Soil Bacterial Diversity Impacted by Conversion of Secondary Forest to Rubber or Eucalyptus Plantations: A Case Study of Hainan Island, South China

Rubber plantation (RP) is the most important economic forest of Hainan Island, South China. In addition, eucalyptus plantations (EP), used as shelter forests, were planted to protect the rubber plantations from typhoon hazards in the 1980s. To date, few studies have examined the effects on bacterial composition and diversity after secondary tropical forests (SF) have been converted into RP or EP. This study investigated the bacterial communities of RP, EP, and SF using an Illumina high-throughput sequencing analysis. Our findings revealed the following First, there were significant differences between RP, EP, and SF in bacterial compositions at both the phylum and family levels. Second, the Shannon indices of RP and EP were significantly higher than that of SF. The Simpson dominance index of SF was 0.012, which was significantly higher than those of RP and EP, indicating that the diversities of RP and EP were higher than that of SF. Abundance rank curves confirmed that the taxonomic compositions in EP and RP were relatively uniformly distributed compared with that in SF, which results in the higher diversities of RP and EP. Third, Soil nutrition (total nitrogen, total phosphorus, and total potassium), which explained 43.05% of the total variance of taxonomic composition, was the most important factor affecting the soil bacterial community structure in this region. In conclusion, soil nutrition has increased, mainly due to the application of fertilizers, after SF conversion to RP and EP, which, in turn, has resulted in significant changes in the bacterial community composition as well as a general increase in bacterial community diversity.