Responses of Soil Organic Carbon Mineralization and Microbial Communities to Leaf Litter Addition under Different Soil Layers

The mechanism of how soil carbon pools change when coniferous forests are converted into conifer-broadleaf mixed forests is poorly understood. In this study, the impact of additional carbon inputs on soil organic carbon mineralization and microbial communities was evaluated. In a microcosm incubation experiment, three types of C-13-labeled litter (Pinustabulaeformis (PT), Robiniapseudoacacia (RP), and a mixture of PT and RP (1:1, PR)) were added in to top (0-20 cm) and deep (60-80 cm) soil collected from a Chinese pine plantation. The priming effect (PE) and specific microbial groups involved in PE were studied. PT and RP addition to topsoil induced a negative PE. In deep soil, the decomposition rates of soil organic matter (SOM) after adding PT and mixture increased by 16.6% and 34.6% compared to those without litter. The addition of RP with a lower C:N ratio had a stronger negative PE than adding PT or mixture. Moreover, the PE in deep soil was more intense after all litter additions. In topsoil, the litter-derived carbon was mainly incorporated into 16:0, 18:1 omega 9c, and 18:1 omega 7c fatty acids. In conclusion, the addition of broadleaf litter into coniferous plantations might be beneficial for enhancing deep soil carbon stocks.