Soil microbial C and N turnover under Cupressus lusitanica and natural forests in southern Ethiopia assessed by decomposition of super(13)C- and super(15)N-labelled litter under field conditions

Aims: Natural forests in Ethiopia are frequently replaced by Cupressus lusitanica plantations, but little is known about consequences of this land use change for soil C and N dynamics. The objectives of the study were: (i) quantification of microbial incorporation of litter-derived C and N under field conditions, (ii) identification of forest management effects on microbial incorporation of litter-derived C and N and (iii) elucidation of soil moisture effects on microbial utilization of litter-derived C and N. Methods: Natural litter in the Munessa forest was replaced by super(13)C and super(15)N labelled litter and its degradation was studied over 2 years. Microbial incorporation of litter-derived C and N was measured by chloroform fumigation extraction and stable isotope analysis. Results: Most of the super(13)C and super(15)N tracer remained in the litter or was incorporated into bulk soil, whereas soil microbial biomass showed minor incorporation. Silvicultural management practices influenced microbial litter-derived C utilization with increased microbial incorporation under wet soil conditions under plantations. Thinning of Cupressus trees led to increased litter decomposition during dry soil conditions. Conclusion: Soil humidity is the main influencing factor for microbial turnover of litter-derived C in this ecosystem. Fast-growing tree plantations had no negative effects on microbial C and N turnover when compared to natural forests.