The biogeochemical impact of ectomycorrhizal conifers on major soil elements (Al, Fe, K and Si)

Mobilisation of nutrients and dissolution of minerals are of key importance for plant growth and soil formation, as well as long term ecosystem sustainability. The effects of Pinus sylvestris seedlings, ectomycorrhizal colonisation and potassium supply on the mobilisation of Al, Fe, K and Si were studied in a soil column experiment. Budgets were constructed considering amounts in drainage water, accumulation in plants and changes in the pools of exchangeable ions (BaCl2 extractions). Drainage was the most important sink under the experimental conditions imposed, but the other two pools were also of quantitative significance. Plants had a significant positive effect on the total quantities of all elements mobilized. Mycorrhizal colonisation had limited quantitative impact on the mobilization, probably because the chosen mycorrhizal fungi did not cause any growth promotion in this experiment. Despite this, a multivariate analysis (PCA) showed a clear separate grouping of mycorrhizal, non-mycorrhizal and no-plant treatments, and in particular Si and K mobilization was related to soil biological variables which in turn were affected by the presence of mycorrhiza. When K was omitted from the watering solution, plants were able to mobilise significantly more K, which was reflected in plant uptake and a potential replenishment of the exchangeable pool. Up-scaling of total Al, K and Si mobilization to field conditions resulted in rates between equal to and up to 10 times higher than the average historical weathering rate.