Effects of Warming and Nitrogen Addition on the Soil Bacterial Community in a Subtropical Chinese Fir Plantation

Soil warming has the potential to alter bacterial communities, affecting carbon (C) storage and nitrogen (N) cycling in forest ecosystems. We studied bacterial community changes by warming soil and adding two N-levels (40 and 80 kg N ha(-1) year(-1)) for two years in a subtropical plantation of Chinese fir (Cunninghamia lanceolate (Lamb.) Hook) in southern China. Soil warming significantly changed the bacterial community structure, causing decreases in Proteobacteria and Acidobacteria, while increasing Actinobacteria and Chloroflexi. The high N addition had a greater impact on the bacterial community structure than the low N addition. Warming shifted the bacterial community towards oligotrophic taxa, while N addition could dilute this tendency. Results of the ecological networks indicated that warming resulted in a more complicated co-occurrence network and an increased interaction between different phylum communities, while N addition enhanced the cooperation within communities pertaining to the same phylum. The changes to the soil properties, typical catabolism enzymes, and plant growth also showed that soil warming and N addition accelerated the C and N cycles in the soil, and lead to an increased upward flow of N (from underground to aboveground) and decomposition rate of soil organic carbon (SOC). Overall, the results provided insights into the bacterial community and soil C and N cycling change at a subtropical plantation.