The response of root traits to precipitation change of herbaceous species in temperate steppes

Plasticity of root traits plays an important role in plant growth and survival under changing climate. Shift in precipitation is one of the most pertinent global change factors driving changes in structure and function of grasslands. However, few studies have investigated intraspecific variation of root traits in response to precipitation change under field conditions. We conducted a 10-year simulated increased precipitation experiment in a temperate grassland and a 700-km regional scale transect along a precipitation gradient ranging from 144.23 to 412.29 mm in northern China. The morphological, chemical and anatomical traits of the first two-order roots were determined on 15 common herbaceous species in the manipulation experiment and two regionally common species (Leymus chinensis, Artemisia frigida) along a precipitation gradient. We found that most of the root traits of the herbaceous species exhibited no significant responses to water addition. The two regionally common species adjusted their root traits at sites with the annual precipitation lower than certain value, that is 250 and 160 mm for L. chinensis and A. frigida, respectively. These results indicate that root traits of the herbaceous species exhibit little plasticity in response to precipitation change and that the adjustment of root traits occurs when the range of annual precipitation exceeds a certain threshold. Root traits of L. chinensis and A. frigida varied differently both in manipulation experiment and along the precipitation gradient. Root traits of L. chinensis were relatively constant, while A. frigida adjusted their morphological root traits in response to water addition. Moreover, L. chinensis showed higher specific root length (SRL) and area, and root N contents at sites with annual precipitation lower than c. 250 mm. In contrast, A. frigida displayed thicker roots with lower SRL and area at sites with annual precipitation lower than c. 160 mm. Our results showed that root traits of herbaceous species in temperate grasslands exhibited little plasticity and that different species have evolved diverse adaptive strategies in response to precipitation change. These novel findings provide valuable information to predict responses of temperate grasslands to future climate change