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C and N natural abundance of the soil microbial biomass |
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| Authors: | Paul Dijkstra Ayaka Ishizu Stephen C Hart Egbert Schwartz Bruce A Hungate |
| Institution: | a Department of Biological Sciences, Northern Arizona University, P.O. Box 5640, Flagstaff, AZ 86011, USA b Colorado Plateau Stable Isotope Laboratory, Northern Arizona University, P.O. Box 5640, Flagstaff, AZ 86011, USA c School of Forestry, Northern Arizona University, P.O. Box 5018, Flagstaff, AZ 86011, USA. d Merriam-Powell Center for Environmental Research, Northern Arizona University, P.O. Box 5640, Flagstaff, AZ 86011, USA e Institute of Forest SB RAS, Krasnoyarsk, 660036, Russia |
| Abstract: | Stable isotope analysis is a powerful tool in the study of soil organic matter formation. It is often observed that more decomposed soil organic matter is 13C, and especially 15N-enriched relative to fresh litter and recent organic matter. We investigated whether this shift in isotope composition relates to the isotope composition of the microbial biomass, an important source for soil organic matter. We developed a new approach to determine the natural abundance C and N isotope composition of the microbial biomass across a broad range of soil types, vegetation, and climates. We found consistently that the soil microbial biomass was 15N-enriched relative to the total (3.2 ‰) and extractable N pools (3.7 ‰), and 13C-enriched relative to the extractable C pool (2.5 ‰). The microbial biomass was also 13C-enriched relative to total C for soils that exhibited a C3-plant signature (1.6 ‰), but 13C-depleted for soils with a C4 signature (−1.1 ‰). The latter was probably associated with an increase of annual C3 forbs in C4 grasslands after an extreme drought. These findings are in agreement with the proposed contribution of microbial products to the stabilized soil organic matter and may help explain the shift in isotope composition during soil organic matter formation. |
| Keywords: | 15N 13C Carbon Natural abundance Nitrogen Stable isotopes Soil organic matter |
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