Effect of increased concentration of soil CO2 on intermittent flushes of seed germination in Echinochloa crus-galli var. crus-galli

Abstract

Soil-buried seeds of barnyardgrass (Echinochloa crus-galli vat. crus-galli) germinated from April to June in three intermittent flushes. The later two flushes of germination occurred after heavy rainfall. Carbon dioxide concentration in soil air transiently increased to 30 dm3 m-3 after the rainfall, probably due to the increase in soil temperature and water potential. Germination of exhumed seeds was stimulated by exposure to CO2 at 30 dm3 m-3. Fluctuating temperature, light, water, ethylene, and nitrate are known to promote seed germination in many species. However, of these environmental factors, within ranges found in the field, only CO2 was effective in enhancing the germination of barnyardgrass seeds. We conclude that soil CO2 is responsible for causing intermittent flushes of germination. Detection of vegetation gaps may be explained by the responsiveness of buried seeds to CO2.