Rice Research: Open Access
Open Access

Climate change impact on agricultural crops is posing serious threat to global food security. Global climate change models predict increase in mean air temperature up to 2.6° and 4.8°C by 2065 and end of twenty-first century, respectively with doubling of current CO₂ concentration [1]. Despite of climate change constrains, predictions were made for increasing global food production by 70% to feed growing population by 2050 [2]. As a most important cereal crop, rice feeds more than 3 billion people and its contribution in total calorie intake in humans is >20%. It is majorly produced and consumed in Asia where it accounts for 40% to 80% of the calories in the diet [3]. Increase in global mean temperature [1] and unpredicted heat spikes at regional level [4] are catastrophic to rice yield and quality when coinciding with sensitive growth stages. In parallel, the sub-tropical and tropical rice-producing areas are anticipated to be more threatened by temperature increase [1]. Unprecedented increase in night-time and day-time temperature is documented for current and future climate. India is one of the key hotspots for warming in near future [5]. Increase in day-time temperature during sensitive reproductive stage could induce poor anther dehiscence, reduced pollen production, pollen germination and pollen tube growth resulting in higher spikelet sterility and poor seed set in rice [6-8]. Conversely, high night-time temperature from panicle initiation to physiological maturity adversely affected rice grain yield majorly due to reduction in nitrogen and non-structural carbohydrate translocation after anthesis, which results in poor grain filling [9-10]. Moreover, night-time temperature induced reduction in grain yield in rice was attributed to increased night respiration, reduced photosynthesis and total biomass [10-12].

A concomitant rise in atmospheric CO₂ concentration with increase in mean daily temperature due to rapid increase in night-time temperature (T_min) than day-time temperature (T_max) is narrowing the diurnal temperature amplitude under climate change. Interestingly, increase in T_min has been reported to be three times faster over increasing T_max. This is resulting in more frequent warmer nights and decreasing day/night differential (amplitude) in near and upcoming future [13]. Impact of increasing T_min and T_max is documented with yield penalty in rice. Conversely, elevated CO₂ (e[CO₂]) has been known to enhance rice productivity with stimulation in current photosynthesis and growth rate. However, role of e[CO₂] in combination to high day-time temperature has received attention and results suggest that high day-time temperature can offsets the e[CO₂] effects and grain quality may be further deteriorated [14-17]. Similarly role of e[CO₂] and high night-time temperature has received attention too [18]. Elevated [CO₂] with a narrowed temperature amplitude resulting from high day- and night-time temperature are inevitable combination of current and future climate and requires ample interest. There are few studies on the thermal amplitude in crops such as wheat [19], rice [20] and maize [21]. The importance of day/night differential has received considerable attention in relation to the growth and yield. It has been reported that plant growth would be favored by low night temperatures as this would reduce respiratory losses at a time when the supply of carbohydrate might become limiting. However, dry matter production for a wide range of crops grown under constant but optimal temperature is equal to and often greater than dry matter production by the same crops grown under differential day/night temperatures with the same mean value. Change in temperature amplitude from 10°C to 20°C has been reported to reduce growth. Further, the contribution of the amplitude of daily variation of 15°C (32.5/17.5°C) could increase carbon-use efficiency in mature leaves and roots of orange trees, leading to increased leaf area index and photosynthetic rates compared with 0°C (25/25°C) daily variation [22]. Differential impact of high day- and night-time temperature along with possible effect of varying amplitude has been advocated [23]. Differential mechanisms leading to high day and high night temperature stress-induced loss in yield and quality in rice has been reported recently [24]. Interestingly, there are no reports hitherto on rice response to temperature amplitude in combination to e[CO₂]. Hence, it is of utmost importance to analyze growth, carbon assimilation and source sink dynamics under varying temperature amplitude under e[CO₂]. The mechanistic understanding on that under future climate could address the unknown effect of temperature amplitude under enriched [CO₂] environment. Identification of traits affecting under varying temperature amplitude could be important key entry points for future studies and making inroads to rice resilience under future diurnally varying temperature amplitude under e[CO₂].