Seasonal changes in the width and structure of non-collapsed phloem affect the assessment of its potential conducting efficiency

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Seasonal changes in the width and structure of non-collapsed phloem affect the assessment of its potential conducting efficiency_x000D_ _x000D_ Quantitative phloem anatomy is increasingly used in dendroecological studies, since recent evidence shows that phloem traits are a valuable indicator of the morphological and physiological strategies of tree performance in different environments However, seasonal changes in the width and structure of non-collapsed phloem are usually not considered, although they may significantly affect the assessment of its potential conducting efficiency. Our data on three common European temperate tree species (i.e., Norway spruce, common beech and sessile oak) confirmed that the seasonal dynamics of phloem formation and the collapse of sieve elements significantly affect the structure and width of the non-collapsed phloem. In combination with sieve element characteristics, they determine the conducting potential of the NCPH, which is not constant throughout the growing season. To observe that trend we investigated phloem samples repeatedly taken at 7-10-day intervals during the growing season, using light microscopy. The results indicate that sampling time should be considered when comparing quantitative phloem anatomy data from different laboratories, indicating the need for a uniform sampling protocol and methodology._x000D_

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