The growth response of plants to elevated CO2 under non-optimal environmental conditions

Abstract

Under benign environmental conditions, plant growth is generally stimulated by elevated atmospheric CO concentrations. When environmental conditions become sub- or supra-optimal for growth, changes in the biomass enhancement ratio (BER; total plant biomass at elevated CO divided by plant biomass at the current CO level) may occur. We analysed literature sources that studied CO×environment interactions on the growth of herbaceous species and tree seedlings during the vegetative phase. For each experiment we calculated the difference in BER for plants that were grown under 'optimal' and 'non-optimal' conditions. Assuming that interactions would be most apparent if the environmental stress strongly diminished growth, we scaled the difference in the BER values by the growth reduction due to the stress factor. In our compilation we found a large variability in CO×environment interactions between experiments. To test the impact of experimental design, we simulated a range of analyses with a plant-to-plant variation in size common in experimental plant populations, in combination with a number of replicates generally used in CO×environment studies. A similar variation in results was found as in the compilation of real experiments, showing the strong impact of stochasticity. We therefore caution against strong inferences derived from single experiments and suggest rather a reliance on average interactions across a range of experiments. Averaged over the literature data available, low soil nutrient supply or sub-optimal temperatures were found to reduce the proportional growth stimulation of elevated CO. In contrast, BER increased when plants were grown at low water supply, albeit relatively modestly. Reduced irradiance or high salinity caused BER to increase in some cases and decrease in others, resulting in an average interaction with elevated CO that was not significant. Under high ozone concentrations, the relative growth enhancement by elevated CO was strongly increased, to the extent that high CO even compensated in an absolute way for the harmful effect of ozone on growth. No systematic difference in response was found between herbaceous and woody species for any of the environmental variables considered.

Nitrate assimilation in plant shoots depends on photorespiration

“…If CO 2 inhibition of shoot NO 3 Ϫ assimilation were common among C 3 species, it could account for several responses of plants to elevated CO 2 , including the decline in shoot protein and the diminished activities of photosynthetic enzymes. Nitrogen availability determines plant responses to elevated CO 2 concentrations more than any other environmental factor (52,53), but ecosystems show a broad range of responses to elevated CO 2 concentrations, possibly as a result of the seasonal and spatial fluctuations in the relative availabilities of NH 4 ϩ and NO 3 Ϫ . For instance, ecosystems in which NH 4 ϩ is the dominant nitrogen form, such as pine forests (54) or wetlands (55), show a relatively large increase (Ϸ25%) in net primary productivity under CO 2 enrichment, whereas ecosystems in which NO 3 Ϫ is dominant, such as grasslands (56) or wheat fields, at standard fertilizer levels (low fertilizer treatment at Maricopa, AZ; ref.…”

CO<sub>2</sub> enrichment increases nutrient leaching from model forest ecosystems in subtropical China

“…There are some reports showed that the magnitude of the plant growth response to elevated CO 2 may vary greatly depending on soil nutrients conditions (Stitt and Krapp, 1999;Poorter and Perez-Soba, 2001). Our experiment showed larger losses of mineral nutrients (K + , Ca 2+ and Mg 2+ ) under elevated atmospheric CO 2 concentrations in subtropical China.…”

Growth of a poplar short rotation coppice under elevated atmospheric CO2 concentrations (EUROFACE) depends on fertilization and species

“…Interactions between CO 2 and N varied between experiments [28], but it is often accepted that only with non-deficient N availability, elevated CO 2 can stimulate growth and biomass production [25,30,32,41]. Previous findings from the POP-FACE study (the present EUROFACE study) showed that FACE enhanced the optical LAI of the high density plantation in the first year and in spring of the second year after planting as a result of a stimulation of individual leaf area and tree dimensions [12].…”