Evaluation Of The Soil Quality And Study On Soil Bacterial Diversity Of Shelterbelts In The Black Soil Region

The black soil area in Northeast China is one of the four famous black soil areas in the world.Since the reclamation in the late Qing Dynasty,the unreasonable cultivation and the increasing production activities resulted from serious soil erosion and accelerated soil degradation.To restore the ecological environment and reduce soil erosion,especially wind erosion,people in the typical black soil area in the western part of Heilongjiang Province began large-scale planting of shelterbelts with major afforestation species such as Populus,Larix gmelinii,Pinus sylvestris var.mongholica Litv.,Fraxinus mandshurica Rupr.,Salix saposhnikovii since the 1980s.These man-made shelterbelts have become an important part of the region's agroforestry ecosystem,a part of the 'Three-North Shelterbelt Project',the largest ecological forestry project in the world.It provides an important ecological barrier for local agricultural production and living and plays a great role in ensuring high and stable crop yield,preventing wind and fixing sand,and regulating microclimate.However,in recent years,stand degradation has occurred in many areas of the farmland shelterbelt,and there are many reports on the decline of the artificial forest.One of the main reasons for the decline of the plantation is the deterioration of soil quality.As an important part of the plantation ecosystem,forest soil is the pivot of nutrient element transformation in the main place of life activities,which is of great significance to the healthy growth and development of trees.To study the change rules of soil quality of forestland,scientifically and comprehensively evaluate soil quality,explore the change of soil bacterial community and the effect of influencing factors to maintain soil productivity for a long time is the focus of current agricultural and forestry research.Given mentioned above,Baiquan County,a major agricultural county in the typical black soil area in the west of Heilongjiang Province,was selected as the research area.In the research area,a total of 14 kinds of sample plots were selected as the research objects,i.e.five types of shelterbelts with the same forest ages(nineteen years),i.e.Populus×xiaohei pure forest shelterbelts(X),Larix gmelinii(Rupr.)Kuzen.pure forest shelterbelts(L),Pinus sylvestris var.mongholica Litv.pure forest shelterbelts(Z),mixed forest shelterbelts Fraxinus mandshurica Rupr.mixed with Larix gmelinii(Rupr.)Kuzen.(SL),mixed forest shelterbelts Pinus sylvestris var.mongholica Litv.mixed with Larix gmelinii(Rupr.)Kuzen(ZL),and six kinds of Populus×xiaohei shelterbelts with different forest ages which included young forest(X09),mid-maturity forest(X03),near-maturity forest(X99),early maturity forest(X95),late maturity forest(X88)and post-maturity forest(X84);and four kinds of Larix gmelinii(Rupr.)Kuzen.shelterbelts with different forest ages which included young forest(L99),mid-maturity forest(L92),early near-maturity forest(L87),late near-maturity forest(L81);and one control sample plot abandoned arable for 20 years(CK).Among the above sample plots,X and X99,and L and L99 are the same sample plots,only they are called differently in different research series.Twenty kinds of soil indicators were determined in the 0-60 cm soil layer of shelterbelts with different types of accompanied with the same forest ages and with the different forest ages,and soil bacterial 16S rDNA diversity was determined in the surface soil(0-20 cm soil layer)of different types of shelterbelts with the same forest ages.Using a space-for-time substitution,the changes in soil quality of shelterbelts vary with different forest ages was studied.And the variation in soil quality was assessed using one-way ANOVAs and the least significant difference tests(LSD).The minimum data set(MDS)of soil quality evaluation was selected by principal component analysis(PCA)to overcome the multicollinearity of the soil index system and was used for the comprehensive evaluation of soil quality.High throughput sequencing(HTS)and bioinformatics analysis were used to obtain the diversity of soil bacteria in the different types of shelterbelts.The function of the bacterial community was analyzed by comparing the KEGG metabolic pathway database,and the potential of soil function in the different type of shelterbelts was predicted according to the relative abundance of functional genes referring to C,N,P,S.The redundancy analysis(RDA)of soil properties and species with significant differences between different types of shelterbelts were performed,and the important soil properties affecting soil bacterial diversity were obtained.The main results of this study are as follows:1.Changes in and evaluation of soil quality of the different type of shelterbelts(1)The L,Z,SL all significantly increased soil bulk density(BD)compared to CK.Among all type of shelterbelts,the soil saturated holding-water capacity(SHC),soil capillary holding-water capacity(CHC),soil field holding-water capacity(FHC),soil capillary porosity(CP),soil total porosity(Pt),and soil aeration(Ae)in the ZL all were the largest,while the SHC,CHC,FHC,in the L,and the CP,Pt,in the X and the Ae in X all were the smallest.Compared with CK,the X,L,SL all significantly reduced SHC,CHC,FHC.The ZL significantly increased CP,Pt compared with other forest shelterbelts and CK.All forest shelterbelts significantly increased Ae,and Ac in the ZL significantly increased compared with X and SL.The Z significantly improved soil non-capillary porosity(NCP)than CK and L.All type of shelterbelts significantly reduced soil moisture content(MCg),and the reduction in ZL was significantly greater than X but significantly less than L.Compared with CK,all forest shelterbelts significantly reduced soil pH,soil total organic carbon content(TOC),soil total nitrogen content(TN),soil total phosphorus content(TP).The X,L,ZL all significantly reduced soil nitrate-nitrogen content(NN),while Z significantly increased NN.The X,L,Z,SL all increased soil available phosphorus content(AK)significantly,and X increased most significantly.Compared with other types,X significantly reduced soil pH but significantly increased soil ammonium nitrogen content(AN).The X,L,SL all significantly reduce TOC compared with ZL.The L significantly increased soil available phosphorus content(AP),but significantly decreased TP.The Z or the SL significantly reduces AP.The ability of each type of shelterbelts to maintain soil microbial biomass carbon content(MBC)and soil microbial biomass nitrogen content(MBN)was X>Z>SL>ZL>L.(2)Six indexes of FHC,Ae,TOC,NN,AK,TK were included in MDS selected for soil quality evaluation of different types of shelterbelts.The SQI(soil quality index)of shelterbelts with different types was Z>ZL>SL>L>X.2.Changes in and evaluation of soil quality of Populus×xiaohei shelterbelts with different forest ages(1)With the increase of forest age,BD decreases first,then increases,then reaches the maximum in the mid-maturity forest,and then decreases gradually.The SHC,CHC,FHC,NCP,MCg changes in the same direction.The Ae continued to increase and reached the maximum in late maturity forest,and was significantly higher than CK in maturity forest and post-maturity forest.With the increase of forest age,shelterbelts significantly reduced soil pH,TOC,TN,TP,and increased AN and AK.The NN was significantly reduced at other forest ages except for the young forest.The change of AP at each forest age is relatively complex,which is significantly lower than CK in early maturity forest,and significantly higher than CK in late maturity forest and post-maturity forest.The MBC of the young forest did not change significantly,but the MBC of other forest ages significantly decreased compared with CK.The MBN was significantly reduced in the mid-maturity forest and post-maturity forests compared with CK,while MBN was significantly increased in young forests compared with other forest ages.(2)The MDS selected for soil quality evaluation of the Populus×xiaohei shelterbelts with different forest ages contained five indexes,i.e.FHC,Ae,NN,AN,TK.The SQI was ranked as X88>X84>X95>X99>X09>X03>CK.The Populus×xiaohei shelterbelts significantly improved the soil quality except for the mid-maturity forest.The SQI of each soil layer of the shelterbelt was higher than that of the control soil layer.The maximum of SQI in each soil layer generally appeared in maturity forest or post-maturity forest,and the minimum appeared in the young forest or mid-maturity forest.3.Changes in and evaluation of soil quality of Larix gmelinii shelterbelts with different forest ages(1)The Larix gmelinii shelterbelts with different forest ages increased BD and significantly reduced SHC,CHC,FHC.The NCP was significantly reduced in the early near-maturity forest compared with the late near-maturity forest.The CP and Pt were significantly reduced in the late near-maturity compared with other forest ages.Compared with CK,each forest age significantly reduced MCg,but significantly increased Ae,and the Ae of the young forest or the mid-maturity forest was significantly higher than the near-maturity forest.The soil pH,TOC,TN,TP were significantly reduced in all forest age shelterbelts,among which,the soil pH of young forests was significantly higher than that of other forest ages,the soil pH of the mid-maturity forest was significantly lower than that of the late near-maturity forest,and the TP of the early near-maturity forest was significantly higher than that of other forest ages.The AN,AP,AK were increased in each forest age,among which,the AN,AK were significantly increased in the late near-maturity forest compared with the near-maturity forest,and AP was significantly increased in the mid-maturity forest compared with other forest ages.The NN was significantly increased in the late near-maturity forest,while the TK was significantly increased in the young forest.The NMBC or MBN of each soil layer of the Larix gmelinii shelterbelts with different forest ages decreased significantly compared with CK.(2)The MDS selected for soil quality evaluation of the Larix gmelinii shelterbelts with different forest ages contained five indexes,i.e.SHC,NCP,MCg,NN,and AK.The SQI of the Larix gmelinii shelterbelts with different forest ages ranked as L99>L81>L92>L87>CK.Compared with CK,although SQI of Larix gmelinii shelterbelts have a slightly increased,it does not reach a significant degree.The SQI in the 0-20 cm soil layer of the Larix gmelinii shelterbelts was higher than that in the control,while the SQI in the 20-40 cm soil layer was lower than that in the control,and this difference reached a significant level in the late near-maturity forest.The maximum SQI in the 10-20 cm soil layer and the 40-60 cm soil layer appeared in the young forest,and the maximum SQI in the 0-10 cm and 20-40 cm soil layer appeared in the near-maturity forest L81 and L87,respectively.The minimum SQI of each soil layer appeared in deeper soil with the increase of forest age.4.Soil bacterial diversity and influencing factors of different type of shelterbelts(1)The soil bacterial communities varied among all types of shelterbelts.The dominant phyla in soil bacterial of all types of shelterbelts were Actinomycetes,Proteobacteria,Acidobacteria,Chlorobacteria,and Blastomycetes,but Actinomycetes showed the greatest variation in abundance among sites.The dominant genera in soil bacterial of all types of shelterbelts were Krasilnikovia,Rubrobacter,RB41,and the dominant genera were most widely distributed in Z.Actinoplanes and Krasilnikovia are the genera with the largest difference in the abundance of soil bacterial community in the shelterbelts of 0-10 cm soil layer and 10-20 cm soil layer respectively and are also the key genera for the construction of soil bacterial community in these two soil layers.The number of unique OTUs of soil bacteria was higher in the 0-10 cm soil layer than in the 10-20 cm soil layer,and in CK was higher than in the shelterbelts.The total number of OTUs in ZL is the largest.(2)Soil bacteria of different types of shelterbelts have different functions,such as carbon fixation,and the decomposition or assimilation of organic matters,nitrogen fixation or nitrogen assimilation,phosphorus solubilization,sulfate assimilation or dissimilation.Among them,the comprehensive potential of the bacteria gene function of the SL is strong,while the X is poor,and the ZL,Z,L are at a medium level.(3)The soil properties factors that have an important influence on the changes of the soil bacterial community in different soil layers of shelterbelt are different.In the 0-10 cm soil layer,these properties included AK,TN,Ae;while in 10-20 cm soil layer these properties included pH,AN,MCg,TOC.In conclusion,Different types of shelterbelts can differentially affect soil physicochemical properties and bacterial distributions and community composition;although the soil properties of the Populus×xiaohei or the Larix gmelinii(Rupr.)Kuzen.pure forest shelterbelts with different forest ages varied with the forest age,the comprehensive quality of the soil was improved;Considering the forest soil sustainable development,the Pinus sylvestris var.mongholica Litv.should be given priority in the pure forest model,as well as Pinus sylvestris var.mongholica Litv.mixed with Larix gmelinii(Rupr.)Kuzen in the mixed forest model;Afforestation tree species is an important factor driving variation in soil properties and soil bacterial communities,and changes in soil bacterial communities result from the interaction of tree species identity and soil properties.These studies can provide theoretical support for the selection and optimization of tree species constructing the farmland shelterbelts,the regulation and control of forest soil in farmland shelterbelts,and the selection and adjustment of farmland shelterbelts renewal mode in the research area.