Effects Of Fertilization On Soil Microbiological Characteristics Of Typical Coniferous Plantation In Northeast Of China

There is a large area of artificial forest in the eastern forest area of Northeast China.In particular,Pinus sylvestris var.mongolica,Picea koraiensis,Larix olgensis and Pinus koraiensis are the most.How to improve its stand productivity is becoming a hot spot in the study of plantation productivity formation mechanism.The available measures to improve stand productivity focus on density regulation（such as thinning）and forest nutrition management（such as fertilization）.There have been many reports on the former,while the latter research is rare.Fertilization to the soil,the quality of soil fertility changes due to fertilizer addition,thus affecting soil microbial biomass and community structure.Soil microorganisms affected by fertilization can affect the growth of aboveground plants by changing soil nutrient cycling and increasing or inhibiting pathogenic bacteria.Therefore,the regulation of soil microbial processes can be used as an evaluation index to improve plant productivity and reduce the adverse effects of fertilizers on the soil environment,thus contributing to the sustainability of forestry ecosystems.However,it is not clear how fertilizer addition regulates soil microbial biomass and community structure composition,which limits our understanding of soil microorganisms in fertilizer addition.In this study,Pinus sylvestris var.mongolica forest（planted in the spring of 1976）,Picea koraiensis forest（planted in the spring of 1977）,Larix olgensis forest（planted in the spring of 1988）and Pinus koraiensis forest（planted in the spring of 1976）in Mengjiagang Forest Farm of Jiamusi City in the eastern part of Northeast China were selected as the research objects.Four treatments(control CK,no fertilization;nitrogen fertilizer N,nitrogen 250 kg·hm^-2;nitrogen and phosphorus fertilizer NP,nitrogen 250 kg·hm^-2+phosphorus 50 kg·hm^-2;physicochemical properties and soil microbiological characteristics of surface soil（0～10cm）after 3 years of NPK(N 250kg·hm^-2+P 50 kg·hm^-2+K 30 kg·hm^-2)application were investigated to explore the relationship between soil microbial community composition（bacterial and fungal communities）and soil fertility indicators.Main research results:（1）Different forest types have different fertilization types that are conducive to the growth of soil microorganismsWhen soil microbial biomass carbon and nitrogen were used to reflect the growth status of soil microorganisms.Single application of nitrogen fertilizer is most conducive to the growth of soil microorganisms in Pinus sylvestris var.mongolica plantation and Larix olgensis plantation,but the simultaneous application of nitrogen fertilizer and phosphorus fertilizer or phosphorus and potassium fertilizer is not conducive to the growth of soil microorganisms in Pinus sylvestris var.mongolica plantation and Larix olgensis plantation.In contrast,Picea koraiensis and Pinus koraiensis plantations are opposite to Pinus sylvestris var.mongolica plantation and Larix olgensis plantation,and phosphorus and potassium fertilizers must be added while applying nitrogen fertilizer.（2）The influencing factors of soil microbial biomass carbon and nitrogen were different in different forest typesIn terms of soil microbial biomass carbon（MBC）,Pinus sylvestris var.mongolica plantation was significantly affected by soil p H and dissolved organic carbon（P<0.05）,especially the latter was the most important dissolved organic carbon;Soil MBC in Larix olgensis plantation was also affected by organic carbon（P<0.05）;Soil MBC Picea koraiensis forest was mainly affected by soil available potassium and organic carbon（P<0.05）,especially the former;The MBC of Pinus koraiensis soil was mainly affected by soil total phosphorus and total potassium（P<0.05）,and the main controlling factor was total phosphorus.In terms of soil microbial biomass nitrogen（MBN）,Pinus sylvestris var.mongolica plantation was mainly affected by soil total phosphorus（P<0.05）and soluble organic carbon（P<0.05）,and the main controlling factor was total phosphorus.The soil MBN in the Picea koraiensis plantation was also dominated by phosphorus,but it was affected by available phosphorus（P<0.05）.The soil MBN of Larix olgensis plantation was affected by soil total nitrogen（P<0.05）and available phosphorus（P<0.05）,and the main controlling factor was total nitrogen.The Pinus koraiensis plantation was consistent with the Larix olgensis plantation,and the main controlling factor was also total nitrogen,but it was also affected by soil total phosphorus（P<0.05）.（3）Fertilization not only significantly affected the surface soil bacterial community structure,but also the latter was affected by the type of fertilization.Under different fertilization treatments,there were significant differences in bacterial richness and community structure in surface soil（taking Larix olgensis plantation as an example,the same below）.The bacterial diversity of surface soil under fertilization treatment was low,but the bacterial richness was high,especially under single nitrogen fertilizer treatment.However,with the combined application of phosphorus fertilizer and phosphorus potassium fertilizer,the soil bacterial richness showed a decreasing trend.Non-metric multidimensional scaling（NMDS）analysis showed that there were significant differences in soil bacterial community composition between nitrogen and phosphorus treatments and CK treatment.The bacterial community structure changed after fertilization.Although the bacterial community composition was similar at the phylum and class levels,there were significant differences in the bacterial community at the genus and species levels.The combined application of nitrogen and phosphorus fertilizers can significantly promote the growth of dominant bacteria in the surface soil bacterial community.From the perspective of soil bacterial community structure,richness and dominant community,it is not necessary to add potassium fertilizer when applying nitrogen fertilizer,but phosphorus fertilizer can be added.（4）Fertilization not only significantly affected the surface soil fungal community structure,but also the latter was affected by the type of fertilization.Under different fertilization treatments,the fungal richness,diversity and OTU number of surface soil reached the highest under the condition of nitrogen and phosphorus fertilization.Fertilization treatments increased the dominant species diversity of the fungal community.NMDS analysis showed that although the fungal community composition was similar between fertilization treatments,it was significantly separated from the control,especially in the treatment of nitrogen,phosphorus and potassium fertilization.The fungal community structure changed after fertilization.Although the fungal community composition was similar at the phylum and class levels,there were significant differences in the fungal community at the genus and species levels.Nitrogen application can significantly promote the growth of dominant bacteria in the surface soil fungal community.From the perspective of soil fungal community structure,richness,diversity and dominant community,the mixed application of nitrogen fertilizer and phosphorus fertilizer is more conducive to the growth of soil fungi.Although fertilization can significantly affect the bacterial and fungal community structure,the main controlling factors of the two changes are different.（5）Fertilization Although fertilization can significantly affect the soil bacterial and fungal community structure,the main controlling factors of the two changes are different.Although the relative abundance of soil bacterial and fungal communities was significantly correlated with soil physical and chemical properties（P<0.05）,the main influencing factors of bacterial community structure were soil total phosphorus and total potassium,while the key influencing factor of soil fungal community structure was soil organic carbon.（6）Fertilization can not only significantly affect the function of surface soil microbial community,but also various functional communities are affected by the type of fertilization.In the bacterial functional community,compared with CK treatment.the chemoheterotrophy bacteria in the fertilization treatment increased by 6.83%～10.45%;The aerobic chemoheterotrophy bacteria increased by 6.72%～10.73%.Nitrogen-fixing bacteria increased by 7.41%～18.76%;nitrification functional bacteria increased by 0.28%～28.04%;Nitrification decreased by 7.38%～20.32%;sulfur respiration decreased by 11.34%～17.09%;aerobic ammonia oxidation decreased by 4.34%～13.03%.In the fungal functional community,compared with CK treatment,the mycorrhizae of Ericoid Mycorrhizal increased by68.84%～231.66%;All kinds of saprophytic bacteria increased by 1.16%and 32.26%under N treatment and NP treatment,and decreased by 12.45%under NPK treatment.The plant pathogenic bacteria decreased by 6.58%and 5.26%under the conditions of nitrogen fertilizer and nitrogen and phosphorus fertilizer,and increased by 31.58%under the conditions of nitrogen,phosphorus and potassium fertilizer.Fertilization treatment significantly promoted the functional diversity of some soil microbial communities,which was mainly reflected in the improvement of organic matter metabolism,microbial metabolism,cellulose decomposition and nitrogen fixation in the surface soil bacterial flora under the conditions of nitrogen fertilizer,nitrogen,phosphorus and potassium fertilizer.Under the condition of nitrogen fertilizer application,the function of soil fungal mycorrhiza fungi was improved.From the perspective of soil microbial community development,it is not necessary to add potassium fertilizer when applying nitrogen fertilizer and nitrogen and phosphorus fertilizer.Because the addition of potassium fertilizer reduced nitrification,sulfur respiration,aerobic ammonia oxidation,and various saprophytic bacteria functions,increased the functional abundance of plant pathogens,resulting in a decrease in various functions of soil microorganisms,and plants were more susceptible to pathogens and affected plant growth.（7）Although fertilization can significantly affect the structure of bacterial and fungal community functional flora,the main controlling factors of various functional flora are different.In the bacterial functional community,the main controlling factor of cellulose decomposition function was soil p H,and its abundance was significantly negatively correlated with soil p H（P<0.05）.There was a significant negative correlation between animal pathogenic organisms and soil total potassium content and p H value（P<0.05）.Ectomycorrhizal fungi were significantly negatively correlated with soil organic carbon（P<0.05）.Wood saprophytic organisms were significantly negatively correlated with soil organic carbon and available phosphorus content（P<0.05）.