Plant-plant interactions and N fertilization shape soil bacterial and fungal communities 
Guo et al., 2019

Highlights  
•      Neighbor plant negatively affected plant growth, in particular for L. kaempferi. 
•      Inter-specific plant interactions raised bacterial and fungal diversity in added N. 
•      L. olgensis and N addition induced the dominance of the Basidiomycota community.
•      L. olgensis mainly affected microbial community in inter-specific associations.  

Abstract  

The impact of conspecific and heterospecific neighboring plants on soil bacterial and fungal communities has never been explored in a forest ecosystem. In the present study, we first investigated soil microbial communities in three plantations: Larix kaempferi monoculture, L. olgensis monoculture and their mixture. Then, a two-year growth experiment was conducted to investigate the effects of intra- and inter-specific interactions of L. kaempferi and L. olgensis on rhizosphere microbial communities at two different nitrogen levels. The results demonstrated clear differences in the beta-diversity and composition of bacteria and fungi among the three plantations, which implied the presence of different effects of plant-plant interactions on soil microbial communities. The results of the pot experiment showed that L. kaempferi suffered from greater neighbor effects from its conspecific neighbor regardless of N fertilization, although the effect declined when L. kaempferi was grown with L. olgensis under N fertilization. Changes in intra- and inter-specific plant interactions significantly impacted the chemical and biological properties of soil under N fertilization, with lower concentrations of NH4+, and lower soil microbial biomass (CMic) and soil carbon nitrogen biomass (NMic) under intra-specific plant interactions of L. kaempferi (KK) compared to inter-specific interactions of L. kaempferi and L. olgensis (KO). N fertilization increased bacterial and fungal alpha diversities in the rhizosphere soil of KO. For the beta diversity, the PERMANOVA results demonstrated that there was a significant impact of intra- and inter-specific plant interactions on soil microbial communities, with KK significantly differing from intra-specific plant interactions of L. olgensis (OO) and KO. The two plant species and N fertilization showed specific effects on the soil microbial composition, particularly on the fungal community. Both L. olgensis and N fertilization increased the abundance of Ascomycota but reduced that of Basidiomycota, and even shifted the dominance from Basidiomycota to Ascomycota under KO combined with N fertilization.

Bacterial (a) and fungal (b) taxa with different abundance changes in two-plant pots between N-treated (N+) and control (N-) soil, irrespective of plant-plant interactions (Class: N treatment; Subclass: Plant-plant interactions), as detected by LEfSe analysis. The taxa with the absolute LDA scores over 3 and P values less than 0.05 are shown.

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