Populus euphratica Seedlings Adapt to a Wider Range of Hydrological Conditions in Different Sediment Types through the Adaptive Plasticity of Roots

Populus euphratica Oliv. is the dominant tree species in the riparian forest ecosystems along the arid inland rivers of China. More than 90% of this existing tree species in China is distributed in the Tarim River Basin of Xinjiang, and P. euphratica is widely considered a major ecological and evolutionary driver in this arid environment. P. euphratica inhabiting such an arid area must accommodate a wide range of hydrological fluctuations. The responses of P. euphratica seedling to the hydrological fluctuations are important in determining the distributions of this woody species in these environments.

P. euphratica plants are phreatophytes and highly dependent on groundwater, they usually access to the groundwater by their roots. Therefore, root system is essential for the seedling establishment and the sustainable growth of P. euphratica plants. However, there are few studies about the responses of root systems of P. euphratica plants at the seedling stage to the hydrological fluctuations in the Tarim River Basin.

To assess the adaptive phenotypic plasticity of root systems of P. euphratica seedlings in relation to the highly variable water table depths, WANG Lijuan et al. investigated the root traits of P. euphratica seedlings under a range of riparian hydrological conditions simulated using lysimeters filled with clay or clay/river sand. P. euphratica seeds were sown in trays of damp soil in a nursery during September 2011. Then researchers selected two hundred seedlings after nine months of growth in damp conditions and transplanted them in individual lysimeters to simulate the hydrological conditions of the riparian floodplain. The experiment was conducted over a period of 75 days, from 15 July to 30 September of 2012.

During the experimental period, P. euphratica seedlings exhibited considerable adaptive responses to the hydrological fluctuations, and no seedling mortality occurred. The total biomass of the roots was significantly higher at deeper water table depths, and the total root length increased with the decreases of water table depths. The responses of seedling root traits to the sediment types was generally significant under the same hydrological conditions, with higher root number in clay sediment under shallower water table conditions while greater root depth in clay/river sand sediment under deeper water table conditions. However, the sediment effect was not significant for biomass allocation. Seedlings responded to lower water availability via greater root elongation, and root elongation occurred more rapidly under deeper water table depths in clay/river sand sediment than in clay sediment. P. euphratica seedlings are likely to increase their root length to obtain more water under a deeper water table. The result indicated that P. euphratica seedlings are capable of adapting to a wider range of hydrological conditions in different sediment types through plastic responses in root traits.

The result was published in PLoS ONE on 5 March 2015.

Contact:

Prof. ZHAO Chengyi

Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences

E-mail: zcy@ms.xjb.ac.cn