Radial growth dynamics in poplar Oxford clone subjected to drought and ozone stress

Drought and tropospheric ozone (O3) are two environmental stress factors that in the future are predicted to affect forest health and tree growth. Fast growing tree species are known to be sensitive to these factors, reducing their ability in fixing carbon. The radial growth of one year-old potted-plants of Populus maximowiczii Henry x P. x berolinensis Dippel (Oxford clone) subjected to drought and O3 was analyzed by means of the pinning method. The experiment was carried out in 2008 at the open-top chambers facilities at Curno (C.R.IN.ES., Lombardy, North Italy).The pinning method allows to monitoring of cambial activity, i.e., the intra-annual xylem growth, i.e., the formation of new woody cells. Cambial activity was checked every 2 weeks from 10th June until 5th August. Every 2 weeks we made a wound in the stem using a thin needle (pin) and for each time interval between two pinning dates, we counted the number of cells, as measure of the wood formation during this period. We assessed the number of vessels and fibers, as well as the lumen area and diameter of the vessels. The intra-annual growth of the poplar resulted not affected by neither water availability nor O3. Wood properties were affected by drought, with a higher number of the vessels and fibers in dried than in wet condition. The vessels were smaller in dried than in wet regime. The results suggest that in poplar, well known species O3-sensitive, the radial growth is not affected in short period, despite the physiological (such as photosynthesis) functions are reduced