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 germinat ion and seedling performance. We collected seeds from mother plants of Brom us erectus grown in field plots at ambient and elevated CO2 (m-CO2, materna l CO2) and germinated them in the greenhouse in a reciprocal design under a mbient and elevated CO2 (o-CO2, offspring CO2). This design allowed us to e xamine both the direct effects of elevated CO, on germination and seedling growth and the indirect (maternal) effects via altered seed quality. Elevat ed m-CO2 significantly increased seed mass and increased the C:N ratio of s eeds from field-grown plants. Percentage and rate of germination were not a ffected 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 covaria te in ANOVA, a negative effect of m-CO2 on seedling size appeared which inc reased with increasing seed mass (significant covariateXm-CO2 interaction). This may indicate that the advantage of increased seed mass at elevated m- CO2 was offset by the reduced concentration of nitrogen land possibly other nutrients) in these seeds. In contrast to m-CO2, elevated o-CO2 greatly in creased seedling size, and this stimulatory effect of elevated o-CO2 was fo und to increase with increasing seed mass (significant covariateXo-CO2 inte raction). Taken together, these results suggest that in B. erectus transgen erational effects of elevated CO2 are relatively small. However, other fact ors (genetic and environmental) that contribute to variation in seed provis ioning can critically influence the responsiveness of seedlings to elevated CO2.