Contribution of fine root to soil nutrient heterogeneity at two sides of the bamboo and broad-leaved forest interface

Aims The encroachment of Phyllostachys pubescens into woodland was commonly thought to lead to a change in the amount of nutrient stored in the ecosystems. Our objective was to investigate the soil nutrients of soil organic carbon (SOC), total nitrogen (STN) and total phosphorous (STP) heterogeneity at two sides of the bamboo and broad-leaved forest interface (BBLFI), i.e., P. pubescens forest (PPF) - evergreen broad-leaved forest (EBF) transition, and to quantify the contribution of fine roots to the accumulative difference in soil nutrients.
Methods We selected typical BBLFI plots straddling PPF and EBF in natural areas around the Dagangshan Forest Ecosystem Research Station, State Forestry Administration. We investigated the distribution and dynamics of soil nutrients, fine root biomass, annual production and decomposition rate in 2010-2011 by means of sequential coring and ingrowth into cores. We calculated the fine roots C, N and P stocks, SOC, STN and STP pools and the contribution of fine roots to soil nutrient heterogeneity at two sides of BBLFI.
Important findings There was a significant soil nutrient difference between the two sides of BBLFI. The SOC and STN contents in PPF were 20.51 and 0.53 g·kg^-1, respectively, which were higher than in EBF by 34.53% and 50.35%, respectively, but the STP was 25.54% lower. Fine root biomass, nutrient stock and amount of return to soil between two sides of BBLFI were also obviously different. PPF root biomass was 1201.60 g·m^-2, which is 5.86 times as much as EBF. Nutrient stock was 591.42 g C·m^-2, 5.44 g N·m^-2 and 0.25 g P·m^-2, which were 6.12, 3.77 and 3.11 times higher than EBF. The amount of return nutrient was 278.54 g C·m^-2·a^-1, 2.36 g N·m^-2·a^-1 and 0.11 g P·m^-2·a^-1, which were 6.93, 4.29 and 3.67 times higher than EBF, respectively. The fine roots of the two sides decomposed at almost the same rate. The annual contribution of fine roots to the soil nutrient heterogeneity was 76.79% for SOC and 28.33% for STN, but P returned from dead fine root slowed the progression of forming STP heterogeneity by 6.17% annually. These findings indicated that bamboo encroachment had changed the EBF soil nutrients, leading to a significant accumulative soil nutrient heterogeneity at two sides of BBLFI, and fine roots played an important role in forming this heterogeneity for SOC and STN.