Use of strontium isotopes and foliar K content to estimate weathering of biotite induced by pine seedlings colonised by ectomycorrhizal fungi from two different soils
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Pinus sylvestris seedlings, colonised by ectomycorrhizal (EM) fungi from either of two different soils (untreated forest soil and a limed soil from a clear cut area), were grown with or without biotite as a source of K. The biotite was naturally enriched in 87Sr and the ratio of 87Sr/ 86Sr in the plant biomass was estimated and used as a marker for biotite weathering and compared to estimates of weathering based on foliar content of K. Different nutrient regimes were used to expose the seedlings to deficiencies of K with and without an application of nitrogen (NH4NO3) in excess of seedling demand. The seedlings were grown for 220 days and the elemental composition of the shoots were analysed at harvest. The EM colonisation was followed by analysing the concentration of ergosterol in the roots and the soils. Bacterial activity of the soil was estimated by the thymidine incorporation technique. The concentration of organic acids in the soil solution was measured in the soil in which seedlings colonised by EM fungi from the untreated forest soil were grown. It was found that seedlings colonised by EM fungi from untreated forest soil had taken up more K in treatments with biotite addition compared to seedlings colonised by EM fungi from the limed forest soil (p<0.05). Seedlings from untreated forest soil had larger shoots and contained more K when grown with biotite compared to KCl as K source, indicating that biotite had a stimulatory effect on the growth of these seedlings which was not related to K uptake. Seedlings from the limed soil, on the other hand, had similar foliar K content when grown with either biotite or KCl as K source. The larger uptake of K in seedlings from untreated forest soil was not an effect of a more developed EM colonisation of the roots since seedlings from the limed soil had a higher ergosterol concentration both in the soil and in the roots. Nutrient regimes had no significant influence on the total uptake of K but the 87Sr/ 86Sr isotope ratio in the plant biomass indicated that seedlings grown with excess nitrogen supply had taken up proportionally less Sr from the biotite (1.8% of total Sr content) compared to seedlings grown with a moderate nitrogen supply (5.0%). Furthermore, seedlings grown with excess nitrogen supply had a reduced fungal colonisation of roots and soil and bacterial activity was lower in these soils. The 87Sr/ 86Sr ratio in the plant biomass was positively correlated with fungal colonisation of the roots (r2=0.98), which may indicate that the fungus was involved in releasing Sr from the biotite. Uptake of K from biotite was not related to the amount of organic acids in the soil solution. Oxalic acid was positively related to the amount of ergosterol in the root, suggesting that oxalic acid in the soil solution originates from the EM symbionts. The accuracy of the estimations of biotite weathering based on K uptake by the seedlings in comparison with the 87Sr/86Sr isotope ratio measured in the shoots is discussed.
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- Andersson F, Bergholm J, Hallbäcken L, Popovic B, Möller G and Petterson F 1996 Farabolförsöket, försurning, kalkning och kvävegödsling av en sydöstsvensk granskog. Swedish University of Agricultural Sciences, Department of Ecology and Environmental Sciences. Box 7072, 750 07 Uppsala, Sweden, Rapport nr. 70.Google Scholar
- Graustein W C 1989 87Sr/86Sr ratios measure the sources and flow of strontium in terrestrial ecosystems. In Stable Isotopes in Ecological Research. Eds Rundel, Ehleringer and Nagy. Ecological studies, Vol 68. pp 491–512. Springer Verlag, New York.Google Scholar
- Harley J L 1989 The significance of Mycorrhiza. Mycol. Res. 92, 129–139.Google Scholar
- Jongbloed R H and Borst-Pauwels G W F H 1992 Effects of aluminium and pH on growth and K uptake by three ectomycorrhizal fungi in liquid culture Plant Soil 140, 157–165.Google Scholar
- Lapeyrie F, Ranger J and Vairelles D 1991 Phosphate-solubilizing activity of ectomycorrhizal fungi in vitro. Can. J. Bot. 69, 342–346.Google Scholar
- Mahmood S 2000 Ectomycorrhizal community structure and function in relation to forest residue harvesting and wood ash applications. PhD thesis, University of Lund, Sweden.Google Scholar
- Marschner H 1995 Mineral nutrition of higher plants. Academic Press, London.Google Scholar
- Nohrstedt H-Ö, Arnebrant K, Bååth E and Söderström B 1989 Change in carbon content, respiration rate, ATP content and microbial biomass in nitrogen-fertilized pine forest soils in Sweden. Can. J. For. Res. 19, 323–328.Google Scholar
- Read, D J 1991 Mycorrhizas in ecosystems Experientia 47, 376–391.Google Scholar
- Smith S E and Read D J 1997 Mycorrhizal Symbiosis. Academic Press, London.Google Scholar
- Tamm C O 1991 Nitrogen in terrestrial ecosystems. Springer Verlag, Berlin.Google Scholar