[…] In discussing their findings, Cruz et al. report that compared to ambient levels of CO2, elevated CO2 increased photosynthesis by 24 and 31 percent in the low and high N treatments, respectively. Plant height, stem diameter and leaf area in the high N treatment were also enhanced by 15.4, 14.0 and 26.8 percent, respectively, and by similar amounts for the height and stem diameter in the low N treatment. Elevated CO2 also increased the biomass of leaf, stem plus petiole, and root dry mass of papaya plants regardless of N treatment, leading to total dry mass enhancements of 56.6 percent in the high N treatments and 64.1 percent in the low N treatments (see figure below).
Figure 1. Total dry mass of papaya plants grown in controlled chambers at two different CO2 concentrations (High and Low; 750 and 390 ppm) and two different N treatments (High and Low; 8 mM NO3– or 3 mM NO3–). Adapted from Cruz et al. (2016).
Cruz et al. also report that “significant, but minor, differences were observed in total N content (leaf plus stem + petiole plus roots) between plants grown at different CO2 concentrations, but the same N levels.” Consequently, plant Nitrogen Use Efficiency (NUE) – the amount of carbon fixed per N unit – was around 40 percent greater in the CO2-enriched environments, regardless of the N level in the soil.
Commenting on their findings, Cruz et al. write that contrary to some other studies, which have suggested that low N reduces plant responses to increased CO2 levels, they found no such decline. In fact, their data indicate that elevated CO2 “alleviated the effect of low N on dry matter accumulation in papaya,” which they surmised is at least partially explained by a larger leaf area and higher rate of photosynthesis per leaf area unit observed under elevated CO2.
In light of all of the above, Cruz et al. conclude that “an increase in the atmospheric CO2 concentration [is] beneficial for dry mass production of papaya and alleviate[s] the negative effects of N reduction in the substrate on papaya growth.” Thus, in the future, those who cultivate this fruit of angels should find an angel in the ongoing rise in atmospheric CO2.
Nothing about the benefits of CO2 surprises any more. The only surprise is that the Green Left continue to ignore the data, hence the truth.
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