Increasing seedling number alleviates the adverse effects of warming on grain yield and reduces greenhouse gas emission in late-season rice

Abstract

To address the adverse effects of warming on late-season rice, we investigated the impact of increasing the number of seedlings on rice yield, quality, and greenhouse gas (GHG) emissions under canopy warming conditions using the free-air temperature increase (FATI) system. Three treatments were implemented: ambient temperature with two seedlings hill^-1 (CKS1), canopy warming with two seedlings hill^-1 (WS1), and canopy warming with four seedlings hill^-1 (WS2). FATI increased rice canopy temperature and soil temperature by an average of 1.9–2.2°C and 0.6–0.8°C, respectively, over the two years. The yield in WS1 was significantly reduced by 10.1%–12.1% compared with CKS1, which was attributed to a significant decrease in total spikelets m^-2 and spikelets panicle^-1, despite a notable increase in filled grains in 2023. However, WS2 demonstrated no significant change in yield compared with CKS1. Analysis of yield components revealed that WS2 exhibited significantly higher panicles m^-2 than CKS1, while the spikelets panicle^-1 were significantly lower than CKS1. No significant changes were observed in grain weight and processing and appearance qualities. Compared with that under CKS1, CH₄ was significantly reduced under WS2 treatment in both years, and the global warming potential (GWP) and GHG intensity (GHGI) showed a decrease, with notable differences observed in 2022. Therefore, increasing the number of seedlings hill^-1 can alleviate the negative impacts of canopy warming on grain yield and reduce GHG emissions in late-season rice.