Sequestration and turnover of bacterial- and fungal-derived carbon in a temperate grassland soil under long-term elevated atmospheric pCO(2)

摘要

Temperate grasslands contribute about 20% to the global C budget. Elevation of atmospheric CO2 concentration (pCO(2)) could lead to additional C sequestration into these ecosystems. Microbial-derived C in the soil comprising about 1-5% of total soil organic carbon may be an important 'pool' for long-term storage of C under future increased atmospheric CO2 concentrations. In our study, the impact of elevated pCO(2) on bacterial- and fungal-derived C in the soil of Lolium perenne pastures was investigated under free air carbon dioxide enrichment (FACE) conditions. For 7 years, L. perenne swards were exposed to ambient and elevated pCO(2) (36 and 60 Pa pCO(2), respectively). The additional CO2 in the FACE plots was depleted in C-13 compared with ambient plots, so that 'new' (< 7 years) C inputs in the form of microbial-derived residues could be determined by means of stable C isotope analysis. Amino sugars in soil are reliable organic biomarkers for indicating the presence of microbial-derived residues, with particular amino sugars indicative of either bacterial or fungal origin. It is assumed that amino sugars are stabilized to a significant extent in soil, and so may play an important role in long-term C storage. In our study, we were also able to discriminate between 'old' (> 7 years) and 'new' microbial-derived C using compound-specific delta C-13 analysis of individual amino sugars. This new tool was very useful in investigating the potential for C storage in microbial-derived residues and the turnover of this C in soil under increased atmospheric pCO(2).