Predicting biomass of bilberry (Vaccinium myrtillus) using rank distribution and root-to-shoot ratio models

Investigation of relationships between biomass of different plant compartments is important because their varying turnover rates affect the amount and composition of aboveground and belowground litter, which has a direct effect on nutrient cycling and carbon accumulation in soil. A study of biomass partitioning amongst compartments of the bilberry ( Vaccinium myrtillus L.), a common clonal dwarf shrub in boreal coniferous forests, was carried out at eleven study sites in Finland. We hypothesize that the biomass partitioning of bilberry follows a common pattern across a variety of edaphic conditions and geographic range, and this pattern can be modelled by the rank distribution of compartment biomasses. We found that the highest portion of the total biomass belonged to rhizomes, which were followed by shoot stems, roots and leaves. Furthermore, this pattern was observed regardless of the latitudinal zone (northern or southern Finland), site fertility level measured as soil C/N ratio and canopy-dominant tree species (pine or spruce). However, the observed ratios between biomass compartments varied between different sites. In particular, we found that the exact ratio between above- and belowground biomass was dependent on the C/N ratio of the soil organic layer (exponential model, R 2 = 0.443), showing that bilberry allocates more biomass to belowground parts in the nutrient poor than in the nutrient-rich sites. The results suggested that there are uniform regularities in the structural organization within the plant species representing clonal growth form of dwarf shrubs. This observation enables us to use the rank distribution of compartments in modelling biomass partitioning of bilberry in a wide range of environmental conditions, although the mechanisms underlying such regularities require further investigation.