Nutrient limitation and metal toxicity have been implicated in changes of grassland communities by nitrogen (N) deposition. Below‐ground processes, especially those at the soil–root interface, play important roles in determining variation in nutrient concentrations in plants. However, few studies have specifically focused on the roles of these processes in mineral‐element acquisition in grassland plants in response to N enrichment. Here we investigated the contributions of below‐ground processes at the soil–root interface to the differential acquisition of phosphorus (P), calcium (Ca) and manganese (Mn) by forbs and grasses of a temperate steppe in response to N addition by combining field and glasshouse experiments. Nitrogen addition increased the concentrations of both leaf P ([P]) and Mn ([Mn]) and decreased leaf [Ca] of forbs while it had little effects on leaf concentrations of these elements in grasses. Nitrogen addition led to a higher activity of acid phosphatase in the rhizosphere of forbs, and greater release of protons and carboxylates from forb roots than grass roots, contributing to the differential [P], [Ca] and [Mn] in the leaves of forbs and grasses. Applying oxalate to soil to simulate the release of carboxylates by N enrichment enhanced [P] and [Mn], and decreased [Ca] in the soil solution. However, addition of hydrogen‐ion increased [P], [Mn] and [Ca] in the soil solution. Lime addition mitigated the N‐addition‐induced soil acidification while it did not abolish the stimulatory effect of short‐term N addition on leaf [P] and [Mn] of forbs. Therefore, we conclude that differences in the eco‐physiological processes at the soil–root interface account for changes in leaf [P], [Ca] and [Mn] under short‐term N addition, and that soil acidification aggravates the responses of these elements, especially [Ca] and [Mn], to long‐term N enrichment. Synthesis. Our results highlight the contribution of below‐ground processes, especially those at the soil–root interface, to variation in plant element concentrations between dominant forbs and grasses in the temperate steppe. These findings greatly enhance our mechanistic understanding of the effects of N deposition on grassland communities.

Belowground plant traits play important roles in plant diversity loss driven by atmospheric nitrogen (N) deposition. However, the way N enrichment shapes plant microhabitats by patterning belowground traits and finally determines aboveground responses is poorly understood. Here, we investigated the rhizosheath trait of 74 plant species in seven N-addition simulation experiments across multiple grassland ecosystems in China. We found that rhizosheath formation differed among plant functional groups and contributed to changes in plant community composition induced by N enrichment. Compared with forb species, grass and sedge species exhibited distinct rhizosheaths; moreover, grasses and sedges expanded their rhizosheaths with increasing N-addition rate which allowed them to colonize belowground habitats. Grasses also shaped a different microenvironment around their roots compared with forbs by affecting the physicochemical, biological, and stress-avoiding properties of their rhizosphere soil. Rhizosheaths act as a "biofilm-like shield" by the accumulation of protective compounds, carboxylic anions and polysaccharides, determined by both plants and microorganisms. This enhanced the tolerance of grasses and sedges to stresses induced by N enrichment. Conversely, forbs lacked the protective rhizosheaths which renders their roots sensitive to stresses induced by N enrichment, thus contributing to their disappearance under N-enriched conditions. This study uncovers the processes by which belowground facilitation and trait matching affect aboveground responses under conditions of N enrichment, which advances our