Grain production space reconstruction not only concerns China's food security, but also has a profound impact on regional economic development and ecological protection. From three dimensions of quantity, production potential and spatial pattern, the paper employs GAEZ (Global Agro-Ecological Zones) model, landscape pattern index and gravity center model to discuss the grain production space reconstruction of China from 1980 to 2018. Studies have shown that: (1) In terms of quantity, grain production space gradually decreases from south to north, and the total area remains almost unchanged, but it has frequent internal conversion. The grain production space has been transformed into other land use types, amounting to about 64.58 million hm², of which the Grain for Green and construction land expansion account for roughly 90%. The other land use types have been converted into grain production space, reaching 66.8 million hm², of which deforestation and grassland reclamation account for 75%. (2) From production potential, the total amount showed decreasing trends in the past 40 years, while the spatial distribution presents a pattern of "high in the east and low in the west", showing an obvious gradient difference from east to west. The decrease of total production potential of grain production space was mainly caused by the Grain for Green and construction land expansion, resulting in the decrease of grain production space with medium-low, medium and medium-high potential levels; However, its total increase was mainly attributed to the deforestation and grassland reclamation, leading to an increase of grain production space with medium and medium-high potential levels. (3) Due to the aggravation of human activities, the landscape pattern of China's grain production space has undergone significant changes since the 1980s. Its scale gradually decreased, the shape tended to be complex, and the distance gradually became far. Meanwhile, the quantity gravity center has moved southward, but not too far. The gravity center of its production potential has been moving to the northeast, with a distance of 82.74 km. This paper enriches the research setup of land system, and provides the basis for guaranteeing food security and realizing food production space's sustainable and intensive use.

China is feeding roughly 20% of the world's population with less than 9% of the world's cultivated land. The food security at national and regional scales has been a major concern. In this study, we took the province-level area as the research unit and utilized GIS spatial analysis and statistical tools to examine the overall characteristics of grain production changes, the evolution characteristics of regional patterns and the impact of these changes on regional grain supply and demand pattern in China during 1999-2018. The results showed that the total national grain output significantly increased with an annual rate of 1.1 million tons. The total grain output of Northern China showed a significant growth trend, while that of Southern China remained stable. The increment of maize yield played a leading role in these changes. The spatio-temporal yield variations of five major food crops (rice, wheat, maize, beans and tubers) were quite different in the past 20 years at provincial-level scale. The change of grain yield had great influence on regional grain supply and demand pattern. Particularly, Guangdong, Zhejiang and Fujian provinces located in the southeast coastal region had changed from supply-oriented provinces of major grains with rice and wheat into demand-oriented provinces. However, the per capita share of grain was 368.0 kg/person in Y 1999-2003 period(the five-year average during 1999-2003) and 461.5 kg/person in Y 2014-2018 period (the five-year average during 2014-2018) at national-level scale, respectively; and the per capita share of the two major grains was 220.3 kg/person and 247.6 kg/person in Y 1999-2003 and Y 2014-2018 periods, respectively. The change of sown area was the direct reason for the change of grain crop yield at national and regional scales. Nevertheless, the fundamental reason was more attributed to the change of attribution, function and quality, which is driven by land use value. Our study classified the reasons for the decrement of cultivated land into "non-agriculture" "non-grain" "wastage" and "ecology" types. Considering the formation causes of each type, the corresponding countermeasures and suggestions for the sustainable use of regional cultivated land were put forward in order to provide reference for the adjustment of regional grain planting pattern and the transformation of demand-oriented provinces of two major types of grain to self-sufficient provinces.

The countries along the Belt and Road are regarded as the world's important food production and consumption areas, so it is of great significance to carry out the regional food security research. The paper aims to focus on cereals consumption, analyze the spatial and temporal patterns of the cereals consumption quantity and structure of these areas during 1995-2017, and reveal their influencing factors. The results show that: (1) From 1995 to 2017, the total cereals consumption and per capita volume presented an increasing trend and the total cereals accounted for about 55%-59% of the world's total. The per capita consumption increased to 367 kg in 2017, which was 95% of the world level. (2) From 1995 to 2017, the other use and processing consumption increased dramatically, feed and food increased rapidly, but the losses and seed increased slowly, which showed a "Food-based and Feed-assisted" cereals consumption structure that was at the primary stage of cereals consumption. (3) The spatial difference of the total cereals consumption is obvious and the per capita consumption is small. The cereals consumption level is very high in Central and Eastern European countries, but it is generally low in countries with a large population, small island areas, or poor cereals production conditions. (4) The spatial difference in per capita consumption of various types of cereals is not obvious except for the total amount of feed. Nearly half of the countries are still dominated by food, and about one-quarter of the countries have completed the upgrade of the cereals consumption structure that has shifted to a relatively balanced consumption structure. (5) The cumulative contribution rate of population and consumption level is about 43% and 57%. In Central Asia, Southeast Asia and South Asia, most countries are jointly affected by consumption level and population. West Asia and the Middle East are significantly affected by population. The cumulative contribution of population and consumption level have large differences in Central and Eastern Europe. The cumulative contribution of food and feed accounted for about 46% and 34%, respectively. South Asia and Southeast Asia were mostly dominated by foods, China-Mongolia-Russia and Central Asia were mostly dominated by feed, and Central and Eastern Europe and Indochina Peninsula were mostly integrated contributors.

In this paper, the spatial center of gravity model and spatial mismatch index method was applied to systematically analyze the spatio-temporal pattern, spatial mismatch characteristics, and influencing factors of global population and food in 1990-2017. The results showed that: (1) In the past 30 years, the global population and food has showed a growth trend, but their change characteristics are obviously different in temporal distribution. The per capita food production has obvious spatial differences in the world, and the contradiction between population and food in most countries is serious. (2) On the global scale, there is an obvious spatial mismatch between the center of gravity of population and food, which shows a trend of reverse mismatch in spatial distribution. (3) On the national scale, the regional difference of spatial mismatch between population and food is obvious, showing a spatial pattern of "positive mismatch area - negative mismatch area - positive mismatch area" from south to north. Negative high mismatch regions are stable in countries such as India and Japan, and positive high mismatch regions are stable in countries such as the United States and Canada. (4) The spatial mismatch pattern of population and food on all continents is basically stable, and the countries whose spatial mismatch index changes direction are distributed in Asia, Europe, South America and Africa. (5) The combined effect of natural environment, international environment, agricultural development and social factors has obvious regional differences in the spatial distribution of population and food, thus forming a spatial mismatch pattern between global population and food. It is necessary to accelerate the structural reform of agricultural supply side, enhance agricultural competitiveness and food self-sufficiency rate, reasonably allocate and deal with both domestic and international markets and resources, construct countermeasures to avoid fluctuations and uncertainties in world grain trade, and build a guarantee system for China's agricultural ecological security and food security.