Biogeochemical stoichiometry of soil and plant functional groups along a primary successional gradient following glacial retreat on the eastern Tibetan plateau

Di-nitrogen (N2)-fixing plants are crucial for vegetation development following glacial retreat; however, there is currently limited understanding of how the shifting of N2-fixing and non N2-fixing plant groups may influence the stoichiometric composition of the developing plant community and associated soils. Carbon (C), nitrogen (N), and phosphorus (P) concentrations and elementary stoichiometry were investigated in soil and the N2-fixing and non-N2-fixing plant communities across a 127-yr glacial primary succession chronosequence on the eastern slope of the Qinghai-Tibetan Plateau. Soil organic C (SOC), total N (TN), and available P (AP) gradually increased along succession, but total P (TP) was greatest at the 37-yr site, resulting in an increasing trend of soil N:P and a decreasing trend of N:AP ratios along the chronosequence. N2-fixing species had higher foliar N and P concentrations than non-N2-fixing species and exhibited a higher leaf N:P ratios in early stages (37 yr and younger) of the succession. Elementary concentration and C, N, P stoichiometry in plant leaves were strongly associated with both N2-fixing and non-N2 fixing plant biomasses, while those in soils were related only with the biomass of non-N2 fixing species. The community-weighted leaf N:P ratios increased from 14.0 at 7-yr to 19.9 at 59-yr and then decreased to 12.9 at 127-yr after glacial retreat, suggests the ecosystem as a whole is not N- or P-limited at the beginning of primary succession, but may become P-limited at the middle stages and then shift towards N limitation at the late successional stages. The results confirm that both N2-fixing and non-N2-fixing species can overcome N limitation in the early primary succession and highlights the different roles of pioneer N2-fixing and non-N2-fixing species in mediating vegetation and soil C, N and P stoichiometry with primary succession following glacial retreat.