Effects of nitrogen and phosphorus addition on the trace elements of plant functional groups in meadow steppe

Increasing the input of nutrients in terrestrial ecosystems alters the bioavailability of trace elements in soil, thereby influencing plant community productivity. However, the effects of adding nitrogen (N) and phosphorus (P) on the contents of the trace elements and stoichiometric characteristics of plant functional groups in Hulunbuir meadow steppe grassland have yet to be sufficiently determined. In this study, we adopted a two-factor randomized block design to examine the effects of N addition 0 g·(m⁻²·a)⁻¹ (N₀)、1.55 g·(m⁻²·a)⁻¹ (N₁)、13.95 g·(m⁻²·a)⁻¹ (N₂), P addition 0 g·(m⁻²·a)⁻¹ (P₀)、5.24 g·(m⁻²·a)⁻¹ (P₁), and their interactions on the trace element (Fe, Mn, Cu and Zn) contents and aboveground biomass of plant functional groups in a Hulunbuir meadow steppe from 2018 to 2020. The results revealed that compared with the control treatment (N₀P₀), the addition of N led to significant reductions in the Fe contents and Fe:Cu and Mn:Cu ratios of Gramineae (P < 0.05), with respective reductions of 52.46%, 61.84%, and 47.39% recorded in response to the N₂P₀ treatment. Contrastingly, there was a significant 33.30% increase in the Fe content of Leguminosae. The addition of P resulted in significant reductions in the Fe contents of Compositae, and corresponding reductions in the ratios of Fe:Cu and Fe:Zn. Furthermore, interactions between the added N and P were found to have significant effects on the contents of Mn in Compositae and Cu and Zn contents in Leguminosae. Compared with the control (N₀P₀), a higher level of N supplementation (N₂P₀) promoted significant increases in the contents of Cu and Zn in Leguminosae and Mn contents of Compositae, whereas there significant reductions in these elements in response to the combined addition with P (N₂P₁). Moreover, there was a significant increase in the relative biomass of Gramineae in response to the addition of N, and the observed changes in relative biomass were found to be significantly negatively correlated with the contents of Fe, Mn, and Zn, and the ratios of Fe:Cu, Fe:Zn, Mn:Cu, and Mn:Zn. Overall, our findings revealed differences in the trace element utilization strategies of plants in different functional groups, with the homeostasis of trace elements being significantly influenced by the addition of N and P.