Interactions between base cation / aluminium ratio and ectomycorrhizal status and their effects on growth and nutrient uptake of Pinus sylvestris.

AHONEN-JONNARTH, ULLA¹, ANDERS GÖRANSSON² & ROGER FINLAY¹.

¹Department of Forest Mycology & Pathology, SLU, Box 7026, S-750 07 Uppsala, SWEDEN. ²Department of Production Ecology, SLU, Box 7042, S-750 07 Uppsala, SWEDEN.

There is disagreement in Sweden about the severity of forest damage caused by acidification and the need for remedial actions such as liming. Use of the molar ratio of base cations to aluminium (Ca+Mg+K)/Al) as a tool for determining critical loads of acidic deposition has been criticised for ignoring rhizosphere complexity. The aim of our study is to investigate the response of Pinus sylvestris seedlings to variations in BC/Al ratio and the extent to which these responses are modified by the presence of symbiotic ectomycorrhizal fungi. Seedlings were grown in silver sand in a semi-hydroponic system allowing steady state growth and received nutrient solution containing N, K, Ca and Mg in the proportions 100:35:3:4. Plants were either colonised by Laccaria bicolor or left uninfected. The seedlings were harvested 47, 59, 69, 80, 91 and 102 days after planting. All seedlings initially received the same nutrient solution without aluminium. After 69 days the remaining seedlings received either a solution with the molar ratio [Ca+Mg+K]/[Al] = 1.0 or [Ca+Mg+K]/[Al] = 0.6 ([Ca+Mg]/[Al]=0.1)
The seedlings had the same relative growth rate (about 4 %) both before and after introduction of the Al-treatment and at both BC/Al -levels. Biomass of the seedlings was not decreased due to aluminium treatments either in mycorrhizal or non-mycorrhizal seedlings. The biomass of non-mycorrhizal seedlings was slightly higher in all treatments. Further experiments, using natural substrates, are in progress to investigate the possible role of organic acid production and mineral weathering by the mycorrhizal mycelium.