Afforestation on grassland strongly influences structure and functions of soil microbe. However, the composition and abundance of soil microbe (bacteria and fugal) changes, as well as their controlling factors are still poorly understood. Here we investigated the changes in soil properties and soil microbe after natural grasslands planted by Chinese pine (Pinus tabuliformis) on the Loess Plateau of China using high-throughput sequencing of the 16S rRNA and ITS rRNA gene. Soil sampling was conducted in three paired Chinese pine forestlands (FL) and their adjacent natural grasslands (GL), and also their transition zones (TZ) from grasslands to forestlands. Three parallel transects were established perpendicular to the forest-grass boundary. Along each transect, one sampling plot (1 m × 1 m) in the center of each land use type was set. Litter and humus were removed before soil sampling. Our objectives were to (1) assess the changes of composition and diversity of soil bacterial and fungal communities after natural grassland conversed to Chinese pine plantation; (2) investigate the composition and structure of soil bacterial and fungal communities under transition zones from grassland to forestland; (3) identify the soil properties tightly linked to the structure and diversity of bacterial and fungal communities.
Results/Conclusions
The results showed that soil bacterial diversity had no significantly difference among three sites in GL, TZ, and FL, but soil fungal diversity in GL were significant higher than those in FL and TZ sites (p<0.05). The proportion of co-owning OTUs in soil bacterial community were much higher than that in soil fungal community among the three sites. The dominated bacterial phylum shifted from Proteobacteria to Actinobacteria while the dominated fungal phylum transitioned from Ascomycota to Basidiomycota after grassland conversed to Chinese pine forestland. The functional groups of fungal community transformed from saprophytic to symbiotic fungi in comparing GL to FL sites. Both soil bacterial and fungal communities in TZ sites showed great similarity with that in FL sites. In addition, SAN, TN and C/N were the most important factors in determining soil bacterial and fungal communities among soil properties such as ST, SM, Clay, Silt, SIC, SOC, TN and SAN. The results indicated both soil bacterial and fungal communities changed significantly after planting Chinese pine in the grassland, and soil fungi were more sensitive than bacteria in responding of grassland afforestation, and soil N plays a key role in controlling soil microbe diversity.