Effect Of Biochars Prepared From Different Feedstocks And Pyrolysis Temperatures On The Structure And Function Of Microbial Communities In A Bamboo(Phyllostachys Praecox) Plantation Soil

Lei bamboo（Phyllostachys praecox）is an excellent bamboo species for shoots in South China,with early shoots and high economic value.Lei bamboo plantation has adopted management practices,such as winter mulch and heavy fertilization for a long time,resulting in several problems such as soil acidification,nutrient leaching and fertility decline in recent years.Biochar has been considered as a potential soil amendment,because it has abundanct alkaline components and highly porous structure,which can ameliorate soil acidity and provide suitable habitats for microorganisms.However,the amelioration effect of biochar on soil acidification,nutrient and microbial functional status may vary depending on the properties of biochar,among which feedstock and pyrolysis temperature are two important factors.Clarifying the influence of biochar prepared from different feedstocks and pyrolysis temperatures on soil acidity,nutrients,soil enzyme activity,microbial community composition and nutrient utilization status in the bamboo forest,can improve the utilization of soil nutrients,bamboo forest productivity and carbon sequestration.Therefore,this study prepared three biochars from corn straw（CB）,bamboo（BB）and peel of Carya cathayensis（PB）,and also pyrolyzed the peel of Carya cathayensis at 350℃（B350）,500℃（B500）,700℃（B700）to produced three biochars differing in pyrolysis temperatures.By collecting the soil from a typical Lei bamboo forest,two pot experiments were performed（the first experiment was set up with 4 treatments:control,2%（mass ratio）CB,2%BB,2%PB;the second experiment was set up with 5 treatments:control,2%（mass ratio）peel of Carya cathayensis（B0）,2%B350,2%B500,2%B700）.Changes in soil physical and chemical properties,microbial community structure,enzyme activity and its ecological stoichiometric characteristics,and microbial C source metabolic function were determined three months after biochar incorporation.The main results are as follows:（1）Biochar prepared from different feedstocks reduced the soil acidity and improved the soil quality and fertility of the bamboo plantation,but their effectiveness varied with the feedstocks.Compared with the control,corn stalk charcoal（CB）and peel of Carya cathayensis derived biochar（PB）significantly increased soil p H（P<0.05）,while bamboo biochar（BB）did not change it significantly.CB and PB treatments significantly（P<0.05）reduced soil exchangeable H⁺,Al³⁺and exchangeable acid content;while BB only significantly reduced soil exchangeable H⁺content.The application of biochar increased soil microbial biomass and enhanced soil enzyme activity.CB and PB significantly（P<0.05）increased the total concentrations of soil phospholipid fatty acids（PLFAs）（increased by 52.84%and58.21%）,gram-positive bacteria（G⁺）（by 45.52%and 57.77%）,and gram-negative bacteria（G^-）（by54.04%and 51.57%）,actinomycetes（by 53.21%and 52.45%）and fungi（by 65.07%and 75.37%）,while bamboo biochar（BB）had no significant effect on them.The activities of soilα-glucosidase,cellobiohydrolase,N-acetyl-β-glucosaminidase,phosphatase and dehydrogenase were significantly enhanced by PB amendment（P<0.05）by 139%,82%,56%,22%and 103%,respectively.The application of CB and BB did not significantly affect soil enzyme activities.The three biochars significantly increased soil basal respiration and the substrate-induced respiration rates（P<0.05）,with PB treatment had a higher rate than that of CB and BB（P<0.05）.（2）Biochars prepared at different pyrolysis temperatures had different effects on soil acidification amelioration,and changed soil enzyme activities and stoichiometric characteristics and microbial nutrient utilization efficiency.The biochars prepared at the three temperatures significantly increased soil p H（P<0.05）,reduced the exchangeable H⁺,exchangeable Al³⁺and exchangeable acid contents.Moreover,B700 and B500 treatments had greater amelioration effect than that of the B350 treatment.B500 and B700 significantly（P<0.05）increased total soil nitrogen（TN）and soluble nitrogen（DN）contents,while reduced the dissolved organic carbon（DOC）content.Only B350 treatment significantly increased the microbial biomass carbon（MBC）,microbial biomass nitrogen（MBN）and total PLFAs by32%,43%,and 56%,respectively.With increasing of the pyrolysis temperature of biochar,the ratio of soil C/N acquiring enzyme activities gradually increased（P<0.05）.The results of threshold elemental ratio(TER_C:N)and substrate-induced respiration showed that the soil microorganisms under the treatment of B0 were mainly limited by N,while those under the treatment of B500 and B700 were mainly limited by C.Compared with the B350 treatment,the B500 and B700 treatments havd higher microbial carbon use efficiency（CUE）but lower microbial nitrogen use efficiency（NUE）.Structural equation model analysis showed that biochar prepared at different pyrolysis temperatures affected CUE through affecting the C:N imbalance between carbon and nitrogen availability and microorganisms;whereas biochar affected NUE by affecting soil p H and the ratio of fungi to bacteria.Biochar prepared at high temperature strengthened soil microbial C limitation,but weakened microbial N limitation.In summary,our study suggested that biochar addition can reduce soil acidity,improve soil fertility,microbial abundance and activity,but their effects vary depending on the feedstock and pyrolysis temperature.Therefore,a reasonable selection of feedstock and pyrolysis temperature for preparing biochar can not only promote soil acidification remendiation,but also have important significance for regulating the efficiency of soil microbial nutrient utilization and enhancing soil carbon sequestration.