Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology

Nitrogen deficiency precludes a growth response to CO2 enrichment in C3 and C4 Panicum grasses

Oula Ghannoum and Jann P. Conroy

Australian Journal of Plant Physiology 25(5) 627 - 636
Published: 1998


We investigated the interaction of nitrogen (N) supply and CO2 enrichment on the growth and photosynthesis of Panicum laxum (C3), P. coloratum (C4) and P. antidotale (C4). Plants were grown at ambient CO2 partial pressures (pa) of either 36 (low) or 71 (high) Pa, in potted soil supplied with 0 (low) or 60 (high) mg N kg-1 soil week-1. Elevated CO2 enhanced total plant dry mass of all three species by approximately 28% under high N supply, but had no effect on biomass accumulation under N deficiency. CO2 enrichment resulted in reductions of CO2 assimilation rates (A; measured at comparable pa) of P. laxum, indicating acclimation of photosynthesis. This acclimation, which was more pronounced under N stress, was unrelated to changes in leaf N or non-structural carbohydrate concentrations, because neither were affected by CO2 enrichment. In the C4 grasses grown at low N, A were fully saturated at the current ambient pa, whereas at high N, A increased slightly when CO2 was raised to 71 Pa. N deficiency reduced the initial slope of the CO2 response curve of A in P. antidotale, and this effect was more pronounced at high CO2. In conclusion, the preclusion of a growth response to CO2 enrichment by N deficiency was correlated with a strong inhibition of A in the C3 species, and the saturation of A at below current atmospheric pa in C4 species.

© CSIRO 1998

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