grassroots president草根总统
grassroots community基层社区
grassroots globalization草根全球化
grassroots election基层选举
Grassroots Pantry豆苗居;小清新口味
Grassroots work基层基础工作
grassroots type即草根类
Grassroots Mobilization草根动员
Grassroots Manager基层管理人员
N-PLURAL（复数型名词） The grassroots of an organization or movement are the ordinary people who form the main part of it, rather than its leaders. (组织、运动的) 基层
You have to join the party at grassroots level from what I understand.
据我的了解，你得由基层组织入党。