The distribution of arbuscular mycorrhizal fungal communities at soil aggregate level in subtropical grasslands

Arbuscular mycorrhizal fungi (AMF) community assembly has been investigated at regional and local scales, but was largely unknown at micro-scale. The AMF community at soil aggregate level was studied to promote the understanding of their distribution at micro-scale. Surface soil associated with Eremochloa ophiuroides, Imperata cylindrica and Paspalum notatum were sieved into three fractions: large macroaggregates (LMA, >2mm), small macroaggregates (SMA, 0.25-2mm) and microaggregates (MA, <0.25mm). Illumina MiSeq sequencing revealed that AMF communities were dominated by Glomus (>90%) and Paraglomus (>6%), across plants. Higher AMF diversity was found in SMA or MA than LMA, which was positively related to soil nutrient levels. The soil pH and available phosphorus were related to the AMF diversity in SMA, while available potassium (AK) was related to the AMF diversity in MA. The correlation between Glomus, Claroideoglomus, or Paraglomus and soil pH or available phosphorus in SMA, and between Glomus and AK in MA could explain AMF diversity changes. The AMF community composition was consistent in three soil aggregate fractions. Our results demonstrate that AMF diversity, but not community composition, differ across soil aggregate sizes. The AMF diversity changes are related to edaphic factors, following a microscale-dependent pattern.