Abstract: 【Objective】 To explore the photosynthetic characteristics of Cyperus esculeutus under density-sowing date coupling in the central and western regions of Inner Mongolia,and to determine the appropriate sowing time and density for the cultivation of Cyperus esculeutus. 【Methods】 The experiment was carried out in the experimental base of Inner Mongolia Academy of Agricultural and Animal Husbandry Sciences. Fengchan No.2 was used as the test material with the split zone design,two sowing dates（S1 on April 30;S2 on May 10）and 3 densities（60 000 plants/hm² named D1;120 000 plants/hm² named D2;180 000 plants/hm² named D3）.The daily changes of net photosynthetic rate（Pn）,transpiration rate（Tr）,stomatal conductance（Gs）and intercellular CO₂ concentration（Ci）of the main stem leaves of Cyperus esculeutus at different growth periods were analysed. 【Results】 The diurnal variation trend of Pn,Tr and Gs of Cyperus esculeutus under the density-different sowing dates coupling was “M” shape,and the double peak values of Pn,Tr and Gs were at 10：00 and 13：00,10：00 and 14：00,12：00 and 14：00 at tuber primary stage,tuber swelling stage and tuber maturity stage,respectively. The diurnal variation of Ci presented a“U” shape distribution with the peak values at 8：00 and 18：00. The diurnal variation of Pn,Tr and Gs were all expressed as the tuber primary stage>tuber swelling stage>tuber maturity stage at the beginning of tuber. The daily average Pn and Gs were the highest in S2D3 treatment and significantly different from other treatments（P<0.05）,they were 16.086 7 μmol/（m²·s）,0.148 0 mol/（m²·s）respectively;the daily average Tr of S2D3 at tuber primary stage was the largest and significantly different from that of S1D3,S1D2 and S2D2（P<0.05）,at 0.003 7 mol/（m²·s）;Ci trough value appeared at 12：00 in tuber primary stage,13：00 at the swelling stage and maturity stage of tuber. The daily average Ci was the highest in S2D3 treatment at tuber primary stage and was significantly different from S1D1,S1D2 and S2D2 treatments（P<0.05）,at 142.959 6 μmol/mol. 【Conclusion】 The most suitable sowing date of Cyperus esculentus in central and western Inner Mongolia was mid-May with the density 180 000 plants/hm².

Key words: Cyperus esculentus, Sowing date, Planting density, Photosynthetic characteristics