Maternal and direct effects of elevated CO2 on seed provisioning, germination and seedling growth in Bromus erectus.

Elevated CO2 can affect plant fitness not only through its effects on seed production but also by altering the quality of seeds and therefore germination and seedling performance. We collected seeds from mother plants of Bromus erectus grown in field plots at ambient and elevated CO2 (m-CO2, maternal CO2) and germinated them in the greenhouse in a reciprocal design under ambient and elevated CO2 (o-CO2, offspring CO2). This design allowed us to examine both the direct effects of elevated CO2 on germination and seedling growth and the indirect (maternal) effects via altered seed quality. Elevated m-CO2 significantly increased seed mass and increased the C:N ratio of seeds from field-grown plants. Percentage and rate of germination were not affected by the m-CO2 or o-CO2 treatments. Similarly, elevated m-CO2 had no significant effect on seedling size as estimated by the total leaf length. When differences in seed mass were adjusted by using seed mass as a covariate in ANOVA, a negative effect of m-CO2 on seedling size appeared which increased with increasing seed mass (significant covariate×m-CO2 interaction). This may indicate that the advantage of increased seed mass at elevated m-CO2 was offset by the reduced concentration of nitrogen (and possibly other nutrients) in these seeds. In contrast to m-CO2, elevated o-CO2 greatly increased seedling size, and this stimulatory effect of elevated o-CO2 was found to increase with increasing seed mass (significant covariate×o-CO2 interaction). Taken together, these results suggest that in B. erectus transgenerational effects of elevated CO2 are relatively small. However, other factors (genetic and environmental) that contribute to variation in seed provisioning can critically influence the responsiveness of seedlings to elevated CO2.