Document: LEW-3-34-57

Developmental and physiological constraints on the CO₂ response of a developmentally-determinant plant.

LEWIS, J.D.* ¹, X.Z.WANG ², K.L.GRIFFIN ² and D.T.TISSUE ³

Fordham University, Armonk, NY 10504 ¹
Columbia University, Palisades, NY 10964 ²
Texas Tech University, Lubbock, TX 79409 ³

Abstract:
Plant responses to growth in elevated CO₂ may be regulated by both developmental and physiological factors, although few studies have examined the relative effects of these processes. To examine the relative effects of these processes on photosynthetic responses to elevated CO₂ in a developmentally-determinant plant, we grew Xanthium sp. (common cocklebur) in chambers maintained at either 365 or 730 ppm CO₂, with an 18 h photoperiod and a non-limiting nutrient supply. To compare photosynthetic responses at different developmental stages, six cohorts were planted at five-day intervals. For each cohort, measurements were initiated 15 days after emergence and were continued every five days until 45 days after the emergence of the first cohort. Across cohorts, mean net photosynthetic rates were 35 ^-2 s^-1 initially and declined 7% per week until initiation of flowering. As a result, on a given day, mean net photosynthetic rates were higher in younger compared to older cohorts. Growth in elevated CO₂ increased mean net photosynthetic rates 28% on average. Additionally, plants grown in ambient and elevated CO₂ had similar net photosynthetic rates when measured at a common CO₂ concentration, indicating that growth in elevated CO₂ did not induce photosynthetic downregulation. Responses to growth in elevated CO₂ did not vary significantly across plant age or measurement day. For plants grown in elevated CO₂, increased carbohydrate sink capacity offset increased source activity during the vegetative growth stage.

Keywords: climate change, developmental stage, elevated carbon dioxide, photosynthesis, Xanthium

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.