Direct-seeded rice reduces methane emissions by improving root physiological characteristics through affecting the water status of paddy fields

Both direct-seeded rice (DSR) and water-saving irrigation effectively reduce methane (CH4) emissions from paddy fields. However, little is known about the effects of water-saving irrigation with DSR on root growth and CH4 emissions in paddy fields. In this study, a field experiment was conducted with three treatments including transplanted flooded rice (TFR), direct-seeded flooded (DSF), and direct-seeded alternate wetting and drying (DSA), and root morphological and physiological traits and CH4 emissions were determined. Compared to TFR, DSR (DSF and DSA) significantly decreased CH4 emissions at all growth stages and reduced total CH4 emissions by 85.6-96.8%. Root morphological traits were significantly and positively correlated with total CH4 emissions, whereas root oxidation activity (ROA); root oxygen loss (ROL); and root organic acids malic acid (MA), succinic acid (SA) and citric acid (CA) were significantly and negatively correlated with total CH4 emissions. The flooding depth (FD), flooding period (FP), and total water input (TWI) were 34.1%, 17.8%, and 22.1% lower for DSF and 79.5%, 88.2%, and 53.7% lower for DSA, respectively, compared with those of TFR, which showed a significant positive correlation with CH4 emissions. These results suggest that DSF and DSA improve the root physiological traits of rice by regulating the water status of paddy fields, which in turn lead to CH4 reduction. The results of this study are essential for developing sustainable management practices for paddy soils and reducing greenhouse gas emissions.