Predicting responses of photosynthesis and root fraction to elevated (CO 2 ) a : interactions among carbon, nitrogen, and growth *

Predicting responses of photosynthesis and root fraction to elevated (CO 2 ) a : interactions... ABSTRACT At elevated atmospheric CO2 concentrations ((CO2)a), photosynthetic capacity (Amax) and root fraction (ηR, the ratio of root to plant dry mass) increased in some studies and decreased in others. Here, we have explored possible causes of this, focusing on the relative magnitudes of the effects of elevated (CO2)a on specific leaf (nm) and plant (np) nitrogen concentrations, leaf mass per unit area (h), and plant nitrogen productivity (α). In our survey of 39 studies with 35 species, we found that elevated (CO2)a led to decreased nm and np in all the studies and to increased h and α in most of the studies. The magnitudes of these changes varied with species and with experimental conditions. Based on a model that integrated (CO2)a‐induced changes in leaf nitrogen into a biochemically based model of leaf photosynthesis, we predicted that, to a first approximation, photosynthesis will be upregulated (Amax will increase) when growth at increased (CO2)a leads to increases in h that are larger than decreases in nm. Photosynthesis will be downregulated (Amax will decrease) when increases in h are smaller than decreases in nm. The model suggests that photosynthetic capacity increases at elevated (CO2)a only when additional leaf mesophyll more than compensates the effects of nitrogen dilution. We considered two kinds of regulatory paradigms that could lead to varying responses of ηR to elevated (CO2)a, and compared the predictions of each with the data. A simple static model based on the functional balance concept predicts that ηR should increase when neither np nor h is very responsive to elevated (CO2)a. The quantitative and qualitative agreement of the predictions with data from the literature, however, is poor. A model that predicts ηR from the relative sensitivities of photosynthesis and relative growth rate to elevated (CO2)a corresponds much more closely to the observations. In general, root fraction increases if the response of photosynthesis to (CO2)a is greater than that of relative growth rate. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Plant Cell & Environment Wiley

Predicting responses of photosynthesis and root fraction to elevated (CO 2 ) a : interactions among carbon, nitrogen, and growth *

Plant Cell & Environment, Volume 17 (11) – Nov 1, 1994

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Publisher
Wiley
Copyright
Copyright © 1994 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0140-7791
eISSN
1365-3040
D.O.I.
10.1111/j.1365-3040.1994.tb02017.x
Publisher site
See Article on Publisher Site

Abstract

ABSTRACT At elevated atmospheric CO2 concentrations ((CO2)a), photosynthetic capacity (Amax) and root fraction (ηR, the ratio of root to plant dry mass) increased in some studies and decreased in others. Here, we have explored possible causes of this, focusing on the relative magnitudes of the effects of elevated (CO2)a on specific leaf (nm) and plant (np) nitrogen concentrations, leaf mass per unit area (h), and plant nitrogen productivity (α). In our survey of 39 studies with 35 species, we found that elevated (CO2)a led to decreased nm and np in all the studies and to increased h and α in most of the studies. The magnitudes of these changes varied with species and with experimental conditions. Based on a model that integrated (CO2)a‐induced changes in leaf nitrogen into a biochemically based model of leaf photosynthesis, we predicted that, to a first approximation, photosynthesis will be upregulated (Amax will increase) when growth at increased (CO2)a leads to increases in h that are larger than decreases in nm. Photosynthesis will be downregulated (Amax will decrease) when increases in h are smaller than decreases in nm. The model suggests that photosynthetic capacity increases at elevated (CO2)a only when additional leaf mesophyll more than compensates the effects of nitrogen dilution. We considered two kinds of regulatory paradigms that could lead to varying responses of ηR to elevated (CO2)a, and compared the predictions of each with the data. A simple static model based on the functional balance concept predicts that ηR should increase when neither np nor h is very responsive to elevated (CO2)a. The quantitative and qualitative agreement of the predictions with data from the literature, however, is poor. A model that predicts ηR from the relative sensitivities of photosynthesis and relative growth rate to elevated (CO2)a corresponds much more closely to the observations. In general, root fraction increases if the response of photosynthesis to (CO2)a is greater than that of relative growth rate.

Journal

Plant Cell & EnvironmentWiley

Published: Nov 1, 1994

References

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