The fingerprints of climate warming on cereal crops phenology and adaptation options - Scientific Reports

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• The effect of temperature on crop phenology could be documented by using GDD or heat units.

• Normally, the longer the optimum growing season, then higher the duration for maximum grain production.

• Plant metabolic processes are controlled by weather variables like maximum and minimum temperature, solar radiation, carbon dioxide concentration and availability of water11,12,13,14,15,16,17. Cereal crop production is influenced by extreme climatic conditions, like heat waves, storms, drought, salinity and flooding

• Food security and climate change mitigation are major challenges in developing countries. Changes in management practices such as fertilizer use efficiency, use of organic fertilizers, use of legume with grasses, optimization of irrigation water, plant breeding and genetic modifications and selection of cultivars in field could be good mitigation strategies to coup climate change15,34,35. These adaptive mitigation strategies could help to design resilience systems to future climate change. Similarly, promotion of climate smart agriculture (CSA) could help to mitigate the challenges of climate change. CSA aims to transform and redirect agricultural system to support sustainable development and food security under changing climate. It integrates three elements of sustainable development (economic, social, and environmental) by addressing food security and climate change. It has three main pillars (i) Sustainably increasing agricultural productivity and incomes (ii) Adapting and building resilience to climate change and (iii) Reducing and/or removing greenhouse gas emissions.

• The predicted changes in temperature during the next 40 to 70 years are expected to be in the range of 2–3 °C in different regions. Intensity and duration of warming trends and heat wave events are predicted to become more extreme in future than at present and during last decade67,68,69. Extreme temperature events have short-term spells of a few days with temperature increases over 5.0 °C above normal. Frost caused sterility and abortion of grain whilst extreme heat caused a decrease in the number of grains and reduced grain filling duration70,71,72. Day-to-day minimum temperatures will rise more rapidly compared to daily maximum temperatures leading to increased mean temperatures. These variations have detrimental effects on yield52,73. The work by Srivastava et al.74 concluded that maximum temperature affects the maize grain yield more than the minimum temperature under variable CO2 levels in both irrigated and rainfed conditions. Furthermore, their study confirmed that maize yield was low for RCP 2.6, 4.5, 6.0, and 8.5 under irrigated as compared to rainfed condition. If such changes in temperature will remain occurring in future, then adaptation strategies such as change in sowing date and cultivars shifts are needed to offset such impacts

• Crop phenology is the most significant feature of crop adaptation, and spatial and temporal changes in phenological stages and phases provide well-built indications of the biological influence of thermal trend. Change in phenological seasonality is having both direct and indirect effects on natural vegetation and cereal crop productivity25,26,79,80,81. Measured climate-warming trends have been implicated as a reason for accelerated cereal crop growth rates and reduced growing durations. Since phenology is highly sensitive to climate change and has significant impact on carbon balance. Thus the asymmetric and opposing response of phenology to daytime and night-time was studied by Wang et al.82 and concluded that Tmax and night-time Tmin had opposite effects on the timing of start of the season, delayed end of the season and prolonged length of growing season.

• Phenology is well known climate change indicator. However, there is a lack of critical analysis of climatic warming impacts on cereal phenology shift and management of climatic impacts to ensure future global food security.

• Role of phenological stages and phases in cereal crop grain production Cereal crop phenology is very sensitive to climate change88 as compared to other agronomic crops; consequently, phenological changes are frequently used to measure how climate warming influences the agricultural ecosystems in a particular region107,108,109. Numerous methods have been utilized to elucidate the intensity of the effect of climate change on agronomic cereal crops. The methods include analysis of satellite images on vegetation greenness, measurement of net primary production with Normalized Difference Vegetation Index (NDVI), and particularly, determination of temporal and spatial variations in phenological seasonality26,79,110,111,112,113,114,115. The data on stages and phases of cereal crop phenology and climate meteorological data are collected from phenological networks or through designated observation stations.

• Wheat phenology has been affected by climate warming worldwide. Identifying phenological responses to climate warming is tough due to regularly shifting sowing dates and the introduction of new cultivars. Wheat phenological trend from sowing to maturity is presented in Table 5. The results showed that it remained maximum in northwest China during 1983 to 2004 (sowing = 13.2 days decade−1, emergence = 9.8 days decade−1, anthesis = 11.0 days decade−1 and maturity = 10.8 days decade−1).