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Title: Carbon dioxide stimulation of photosynthesis in Liquidambar styraciflua is not sustained during a 12-year field experiment

Elevated atmospheric CO2 (eCO2) often increases photosynthetic CO2 assimilation (A) in field studies of temperate tree species, although there is evidence that the increases may decline through time due to biochemical and morphological acclimation, and environmental constraints. Indeed, at the free air CO2 enrichment (FACE) study in Oak Ridge, Tennessee, A was increased in 12-year-old sweetgum trees following two years of ~40% enhancement of CO2. A was re-assessed a decade later to determine if initial enhancement of eCO2 was sustained through time. Measurements were conducted at prevailing CO2 and temperature on detached, re-hydrated branches using a portable gas exchange system. Photosynthetic CO2 response curves (A versus the CO2 concentration in the intercellular air space (Ci); or A-Ci curves) were contrasted with earlier measurements using consistent leaf photosynthesis model equations. We accessed relationships between light-saturated photosynthesis (Asat), maximum electron transport rate (Jmax), maximum Rubisco activity (Vcmax) chlorophyll content and foliar nitrogen (N) and chlorophyll content. In 1999, light-saturated photosynthesis (Asat) for eCO2 treatments was 15.4 ± 0.8 μmol m-2 s-1, 22% higher than aCO2 treatments (P<0.01). By 2009, Asat declined to <50% of 1999 values, and there was no longer a significant effect of eCO2 (Asat = 6.9 or 5.7 ±more » 0.7 μmol m-2 s-1 for eCO2 or aCO2, respectively). In 1999, there was no treatment effect on area-based foliar N; however, by 2008, N content in eCO2 foliage was 17% less than in aCO2 foliage. Photosynthetic N use efficiency (Asat:N) was greater in eCO2 in 1999 resulting in greater Asat despite similar N content, but the enhanced efficiency in eCO2 trees was lost as foliar N declined to sub-optimal levels. There was no treatment difference in the declining linear relationships between Jmax or Vcmax with declining N, or in the ratio of Jmax:Vcmax through time. Results suggest that initial enhancement of photosynthesis to elevated CO2 will not be sustained through time if nitrogen becomes limited.« less
 [1] ;  [1] ;  [2] ;  [1] ;  [3]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Macquarie Univ., NSW (Australia)
  3. Univ. of Western Sydney, Richmond, NSW (Australia)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
AoB Plants
Additional Journal Information:
Journal Volume: 7; Journal ID: ISSN 2041-2851
Oxford University Press; Annals of Botany Company
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
60 APPLIED LIFE SCIENCES; Acclimation; down-regulation; free-air CO2 enrichment; nitrogen limitation; sweetgum.; 54 ENVIRONMENTAL SCIENCES; sweetgum
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1261417