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Effects Of Fire Disturbance On Dahurian Larch Forest Soil Nitrogen Availability In Da Xing'an Mountains,China

Posted on:2019-07-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:T X HuFull Text:PDF
GTID:1360330548974175Subject:Forest fire prevention
Abstract/Summary:PDF Full Text Request
The Da Xing'an Mountians area is the main distribution area of boreal forest ecosystem of China,and it is also a frequent forest fires occurrence area in China.Nitrogen is one of the most important nutrient element that limits the boreal forest ecosystem,it plays an important role in maintaining the climax community stability of forest ecosystem and maintaining the proportion of three species in forest ecosystem.Study the effects of fire disturbance on soil nitrogen availability and its post-fire change pattern in forest ecosystem has great important ecological significance for revealing the succession process of post-fire forest ecosystem and the restoration mechanism of post-fire forest ecosystem.This study selected the typical forest(Larix gmelinii)ecosystem of Da Xing'an Mountians to carry out research.In this study,the effects of different years(3 year,9 year,28 year)post-fire and different restoration types(nature restoration,afforestation)on 0-10cm and 10-20cm soil microbial nitrogen immobilization and transformation,and the mineralization rate of soil organic nitrogen were systematically studied by in situ incubation method in severe burned plots.In addition,the change pattern of soil nitrogen mineralization rate in short-term after fire disturbance was investigated under laboratory incubation condition.The results of this study will provide the data foundation for quantification the change of the regional nitrogen cycling after fire disturbance,and that will provide a scientific basis for improving the productivity and biodiversity of boreal forest ecosystem,strengthening post-fire forest ecosystem management and establishing post-fire forest ecosystem restoration strategies.The main results are as follows:(1)Study on the post-fire change pattern of soil microbial biomass nitrogen found that 0-10cm soil microbial biomass nitrogen did not significantly changed after 3 years fire disturbance,0-10cm soil microbial biomass nitrogen significantly decreased from 3 years to 9 years after fire disturbance,0-10cm soil microbial biomass nitrogen almost returned to pre-fire level after 28 years fire disturbance.10-20cm soil microbial biomass nitrogen significantly increased after 3 years fire disturbance,10-20cm soil microbial biomass nitrogen almost return to pre-fire level from 9 to 28 years after fire disturbance.Compared with the control plots,the mean value of 0-10cm and 10-20cm soil microbial biomass C/N in different years post-fire plots were much smaller and more stable.0-10cm soil microbial biomass nitrogen had no significant correlation with soil net mineralization rate in 3 years post-fire plots,while 0-10cm soil microbial biomass nitrogen had significantly positive relationship with soil mineralization rate in 9 and 28 years post-fire plots,and the determination coefficient of regression in post-fire plots was higher than that in corresponding control plots,which range from 0.48 to 0.51.The main impact factors of soil microbial biomass nitrogen in different years post-fire plots were different.pH was the main impact factor of 0-10cm soil microbial biomass nitrogen in 3 years post-fire plots,soil water content and soil available phosphorus were the main impact factors of 0-10cm soil microbial biomass nitrogen in 9 years post-fire plots,soil available phosphorus and available potassium were the main impact factors of 0-10cm soil microbial biomass nitrogen in 28 years post-fire plots.(2)Compared with control plots,3 years,9 years,28 years plots 0-10cm soil inorganic nitrogen decreased by approximately 6%,21%and 23%,respectively,3 years,9 years,28 years plots 10-20cm soil inorganic nitrogen decreased approximately 11%,25%,25%,respectively.The proportion of 0-10cm and 10-20cm soil nitrate nitrogen to total inorganic nitrogen were all increased in 3 years and 9 years post-fire plots,while the proportion of 0-10cm and 10-20cm soil nitrate nitrogen to total inorganic nitrogen were all decreased in 28 years post-fire plots.Compared with the control plots,the 0-10cm soil net mineralization rate significantly increased in 3 years post-fire plots,the 0-10cm soil net mineralization rate decreased approximately 26%in 9 years post-fire plots,and the 0-10cm soil net mineralization rate almost return to pre-fire level in 28 years post-fire plots,while 10-20cm soil net mineralization rate did not significantly change in 3 years,9 years,28 years post-fire plots.This results indicate that the 10-20cm soil net mineralization rate response to fire was not so significant as 0-10cm soil net mineralization rate.Soil available phosphorus of soil available potassium were the main impact factors of 0-10cm soil net mineralization rate in 3 years post-fire plots,soil water content,soil available phosphorus,soil microbial biomass nitrogen and soil microbial biomass carbon were the main impact factors of 0-10cm soil net mineralization rate in 9 years post-fire plots,soil water content,soil available phosphorus and soil microbial biomass nitrogen were the main impact factors of 0-10cm soil net mineralization rate in 28 years post-fire plots.This results indicated that 0-10cm soil net mineralization rate after 3 years fire disturbance was mainly controlled by soil available nutrient elements,0-10cm soil net mineralization rate after 9 to 28 year fire disturbance was influenced by soil water content,soil available nutrient elements and soil microbial activity.(3)0-10cm and 10-20cm soil microbial biomass nitrogen in nature restoration plots was approximately 44%and 28%higher than that in afforestation plots.The nature restoration type was more beneficial to the improvement of soil biomass nitrogen.0-10cm soil ammonium nitrogen,nitrate nitrogen and inorganic nitrogen in nature restoration plots was approximately 70%,29%and 67%higher than that in afforestation plots,respectively.10-20cm soil ammonium nitrogen,nitrate nitrogen and inorganic nitrogen in nature restoration plots was approximately 35%,6%and 34%higher than that in afforestation plots,respectively.The nature restoration type was more conductive to the recovery of soil inorganic nitrogen mineralization rate.The 0-10cm soil net mineralization rate was 3.6 times higher than that in afforestation plots.Nature restoration type was more conductive to forest plant biodiversity and legume recovery after fire disturbance.The recovery of legumes and increase of soil microbial biomass nitrogen may be the main reason for the increase of soil net mineralization rate after fire disturbance.(4)0-10cm post-fire soil inorganic nitrogen and its component increased under laboratory incubation condition.0-10cm post-fire soil ammonium nitrogen,nitrate nitrogen and inorganic nitrogen approximately 40%,27%and 34%higher than that in control plots,respectively.The post-fire 0-10cm soil inorganic nitrogen was increased from 0 to 3 days,and gradually decreased from 6 to 50 day during laboratory incubation period.This result indicated that post-fire 0-10cm soil was dominated by the nitrogen mineralization process from 0 to 3 days,while it was dominated by the nitrogen immobilization process from 6 to 50 day.3 to 6 days of laboratory incubation was the transformation time point of post-fire 0-10cm soil mineralization to immobilization.0-10cm and 10-20cm soil net mineralization rate significantly increased at 0 day of laboratory incubation,0-10cm soil net ammonification rate,net nitrification rate and net mineralization rate increased by 1.7 times,14.7 times and 2.4 times after fire disturbance,respectively.But there was no significant difference between post-fire plots 0-10cm and 10-20cm soil net mineralization rate and corresponding control plots 0-10cm and 10-20cm soil net mineralization rate at the end of the laboratory incubation.0-10cm soil net mineralization rate was negatively correlated with soil available potassium,soil microbial biomass nitrogen and soil microbial biomass carbon.10-20cm soil net mineralization rete was negatively correlated with soil microbial biomass nitrogen and soil microbial biomass carbon.This result indicated that soil net mineralization rate under the laboratory incubation was mainly influenced by soil available nutrient and microbial activity.
Keywords/Search Tags:Fire disturbance, Boreal forest, Larix gmelinii, Mineralization rate, Soil microbial biomass nitrogen, Nitrogen cycling
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