Soil Co2 Emission Reduction by Unknown Bacterial Species Via Promoting Lactic Acid Fermentation in the Qinghai-Tibetan Plateau Alpine Meadow

Abstract

Highly variable soil microbial respiration among grasslands has been identified as a major cause of uncertainty in regional carbon (C) budget estimation in the Qinghai-Tibetan Plateau; microbial metabolism mechanisms might explain this variation, but remain elusive. Therefore, we investigated soil CO2 production and the associated functional genes in incubated soils from two major alpine grasslands on the Qinghai-Tibetan Plateau. The results showed that the cumulative CO2 emissions from alpine meadow soils were 71%-83% lower than those from alpine steppe soils. Both the enriched genes encoding fermentation and glycolysis (Embden-Meyerhof pathway (EMP)) and the diminished genes encoding tricarboxylic acid cycle (TCA) and phosphate pentose pathway (PPP) explained the CO2 emission reduction in the alpine meadow soils. The EMP: PPP and fermentation: TCA cycle ratios in alpine meadow soils were 1.45- and 1.50-fold, respectively, higher than those in alpine steppe soils, respectively. Such shifts in metabolic pathways were primarily caused by the increasing dominance of an unknown species of Desulfobacteraceae with high glycolytic potential, carrying a higher abundance of ldh genes during fermentation. These unknown species were promoted by warmer temperatures and higher precipitation in the alpine meadows, indicating a strong warming-induced microbial regulation of soil C decomposition by shifting cellular metabolism. Further studies on the unknown species would enhance our understanding and predictability of C cycling in alpine grasslands.

Keywords: cellular metabolism, carbon decomposition, assembled genomes, grassland type, metagenomic sequencing