Litter mixing significantly affects decomposition in the Hulun Buir meadow steppe of Inner Mongolia, China

Aims We explored the decomposition rates of single- and mixed-species litter, the litter-mixing effect and the effect of component litters in a mixture on decomposition. Methods In a litter bag experiment, shoot litters from two dominant grasses (Leymus chinensis and Stipa baicalensis) and one legume (Melissitus ruthenica) were decomposed separately and as a mixture from May 2010 to September 2011 in the Hulun Buir meadow steppe of Inner Mongolia, China. We separated the litter mixture into its individual component litters (i.e. the different single-species litters) and analyzed the changes in litter mass remaining and litter nitrogen (N) remaining during single-and mixed-species litter decomposition. Important Findings (i) Litter mixing had significant positive effects on litter decomposition. The litter-mixing effect was strongest for the mixture of S. baicalensis and L. chinensis litters, followed by the mixture of S. baicalensis and M. ruthenica litters. (ii) Single-species component litters decomposed faster in the mixtures than separately (positive effect), but these effects were not significant for legume species M. ruthenica litter. Relative to single-species litter decomposition, the decomposition rates of the two grass (S. baicalensis and L. chinensis) litters significantly increased when they were mixed with each other or with M. ruthenica litter. (iii) For each species litter type, the percentage of litter N remaining during decomposition (NR) differed between the single-species litter and mixed litter treatments. The NR of S. baicalensis litter was higher when it was decomposed in the mixture than in isolation. However, the NR of L. chinensis litter was lowest in its mixture with M. ruthenica among the treatments. Regardless of its decomposition in the mixture or in isolation, the NR of M. ruthenica litter varied little among treatments. There was a significant positive relationship between the NR and percentage of initial litter mass remaining in both the single litter and mixed litter treatments. These results suggest that N transfer may happen among component litters in mixture and further affect the decomposition.