Priming Effect and Respiratory Quotient in a Forest Soil Amended with Glucose

Abstract

Soil respiration is a key process in global carbon cycling. Therefore, the response of respiration, carbon isotopic characteristic of the CO ₂ evolved and the respiratory quotient, defined as the ratio of mol CO₂ evolution per mol O ₂ uptake, was studied for beech forest topsoil after low to high addition of the readily available C4-plant derived glucose. The low glucose rate that corresponded to the 2-week C input by root exudates and plant residues in the field stimulated respiration for 1 day only. The 10-fold higher rate of 500 μ g glucose-C g ⁻¹ soil increased respiration for about 1 week and the highest rate of 2000 μ g glucose-C g ⁻¹ soil, which corresponds to the typical rate of the microbial biomass method by substrate-induced respiration induced more than 4-week stimulated respiration. When the respiration rates have returned to the control level, the carbon isotopic characteristic of the CO ₂ evolved indicated that the CO ₂ is still derived from glucose metabolites. We concluded that priming effect of the C3-plant derived soil organic matter and soil respiratory quotient value were increased simultaneously and effects were correlated to the glucose rate.

Keywords:

• ¹³C-CO₂ signature
• forest
• respiratory quotient
• short and long-time priming effects
• soil organic matter degradation
• soil respiration

Acknowledgments

This study was supported by DFG (Deutsche Forschungsgemeinschaft), Project 436RUS17/55/04. The Russian Academy of Sciences (Program of RAS “Physicochemical and Cell Biology”) also supported the study. We thank Eckehard Eichwald and Dr. Christian Knoblauch for their great support in carbon isotope analysis.

Notes

¹This technique is limited when analyzing soils with high pH values since CO₂ is dissolved in H₂O and absorbed by CaCO₃ leading to the formation of Ca(HCO₃)₂.

²Infra Red Gas Analyzer, which is sensitive for CO₂ measurements.

³No detection option is indicated by brackets.

^a See equation [3] F = (δ¹³C_MIX−δ¹³C_GLU)/ (δ¹³C_SOM−δ¹³C_GLU), where δ¹³C_SOM = −26.66‰ and δ¹³C_GLU = −11.4‰.

^b SOM-CO₂ = F * CO₂ [μ g C-CO₂ g^{− 1}soil].

^c See equation [4].