Adaptive mechanisms and genomic plasticity for drought tolerance identified in European black poplar (Populus nigra L.): Adaptatie en genomische plasticiteit voor droogte resistentie bij de Europese zwarte populier (Populus nigra L.)

Abstract

Summer droughts are likely to increase in frequency and intensity across Europe, yet long-lived trees may have limited drought resilience. It is therefore critical that we improve our understanding of phenotypic plasticity to drought in natural populations for ecologically and economically important trees such as Populus. A common garden experiment was conducted using approximately 500 wild Populus nigra trees,collected from 11 river populations across Europe. Phenotypic variation was found across the collection, with southern genotypes from Spain and France characterised by small leaves and limited biomass production. To examine the relationship between phenotypic variation and drought resilience, six genotypes with contrasting leaf morphologies were subjected to a water deficit experiment. ‘North eastern’ genotypes were collected at wet sites and responded to water deficit with reduced biomass growth, slow stomatal closure and reduced water use efficiency (WUE) assessed by C. In contrast, ‘southern’ genotypes originating from arid sites showed rapid
stomatal closure, improved WUE and limited leaf loss. Transcriptome analyses of a genotype from Spain and another from northern Italy, revealed dramatic differences in gene expression response to water deficit. Transcripts controlling leaf development and stomatal patterning, including ANT, CLV1, ERL1, TMM and a carbonic anhydrase gene were down-regulated in an Italian genotype (Ita) but not in a Spanish clone (Sp2) in response to drought.