Journal of Animal and Plant Sciences
J. Anim. Plant Sci. [ISSN 2071 - 7024]
Volume 5 (2): 483 - 493. Published December 23, 2009.
Leaf growth and photosynthetic capacity as affected by leaf position, plant nutritional status and growth stage in Dioscorea alata L.
V.K. Hgaza*,**,***, L.N. Diby **.***, S. Aké*, and E. Frossard****
* Laboratory of Plant Physiology, UFR Biosciences, University of Cocody-Abidjan, Côte d’Ivoire
**
Swiss Center for Scientific Research, Abidjan, Côte d’Ivoire;
***
Department of Water, Forest and Environment, National Institute of Technology FHB, Yamoussoukro, Côte d’Ivoire
****
ETH Zurich, Institute of Plant Sciences, Switzerland
* Corresponding author Email: hgazat.kouame@csrs.ci
SUMMARY
Because nitrogen (N) deficiency can significantly decrease yam (Dioscorea spp) tuber yield, it is necessary to monitor and ensure adequate N availability. This study was undertaken (i) to identify optimal leaf position on the vine for the prediction of nitrogen response using the SPAD-502 Chlorophyll meter and (ii) to assess the effect of plant growth stage and its nutritional status on leaf photosynthetic capacity. The photosynthetic capacity of D. alata cv TDa 95/00010 leaves was estimated through the specific leaf nitrogen, leaf stomatal conductance and leaf carbon content under field conditions. Individual leaves from the apex to the base on the vine were monitored during vegetative growth stage and during tuber bulking phase under fertilization and non-fertilization conditions. Measurement of leaf N content, leaf expansion rate and SPAD readings was additionally conducted on individual leaves along the vine. The leaf area and SPAD readings increased with plant age while leaf N content decreased. Results indicated that leaves at different positions on the vine differed in photosynthetic capacity. Both young (below 4th position) and older (above 20th position) leaves had lower photosynthetic capacity than the intermediate mature leaves. The yam leaves reached their maximum photosynthetic capacity at between the 4th to the 7th position indicating the optimal leaf position for the prediction of nitrogen response using the SPAD-502 Chlorophyll meter. The photosynthetic performance of mature leaves was related to the plant growth stage and its nutritional status, being higher under fertilization and at tuber bulking phase. By contrast, nitrogen was remobilized for older leaves at this time under non-fertilisation conditions. The results suggest that tuber bulking phase is a critical yield-formation period in which changes in photosynthetic capacity of leaves due to nitrogen deficiency could compromise the yield
Key words: Fertilization, growth stage, leaf position; SPAD-502 chlorophyll meter, photosynthetic capacity
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