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Application of fungistatics in soil reduces N uptake by an arctic ericoid shrub (Vaccinium vitis-idaea)

     ¹ Biology, Appalachian State University, 572 Rivers St., Boone, NC, 28608, United States of America
² Kansas State University, Manhattan, KS
³ Division of Biology, Kansas State University, Manhattan, Kansas
⁴ Lawrence Berkeley National Laboratory, Berkeley, CA
⁵ Division of Biology, Kansas State University, 125 Ackert Hall, Manhattan, KS, 66506, United States of America

In the arctic tundra, soil N is highly limiting, N mineralization is slow, and organic N greatly exceeds inorganic N. We studied the effects of fungistatics (azoxystrobin [Quadris®] or propiconazole [Tilt®]) on the fungi isolated from ericaceous plant roots in vitro. To test the phytotoxicity of the two fungistatics, we also tested their effects on growth and nitrogen uptake of an ericaceous plant (Vaccinium uliginosum) in a closed Petri plate system without root-associated fungi. Finally, to evaluate the fungistatic effects in an in vivo experiment, we applied fungistatics and nitrogen isotopes to intact tundra soil cores from Toolik Lake, Alaska, and examined the ammonium-N and glycine-N use by Vaccinium vitis-idaea with and without the fungistatics. The experiments on fungal pure cultures showed that Tilt® was more effective in reducing fungal colony growth in vitro than Quadris®, which was highly variable among the fungal strains. Laboratory experiments aiming to test the fungistatic effects on plant performance in vitro showed that neither Quadris® nor Tilt® affected V. uliginosum growth or N uptake. In this experiment V. uliginosum assimilated more than twenty times more ammonium-N than glycine-N. The intact tundra core experiment provided contrasting results. After ten wk of fungistatic application in the growth chamber V. vitis-idaea leaf %N was 10% lower and the amount of leaf ¹⁵N acquired was reduced from labeled ammonium (33%) and glycine (40%) during the 4 d isotope treatment period. In contrast to the in vitro experiment, leaf ¹⁵N assimilation from glycine was three times higher than from ¹⁵NH4 in the treatments that received no fungistatics. We conclude that the function of the fungal communities is essential to the acquisition of N from organic sources and speculate that N acquisition from inorganic sources is mainly inhibited by competition with the complex soil microbial communities.

Key words: amino acid, nitrogen cycle, plant nutrition, tundra