Insights into soil phosphorus biogeochemistry using new NMR techniques and P fertilization experiments

Phosphorus is considered a limiting nutrient in many ecosystems, and is therefore likely to constrain global carbon sinks. A thorough understanding of organic P composition in soils is vital across fields, from agriculture to ecology. Organic phosphorus (P) is a large fraction of soil P, but its speciation is still poorly understood.

NMR spectroscopy gives important insights into the speciation of soil P, because each P species gives rise a specific signal, and information on molecular weight can also be obtained from NMR spectra. Here we present new methodology to define soil P speciation, results concerning identification of P monoesters in soils, and on P speciation in tropical ecosystems.

Orthophosphate monoesters, with are intrinsically linked to P biochemistry, make up a central region in ³¹P NMR spectra. This region often contains resolved signals overlaid on a background. The resolved signals have been identified, but the background hampers their quantification. More important, the background can represent a large fraction of soil P, but its P biogeochemistry is completely enigmatic.

We have previously reported that the background is not composed of macromolecular P species. Instead, measurements of the true linewidths of the signals revealed that the background is composed of hundreds of small-molecule P species (Haddad et al., 2024). Here we show that the background contains a large number of P monoesters, and we present data on their identity based on a combination of MS-metabolomics and new NMR experiments, to understand the origin and ecological significance of this large unexplored P pool.

Highly weathered soils in the tropics often contain low P levels. In two tropical forests in French Guiana, the effect of P fertilization in these ecosystems has been studied (Lugli et al., 2023). Here we present NMR data on the P speciation in the two forests which differ in nutrient status, and on the effect of P fertilization on P speciation.

 

Haddad, L.; Vincent, A. G.; Giesler, R.; Schleucher, J. Small Molecules Dominate Organic Phosphorus in NaOH-EDTA Extracts of Soils as Determined by 31P NMR. Sci. Total Environ. 2024, 931, 172496.

Lugli LF., Fuchslueger L et al. Contrasting responses of fine root biomass and traits to large-scale nitrogen and phosphorus addition in tropical forests in the Guiana shield. Oikos 2024:e10412