Objective  Botanical garden (BG) is a type of specified green space, which collects and records living plants for conservation, display, scientific research, public viewing and recreation. As an important carrier of plant diversity conservation, BGs can help play the role of plant diversity in maintaining urban ecological balance. Under the background of biodiversity conservation, the importance of plant diversity conservation is increasing, and the construction and development of BGs have attracted more attention. It is of great significance to analyze the spatiotemporal distribution characteristics and put forward the construction strategy of BGs to effectively conserve and enhance plant diversity in China.

Methods  Mathematical statistics and GIS spatial analysis are adopted in this research. Firstly, through statistical analysis, this research analyzes the current conservation situation of native plant species in major regions, including the quantity and conservation rate thereof. After that, relying on GIS spatial analysis, the research explores the spatiotemporal distribution characteristics and plant diversity conservation of 229 BGs in China, including the quantity, area, spatial distribution and plant conservation thereof, providing basic support for the construction of China's BGs system.

Results  Based on the analysis of spatiotemporal distribution characteristics and plant diversity conservation of BGs, the research summarizes the following three outcomes.1) The conservation rate of plant species in China is 41.2%, indicating that the conservation level thereof needs to be further improved. There exists a spatial difference between northern and southern China. The conservation rate of plant species in northeastern China and Beijing-Tianjin-Hebei region is higher than that in Jiangsu and Hunan provinces. The main reason is that the rapid economic development in southern China has led to the lack of plant species conservation, resulting in habitat loss and fragmentation, environmental pollution and other problems, which further hinders the conservation of plant species. 2) The quantity of BGs in China has been increasing, and the development thereof has experienced three peak periods. So far, totally 229 BGs have been established in China. About 90% of BGs are concentrated in southeastern China, and the quantity of BGs in eastern China is significantly different from that in western China. Besides, the quantity distribution of BGs is sparse in western China and dense in eastern China, and the average area scale of BGs in western China is larger than that in eastern China. The reasons may be described as follows: there exist diverse landforms, sufficient rainfall and abundant water resources in southeastern China, which have created the diversity of plants and provided excellent natural conditions for the construction of BGs; meanwhile, the high-density urban construction activities in southeastern China make the quantity of BGs large while the area small; western China is sparsely populated, and the construction of BGs is rarely limited by urban land use, leading to a large average area of BGs. 3) BGs are the main space of plant diversity conservation within the boundaries of urban development. With the improvement of construction, the function of BGs has gradually improved, enabling them to play an increasingly important role in the conservation of plant diversity. BGs have well-conserved plant diversity through various ways, including ex situ conservation of endangered species, species regression, reconstruction of wild populations, research on the development and utilization of plant resources, publicity and education of plant conservation, etc., thanks to which phased results have already been achieved. The 229 BGs have collected and preserved more than 23, 000 plant species, accounting for 66.7% of the flora, initially forming the ex situ conservation pattern. Among them, 2, 620 seriously threatened native plants and 1, 289 species of endangered plants have been effectively conserved, respectively accounting for 42% and 41% of the total number thereof in China. In addition, the experimental ex situ conservation facilities in BGs have reached a certain scale, greatly promoting the conservation of plant diversity.

Conclusion  1) The research finds that there exists an imbalance between the space layout of BGs and the requirements of plant diversity conservation. Despite the large number of BGs in the eastern coastal region, the BGs in Eastern China are not evenly distributed to cover all floras, leading to a gap in plant diversity conservation, which entails BG construction to be planned as a whole at the national level. 2) According to the natural conditions, socio-economic conditions, and the distribution of plant species under conservation, the layout of BGs should be comprehensively planned at the national or regional scale. The spatial pattern of BGs should cover different ecosystem types, and different geographical conditions and climatic environments. New BGs are supposed to be established in key areas without any BG yet. 3) In order to improve the information platform of the National Germplasm Resource Bank and the national BGs system, the layout of BGs in regions with rich biodiversity or recognized as biodiversity hotspots in China should be further improved, for which in situ and ex situ conservation systems should be established and scientific research strengthened. 4)In the future, in situ, ex situ and near-field conservation should be comprehensively used to build the plant diversity conservation system, which plays a better role in plant diversity conservation.