Application of a high-throughput laboratory method to assess litter decomposition rates in multiple-species experiments

Laboratory decomposition experiments measuring the mineralization of C from plant residue are increasingly used to test the effects of different litter sources and soil conditions. To date, the most widely used methods are infra-red gas analysis (IRGA) and gas chromatography, which are time-consuming, and relatively expensive and complex to operate. The aim of this study was to devise a simple and rapid laboratory method to assess litter decomposition rates at frequent time intervals. We modified the MicroResp system to measure the amount of CO2 produced by two soils supporting contrasting microbial communities and containing the litter of eight crop species. The method was sensitive enough to differentiate both soil microbial communities and litter qualities. The method combines the accuracy of gas chromatography with the speed of absorbance measurements obtained via microplate readers. This technique provides an effective means for devising complex litter decomposition experiments capable of addressing the joint influence of multiple species, soil communities, environmental conditions, and their multiple interactions. 2012 Elsevier Ltd. All rights reserved. In terrestrial ecosystems, more than 50% of net primary production is transferred to the soil via the litter decomposition pathway (Wardle et al., 2004). The pace of this transfer is known to be controlled by a suite of factors acting at different scales, chiefly climate, litter chemistry and soil biota (Hättenschwiler et al., 2005; Cornwell et al., 2008). Research on litter decomposition has provided key decomposition metrics that are readily comparable among litter sources and soil conditions, at least within individual experiments. This has led to the rise of decomposition studies run under controlled laboratory conditions. In thesemicrocosm studies, litter decomposition is considered as the mineralization of C from plant residue, measured as CO2 production (Aerts and de Caluwe, 1997). To date, the most widely used methods to measure CO2 production in litter incubations are infra-red gas analysis (IRGA) and gas chromatography. These methods are more accurate than classical estimations of soil respiration using soda lime (Teuben, 1991) or alkali traps (Froment, 1972), but are time-consuming, relatively expensive and complex to operate, requiring specific skills (Mondini et al., 2010). Also, the fact that they are timeconsuming precludes their widespread use in large multi-species screening experiments. The aim of this study was to devise a simple and rapid laboratory method to assess litter decomposition rates at frequent time intervals. We assessed the reliability of the method by testing a gradient of litter quality and two soils with contrasting microbial communities, where an increase in decomposition was anticipated via higher litter quality and higher soil microbial functional diversity. We analyzed soil respiration, a measure of decomposition, with a modified procedure of the MicroResp system (Campbell et al., 2003). This is a whole-soil method based on community level physiological profiles obtained by testing different carbon sources of contrasting recalcitrance. The substrate utilization rates of the carbon sources correspond to the catabolic activity of the microbial community and have been used to analyze microbial functional diversity (Ginzburg et al., 2008) or heterotrophic evenness (Schipper et al., 2001). In this study, we modified the MicroResp system to measure the amount of CO2 that is being respired by soil * Corresponding author. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, USA. E-mail address: [email protected] (P. García-Palacios).