Root proliferation, soil fauna and plant nitrogen capture from nutrient-rich patches in soil

We investigated interactions between plant roots, protozoa and nematodes after addition of patches containing inorganic or organic nitrogen in order to determine whether root proliferation could explain the capture of N by the plant from the patch. Decomposition of a 15N/13C, dual-labelled, organic patch in the absence of plant roots was also examined. In the decomposing patch the amounts of 13C and 15N remaining co-varied and both declined with time. Nematode numbers increased. However, protozoan biomass and inorganic N (NO3− and NH4+) availability did not significantly alter as decomposition of the patch progressed. Addition of inorganic N patches, as NH4NO3 solutions, to the first lateral to emerge from the main seminal root axis of Lolium perenne L. seedlings had no effect on root growth compared with controls 16 d after addition. Protozoan biomass increased. Furthermore, log protozoan biomass and NO3− concentrations of the growth medium were significantly (P62%) of the 15N initially added remained in the patch at harvest. Much less (c. 13–21%) 13C remained in the patch. Protozoan biomass and nematode numbers increased significantly (P