Divergent responses of fine root decomposition to removal of understory plants and overstory trees in subtropical Eucalyptus urophylla plantations

Aims Plant fine roots play an important role in forest nutrient cycling. However, how fine root decomposition responds to plant removal is poorly understood. We aimed to examine the effects of understory plants and overstory trees removal on fine root decomposition in 8- and 29-year-old (young and mature, respectively) Eucalyptus urophylla plantations. Methods A field decomposition experiment of fine roots from E. urophylla and Dicranopteris dichotoma was performed. The fine roots of E. urophylla were divided into two groups: the first two orders and the third to fifth orders. Mass remaining, carbon (C) and nutrients (nitrogen: N, phosphorus: P) remaining in fine roots were determined. Results Understory removal retarded decomposition of lower-order roots of E. urophylla in the young plantation and decomposition of fine root of D. dichotoma in the mature plantation, but it did not affect root N and P remaining in either plantation. Unexpectedly, tree removal did not affect fine root decomposition, and nutrients remaining of E. urophylla and D. dichotoma. Stand age significantly influenced fine root N remaining and root branch order affected fine root decomposition and nutrients remaining. Conclusions Fine root decomposition exhibited divergent responses to understory removal and the effects depended on stand age and root branch order, but no response to tree removal. In addition, fine root nutrient dynamics exhibited various responses to stand age and root branch order. Understory plants, stand age, and root branch order should be considered when assessing the decomposition and nutrient cycling of fine roots in subtropical plantation forests.