Heai Xiao

Mobilisation of inorganic phosphorus induced by rice straw in aggregates of a highly weathered upland soil.

BACKGROUND Microorganisms mediate biochemical transformations of phosphorus (P) in soil. This is of particular importance in highly weathered soils, which are usually P deficient. This study aimed to extend understanding of the separate role of bacteria and fungi in P transformations in aggregates of a highly weathered soil, by adding P-stripped rice straw and microorganism inhibitors to aggregates. RESULTS The amount of microbial biomass phosphorus (MB-P) in the treatment with rice straw alone increased by over two-fold during 16 days. At the end of 28 d, the amount of inorganic-P in Fe-, Al-, and Ca-bound fractions decreased, whilst the amount of organic-P increased substantially (P < 0.01). The effect of bacterial inhibitors (tetracycline and streptomycin sulphate) on P immobilisation was very small in the early phase (0-4 d), but became pronounced after 8 days, whilst the fungal inhibitor (actidione) initially caused a decrease in P immobilisation by about 60%, but had no effect after that. CONCLUSION Fungi and bacteria immobilise P in soil aggregates, with fungi being responsible initially. However, bacteria become dominant subsequently and immobilise P from the inorganic fractions.