Effect Of UV-B On Labile Organic Carbon And Enzyme Activity In Black Soil

Black soil is a valuable natural resource and is known for its high fertility.The northeastern black soil area is one of the main grain producing areas in my country,with a large area of black soil,which is the soil with the highest organic matter content.Soil degradation is the result of a combination of human and natural factors.The thickness of the black soil layer decreases by an average of 0.3～2mm per year,and the fertility and quality are also threatened.UV radiation is one of the natural factors that lead to soil degradation.Ultraviolet radiation includes UV-A,UV-B and UV-C bands,of which UV-B radiation is the most destructive.The thinning of the ozone layer in the stratosphere leads to the increase of UV-B radiation reaching the surface,which directly or indirectly affects the input and output of carbon and nitrogen in the soil ecosystem,and also causes changes in soil enzyme activities.In this paper,natural black soil was taken as the research object,and culture experiments were used to simulate UV-B radiation treatment to study the changes of soil respiration（RS）,soil labile organic carbon,soil inorganic nitrogen and related soil enzyme activities.The protection effect of soil provides a theoretical basis for the mechanism of black soil degradation.This experiment was carried out in a constant temperature incubator.The radiation intensity of medium-wavelength ultraviolet light（UV-B）was about 1.50W·m^-2.The dark+25%soil water content（D+W1）was set as the control,and the medium-wavelength ultraviolet light was irradiated+25%soil water content（UV-B+W1）,medium wavelength ultraviolet light irradiation+50%soil water content（UV-B+W2）,3 treatments,the irradiation time was 7d,14d,21d and 28d,3 times Repeat;in addition,the carbon level of UV-B irradiation and biochar treatment（Bc+UV-B）was set to(5.98 g·kg^-1),and the addition of biochar without irradiation was used as a control,and the irradiation time was 21d,and repeated 3 times.The results of the study are as follows:（1）RS was significantly affected by UV-B radiation,and the RS of UV-B+W1 treatment was lower than that of D+W1 treatment.Compared with UV-B+W2 treatment,the RS was basically the same,and the difference was not significant（P>0.05）.RS increased significantly before all treatments at 7d,and stabilized after 21d.The maximum value was 968mg·kg^-1under 28d dark treatment.（2）The content of dissolved organic carbon（DOC）in soil treated with UV-B radiation increased significantly,and the content of DOC in UV-B+W1 treatment was the highest（28d）,which increased by 156.1 mg·kg^-1.The contents of soil organic carbon（SOC）,soil oxidizable organic carbon（ROOC）and soil microbial biomass carbon（MBC）decreased by 9.0%,27.5%and10.3%,respectively.（3）UV-B radiation treatment had a significant effect on soil inorganic nitrogen（NH₄⁺-N,NO₃^--N）content.With the extension of radiation time,the soil NH₄⁺-N content decreased significantly,while the soil NO₃^--N content increased significantly.The soil NH₄⁺-N,NO₃^--N content showed different trends in different water treatments.Compared with W2,the soil NH₄⁺-N content in W1 treatment was higher and the soil NO₃^--N content was lower.With the extension of radiation days,all treatments showed a continuous decrease in soil NH₄⁺-N content,with a maximum decrease of 91.0%.The content of soil NO₃^--N continued to increase,with a maximum increase of 129.2%.（4）Compared with dark treatment,soil enzyme activity decreased under UV-B radiation,in which soilβ-glucosidase activity was significantly different,while other enzyme activities were not significant.Compared with UV-B+W1 treatment,soil sucrase activity,soil cellulase activity and soilβ-glucosidase activity of UV-B+W2 treatment showed an increasing trend,while soil urease activity showed a downward trend.Soil sucrase decreased at most 4.0 mg·g^-1·d^-1,soil cellulase decreased at most 26.5 mg·g^-1·d^-1,soilβ-glucosidase decreased at most 2.4 mol·h^-1·kg^-1,and soil urease decreased at most 4.8%.（5）The addition of biochar could inhibit the effect of UV-B radiation on soil labile organic carbon,and the decrease of soil organic carbon content was lower than that without biochar addition.The addition of biochar did not significantly increase the contents of soil dissolved organic carbon,soil oxidizable organic carbon and soil microbial biomass carbon,but significantly increased soil organic carbon.In summary,UV-B radiation can change the labile organic carbon content,NH₄⁺-N,NO₃^--N conversion and soil enzyme activities in black soil;after biochar addition,it can inhibit the decrease of soil organic carbon content under UV-B radiation.The effects of UV-B radiation on soils were attenuated by the addition of biochar.The purpose of black soil protection can be achieved by adding biochar.