Paper Reviewed
Wang, J., Liu, X., Zhang, X. Li, L., Lam, S.K. and Pan, G. 2019. Changes in plant C, N and P ratios under elevated [CO2] and canopy warming in a rice-winter wheat rotation system. Scientific Reports 9: 5424, DOI: 10.1038/s41598-019-41944-1.

Introducing their work, Wang et al. (2019) state that future plant growth might be constrained by nutrient deficiency under elevated atmospheric CO2 concentrations, where enhanced growth stimulated by higher CO2 levels may be tempered by an enhanced demand for nutrients to sustain that growth. And thus they go on to explore this possibility in a rice and winter wheat cropping rotation conducted in 2012 and 2013.

The experiment was conducted at a field location of the Institute of Resource, Ecosystem and Environment of Agriculture, Nanjiang Agricultural University, in the subtropical climate of Jiangsu Province, China. Treatment conditions included a Free-air CO2 Enrichment (FACE) design in which rice (Oryza sativa, cv. Changyou No. 5) and wheat (Triticum aestivum, cv. Yangmai No. 14) plants were grown under either ambient or elevated CO2 concentrations (514 ppm for rice and 505 ppm for wheat) and either ambient or elevated temperatures (+1.8 °C above ambient for rice and +1.5 °C above ambient for wheat, which warming of the canopy air was achieved via infrared heating) across the growing season. At stem elongation, heading and ripening stages for both plants, samples were collected and analyzed to determine carbon (C), nitrogen (N) and phosphorus (P) concentrations.

In describing their findings, Wang et al. report that elevated CO2 reduced whole-plant N concentration by 10.7% and 7.4% for rice and wheat, respectively (see Figure 1). Warming, in contrast, increased it by 12.4% for rice and 10.5% for wheat. N concentrations in the elevated CO2 and elevated temperature treatment were not statistically different from that observed for rice or wheat under control (ambient temperature and ambient CO2) conditions.

With respect to plant P concentration, as also shown in the figure below, elevated CO2 decreased it in rice (by 10%) but had no effect in wheat. Warming, on the other hand, increased P concentration in wheat by 14.8% but had no effect in rice. And in the combined elevated CO2 and elevated temperature treatment, P concentration did not change in rice but rose by 19% in wheat.

Commenting on their findings, Wang et al. say that "the responses of nutrient uptake and ratios under combined elevated CO2 and warming were different from that under elevated CO2 or warming alone," which "suggests that an offset effect exists between elevated CO2 and warming." Thus, in the future, if both temperatures and atmospheric CO2 concentrations rise, rice and wheat N concentrations will likely remain unchanged, rice P concentrations will also stay the same, whereas wheat P concentrations will increase. And that bodes well for future food production needs.

Figure 1. Changes in whole-plant nitrogen (N) and phosphorus (P) concentrations for rice and wheat averaged across three growth stages under various treatment conditions (CK = ambient CO2 and ambient temperature, CE = elevated CO2 and ambient temperature, WA = ambient CO2 and elevated temperature, CW = elevated CO2 and elevated temperature). Different letters indicate significant differences between treatments at p < 0.05. Source: Wang et al. (2019).