Spergula arvenis produces two types of seeds that differ in the absence (non papillate, NP) or presence (papillate, P) of papilla on the seed coat. Corn spurry inhabits cultivated soils and ruderal fields and usually encounters substantial variations in soil nutrients. The objective of this study was to determine the effects of nitrate concentrations and temperature (10–30°C) on the germination of heteromorphic seeds. NP and P seeds were characterized by different nitrate optima, dormancy-breaking temperature and initial germination times. NP seeds germinated better and faster than P seeds. NP seeds germinated at all nitrate solutions and all temperatures. NP seeds responded to 5 mM nitrate concentration at 15, 20 and 30°C. In 25 and 50 mM KNO₃ solution, the germination was relatively high and leveled out at a wider temperature range (15–30°C). The highest germination of NP seeds was at 25°C (25, 50 mM KNO₃). NP seeds began to germinate on the second day of the germination test at 15–30°C (in 25 mM KNO₃ solution) and at 20–30°C (in 50 mM KNO₃ solution). The germination percentage of P seeds was lower than NP seeds under identical conditions. P seeds in water failed to sprout at any of the applied incubation temperatures. Seeds incubated in low and medium nitrate concentrations did not germinate or germinated weakly at all temperatures. Seed dormancy was released in solutions with high nitrate levels incubated at 10–25°C. The highest germination of P seeds was at 50 mM solution and at 15°C. Under these conditions, the P seeds germinated the most (reaching 43%), with the initial germination being observed on experimental day 3,7. P seeds had more requirements for germination than NP seeds. However, in 50 mM KNO₃ solution the range of temperatures over which these seeds were able to germinate was the same regardless of seed type. Nevertheless, the percentage of NP germinants was still much higher. The different requirements for germination of NP and P seeds may result in the production of two offspring cohorts that differ in response to nitrate levels in the soil, population density and temperature conditions. Most likely, this germination strategy is an important mechanism of ecological adaptation that enables the survival of S. arvensis plants in an unpredictable environment.
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