BIOSTIMULATION OF LOLIUM-PERENNE L GROWTH WITH NITROGEN EXCRETED BY LUMBRICUS-TERRESTRIS L - FLOW MEASUREMENT IN THE LABORATORY

The effect of earthworms (Lumbricus terrestris L.) on plant (Lolium pe renne L.) growth (total plant biomass, leaves to roots ratios), and th e partitioning of C and N between plants, earthworms and microbial bio mass were studied in microcosms under controlled conditions for 42 and 65 days. Lumbricus terrestris was fed with N-15-labelled or unlabelle d litter, depending on the experiment. Three experiments were carried out. (1) After 113 days plants (Lolium perenne L.) were no longer grow ing despite regular addition of N-15-labelled litter of low C:N ratio (9.5) regularly brought to microcosms. Then one earthworm (Lumbricus t errestris L.) was introduced into each microcosm and was fed with unla belled litter during the next 65 days (experiment called ''avec lombri ciens introduits''). The plants decreased their N-15 enrichment and, i n addition, the total plant biomass and the N concentration in plants (mg g-1 plant) significantly increased. (2) Plants were grown from see d in microcosms already containing a L. terrestris (experiment called ''avec lombriciens maintenus''). After 113 days, the growth of plants seemed arrested but during the next 42 days, the plants grew again. To explain this phenomenon the authors suggest that earthworms ingested their faeces again, and then released N and other nutrients that had b een complexed to microbial biomass, so stimulating plant growth. (3) T he nitrogen flow (mg day-1 through L. terrestris was measured in micro cosms. Values obtained by direct measurement and by calculation were i n agreement. Daily nitrogen flux varied from 13.6% to 14.3% of total b ody nitrogen, depending on the experiment. This difference could indic ate that L. terrestris principally ingests litter but also surface and subsurface casts.