Abstract/Summary

Plant root and shoot fractions differ strongly in tissue quality (i.e. concentrations of soluble and recalcitrantcomponents), affecting their decomposition in soil and, in turn, their respective impacts on greenhouse gasemissions and soil C storage. Therefore, root and shoot residues can be used as model substrates to investigatethe impact of tissue quality on soil processes. To this end, we used13C-labelled ryegrass root and shoot residuesto quantify their rates of C mineralization, assessed the impacts of residue addition on microbial activity andmineralization of native soil organic matter (SOM) and investigated the influence of root and shoot residues on Cpartitioning in SOM fractions. This was done using controlled incubation of soil amended with milled root orshoot material and soil only. Addition of shoot residues resulted in higher residue C mineralization rates, ac-celerated soil microbial activity, and increased SOM priming more than root residues particularly in thefirst 12days. Nevertheless, for thefirst time, we found that at the end of the experiment (36 d) the amount of residue Cretained in soil was similar in rootversusshoot residue amended soil but net C gain in soil was 44% less in theshoot residue treatment. This is because SOM priming, especially during the initial period of incubation, wasgreater in the shoot residue treatment. This suggests that low-quality root residues can lower soil CO2emissionsand increase soil C stocks because of not only slow tissue turnover, but also weaker impact on SOM priming.