Our food in a changing climate: growth, yield, and nutrient changes of sweet potato grown across the spectrum of Co2 concentrations projected in the next 150 years

Abstract

The majority of CO2 fertilization studies have focused on rice, wheat, and soybean; however, climate change is expected to have greatest impact on regions of the world that rely heavily on root crops. This is the first study of its kind to determine how CO2 fertilization effects Ipomoea batatas Lam. (sweet potato) growth and nutrient concentrations across a full trajectory of CO2 concentrations projected for the next 150 years. A total of 64 sweet potato plants were grown to maturity in a split plot designed study with CO2 concentration (353, 763, 1,109, and 1,515 ppm) as the whole plot factor and fertilizer (conventional vs. organic) as the split-plot factor. We observed increases in average above-ground dry biomass at 763 ppm (24%, 13%), 1,109 ppm (25%, 41%), and 1,515 ppm (31%, 43%) and average storage root dry biomass increased at 763 ppm (95%, 88%), 1,109 ppm (99%, 62%), and 1,515 ppm (118%, 71%) for both conventional and organic treatments, respectively. Chemical analyses suggest that the increased biomass may be nutrient depleted due to significant (P < 0.05) increases in carbohydrates (4.4%, 2.0%) and decreases in protein (-34.6%,-28.6%) and phosphorus (-24.0%,-11.3%) concentrations for both the conventional and organic treatment, respectively. Significant decreases in magnesium (-25.8%) and decreasing trends (P < 0.1) were also found for calcium (-46.7%), sodium (-18.4%), iron (-42.1%) and manganese (-70.8%) for the conventional treatment. Decreased nutrient content of I. batatas grown under elevated CO2 could have negative implications globally, especially in developing countries that are already nutrient limited. The storage root biomass response of sweet potato exceeded the extrapolated trajectory of non-root crop experiments by 63 percent at 1520 ppm, indicating sweet potato may be better at utilizing very high atmospheric CO2 concentrations compared to non-root crop species. Storage root fertilization under very high CO2 concentrations could dramatically supplement crop production in some of the poorest nations of the world, provided that the response found for sweet potato represents a generalized root-crop response and can be extrapolated to agricultural systems. The dramatically enhanced performance of conventionally (i.e., synthetic) over organically (i.e., manure-based) fertilized plants suggests that optimal nutrient availability will be crucial for support of enhanced crop production at elevated pCO2.