Abstract
Effect of diurnal temperature amplitude on carbon tradeoff (photosynthesis vs. respiration) and growth are not well documented in C4 crops, especially under changing temperatures of light (daytime) and dark (nighttime) phases in 24 h of a day. Fluctuations in daytime and nighttime temperatures due to climate change narrows diurnal temperature amplitude which can alter circadian rhythms in plant, thus influence the ability of plants to cope with temperature changes and cause contradictory responses in carbon tradeoff, particularly in night respiration during dark phase, and growth. Sorghum [Sorghum bicolor (L.) Moench] is a key C4 cereal crop grown in high temperature challenging agro-climatic regions. Hence, it is important to understand its response to diurnal temperature amplitude. This is the first systematic investigation using controlled environmental facility to monitor the response of sorghum to different diurnal temperature amplitudes with same mean temperature. Two sorghum hybrids (DK 53 and DK 28E) were grown under optimum (27°C) and high (35°C) mean temperatures with three different diurnal temperature amplitudes (2, 10, and 18°C) accomplished by modulating daytime and nighttime temperatures [optimum daytime and nighttime temperatures (ODNT): 28/26, 32/22, and 36/18°C and high daytime and nighttime temperatures (HDNT): 36/34, 40/30, and 44/26°C]. After exposure to different temperature conditions, total soluble sugars, starch, total leaf area and biomass were reduced, while night respiration and specific leaf area were increased with narrowing of diurnal temperature amplitude (18 to 2°C) of HDNT followed by ODNT. However, there was no influence on photosynthesis across different ODNT and HDNT. Contradiction in response of foliar gas exchange and growth suggests higher contribution of night respiration for maintenance rather than growth with narrowing of diurnal temperature amplitude of ODNT and HDNT. Results imply that diurnal temperature amplitude has immense impact on the carbon tradeoff and growth, regardless of hybrid variation. Hence, diurnal temperature amplitude and night respiration should be considered while quantifying response and screening for high temperature tolerance in sorghum genotypes and comprehensive understanding of dark phase mechanisms which are coupled with stress response can further strengthen screening procedures.
Highlights
Sorghum (Sorghum bicolor (L.) Moench) is an economically important C4 cereal crop for more than 500 million people around the globe due to its versatile usage as staple food, bioenergy, feed for livestock and industrial products (Maikasuwa and Ala, 2013; Tari et al, 2013; Ciampitti and Prasad, 2020)
In spite of differences among hybrids and diurnal temperature amplitudes, growth of seedlings indicated by total aboveground biomass accumulation (TB) and total leaf area (TLA) were significantly (P
Seedlings exposed to ODNT with highest diurnal temperature amplitude (18°C) recorded higher total above ground biomass (TB) and TLA; and lowest Specific leaf area (SLA), while lowest TB and TLA and higher SLA was observed under HDNT with narrow diurnal temperature amplitude (2°C) across different day and night conditions (Table 1 and Figure 2)
Summary
Sorghum (Sorghum bicolor (L.) Moench) is an economically important C4 cereal crop for more than 500 million people around the globe due to its versatile usage as staple food, bioenergy, feed for livestock and industrial products (Maikasuwa and Ala, 2013; Tari et al, 2013; Ciampitti and Prasad, 2020). Sorghum occupies an important role in global food security along with other cereal crops such as wheat, millets, rice and maize (Ciampitti and Prasad, 2020; Maswada et al, 2020). Negative impacts of high daytime and nighttime temperatures on different cereal crops has been well documented including in finger millet (Opole et al, 2018), maize (Sunoj et al, 2016; Lizaso et al, 2018), rice (Prasad et al, 2006a; Lin et al, 2020; Wang et al, 2020), and wheat (Prasad et al, 2008b; Prasad et al, 2015; Impa et al, 2018)
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