Ameliorating heat stressed conditions in wheat by altering its physiological and phenotypic traits associated with varying nitrogen levels

Abstract

Currently, more than half of the global nations cultivating wheat crops are facing severe consequences of climate change and its associated heat stress in terms of quantitative and qualitative yield losses. Plants exposed to heat stress need a balanced and adequate amount of mineral nutrients to counter its ill effects. Therefore, the present study was designed to investigate the potential effects of heat stress applied during the vegetative growth period (Zadoks growth scale: ZGS 5-60) on physiological and phenotypic traits of wheat (Triticum aestivum) crop subjected to variable rates of nitrogen (N). In this experiment, wheat plants of cv. ‘Punjab-2011’ were exposed to two levels of temperature i.e. heat stress (HS) and control or non-heat stress (NHS), and three N rates (N50 = 50 kg ha-1, N100= 100 kg ha-1 and N150 = 150 kg ha-1). The experiment was executed under controlled conditions in a completely randomized design (CRD) with six replications. One set of eighteen pots containing wheat seedlings was placed in a compartment of the greenhouse under heat-stressed conditions, while another set was placed in another compartment under non-heated conditions. The greenhouse compartments were equipped with a heating and cooling system to maintain desired ecological conditions. Pots in heated chamber were kept for 60 days from emergence (ZGS = 5-60), and then shifted to non-heated chamber till harvesting. The temperature in heat stress treatment was almost 2 ± 0.47 °C higher than in non-heated treatment. The results indicated that HS significantly reduced the photosynthetic rate by 42.52%, leaf photosynthetic efficiency by 56.82%, chlorophyll scores by 20.11%, relative water contents (RWC) by 12.81%, tillers by 48.21%, grain weight by 21.47% and grain yield by 68.20% relative to NHS conditions. These reductions were more prominent in plants subjected to a limited N dose rate (50 kg N ha-1). Furthermore, the results also revealed higher transpiration rate, stomatal conductance, and membrane ruptures under HS with N50 treatment.  However, N150 treatment compensated for the detrimental effects of HS on wheat plants by improving the photosynthetic rate and efficiencies, higher RWC, more stability of membrane and pigments, more tillers, and higher grain weight, and grain yield of wheat. Additionally, grain yield was negatively correlated with transpiration rate, stomatal conductance, internal CO2 concentration, and membrane leakage. In conclusion, a high dose rate of N under high temperatures during vegetative growth could alleviate the magnitude of penalties to grain yield and enhance the potential of wheat crops to withstand heat-induced detrimental effects.