Leaf leachates have the potential to influence soil nitrification via changes in ammonia‐oxidizing archaea and bacteria populations

Soil nitrogen (N) transformation is mainly controlled by microorganisms. Different plant species have specific effects on soil ammonia‐oxidizing archaea (AOA) and bacteria (AOB). Furthermore, plant secondary metabolites have dramatic influences on soil N transformation and soil ammonia‐oxidizers. However, no study has directly linked the changes in soil AOA and AOB communities to N transformation due to different plant species' leaf leachates, including comparing invasive versus native plants. We selected three invasive species, Wedelia trilobata, Ipomoea cairica and Mikania micrantha, and two native species, Wedelia chinensis and Merremia hederacea, and incubated soil with high and low concentrations of leaf leachates from the five species. Soil N transformation and ammonia oxidizer communities (based on quantitative PCR and 16S rRNA high‐throughput sequencing) were determined. Leaf leachates significantly affected soil N transformation and soil AOA and AOB abundance, and the effects were dependent on the plant species and leachate concentration. The leachate of W. chinensis increased soil net nitrification rates (NNR), whereas that of M. micrantha increased soil nitrate (NO₃⁻) and NNR. The leachate of M. micrantha increased AOB amoA genes, whereas that of M. hederacea decreased AOA amoA genes. At the higher concentration, all leachates showed inhibitory effects on the relative abundance of all AOA taxonomic groups. Phenolics, flavonoids and organic carbon in leaf leachates had a negative correlation with soil NO₃⁻, NNR and the amoA genes of AOA and AOB, whereas NH₄⁺ and NO₃⁻ in leachates showed a positive correlation. Among the five species, the invasive species M. micrantha had the strongest positive effect on soil N transformation and AOB abundance. The altered soil ammonia oxidizer communities and modified N process rates induced by leaf leachates provide an explanatory mechanism for the differential effects of plant species on N cycling. HIGHLIGHTS: Link changes in soil AOA and AOB to N cycling due to leaf leachates. Specific plants can dramatically alter soil ammonia‐oxidizer presence and abundance. Effects of invasive plants on soil N and AOB are mainly driven by M. micrantha. High concentrations of plant leachates reduced the relative abundance of AOA groups.