Portable, reliable, low-cost whole-tree open systems for gas exchange studies have evolved recently alongside leaf systems. The advent of portable, battery-operated Infrared Gas Analyzers (IRGA) has provided the core of these systems, which previously were based on bulky, less rugged laboratory equipment. Single-leaf photosynthesis units can be turned into whole-tree systems with few modifications: a plastic chamber to enclose the canopy and a fan to provide the flow of air through the system. With high turnover rates of the air volume in the chamber, temperature can be fairly well controlled without use of air conditioners. Air CO2 concentration, T and %RH are measured at the inlet and outlet. These systems are fairly simple to build and operate under field conditions with very diverse trees, including apple, kiwi, peach, grape, and even large, freestanding cherry trees. They allow observations at the whole-tree level and appear promising for several areas of research, such as ecophysiology, model validation, stress physiology, tree training and orchard systems. However, whole-tree systems do present a variety of methodological problems which need addressing: CO2 and H2O measurement, light scattering by chamber material, accurate air flow measurement, light measurement inside the chamber, and leaf area measurement. Also, can we look at a whole canopy as we do a single leaf! This paper presents a brief overview and discussion of some of these points.
