Plantago Species Show Germination Improvement as a Function of Nitrate and Temperature

At the optimum temperature, which is the ideal range in which seeds germinate most efficiently, seed germination may be lower than expected under favorable conditions, and this is indicative of seed dormancy. Also, germination may be enhanced by additional and interacting factors, such as nitrate and light. However, little is known about the interplay between temperature, nitrate, and seed germination. Using seeds from 22 accessions of four Plantago species that occupy distinct pedoclimates, we applied a factorial experimental design to assess the relationship between exogenously applied nitrate (KNO3) and temperature on germination in a Petri dish experiment. The data explore the relationship between seed germination, temperatures, and seed- and maternal-source soil N content as either nitrite (NO2−), nitrate (NO3−), or ammonium (NH4+). The interpretation also considered the total N and C contents of seeds, and the soil of the maternal plant (of the test seed) sources. Significant interspecific effects of nitrate and temperature on seed germination were observed. The capacity of nitrate to enhance final germination may be diminished substantially at supra-optimum temperatures, e.g., P. lagopus germination at 15 °C was 7% lower than that seen for water-only treatment. In contrast, at sub-optimum and alternating temperatures, nitrate enhanced final germination differentially across the species tested. This suggests a shift to enhanced germination at lower temperatures in the presence of sufficient soil nitrate, facilitating seedling establishment earlier in the growing season. The seeds of some Plantago species showed increased germination as a function of nitrate and temperature, particularly those of P. lagopus. The findings indicate that species (and genotype) responses correlated with the prevailing temperature and rainfall patterns of the locality; such local adaptation would ensure that seed germination and establishment occur during a period when environmental conditions are optimal.