Effects of silicon and nitrogen fertilization on the growth and net photosynthetic rate of Thermopsis lanceolata in an alpine meadow

To clarify the effect of the addition of nitrogen and silicon fertilizer on the growth and net photosynthetic rate of Thermopsis lanceolate, we set up experiments in an alpine meadow. The treatments were nitrogen fertilizer (60 g·m^–2) addition, silicon fertilizer (0, 4, 8, and 12 g·m^–2) addition, and mixed addition of nitrogen and silicon fertilizer. The results are as follows: 1) after nitrogen fertilizer, silicon fertilizer, and mixed fertilizer addition, the plant height of T. lanceolate increased to various degrees; 2) after silicon fertilizer was added, with the increase in application, plant biomass, leaf biomass, specific leaf area, and net photosynthetic rate assumed a trend where it first increased and subsequently decreased; 3) after nitrogen fertilizer was added, plant biomass, leaf biomass, specific leaf area, and net photosynthetic rate decreased significantly (P < 0.05); 4) compared with nitrogen fertilizer addition alone, addition of silicon fertilizer along with nitrogen fertilizer (NSi₁、NSi₂、and NSi₃) enhanced the specific leaf area and net photosynthetic rate of the plant; and 5) there was a significant positive correlation between specific leaf area and net photosynthetic rate in the plant. Our studies found that nitrogen fertilizer addition inhibited the growth of T. lanceolate and decreased net photosynthetic rate; however, addition of silicon fertilizer along with nitrogen fertilizer improved both characteristics.