Seed germination ecology of Eragrostis plana, an invasive weed of South American pasture lands.
Eragrostis plana is a warm-season perennial grass non-native to Brazil and has become a serious weed in pasture lands of Southern South America. The objective of this work was to evaluate the influence of environmental factors on seed germination and seedling emergence. Seeds germinated at constant temperatures from 15 up to 40°C, but germination percentages were higher than 94% only at alternate temperatures. Seeds completed the germination process in less than five days at 35/20°C. Light exposure boosted normal seedling frequency by 11%. Germination increased from 0 to 98% as water potential increased from -1.2 to 0 MPa, and 87% of the ungerminated seeds from -0.4 to -1.2 MPa germinated after the removal of the water restriction condition. Germination was equal or higher than 90% at sodium chloride concentrations up to 120 mM, but normal seedling frequency decreased progressively along concentration increase. The highest emergence rate (87%) was observed with seeds placed on the soil surface, while no emergence occurred at a depth of 4 cm. This set of information indicates that germination and emergence can occur over a wide range of conditions. Nevertheless, management strategies for E. plana must consider reducing the exposition of the seeds to germination triggering factors, such as exposition to radiation, diurnal temperature variation and moisture conditions. Measures may include soil cover or ploughing.