Influence of plant roots on C and P metabolism in soil

Summary A technique for studying the modification of soil by plant roots is described. Using it, soil zones differently affected by plant roots can be separated for subsequent analysis. With this method, the transfer of C from roots of¹⁴C-labelled maize plants into soil and the change in soil C and P fractions were investigated.The results show that the C released from roots to soil was 13% of the total assimilated C. The remaining root-derived C in soil was relatively small (15%). Maize roots induced a decrease in organic soil C and in both total and isotopically exchangeable soil P. On the other hand they increased the microbial biomass C, phosphatase activity, bicarbonate extractable organic P and phospholipid P and enhanced the incorporation of³²P into organic P fractions. Both root C and root influences were detectable outside the immediate root zone.These results demonstrate an intensive C turnover and P mobilization in the rhizosphere soil, including some organic P fractions, and suggest that the actual rhizosphere may be greater than is generally assumed.