Abstract
Soil phosphorus (P) pool is intimately connected to organic carbon (OC), especially mineral-associated OC (MAOC). However, the relationship and mechanism between MAOC fractions and P fractions and their response to fertilization remain unclear. According to a long-term field trial in black soil, topsoils from no-fertilizer control, chemical fertilizer (36 kg P ha-1), and straw addition (42 kg P ha-1) for 21 and 29 years were collected, and organo-mineral complexes (< 20 µm) were separated and analyzed. Compared to no-fertilizer control, chemical fertilizer resulted in soil acidification (soil pH 6.15–6.27), increasing the contents of the MAOC fraction bound to minerals by weak linkages in complexes. Straw addition maintained soil pH at 7.53–7.84, and the contents of some MAOC fractions (which were remaining water-soluble, bound by cations, encapsulated by resistant carbonate, and insoluble humin) were significantly higher than that of chemical fertilizer. Fertilization applications increased total P contents in organo-mineral complexes, with similar levels of total P observed between chemical fertilizer and straw addition. Chemical fertilizer mainly increased highly labile inorganic P (Pi) extracted from resin, NaHCO3 and NaOH, as well as organic P (Po) extracted by NaHCO3, and straw addition mainly increased moderately labile Pi extracted from dilute HCl. Correlation analysis showed that the increased and dominant MAOC fractions had positive relationships with the increased P fractions. X-ray absorption near-edge structure (XANES) spectroscopy further identified that chemical fertilizer increased the proportion of AlPO4, suggesting that MAOC promotes the retention of labile P via association with Al under weakly acidic conditions. Straw addition increased the proportion of Ca3(PO4)2 and Ca5(PO4)3OH; moreover, it also increased the maximum P sorption capacity of complexes, suggesting that MAOC enhances P sorption via association with Ca under weakly alkaline conditions and that adsorbed P will transform into more stable Ca-associated P. Our findings demonstrate that MAOC promotes P accumulation via association with different P fractions, and these processes are mineral and pH-dependent.
Published Version
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