Biomass production, foliar and root characteristics and nutrient accumulation in young silver birch (Betula pendula Roth.) stand growing on abandoned agricultural land

摘要

The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics of a 8-year-old silver birch (Betula pendula} natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current annual production after eight growing seasons was 31.2 and 11.9 t DM ha~(-1), respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass ofthe stand. Carbon sequestration in tree biomass reaches roughly 17.5 t C ha~(-1) during the first 8 years. The biomass of the fine roots (d < 2 mm) was 1.7 +- 0.2 t DM ha~(-1) and 76.2% of it was located in the 20 cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7 m~2m~(-2)and specific leaf area (SLA) 15.0 +- 0.1 m~2 kg~(-1). The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared with the lower part. The short-root specific area (SRA) in the 30 cm topsoil was 182.9 +- 9.5 m~2 kg~(-1), specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry massunit of short roots were 145.3 +- 8.6 m g~(-1), 58.6 +-3.0 kg m~(-3) and 103.7 +- 5.5 tips nig~(-1), respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6, 25.0 and 56.6 kg ha~(-1), respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7 kg ha~(-1) yr~(-1) (55 and 27%), respectively, of which 29.1 kg ha~(-1) N and 2.8 kg ha~(-1) P were accumulated in the above-ground part of the stand.