Effects of short-term nitrogen addition on root exudates of typical species in an Inner Mongolia temperate steppe

Abstract

The species-specific responses of root exudates to nitrogen (N) addition and their interannual variations remain poorly characterized in temperate grasslands. A two-Yr field experiment with five nitrogen addition treatments (0, 10, 20, 40, 80 g N m−2 yr−1) was carried out on three species: Leymus chinensis (L. chinensis), Artemisia frigida (A. frigida), and Potentilla tanacetifolia (P. tanacetifolia) in an Inner Mongolia temperate steppe, to quantify their root carbon (C) and nitrogen (N) exudation and clarify linkages among root exudation, plant biomass and soil inorganic N. Shoot and root biomass, root exudates and soil physicochemical variables were quantified by clipping, root auger, in situ collection and continuous flow analysis. Results demonstrated marked interannual and interspecific variation in root C and N exudation rates. In 2022, low-moderate N (N10–N20) increased root C exudation rates of L. chinensis and A. frigida, while high N (N40–N80) reduced it; the opposite occurred in 2023. Root N exudation declined all three species in 2023. L. chinensis had higher root C and N exudation rates than other species. C:N ratios of root exudates ranged 0.2-18 across N treatments. Notably, the graminoid L. chinensis showed positive correlation of root C exudation with aboveground biomass, and root N exudation negatively correlated with soil inorganic N, showing plastic exudate adjustment to growth and soil N supply. Two non-graminoids exhibited conservative exudation strategies. Disparities stem from divergent resource allocation and root–microbe interactions. Long-term research integrating root traits and microbial feedbacks helps predict N deposition impacts on temperate steppes.