Comparative examinations of gas exchange and biometric parameters of eight fast-growing poplar clones

The establishment of short-rotation poplar plantations for the sustainable production of raw material and energy is often limited by low precipitation and poor soil conditions. Breeding research must therefore focus on combining performance with drought tolerance. Eight poplar clones were generated by tissue culture. Three times during seasonal development, photosynthesis and transpiration were measured in fully developed leaves under controlled conditions in a climate chamber. Light response curves were modelled based on these data. The efficiency of water use was analysed for all clones under well-watered conditions, and partly significant differences were observed with regard to intrinsic water use efficiency (WUE). Moreover, at the end of the season, the plants were considerably different in their biometrics, particularly in the shoot–root relationship, which might substantially influence drought resistance. A general ranking of the performance of the clones is difficult because certain physiological parameters turn over during the course of the season. However, certain “strategies” that could be divided into “generalist” and “specialist” stand out for individual clones. The aspen clone Großdubrau 1 (“specialist”) showed the maximum height, the greatest seasonal differences in WUE and the most weakly developed root system. By contrast, the poplar clone Max 2 (“generalist”) had the lowest height increase but a well-developed root system and lower volatility in WUE. Thus, drought tolerance under stress conditions may exhibit a degree of predictability. Therefore, a dry stress experiment is planned to test the two contrasting clones.