Changes in soil free-living nematode communities and their trophic composition along a climatic gradient

Tal Levi,Stanislav Pen-Mouratov,Chen Sherman,Yosef Steinberger

doi:10.4236/oje.2012.22010

Abstract

Ambiguity exists concerning the effects of climate on soil nematode-community composition. In this study, we examined the free-living nematode communities in soil along a climatic gradient representing humid-Mediterranean, Mediterranean, semi-arid, and arid climate types. The relationships between abiotic soil characteristics (organic carbon, soil moisture (SM), water-holding capacity) and nematode parameters, such as abundance, trophic group composition, and diversity indices, were explored in the context of climate and seasonality. Nematode abundance was lowest at the arid site. At the humid Mediterranean and Mediterranean locations, nematode abundance reached its peak in winter, while at the semi-arid and arid sites, an almost opposite trend was observed, with lowest abundances in winter, presumably due to a nutrient washout from the soil profile during the rainy season. On the trophic level, one trophic group demonstrated a positive correlation with SM and one trophic group demonstrated a negative one at each location, while the other two groups remained constant. Fungi-feeding nematodes were found to be unaffected by SM at the humid-Mediterranean and Mediterranean locations, while at the semi-arid and arid sites their proportion increased in correlation with decreasing SM. Bacteria-feeders increased with SM at the arid site, were unaffected at the semi-arid location, and decreased with SM at the humid-Mediterranean and Mediterranean sites. Plant-parasites were associated with SM only at the humid-Mediterranean site. Omnivores-predators were positively affected by SM at the two middle locations, staying constant at the humid-Mediterranean and arid sites. These findings point to the strong linkage existing between nematode trophic behavior and climatic factors, demonstrating distinctive communal fingerprints for each climate type.

Highlights

The biological component of soil acts as a highly complex entity of flora and fauna embedded in the soil physical matrix, and controlled by a highly complex yet firm ecological consistency
The mean total annual rainfall during the 3-year study period at the humid-Mediterranean, Mediterranean, and semi-arid locations (616, 442, and 200 mm, respectively), was 21%, 18%, and 33%, respectively, lower than the multiannual average (Table 1). This is in contrast to an addition of 11% above the average at the arid site (100 mm) that was found for this three-year period
Using SMWHC allowed us to compare between the sites during the study period in order to evaluate changes in moisture availability as a function of soil holding capacity

Summary

Introduction

The biological component of soil acts as a highly complex entity of flora and fauna embedded in the soil physical matrix, and controlled by a highly complex yet firm ecological consistency. The soil milieu enables the existence of a large diversity of underground organisms: microflora (bacteria and fungi), microfauna (protozoa), mesofauna (nematodes and arthropods), etc. Most of these organisms inhabit the 0 - 30 cm soil layer, in the spaces between soil particles where the soil moisture and organic matter are available [1]. Soil free-living nematodes are known to be one of the most abundant multicellular organisms among all soil organisms [3,4] They are common in both terrestrial and aquatic ecosystems in all climates, even in the most extreme environments, where water availability is very low [5,6]. The soil free-living nematode community composition, size, and level of activity are influenced by abiotic factors (e.g., soil temperature and moisture, the amount of organic matter, and pH), and food resources [8]

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