Tokyo stocks opened sharply lower Tuesday, with the Nikkei index falling below the 26,000 mark for the first time in about two months, as the market reflected concern over the adverse impact of China’s stringent COVID-19 restrictions on the global economy. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 443.56 points, or 1.69 percent, from Monday to 25,875.78. The broader Topix index was down 32.26 points, or 1.72 percent, at 1,846.13. On the top-tier Prime Market, decliners were led by mining, air transportation and nonferrous metal issues. At 9 a.m., the dollar fe…