Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA.
Mycologia. 2010 Jul-Aug;102(4):822-34. doi: 10.3852/09-224.
In 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. In addition to testing 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 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 an order of magnitude more ammonium-N than glycine-N. The intact tundra core experiment provided contrasting results. After 10 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. 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 complex soil microbial communities.
在北极苔原生态系统中，土壤中的氮元素高度受限，氮的矿化作用缓慢，有机氮大大超过无机氮。我们研究了杀菌剂（肟菌酯[Quadris]或丙环唑[Tilt]）对从石南科植物根系中分离出来的真菌的影响。除了测试这两种杀菌剂的植物毒性外，我们还在一个没有根相关真菌的封闭培养皿系统中测试了它们对石南科植物（Vaccinium uliginosum）生长和氮吸收的影响。最后，为了在体内实验中评估杀菌剂的效果，我们将杀菌剂和氮同位素应用于来自阿拉斯加图利湖的完整苔原生态系统土壤芯，并检查了有和没有杀菌剂的 Vaccinium vitis-idaea 对铵-N 和甘氨酸-N 的利用。真菌纯培养实验表明，在体外，丙环唑比肟菌酯更有效地抑制真菌菌落生长，而肟菌酯在真菌菌株间的变异很大。旨在测试杀菌剂对植物体外生长的影响的实验室实验表明，Quadris 和 Tilt 都没有影响 V. uliginosum 的生长或氮吸收。在这个实验中，V. uliginosum 同化的铵-N 比甘氨酸-N 多一个数量级。完整的苔原生态系统核心实验提供了对比的结果。在生长室中应用杀菌剂 10 周后，V. vitis-idaea 的叶片%N 降低了 10%，在 4 天的同位素处理期间，标记的铵（33%）和甘氨酸（40%）的叶片 15N 摄取量减少。与体外实验相比，在未施加杀菌剂的处理中，从甘氨酸中同化的叶片 15N 是从 15NH4 同化的叶片 15N 的三倍。我们得出的结论是，真菌群落的功能对于从有机来源获取氮是必不可少的，并推测从无机来源获取氮主要受到与复杂土壤微生物群落竞争的抑制。
