Effect of Long-Term Nitrogen Fertilization on Mycorrhizal Fungi Associated with a Dominant Grass in a Chihuahuan Desert Grassland at the Sevilleta National Wildlife Refuge, New Mexico (2005)

We studied the diversity of arbuscular mycorrhizal fungi (AMF) in a semiarid grassland and the effect of long-term nitrogen (N) fertilization on this fungal community. Root samples of Bouteloua gracilis were collected at the Sevilleta National Wildlife Refuge (New Mexico, USA) from control and N-amended plots that have been fertilized since 1995. Small subunit rDNA was amplified using AMF specific primers NS31 and AM1. The diversity of AMF was low in comparison with other ecosystems, only seven operational taxonomic units (OTU) were found in B. gracilis and all belong to the genus Glomus. The dominant OTU was closely related to the ubiquitous G. intraradices/G. fasciculatum group. N-amended plots showed a reduction in the abundance of the dominant OTU and an increase in AMF diversity. The greater AMF diversity in roots from N-amended plots may have been the result of displacement of the dominant OTU, which facilitated detection of uncommon AMF. The long-term implications of AMF responses to N enrichment for plant carbon allocation and plant community structure remain unclear.

本研究探究了半干旱草原中丛枝菌根真菌（arbuscular mycorrhizal fungi, AMF）的多样性，以及长期施氮（nitrogen, N）对该真菌群落的影响。研究于美国新墨西哥州塞维利塔国家野生动物保护区开展，采集了自1995年起持续施氮的处理样地与对照样地中格兰马草（Bouteloua gracilis）的根系样本。采用AMF特异性引物NS31与AM1扩增小亚基核糖体DNA（small subunit rDNA）。相较于其他生态系统，该区域AMF多样性较低，仅在格兰马草根系中发现7个操作分类单元（operational taxonomic units, OTU），且全部隶属于球囊霉属（Glomus）。优势OTU与广泛分布的根内球囊霉/束生球囊霉类群（G. intraradices/G. fasciculatum）亲缘关系紧密。施氮样地中优势OTU的丰度有所降低，AMF多样性则有所提升。施氮样地根系中AMF多样性更高，可能源于优势OTU被替代，这使得稀有AMF得以被检测到。目前尚不清楚AMF对氮富集的响应对植物碳分配与植物群落结构的长期影响。