Photosynthetic acclimation of Pinus taeda (loblolly pine) to long-term growth in elevated pCO2 (FACE)
2002
Rogers, A. | Ellsworth, D.S.
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.
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