Do oribatid mites of tropical montane rainforests respond to nitrogen and phosphorus additions?

Abstract

Nitrogen (N) and phosphorus (P) depositions worldwide are increasing the risks of biodiversity and functionality loss in terrestrial ecosystems, particularly in tropical regions. However, the effects of increased nutrient inputs on soil biodiversity in tropical regions remain largely unknown. Here, we investigated the response of one of the most diverse groups of soil invertebrates, oribatid mites (Acari: Oribatida), to the long-term input of moderate rates of N and P into montane rainforests along an altitudinal gradient (1000, 2000, and 3000 m) in Ecuador. The response of oribatid mites to nutrient additions was investigated after 1, 3, and 10 years. Overall, variations in oribatid mite diversity and richness due to nutrient additions were low and restricted to the 1000-m site, where the combined addition of N and P resulted in significantly reduced density and richness of oribatid mites after 10 years. In general, oribatid mite community compositions differed strongly between the altitudinal sites and remained remarkably stable across the study period. Changes in oribatid mite community composition during the study period were driven by changes in temperature, precipitation, and relative humidity rather than by the addition of N and P. Our results suggest that oribatid mites in tropical montane rainforests are rather insensitive to moderate additional input of N and P, pointing to an outstanding stability of these soil animal communities. Shifts in climatic factors, rather than changes in resource-associated factors such as nutrients, may pose a more significant threat to oribatid mite communities of tropical montane rainforests.