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Photosynthesis, respiration, and net primary production of sunflower stands in ambient and elevated atmospheric CO 2 concentrations: an invariant NPP:GPP ratio?
Author(s) -
Cheng Weixin,
Sims Daniel A.,
Luo Yiqi,
Coleman James S.,
Johnson Dale W.
Publication year - 2000
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1046/j.1365-2486.2000.00367.x
Subject(s) - primary production , photosynthesis , respiration , zoology , isotopologue , environmental science , atmospheric sciences , chemistry , ecosystem , botany , ecology , biology , physics , biochemistry , organic chemistry , molecule
Summary The effect of elevated CO 2 on photosynthesis, respiration, and growth efficiency of sunflower plants at the whole‐stand level was investigated using a whole‐system gas exchange facility (the EcoCELLs at the Desert Research Institute) and a 13 C natural tracer method. Total daily photosynthesis (GPP), net primary production (NPP), and respiration under the elevated CO 2 treatment were consistently higher than under the ambient CO 2 treatment. The overall level of enhancement due to elevated CO 2 was consistent with published results for a typical C3 plant species. The patterns of daily GPP and NPP through time approximated logistic curves under both CO 2 treatments. Regression analysis indicated that both the rate of increase (the parameter ‘ r ’) and the maximum value (the parameter ‘ k ’) of daily GPP and NPP under the elevated CO 2 treatment were significantly higher than under the ambient CO 2 treatment. The percentage increase in daily GPP due to elevated CO 2 varied systematically through time according to the logistic equations used for the two treatments. The GPP increase due to elevated CO 2 ranged from approximately 10% initially to 73% at the peak, while declining to about 33%, as predicted by the ratio of the two maximum values. Different values of percentage increase in GPP and NPP were obtained at different sampling times. This result demonstrated that one‐time measurements of percentage increases due to elevated CO 2 could be misleading, thereby making interpretation difficult. Although rhizosphere respiration was substantially enhanced by elevated CO 2 , no effect of elevated CO 2 on R:P (respiration:photosynthesis) was found, suggesting an invariant NPP:GPP ratio during the entire experiment. Further validation of the notion of an invariant NPP:GPP ratio may significantly simplify the process of quantifying terrestrial carbon sequestration by directly relating total photosynthesis to net primary production.