Effects Of Rainfall Change On Soil Microbial Characteristics In Korean Pine Broad-leaved Forest

The zonal climax vegetation in northeastern China is Korean pine broad-leaved forest; this type of vegetation plays a significant ecological role in the region. Changbai Mountain is an ideal area to study the effects, either positive or negative, of change in rainfall on temperate forests. This study analyzed the two important indexes of underground ecosystem processes which are soil microbial biomass carbon and microbial biomass nitrogen response to rainfall by±30%in Korean pine broad-leaved forest of Changbai Mountain. The present research aimed at finding out the differences in the diversity of bacterial community in different layer and rainfalls. In this study, we delineated plots in the virgin, Korean pine broad-leaved forest on Changbai Mountain and analyzed differences in the diversity of the bacterial community in surface (at soil depths of0to5cm and5to10cm) and rhizosphere soils between rainfall controlled plots (increased (+) or decreased (-) by30%) and control plots. Bacteria were identified using the high-throughput454sequencing method. The main research conclusions are as follows:The influence of rainfall change on soil physical and chemical properties was significantly.Under different rainfall conditions,except for carbon nitrogen ratio, organic carbon, total nitrogen, pH, effective phosphorus, bulk density and moisture content have significant difference.Soil total nitrogen, organic carbon effective phosphorus, pH and moisture content were increased with the increase of rainfall, soil bulk density decreased with increasing rainfall.In terms of soil spatial location, the bulk density increases with the increase of soil depth, other indicators are decreased with the increase of soil depth.During May to September, soil microbial biomass carbon(879.09mg·kg-1) and microbial biomass nitrogen(100.03mg·kg-1) decreased with soil depth. With the increase of rainfall, soil microbial biomass carbon and nitrogen were increased, and the rangeability is bigger in0-5cm soil than in5～10cm soil. Soil microbial biomass carbon and nitrogen ratio declined with the increase of rainfall.The effects of±30%rainfall on the means of soil microbial biomass carbon and microbial biomass nitrogen in the growing season were significant. The dynamics were much clear for the+30%rainfall. Both microbial biomass carbon and nitrogen showed similar seasonal patterns,in which they showed lowest in May,then rise then reduce then rise again, had1-2peaks in the growing season.However,the values and occurring times of the peaks varied with rainfall and soil layers.The seasonal variations in the microbial biomass carbon and nitrogen were greater at the0～5cm soil layer than those at5～10cm. Microbial biomass carbon and nitrogen were significantly positively related to organic matter and total nitrogen content respectively. The difference of soil physical and chemical properties caused by rainfall change is the main factors contributed to the differences in spatio-temporal patterns of the soil microbial biomass in the three rainfall forests.We obtained a total299,181effective gene sequences, or271,496optimized sequences, with a mean value of33,242sequences for each soil sample. Bacterial diversity and abundance declined with increasing soil depths. In the surface soil from0to5cm, the control plots> sample plots with rainfall+30%>sample plots with rainfall-30%, while in the surface soil from5to10cm, sample plots of rainfall+30%>sample plots rainfall-30%>the control plots. Bacterial diversity and abundance in rhizosphere soil decreased with increased rainfall. The dominant bacterial community was the same among the sample plots with different rainfall levels and included the following type:Proteobacteria, Acidobacteria, Actinobacteria, Planctomycetes, and Chloroflexi. This result implies that variation in rainfall did not change the composition of the dominant bacterial community but affected bacterial abundance and the response patterns of the dominant community to variation in rainfall. In all of the investigated bacterial genera, variation in precipitation had the greatest impact on the abundance of Bradyrhizobium, Delftia, Nitrospiraceae Nitrospira, and Candidates_Koribacter.