Fine Root Biomass, Production, Turnover Rates, and Nutrient Contents in Boreal Forest Ecosystems in Relation to Species, Climate, Fertility, and Stand Age: Literature Review and Meta-Analyses

Fine roots <2 mm in diameter play a key role in regulating the biogeochemical cycles of ecosystems and are important to our understanding of ecosystem responses to global climate changes. Given the sensitivity of fine roots, especially in boreal region, to climate changes, it is important to assess whether and to what extent fine roots in this region change with climates. Here, in this synthesis, a data set of 218 root studies were complied to examine fine root patterns in the boreal forest in relation to site and climatic factors. The mean fine root biomass in the boreal forest was 5.28 Mg ha−1, and the production of fine roots was 2.82 Mg ha−1 yr−1, accounting for 32% of annual net primary production of the boreal forest. Fine roots in the boreal forest on average turned over 1.07 times per year. Fine roots contained 50.9 kg ha−1 of nitrogen (N) and 3.63 kg ha−1 of phosphorous (P). In total, fine roots in the boreal forest ecosystems contain 6.1 × 107 Mg N and 4.4×106Mg P pools, respectively, about 10% of the global nutrients of fine roots. Fine root biomass, production, and turnover rate generally increased with increasing mean annual temperature and precipitation. Fine root biomass in the boreal forest decreased significantly with soil N and P availability. With increasing stand age, fine root biomass increased until about 100 years old for forest stands and then leveled off or decreased thereafter. These results of meta analysis suggest that environmental factors strongly influence fine root biomass, production, and turnover in boreal forest, and future studies should place a particular emphasis on the root-environment relationships.