Effects Of Prescribed Burning On The Spatio-temporal Heterogeneity Of Soil Stoichiometry In Three Plantations

Carbon(C),nitrogen(N)and phosphorus(P)elements are the core of nutrient cycling and transformation in forest ecosystems,regulating and driving the growth of forest ecosystem vegetation,community structure and underground soil processes.With global climate change,extreme climates event increase,and global wildfires occur frequently,profoundly changing global forest fire patterns.Prescribed burning as a means of cleaning up combustibles in the forest and effectively reducing the risk of fire has attracted more and more attention.Prescribed burning will change the stoichiometry of elements in the ecosystem,reflecting the changes in the pattern ofbiogeochemical cycles after the prescribed burning.Therefore,a better understanding of the impact of prescribed burning on the biogeochemical cycle plays an important role in understanding the nutrient cycle and impact mechanism of forest ecosystems,and predicting the structure,function and stability of ecosystems under the background of climate change.To this end,the Larix gmelinii forest,Pinus koraiensis forest and Quercus mongolica forest of Hongqi Forest Farm in Hegang City,Heilongjiang Province were taken as the research objects.The prescribed burning was carried out in early November 2018.Soil samples were taken at different times after the prescribed burning,and laboratory experiments were performed to analyze the three plantations in different periods after the prescribed burning.The dynamic changes of soil stoichiometry in time and space,quantitatively discuss the influence mechanism of the time and space changes of soil stoichiometry,and provide basic data and theoretical basis for the rationality of the implementation of prescribed burning in the temperate forest ecosystem in the Northeast China.The main results are as follows:(1)The content of organic carbon(SOC),total nitrogen(TN),and total phosphorus(TP)in the upper and lower soil layers of the three plantations control plots and the prescribed burning plots were significantly different between sampling times(p<0.05).Within a short period of time after the prescribed burning(24h),the TN and SOC contents of the 0?10 cm soil of the three plantations were significantly higher than the control,and the TP contents were not significantly different from the control.One year after the prescribed burning,compared with the control,the SOC contents of the upper and lower soils of the three plantations had no significant difference,the soil TN and TP content of Pinus koraiensis forest and Quercus mongolica forest had no significant difference compared with the control plots,the contents of TN and TP in the soil of the Larix gmelinii forest showed a significant decrease.24h after the prescribed burning,the soil C:N of the upper layer of the Larix gmelinii forest and the Pinus koraiensis forest were significantly lower than that of the control plots,and the soil C:N of the Quercus mongolica forest was significantly higher than that of the control.With the increase of the recovery time after the prescribed burning,the C:N of the three plantations recovered to the level before the prescribed burning.The C:P of the upper soil of the Pinus koraiensis forest was significantly greater than the control 5 months after the prescribed burning.Prescribed burning had no significant effect on the soil N:P of the three plantations.The variance decomposition showed that the interaction of prescribed burning,sampling time,and forest type were the main factors explaining the variation of soil C:N,C:P,and N:P.(2)Pre-prescribed burning,the C/(C0+C)of SOC and TN content of Larix gmelinii forest,Pinus koraiensis forest,and Quercus mongolica forest were all greater than 0.75,showing strong spatial heterogeneity,and the ranges of variation were small,ranging from 1.86 to 2.07 m and 1.44 to 1.71 m.With the recovery of time after the prescribed burning,the spatial heterogeneity of the SOC and TN content of the three plantations decreased to varying degrees,especially the SOC content of the Quercus mongolica forest and the TN content of the Larix gmelinii forest one year after the prescribed burning,which C/(C0+C)was between 0.25 and 0.75,showing moderate spatial heterogeneity.One year after the prescribed burning,the C/(C0+C)of soil TP contents in the Larix gmelinii forest,Pinus koraiensis forest and Quercus mongolica forest were greater than 0.75,showing strong spatial heterogeneity and the spatial distributions of TP content were mainly affected by structural factors.The spatial heterogeneity of soil C:N and N:P in the Quercus mongolica forest increased within a short time after the prescribed burning(24h).As the recovery time after the prescribed burning increased,the soil stoichiometry of the forest tended to be homogeneous again.Soil pH was the most important factor affecting the spatial distribution of soil C:P and N:P in Larix gmelinii forest one year after the prescribed burning.In addition,topographical factors were the most important factor in the spatial variability of soil N:P after the prescribed burning of Pinus koraiensis forest.