טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSharon Rakefet
SubjectContribution of Invertebrate Groups to Leaf Litter
Decomposition in Oak-Wood Soil
DepartmentDepartment of Biology
Supervisors Professor Emeritus Zeev Arad
Dr. G. Degani


Abstract

The aims of this research were: A. Description of the invertebrate community in the forest floor of Oak-forests in the Mediterranean region and to study the effect of rock substrate, climatic changes and nutrient levels on the community structure. B. To study the effect of climatic changes on the decomposition rate in the forest floor and the role of invertebrate biodiversity in the decomposition process, focusing on comparison of two trophic levels: decomposer (isopod) and predator (carabid).

The research site was Odem forest in the northern part of the Golan Hights and, in the first research year, in the Baram forest, in the western Galilee mountains. Leaf litter, top-soil and fallen leaves were sampled during the first year in both forests. Organic matter and minerals (nitrogen, calcium, phosphorous) were measured. Invertebrates were extracted from other samples using Berlese funnels, classified to different taxa and counted. The 2nd part of the research focussed on the leaf litter in Odem forest. Leaf litter samples were collected at the beginning of each season, put in litter bags (microcosm) and buried in the leaf litter of the forest floor. To some of the litter bags I added isopods (Armadillo officinalis) each season, or different combinations of isopods with carabids (Carabus hemprichi),  tenebrionids (Pachyscelis rotundata) and limax (Limax cecconii). At the beginning and at the end of each season sample moisture, organic matter and chemical elements (cellulose, lignin, nitrogen and nitrate) contents were measured, as well as bacterial total counts. Leaf litter mass loss was calculated. Invertebrates were extracted with Berlese funnels from other samples collected on the same day from the same plot. Invertebrates were also collected in pitfall traps situated between the plots. At the same time, laboratory experiments were conducted. The effect of temperature (16°C, 25°C), isopod biomass, and the addition of a predator (carabid) on leaf litter mass loss, organic matter content and bacterial total count was measured in leaf litter, with and without isopods.

Climatic conditions affected decomposition rate, which peaked in winter, but this effect is indirect and is mediated by the effect of climatic factors on the soil fauna. Rock substrate affects decomposition indirectly through its effect on the amount and chemical composition of the fallen leaves, and the chemical composition affects the decomposition rate. Rock substrate does not affect invertebrate biodiversity and density but affects the relative abundance of some groups. Invertebrate biodiversity affects decomposition rate and organic matter mineralization. Isopods contribute to the physical and chemical decomposition, although its effect in the forest floor is much smaller than usually attributed to it, based on laboratory experiments. Carabids have a direct effect on decomposition rate and not only by predation that control other groups’ population. Every method, whether collecting animals or manipulation in-situ has advantages and disadvantages that should be taken into account when drawing conclusions.