Summary Vertical root segregation and the resulting niche partitioning can be a key underpinning of species coexistence. This could result from substantial interspecific variations in root profiles and rooting plasticity in response to soil heterogeneity and neighbours, but they remain largely untested in forest communities. In a diverse forest in subtropical China, we randomly sampled > 4000 root samples from 625 0–30 cm soil profiles. Using morphological and DNA‐based methods, we identified 109 woody plant species, determined the degree of vertical fine‐root segregation, and examined rooting plasticity in response to soil heterogeneity and neighbour structure. We found no evidence of vertical fine‐root segregation among cooccurring species. By contrast, root abundance of different species tended to be positively correlated within soil zones. Underlying these findings was a lack of interspecific variation in fine‐root profiles with over 90% of species concentrated in the 0–10 cm soil zone with only one species dominating in the 10–20 cm soil zone. Root profiles exhibited low responsiveness to root neighbours but tended to be shallow in soils with low phosphorus and copper content. These findings suggest that if there is niche differentiation leading to coexistence in this diverse forest, it would be occurring by mechanisms other than vertical fine‐root segregation.