Field Sandbur (Cenchrus pauciflorus) Seeds in the Same Bur Respond Differently to Temperature and Water Potential in Relation to Germination in a Semi-Arid Environment, China

The success of a biological invasion relies on the environment and is closely linked to factors such as water and temperature. Invasive plant species display different seed characteristics, including shape. Field sandbur (Cenchrus pauciflorus) is a globally widespread invasive species capable of adapting to broad environmental conditions. However, its germination response to water and temperature still remains unclear. C. pauciflorus contains two seeds in the same bur that differ in size: big seeds (M) and small seeds (P). Separate greenhouse experiments were conducted under different temperature regimes (0/10°C, 5/15°C, 10/20°C, 15/25°C, 18/28°C, 20/30°C and 25/35°C) and water potentials (-1.50Mpa, -1.00Mpa, -0.75Mpa, -0.50Mpa, -0.25Mpa and 0Mpa) for M and P seeds. The results support the hypothesis that germination of C. pauciflorus is significantly influenced by seed type, temperature and water potential. M and P seeds responded differently to varied alternative temperatures and water potentials. However, M and P seeds were more sensitive to water potential than to temperature. Optimal conditions for M and P seed germination were measured at 25/35°C (night temperature/day temperature) and 20/30°C, respectively. In contrast, the highest germination rate was observed for the 0Mpa of the water potential treatment. Additionally, base temperature (Tbase) and base water potential (Wbase) were lower for M (7.7°C, -1.11Mpa at 10/20°C, and -1.07Mpa at 20/30°C) than for P (9.4°C, -0.92Mpa at 10/20°C, and -0.52Mpa at 20/30°C). These different germination strategies of M and P seeds with respect to temperature and water potential increased overall plant propagation. These results indicate that tropical and subtropical regions water potentials beyond -0.50Mpa (10/20°C) or -1.00Mpa (20/30°C) face a potential risk of C. pauciflorus invasion.