To illustrate the interplay between top-down and bottom-up forces on the soil microbial community and
activity, we conducted a 3-year field experiment investigating the interactions of the dominant, exotic
earthworm Pontoscolex corethrurus and the native plant Evodia lepta in subtropical soil. We found that
both earthworms and plants were able to regulate soil carbon (C) and phosphorous (P) dynamics by
affecting the soil fungi-to-bacteria ratio, as well as the labile C and available P content. The increase in
soil respiration in plots with only earthworms was mainly due to the increased proportion of soil bacteria
that had a fast turnover and low assimilation efficiency. The increase in soil respiration in plots with only
plants was possibly due to an increase in the metabolic quotient of soil microorganisms under the stress
of soil available P. The significant decrease of soil available P and increase in soil phosphatase activity
indicated an intensified demand for soil available P when plants were present; accordingly, earthworms'
effect on soil available P was only significant in plots with plants. Overall, when plants were present, the
soil fungi-to-bacteria ratio (F/B) and C dynamics changed in a similar way regardless of the reduction of
the earthworm populations. The earthworms’ effects on soil P processes were enhanced by the presence
of plants. These indicated that plants were one of the key regulators of the effects of earthworms on the
soil microbial community and its activity in this subtropical ecosystem.