Effects of nitrogen-water interaction on fine root morphology and production in a mixed Pinus koraiensis forest in Changbai Mountains, northeastern China

Changing soil nutrient and water profoundly influence carbon allocation in the forest ecosystem, and then impact morphology and production of tree fine roots. We studied the responses of fine root morphology and production in scenarios of increased nitrogen deposition (50 kg/(ha·yr)) and decreased precipitation (30% throughfall, about 210 mm/yr) in a broadleaf-Pinus koraiensis forest in Changbai Mountains, northeastern China. Results demonstrated that various factors (treatment, sampling date, soil layer) collectively influenced the morphology and production of fine roots. Nitrogen fertilization (N) significantly decreased the diameter, but increased specific root length of fine roots in 0-10 cm soil layer, the root length density in dry treatment plots (D) had been raised by 1.55-2.44 times and the production of fine roots increased by 104 g/(m·yr) as compared with CK plots, decreased throughfall and nitrogen fertilization (DN) significantly increased the diameter and production of fine roots in 10-20 cm soil layer. Thus, there might be the functional differentiation on nitrogen and water uptake of fine roots in different soil layers in the mixed Pinus koraiensis forest, and the spatial-temporal variations of fine root morphology and production are activated by nitrogen deposition, changed precipitation and their interactions.