Effects Of Reed Biochar On Soil Properties And Functions Of Ash Plantations In Xiong’an New Area

Reed（Phragmites australis）,a typical wetland plant,is an important cash crop in the Baiyang Lake,Xiong’an New Area,Hebei Province,it has become an endogenous pollutant in the Baiyang Lake area due to untimely harvesting.In this study,1%of reed biochar was added to the soil of Fraxinus chinensis plantation in a greenhouse incubation experiment,mixed well and incubated continuously at constant temperature and humidity,in order to explore the potential of comprehensive exploitation of reed.Soil physicochemical properties,enzyme activity,bacterial community characteristics and multifunctionality were analyzed on 30^th（T30）,60^th（T60）,120^th（T120）,180^th（T180）and 300^th（T300）days of incubation in order to clarify the effect of reed biochar addition on soil improvement in“the Forest of Xiong’an”.The main findings of the study are as follows.1.Soil p H decreased significantly on 30^th and 120^th days with the addition of reed biochar;biochar treatment significantly increased soil electrical conductivity by 15.15%～28.90%,indicating that biochar can increase the rate of soil ion exchange;biochar has some water retention capacity,but did not significantly change soil water content,and the water retention capacity decreased as biochar aged in the soil;the addition of biochar incubated soil ammonium nitrogen content significantly decreased on 30^th and 300^th days,and soil nitrate nitrogen content significantly decreased on 120^th day,indicating that biochar reduced the leaching and leaching of nitrogen,which was related to the adsorption effect of biochar;soil exo-β-1,4-glucanase activity significantly increased on 30^th day after biochar application,indicating that biochar could promote cellulose decomposition in soil in the short term;the addition of biochar had no significant effect on soil sucrase,β-glucosidase and dehydrogenase activities.2.Actinobacteria,Proteobacteria,Acidobacteria and Chloroflexi were the dominant bacterial phyla in ash plantation soils.Biochar application had a significant effect on the dominant bacterial phyla in the soil,with a significant decrease in the relative abundance of Actinobacteria at the middle(60^th and 120^th days)and late(180^th and 300^th days)of incubation,and a significant increase in the relative abundance of Gemmatimonadetes,Firmicutes,and Bacteroidetes.Biochar significantly increased the Shannon diversity of the soil bacterial community,and theβ-diversity of the soil bacterial community changed significantly at 120^thand 180^th days of incubation,indicating that biochar requires a certain action time to affect the structure of the soil bacterial community.3.Biochar application significantly increased soil cbb L and 16S r RNA gene copy numbers at 30th and 60th days;nif H,nir K and pqq C gene copy numbers at 60^th day;and nir K and cbb L gene copy numbers decreased significantly at 300^th day.It is shown that soil application of biochar promotes CO₂ fixation,nitrogen fixation,denitrification and inorganic phosphorus solubilization in the short term by increasing the abundance of the corresponding functional genes,increases bacterial biomass,promotes soil nutrient turnover and promotes soil carbon and nitrogen sequestration in the later stages.After 120^th day,biochar-induced changes in soil electrical conductivity were the primary influencing factor for altered soil bacterial community structure.Co-occurrence network analysis showed that biochar enhanced bacterial network complexity in the early and late periods of incubation.Biochar significantly altered the composition of keystone species in the co-occurrence network,increased the number of keystone species at 120^th and 180^th days,and enhanced network stability,indicating that biochar provides more complex organic matter to the soil bacterial community and enhances the interaction of soil bacteria.Bacterial keystone taxa were dominated by moderate taxa（91 OTUs,67.91%）,followed by conditionally abundant taxa（42 OTUs,31.34%）.Homogeneous dispersal dominated the bacterial community assembly process,and the bacterial community tended to converge throughout the incubation process,biochar did not significantly affect this process.Path modeling analysis showed that the effect of biochar on soil function was fluctuating,and the total effect of soil variables and bacterial network parameters on soil function was positive,while the total effect ofα-diversity on soil function was predominantly negative.In summary,this study used incubation experiment to clarify the effects of reed biochar on soil properties and functions in the ash tree plantation.The results showed that the impact of reed biochar on soil was mainly concentrated in the short term after its introduction,driving an increase in bacterial biomass,nutrient turnover rate,soil bacterial community diversity,and complexity and stability of soil bacterial co-occurrence networks,making it a good soil amendment.The findings of this study can promote the widespread application of reed biochar,which will contribute to the economic benefits of reed in the Baiyang Lake and the sustainable and healthy development of“the Forest of Xiong’an”.