Characteristics Of Soil Microbial Biomass Carbon,nitrogen And Phosphorus In Burned Area Of Larix Gmelini Forest

Forest fire was an important disturbance factor of forest ecosystem,which significantly affected the activity and function of soil microorganisms in burned areas.Compared with other soil physical and chemical properties,Soil Microbial Biomass Carbon(MBC),Nitrogen(MBN)and Phosphorus(MBP)were more susceptible to fire disturbance,and Soil Dissolved Organic Carbon(DOC),Dissolved Nitrogen(DN)and Available Phosphorus(AP)were the most easily used nutrients by soil microorganisms.DOC,DN and AP and MBC,MBN and MBP would change synergistically with the recovery time after fire.Therefore,this paper aims to understand the characteristics of DOC,DN and AP and MBC,MBN and MBP in the burned area of Larix gmelinii forest in a long-time scale,and explore the recovery mechanism of soil microorganisms in the burned area,so as to provide reference for further understanding the ecological recovery mechanism in the burned area.In order to explore the effect of forest fire on MBC,MBN and MBP,as well as the effect of DOC,DN and AP on MBC,MBN and MBP under the background of fire disturbance,this study selected the burned area in Tahe area of Daxinganling Mountains from 1990 to 2018 as the experimental sample,and selected the nearby unburned area as the control sample.Using the research method of “space for time”,80 samples were set up,and the surface soil was 0 –10 cm.At the same time,the altitude,slope gradient,slope aspect and slope position information of each sample were collected,and the site conditions of each burned area were at a small spatial scale.Finally,the variation of MBC,MBN and MBP indexes under the effect of recovery time and topographic factors in the burned area was measured and analyzed.The main research results are as follows:(1)Importance of fire disturbance and topography to DOC,DN and APForest fire and topography significantly changed the contents of DOC,DN and AP.The recovery time after fire significantly affected the contents of DOC,DN and AP;The contents of DOC,DN and AP at mid-altitude B in T2 period were significantly higher than those at altitude A;compared with the T4 period,the contents of DOC and AP were significantly different in the T1,T2 and T3 periods of P1 slope,while there was no significant difference in the P2 slope;The contents of DOC and AP in the south slope were significantly higher than those in other slope aspects during T3,and there was no significant difference in DOC among the four slope aspects during T4;DOC and DN contents in T1 period were relatively lower than those in other slope positions,while AP contents in T2 period were relatively lower.(2)The importance of fire disturbance and topography on MBC,MBN and MBPThe contents of MBC,MBN and MBP decreased in T1 and T2,and increased in T3;At T1,the contents of MBC and MBN at altitude A were significantly higher than those at altitude B,but the difference of MBP content was not significant.At T2 and T3,the contents of MBC and MBN between the two groups were not significantly different,but the difference of MBP content was significant.The content of MBC,MBN and MBP in T3 period of P1 slope and P2 slope was still lower than that in T4 period,but in P3 slope,only the content of MBN in T3 period was still lower than that in T4 period,and the content of MBC and MBP in T3 period was higher than that in T4 period.MBC and MBN contents in the west slope were significantly higher than those in the east slope and the south slope during T1 period.At the downhill position,there was no significant difference in MBC content between T1,T2 and T3 periods and T4 periods.(3)Effects of fire disturbance,topography and DOC,DN and AP on MBC,MBN and MBPThe changes of DOC and MBC were similar.The content of DOC and MBC decreased at T2 and increased at T3 after fire.The content of DN was significantly different at T1 after fire.The content of MBN was significantly different at T2 and T3.The content of AP and MBP was significantly different at T1 and T2,T2 and T3.During T1,T2 and T3,when the difference of DOC content between the two groups was significant,the difference of MBC content was not significant,while when the difference of DOC content between the two groups was not significant,the difference of MBC content was significant.MBC,MBN and MBP had no significant difference at P3 slope,while the content of DOC 、 DN 、 AP had significant difference at P3 slope;The contents of DOC and MBC in the southern slope were significantly higher than those in other slope aspects at T3.At T1,the trend of AP and MBP was opposite.The content of AP in the eastern slope and the western slope was significantly higher than that in the southern slope,while the content of MBP in the southern slope was significantly higher than that in the eastern slope and the western slope.There was no significant difference in AP in each slope aspect at T2,but there was significant difference in MBP between the eastern slope and the western slope.Compared with AP,the content of MBP was more sensitive to the recovery time after fire.The interaction between slope aspect and fire duration had significant effects on DOC,AP,MBC,MBN and MBP.The results of structural equation model show that the recovery time after fire can indirectly affect MBC and MBN by affecting DN,slope position can indirectly affect MBN by affecting DN,AP can indirectly affect MBP,altitude can indirectly affect MBP by affecting DOC.The influence of fire on soil microorganisms was relatively persistent.With the restoration of fire sites,the influence of topographic factors on DOC,DN,AP,MBC,MBN and MBP began to deepen.The north-south slope direction was of great significance to the restoration of fire sites of Larix gmelinii forest in Daxinganling Mountains.The soil microorganisms in the south slope are more active than those in the north slope,and the south slope can recover to the pre-fire level faster than the north slope.