Fine Scale Determinants of Soil Litter Fauna on a Mediterranean Mixed Oak Forest Invaded by the Exotic Soil-Borne Pathogen Phytophthora cinnamomi

Alejandro Jiménez-Chacón,Lorena Gómez-Aparicio,Pablo Homet,Oscar Godoy,Luis Matías

doi:10.3390/f9040218

Abstract

There is growing recognition of the importance of soil fauna for modulating nutrient cycling processes such as litter decomposition. However, little is known about the drivers promoting changes in soil fauna abundance on a local scale. We explored this gap of knowledge in a mixed oak forest of Southern Spain, which is under decline due to the invasion of the exotic soil-borne pathogen Phytophthora cinnamomi. Meso-invertebrate abundance found in soil litter was estimated at the suborder level. We then explored their statistical correlations with respect to light availability, tree and litter characteristics, and P. cinnamomi abundance. Oribatida and Entomobryomporpha were the most abundant groups of Acari and Collembola, respectively. According to their trophic level, predator and detritivore abundances were positively correlated while detritivores were, in turn, positively correlated with pathogen abundance and negatively influenced by light availability and tree defoliation. These overall trends differed between groups. Among detritivores, Diplopoda preferred highly decomposed litter while Oribatida and Psocoptera preferred darker environments and Poduromorpha were selected for environments with lower tree defoliation. Our results show the predominant role of light availability in influencing litter fauna abundances at local scales and suggest that the invasive soil-borne pathogen P. cinnamomi is integrated in these complex relationships.

Highlights

There is growing recognition that soil fauna plays a major role in litter decomposition [1,2].The way soil fauna mediates litter decomposition involves several simultaneous processes
Understanding basic forest ecosystem processes such as litter decomposition and nutrient cycling would strongly benefit from characterizing the abundance and composition of mesofauna associated with forest litter
Both Acari and Collembola have been extensively studied as environmental indicators of soil quality [56,57], and our analyses clearly selected light availability as the most important predictor of their abundances

Summary

Introduction

There is growing recognition that soil fauna plays a major role in litter decomposition [1,2].The way soil fauna mediates litter decomposition involves several simultaneous processes. As soon as leaf litter falls from trees, invertebrate detritivores start feeding and breaking litter down into small pieces This fragmentation process increases the litter surface area by accelerating the inoculation and activity of bacteria and fungi that transform these smaller pieces into inorganic molecules such as phosphate, water, carbon dioxide, or ammonium [3,4,5]. Parallel to this herbivory process, soil litter contains different groups of predators by controlling the abundance of these invertebrate detritivores through a diverse range of feeding strategies [6]. These multi-trophic interactions result in complex processes that are responsible for creating soil fertility, maintaining soil health [7], and determining

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