Effects Of Fire Disturbance On The Soil Properties And C/N/P Stoichiometry In The Boreal Forest Of Great Xing'an Mountains

Forest fire is an important natural disturbance that regulates quantity and heterogeneity of soil nutrients in boreal forests.The effects of fire on soil C,N and P pool is different,and the recovery of each element is not synchronized,and hence soil stoichiometry may greatly change during the post-fire early succession,which may affect the biogeochemical processes and the vegetation regeneration after fire.To clarify the mechanisms of fire effects on soil C/N/P stoichiometry in the Great Xing'an Mountains,the proposed research was set to systematically study the relationship between the controlling factors(e.g.,fire severity,topography,time since the fire(TSLF),post-fire soil environments,litter)and soil C/N/P stoichiometry using field investigation,laboratory analysis and statistical model methods.The goal of this research was to examine effects of fire on soil C/N/P stoichiometry,and to unravel the key driving factors.This research has got the following results:1)Forest fire and topography significantly affected physical,chemical and biological soil properties.One year after the fire,soil water content(SWC),dissolved organic carbon(DOC),soil microbial biomass(SMB)and bacterial diversity significantly decreased;while soil pH,dissolved organic nitrogen(DON)and available phosphorus greatly increased.And forest fire exerted no significant effects on other soil property indicators.Eleven years after the fire,SMB,DON and available potassium were significantly lower relative to the control,and other soil indicators had recovered to pre-fire levels.In the control site,north-facing slope soils had higher SWC,and lower pH,DOC and DON relative to the south-facing slopes.In the burned site,there was no significant difference between the two slopes,except for SWC in the 11-year-post-fire site.In the 1-year-post-fire site,there were greater changes in soil properties on the north-facing slopes.In the control site,most soil properties were related to the aspect,slope and elevation.However,in the 1-year-post-fire site,the relationship between soil properties and topographic factors became weaker,and eleven years after the fire,the relationship became stronger.2)There was no significant difference in litter TC and TN between the burned and control sites.However,in the 5-year-post-fire site,litter TP significantly decreased by 48 % relative to the control and still was significantly low relative to thecontrol 16 years after the fire.In the 5-year-post-fire site,organic soil TC and TN were not significantly different relative to the control.Sixteen years after the fire,TC in the organic soils significantly increased by 38 %,but was not different with the control;organic soil TN significantly increased by 59 % and was higher than the control;while organic soil TP significantly decreased to the control level.Forest fire showed no effects on the mineral soil TC and TN and significantly increased its TP and even to the 16 years post fire.In the control site,there were close relationships between TC,TN and TP in the mineral soils and those in the litter.In the5-year-post-fire site,there were close relationships between TC,TN and TP in the mineral soils and those in the organic soils.In the 16-year-post-fire site,there were close relationships between TC,TN and TP among the litter,mineral and organic soils.3)Forest fire significantly affected litter and organic soil C/N/P stoichiometry.Five years after the fire,litter C/P and N/P ratios significantly increased and then recovered to the control level 16 years after the fire.There was no significant difference in litter C/N ratios between the control and 5-year-post-fire sites,while litter C/N ratios in the 16-year-post-fire site were significantly higher than in the control.In the 5-year-post-fire site,organic soil C/N ratios were significantly higher relative to the control.In the 16-year-post-fire site,organic soil C/N ratios recovered to the control level,but its C/P and N/P ratios were still higher relative to the control.Forest fire lessened the relationship between C/N/P stoichiometry of organic soils and litter,and decreased the correlation numbers between the C/N/P stoichiometry of litter and organic soils and soil properties.Fire severity,topography,TSLF and soil environments explained more than 60 % of the total variance for litter stoichiometry and more than 40 % for organic soil stoichiometry.TSLF and topography were the more important factors affecting litter stoichiometry,while TSLF was the most important factor affecting organic soil stoichiometry.