Elevated CO2 enhances rice root growth under alternate wetting and drying irrigation by involving ABA response: Evidence from the seedling stage

The atmospheric CO2 enrichment can seriously affect rice root growth. Alternate wetting and drying (AWD) irrigation, which can also increase root growth, is a widely promoted water-saving technology for future climate, yet how elevated CO2 (eCO(2)) influences rice root growth under AWD remains unclear. In the present study, we examined the root growth of Yangdao 6 (YD 6) and Koshihikari (KOS) cultured under different water irrigation regimes (well-watered and AWD) and CO2 concentration (400 and 800 ppm). AWD reduced shoot dry weight of KOS compared with WW under ambient CO2 (400 ppm, aCO(2)), while the shoot dry weight of KOS showed no difference between WW and AWD treatments under eCO(2). Additional, under aCO(2), AWD did not affect the exhibited similar root dry weight, length, total surface area, and volume of YD 6 and KOS relative to WW. However, under eCO(2), AWD significantly promoted the root dry weight, root length, total root surface area, and root volume of YD 6 and KOS. Furthermore, root ABA content of YD 6 and KOS was significantly higher under AWD than under WW. Then, the OsNCED3 (a key gene for ABA biosynthesis) RNAi lines were used to check the role of ABA in root growth under eCO(2) with AWD conditions. The results showed that AWD increased the ABA content and root parameters of WT but not the OsNCED3 RNAi lines under eCO(2). Overall, the results suggest that eCO(2) can improve rice root growth under AWD by involving root ABA, which contributes to the understanding of water-saving irrigation on rice in the future climate.