DEVELOPING A PROTOCOL TO MANIPULATE SOIL BIOTA IN EXPERIMENTAL MICROCOSMS

Abstract

Nematodes are an important fraction of the soil faunal community, which have been widely explored in ecological studies aimed at assessing the relationship between below-ground diversity and key functions of terrestrial ecosystems. These studies have used methods to manipulate the fauna that generally alter the physical, chemical, and biological characteristics of the soil and do not represent the biotic and abiotic complexity of the environment in its natural state. In this research project, we aim to develop an effective method for excluding fauna from non-deformed soil samples that does not cause significant changes in soil microbial communities. To this end, an experiment will be carried out in the laboratory, employing a completely randomized design to evaluate three different treatments: (i) heating/freezing cycles (12 hours at 65°C, followed by 24 hours at -20°C, and then 12 hours at 65°C again); (ii) heating for 48 hours at 65°C; and (iii) control (samples kept at 4°C), applied to soil samples with their physical structure preserved in three different volumes: 100, 500, and 100 cm3. The soil samples will be collected at the Griffy Woods property of the Indiana University Research and Teaching Preserve in Monroe County, Indiana, USA. At the end of the experiment, the nematodes will be counted and identified using an inverted microscope, and the first 150 nematodes per sample will be classified into five different trophic groups: bacterial-feeders, fungal-feeders, root-feeders, omnivores, and predators. In addition, the composition, structure, and diversity of soil bacterial and fungal communities will be analysed by sequencing the 16S rRNA and ITS, respectively. The results will be subjected to principal component analysis, and the differences between treatments will be evaluated by PERMANOVA analysis. The relative abundance of bacteria and fungi will be subjected to two-sided Welch's t-test, and the population density of nematode feeding groups will be subjected to the Kruskal-Wallis non-parametric analysis of variance. This study will establish a reliable defaunation method that does not cause significant changes in the soil microbial community, allowing it to be used in microbial ecology studies.