Study on the Suitable Area of Ratoon Rice in China Under Climate Change.

Ratoon rice is a special cultivation system developed based on the regenerative capacity of rice axillary buds. Its core mechanism lies in regulating the regeneration potential of stubble axillary buds through agronomic practices. After harvesting the main-season rice, dormant buds are induced to sprout and form secondary tillers, which eventually develop into effective panicles, thereby achieving "one planting with two harvests." In this study, 167 occurrence records of ratoon rice, nine environmental variables, and three future climate scenarios proposed in CMIP6 (SSP1-2.6, SSP2-4.5, and SSP5-8.5) were used to predict the suitable cultivation area of ratoon rice in China using the MaxEnt model. The results showed that the main environmental factors influencing the distribution of ratoon rice were accumulated temperature during the safe growth period, length of the safe growth period, altitude, hydrothermal coefficient in August, mean temperature in September, and precipitation from March to September. The optimal ranges of these factors were 4314°C-5497°C, 191-225 days, 0-511 m, 0.3-11.4, and 21.0°C-25.2°C, respectively. Under the current climate scenario, the potential suitable area of ratoon rice in China was mainly distributed south of the Qinling-Huaihe line (92.39°-121.96° E, 18.23°-30.36° N), covering a total area of 193.90 × 104 km2. Compared with the current scenario, the total suitable area of ratoon rice is projected to increase by 5.5%-11.9% in the 2050s and by 8.5%-9.6% in the 2090s under the three climate scenarios. By the 2050s, the suitable and highly suitable areas in Sichuan and Chongqing show little change across the three climate scenarios, whereas the suitable areas in the middle and lower reaches of the Yangtze River increase markedly. The newly expanded suitable areas are mainly concentrated in southern Hunan, the central parts of Hubei, Jiangxi, and Anhui, and western Zhejiang. By the 2090s, the suitable and highly suitable areas in Sichuan and Chongqing still exhibit little change under the three climate scenarios, while the highly suitable areas in the middle and lower reaches of the Yangtze River continue to expand, with newly added highly suitable zones comparable to those in the 2050s. Accordingly, we infer that autumn thermal conditions north of the Qinling-Huaihe line will remain a limiting factor for the northward expansion of ratoon rice, whereas moderately increased autumn temperatures south of the Qinling-Huaihe line will be favorable for ratoon rice cultivation. Most moderately and marginally suitable zones in the middle and lower reaches of the Yangtze River are expected to shift into highly or moderately suitable zones, especially in southern Hunan, the central parts of Hubei, Jiangxi and Anhui, and western Zhejiang, where new highly suitable areas are projected to emerge. These regions could therefore be prioritized for appropriately scaled ratoon rice cultivation in the future.