Aluminum (Al) and iron (Fe) (hydr)oxides have been considered the primary phosphorus (P) sinks in many acidic soils. However, low contents of Al/Fe (hydr)oxides and their limited pH-dependent sorption capacity in temperate soils with pH 5.5-7 question their dominant role in P retention and suggest the importance of other P retention pathways. This study presents a newly developed nanoscale secondary ion mass spectrometry (NanoSIMS) method that spatially and operationally identifies inorganic phosphorus (IP) and organic phosphorus (OP) in natural soils by integrating 31 P 16 O 2 - /( 31 P - + 31 P 16 O 2 - ) and 12 C 14 N - /( 12 C - + 12 C 14 N - ) ratios. This method enables mapping IP and OP distributions on natural soil microaggregate surfaces. Our results exhibit that phyllosilicates and their associated OM spatially associated with over 85% of total P observed on microaggregate surfaces in four loamy, slightly acidic temperate soils in Southeast Germany. The association of phyllosilicates with OM doubles the P retention density (the proportion of surface area occupied by P within each mineral/OM constituent), highlighting the important role of phyllosilicate-OM associations in P retention beyond the individual P retention capacity of OM-free phyllosilicates. Spatial mapping revealed two contrasting P associations: (i) IP and myo -inositol hexaphosphate predominant on phyllosilicate surfaces with minimal N signals, and (ii) OP predominates in phyllosilicate-associated OM in the form of N-rich microbial biomass/necromass and plant residues. These distinct spatial patterns may imply potentially different microscale P associations, although their functional significance for soil P cycling requires further investigation with complementary spectroscopic methods. Our study demonstrates the spatial importance of phyllosilicates and phyllosilicate-associated OM for P retention through two distinct P association patterns in slightly acidic temperate soils with low Al/Fe (hydr)oxide contents. Establishing the functionality of these spatial patterns in controlling soil P availability requires further research integrating molecular speciation, desorption kinetics, and mineralization monitoring. • NanoSIMS spatially identifies organic (OP) and inorganic phosphorus (IP) patterns • Phyllosilicates associate >85% of total phosphorus (P) on microaggregate surfaces • Phyllosilicates associated with organic matter (OM) double P retention density • OP is primarily concentrated in nitrogen-rich OM • P retention dominates by phyllosilicate–OM associations in pH 5.5-7 temperate soils
Lei et al. (Sun,) studied this question.