A dual isotopic approach using radioactive phosphorus and the isotopic composition of oxygen associated to phosphorus to understand plant reaction to a change in P nutrition

Abstract

Background Changing the phosphorus (P) nutrition leads to changes in plant metabolism. The aim of this study was to investigate how these changes are reflected in the distribution of 33P and the isotopic composition of oxygen associated to P (δ18OP) in different plant parts of soybean (Glycine max cv. Toliman). Two P pools were extracted sequentially with 0.3 M trichloroacetic acid (TCA P) and 10 M nitric acid (HNO3; residual P).ResultsThe δ18OP of TCA P in the old leaves of the − P plants (23.8‰) significantly decreased compared to the + P plants (27.4‰). The 33P data point to an enhanced mobilisation of P from residual P in the old leaves of the − P plants compared to the + P plants.ConclusionsOmitting P for 10 days lead to a translocation of P from source to sink organs in soybeans. This was accompanied by a significant lowering of the δ18OP of TCA P in the source organs due to the enzymatic hydrolysis of organic P. Combining 33P and δ18OP can provide useful insights in plant responses to P omission at an early stage.

Combining spectroscopic and isotopic techniques gives a dynamic view of phosphorus cycling in soil

“…A recent study showed that water within microbes may have a different isotopic composition than water outside of the cells 41 , which implies that equilibrium δ 18 O P could be different from the one calculated using δ 18 O of soil water. Alternatively, it has been shown that when P is in short supply, δ 18 O P of plant P decreased due to increased recycling of organic P by hydrolyzing enzymes within plant tissue 42 . We consider the most likely explanation for the lower δ 18 O P of microbial P at high rainfall sites to be tighter intramicrobial P recycling.…”

A dual isotopic (32P and 18O) incubation study to disentangle mechanisms controlling phosphorus cycling in soils from a climatic gradient (Kohala, Hawaii)

“…Thus, the phosphate which had been taken up had lost its 18 O signature due to a rapid turnover of P within roots. Pfahler et al (2017) supplied soybeans with 33 P labelled phosphate and measured the changes in δ 18 O-P after having stopped or not stopped P inputs. With the 33 P tracing, the authors quantified the transfer of P from older plant leaves to younger plant organs when P inputs to the plants were stopped.…”

Perspectives from the Fritz‐Scheffer Awardee 2019. Oxygen isotopes in phosphate—The key to phosphorus tracing?

“…Accordingly, in cropland soils, the increasing δ 18 O P values in the higher content classes might indicate a greater contribution of fertilizer P, which is characterized by δ 18 O P values of approximately 20 ‰ ( McLaughlin et al., 2006b; Young et al., 2009; Amelung et al., 2015). Similarly, in grassland soils, δ 18 O P values in the range of 20–25‰ could point to P derived from plant litter, which is typically characterized by higher isotope values ( Pfahler et al., 2013, 2017; Tamburini et al., 2018). Thus, across ecosystems, the trend of increasing δ 18 O P values with increasing soil P content should point toward P inputs in excess of P demand ( Bauke et al., 2018), which are not utilized by plants and thus not included efficiently into P cycling in the soil.…”