Variation in morphological and chemical traits of Mediterranean tree roots: linkage with leaf traits and soil conditions

Aims Root functions are multiple and essential for the growth and survival of terrestrial plants. The aim of this work was to analyse the main trends in the variation of root traits, their coordination with leaf traits and their relationships with soil conditions. Methods We measured the variation of 27 fine root traits (five morphological, 20 chemical and two isotopic signatures) in trees of seven species of a mixed plantation in a metal-contaminated and remediated site of Southern Spain. Results We found evidences supporting the existence of a root economics spectrum (RES). However, other dimensions were identified as being independent of the main RES: mainly the variation in the carbon concentration, the accumulation of trace elements associated with tolerance of metal-rich soils, and the fractionation of delta N-15 as a time-integrated trait of mycorrhizal-mediated nutrition. In general, roots and leaves were functionally coordinated, although most of the trace elements showed strong root-leaf discordance. The soil conditions interacted with the fine root traits in feedback processes. The ability of tree roots to accumulate trace elements and to reduce their translocation to leaves is a desirable trait for the phytoremediation of metal-contaminated soils. Conclusions Roots are multifunctional. Understanding the variations in the root traits of trees will help us to predict both the responses of forests to global changes, including soil contamination, and the provision of soil-based ecosystem services.