The significance of rotation periods for mycorrhiza formation in Short Rotation Coppice

Rotation periods control not only the above-ground growth but also the assimilate transfer to the root systems in Short Rotation Coppice (SRC). Since assimilates are needed for the nutrient supply of associated mycorrhizal fungi, their control by rotation period length seems most probable. One poplar (Populus nigra × maximowiczii cv. Max 4) and one willow clone (Salix viminalis clone 78–101) cultivated as SRC were investigated on their ectomycorrhiza formation in response to 15 years of continuous different rotation periods (three and six years) at the same test site in Northern Germany. On the poplar clone the frequency of ectomycorrhizae was significantly lower in 6-year than in 3-year rotation. On the willow clone frequency of ectomycorrhizae was not significantly affected, but the portion of dead fine roots was significantly higher in the 6-year than in the 3-year rotation in autumn. In both rotation systems, the frequency of ectomycorrhizal (EM) colonisation was significantly higher in autumn than in spring. Five EM morphotypes were found on the poplar and seven on the willow clone. EM morphotypes which were common on both clones were formed with two fungal partners of the Pezizales (Geopora cervina, Tuber rufum), one of the Agaricales (Laccaria sp.) and one of the Thelephorales (Thelephoraceae). In spring G. cervina constituted the largest part of all observed EM morphotypes on P. nigra × maximowiczii and S. viminalis. The results indicated a selective promotion of EM formation of some Pezizales (Tuber and Peziza spp.) and some Agaricales (Laccaria spp.) due to shorter rotations, and a selective promotion of other Agaricales (Inocybe sp.) and Boletales (Scleroderma spp.) due to longer rotations. This might allow selective manipulation of the mycorrhizal diversity by the selection of the rotation system. A future challenge will be to select which mycorrhizal diversity might be more advantageous for the vitality and biomass production of poplar and willow clones.