Soil carbon turnover in the McMurdo Dry Valleys, Antarctica

Terrestrial ecosystems of the Antarctic Dry Valleys are among the most inhospitable soil environments on Earth due to climate and substrate limitations over biota. These ecosystems present a challenge to understanding controls over carbon (C) cycling because likely sources of organic matter are 102–104 yrs old and in situ soil respiration is typically less than 1.0 μmol CO2 m−2 s−1. In this paper we describe an analytical approach to characterize kinetic pools of labile and recalcitrant soil C, and estimate C turnover in dry valley soils based upon these descriptions. Rate parameters for C turnover were derived from laboratory incubations conducted under a range of soil moistures and temperatures. We developed a C flux and reservoir model using these rate parameters along with published estimates of internal C transformations in soil microbial ecosystems, and a previously described primary production (NPP) model for Antarctic endolithic communities. We found that decomposition in 120 d incubations was well described by double-exponential rate kinetics, and that temperature, moisture and substrate availability significantly influenced observed rates of soil respiration. Simulations of soil C cycling based upon these parameters produced initially high rates of soil respiration following inputs of external organic matter, with mean residence times for C of 10–60 yrs. Soil organic C content equilibrated at 44–140% of observed levels within 1000 yrs. Simulations of equilibrium C were sensitive to NPP, microbial efficiency (Y), and the distribution of C inputs into labile and passive pools, indicating that more thorough investigation of microbial influence over the C cycle in dry valley soils is necessary.