Validation of a canopy photosynthesis model for cocksfoot pastures grown under different light regimes |
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Authors: | P L Peri D J Moot D L McNeil |
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Institution: | (1) Universidad Nacional de la Patagonia Austral-INTA-CONICET, cc 332, (CP 9400), Río Gallegos, Santa Cruz, Argentina;(2) Agriculture and Life Sciences Division, Lincoln University, P.O. Box 84, Canterbury, New Zealand;(3) Department of Primary Industries, VIDA, Victoria, PMB 260, Australia |
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Abstract: | Daily net canopy photosynthesis (P
n) was predicted for cocksfoot (Dactylis glomerata L.) canopies grown under different light regimes by integration of a leaf photosynthesis model developed for the light-saturated
photosynthetic rate (P
max), photosynthetic efficiency (α) and the degree of curvature (θ) of the leaf light–response curve. When shade was the only
limiting factor, the maximum P
n (P
nmax) was predicted to decrease approximately linearly from 33.4 g CO2 m−2 d−1 to zero as photosynthetic photon flux density (PPFD) fell from full sunlight (1800 μmol m−2 s−1 PPFD) to 10% of this in a fluctuating light regime. It was also predicted that at 50% transmissivity P
nmax was higher for a continuous light regime (10.4 g CO2 m−2 d−1) than for a fluctuating light regime with the same intensity (8.4 g CO2 m−2 d−1). The canopy photosynthesis model was then used to predict dry matter (DM) production for cocksfoot field grown pastures
under a diverse range of temperature, herbage nitrogen content and water status conditions in fluctuating light regimes. This
prediction required inclusion of leaf area index and leaf canopy angle from field measurements. The model explained about
85% of the variation in observed cocksfoot DM production for a range from 6 to 118 kg DM ha−1 d−1. The proposed model improves understanding of pasture growth prediction through integration of relationships between shade
limitations in fluctuating light regimes and other environmental factors that affect the canopy photosynthetic rate of cocksfoot
pastures in silvopastoral systems. |
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Keywords: | Dactylis glomerata Fluctuating light Leaf area index Leaf canopy angle Light interception Pasture Simulation |
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