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Whole-Canopy Gas Exchange and Light Interception of Vertically Trained Vitis vinifera L. under Direct and Diffuse Light

¹ Formerly, Postgraduate student, Centre for Viticulture and Oenology, Lincoln University, Canterbury, New Zealand, presently, National viticulturist, Foster’s Group Ltd, Adelaide 5072, Australia, and Affiliate senior lecturer, School of Agriculture, Food and Wine, University of Adelaide, Glen Osmond 5064, Australia; ² Formerly, Senior lecturer in Viticulture, Centre for Viticulture and Oenology, Lincoln University, Canterbury, New Zealand, presently, Senior scientist, New Zealand Institute for Plant and Food Research Limited, Marlborough Wine Research Centre, PO Box 845, Blenheim, New Zealand; ³ Professor of Horticulture, Michigan State University, East Lansing, MI 48824, USA; ⁴ Associate professor of Environmental Physics and Environmental Education, Soil and Physical Sciences Group, Lincoln University, Canterbury, New Zealand; and ⁵ Senior scientist, New Zealand Institute for Plant and Food Research Limited, Nelson Research Centre, Motueka, New Zealand.

Acknowledgments: This project has been financially supported by New Zealand Winegrowers, the Agricultural and Marketing Research and Development Trust (AGMARDT), and Lincoln University.

The authors acknowledge the technical assistance of Andrew Baken with the development of the whole plant photosynthesis system and Adam Friend with its implementation. The help provided by Alan Lakso and Rick Piccioni (Cornell University) with using pressure sensors to measure air flow through the chambers was appreciated.

^* Corresponding author (email: MTrought{at}hortresearch.co.nz; fax: +64 3 984 4310)

A portable, open gas exchange system was developed that enabled the simultaneous measurement of net carbon dioxide exchange (NCE) and transpiration of eight mature Sauvignon blanc grapevines in the field. On clear and cloudy days NCE and transpiration were closely related to the modeled interception of photosynthetically active radiation (PAR). On clear days, the relationship between photosynthesis and incident PAR was poor and NCE peaked in the vertically trained, north-south orientated rows three hours before and after solar noon, resulting in a distinct bimodal pattern to vine gas exchange, which was not evident on cloudy days. Under diffuse light (cloudy) conditions, the vines appeared to be more efficient, photosynthesizing at a higher rate per calculated unit of light intercepted. This efficiency was probably due to the saturation of the exterior and shading of interior leaves under clear conditions, while under diffuse conditions the increased scattered light enhanced the irradiance received by the leaves in the interior of the canopy. Despite the improved light use efficiency under diffuse conditions, lower light intensities meant that CO₂ exchange was normally lower than that recorded during clear days. The effect of the chambers on the sap flux velocity up the vine stems was minor, which suggests that their effect on vine microclimate and resulting transpiration was minimal. There was a strong relationship between concurrent transpiration and sap flux velocity, which was not improved by the use of a time delay between transpiration and sap flux, and suggests that the vines do not rely greatly on water stored in the trunk and other vegetative organs above the ground (capacitance) for transpiration under these conditions.

Key words: grapevine, photosynthesis, transpiration, light interception, sap flux, direct and diffuse radiation