Measurements of light interception and utilization in an apple orchard.

摘要

Measurements of light interception and calculations of whole-canopy transpiration and photosynthesis, carried out near Palmerston north, New Zealand, are reported for a 14-year-old apple tree (Malus domestica [M. pumila] cv. Splendour on MM.106 rootstock). Light measurements were made using a 'whole-plant' radiometer known as the Whirligig. This instrument monitors the total amount of photosynthetic active radiation (PAR, 400-700 nm) and the total amount of all-wave radiation (400-5000 nm) absorbedby a single tree. Data from the Whirligig were used to estimate the distribution of PAR over the total leaf area of the tree. This PAR distribution is then combined with leaf stomatal conductance and leaf net photosynthesis response functions to estimate the rates of transpiration and photosynthesis from the whole canopy. In this paper, our Whirligig calculations of transpiration were in good agreement with independent measurements of sap flow recorded using heat-pulse sensors located in the tree trunk. Furthermore, our Whirligig estimates of net CO2 exchange are comparable to values reported for apple trees enclosed in whole-canopy chambers. We conclude that the Whirligig is a good instrument to 'scale-up' transpiration and photosynthesis measurements from a single leaf to the whole tree.