Soil pore structure shaped compositions and structures of soil microbial community during 13C-labelled maize straw decomposition

Abstract

Soil pore structure regulates water movement, gas exchange and determines the heterogeneous distribution of nutrients, thereby exerting significant influence on microorganisms. However, the specific contributions and limitations of pores of different sizes on soil microbial communities during straw decomposition, as well as the variations in pore structure throughout this process, remain unknown. To address this, a 57-day soil incubation experiment was conducted, using ¹³C-labelled maize straw with two soil types: Shajiang black soil (Vertisols) and Fluvo-aquic soil (Cambisols). The experiment was set at two bulk densities: 1.2 g cm⁻³ and 1.5 g cm⁻³. The variations in pore structure before and after the incubation experiment were quantified using X-ray micro-computed tomography (μCT). To analyze microbial C content from straw, ¹³C-Phospholipid fatty acids (¹³C-PLFAs) were used, and 16S rDNA high-throughput sequencing was employed to determine bacterial community structure after the incubation. The resulted showed that Shajiang black soil exhibited a 50.5 % increase of total PLFA-C content from straw than Fluvo-aquic soil at a bulk density of 1.5 g cm⁻³ (P < 0.05). Specifically, Gram-positive bacteria (G+), Gram-negative bacteria (G−) and actinobacteria PLFA-C content increased by 105.2 %, 55.0 % and 73.6 % (P < 0.05). Redundancy analysis (RDA) showed that >100 μm pores in diameter (Ø) facilitated the colonization of microorganisms (G+, G− and actinobacteria). Specifically, bacteria (including G+, G−, and common bacteria, accounted for 37.6 %, 15.7 % and 22.1 % of straw-derived PLFA-C in relation to the total amount of straw-enriched PLFA-C) were key contributors to straw decomposition and were associated with the formation of 50–200 μm Ø pores. Meanwhile, fungal activity was primarily responsible for changes in the 20–50 μm Ø pore structure. These findings emphasize that >100 μm Ø pores created a favorable physical environment for microbial communities on straw decomposition, highlighting the pivotal role of microbial activity in shaping soil pore structure.