Photosynthetic acclimation of Pinus taeda (loblolly pine) to long‐term growth in elevated pCO2 (FACE)

Publisher Website
Google Scholar
Abstract
Growth in elevated pCO2 generally leads to a stimulation of net CO2 uptake rate. However, with long‐term growth the magnitude of this stimulation is often reduced. This phenomenon, termed acclimation, has been largely attributed to a loss of Rubisco (ribulose 1,5 bisphosphate carboxylase). The mechanism by which Rubisco content declines with long‐term growth is not certain. There is evidence for a sugar‐mediated, selective down‐regulation of Rubisco protein and also for a non‐selective loss of total leaf nitrogen, which impacts Rubisco levels indirectly. Over a season, and including needles at different developmental stages, we investigated these two potential mechanisms in well‐developed Pinus taeda grown for approximately 2·5 years in elevated (56 Pa) pCO2 using free air CO2 enrichment technology. Photosynthetic acclimation, as manifested by a decrease in the activity of Rubisco measured both in vivo (− 25%, via gas exchange) and in vitro (− 35%, via enzyme assays), was observed with growth in elevated pCO2. This acclimation was observed in one‐year‐old needles but not in current‐year needles. Needles exhibiting acclimation had reduced levels of Lsu Rubisco (− 25%) and an increased foliar carbohydrate content (+ 30%) but showed no evidence of a decrease in needle nitrogen or total protein content. These data support the concept that photosynthetic acclimation in elevated pCO2 is caused by a selective down‐regulation of Rubisco.