Photosynthetic responses of cottonwood seedlings grown in glacial through future atmospheric [CO2] vary with phosphorus supply.
Plants often exhibit proportionately larger photosynthetic responses to the transition from glacial to modern [CO(2)] than from modern to future [CO(2)]. Although this pattern may reflect increased nutrient demand with increasing [CO(2)], few studies have examined the role of nutrient supply in regulating responses to the range of [CO(2)] from glacial to future [CO(2)]. 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 micromol mol(-1)), modern (350 µmol mol(-1)) and future (700 micromol mol(-1)) [CO(2)]. The A(sat) (light-saturated net photosynthetic rates at the growth [CO(2)]) response to future [CO(2)] decreased with decreasing P supply such that there was no response at the lowest P supply. However, P supply did not affect A(sat) responses to an increase from glacial to modern [CO(2)]. Photosynthetic capacity [e.g., final rubisco activity, apparent, maximal Rubisco-limited rate of photosynthesis (V(cmax)), apparent, maximal electron transport-limited rate of photosynthesis (J(max))], stomatal conductance (g(s)) and leaf P generally increased with increasing P supply but decreased with increasing [CO(2)]. Measures of carbohydrate sink capacity (e.g., leaf mass per unit leaf area, leaf starch) increased with both increasing P supply and increasing [CO(2)]. Changes in V(cmax) and g(s) together accounted for 78% of the variation in A(sat) among [CO(2)] and P treatments, suggesting significant biochemical and stomatal controls on photosynthesis. However, A(sat) responses to increasing [CO(2)] did not reflect the changes in the carbohydrate sink capacity. These results have important implications because low P already constrains responses to increasing [CO(2)] in many ecosystems, and our results suggest that the P demand will increasingly affect A(sat) in cottonwood as [CO(2)] continues to increase.
Tissue
David T
DT
University of Western Sydney, Centre for Plants and the Environment, Richmond, NSW 2753, Australia. d.tissue@uws.edu.au
Lewis
James D
JD
D000222:Adaptation, Physiological; D002245:Carbon Dioxide / Q000378:metabolism*; D057231:Climate Change; D017753:Ecosystem; D004579:Electron Transport; D007700:Kinetics; D010758:Phosphorus / Q000378:metabolism*; D010788:Photosynthesis; D010940:Plant Proteins / Q000378:metabolism; D054046:Plant Stomata / Q000378:metabolism; D032107:Populus / Q000254:growth & development / Q000378:metabolism*; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D036226:Seedlings / Q000254:growth & development / Q000378:metabolism*
D010940:Plant Proteins; D002245:Carbon Dioxide; D010758:Phosphorus; D012273:Ribulose-Bisphosphate Carboxylase