Drought adaptability of phreatophytes: Insight from vertical root distribution in drylands of China

Aims: The vertical distribution of plant roots is a comprehensive result of plant adaptation to the environment. Limited knowledge on fine vertical root distributions and complex interactions between roots and environmental variables hinders our ability to reliably predict climatic impacts on vegetation dynamics. This study attempts to understand the drought adaptability of plants in arid areas from the perspective of the relationship between vertical root distribution and surroundings. Methods: By analyzing root profiles compiled from published studies, the root vertical profiles of two typical phreatophytes, Tamarix ramosissima and Populus euphratica, and their relationships with environmental factors were investigated. A conceptual model was adopted to link the parameter distribution frequency with plant drought adaptability. Important Findings: The strong hydrotropism (groundwater-dependent) and flexible water-use strategy of T. ramosissima and P. euphratica help both species survive in hyperarid climates. The differences in the developmental environments between T. ramosissima and P. euphratica can be explained well by the different distribution characteristics of root profiles. That is, higher root plasticity helps T. ramosissima develop a more efficient water-use strategy and therefore survive in more diverse climatic and soil conditions than P. euphratica. We conclude that the higher variation in root profile characteristics of phreatophytes can have greater root adaptability to the surroundings and thus wider hydrological niches and stronger ecological resilience. The inadequacy of models in describing root plasticity limits the accuracy of predicting the future response of vegetation to climate change, which calls for developing process-based dynamic root schemes in Earth system models.