Response of Collembola to the addition of nutrients along an altitudinal gradient of tropical montane rainforests

Abstract

Soil microarthropods are important drivers of decomposition processes in terrestrial ecosystems. However, the factors controlling their density and diversity are little understood especially in tropical ecosystems. In this study, we focus on how soil Collembola communities along an altitudinal gradient in the tropical Andes respond to moderate nutrient additions. Nitrogen (N) and phosphorus (P) were added twice annually in a full-factorial design and Collembola communities were investigated at three sites (1000, 2000, 3000 m) along the altitudinal gradient, one and six years after the first nutrient addition. We expected Collembola to significantly respond to nutrient additions with the effect being similar in different taxonomic groups of Collembola, and increasing with the duration of the experiment and with increasing altitude. Further, we expected species richness to decline but body size to increase with both nutrient addition and increasing altitude. Both density and species richness of Collembola were low as compared to temperate regions and decreased significantly with increasing altitude. Contrasting our expectations, different groups of Collembola responded differently to nutrient additions with their response varying with altitude. The density of the dominant group of Entomobryomorpha was increased by the addition of P at higher altitude but decreased at lower altitude. By contrast, the density of Poduromopha and Symphypleona was increased by the addition of N at lower altitude but decreased at higher altitude. Notably, only the effect of the addition of P on Entomobryomorpha increased with duration of the experiment. Body size of Collembola significantly increased by the addition of N and also with increasing altitude. The results suggest that resource quality and availability rather than the amount of resources are controlling Collembola communities in tropical montane rainforests. In these ecosystems changes in human-mediated nutrient deposition therefore, are likely to affect the structure and functioning of Collembola communities as major detritivore soil animals.