Family- and population-level responses to atmospheric CO2 concentration: gas exchange and the allocation of C, N, and biomass in Plantago lanceolata (Plantaginaceae)
American Journal of Botany
To ascertain the inheritance of responses to changing atmospheric CO 2 content, we partitioned response to elevated CO 2 in Plantago lanceolata between families and populations in 18 families in two populations. Plants were grown in 35 Pa and 71 Pa partial pressure of CO 2 (pCO 2 ) in open-top chambers. We measured above-and belowground mass, carbon (C), nitrogen (N), hexose sugar, and gas exchange properties in both CO 2 treatments. Families within populations differed in mass, mass
... ss, mass allocation, root : shoot ratios, aboveground percentage N, C : N ratio, and gas exchange properties. The CO 2 ϫ family interaction is the main indicator of potential evolutionary responses to changing CO 2 . Significant CO 2 ϫ family interactions were observed for N content, C : N ratio, and photosynthetic rate (A: instantaneous light-saturated carbon assimilation capacity), intercellular CO 2 concentration, transpiration rate (E), and water use efficiency (WUE ϭ A/E), but not for stomatal conductance. Families differed significantly in acclimation across time. The ratio of A in elevated vs. ambient growth CO 2 , when measured at a common internal CO 2 partial pressure was 0.79, indicating downregulation of A under CO 2 enrichment. Mass, C : N ratio, percentage, C (%C), and soluble sugar all increased significantly but overall %N did not change. Increases in %C and sugar were significant and were coincident with redistribution of N aboveground. The observed variation among populations and families in response to CO 2 is evidence of genetic variation in response and therefore of the potential for novel evolutionary trajectories with rising atmospheric CO 2 .