Microbial dynamics and litter decomposition under a changed climate in a Dutch heathland

Climate change scenarios predict changes in temperature and precipitation. The effect of a modest temperature increase and repeated summer droughts on the rate of litter decomposition and microbial biomass dynamics was studied by a field scale manipulation experiment at a phosphorus (P) deficient dry heathland ecosystem in the Netherlands. Retractable covers were used to create artificial nighttime warming or prolonged summer drought in the experimental plots. The warming treatment initially enhanced litter mass loss and two consecutive years of summer drought retarded litter decomposition rate. Microbial carbon (C), nitrogen (N) and P immobilization was affected by the warming treatment as well as by the drought treatment. Enhanced temperatures resulted in increased microbial biomass C during the first half year of incubation, whereas the first drought treatment significantly retarded microbial N and P immobilization. The delayed net microbial N and P immobilization in the drought plots prevented net N and P mineralization. After 1 year microbial biomass C, N and P were significantly higher in the drought plots, probably as a result of availability of new substrate caused by the drying and rewetting process. Although microbial biomass was higher in the drought plots, the microbial C/N ratio was equal to the control and varied between 6 and 8. This suggested that in both the control and drought plots, the microbial community was dominated by bacteria at the longer term. Both treatments reduced net P mineralization and together with decreased foliar P concentrations this indicated the progressive importance of P limitation in restraining plant growth in this N saturated ecosystem.