Effects of free-air CO₂ enrichment on heat-induced sterility and pollination in rice
Kobayasi, Kazuhiro | Eydi, Mohammad Jawid | Sakai, Hidemitsu | Tokida, Takeshi | Nakamura, Hirofumi | Usui, Yasuhiro | Yoshimoto, Mayumi | Hasegawa, Toshihiro
Global climate changes may cause heat-induced sterility in rice, threatening the global production of this important crop. Although little is currently known about the combined effects of the concentration of atmospheric CO₂ ([CO₂]) and temperature on heat-induced sterility, elevated [CO₂] (E-[CO₂]) will likely increase the panicle temperature and thereby exacerbate heat-induced sterility, but this was not tested in open fields. Therefore, we investigated the effect of E-[CO₂] on heat-induced sterility and sterility-related traits in rice by increasing E-[CO₂] by approximately 200 μmol mol⁻¹ above ambient levels using a free-air CO₂ enrichment (FACE) facility for six growing seasons with variable growing season temperatures. The percentage fertility was not significantly correlated with the air temperature (Tₐ) between 09:00 and 12:00 on each flowering day, but it did significantly vary among the years, with 2011 experiencing cool temperatures resulting in chilling-induced mild sterility. When data from 2011 were removed, there was a significant negative correlation between fertility and Tₐ between 09:00 and 12:00 on each flowering day under E-[CO₂], whereas no such effect was seen under ambient [CO₂]. E-[CO₂] also significantly reduced the number of pollen grains deposited on the stigma by 10%, but it slightly increased the anther length by 1.3%, indicating that it had both negative and positive effects on heat-induced sterility. These findings suggest that E-[CO₂] affects many traits related to heat-induced sterility and may sometimes exacerbate sterility by reducing pollen grain deposition. Abbreviations: A-[CO₂]: ambient CO₂; [CO₂]: the concentration of carbon dioxide; E-[CO₂]: elevated [CO₂]; FACE: free-air CO₂ enrichment; Tₐ: air temperature
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