested with an independent set of data obtained for the tree and seedlings. Total light-driven electron flows derived from chlorophyll fluorescence data obtained at different leaf temperatures were consistent with values computed by the model. The model was also tested with branch bag data acquired from a three-year-old potted walnut tree. Despite a relatively large variance between observed and simulated values, the model predicted stomatal conductance and photosynthesis reasonably well at the branch scale. The results indicate that the photosynthesis-conductance model developed here is robust and can be applied to walnut trees and seedlings under various environmental conditions where water is non-limiting.