| Carex siderosticta Hance,a genus of Carex in the Salicaceae family.It has a wide range of temperature adaptation and is suitable for planting in both the north and south of China,and is a good garden ground cover plant that can be widely used in soil and water conservation and urban landscaping construction.Soil freezing and thawing is a phenomenon in which the soil layer alternates between freezing and melting due to periodic changes in atmospheric temperature,and is particularly pronounced in the north-east.The freeze-thaw cycle directly or indirectly affects the growth and development of Carex siderosticta Hance through its influence on soil nutrients,enzyme activities and microbial community structure,so we studied the physiological characteristics of soil and plants in the rhizosphere of Carex siderosticta Hance cycle.In this paper,by measuring organic carbon,alkali-hydrolyzable nitrogen,available phosphorus,sucrase,catalase,urease,fibrinodisase and bacterial microbial community structure in soil,the response of freeze-thaw in situ-to-situ soil in spring,summer,autumn and winter to soil physicochemical and enzyme activity and microbial community structure was discussed,and the rhizosphere soil of Carex siderosticta Hance was summarized by measuring the amplitude of freeze-thaw temperature difference of-5℃～10℃ and-3℃～2 ℃ and the four cycles of 2,4,8 and 10 in combination with indoor simulation,root configuration,leaf physiology and root physiology response mechanism to freeze-thaw cycle,the results are as follows:(1)The contents of organic carbon,alkali-hydrolyzed nitrogen and available phosphorus in the field were higher than those in deep soil,and the seasonal organic carbon showed an upward trend and increased significantly during the thaw-complete freezing period(P < 0.05).Alkaline hydrolyzable nitrogen was characterized by first decreasing and then increasing.The soil available phosphorus content first increased and then decreased,and the minimum available phosphorus value in the soil during the thawing period was only 0.03 mg/kg.The enzyme activities of surface soil were higher than those in deep soil,and the activities of urease and sucrase in quaternary soil decreased first and then increased,and the thawing period reached the minimum value,which was 1.55 mg/g and 1.91 mg/g,respectively.Catalase showed an upward trend,and the increase was gradually increasing,and the largest increase was in the complete thawing-thawing period.Fibrinosidase first rises and then falls,and the thawing period reaches a maximum,which can reach 18.7 mg/g.The relative abundance of bacteria in the four seasons were all actinomycetes,proteobacteria,and acidobacteriacetes as the dominant phylums,which accounted for more than 63.13% of the bacterial sequence,and the three dominant phylums accounted for the highest proportion in the treatment group during the freeze-thaw period,reaching 81.86%,and the lowest proportion in the complete freezing period,only 69.17%.(2)In the simulation experiments,the contents of soil organic carbon and alkaline hydrolyzable nitrogen reached the maximum values of 82.94 g/kg and 19.2 mg/kg in the second freeze-thaw cycle,respectively,and reached the minimum values of 56.8 g/kg and 5.91mg/kg,respectively,in addition,the content of the sample group with large temperature difference was always higher than that of the sample group with small temperature range.During the change of enzyme activity,most enzyme activities peak at the 2nd-4th freeze-thaw cycle and then decrease significantly(P < 0.05).The activities of soil fibrinodisase and sucrase were significantly higher than those of the control(P < 0.05)in the second freeze-thaw cycle,and peaked at 8.34 mg/g in the fourth freeze-thaw cycle in the small temperature difference amplitude treatment.The four dominant phylums of bacterial community structure were:Proteobacteria,Firmicutes,Actinomycetes,and Acidobacillus,accounting for 41.79%～54.95,6.02%～24.54%,6.06%～16.21%,3.24%～15.50% of the flora,and the four dominant bacteria accounted for 79.52%～85.34% of the total flora,among which,the 10 th freeze-thaw cycle treatment group accounted for the highest proportion,accounting for 85.34%,and the 4th treatment group with small temperature difference amplitude cycle accounted for the least.79.52%.(3)The results of FTC on the root configuration of Carex siderosticta Hance showed that with the increase of freeze-thaw cycle frequency,the total root length of the root system increased first and then decreased,and the freeze-thaw cycle treatment group reached a maximum at the 4th freeze-thaw cycle,and the peak between the small temperature difference treatment group and the control group reached 763 cm at the 8th freeze-thaw cycle,and the root length was significantly better than that in the small temperature difference amplitude treatment group(P < 0.05),but the total surface area and total volume changes of Carex siderosticta Hance were not significant.The average root diameter and number of apex peaked at the 8th freeze-thaw cycle,about 0.6 mm and 6390.The number of root bifurcations increased significantly at the 4th and 10 th cycles(P < 0.05),and peaked at the 10 th freeze-thaw cycle,with the number of bifurcations being 4724.The small temperature difference amplitude treatment group also reached a maximum at cycle 10 with a bifurcation number of 8325.(4)The response of physiological indexes of Carex siderosticta Hance to freeze-thaw cycle showed that the contents of malondialdehyde and soluble sugar were significantly higher than those in other treatment groups(P < 0.05)in the 4th and 8th temperature difference treatment groups,and the soluble sugar content gradually increased under freeze-thaw cycle treatment,and peaked at 91.82 μmol/g in the 8th cycle.The content of proline first increased and then decreased,and its peak value was 1.015 μmol/g at the 8th cycle,and the small temperature difference amplitude treatment was smaller than the large temperature difference amplitude.In the leaves of Carex siderosticta Hance,the content of malondialdehyde increased significantly in the 8th and 10 th cycles(P < 0.05).The proline content reaches its minimum at cycle 10.The soluble sugar content peaked at 774.89 μmol/g on cycle 8.Root antioxidant enzyme activity peaked at cycles 8-10.Among them,SOD,POD and CAT all reached their maximum values at the 10 th cycle,which were 1.21 U/mg,0.86 U/mg and 1.07 U/mg,respectively.In summary,seasonal freeze-thaw changes during the winter freeze will reduce bacterial abundance and activity,causing microbial lysis and the release of small molecules such as released amino acids and sugars into soil organic matter that can be directly absorbed and used by plants,while during the spring thaw bacterial abundance and activity rebound,the dominant phylum’s percentage increases,the number of freeze-thaw cycles and the magnitude of temperature difference will have a continuous decrease in soil C flux and soluble phosphorus,more The effective substrate was used by microorganisms and plant roots,while at the 4th freeze-thaw cycle almost all nutrients were at the minimum,indicating that microorganisms and plant roots were more adequate at the 4th cycle,while in the process of enzyme activity change,the small temperature difference treatment activity was higher than the large temperature difference treatment and overall lower than the control,indicating that the smaller freeze-thaw temperature difference had less effect on soil enzyme activity than the large temperature difference,in addition In addition,the enzyme activity peaked at the second freeze-thaw cycle in the large temperature difference treatment and at the fourth freeze-thaw cycle in the small temperature difference treatment,indicating that reducing the freeze-thaw temperature difference delayed the peak of the enzyme activity.Freezing and thawing increased the number of root tips and forks in the broadleaf carex root system,promoting root bifurcation and stimulating the production of secondary and tertiary lateral roots.The effects of freezing and thawing on the physiology of Carex siderosticta Hance were more direct in the leaves,with peak osmoregulatory substances and antioxidant enzyme activities occurring almost exclusively at the eighth cycle. |
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