Abstract
Biotic interactions structure ecological communities but abiotic factors affect the strength of these relationships. These interactions are difficult to study in soils due to their vast biodiversity and the many environmental factors that affect soil species. The McMurdo Dry Valleys (MDV), Antarctica, are relatively simple soil ecosystems compared to temperate soils, making them an excellent study system for the trophic relationships of soil. Soil microbes and relatively few species of nematodes, rotifers, tardigrades, springtails, and mites are patchily distributed across the cold, dry landscape, which lacks vascular plants and terrestrial vertebrates. However, glacier and permafrost melt are expected to cause shifts in soil moisture and solutes across this ecosystem. To test how increased moisture and salinity affect soil invertebrates and their biotic interactions, we established a laboratory microcosm experiment (4 community × 2 moisture × 2 salinity treatments). Community treatments were: (1) Bacteria only (control), (2) Scottnema (S. lindsayae + bacteria), (3) Eudorylaimus (E. antarcticus + bacteria), and (4) Mixed (S. lindsayae + E. antarcticus + bacteria). Salinity and moisture treatments were control and high. High moisture reduced S. lindsayae adults, while high salinity reduced the total S. lindsayae population. We found that S. lindsayae exerted top-down control over soil bacteria populations, but this effect was dependent on salinity treatment. In the high salinity treatment, bacteria were released from top-down pressure as S. lindsayae declined. Ours was the first study to empirically demonstrate, although in lab microcosm conditions, top-down control in the MDV soil food web.
Highlights
They ways biological interactions affect communities is a key research theme in ecology
There were significantly less bacterial cells in Bacteria only, Scottnema, and Mixed community treatments compared to the Eudorylaimus community treatment in control salinity microcosms (LSMeans, p < 0.05), but this effect was diminished under high salinity (Figure 1)
E. antarcticus and a negative effect on S. lindsayae, but we found that moisture had no effect on bacteria study mimicked the length of one ‘active’
Summary
They ways biological interactions affect communities is a key research theme in ecology. Studies have shown how biotic interactions affect plants [1], benthic invertebrates [2], and bird communities [3] under varying environmental conditions, but relatively few studies have empirically examined how biotic interactions affect soil community structure and function (but see: [4,5]). This is partly due to the vast biodiversity in soils, where relationships are further confounded by the difficulty of directly observing interactions among microscopic species along with many interacting factors, including plants and aboveground animals. Among the world’s harshest environments, they are a simple ecosystem with very limited diversity of eukaryotes [7,8] compared to temperate ecosystems, making them an excellent
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