Within-branch heterogeneity of the light environment and leaf temperature in a Fagus crenata crown and its significance for photosynthesis calculations

Autor: Atsuhiro Iio, Hiromi Mizunaga, Yachiho Nose, Hisakazu Fukasawa, Yoshitaka Kakubari, Masaaki Naramoto
Rok vydání: 2009
Předmět:
Zdroj: Trees. 23:1053-1064
ISSN: 1432-2285
0931-1890
DOI: 10.1007/s00468-009-0347-7
Popis: On days with clear skies in late August 2002 diurnal changes in the within-branch heterogeneity of photosynthetic photon flux density at the leaf surface (PPFDs) and leaf temperature (T leaf) were measured at natural leaf orientations in the upper and lower layers of a Fagus crenata crown. The PPFDs and T leaf measurements were converted to branch photosynthesis rates (P B; μmol s−1) using a photosynthetic model proposed by Farquhar et al. (Planta 149:78–90, 1980), an empirical stomatal conductance model suggested by Leuning et al. (Plant Cell Environ 18:339–335, 1995), and the total leaf area of the branches. To evaluate the importance of the variation in PPFDs and T leaf on photosynthesis calculations, P B calculated with the observed variation in PPFDs and T leaf was compared with estimates, based on the average (variation-free) values of PPFDs and T leaf, respectively. In both the layers, daily total P B values obtained with T leaf averaging were very close to those obtained with no averaging because of the weak inflection of the net photosynthesis rate (P n) to T leaf curves in the observed T leaf ranges (24.4–36.5 and 21.9–29.1°C in the upper and lower layers, respectively) and relatively small variation in within-branch T leaf at each time of day. This finding applied across potential climate conditions on fine days in August (T leaf range of 19.4–41.5 and 16.9–34.1°C in the upper and lower layers, respectively) and when the spatial scale was increased from branch to leaf layer, which increased the maximum variation in within-branch T leaf from 7.8 to 9.5°C and 4.5 to 5.5°C in the upper and lower layers, respectively. In contrast, averaging PPFDs caused 25–50% and 41–90% overestimation of daily total P B in the upper and lower layers, respectively, due to the sharp curvature in the PPFDs response curve to P n, and relatively large variation in within-branch PPFDs. Further, it led to overestimation of midday depression of P B in the upper layer, possibly because branch structural acclimation to incident light was neglected. Our results indicate that averaged values of T leaf could be used for the estimation of carbon gain at layer scale throughout August, but spatial variations in PPFDs need to be considered in detail for reliable estimates of carbon gain.
Databáze: OpenAIRE
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