No abstract

The formation and ecological roles of sterile flowers in flowering plants are interesting issues in floral biology and evolution. Here, we investigated the morphological and anatomical characteristics of both fertile and sterile flowers of Viburnum macrocephalum f. keteleeri, a self-incompatible and insect-pollinated shrub, during different developmental stages of flowers. In addition, pollinator visitation rates and fruit set were determined in intact inflorescences and those with sterile flowers removed. The results indicate that sterile and fertile flowers were developmentally similar during early developmental stages, and that development of the flower types diverged about 15 days before flowering. In addition, pollinator visitation rates, number of pollen grains on stigmas and fruit set were significantly higher in inflorescences with sterile flowers than those without sterile flowers. The results suggest that sterile flowers of this species evolved from fertile flowers under long-term selective pressure, and play a crucial role in enhancing reproductive success through effectively attracting pollinators to the plant and thus enhancing fruit set.

Over the past 50 years, China's ancient agricultural village landscapes have been transformed by unprecedented social, technological, and ecological changes. Although these dense anthropogenic mosaics of croplands, settlements, and other used lands cover more than 2 million square kilometers across China, the nature of these changes and their environmental impacts remain poorly understood because their spatial scale is generally too small to measure accurately using conventional landchange methods. Here, we investigate the regional consequences of fine-scale landscape changes across China's village regions from 1945 to 2002 using high-resolution, field-validated ecological mapping of a regionally stratified sample of village landscapes at five sites across China, with uncertainties estimated using model-based resampling and Monte Carlo methods. From 1945 to 2002, built surface areas increased by about 7% (90% credible interval = 2-17%) across China's village regions, an increase equivalent to about three times the total urban area of China in 2000. Although this striking result is explained by a near doubling of already large village populations and by lower housing density per capita in rural areas, two unexpected changes were also observed: a 9% net increase (-4% to +21%) in regional cover by closed canopy trees and an 11% net decline (-30% to +3%) in annual crops. These major regional changes were driven primarily by intensive finescale land-transformation processes including tree planting and regrowth around new buildings, cropland abandonment, and by the adoption of perennial crops and improved forestry practices. Moreover, the fragmentation, heterogeneity, and complexity of village landscapes increased over time. By coupling regional sampling and upscaling with observations in the field, this study revealed that fine-scale land-change processes in anthropo- 279genic landscapes have the potential for globally significant environmental consequences that are not anticipated, measured, or explained by conventional coarser resolution approaches to global and regional change measurement or modeling.

In December 2019, an outbreak of pneumonia, which was named COVID-2019, emerged as a global health crisis. Scientists worldwide are engaged in attempts to elucidate the transmission and pathogenic mechanisms of the causative coronavirus. COVID-19 was declared a pandemic by the World Health Organization in March 2020, making it critical to track and review the state of research on COVID-19 to provide guidance for further investigations. Here, bibliometric and knowledge mapping analyses of studies on COVID-19 were performed, including more than 1,500 papers on COVID-19 available in the PubMed and China National Knowledge Infrastructure databases from January 1, 2020 to March 8, 2020. In this review, we found that because of the rapid response of researchers worldwide, the number of COVID-19-related publications showed a high growth trend in the first 10 days of February; among these, the largest number of studies originated in China, the country most affected by pandemic in its early stages. Our findings revealed that the epidemic situation and data accessibility of different research teams have caused obvious difference in emphases of the publications. Besides, there was an unprecedented level of close cooperation and information sharing within the global scientific community relative to previous coronavirus research. We combed and drew the knowledge map of the SARS-CoV-2 literature, explored early status of research on etiology, pathology, epidemiology, treatment, prevention, and control, and discussed knowledge gaps that remain to be urgently addressed. Future perspectives on treatment, prevention, and control are also presented to provide fundamental references for current and future coronavirus research.

This study investigates the relationship between institutional cross‐ownership and corporate tax avoidance in Chinese listed firms. Our findings indicate that the tax avoidance aggressiveness of Chinese listed firms could be significantly motivated by institutional cross‐ownership. This finding is robust to endogeneity tests, namely, propensity score matching estimation, two‐stage least squares regression, generalised method of moments test, and a falsification concern. Further, this positive relationship between institutional cross‐ownership and tax avoidance is more pronounced for listed firms with greater managerial ability and those with higher auditor industry expertise. Finally, such a relationship is more obvious for cross‐owners within the same industry, but only significant for independent cross‐owners, non‐state‐owned enterprises and firms within a less competitive industry. All main findings are robust to various robustness tests.