Effect of Residue Type on Extractable Organic and Microbial Biomass Carbon Fractions Under Long-Term Soil Fertilization
Abstract The labile organic carbon (C) pool plays a vital role in soil biogeochemical transformation and can be used as a sensitive indicator of the response of soil quality to agricultural practice. However, little is known about how residue type and soil fertilization affect the incorporation of residue C into labile organic C pools. A 360-day laboratory incubation was conducted with the addition of 13C-labeled maize residues (root, stem and leaf) to unfertilized and organic-fertilized soils. A greater contribution of residue C to extractable organic C (EOC, 7.2%) was observed in the unfertilized soil than that in the organic-fertilized soil (6.0%). The contribution of residue C to microbial biomass C (MBC) was 20%-50% in the organic-fertilized soil, but only 10%-30% in the unfertilized soil. This suggests that, in organic-fertilized soil, there is accelerated transformation of residue C into microbial biomass and a higher capacity for residue C stabilization through greater, or more efficient anabolism. Moreover, the distribution of leaf C into MBC was higher than that from root and stem in the unfertilized soil, whereas more root C entered to EOC and MBC than from stem and leaf in the organic-fertilized soil. This shows that maize root can also be involved in microbial assimilation, but it depends on the initial soil nutrition. Overall, these findings deepen our understanding of the mechanisms of microbe-mediated C transformation processes, and provide relevant insights into the capture and incorporation of plant residue C into labile organic C pools driven by residue type and soil fertilization.