Abstract: As a unique form of open innovation, the development of open source software（OSS）differs fundamentally from conventional software development and other open innovation activities with fixed procedures, practices and organizers: It allows entities to join voluntarily, innovate autonomously, and operate independently. Consequently, open participation not only facilitates rapid external knowledge acquisition for OSS projects but also subjects them to a significant burden of knowledge absorption. As awareness of the OSS landscape increases, research in the vein has recognized this 'double-edged sword' effect of open participation, but still lacks a holistic theoretical framework to explain it. In addition, scholars fail to systematically consider the multiple dimensions of open participation and clarify the impact of project governance mechanisms on the consequence of open participation. It is imperative to develop a systematic theoretical system to explore the impact of different types of open participation dialectically and comprehensively. Therefore, by adopting the openness paradox perspective and the knowledge base view, the impact mechanism of open participation in OSS projects is framed as a contest between knowledge acquisition and knowledge absorption. On this basis, this study considers the dual facets of open participation, namely breadth and depth, and analyze their diverse effects on the performance of OSS projects. Furthermore, this research places emphasis on the license agreement, a pivotal governance mechanism, to explore its contingent effects within the aforementioned relationships. This study takes 409 OSS projects on the GitHub platform as samples. Following the open innovation research, the breadth of open participation is measured by the number of participants, and the depth of open participation is measured by the number of core participants who are deeply integrated into the software development process. The restrictiveness of licenses is a coding based on type. The performance of OSS projects is measured by their number of downloads. The negative binomial regression model is used to conduct empirical analysis. The empirical results show that the breadth of open participation has an inverted U-shaped relationship with project performance. The influx of participants initially triggers an increase in performance but leads to a decrease after exceeding the threshold. In contrast, the depth of open participation has a U-shaped relationship with project performance. The increase of core participants initially causes a decrease in performance, but leads to an increase after exceeding the threshold. In addition, restrictive licenses reinforce the inverted U-shaped relationship between open participation breadth and project performance. By demonstrating the norms, intentions and preferences, the projects with restrictive licenses can attract more intrinsically motivated participants and motivate them to actively engage in software development. Consequently, such projects experience rapid knowledge acquisition gains in the early stages of breadth growth but face escalating knowledge absorption pressures in the later stages. The managerial implications mainly focus on two aspects. First, for OSS development teams, attracting ordinary contributors is undoubtedly important, but cultivating core contributors holds greater strategic significance. The latter's coordinating function should be leveraged to ensure the project operates orderly and alleviate the pressure of knowledge absorption. Additionally, it is vital to recognize the implicit governance function of license agreements. They can convey a project's values and production model and thus impact the composition of participators and potential knowledge contributions. Second, for open source community operators, boosting the visibility and interaction of core contributors is necessary. Related initiatives contribute to developing a layered organization operational model and elevating the coordination willingness and effectiveness of core contributors in its wake.

Key words: open participation, openness paradox, open source software, knowledge acquisition, knowledge absorption