The effect of ecosystem engineers on N cycling in an arid agroecosystem

Jessica G. Ernakovich1, Theodore A. Evans2, Ben Macdonald3, Mark Farrell4

1 CSIRO Agriculture & Food, PMB 2, Urrbrae, SA, 5064, http://people.csiro.au/E/J/Jessica-Ernakovich, [email protected]

2 School of Animal Biology, University of Western Australia, Perth, WA 6009, [email protected]

3 CSIRO Agriculture & Food, Canberra, ACT, 2601, [email protected]

4 CSIRO Agriculture & Food, PMB 2, Urrbrae, SA, 5064, http://people.csiro.au/F/M/Mark-Farrell.aspx, [email protected]

Abstract

Ecosystem engineers—such as earthworms, termites and ants—are an important component of soil biodiversity and have been shown to contribute to aboveground productivity in native and managed ecosystems. Although their role in physical alteration of soils is appreciated, less is known about their effect on soil nutrient cycling, particularly in arid systems where termites and ants are the dominant ecosystem engineers. We explored the effect of termite reduction and tillage on soil nitrogen (N) biogeochemistry in soils from the northeasternmost wheat growing region in Western Australia. We assessed total soil N, potentially mineralizable N, and dissolved N pools, as well as soil N fluxes, such as proteolysis and N mineralization. We predicted that soils with native termite and ant populations would have greater N pools and rates of transformations between pools. While we found that many soil N pools were up to 2.5 times larger with native termite populations (e.g. dissolved organic N, NH4+), we found that the rate of transformations between pools was reduced relative to the reduced termite plots. While the reason behind this trend needs further exploration, the larger soil N pools in sites with native levels of ecosystem engineers implies that the conservation of soil macrofauna, particularly those that translocate N through the soil profile, may be important in the sustainable management of cropped lands.