Contribution of Biogas Slurry-derived Colloids to Plant P Uptake and Phosphatase Activities: Spatio-temporal Response

Abstract Aims Phosphorus (P)-binding colloids (1–450 nm) have been identified as highly mobile and bioavailable P in terrestrial ecosystems. However, the bioavailability of varied colloidal P (P coll ) sizes remains unclear, especially in situ soils. The purpose of this study was to evaluate the differential contribution of various-sized colloids to plant available P in the rhizosphere and the phosphatase response patterns. Methods In the 45-day rice rhizotron experiment, we applied different size fractioned biogas slurry (BS) colloids with the same total P concentration, including nano-sized colloids (1–20 nm), fine-sized colloids (20–220 nm), and medium-sized colloids (220–450 nm). Colloidal P organic and inorganic fractions, colloidal minerals were investigated in corresponding treatments. Soil zymography was performed during the cultivation period, to examine the processes of enzymic hydrolysis in temporal and spatial dynamics. The biomass and P content of roots and shoots were also recorded. Results The relative bioavailability of colloidal P (RBA coll ) was the highest (64%) for nano-sized BS colloids addition. The phosphatase activities and hotspot areas were found to be significantly 1) correlated with RBA coll , 2) increased by the colloid-free (truly dissolved P) and nano-sized BS fractions, and 3) affected by the plant growth stage. Conclusion We found that the addition of nano-sized BS colloids increased P uptake by plants and improved the P coll bioavailability in the rhizosphere, in which the phosphatase-catalyzed hydrolysis of organic P coll played an important role. Nano-sized BS-derived colloids may be an effective substitute for the use of liquid phosphorus fertilizer.