New Zealand Journal of Agricultural Research abstracts
Modelling net photosynthetic rate of field-grown cocksfoot leaves to
account for regrowth duration
P. L. Peri
Universidad Nacional de la Patagonia
Austral-INTA
Argentina
D. J. Moot*
D. L. McNeil
R. J. Lucas
Soil, Plant and Ecological Sciences Division
Field Service Centre
P.O. Box 84
Lincoln University
Canterbury, New Zealand.
email: moot@lincoln.ac.nz
*Author for correspondence.
Abstract Maximum light-saturated photosynthetic rate
(Pmax) of field-grown cocksfoot (Dactylis glomerata
L.) leaves was measured in a temperate, sub-humid environment (Canterbury,
New Zealand). The aim was to derive an individual function for Pmax
of newly expanded leaves against regrowth duration when other environmental
factors were non-limiting. The decrease in Pmax with regrowth
duration was described by a quadratic function. From 20 to 25 days regrowth,
Pmax per unit of leaf was constant and maximal (27.4 µmol
CO2 m-2 s-1). It then decreased by 0.42
µmol CO2 m-2 s-1 per day of regrowth.
The decline in Pmax was attributed to (i) differences in
chronological age of the youngest expanded leaf as shown by changes in tiller
morphology over time, and (ii) shading within the canopy during leaf expansion.
These factors affected Pmax by decreasing the leaf nitrogen
and chlorophyll content, and stomatal conductance. The function for regrowth
duration was an additional factor included in a multiplicative model to predict
Pmax with different levels of temperature, nitrogen, and
water status, expressed as pre-dawn leaf water potential (ψlp).
The only interaction detected was when water stress increased (ψlp
< -1.2 bar) and leaves had grown for 40-60 days. In this limited situation,
stomatal closure at 40-60 days was greater than expected from the non-limiting
condition. The inclusion of this function into a simple multiplicative model
enabled 80% of the variation in Pmax for individual cocksfoot
leaves to be explained by their temperature, nitrogen, water, and regrowth
status. These functions could then be used to develop a canopy photosynthesis
model for the prediction of cocksfoot pasture production.
Keywords chlorophyll; Dactylis glomerata; leaf
photosynthesis; modelling; morphology; nitrogen; regrowth duration; stomatal
conductance; temperature; water stress
A02015 Received 27 February 2002; accepted 23 December 2002; published
30 June 2003
New Zealand Journal of Agricultural Research, 2003, Vol. 46: 105-115
0028-8233/03/4602-0105 $7.00/0 © The Royal Society of New Zealand
2003
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