Journal Article

Photosynthetic responses of cottonwood seedlings grown in glacial through future atmospheric [CO<sub>2</sub>] vary with phosphorus supply

David T. Tissue and James D. Lewis

Edited by Ülo Niinemets

in Tree Physiology

Volume 30, issue 11, pages 1361-1372
Published in print November 2010 | ISSN: 0829-318X
Published online September 2010 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/tpq077
Photosynthetic responses of cottonwood seedlings grown in glacial through future atmospheric [CO2] vary with phosphorus supply

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Plants often exhibit proportionately larger photosynthetic responses to the transition from glacial to modern [CO2] than from modern to future [CO2]. Although this pattern may reflect increased nutrient demand with increasing [CO2], few studies have examined the role of nutrient supply in regulating responses to the range of [CO2] from glacial to future [CO2]. In this study, we examined the effects of P supply (0.004–0.5 mM) on photosynthetic responses of Populus deltoides (cottonwood) seedlings to glacial (200 µmol mol−1), modern (350 µmol mol−1) and future (700 µmol mol−1) [CO2]. The Asat (light-saturated net photosynthetic rates at the growth [CO2]) response to future [CO2] decreased with decreasing P supply such that there was no response at the lowest P supply. However, P supply did not affect Asat responses to an increase from glacial to modern [CO2]. Photosynthetic capacity [e.g., final rubisco activity, apparent, maximal Rubisco-limited rate of photosynthesis (Vcmax), apparent, maximal electron transport-limited rate of photosynthesis (Jmax)], stomatal conductance (gs) and leaf P generally increased with increasing P supply but decreased with increasing [CO2]. Measures of carbohydrate sink capacity (e.g., leaf mass per unit leaf area, leaf starch) increased with both increasing P supply and increasing [CO2]. Changes in Vcmax and gs together accounted for 78% of the variation in Asat among [CO2] and P treatments, suggesting significant biochemical and stomatal controls on photosynthesis. However, Asat responses to increasing [CO2] did not reflect the changes in the carbohydrate sink capacity. These results have important implications because low P already constrains responses to increasing [CO2] in many ecosystems, and our results suggest that the P demand will increasingly affect Asat in cottonwood as [CO2] continues to increase.

Keywords: climate change; nutrient limitation; photosynthesis; Populus deltoides (eastern cottonwood); Rubisco activity; source:sink balance; stomatal conductance

Journal Article.  7154 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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