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 CO_(2) ([CO_(2)]) and temperature on heat-induced sterility, elevated [CO_(2)] (E-[CO_(2)]) 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-[CO_(2)] on heat-induced sterility and sterility-related traits in rice by increasing E-[CO_(2)] by approximately 200?μmol?mol~(?1) above ambient levels using a free-air CO_(2) enrichment (FACE) facility for six growing seasons with variable growing season temperatures. The percentage fertility was not significantly correlated with the air temperature (T _(a)) 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 T _(a) between 09:00 and 12:00 on each flowering day under E-[CO_(2)], whereas no such effect was seen under ambient [CO_(2)]. E-[CO_(2)] 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-[CO_(2)] affects many traits related to heat-induced sterility and may sometimes exacerbate sterility by reducing pollen grain deposition.
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