• Energy Research

AbstractOne of the many ways that climate change may affect human health is by altering the nutrient content of food crops. However, previous attempts to study the effects of increased atmospheric CO2 on crop nutrition have been limited by small sample sizes and/or artificial growing conditions. Here we present data from a meta-analysis of the nutritional contents of the edible portions of 41 cultivars of six major crop species grown using free-air CO2 enrichment (FACE) technology to expose crops to ambient and elevated CO2 concentrations in otherwise normal field cultivation conditions. This data, collected across three continents, represents over ten times more data on the nutrient content of crops grown in FACE experiments than was previously available. We expect it to be deeply useful to future studies, such as efforts to understand the impacts of elevated atmospheric CO2 on crop macro- and micronutrient concentrations, or attempts to alleviate harmful effects of these changes for the billions of people who depend on these crops for essential nutrients.

Atmospheric CO2 concentrations ([CO2]) have increased by more than 100 μmol mol−1 over the last century and are projected to rise further. Breeding cultivars with a greater response to elevated [CO2] (E-[CO2]) can be an effective adaptation to global climate change. We wondered whether E-[CO2]-responsive cultivars have been unintentionally selected through empirical breeding as [CO2] has increased. If so, modern cultivars may respond better to E-[CO2] than old ones. We conducted free-air CO2 enrichment (FACE) experiments in 2 years to examine whether rice cultivars bred in different eras differ in response to E-[CO2] and to determine any associated traits. We tested five Japanese cultivars: Aikoku (released in 1882), Norin 8 (1934), Koshihikari (1956), Akihikari (1976) and Akidawara (2009). The yields of Aikoku and Norin 8 increased by 19.3% and 30.3%, respectively, under E-[CO2], while those of Koshihikari and Akihikari increased by 15.9% and 3.4%, respectively. However, that of Akidawara, the newest cultivar, also increased by 19.0%. Norin 8’s strong response to E-[CO2] was associated with increases in both spikelet density and percentage of ripened grains, both of which were closely related to nitrogen uptake. These results suggest that breeding has not necessarily improved cultivars’ response to E-[CO2], and that selection for traits such as sink capacity and nitrogen uptake can be effective to improve rice productivity under E-[CO2].

AbstractRising air temperatures are projected to reduce rice yield and quality, whereas increasing atmospheric CO2 concentrations ([CO2]) can increase grain yield. For irrigated rice, ponded water is an important temperature environment, but few open‐field evaluations are available on the combined effects of temperature and [CO2], which limits our ability to predict future rice production. We conducted free‐air CO2 enrichment and soil and water warming experiments, for three growing seasons to determine the yield and quality response to elevated [CO2] (+200 μmol mol−1, E‐[CO2]) and soil and water temperatures (+2 °C, E‐T). E‐[CO2] significantly increased biomass and grain yield by approximately 14% averaged over 3 years, mainly because of increased panicle and spikelet density. E‐T significantly increased biomass but had no significant effect on the grain yield. E‐T decreased days from transplanting to heading by approximately 1%, but days to the maximum tiller number (MTN) stage were reduced by approximately 8%, which limited the panicle density and therefore sink capacity. On the other hand, E‐[CO2] increased days to the MTN stage by approximately 4%, leading to a greater number of tillers. Grain appearance quality was decreased by both treatments, but E‐[CO2] showed a much larger effect than did E‐T. The significant decrease in undamaged grains (UDG) by E‐[CO2] was mainly the result of an increased percentage of white‐base grains (WBSG), which were negatively correlated with grain protein content. A significant decrease in grain protein content by E‐[CO2] accounted in part for the increased WBSG. The dependence of WBSG on grain protein content, however, was different among years; the slope and intercept of the relationship were positively correlated with a heat dose above 26 °C. Year‐to‐year variation in the response of grain appearance quality demonstrated that E‐[CO2] and rising air temperatures synergistically reduce grain appearance quality of rice.

Abstract Increasing concentrations of atmospheric CO2 are projected to have positive effects on crop photosynthesis and yield (CO2 fertilization effect, CFE). High-temperature events, such as heatwaves, during sensitive periods can have significant negative impacts on crop yield and quality; however, the combined effects of elevated CO2 (EC) and short-period elevated temperature (ET) have not been determined in the open field. Here, we show a strong negative interaction between EC and ET obtained from a temperature-free-air controlled enhancement treatment embedded in a season-long free-air CO2 enrichment (FACE) experiment on a japonica rice cultivar, Koshihikari, over three seasons at the Tsukuba FACE facility in Ibaraki, Japan. CFE was 15% at ambient temperature, but it was reduced to 3% by ET, where canopy surface temperature (Tc) was elevated by ∼1.6 °C for 20 d after flowering. Reductions in CFE mainly arose from poor grain setting at Tc above ∼30 °C. High Tc also increased the percentage of chalky grains and substantially decreased the grain appearance quality, although the threshold temperature varied between the seasons. Simultaneous increases in atmospheric CO2 concentration and air temperature are expected to increase daytime canopy temperatures more than air warming alone, thereby affecting grain yield and quality. Crop models without these processes are likely to underestimate the negative impacts of climate change on crop yield and quality. The development of adaptation measures against heat stress, particularly during reproductive and grain-filling periods, needs to be enhanced and accelerated.