The effects of Na pulses on subalpine ecosystems

Abstract

Sodium is an essential nutrient for all animals, and in terrestrial ecosystems it is often difficult for plant consumers to obtain the necessary amount of Na since plants generally do not prosper in high salt environments. While carnivores get adequate salt due to bioaccumulation from their prey, herbivores are limited by Na and often must seek out salt deposits or drink urine to maintain osmotic balance. In ecosystems far from the ocean this Na craving is thought to be even higher. In this study, I used three different experiments in and around the Gothic townsite in the Rocky Mountains of Colorado to examine the use of Na in subalpine ecosystems. These ecosystems have significant Na shortfall; plant and nectar consumers are drawn to resourcess that have higher salt concentrations. Large mammalian herbivores (e.g., deer) grazed selectively in plots sprayed with a 1% NaCl solution suggesting that they have adapted to detect even small amounts of salt. This grazing had cascading consequences: plots with higher Na were grazed more, had higher light availability, and therefore higher soil temperatures. I then examined whether plots with higher temps had higher colonization rates by ant nests. I found that there was an interaction between Na and N and between Na and heat in some instances with T. sessile preferring to colonize warm and salty areas suggesting that heat and Na in conjunction help to increase metabolic efficiency. Given these results, there is a strong indication that Na (though an often overlooked nutrient) may be an important limiting factor in subalpine ecosystems. Thus, with further study we may be able to better understand the activity of food webs whose biochemistry has previously been examined only through biochemical lense of N, C and P.