Regulation of soil amendments on soil physical structure and microbial community in albic layer of albic soil

Albic soil is a typical low yield soil with barrier layer in Northeast China. Due to the dense structure of the barrier layer and the difficulties in water and gas transmission, it restricts crop growth and yield formation. We set up a manipulative experiment, with no amendment (CK) as the control to explore the effects of three amendments: composite amendment (modified bentonite+modified humic acid+calcium oxide, GL), modified bentonite (PR), and modified humic acid (HA) on the physical structure and microbial diversity of albic layer. The results showed that the improvement agent significantly reduced soil bulk density of the albic layer by 3.6% to 5.4%, increased the porosity by 4.7% to 7.0%, and increased the stability of aggregates. Among them, GL treatment enhanced the connectivity of pores by loosening soil particles. PR treatment could improve soil aeration in the short term, but with insufficient stability of aggregate structure. HA treatment enhanced aggregate stability through colloid filling, but had limited improving effect on pore connectivity. Different amendments changed soil microbial community composition in the albic layer. GL treatment significantly increased bacterial diversity, with a 12.9% increase in richness, with the community under which being dominated by Proteobacteria, Bacteroidetes, and Actinobacteria. The PR treatment increased bacterial richness by 17.4%, with the community under which being dominated by Actinobacteria, Proteobacteria, and Ascomycota. HA treatment significantly increased fungal species richness, with a 41.0% increase in Chao1 index. The dominant fungal communities were Ascomycota, Basidiomycota, and Zygomycota. Soil porosity was positively correlated with fungal abundance (r=0.62), and bulk density was positively correlated with actinomycete abundance (r=0.58). In summary, GL treatment had a good physical and biological synergistic effect and was more suitable for loosening the albic layer, improving soil permeability. PR treatment could improve the aeration and microbial activity of the albic layer in the short term, but its promotion effect on the stabi-lity of aggregate structure was limited. Long-term application may facilitate soil structure loosening. HA treatment was suitable for soils with high water retention requirements and the need to enhance aggregate stability.