Protozoa, Nematoda and Lumbricidae in the rhizosphere of Hordelymus europaeus (Poaceae): faunal interactions, response of microorganisms and effects on plant growth

• Published in: Oecologia 1996-01, Vol.106 (1), p.111-126
• Main Authors: Alphei, J, Bonkowski, M, Scheu, S. (Goettingen Univ. (Germany). Zoologisches Inst. Abt. Oekologie)
• Format: Article
• Language: English
• Subjects: ABSORCION DE SUSTANCIAS NUTRITIVAS; ABSORPTION DE SUBSTANCES NUTRITIVES; Agricultural soils; Animal and plant ecology; Animal, plant and microbial ecology; APORRECTODEA; Aporrectodea caliginosa; AZOTE; Biological and medical sciences; Community Ecology; FAUNA DEL SUELO; FAUNE DU SOL; Forest soils; Fundamental and applied biological sciences. Psychology; Leaching; LUMBRICIDAE; Microbial biomass; NEMATODA; Nematodes; NITROGEN; NITROGENO; NUTRIENT UPTAKE; Pellioditis pellio; PLANT GROWTH SUBSTANCES; Plant nutrient supply; POA; Protozoa; RHIZOSPHERE; RIZOSFERA; Soil biochemistry; SOIL FAUNA; Soil microorganisms; Soil nematodes; SUBSTANCE DE CROISSANCE VEGETALE; SUSTANCIAS DE CRECIMIENTO VEGETAL; Synecology; Terrestrial ecosystems
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00334413

Interactions among protozoa (mixed cultures of ciliates, flagellates and naked amoebae), bacteria-feeding nematodes (Pellioditis pellio Schneider) and the endogeic earthworm species Aporrectodea caliginosa (Savigny) were investigated in experimental chambers with soil from a beechwood (Fagus sylvatica L.) on limestone. Experimental chambers were planted with the grass Hordelymus europaeus L. (Poaceae) and three compartments separated by 45-μm mesh were established: rhizosphere, intermediate and non-rhizosphere. The experiment lasted for 16 weeks and the following parameters were measured at the end of the experiment: shoot and root mass of H. europaeus, carbon and nitrogen content in shoots and roots, density of ciliates, amoebae, flagellates and nematodes, microbial biomass (SIR), basal respiration, streptomycin sensitive respiration, ammonium and nitrate contents, phosphate content of soil compartments. In addition, leaching of nutrients (nitrogen and phosphorus) and leachate pH were measured at regular intervals in leachate obtained from suction cups in the experimental chambers. Protozoa stimulated the recovery of nitrifying bacteria following defaunation (by chloroform fumigation) and increased nitrogen losses as nitrate in leachate. In contrast, protozoa and nematodes reduced leaching of phosphate, an effect ascribed to stimulation of microbial growth early in the experiment. Earthworms strongly increased the amount of extractable mineral nitrogen whereas it was strongly reduced by protozoa and nematodes. Both protozoa and nematodes reduced the stimulatory effect of earthworms on nitrogen mineralization. Microbial biomass, basal respiration, and numbers of protozoa and nematodes increased in the vicinity of the root. Protozoa generally caused a decrease in microbial biomass whereas nematodes and earthworms reduced microbial biomass only in the absence of protozoa. None of the animals studied significantly affected basal respiration, but specific respiration of microorganisms (O₂ consumption per unit biomass) was generally higher in animal treatments. The stimulatory effect of nematodes and earthworms, however, occurred only in the absence of protozoa. The sensitivity of respiration to streptomycin suggested that protozoa selectively grazed on bacterial biomass but the bacterial/fungal ratio appeared to be unaffected by grazing of P. pellio. Earthworms reduced root biomass of H. europaeus, although shoot biomass remained unaffected, and concentrations