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The Effects of Elevated CO2 and Temperature on Rice Nutrient Levels

Paper Reviewed
Wang, J., Li, L., Lam, S.K., Zhang, X., Liu, X. and Pan, G. 2018. Changes in nutrient uptake and utilization by rice under simulated climate change conditions: A 2-year experiment in a paddy field. Agricultural and Forest Meteorology 250/251: 202-208.

Much remains to be learned about the potential impacts of elevated atmospheric CO2 on plant nutrients.

In general, studies to date almost conclusively demonstrate that plants growing in elevated CO2 environments tend to extract a larger amount of nutrients from the soil (such as nitrogen, potassium, phosphorus, etc.) and into their tissues on a per plant basis, compared to plants growing at lower atmospheric CO2 concentrations. Consequently, the total nutrient content per plant typically increases with atmospheric CO2 enrichment. Additionally, the amount of plant biomass produced per unit of nutrient uptake, or nutrient use efficiency, also typically rises at higher CO2 levels. Plant nutrient concentration (nutrient amount per unit of plant biomass), on the other hand, has exhibited mixed results, with studies showing increases, decreases or similar concentrations at elevated levels of atmospheric CO2.

One of the latest studies to examine such impacts was recently conducted by Wang et al. (2018). Briefly, they grew rice (Oryza sativa, cv. Changyou No. 5) in outdoor chambers at the experimental farm station of the Institute of Resource, Ecosystem and Environment of Agriculture, Nanjing Agricultural University, Jiangsu Province, China, under two elevated CO2 concentrations (~400 and 500 ppm) and two temperature regimes (ambient and ambient +2C) for two growing seasons (2013 and 2014). During each year, the researchers measured various parameters pertaining to plant growth and nutrient levels at the jointing, heading and ripening stages. Their objective was to examine the changes in plant nutrient concentration, nutrient content, nutrient use efficiency, aboveground biomass and grain yield in response to warming and elevated CO2.

In general, their results revealed that warming alone reduced both aboveground biomass and grain yield, while elevated CO2 alone increased it. In combination (elevated temperature and CO2 treatment), the benefits of an approximate 100 ppm increase in atmospheric CO2 were strong enough to overcome the negative impacts of warming on grain yield, resulting in values that were statistically similar to that observed under control conditions (ambient CO2 and ambient temperature).

With respect to plant nutrient measurements, Wang et al. report in the Conclusion section of their paper that changes in plant nutrient concentration, nutrient content and nutrient use efficiency "were not consistent" among the elements they measured (nitrogen, phosphorus and potassium), across the CO2 and temperature treatments they employed, or the years in which they were studied. In other words, there was no clear trend or signal to support the notion that any of these plant nutrition measures will significantly change in a world of both rising temperature and atmospheric CO2.

Posted 6 July 2018