Family- and population-level responses to atmospheric Co-2 concentration: Gas exchange and the allocation of C, N, and biomass in Plantago lanceolata(Plantaginaceae)

To ascertain the inheritance of responses to changing atmospheric CO2 conte nt, we partitioned response to elevated CO, in Plantago lanceolata between families and populations in 18 families in two populations. Plants were gro wn in 35 Pa and 71 Pa partial pressure of CO2 (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, treatments. Families within populations differed in mass, mass allocation, root : shoot ratios. aboveg round percentage N. C:N ratio, and gas exchange properties. The CO2 x famil y interaction is the main indicator of potential evolutionary responses to changing CO2. Significant CO2 X family interactions were observed for N con tent. C: N ratio, and photosynthetic rate (A: instantaneous light-saturated carbon assimilation capacity), intercellular CO2 consentration, transpirat ion rate (E). and water use efficiency (WUE = AIE). but nut for stomatal co nductance. Families differed significantly in acclimation across time. The ratio of A in elevated vs. ambient growth CO,. when measured at a common in ternal CO, partial pressure was 0.79. indicating downregulation of A under CO2 enrichment. Mass, C : N ratio, percentage, C (%C). and soluble sugar al l increased significantly but overall %N did not change. Increases in %C an d sugar were significant and were coincident with redistribution of N above ground. The observed variation among populations and families in response t o CO? is evidence of genetic variation in response and therefore of the pot ential for novel evolutionary trajectories with rising atmospheric CO,.