Growth and development of species and hybrids of the genus Populus L. in the right-bank forest-steppe of Ukraine

Abstract

The growth and development of vegetative and generative organs of Populus alba L., P. balsamifera L., P. bolleana Lauche, P. × canescens (Ait.) Smith., Р. deltoides Bartr. ex Marsh., P. nigra L., P. nigra cv. Italica (Du Roi) Moench, Р. simonii Corr., P. tremula L., and European-American P. deltoides × P. nigra hybrids ʹI-45/51ʹ, ʹBlanc du Poitouʹ, ʹGelricaʹ, ʹMarilandicaʹ, ʹRobustaʹ, ʹSerotinaʹ, ʹTardif de Champagneʹ, and P. × hybridа clones ʹWeresinaʹ and ʹWitschtejnaʹ were studied outdoor for seven years under current climate change. The development of most Populus species and hybrids started in the second half of March – beginning of April when the phase of bud swelling was reached in correspondence of a significant temperature sum from 68 to 112 °С, depending on the species/hybrid considered. In most species, flowering began on April 20th and lasted 9 to 16 days, temperature sum of 93–139 °С, depending on the species. The duration of linear shoot growth was shorter in native species of the genus Populus (118–130 days) than in introduced species (135–140 days). Fruiting began when the temperature sum reached 217– 234 °С in P. tremula, while in P. balsamifera it required 413 °C. The other species required an intermediate temperature sum (299–329 °С) to reach the same phase, which was accumulated in the first ten-day period of June. Discolouration of leaves depended on the date of first autumn frosts and during the study period was shifted by two to three weeks later. After analyzing the timing of phenological phases of growth and development, species and hybrids were assigned to phenological groups characterized by early, mid or late beginning and end of the vegetation period. The knowledge of thermal requirements for key phenological stages is expected to be useful for modelling and predicting growth, flowering and fruiting of poplars, which is crucial to create efficient and productive bioenergy plantations and to take anti-allergic measures during fruiting in the Right-Bank Forest-Steppe of Ukraine.