Competition increased fine root biomass in Chinese fir (Cunninghamia lanceolata) plantations in Subtropical China

Fine roots play a prominent role in plants’ acquisition of nutrients and water from the soil, and their amounts and dynamics determine trees’ growth and adaptation to environmental stress. However, the relationship between fine tree roots (including absorptive roots and fine transport roots) and forest biomass or fine understory vegetation roots (understory roots) remains poorly understood, which was the main objective of this study. We selected 20 plots in Chinese fir (Cunninghamia lanceolata) plantation forests of the similar ages (23 years old on average) in different areas with various levels of forest biomass in subtropical China to assess the above-mentioned relationship. Forest biomass was used as a proxy for soil condition. We found that all fine root biomass of trees and understory vegetation were significantly and negatively correlated with forest biomass. To our surprise, both total Chinese fir fine root biomass (absorptive roots and fine transport roots) and fine transport root biomass showed significant and positive correlations with understory root biomass. These results clearly demonstrate that fine tree root biomass is significantly promoted and increased due to competition from understory vegetation where forest biomass is low.