Survival and feeding activity of Protaphorura armata (Collembola) in different composts

Composting is a biological process in which organic biodegradable wastes are converted into a hygienic humus-rich product, compost, used in agriculture as amendment to improve soil structure and promote plant growth. Compost has also been shown to have the potential to provide biological control against plant diseases caused by different microrganisms. The suppressive effect seems to be related to indigenous microbial consortia. However, this effect is not stable, depending mostly on the origin and quality of the compost. To improve the stability and reproducibility of the biocontrol effect, selected strains of microbial antagonists have been added to composts. In soils enriched or not-enriched composts come in contact with components of the soil community; however, the effects of composts on soil animals have been scarcely investigated. In this study we intend to evaluate the interactions between some composts, enriched or not enriched with a strain of the mycoparasitic fungus Trichoderma atroviride, with the collembolan Protaphorura armata. In our previous studies this collembolan species had a biological control effect against diseases caused by different soil-borne fungal pathogens. The products used are: i) spent mushroom (Agaricus bisporus) compost derived from wheat straw-bedded horse manure taken after steaming at the end of the mushroom production process; ii)and taken 3 months later, iii) compost derived from fruit, vegetable and garden wastes. One half of these organic products were enriched with a sporal suspensio of T. atroviride to obtain a final concentration of 8 x 105 conidia ml-1 product. A part of mature spent mushroom compost was amended with Calcium-Lignosulphonate (Ca-Ls) (1% v/w), a by-product of the acid sulfite pulping process with low pH and chelating activity potentially improving the establishment of T. atroviride in the compost and thus the biocontrol effect of this organic product. Interactions with P. armata were studied by introducing sexually mature animals, starved for 48 h, in glass jars containing 30 ml each organic product separately. All jars were maintained under controlled conditions at 20°C for two months. Thereafter, animals were extracted, counted and their gut content examined.All compost products enriched or not with the mycoparasitic fungus did not affect P. armata survival, and in no case did they block animal reproduction or development. Moreover, the presence of Ca-Lignosulphonate did not affect the animal survival. In a few cases light microscope observations of gut content of all animals used in the test revealed the presence of T. atroviride conidia. Tests carried out to study the viability of conidia contained in the faecal pellets, showed that these conidia were able to germinate on agar medium. The data obtained support a condition of coexistence between P. armata and T. atroviride in composts. The next step will be to study the biocontrol effect of composts enriched with T. atroviride and Collembola against plant diseases caused by soil borne fungi.