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Soil microbial communities play a key role in ecological processes; however, the effects of fire, and post-fire management practices such as hydroseeding, on microbial abundance and activity are still poorly known. We sampled surface soil (0–10 cm) from unburned (UNB), burned and naturally regenerating (NAT), and burned but hydroseeded (HYD) chaparral stands on the campus of California State University San Marcos five years after fire. Soil was analyzed for microbial biomass carbon (C), bacterial taxonomic composition at the phylum level, and microbial activity (enzyme activity and nitrification) to test the hypothesis that fire and hydroseeding would significantly alter microbial abundance and activity. Total soil nitrogen (N) and C, microbial C, enzyme activity, and nitrification rate were significantly lower in burned stands than in the UNB stand; however, some of these patterns were affected by hydroseeding. Carbon inputs from hydroseeding, and associated changes in the composition of colonizing plant species, caused soil C and N and microbial C to be similar in the HYD and UNB stands. Relative abundances of bacterial taxa were similar for the UNB, HYD, and NAT stands, and there were no significant differences in taxonomic diversity between the stands. Activities of key C (β-glucosidase, peroxidase) and nutrient (N-acetylglucosaminidase (NAGase), phosphatase) cycling enzymes were significantly lower in burned stands, but hydroseeding did not affect their activities, and the declines in enzyme activity were due in part to declines in microbial biomass, soil C and N pools, and increases in pH. Our data suggest that fire and post-fire treatments alter soil microbial biomass and activity for years after fire, which will affect ecosystem C and N cycling and management of fire-prone semi-arid shrublands like chaparral. |
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