STIMULATION OF DECOMPOSITION OF SPARTINA-ANGLICA LEAVES BY THE BACTERIVOROUS MARINE NEMATODE DIPLOLAIMELLOIDES-BRUCIEI (MONHYSTERIDAE)

The bacterivorous nematode Diplolaimelloides bruciei was found in association with above-ground decaying plant parts of the halophyte Spartina anglica. The effect of this nematode on decomposition of S. anglica leaves was investigated in laboratory experiments. CO2-production, losses of dry weight, carbon and nitrogen of the decaying leaves were examined. The influence of leaf age was investigated in these experiments. In the presence of nematodes, CO2-production of green, decaying leaves increased by 20-25%. Losses of dry weight, carbon and nitrogen during decomposition increased with at least 30%. On yellow, more senescent, leaves no effect on CO2-production was found, but losses of dry weight, carbon and.nitrogen tended to be higher in the presence of nematodes. In the presence of nematodes, more carbon was lost from the leaves than could be explained by CO2-production alone. Budget calculations indicate that the difference was mainly due to incorporation of carbon in nematode biomass. The minimal nematode population density at which the nematodes have any measurable stimulatory effect was estimated at 4000 ind.g-1 of dry leaves. Field population densities are often of the same order of magnitude. The results showed clearly that D. bruciei enhanced the decomposition rate of S. anglica leaves. The extent depends on leaf condition and the population density of this nematode.