THE FORMS OF PHOSPHORUS IN HUMIC AND FULVIC-ACIDS OF A TOPOSEQUENCE OF ALPINE SOILS IN THE NORTHERN CAUCASUS

Chemical fractionation and P-31 nuclear magnetic resonance (NMR) spect roscopy of humic acids (HA) and fulvic acids (FA) were used to charact erize the forms of phosphorus and their changes within a toposequence of alpine soils at the Mt. Malaya Khatipara (Teberda reserve, northwes tern Caucasus). Sodium hydroxide extracted 66-82% of total phosphorus from A horizons and 28-51% from B horizons. Organic P amounted to 92-9 9% of NaOH-extractable P. HA represented the major part of extracted o rganic P (52-90%). The P species in HA and FA comprised phosphate mono esters (40-86%), phosphate diesters (up to 22%), phosphonates (up to 8 %), sugar-diester phosphates (up to 14%), pyrophosphates (up to 11%), polyphosphates (up to 16%), and unknown compounds (up to 6%). Inorgani c orthophosphate was found in appreciable proportions only in HA of or ganic horizons and in FA (up to 16%). The percentages of phosphonates and phosphate diesters were higher in HA, those of sugar diesters and pyrophosphates were higher in FA. Within the toposequence, the contrib ution of labile P species to total P in HA of surface soil layers incr eased with increasing thickness of snow cover during winter and corres pondingly shorter vegetation periods. The P-species distributions in H A of subsoil horizons were rather similar throughout the toposequence. HA of the surface soils thus seemed to best characterize the P dynami cs in these soils. (C) 1997 Elsevier Science B.V.