| Rice is one of the most important crops in the world, and its production is related to the national food security, economic development and people’s living standards. With the continuous increase of greenhouse effect, high temperature is becoming a major risk to crop production. Booting and flowering stages are the most sensitive stages in response to high temperature in rice. Two-year experiments were conducted in the rice growing season from May to October in 2012 and 2013. Two japonica rice cultivars ’Nanjing41’(heat-sensitive) and ’Wuxiangjing14’(moderate heat-tolerance) were used in each experiment. Seedlings were raised in the field, and then transplanted to plastic pots. At booting stage, pots were to four phytotron rooms severally with the maximum/minimum temperature gradients of T1 (32/22℃), T2 (35/25℃), T3 (38/28℃) and T4 (41/31℃). Durations of T1 & T2 were designed as 4 days (D2), and durations of T3 & T4 were designed as 2 days (Dl),4 days (D2),6 days (D3) at booting stage. Through the measurement of leaf SPAD, net photosynthetic rate, leaf area index, organ nitrogen content, soluble sugar content, organ dry matter, yield component and yield, we determined the effects of high temperature at booting stage on leaf photosynthesis, accumulation and partitioning of assimilation, and yield formation in rice. Results will benifit the estimate of rice production, the development of management measure and food security under climate change in China.1. Effects of high temperature on phenology and photosynthetic production in rice at booting stage. Compared with T1D2, T2D2 treatment, the first-flowering dates under T3D2, T3D3, T4D2, T4D3 treatments advanced one day, but there was no significant difference in the growing period after flowering. During the period under high temperature, transpiration rate (Trmol), stomatal conductance (Cond) and net photosynthetic rate (Pn) in rice leaves all became large with the increase of temperature levels. After the 4 or 6-days high temperature treatments with different temperature levels, net photosynthetic rate (Pn) in flag leaf under T1, T2 treatments could quickly return to the value before high temperature treatment. However, Pn under T3, T4 treatments were obviously less than T1, T2 treatments. Compared with T1, T2 treatment, T3, T4 treatments showed the higher leaf area index (LAI), leaf area nitrogen index (LANI) and leaf SPAD in the late growth stage due to the delay of leaf senescence, and could maintain a relatively stable leaf photosynthetic efficiency for a long period. With the rise of the temperature levels and durations in the treatment, the difference between each indices gradually increased. The effects of high temperature at booting on rice photosynthetic production might not be the main reason for yield loss.2. Effects of high temperature at booting stage on assimilates accumulation, distribution and yield in rice. Compared with T1 temperature treatment, the total aboveground dry matter, panicle dry matter and partitioning index significantly reduced after high temperature treatment at booting stage, and the impacts enlarged with the increase of duration in the same temperature level. Nitrogen content and soluble sugar content in leaves and stems increased after high temperature treatment. Yield, number of spikelets per panicle, seed-setting rate and 1000-grain weight significantly decreased under high temperature treatment after booting stage. Seed-setting rate in Wuxiangjing 14 was higher than that in Nanjing41 under the same high temperature treatment. The transportation of reserve use and nitrogen accumulation before anthesis were significantly limited under the high temperature treatments of T3, T4. This phenomenon led to an appearance of secondary panicle in late growth stage under T3, T4 treatments. Therefore, the number of panicle in maturity, vegetative organ dry matter and nitrogen accumulation significantly increased with the increasing temperature level, and the impact enlarged with the rise of duration. |
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