Populus nigra as keystone species able to cope with the ongoing climate change

Abstract

International audiencePopulus nigra L. is one important species of the european alluvial forests, that are protected under Habitats directive 92/43/EEC in Europe. This species is often regarded as good indicator of geomorphological and biological quality of this ecosytem and is an active support of riparian biodiversity. This species is threatened by anthropogenic disturbances and gene introgression, justifying a french and european (EUFORGEN) programme on in situ and ex situ conservation of its genetic resources. In addition, riparian forest ecosystem and trees will face global and local climate modifications this century. Populus nigra, that establishes naturally within or along the active channel and that is strictly dependent of the morphodynamics of the river, will be exposed to three new threats : (i) enhancement of the frequency and severity of drought with summer decrease of the water table level, (ii) extreme heat waves, especially in summer (temperature is a key factor for survival and development of seedlings) and (iii) more intense flooding. The basis for the ability of trees to survive, adapt and evolve under changing environmental conditions is genetic diversity and the adaptive capacity to such changes involve three processes : (a) plasticity, i.e. the capacity of existing trees to respond differently to different environmental conditions ; (b) adaptation, which includes adaptive genetic diversity and the occurrence of natural selection in a dynamic system and (c) migration potential through natural dissemination of seeds to more suitable areas. This presentation will focuss on the two first responses in Populus nigra, as the third process is restricted, due to the limited capacity of this pionneer species to migrate in latitude or elevation along the constrained range of the fluvial corridors. Data on genetic diversity and phenotypic variability of adaptative traits in french populations (foliar characteristics, water relations, architecture, floral and foliar phenology…) and from in situ and ex situ experiments, testing drought and temperature in different genetic material (cuttings, seedlings) in various conditions (sandy banks, nursery, greenhouses, growth chambers) will be presented. This communication will demonstrate that Populus nigra has resources (genetic characteristics) and mechanisms (ecophysiological characteristics) to cope with the ongoing climate change. This research was mainly supported by regional, national and european funds and realized under the french Populus nigra genetic resource conservation programme