AOBPreview originally published online on September 10, 2003
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Annals of Botany 92: 679-688, 2003
© 2003 Annals of Botany Company
Vertical Leaf Nitrogen Distribution in Relation to Nitrogen Status in Grassland Plants
1 Lehrstuhl für Grünlandlehre, Technische Universität München, D-85350 Freising, Germany
* For correspondence. E-mail loetscher{at}wzw.tum.de
Received: 2 July 2003;; Returned for revision: 11 July 2003. Accepted: 28 July 2003; Published electronically: 10 September 2003
Vertical gradients of leaf nitrogen (N) per unit leaf area (NLA) are viewed as plastic responses that optimize N utilization with respect to carbon assimilation. However, it has been shown that plant species, sowing density and N availability affect the steepness of the NLA gradient relative to the photon flux density (PFD) gradient. This paper tests the hypothesis that such variation is related to the N status of the plant. The N status was analysed using the concept of the critical N concentration (Ncrit) in which shoot N per unit dry mass (NSM) decreases with shoot mass, and a negative deviation of actual NSM from Ncrit indicates N shortage in the plant. The hypothesis was tested with contrasting grassland species Medicago sativa, Dactylis glomerata and Taraxacum officinale by varying PFD and N availability, plant density and hierarchical positions of individuals within stands. Combinations of all treatments showed a general negative correlation between the N allocation coefficient (i.e. the slope of the NLA–PFD relationship) and NSM for all three species. Thus, NLA, relative to PFD, gradients became steeper with increasing shoot mass and increasing N shortage in the plant. These data are consistent with the view that internal N availability is an important factor in modifying the NLA gradient.
Key words: Dactylis glomerata, grassland species, light profile, leaf nitrogen distribution, Medicago sativa, plant nitrogen status, size hierarchy, Taraxacum officinale.
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