Guar responses to temperature: Estimation of cardinal temperatures and photosynthetic parameters

Highlights

• The vegetative growth of guar is sensitive at low temperatures (<20 °C) and has optimum rates at 34.1 °C.

• Higher temperature regimes (36/28 and 40/32 °C) suppresses the flower initiation.

• Grain production occurs within a narrow temperature range of 19–31 °C.

• Guar acclimatizes its photosynthetic rate to heat stress by allowing a higher rate of electron transport.

Abstract

Temperature is the primary environmental determinant of geographic distribution and productivity of plant species. There has been increased interest in the cultivation of guar [Cyamopsis tetragonoloba (L.) Taub.] in many countries including the United States due to the high demand of guar gum in the oil fracking industry. However, information on gaur response to temperature is still lacking in the current literature. An experiment was conducted using six different day/night temperature regimes (20/12, 24/16, 28/20, 32/24, 36/28 and 40/32 °C) maintained inside walk-in growth chambers of the Controlled Environment Research Facility at Oklahoma State University. The objectives of this study were to evaluate the temperature responses of vegetative growth, development, and reproduction of guar to estimate cardinal temperatures, and to evaluate photosynthetic responses to temperature gradient. The vegetative growth of guar was sensitive to low temperature (<20 °C), and has high mean cardinal temperatures (T_min, T_opt, and T_max) for biomass accumulation (14.2, 34.1 and 48.2 °C). Plants exhibited reproductive development within a narrow range (19–31 °C) with maximum pod yields observed at a T_opt of 25 °C. Higher temperature regimes (36/28 and 40/32 °C) completely suppressed flower initiation in guar. Responses of photosynthesis to both light and internal CO₂ concentration (A-C_i) suggested guar photosynthetic rates increased under high temperature through an increased rate of electron transport. The identified cardinal temperatures and photosynthesis parameters can be used to develop mechanistic crop models to simulate adaptation strategies for guar. Further research is required to investigate the basis for suppression of flower bud initiation under heat stress.

Introduction

Multi-use crops that have value as food, fodder, and bio-products can provide producers with diverse sources of income. Guar [Cyamopsis tetragonoloba (L.) Taub.] a member of Leguminosae family, also known as cluster bean, is gaining interest in some drought-prone regions due to its high water use efficiency (Meftahizadeh et al., 2019). Guar has a C₃ photosynthetic mechanism, and is mainly cultivated between latitudes 40 °N and 10 °N. Both India and Pakistan are the leading producers, and account for about 95% of the global production of guar grain (Malhotra and Sharma, 2013). Guar endosperm contains highly water-soluble galactomannans (guar gum), which are used as a thickening and gelling agent in numerous industries such as food, textile, paper, pharmaceuticals, cosmetics, paint, and oil drilling (Singla et al., 2016a). While primarily grown for seed production, guar is also utilized as a vegetable, forage, and green manure crop in India (Baath et al., 2018). In comparison, guar has been evaluated as dryland or catch crop in parts of Oklahoma and Texas in the southern United States (Noureddine et al., 2015).

In the last few years, the price and trade of guar gum have increased globally because of its use in the petroleum industry for hydraulic fracking and well drilling (Gresta et al., 2013). The US fracking industry has been serving as the world’s largest consumer of guar gum, with the majority of its demand being fulfilled through imports from India (Singh, 2014). The United States imported guar gum worth 3.5, 1.7, and 1.3 billion USD from India in 2012, 2013, and 2014, respectively (APEDA Agri Exchange, 2019). Consequently, guar cultivation has been expanding into non-traditional areas in the United States and other countries (Soleimani et al., 2015; Singla et al., 2016b; Zubair et al., 2017; Chiofalo et al., 2018), where the crop may encounter extreme high or low temperatures.

Temperature is the major limiting factor for plant growth and plays a significant role in determining the distribution of plant species into diverse environments (Mittler, 2006). High temperature can alter biomass allocation by affecting rates of stem elongation, branching, leaf addition, expansion of leaf area, and cause flower abortion or fruit damage (Konsens et al., 1991; Reddy et al., 1995​; Singh et al., 2007; Goraya et al., 2017). In comparison, exposure to cooler temperatures can result in growth inhibition and delayed maturation, or cause irreversible injury and death of plants, especially for tropical and subtropical species (Lukatkin et al., 2012). Each species has its specific range of cardinal temperatures with minimum (T_min), optimum (T_opt), and maximum (T_max) temperatures that determines the geographic limits for growth. Maximum rate of growth and development occurs around the optimum temperature (T_opt) range (Hatfield and Prueger, 2015). The cardinal temperatures can be used to summarize biological responses of guar to temperature and for the development of mechanistic simulation models. Simulation models can serve as valuable tools to assess the adaptability of guar to different agrometeorological conditions and uncertainties related to management strategies (Singh et al., 2016). However, no such information on cardinal temperatures exists for guar within the current literature.

Photosynthesis is recognized as the most temperature-dependent process in plants and is widely used in understanding physiological tolerance and adaptation of different species to changing temperature (Hikosaka et al., 2005). A change in temperature can cause damage to the photosynthetic machinery of plants including photosystems, photosynthetic pigments, electron transport, and carbon fixation, resulting in suppression of photosynthetic efficiency of plants (Mathur et al., 2014). However, several plants have an inherent capability to acclimatize their photosynthetic apparatus, and shift T_opt for photosynthesis as the temperature fluctuates from the seasonal normal (Yamori et al., 2014). In C₃ species, electron transport capacity is an important factor controlling photosynthetic acclimation at high temperatures, which varies depending on the plant species (Schrader et al., 2004; Wise et al., 2004; Cen and Sage, 2005; Yamori et al., 2010).

Research on growth responses of guar to temperature is essential, especially in the current era of climate variability and change, when most crop yields are expected to decline with an increase in temperature (Myers et al., 2017). Further, an examination of the photosynthetic response of guar to changing temperature in relation to the electron transport rate (ETR) is vital to understand its physiological and biochemical mechanisms for possible acclimation to temperature. Therefore, the objectives of this study were (1) to estimate cardinal temperatures of guar growth and development parameters, and (2) to evaluate photosynthetic responses of guar to temperature.