Abstract: Stand density has an important influence on the growth of individual trees and the accumulation of stand volume; however, the relationship between stand density and tree’s fine roots is still not well understood. We conducted an experiment in Fraxinus mandschurica Rupr. plantations with four planting densities (Treatment I: 1.0 m×1.0 m, II: 1.5 m×1.5 m, III: 2.0 m×2.0 m, and IV: 1.5 m×3.0 m) in Maoershan, Heilongjiang, China, and measured the diameter at breast height (DBH), selfthinning proportion from 2012 to 2016, leaf biomass production in 2013, 2014 and 2016, and used soil core and ingrowth core methods to estimate the standing biomass and biomass production of fine roots (diameter ≤2.0 mm ) and absorptive roots (diameter ≤0.5 mm). Results showed that the Treatment I had the highest branching intensity (31.55%) and the lowest tree height, while Treatment III had the largest mean DBH and tree height. Leaf biomass production increased with increasing stand age across all treatments, with the maximum occurring in Treatment II. Treatment I had the highest total selfthinning proportion. During the study period, the survivorship of living trees at the plot level was negatively correlated with annual leaf biomass production and increment of DBH (the former was statistically significant). Both fine roots and absorptive roots showed the largest standing biomass and production in Treatment IV, in which standing biomasses of absorptive roots were (184.62±17.73), (146.45±5.59), (150.32±5.39) and (242.81±19.07) g·m^-2 in Treatment I to IV, respectively. At the plot level, both standing biomass and production of absorptive roots were negatively correlated with stand density (the latter was statistically significant). Ratios of annual production of absorptive roots to leaf production and to annual increment of DBH were the highest in Treatment IV, but were similar among the other three treatments. In summary, the initial planting density of 2500 ind·hm^-2 was the optimal choice as manifested by the largest mean DBH and tree height, higher survivorship of living trees as well as the balanced biomass allocation between absorptive roots and leaves.

Key words: Tilia Linn., allometric equation, Jackknifing technique, biomass, additive system