Ecological stoichiometric characteristics of the fine roots and rhizosphere soil of dominant plants at different altitudes in the Helan Mountains

In order to determine the variation characteristics and correlation of carbon (C), nitrogen (N), and phosphorus (P) contents in dominant plant fine roots and rhizosphere soil, as well as their ecological stoichiometric ratios, along an altitudinal gradient, we assessed five typical vegetation types (desert steppe, low mountain shrubland, evergreen coniferous forest, subalpine shrub meadow, and alpine shrub meadow) in the Helan Mountains from August to September 2023. We collected the fine roots of dominant plants and rhizosphere soil and determined their C, N, and P contents. The results revealed the total C in dominant plant fine roots and the C ꞉ N ratio increased with altitude, whereas the C ꞉ P and N ꞉ P ratios in rhizosphere soil showed an opposite trend. Comparatively, the total N and total P contents in dominant plant fine roots and the C ꞉ N ratio in rhizosphere soil showed an initial increase followed by a subsequent decline with increasing altitude, characterized by an inverted “V” distribution, with the maximum values being recorded in the evergreen coniferous forest, which was opposite to the trend observed for the C ꞉ P ratio in the dominant plant fine roots. In addition, we detected significant positive correlations between total C in the dominant plant fine roots and the organic C (P = 0.041), total N (P = 0.016), C ꞉ P ratio (P = 0.013), and N ꞉ P ratio (P = 0.007) in rhizosphere soil at different altitudes. Compared with lower altitudes (desert steppe and low mountain shrubland), we observed P limitation in the rhizosphere soil at higher altitudes (subalpine shrub meadow and alpine shrub meadow). The findings of this study will provide a scientific basis for the ecological restoration and long-term development of mountain ecosystems.