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

Abstract

The biochemically based leaf photosynthesis model proposed by Farquhar et al. (1980) and the stomatal conductance model proposed by Jarvis (1976) were parameterized for walnut. Responses of photosynthesis to CO(2) and irradiance were used to determine the key parameters of the photosynthesis model. Concurrently, stomatal conductance responses to leaf irradiance (Q), leaf temperature (T(l)), water vapor pressure deficit at the leaf surface (D), and air CO(2) concentration at the leaf surface (C(s)) 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, and from sunlit and shaded greenhouse-grown seedlings. The three key parameters of the photosynthesis model (maximum carboxylation rate V(cmax), electron transport capacity J(max), and dark respiration rate R(d)) and the key parameter of the conductance model (reference stomatal conductance, g(sref)) 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. Our 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 acclimation to leaf irradiance. Strong correlations were found between stomatal conductance g(s) and Q, D and C(s), whereas the relationship between g(s) and T(l) 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.

Influence of radiation and drought on gas exchange of Austrocedrus chilensis seedlings

“…Compared with other species, A. chilensis shares some physiological characteristics with shade tolerant species. Stomata of A. chilensis were fully open at values of PPFD around 50 µmol m -2 s -1 , whereas in "heliophilous" species, maximum stomata aperture is reached at values of PPFD of 280-400 µmol m -2 s -1 (Leverenz 1995, Le Roux et al 1999. In addition, light compensation point was comparatively low (10 compared to 16, 23 and 19 µmol m -2 s -1 for P. ponderosa, Pseudotsuga menziesii (Mirb.)…”

Links between tree structure and functional leaf traits in the tropical forest tree Dicorynia guianensis Amshoff (Caesalpiniaceae)

“…These authors found that changes in LMA were more important than changes in nitrogen for leaf light acclimation. The control of photosynthetic light acclimation by LMA has been observed for many tree species (Le Roux et al [44,45] and for several shade-tolerant herbaceous species [80]. Comparison of these different results shows that there is no universal rule concerning the relative importance of the factors controlling the light acclimation of photosynthetic capacities.…”

Does ontogeny modulate irradiance-elicited plasticity of leaf traits in saplings of rain-forest tree species? A test with Dicorynia guianensis and Tachigali melinonii (Fabaceae, Caesalpinioideae)

“…A-C i curves were used to estimate: (1) V cmax , the maximal rate of RuBP carboxylation, i.e., the potential activity of Rubisco in the absence of limitation by CO 2 availability and photorespiration and (2) J max , the maximal light-driven electron flux. For a detailed description of the equation set, see Le Roux et al (1999). Primary model parameters and their temperature dependencies are listed in …”