Influence of Fine Root Functional Diversity on Fine Root Biomass Variations in Warm-Temperate and Subtropical Forests

Abstract

Functional diversity predicts ecosystem functions and strengthens the species diversity and ecosystem function relationship. The relationship between fine root biomass (FRB) and functional diversity in nitrogen (N) deposition is not completely understood. In subtropical and warm-temperate forests, we compared FRB and functional diversity under canopy and understory N addition (CAN and UAN, respectively) rates of 0, 25, and 50 kg N ha-1 yr-1. CAN and UAN decreased the community's FRB by up to 57.2% in subtropical forests and increased the community's FRB up to 69.3% in warm-temperate forests during the growing period. The functional richness index (FRic) of fine roots was negatively correlated with community FRB in subtropical forests during the growing period (p = 0.012), and NO3-N in the soil had the highest explanatory power for FRB variation (32.0%; p = 0.006). FRic was positively correlated with community FRB in warm-temperate forests (p = 0.011) and had the highest explanatory power (26.5%; p = 0.002). In warm-temperate forests, the synergistic increase in FRic and FRB increased nutrient uptake, whereas in subtropical forests, either N restricted fine root growth or FRic compensated for the decrease in FRB. These findings showed that ecosystems responded differently to N addition and that FRB varied based on functional diversity.

Keywords: canopy addition nitrogen, fine root biomass, functional diversity, subtropical forest, understory addition nitrogen, warm-temperate forest