Biomass of extramatrical ectomycorrhizal mycelium and fine roots in a young Norway spruce stand - a study using ingrowth bags with different substrates

摘要

The partitioning of below ground carbon inputs into roots and extramatrical ectomycorrhizal mycelium (ECM) is crucial for the C cycle in forest soils. Here we studied simultaneously the newly grown biomass of ECM and fine roots in a young Norway spruce stand. Ingrowth mesh bags of 16 cm diameter and 12 cm height were placed in the upper soil and left for 12 to 16 months. The 2 mm mesh size allowed the ingrowth of fungal hyphae and roots whereas a 45 mu m mesh size allowed only the ingrowth of hyphae. The mesh bags were filled with either EA horizon soil, pure quartz sand or crushed granite. Controls without any ingrowth were established for each substrate by solid tubes (2010) and by 1 mu m mesh bags (2011). The fungal biomass in the substrates was estimated by the PLFA 18:2 omega 6,9 and ECM biomass was calculated as difference between fungal biomass in mesh bags and controls. The maximum ECM biomass was 438 kg ha(-1) in October 2010 in 2 mm mesh bags with EA substrate, and the minimum was close to zero in 2011 in 45 mu m mesh bags with quartz sand. The high P content of the crushed granite did not influence the ECM biomass. Fine root biomass reached a maximum of 2,343 kg ha(-1) in October 2010 in mesh bags with quartz sand after 16 months exposure. In quartz sand and crushed granite, ECM biomass correlated positively with fine root biomass and the number of root tips, and negatively with specific root length. The ratio of ECM biomass/fine root biomass in October ranged from 0.1 to 0.3 in quartz sand and crushed granite, but from 0.7 to 1.8 in the EA substrate. The results for the EA substrate suggest a large C flux to ECM under field conditions.