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Light Environment, Nitrogen Content, and Carbon Balance of Basal Leaves of Sunflower Canopies
Author(s) -
Rousseaux M. C.,
Hall A. J.,
Sánhez R. A.
Publication year - 1999
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1999.0011183x003900040023x
Subject(s) - canopy , helianthus annuus , photosynthesis , biology , nitrogen , botany , sunflower , horticulture , carbon fibers , basal (medicine) , chemistry , mathematics , organic chemistry , algorithm , composite number , insulin , endocrinology
A good association between leaf N and photosynthetic photon flux density (PPFD) canopy distribution profiles has often been found. However, it is not clear whether N export from basal leaves anticipates the reduction in basal leaf PPFD that occurs as the canopy develops; our first objective was to examine this issue. We documented the dynamics of the light environment and specific leaf nitrogen (Nf) for target leaves at a single level of insertion under sunflower ( Helianthus annuus L.) canopies grown at 0.47, 1.18, and 4.76 plants m −2 and contrasted observed Nf with the estimated value of Nf required to maximize net carbon exchange (NCE) for the actual PPFD impinging on target leaves. The second objective of this work was to define the relationships between Nf and PPFD and between Nf and the spectral composition of light impinging on basal leaves. Paired (red and farred) photodiode sensors placed on the adaxial leaf surface were used to document light quality dynamics of basal leaves. Measured Nf was greater than or similar to that required to maximize NCE for 79% of the observations made between achievement of maximum target leaf area and senescence of these leaves. Nf showed a strong association with both red/far‐red ratio of light impinging on target leaves and PPFD, but the association was stronger for the former variable. We conclude that N export from basal leaves does not precede PPFD reduction and that the red/far‐red ratio is a better predictor of Nf gradients within the canopy than PPFD.