干旱区生态环境知识资源中心

1. Two trends are consistent across the response of plant species to growth at elevated CO(2): decreased leaf nitrogen content and increased photosynthetic gas exchange. While both of these are very important to the understanding of plant and ecosystem responses to climate change, little research has evaluated the consequences of these patterns on reproductive allocation and seed production.

2. For this reason, Bromus madritensis ssp. rubens was grown in ambient (360 mu mol mol(-1)), x 1.5 ambient (550 mu mol mol(-1)) and elevated (700 mu mol mol(-1)) CO(2) environments to compare the relationship between allocation to growth and reproduction as a function of CO(2) growth environment.

3. There were no differences in final total biomass or reproductive mass between CO(2) growth environments. There were significant decreases in reproductive mass per unit total mass and per unit vegetative mass, but not per unit leaf surface area (LSA), as growth CO(2) environment increased from 360 to 700 mu mol mol(-1) CO(2). Despite these decreases, the number of seeds produced per unit LSA in elevated CO(2) significantly increased as compared to ambient CO(2). These results may be owing to a shift in allocation to greater investment in vegetative growth as compared to reproduction under elevated levels of atmospheric CO(2).

4. Prior to reproduction, there were no significant differences between CO(2) treatments in carbon uptake by leaves. In contrast, plants grown in elevated CO(2) did not show a decline in photosynthetic rate during seed filling, suggesting that nitrogen may not have been re-translocated from leaves to seeds as apparently occurred in ambient plants.

5. Patterns measured here may partially explain the parental effect of CO(2) environment exhibited in Bromus. Seeds produced from elevated parental CO(2) growth conditions lead to seedlings that produce smaller leaves that are delayed in development and smaller roots as compared to structures produced by seeds from ambient-grown parents.

6. Because the success of Bromus is partially owing to its ability to produce large numbers of viable seeds, these changes in reproductive allocation and subsequent seedling performance with respect to growth in an elevated CO(2) environment may have impacts on community composition in the Mojave Desert.