Effect of seed position in spikelet on life history of Eremopyrum distans (Poaceae) from the cold desert of north-west China.

BACKGROUND AND AIMS Most studies on seed position-dependent effects have focused on germination characteristics. Our aim was to determine the effects of seed position in the spikelet on differences in timing of germination and on the ecological life history of the grass Eremopyrum distans in its cold desert habitat. METHODS For seeds in three spikelet positions, morphology, mass and dormancy/germination characteristics were determined in the laboratory, and seeds planted in field plots with and without watering were followed to reproduction to investigate seedling emergence and survival, plant size and seed production. KEY RESULTS After maturation, of the seeds within the spikelet, basal ones (group 1) are the largest and have the highest proportion with physiological dormancy, while distal ones (group 3) are the smallest and have the highest proportion of non-dormant seeds. A higher percentage of seeds after-ripened in groups 2 and 3 than in group 1. Seeds sown in the field in early summer and watered at short, regular intervals germinated primarily in autumn, while those under natural soil moisture conditions germinated only in spring. Both cohorts completed their life cycle in early summer. Seeds in group 1 had lower percentages of seedling emergence and higher percentages of seedling survival than those in groups 2 and 3. Also, plants from group 1 seeds were larger and produced more seeds per plant than those from groups 2 and 3. CONCLUSIONS Seed position-dependent mass was associated with quantitative differences in several life history traits of E. distans. The environmentally enforced (low soil moisture) delay of germination from autumn to spring results in a reduction in fitness via reduction in number of seeds produced per plant.