The use of soil biostructures created by soil fauna ecosystem engineers fed with different organic materials as inoculum source of arbuscular mycorrhiza fungi on cocoa seedling

Abstract

Soil fauna as ecosystem engineers has the ability to create soil biostructures, with the capacity to save arbuscular mycorrhizal fungi (AMF) spores. This study, therefore, aimed at investigating the AMF spore density in the biostructures created by cooperation between earthworms and ants with a different organic matter composition, and to analyze the biostructures' potential as a source of AMF inoculum on cocoa seedlings. In the first experiment, a combination of earthworms (0, 10, or 20 pieces) and ants (0, 10, or 20 pieces) composition, as well as a mixture of Gliricidia sepium leaves (GSL), cocoa shell bean (CSB), and sago dregs (SD)(w/w/w) was tested. Meanwhile, in the second experiment, the effect of biostructures on cocoa seedlings grown in unsterile soil was examined. According to the results, the highest (46.67±13.65) AMF spore density was obtained using 20 earthworms+10 ants with 50%GSL+50%CSB + 0%SD treatment, the lowest (12.67±3.78) spore count was obtained using 20 earthworms+10 ants with 25%GSL+25%CSB+50%SD. The total AMF spores were positively correlated (r2= 0.74) with the total P, but negatively correlated (r2= -0.53) with the C/N ratio. Therefore, biostructure application increased AMF spores number in the rhizosphere and the percent infection. Furthermore, biostructures resulting from the collaborative activity between different soil fauna ecosystem engineers were able to facilitate the germination of AMF spores and infect plant roots growing in non-sterile soil.