Elevation-driven variations in soil-plant stoichiometry and heavy metal dynamics in coniferous and Oak Forests of Gilgit Baltistan (GB), Pakistan

This study examined the effects of elevation gradients on on soil and plant stoichiometry and heavy metals distribution in Mixed Coniferous Forests (MCF) and Oak Forests (OF). Soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) were significantly higher at the 10 cm soil depth at elevation EL-2, followed by EL-3, in both forests; whereas the lowest values were observed at EL-1. MCF exhibited significantly higher SOC, TN, and TP concentrations than OF. Similarly, leaf carbon, nitrogen, and phosphorus concentrations were highest EL-2. In oak forests, leaf carbon, nitrogen, and phosphorus concentrations reached 458.4 mg kg  ⁻  ¹, 4.42 mg kg  ⁻  ¹, and 2.54 mg kg  ⁻  ¹, respectively. The Corresponding values in MCF were 472 mg kg  ⁻  ¹, 16.1 mg kg  ⁻  ¹, and 1.9 mg kg  ⁻  ¹, respectively, indicating greater nutrient accumulation at the mid-elevation site (EL-2). The leaf C:N ratio was significantly higher at EL-2, whereas the C:P and N:P ratios did not differ significantly among elevations. A similar pattern was observed in branches, bark, and litter. At EL-2 site, soil nickel (Ni), lead (Pb), cadmium (Cd), copper (Cu), and iron (Fe) concentrations at the 10 cm soil depth were significantly lower in MCF than in OF. Conversely, plant tissues in MCF exhibited higher concentrations of Ni, Pb, zinc (Zn), Cd, Cu, and Fe than those in OF at EL-1. Soil and plant stoichiometry are fundamental components of ecosystem functioning and nutrient cycling, and elevation gradients also play a critical role in regulating these processes. These findings offer valuable insights for developing sustainable forest management strategies that aim to mitigate heavy metal pollution in high-altitude ecosystems.