Response Of Soil Respiration To Biomass Charcoal Addition And Its Mechanism In Sargassum Pine Plantation Forest

Pinus massoniana is a fast-growing afforestation species widely distributed in subtropical regions,with strong carbon sequestration capacity,and plays an important role as a carbon sink in the overall strategic objective of "double carbon".However,soil respiration rate is one of the important factors affecting the final carbon sink intensity of the ecosystem,and how to effectively reduce soil respiration rate and carbon emission is the core of further enhancing the carbon sequestration capacity of Sargassum pine plantation.Biomass carbon is an excellent soil conditioner,because of its high stability,large specific surface area,rich porosity and strong adsorption,it can not only improve soil fertility and soil environment,but also directly or indirectly affect soil respiration rate by changing soil physical and chemical properties,enzyme activity,microbial community structure,etc.It plays an important role in enhancing the carbon sequestration capacity of soil and ecosystem.It plays an important role in enhancing the carbon sequestration capacity of soil and ecosystem.In this study,three different treatments were set up in the plantation of Horsetail pine at the Forest Ecology Station of Central South University of Forestry and Technology:control(CK),no biomass charcoal added;treatment 1(B1),biomass charcoal added at 500 g-1·m-2;and treatment 2(B2),biomass charcoal added at 1500 g-1·m-2,and a one-year localization study was conducted.During this period,four soil samples were collected in December 2021,March,June and September 2022,and were used to analyze the differences in soil physicochemical properties,enzyme activity and microbial community structure under different biomass charcoal treatments in order to explore the process of the effect of different biomass charcoal treatments on soil respiration.The main findings of this paper are as follows:(1)Soil respiration in the plantation forest of Sargassum pine had obvious seasonal dynamic changes,showing a single-peaked curve trend,with its maximum value in July to August and minimum value in January to February.The annual average rate of soil respiration showed B2>CK>B1.Compared with the CK treatment,the annual average rate of soil respiration decreased by 6.07%under B1 treatment and increased by 1.53%under B2 treatment,but there was no significant difference between the treatments(p>0.05).(2)Under different treatment conditions,B1 and B2 treatments significantly increased soil water content(SWC),pH,and significantly increased soil total nitrogen(TN),organic carbon(SOC),fast-acting phosphorus(AP),fast-acting potassium(AK),soluble organic carbon(DOC),and microbial mass carbon(MBC)contents,and soil pH,soil water content(SWC),fast-acting phosphorus(AP),and fast-acting potassium(AK)were significantly correlated with the amount of biomass charcoal added.(3)Biomass charcoal addition significantly increased soil sucrase(INV),urease(UR),and acid phosphatase(ACP)activities,with 25.8%,33.4%,and 17.5%increase in soil enzyme activities under B2 treatment,respectively.While catalase(CAT)activity was decreased under B1 and B2 treatments and the difference between treatments was not significant(p>0.05).(4)Biomass charcoal addition increased soil microbial abundance,in which bacteria changed bacterial community composition at the phylum,genus,and OTU taxonomic levels.The dominant bacterial phyla were Proteobacteria,Acidobacteria,Actinobacteria,and Chloroflexi,and the B1 and B2 treatments increased the relative abundance of Chloroflexi and decreased the abundance of Proteobacteria and Acidobacteria.Proteobacteria and Acidobacteria.(5)The dominant phyla of soil fungi were Basidiomycota,Ascomycota and Mortierellomycota,and the relative abundance of Basidiomycota was reduced under B1 and B2 treatments,while the other dominant phyla did not change significantly.(6)Soil respiration was highly significantly and exponentially correlated with soil temperature under different treatments(p<0.01),and temperature sensitivity(Q10)was significantly reduced under B1 treatment compared with CK treatment and B2 treatment(p<0.05),and there was no significant correlation with soil water content(SWC);soil respiration was significantly correlated with soil acid phosphatase(ACP),total nitrogen(TN),fast-acting potassium(AK),and soluble organic carbon(SOC)under different treatments.AK),soluble organic carbon(DOC),and microbial mass carbon(MBC)under different treatments,but there was no significant correlation between soil respiration rate and soil bacterial and fungal communities under different treatments.In summary,the soil environmental factors were significantly changed under different biomass charcoal treatments.This study found that B1 treatment could reduce soil respiration rate,improve soil carbon source utilization,and enhance soil carbon sequestration capacity,which is conducive to reducing soil CO2 emissions and providing theoretical basis and data support for the early achievement of the "double carbon" goal.