The Effects of parental CO2 and offspring nutrient environment on initial growth and photosynthesis in an annual grass

Document Type



Seeds of Bromus madritensis ssp. rubens (red brome, an exotic annual grass in the Mojave Desert), from parents grown at three CO2 levels (360, 550, and 700 μmol mol−1), were grown in factorial CO2 (360, 550, and 700 μmol mol−1) and nutrient (zero addition, 1:40‐strength, and 1:10‐strength Hoagland’s solution) environments to evaluate parental CO2 effects on offspring performance characteristics across a range of developmental environments. We evaluated growth rate, leaf nitrogen content, and photosynthetic gas exchange over a 3‐wk period. Seedlings from elevated‐CO2 parental seed sources (2 x AMB seedlings) had reduced growth rates compared with seedlings from ambient CO2–grown parents (AMB seedlings). As compared to 360, 550 and 700 μmol mol−1 CO2‐stimulated relative growth rate (RGR) for most seedlings, the degree of stimulation was greatest for the AMB seedlings and least for the 2 x AMB seedlings. Instantaneous rates of photosynthesis mirrored the pattern of RGR across the parental CO2 and seedling CO2 treatment combinations. At 360 μmol mol−1 CO2, photosynthetic rates of 2 x AMB seedlings were half that of AMB seedlings, but at 700 μmol mol−1 CO2, their photosynthetic rates were not statistically different. Analysis of A‐Ci response curves indicates that 2 x AMB seedlings had reduced Rubisco activity compared with AMB seedlings, most likely as a result of less total nitrogen investment in leaves. AMB seedlings responded to low levels of nutrient input (1:40 Hoagland’s solution) with increased growth rates and leaf nitrogen content compared with zero nutrient addition. The 2 x AMB seedlings required the application of 1:10 Hoagland’s before an increase in these two parameters, compared with zero nutrient addition. These results indicate that elevated CO2 affects Bromus offspring performance through changes in adult‐seed‐seedling nitrogen dynamics, such that reductions in photosynthesis and growth rates occur in successive generations. Species‐specific allocation patterns that increase or decrease nitrogen allocation to seeds may enhance or diminish the ability of subsequent offspring to respond to an elevated CO2 environment.


Plant Biology