Influence of Potassium Supply on Growth and Uptake of Nitrogen, Phosphorus, and Potassium by Three Ectomycorrhizal Fungal Isolates In Vitro

Abstract

Three ectomycorrhizal fungal isolates, Cenococcum geophilum SIV, a putative isolate of Pisolithus microcarpus and a Pisolithus sp., were cultured in vitro without potassium (K) and with three levels of K supply (as K2SO4). Some growth stimulation by K was observed among the fungi. Potassium in the liquid medium led to increased concentrations of nitrogen (N) and K in the fungi compared to K-free controls, and to higher phosphorus (P) concentrations in Pisolithus sp., but lower P in C. geophilum SIV. In a second experiment, the K influx rates of the fungi from external solutions followed Michaelis-Menten kinetics, indicating that K influx was an active process. Mycorrhizal fungi showed quite small C min values for K influx, ranging from 2.12 to 5.39 μ mol L− 1, in relation to K concentrations in the external solution. Such low C min values might allow the external hyphae to extract K efficiently from K-deficient soils. Furthermore, the fungi had low K m values for K uptake (< 14.85 μ mol L− 1), indicating high affinities and efficiencies of K carriers. Both Pisolithus sp. and P. microcarpus exhibited similar C min and K m values but were different from C. geophilum SIV. Furthermore, I max values varied significantly among the fungi, ranging from 9.60 to 21.63 μ mol g− 1 DM h− 1, perhaps due to variation in the intracellular K concentrations in the ectomycorrhizal fungi.