The fate of18O labelled phosphate in soil/plant systems

Oxygen Isotopes for Unraveling Phosphorus Transformations in the Soil-Plant System: A Review

“…They used KH 2 PO 4 that was labeled with both 18 O and 32 P to test if 18 O could be used as a substitute for radiolabeled phosphate in environmental studies. During a period of 6 mo, at ambient temperature, they could not observe a significant 18 O delabeling of the added KH 2 PO 4 in sterile soils across a wide range of pH; however, they did observe that the 18 O label was lost after 5 wk when plants were grown on these soils (Larsen et al, 1989). They estimated that 5% of excess 18 O was lost for every millimole of CO 2 emitted from biologically active soils ( Johansen et al, 1990).…”

“…The first studies used excess 18 O, which was determined by mass spectrometry (Cohn, 1958), by optical emission of CO + ( Johansen et al, 1990;Larsen et al, 1989), or by 31 P nuclear magnetic resonance (Cohn and Hu, 1978). Only later was the d 18 O in phosphate at natural abundance reported.…”

“…As mentioned above, Larsen et al (1989) were the first to realize that biological activity was responsible for the d 18 O-P changes observed with time in soil-plant systems. Their findings were recently confirmed by Melby et al (2013), who observed that the d 18 O of P extracted by a modified Bray solution had disappeared 50 d after the addition of 18 O-enriched phosphate in incubated nonsterile soils, whereas it remained constant in sterile soils.…”

“…The first studies using O isotopes to study phosphate in soil-plant systems were performed at the end of the 1980s by Saaby-Johansen, Larsen, and Middelboe, who performed a series of experiments using soils, plants, and soil microorganisms (Larsen et al, 1989;Johansen et al, 1990;Middelboe and Saaby, 1998). They used KH 2 PO 4 that was labeled with both 18 O and 32 P to test if 18 O could be used as a substitute for radiolabeled phosphate in environmental studies.…”

“…Soil level: It has been shown by several studies (Angert et al, 2012;Larsen et al, 1989;Tamburini et al, 2012b;Zohar et al, 2010b) that at some point in time the d 18 O-P of soil P compartments will reach equilibrium with water. A better understanding of the kinetics of equilibration between these pools may provide important information on P cycling in soils.…”