Background and Aims

The temperate steppes are dominated by perennial grass and forb species and biogeochemical niche separation exists universally in leaves between grasses and forbs at different scales. However, the underlying physiological mechanisms still remain unresolved.

Methods

We measured macronutrients, micronutrients and total phenolic compounds in both leaves and roots of 19 grass and 39 forb species across the Inner Mongolia grassland in northern China, and investigated relationships between root phenolic compounds and biogeochemical niche separation in both leaves and roots at functional group level.

Key Results

Forbs displayed significantly higher concentrations of both leaf and root macronutrients (N, P, S, K, Ca and Mg) than grasses regardless of species and functional group. Although concentrations of leaf micronutrients (e.g. Fe and Mn) were higher in forbs than in grasses, root concentrations Fe and Mn were extremely low in forbs compared with grasses. Metabonomics and physiological analyses showed that roots of forb plants synthesized and secreted higher concentrations of phenolic compounds than grass plants at both species and functional group level. Concentrations of root macronutrients (C, N, P and Ca) were positively correlated with concentrations of total root phenolic compounds, but concentrations of root micronutrients (Fe and Mn) were negatively associated with concentrations of total root phenolic compounds between grasses and forbs. In addition, multiple leaf mineral concentrations (including P, Mg, Ca, Fe, Mn, Zn and Cu) were positively correlated with concentrations of total root phenolic compounds between grasses and forbs.

Conclusions

Our findings underscore that forb species have evolved higher concentrations of both nutrients and phenolic compounds compared with grass species in steppes of northern China. Root phenol-facilitated nutrient acquisition and transport are involved in leaf and root biogeochemical niche separation between grasses and forbs. These findings may provide valuable insights into predicting species coexistence and biogeochemical cycling in temperate steppes.