Response of leaf stoichiometry of Oxytropis ochrocephala to elevation and slope aspect

Abstract

Slope aspect and elevation gradient, important topographic factors, affect plant growth and leaf carbon:nitrogen:phosphorus (C:N:P) stoichiometry by regulating local water and energy balances. The response of leaf stoichiometry to topographic factors reflects plant adaptation strategies to different habitats. Common in various grasslands across China, Oxytropis ochrocephala Bunge. is well known in pastoral areas for its toxicity. The effects of partial or full slope sunniness (south-facing) or shadiness (north-facing) and elevation (2400 m, 2600 m, 2800 m, 3000 m, or 3200 m) on the leaf C:N:P stoichiometry of O. ochrocephala was investigated in northwest China’s Qilian Mountains. While leaf C:N:P stoichiometry of O. ochrocephala changed with elevation, there was no uniform pattern of change: the greatest leaf C and P concentrations ([C]leaf, and [P]leaf) were measured at an elevation of 2800 m (417.81 g kg−1 and 1.17 g kg−1, respectively); the lowest [C]leaf was 360.43 g kg−1 at 2400 m, and the lowest [P]leaf was 0.81 g kg−1 at 2600 m. The greatest leaf N concentration ([N]leaf) was 38.29 g kg−1 at 3200 m, and the lowest was 31.94 g kg−1 at 2600 m. Leaf C:N, C:P and N:P ratios were all relatively greater at 2600 m. Across the elevation gradient, O. ochrocephala leaf nutrient concentrations and their stoichiometries were mainly determined by mean annual temperature, soil organic carbon, and soil organic carbon to soil total phosphorus ratio. The [C]leaf, [N]leaf, and [P]leaf were significantly greater on north-facing slope aspects (393.86 g kg−1, 38.04 g kg−1, and 1.16 g kg−1, respectively) than on south-facing slope aspects (365.39 g kg−1, 32.98 g kg−1, and 0.92 g kg−1, respectively). Leaf C:N, C:P, and N:P ratios were significantly lower on north-facing slope aspects (10.43, 416.49, and 39.73, respectively) than on south-facing slope aspects (11.14, 512.57, and 45.98, respectively). Differences in leaf nutrient concentrations and their stoichiometries in O. ochrocephala leaves between slope aspects were mainly determined by soil temperature and soil moisture content. In terms of leaf N:P ratios across the elevation gradient and the two slope aspects, results indicated that the growth of O. ochrocephala in the study region was mainly restricted by P.