Seasonal and yearly variations of fine-root biomass and necromass in a Scots pine ( Pinus sylvestris L.) stand

Abstract

Seasonal variations of the Scots pine ( Pinus sylvestris L.), dwarf shrub and grass fine-root biomass and necromass were studied in a pole stage Scots pine stand in eastern Finland during three successive growing seasons. The biomass of Scots pine fine roots varied annually and seasonally in the humus layer between 19±5 g m −2 to 139±22 g m −2, in the upper mineral soil layer between 90±14 g m −2 to 279±0 g m −2, and in the lower mineral soil layer between 68±17 g m −2 to 217±73 g m −2. The seasonal minimum and maximum of understory vegetation fine-root biomass were in the humus layer 35±6 g m −2 and 235±42 g m −2, in the upper mineral soil layer 26±0 g m −2 and 165±0 g m −2, and in the lower mineral soil layer 14±0 g m −2 and 36±5 g m −2. The seasonal fine-root necromass varied in the humus layer from 2±0 g m −2 to 1398±236 g m −2, in the upper mineral soil layer from 86±0 g m −2 to 1267±366 g m −2, and in the lower mineral soil layer from 8±0 g m −2 to 753±306 g m −2. The major part of the living Scots pine fine roots (62%) was in the mineral soil immediately below the humus layer, but almost all dwarf shrub roots and grass roots were in the humus and in the upper mineral soil layers. Most dead fine roots (82%) were in the humus layer and in the uppermost mineral soil layer. The variations of Scots pine fine-root biomass, dwarf shrub and grass fine-root biomass and necromass did not show a distinct and clear pattern within any growing season although there were significant differences between the same month during different growing seasons. Some of the observed variations could be explained by climatic factors related to drought.