Publication Date: 2015.
Modelling the spatial and temporal distribution of leaf nitrogen (N) is central to specify photosynthetic parameters and simulate canopy photosynthesis. Leaf photosynthetic parameters depend on both local light availability and whole-plant N status. The interaction between these two levels of integration has generally been modelled by assuming optimal canopy functioning, which is not supported by experiments. During this study, we examined how a set of empirical relationships with measurable parameters could be used instead to predict photosynthesis at the leaf and whole-canopy levels. The distribution of leaf N per unit area (Na) within the canopy was related to leaf light irradiance and to the nitrogen nutrition index (NNI), a whole-plant variable accounting for plant N status. Na was then used to determine the photosynthetic parameters of a leaf gas exchange model. The model was assessed on alfalfa canopies under contrasting N nutrition and with N2-fixing and non-fixing plants. Three experiments were carried out to parameterize the relationships between Na, leaf irradiance, NNI and photosynthetic parameters. An additional independent data set was used for model evaluation. The N distribution model showed that it was able to predict leaf N on the set of leaves tested. The Na at the top of the canopy appeared to be related linearly to the NNI, whereas the coef- ficient accounting for N allocation remained constant. Photosynthetic parameters were related linearly to Na irrespective of N nutrition and the N acquisition mode. Daily patterns of gas exchange were simulated accurately at the leaf scale. When integrated at the whole-canopy scale, the model predicted that raising N availability above an NNI of 1 did not result in increased net photosynthesis. Overall, the model proposed offered a solution for a dynamic coupling of leaf photosynthesis and canopy N distribution without requiring any optimal functioning hypothesis.
Author affiliation: Louarn, Gaëtan. Institut National de la Recherche Agronomique; Francia
Author affiliation: Frak, Ela. Institut National de la Recherche Agronomique; Francia
Author affiliation: Zaka, Serge. Institut National de la Recherche Agronomique; Francia
Author affiliation: Lebon, Eric. Institut National de la Recherche Agronomique. Unité Mixte de Recherche; Francia
Author affiliation: Prieto, Jorge Alejandro. INTA. Estación Experimental Agropecuaria Mendoza; Argentina
Keywords: Medicago Sativa; Cubierta Vegetal; Fotosíntesis; Nitrógeno; Disponibilidad de Nutrientes; Transpiración; Superficie Foliar; Modelos; Cubierta de Copas; Plant Cover; Photosynthesis; Nitrogen; Nutrient Availability; Transpiration; Leaf Area; Models; Canopy; Nitrogen Nutrition Index; Alfalfa; Canipia.
Repository: INTA Digital (INTA). Instituto Nacional de Tecnología Agropecuaria