RESEARCH ARTICLE Root Plasticity of Populus euphratica Seedlings in Response to Different Water Table Depths and Contrasting Sediment Types

Riparian plants in arid regions face a highly variable water environment controlled by hydro-logical processes. To understand whether riparian plants adapt to such environments through plastic responses, we compared the root traits, biomass allocation and growth of Populus euphraticaOliv. Seedlings grown in lysimeters filled with clay or clay/river sand sediments under inundation and varying water table conditions. We hypothesized that adaptive phenotypic plasticity is likely to develop or be advantageous in seedlings of this species to allow them to adapt desert floodplain environments. Growth was significantly re-duced by inundation. However, rather than following relatively fixed trait and allocation pat-terns, the seedlings displayed adaptive mechanisms involving the development of adventitious roots to enhance plant stability and obtain oxygen, together with a lower pro-portion of root biomass. At the whole-plant level, at deeper water table depths, seedlings al-located more biomass to the roots, and total root length increased with decreasing water table depths, regardless of the sediment, consistent with optimal partitioning theory. The sediment type had a significant effect on seedling root traits. P. euphratica displayed ver