Topography influences primary soil basic properties and bacterial community changes: evidence from volcanic field of 300 years, northeast China

Abstract

Topographic factor has crucial impacts on the rock weathering and soil development. However, few studies have concerned the influence of topographic features on the spatial distribution of soil properties at the initial soil development stage. To explore this, soil samples were collected from 10 soil profiles on scoria cone, and from 18 quadrats on lava plateau along the NNW-SSE toposequence in Laoheishan volcanic field of 300 years, northeast China. Basic indicators such as soil thickness, mechanical composition, organic carbon and total nitrogen and their mineral-associated fractions were measured, and soil bacterial community were identified by 16S rRNA amplicon sequencing method, and their relationships with topography were determined by Spearman rank correlation and pathway analysis. Compared to lava plateau with weak-weathered binary structure thinner than 13 cm, scoria slopes developed typical soil profiles ranging from 7 to 30 cm, with lower clay and silt fraction (e.g. topsoil: 73.75 % vs. 35.57 %), which positively associated with carbon and nitrogen contents (e.g. topsoil organic carbon: 72.32 vs. 38.59 g kg⁻¹). Northern slope had finer particles, richer carbon and nutrients than southern slope, with organic carbon peaked around middle slope position with 116.76 and 34.70 g kg⁻¹, respectively. Northern lava plateau showed distinctive differences from other topographic sites in bacterial phyla structure and functional groups. The total explanation of carbon and nitrogen contents and their stoichiometric ratio values to bacterial phyla structure accounted for 41 %. In conclusion, topography influenced clay fraction gathering, which in turn affected the accumulation of carbon and nutrients. Ultimately, it regulated shifts in bacterial diversity during the initial soil development process. This study will improve understanding of topographic-driven mechanisms of initial soil development and soil characteristics spatial patterns.