title: Use of13C- and phosphate18O-labeled substrate for studying phosphorus and carbon cycling in soils: a proof of concept.
abstract: BACKGROUND
  Stable isotope tracers are commonly used to track the transformations of organic carbon (C) and nitrogen (N) in soils but they have not been used to follow coupled cycles of phosphorus (P) and C because P has only one stable isotope.
  
  
  METHODS
  A novel dually labeled substrate, composed of a13C-labeled glucose backbone attached to a phosphate group with known δ18OPvalue, was used to follow the fate of C and P derived from the same compound. The substrate was amended to soils from two natural oak forests, differing in their P levels, and the δ13C values of respired CO2and the δ18OPvalues of soil bioavailable P were measured.
  
  
  RESULTS
  The δ18OPvalues of the phosphate accumulated in the soil deviated from the expected value of P that is released from phosphomonoesters by enzymatic reactions (3.7 ‰) and were driven towards isotopic equilibrium with soil water (21.1 ‰), a process which is produced as part of microbial metabolism. This suggests that the substrate's P passed through the microbial biomass before accumulating in the soil, reflecting the rapid microbial turnover rate of the added P. A higher fraction of the substrate-C was respired in the higher P soil by the end of the incubation (20.3 % in comparison with 9.1 % in the lower P soil), indicating stronger energy limitation in the higher P soils. The higher13C glucose respiration in the higher P soil also triggered a stronger priming effect than in the lower P soil.
  
  
  CONCLUSIONS
  Our approach demonstrates that13C- and P-18O-dually labeled tracers provide invaluable data on the fate of organic P and C in soils. We encourage biogeochemists and soil scientists to develop similar tracers of this kind. Copyright © 2017 John Wiley & Sons, Ltd.
authors.affiliation: The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Avner
authors.identifier: http://orcid.org/0000-0001-8425-8508
authors.initials: A
authors.lastname: Gross
authors.affiliation: The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel.
authors.forename: Alon
authors.initials: A
authors.lastname: Angert