The Influence Of Warming Or Snow Reduction During The Dormancy Period On Soil Physicochemical Properties And Bacterial Communities In Loess Plateau

As a key biological factor in the terrestrial ecosystem,microorganisms play an important role in regulating soil nutrient cycles and are very sensitive to environmental disturbances,especially winter climate changes.Research on the response of soil nutrients and microbial properties of typical semi-arid grassland to climate change during dormancy is of great significance for predicting the ecological process and functional changes of semi-arid grassland ecosystem under the background of future climate change.In our research,we took the semi-arid grassland in the Yunwushan National Nature Reserve in Ningxia Hui Autonomous Region as the research object.The responses of soil nutrients,enzyme activities and soil bacterial communities properties in the 0-5 cm,5-10 cm,10-15 cm,15-20 cm soil layers of the typical steppe of the Loess Plateau to climate change during the dormant period were studied.Four treatments were set:warming(W),snow reduction(S),interaction of warming and snow reduction(WS)and control(CK).The open-top growth chamber(OTC)was used to simulate warming,and the snow shelter was used to simulate snow reduction.Our results showed that:(1)Warming,snow reduction,and interaction during dormancy were all conducive to the increase of soil temperature in the 0-20 cm soil layer,but each treatment increased soil temperature in different ranges.The effects of warming,snow reduction and interaction on the soil moisture in the range of 0-20 cm soil layer were different.(2)Different experimental treatments significantly increased soil organic carbon,soil total nitrogen,and soil available phosphorus content(p<0.01)The soil organic carbon content decreased with the increasing of soil depth.The total nitrogen content varies inconsistently with the deepening of the soil.The soil available phosphorus content decreased with the increase of soil depth under warming and control.Different experimental treatments significantly affected the soil nitrate nitrogen content,but had no significant effect on the ammonium nitrogen content(p>0.05).Compared with the control,the warming and interaction treatments reduced the soil nitrate nitrogen content in the 5-20 cm soil layer,and the snow reduction increased the nitrate nitrogen content in all soil layers.The nitrate nitrogen content in each soil layer decreased with the increase of soil depth.(3)Under the conditions of warming and snow reduction,the soil microbial biomass carbon and microbial biomass nitrogen content of 0-20 cm soil layer increased compared with the control.Under the conditions of interaction,the microbial biomass carbon and microbial biomass nitrogen content of 0-10 cm soil layer increased compared with the control,and decreased in 10-20 cm soil layer.The soil microbial biomass carbon and microbial biomass nitrogen content gradually decreased with the increasing of soil depth.(4)The activity of BG increased in the 5-10 cm soil layer and decreased in the 15-20 cm soil layer compared with the control.As the soil depth increased,the BG enzyme activity decreased.The activity of NAG increased in the 0-15 cm soil layer under each treatment,but decreased in the 15-20 cm soil layer.The activity of AKP in each soil layer had a downward trend under the warming,snow reduction and interaction.In different treatments,the alkaline phosphatase activity increased and then decreased with the increase of soil depth.Different treatments had no significant effect on soil p H(p>0.05),but different soil depths had significant effects on soil p H(p<0.05).(5)Different treatments had no significant effect on the diversity of soil bacteria in the range of 0-20 cm soil layer(p>0.05).However,the soil bacterial diversity under each treatment in 0-10 cm soil layer had an upward trend compared with the control,and showed a downward trend in 15-20 cm soil layer.The warming,snow reduction and interaction during the dormant period had significant effects on the bacterial community structure.At the same time,different soil layers also played a certain role in the distribution of microbial community structure.(6)At the level of bacterial phyla classification,the first four with greater relative abundance were Proteobacteria,Acidobacteria,Actinobacteria,and Gemmatimonadetes.The relative abundance of Acidobacteria at phylum level decreased in the 0-5 cm and 15-20 cm soil layer with warming,snow reduction and interaction(p<0.05).The relative abundance of Actinobacteria in the 10-20 cm soil layer was the highest under the warming and the smallest under the interaction treatment.The relative abundance of Gemmatimonadetes was also significantly reduced under the interaction in the 0-10 cm soil layer and the 15-20 cm soil layer(p <0.05).(7)Among the soil physical and chemical factors related to the structure of the microbial community,AKP were environmental factors that significantly affected the microbial community.Nitrate nitrogen and total nitrogen content significantly affected soil microbial species diversity.The bacterial community diversity indexes(Shannon,Chao1,and Richness)were all positively correlated with nitrate nitrogen and total nitrogen content.