Quantitative and Qualitative Relationships between Phospholipid Fatty Acid Analysis Biomarkers and Lignin in Soil from the Tibetan Plateau (China) under Laboratory Incubation Conditions

Lignin, an organic compound with a complex structure, is formed through the polymerization of structural units linked by carbon–carbon bonds and ether bonds. The question of whether lignin is labile or resistant to biological and chemical degradation in soil, particularly in alpine ecosystems, remains unresolved. To address this knowledge gap, we analyzed the relationship between phospholipid fatty acid biomarkers and the abundance of lignin components in grassland soils from North Tibet, China. Soil samples were collected from alpine grasslands, including alpine meadows and alpine steppes. The relative abundance of lignin in these alpine grassland soils before and after a 210-day incubation period was measured. Our results indicate that the relative abundance of lignin in the alpine grassland soils decreased during the incubation period. Significant relationships were found between the phospholipid fatty acid biomarkers of bacteria, fungi, Gram-positive bacteria, and Gram-negative bacteria and the relative abundance of lignin components. This research was conducted under laboratory conditions that are optimal for the development of microorganisms but significantly different from the conditions in Tibet. Furthermore, this study contributes to the understanding of soil organic matter degradation and the dynamics of microbial communities in alpine grassland soils in the context of future global warming.