The diversity of plant functional groups in plantations affects soil carbon, but we have limited understanding of the underlying mechanisms for how plant management affects soil carbon dynamics. Here, we conducted a 3-year manipulation experiment of plant functional groups that included understory removal, tree root trenching, and fertilization treatments in 2-year-old and 6-year-old Eucalyptus plantations in the subtropical region. The results showed that soil respiration was significantly suppressed by understory removal (-38%), tree root trenching (-41%), and their interactions (-54%), but that fertilization alone and in interactions had no significant effect. The Chao1 indices for soil bacterial and fungal diversity significantly decreased with understory removal in the 2-year-old plantation and with tree root trenching in the 6-year-old plantation. Soil bacterial and fungal communities were also affected by understory removal and tree root trenching. Soil respiration, physicochemical characteristics, microbial diversity, and community composition were significantly affected by plantation age. Reductions in soil carbon emissions were associated with reductions in plant functional groups and soil microbial groups, while increases in soil respiration were associated with soil physicochemical factors, soil temperature, and plantation age. Our findings highlight that plant managements are of great significance to the soil carbon emission processes in afforested plantations.

Soil respiration was measured by a Li-cor 8100 automated soil flux system (LI-COR Inc., Lincoln, NE, USA); Microbial analysis of soil samples was measured by the Majorbio Inc.