Contrasting depth-related fine root plastic responses to soil warming in a subtropical Chinese fir plantation

Warming-induced soil drought, especially in topsoil, may enlarge the spatial mismatch between nutrients and water along the soil profile, which impedes the uptake of not only water but also nutrients by trees. Therefore, coordinating the acquisition of soil water and nutrients along the soil profile is an important strategy for trees to cope with global warming. This study examined soil depth-related changes in nutrient concentrations, biomass and morphology of fine roots in a Chinese fir plantation after 3 years of large-scale manipulative soil warming. Soil warming (ambient +4°C) increased fine root nitrogen (N) concentrations but decreased fine root phosphorus (P) concentrations across soil depths. Warming did not affect total fine root biomass and its vertical distribution. At the 0–10 cm depth, warming increased specific root length (SRL), specific root area (SRA), fine root diameter (RD) and root length density (RLD) but reduced root tissue density (RTD). In the 40–60 cm layer, warming reduced RD, SRL and RLD while increasing RTD mainly for roots of the 1–2 mm diameter class. Synthesis. We concluded that roots of Chinese fir plantations could adapt to warming-induced moderate water stress through contrasting depth-related root morphological adjustments, probably to optimize the acquisition of both soil water and nutrients. The results of this study are crucial for understanding the adaptation strategies of subtropical forests under future climate conditions.