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Plant Growth Response to CO2 and Nitrogen
(Crops: Wheat) -- Summary

Does a deficiency of soil nitrogen lessen the relative growth and yield stimulation of wheat that is typically provided by elevated levels of atmospheric CO2?

In exploring this question, Smart et al. (1998) grew wheat from seed for 23 days in controlled environment chambers maintained at atmospheric CO2 concentrations of 360 and 1000 ppm and two concentrations of soil nitrate, finding that the extra CO2 increased average plant biomass by approximately 15%, irrespective of soil nitrogen content.  In a more realistic FACE experiment, however, Brooks et al. (2000) grew spring wheat for two seasons at atmospheric CO2 concentrations of 370 and 570 ppm at both high and low levels of nitrogen fertility; and they obtained twice the yield enhancement (16% vs. 8%) in the high nitrogen treatment.

In an experiment with one additional variable, Vilhena-Cardoso and Barnes (2001) grew spring wheat for two months in environmental chambers fumigated with air containing atmospheric CO2 concentrations of either 350 or 700 ppm at ambient and elevated (75 ppb) ozone concentrations, while the plants were simultaneously subjected to either low, medium or high levels of soil nitrogen.  With respect to biomass production, the elevated CO2 treatment increased total plant dry weight by 44, 29 and 12% at the high, medium and low soil nitrogen levels, respectively.  In addition, although elevated ozone alone reduced plant biomass, the simultaneous application of elevated CO2 completely ameliorated its detrimental effects on biomass production, irrespective of soil nitrogen supply.

So why do the plants of some studies experience a major reduction in the relative growth stimulation provided by atmospheric CO2 enrichment under low soil nitrogen conditions, while other studies find the aerial fertilization effect of elevated CO2 to be independent of root-zone nitrogen concentration?  Based on studies of both potted and hydroponically-grown plants, Farage et al. (1998) determined that low root-zone nitrogen concentrations need not lead to photosynthetic acclimation (less than maximum potential rates of photosynthesis) in elevated CO2, as long as root-zone nitrogen supply is adequate to meet plant nitrogen needs to maintain the enhanced relative growth rate that is made possible by atmospheric CO2 enrichment.  When supply cannot meet this need, as is often the case in soils with limited nitrogen reserves, the aerial fertilization effect of atmospheric CO2 enrichment begins to be reduced and less-than-potential CO2-induced growth stimulation is observed.  Nevertheless, the acclimation process is the plant's "first line of defense" to keep its productivity from falling even further than it otherwise would, as it typically mobilizes nitrogen from "excess" rubisco and sends it to more needy plant sink tissues to allow for their continued growth and development (Theobald et al., 1998).

In conclusion, although atmospheric CO2 enrichment tends to increase the growth and yield of wheat under a wide range of soil nitrogen concentrations, including some that are very low, considerably greater CO2-induced enhancements are possible when more soil nitrogen is available, although the response can saturate at high soil nitrogen levels, with excess nitrogen providing little to no extra yield.

Brooks, T.J., Wall, G.W., Pinter Jr., P.J., Kimball, B.A., LaMorte, R.L., Leavitt, S.W., Matthias, A.D., Adamsen, F.J., Hunsaker, D.J. and Webber, A.N.  2000.  Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes. 3. Canopy architecture and gas exchange.  Photosynthesis Research 66: 97-108.

Farage, P.K., McKee, I.F. and Long, S.P.  1998. Does a low nitrogen supply necessarily lead to acclimation of photosynthesis to elevated CO2Plant Physiology 118: 573-580.

Smart, D.R., Ritchie, K., Bloom, A.J. and Bugbee, B.B.  1998.  Nitrogen balance for wheat canopies (Triticum aestivum cv. Veery 10) grown under elevated and ambient CO2 concentrations.  Plant, Cell and Environment 21: 753-763.

Theobald, J.C., Mitchell, R.A.C., Parry, M.A.J. and Lawlor, D.W.  1998.  Estimating the excess investment in ribulose-1,5-bisphosphate carboxylase/oxygenase in leaves of spring wheat grown under elevated CO2Plant Physiology 118: 945-955.

Vilhena-Cardoso, J. and Barnes, J.  2001.  Does nitrogen supply affect the response of wheat (Triticum aestivum cv. Hanno) to the combination of elevated CO2 and O3Journal of Experimental Botany 52: 1901-1911.