[Spatial-temporal characteristics of thermal resources and its influence on the growth of double cropping rice in the middle and lower reaches of the Yangtze River,China.].

The spatial-temporal characteristics of thermal resources are the main factor controlling the spatial distribution patterns of double cropping rice. Based on daily average temperature data collected from 240 weather stations in Hunan, Jiangxi and Hubei provinces, our study analyzed the change characteristics of thermal resources during thermal growth period and safe growth period of double cropping rice in the middle and lower reaches of the Yangtze River. Furthermore, we quantified the change trends of spatial pattern for the rice cropping systems with different rice varieties and the northern limit of double cropping rice. The results indicated that the thermal resources of double cropping rice displayed a significant increasing trend during both thermal and safe growth periods, with an abrupt change in 2000 in terms of the Mann-Kendall test. The safe planting date of early rice advanced for 3-7 days and the safe heading date of late rice delayed for 2 days. Averagely, the safe growth period extended by about 7 days, and the planting northern limit of double cropping rice shifted 200 km northward, approaching to the latitude of 33° N. Meanwhile, many areas with cropping systems of 'early maturing early rice + mid-maturing late rice' and 'mid-maturing early rice + mid-maturing late rice' were replaced by 'mid-maturing early rice + late-maturing late rice'. Our study revealed the feasibility to shift the double cropping rice system northward and replace early and mid-maturing rice variety with mid and late maturing rice variety due to the increa-sing thermal resources during growth period of double cropping rice under climate change.