Abstract
The structure and functioning of decomposer systems heavily relies on soil moisture. However, this has been primarily studied in temperate ecosystems; little is known about how soil moisture affects the microfaunal food web in tropical regions. This lack of knowledge is surprising, since the microfaunal food web controls major ecosystem processes. To evaluate the role of precipitation in the structure of soil food web components (i.e., microorganisms and testate amoebae), we excluded water input by rain in montane rainforests at different altitudes in Ecuador. Rain exclusion strongly reduced microbial biomass and respiration by about 50 %, and fungal biomass by 23 %. In testate amoebae, rain exclusion decreased the density of live cells by 91 % and caused a shift in species composition at each of the altitudes studied, with ergosterol concentrations, microbial biomass, and water content explaining 25 % of the variation in species data. The results document that reduced precipitation negatively affects soil microorganisms, but that the response of testate amoebae markedly exceeds that of bacteria and fungi. This suggests that, in addition to food, low precipitation directly affects the community structure of testate amoebae, with the effect being more pronounced at lower altitudes. Overall, the results show that microorganisms and testate amoebae rapidly respond to a reduction in precipitation, with testate amoebae—representatives of higher trophic levels—being more sensitive. The results imply that precipitation and soil moisture in tropical rainforests are the main factors regulating decomposition and nutrient turnover.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-012-2360-6) contains supplementary material, which is available to authorized users.
Highlights
Keywords Rain exclusion · Testate amoebae · Ergosterol · Microbial biomass · Food web Species diversity is disproportionaly distributed across the globe, with the highest concentrations found in tropical regions (Dirzo and Raven 2003)
The C-to-N ratio of the L/F material signiWcantly increased with increasing altitude (F2,23 = 13.99, P = 0.0017); it was slightly higher in rain exclusion plots at 1,000 and 2,000 and markedly higher at 3,000 m (Table 1)
We experimentally excluded precipitation in montane rainforests at diVerent altitudes to evaluate the role of precipitation in the structure of soil food web components that rely heavily on soil moisture
Summary
Species diversity is disproportionaly distributed across the globe, with the highest concentrations found in tropical regions (Dirzo and Raven 2003). The diversity, abundance, and activity of organisms essentially depends on a few fundamental environmental factors such as temperature and moisture (Magurran and May 1999; Gaston and Blackburn 2000). Climatic factors such as changes in precipitation drive ecosystem processes by modifying water availability and nutrient cycling. The decomposition of organic matter and the associated decomposer community responsible for litter breakdown, critically rely on the availability of water. Precipitation has been shown to drive litter mass loss in grasslands, temperate forests, as well as in tropical forests, predominantly by modifying the structure and activity of microbial and animal communities (Swift et al 1979; Austin and Vitousek 2000; Epstein et al 2002; Lensing and Wise 2007). Microorganisms and microfauna grazers such as protists and nematodes rely on water Wlms in the soil, and soil humidity
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