Interactions between elevated atmospheric CO2 and temperature on rice yield are highly dependent on growth season temperature

Abstract

The projected increase in atmospheric CO2 concentration (CO2) is expected to enhance rice yield, while the temperature increase lowers it. However, how air temperature increase modifies this effect of CO2 fertilization is still unclear, particularly across different ambient temperatures. To investigate this phenomenon, a temperature-free air CO2 enrichment experiment in paddy field was conducted in 2013 and 2014. An japonica rice (Oryza sativa L.) Wuyunjing 23 was exposed to two levels of CO2 (ambient and elevated by 200 μmol mol−1 during daytime) in combination with two temperature regimes (ambient and elevated by ca. 1 ℃ during daytime). Elevated CO2 significantly increased grain yield in both seasons, but temperature impacts on the magnitude of CO2 responses differed between two seasons: a significant CO2 × temperature interaction was detected in 2013 (mean air temperature 26.6 ℃), with 24 % increase in grain yield under ambient temperature vs 8 % under elevated temperature; while in 2014 (mean air temperature 23.6 ℃), a similar CO2-induced increase under ambient (+12 %) and elevated temperature (+16 %) was detected. Plant height significantly increased upon CO2 elevation in 2014 at various growth stages but not in 2013. The effects of CO2 × temperature interaction on grain yield were primarily attributed to variations in panicle (or tiller) numbers, with negligible effects on other yield components. The aboveground biomass patterns mirrored those of grain yield in the responses to CO2, temperature and their interaction, while less effect of CO2 or temperature treatment was found on harvest index. The results demonstrate that interactions between CO2 and temperature on rice are dependent on growth season temperature: high daytime temperature stress during the early growth period of rice can interfere with tillering formation and lead to less yield gain from CO2 enrichment.