Relationships Between Phenolic Contents And Nitrogen Utilization Mechanisms Of Peatland Plants In The Great Hing'an Mountains Area

Phenolic compounds are secondary metabolites that play an important role in plant defense and environmental adaptation.Due to their strong inhibitory effect on microbial activity and soil organic matter decomposition,and their biosynthesis is mainly affected by nitrogen availability,they are therefore critical for understanding the carbon(C)dynamics of vegetation in boreal peatlands and their responses to changes in nitrogen(N)availability in the context of global changes.However,in boreal peatlands,the phenolic metabolism levels of different plants and their responses to changes in plant N availability are still unclear,and the phenolic metabolism levels of plants in northern peatlands also affect plant N utilization strategies,but related research is also very weak.Therefore,this study systematically studied the coupling relationship between plant phenolic metabolism and N utilization.We tested the levels of different phenolic compounds in the leaves of 11 plant species in 18 peatlands in the Great Hing'an Mountains area(the GHM area),Northeastern(NE)China,and their relationships with environmental factors and leaf nutrient status;We analyzed the characteristics of C,N isotope values of plant leaves and their relationships with environmental factors and leaf nutrient status;N-isotope values of leaves were used to calculate the absorption proportion of plants to different N sources by isotopic mixing model.The relationship between phenolic levels and plant N utilization mechanisms was explored.Our results showed that:(1)Phenolic compounds in leaves of peatland plants in the GHM area had significant inter-species and functional-type differences.The trend of graminoids<evergreen shrubs<deciduous shrubs was roughly present between different functional types.This reflected the difference in plant functional trait as an important factor in regulating the level of phenolic metabolism,faster-growing species had lower levels of phenolic compounds.(2)Total phenolic content(TPC)in leaves of graminoids in the GHM area was positively correlated with leaf N and negatively correlated with phosphorus(P)content.Leaf TPC of shrubs was significantly negatively correlated with leaf N content,but not related to leaf P content.This reflected the fact that in the context of increased N availability,graminoids tended to invest more resources in defense,while shrubs invested more resources in growth and the differences in the growth and defense strategies of different functional-type plants in the context of changes in nutrient availability,which may have a certain indication of the expansion of shrubs in boreal peatlands.(3)Isotope characteristics of leaves in peatland plants of the GHM area showed significant differences between species and functional types.The leaves?¹³C and?¹⁵N values of graminoids were significantly higher than those of shrubs,reflecting the differences in water use efficiency and N utilization strategies of graminoids and shrubs.(4)There was a significant positive correlation between the total tannin content(TTC)and the proportional contribution of amino acids(HAA)in the peatland plants of the GHM area,and a significant negative correlation with the proportional contribution of NH₄⁺,but not related to the proportional contribution of NO₃^–,reflecting that plants with the higher phenolic metabolism tend to absorb more organic N.Increased N availability had the opposite effect on the biosynthesis of phenolic compounds in graminoids and shrubs,which revealed the differences in defense and adaptation strategies of plant functional types;A larger utilization proportion of organic N sources and higher phenolic levels of shrubs confirmed that they could fix organic N by forming phenolics-protein complexes,thereby reducing N mineralization and loss caused by microbial activity,and utilizing these N sources to increase their own N availability,which was an adaptation strategy to the N-limited conditions of peatlands.