Abstract: Based on a field experiment with simulated soil acidification through sulfur addition (0, 1, 2, 5, 10, 15, 20, 50 g S·m^-2·a^-1) in Erguna Forest-Steppe Ecotone Station of Chinese Academy of Sciences, we investigated specific leaf area, leaf dry matter content, leaf thickness, plant height, photosynthetic pigment contents and their ratios in two common species (Stipa baicalensis and Pulsatilla turczaninovii) to understand the responses of plant morphological traits and photosynthetic pigments to soil acidification. The results showed that S. baicalensis adapted to soil acidification primarily by changing morphological traits rather than photosynthetic pigments, which had an advantage in accessing light resources. S. baicalensis and P. turczaninovii exhibited similar morphological responses to soil acidification, characterized by a reduction in specific leaf area (with reductions of 12.0% and 8.0%, respectively), an increase in leaf dry matter content (with increases of 3.2% and 0.9%, respectively), and an increase in plant height (with increases of 3.4% and 15.0%, respectively). Leaf photosynthetic pigment concentrations in S. baicalensis showed no response to soil acidification, while P. turczaninovii reduced carotenoid content by 25.7% but increased in the ratio of chlorophyll to carotenoids by 51.4%. These changes were primarily influenced by the decrease of soil nitrate and calcium and magnesium contents induced by soil acidification. The results showed that S. baicalensis adapted to soil acidification primarily by changing morphological traits, which provided an advantage in accessing light resources. However, soil acidification tended to conserve the morphological traits of P. turczaninovii and exert stress on its photosynthetic system.

Key words: meadow grassland; soil acidification; soil nutrient availability; morphological trait; photosynthetic pigment