An uncommon garden experiment: microenvironment has stronger influence on phenotypic variation than epigenetic memory in the clonal Lombardy poplar

Environmental changes can trigger phenotypic variation in plants through epigenetic mechanisms, but strong genetic influences on epigenetic variation and phenotypes make it difficult to isolate and study these effects. We investigated phenotypic plasticity using the Lombardy poplar (Populus nigra cv. ‘Italica’ Duroi), a globaly distributed clonal tree. We surveyed 14 functional traits related to tree growth, ecophysiological and phenological processes in poplar ramets collected along a wide geographical range in Europe and planted under common garden conditions. We investigated whether phenotypic variation was related to geography and historical bioclimatic data of the ramets’ sites of origin using linear mixed effect models. We found significant differences in among ramets from different geographic origins in tree height, number of stems per ramet and duration of bud flush. However, microenvironmental variation in the common garden, captured via block effects, had an even bigger impact on phenotypic variation than the environmental conditions at the sites of origin. Our results show that phenotypic variation in the ramets might be associated to the climate origin from different climates, suggesting possible epigenetic memory. However, such legacy effects might be quickly outweighed by new environmental conditions.