2.1 Study rationale and site descriptions

The study rationale was to determine how climatic variabilities are impacting Japonica rice growth, yield, and quality by assessing the inter-relationships among grain-filling, grain yield, and grain quality at high latitudes in China (Figure 1. Vast climate changes, especially climate warming, in the past have favored the expansion of rice cultivation areas in China, especially in Northeast China (NEC). The change in rice production in NEC occurred due to favorable shifts in climatic components such as precipitation and temperature. Climate change also led to natural hazards such as drought, flooding, and increased invasion of insects, pests, diseases, and weeds. NEC has the highest latitude globally and is one of three major rice-growing regions in China. This region is extremely vulnerable to projected climate change regardless of its undistinguished contributions to global warming. China greatly relies on rice cultivation to ensure the country’s food security, employment, and farmer incomes. Rice grain production has shown irregular changes over the last three decades, although the overall production has shown an increasing trend. Enhancing the Japonica rice adaptation process in mid-high latitudes against future projected warming trends compared to the present requires the assessment of the inter-relationships among grain-filling, grain yield, and grain quality in Japonica rice in response to external climatic driving factors. This understanding will inform targeted research and provide evidence for how Japonica rice may adapt at mid-high latitudes in China.

(A) Map of the study sites. (B) Rationale description of the study (site A: Harbin: site B: Qiqihar; ∆T: change in temperature: Atm Temp: atmospheric temperature; Rad: radiation; RH: relative humidity; RWC: relative water content).

The present study was performed in the Heilongjiang province of NEC, which is situated between 126.6629°E longitude and 45.7421°N latitude. Heilongjiang is the northernmost province of China with a population of 38.17 million and an area of 454,000 km². The climate in this region is a continental monsoon with an annual average temperature ranging between 4°C and –4°C. Winter is generally long and frosty, whereas summer is short and cool. Most of the precipitation is concentrated in summer, with an average annual rainfall of 500–600 mm. Around 59% of the total province area is occupied by mountains. The altitude is low and the interior is relatively flat. Due to obvious climate warming since the last century and measures taken for land reclamation, Heilongjiang has become an important agricultural region for crops such as maize, rice, and sunflower. Two different experimental sites were selected in Heilongjiang province, namely, Harbin and Qiqihar. Harbin, the capital of Heilongjiang province, is situated between 45.7567°N latitude and 126.6424°E longitude. Harbin is dominated by low mountains and hills. The frost-free season lasts 130 days, the annual average rainfall is 400–600 mm, and the mean annual temperature is 3.20°C. Qiqihar, the second largest city in Heilongjiang province, is situated in the west-central part of the province at 47.35°N latitude and 123.91°E longitude. The annual average rainfall is nearly 415 mm, whereas the annual mean surface temperature is 3.95°C. In July, the 24 h average temperature is 23.2°C.