Short-Term Carbon Accumulation in a Semiarid Soil Amended With Glucose Is Compromised By Priming Phenomenon: Relation to Carbon and Microbial Dynamics.

The use of isotopic-enriched carbon compounds provides information regarding the carbon cycling in soils but this information is missing in dry ecosystems such as those of semiarid areas. The fate of carbon, priming effects and microbial utilization of glucose as an example of bioavailable molecule were examined in a semiarid soil with 2.7 g kg^-1 of total organic carbon amended with U¹³C-glucose (99 atom %) at 75 µg C g^-1 soil (LD) or 300 µg C g^-1 soil (HD). Glucose-derived carbon remained in soil after two months of incubation and the percentage was greater in LD (40% of the initial ¹³C added) than in HD (30% of the initial ¹³C added). Comparison of ¹³C content in water- and sodium-pyrophosphate extracts pointed to a significant chemical stabilization of the added carbon (up to 2.4% of the initial ¹³C-glucose) but suggests a major physical fixation. Glucose was subjected to an intense mineralization in the first 17- days reaching 22.8%  (LD) and 40.94% (HD). The stable isotope probing (SIP) of phospholipid fatty acids (PLFAs) by gas-chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) showed that bacteria dominated glucose metabolism in comparison to fungi. Gram-negative populations were initially more involved in glucose assimilation than Gram-positive bacteria (up to 95% of the ¹³C within the microbial community was allocated in Gram-negative typical fatty acids). However, after 4 and 17 days the ¹³C-enrichment in Gram-positive biomarkers increased. The mineralization of soil organic matter as a consequence of microbial triggering by glucose was more intense in HD (6.61% of soil TOC) than LD (1.89% of soil TOC) and reached the highest level after 4 days in HD. The high increase of β-glucosidase activity with glucose addition compared to control soil points that microbial populations involved in SOM mineralization do no regulate the enzyme production after glucose amendment. our data indicated that the intense metabolism of SOM due to priming phenomena compromises the potential carbon sequestration in this semiarid soil amended with glucose.