Variability in seeds\' physicochemical characteristics, germination and seedling growth within and between two French Populus nigra populations
To improve understanding of the physiology, ecology and regeneration requirements of black poplar (Populus nigra), a severely endangered tree species in Europe, we analysed the biochemical composition of seeds from 20 families derived from open pollination of 20 trees in two contrasting environments in France, along the Dr\^ome and Loire rivers. Significant between-family differences were detected. Total lipid contents differed qualitatively between seed of the two populations and were higher in Dr\^ome population (214 more or less 29.8 versus 172.72 more or less 19.77 mg.g\-1 dw). Soluble sugars were less abundant in seeds of the Dr\^ome population (78.78 more or less 10.01 versus 104.10 more or less 25.32 mg.g\-1 dw). The protein content (322 more or less 74.3 mg.g\-1 dw) and quantity of reserve proteins did not differ between seeds of the two populations. Measurements in three consecutive years showed that seeds of the Loire population had significantly higher dry weight (0.69 more or less 0.10 versus 0.45 more or less 0.10 mg.g\-1 dw), but this did not significantly affect the germination rate or root growth of the seedlings measured 5 days after sowing. However, one group of Loire seedlings had substantially longer juvenile roots than another group. Overall, the results suggest that intrinsic qualities of the seeds are not critical factors in early stages and in selection pressure of the species life cycle and recruitment.
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