Nicolás César, Almeida Juan P, Ellström Magnus, Bahr Adam, Bone Sharon E, Rosenstock Nicholas P, Bargar John R, Tunlid Anders, Persson Per, Wallander Håkan
1Microbial Ecology Group, Department of Biology, Lund University, Lund, Sweden.
2Department of Biology, Ecology Building, Lund University, SE 22362 Lund, Sweden.
Plant Soil. 2017;419(1):113-126. doi: 10.1007/s11104-017-3324-8. Epub 2017 Jul 8.
Decomposition and transformation of organic matter (OM) in forest soils are conducted by the concomitant action of saprotrophic and mycorrhizal fungi. Here, we examine chemical changes in OM after fungal colonization in nitrogen fertilized and unfertilized soils from a Norway spruce forest.
Sand-filled bags amended with composted maize leaves were placed in the forest soil and harvested after 17 months. Infrared and near edge X-ray absorption fine structure spectroscopies were used to study the chemical changes in the OM. Fungal community composition of the bags was also evaluated.
The proportion of ectomycorrhizal fungi declined in the fertilized plots, but the overall fungal community composition was similar between N treatments. Decomposition of the OM was, independently of the N level or soil horizon, accompanied by an increase of C/N ratio of the mesh-bag content. Moreover, the proportions of carboxylic compounds in the incubated OM increased in the mineral horizon, while heterocyclic-N compounds decreased, especially in unfertilized plots with higher N demand from the trees.
Our results indicate that more oxidized organic C and less heterocyclic-N proportions in the OM remain after fungal colonization in the mineral layers, and suggest that ectomycorrhizal fungi transfer less heterocyclic-N from the mesh bags to the host trees under high N levels.
森林土壤中有机质（OM）的分解与转化是由腐生真菌和菌根真菌共同作用完成的。在此，我们研究了挪威云杉林施氮和未施氮土壤中真菌定殖后OM的化学变化。
将装有堆肥玉米叶的沙袋置于森林土壤中，17个月后收获。利用红外光谱和近边X射线吸收精细结构光谱研究OM的化学变化。同时评估沙袋中的真菌群落组成。
施肥地块中外生菌根真菌的比例下降，但不同氮处理间的总体真菌群落组成相似。无论氮水平或土壤层次如何，OM的分解都伴随着网袋内容物碳氮比的增加。此外，在矿质层中，培养的OM中羧酸化合物的比例增加，而异环氮化合物减少，尤其是在树木对氮需求较高的未施肥地块。
我们的结果表明，矿质层中真菌定殖后，OM中氧化态有机碳比例增加，异环氮比例降低，这表明在高氮水平下，外生菌根真菌从网袋向寄主树木转移的异环氮较少。
