Nitrogen and phosphorus flow stimulated by bacterial grazer nematodes in mycorrhizosphere of Pinus pinaster

The microbial loop based on the grazing of bacteria by bacterial-feeding nematodes is thought to play a major role in the mineralization of nutrients such as nitrogen (N) and phosphorus (P) in terrestrial ecosystems. This study was undertaken to quantify the effect of bacterial grazing nematodes on root architecture, growth and mineral nutrition (N and P) in the mycorrhizosphere of woody species (Pinus pinaster). Thirty five days simplified sterile experiment was conducted with young mycorrhizal P. pinaster seedlings (inoculated with Hebeloma cylindrosporum) along with bacteria (Bacillus subtilis) and bacterivorous nematodes (Rhabditis sp.). To know better the role of microbial complexity on N nutrition, two N sources, bacterial N labeled with N-15 and nitrate were supplied in the medium. Phosphorus was supplied as insoluble inorganic tri-calcium phosphate (TCP). The results showed that the N-15 flow (4 mu g plant(-1)) from the bacteria to the plant shoots was only significant when nematodes were present. Plants cultivated with bacteria or nematodes also accumulated higher total N and P in their shoots than mycorrihzal ones. These results revealed that the presence of bacterial-feeding nematodes significantly enhanced N and P availability to mycorrihzal P. pinaster seedlings, probably by improving plant use of nitrate and insoluble P supplied in the medium