Effects Of Restoration Pathways On Leaf Functional Traits And Carbon Storage In Larch Forests In Daxing’anling Mountains

Global warming has increased the risk of wildfires.Large wildfires can severely damage forests and are accompanied by a loss of ecosystem function.Community reestablishment is necessary for the restoration of ecosystem functions.During the long-term natural succession recovery process,the main species composition varies and different successional sequences are formed due to the influence of site conditions,especially soil moisture.Different successional top community types are distributed in different successional sequences.Ecosystem functions and growth adaptations differ among community types,and it is important to clarify the drivers of ecosystem functions.Meanwhile,different restoration measures have been adopted to rapidly restore the vegetation destroyed by the mega-fire.Which restoration measure is beneficial to improve ecosystem function has become a strong issue of social concern.Restoration measures can alter community structure and soil nutrients.Natural secondary forests and planted forests are the two main forest types under post-fire restoration measures.While little information is available on the interaction of plant environmental adaptations and plant resource allocation strategies during forest ecosystem restoration.Therefore,in this study,plant communities in the long-term natural succession restoration of Daxing’anling Khanma National Nature Reserve and short-term artificial intervention restoration in Tuqiang Forestry Bureau were used as research objects,and dominant plant and soil samples were collected to conduct a comparative study of plant diversity and carbon storage under different larch community types,different restoration measures and different forest stand types at the community level,to clarify the multivariate relationships between plant diversity and carbon storage.At the same time,a comparative study on physiological and metabolic adaptations was conducted at the species level,taking larch（Larix gmelinii（Rupr.）Kuzen.）between successional tops in a long-term natural successional pathway and recovery states in a short-term artificial intervention as the research objects.（1）In different larch community types,Herbage-Larix gmelinii had high levels of Shannon-Wiener index,Margalef’s richness index,mean weight of specific leaf area（CWM＿SLA）,mean weight of leaf nutrient K（CWM＿K）and amino acids,and low levels of sugars;Rhododendron dauricum-Larix gmelinii had low levels of CWM＿SLA and amino acids,and high levels of sugars and phenols;Ledum palustre-Vaccinium vitis-idaea-Larix gmelinii and Betula fruticosa-Larix gmelinii had high levels of CWM＿SLA,mean weight of leaf nutrient N（CWM＿N）and sugars.Combined with the leaf trait network,it was observed that the modularity and average path length of Herbage-Larix gmelinii were higher than those of the other three larch communities,while the opposite was true for edge density and average degree.Meanwhile,the correlation of single amino acid network was significantly enhanced in the Rhododendron dauricum-Larix gmelinii.In terms of carbon storage,Herbage-Larix gmelinii had higher levels of total tree carbon,soil organic carbon and soil nutrients（N and K）.Further analysis of the pathway model revealed that CWM＿SLA and diversity of diameter measurements at breast height H_DBH had significant positive effects on total tree carbon,while the opposite was true for sugars.Soil N indirectly influenced carbon stock by inversely affecting sugars.Soil N and amino acids had a significant positive effect on soil organic carbon.Slope indirectly affects soil organic carbon by reversing the effect of amino acids.Thus,different larch community types achieve environmental adaptation by regulating functional traits that ultimately influence carbon sink processes.（2）Among the different restoration measures,it was found that compared with natural restoration,artificial afforestation exhibited greater differences in community-weighted mean of functional traits and community structure.Artificial afforestation showed lower levels of coefficient of variation of diameter measurements at breast height（CVDBH）,nutrient traits（Ca,Mg,Zn,and B）,and amino acids.However,it had higher levels of specific leaf area,sugars,and nutrient traits（P,K,and Fe）.Compared to the leaf trait network of artificial afforestation,both natural restoration and artificial regeneration showed an increased number of edges related to sugars,amino acids,and nutrients traits,especially nutrient traits,which increased by 29%and 48%.The degree and betweenness of nutrient traits in artificial afforestation were also lower.In terms of carbon storage,artificial afforestation exhibited the highest levels of total tree carbon,followed by artificial regeneration and natural restoration.In addition,there was no significant difference between larch height and birch height in artificial regeneration in mesophytic habitats,and even higher than birch height in subwet habitats,implying that larch successfully entered the main forest layer.In the long run,the ability of artificial regeneration to sequester carbon will be enhanced compared with natural restoration.Further combined with multiple stepwise regression analysis,coefficient of variation of diameter measurements at breast height(CV_DBH)was the best negative predictor of total tree carbon.We believe that artificial afforestation are conducive to carbon sequestration by regulating functional traits and improving resource use efficiency,while resource limitation under natural restoration is detrimental to carbon sequestration.（3）Most differential leaf functional traits were affected by both of soil nutrients and species composition.Higher ratio of soil N/P in secondary forest implied P limitation,while lower in pine plantation implied N limitation.Secondary forest was dominated by deciduous tree species which had lower mean weight of leaf mass per area（CWM＿LMA）,higher mean weight of leaf nutrients（CWM＿C and CWM＿Mn）and phenols level under P limitation.In contrast,pine plantation was dominated by evergreen tree species which exhibited higher CWM＿LMA and reduced intermediates and hydroxybenzoates under N limitation.Combining the leaf trait networks,it was observed that modularity and average path length were higher in secondary forests than in pine plantation,while the opposite was true for average degree and edge density.Meanwhile,the number of amino acid and phenolic edges in the network of pine plantation was significantly higher.These results implied that secondary forest was maintaining the acquisition strategy by changing nutrient level and enhancing modularity to alleviate P limitation.However,pine plantation strengthened conservative strategy by modifying phenols level and improving synergistic ability of multiple traits to advance the defense function under N limitation.Therefore,natural secondary forests and pine plantation can achieve different ecological strategies by regulating functional traits to adapt to differences in species composition and soil nutrients.（4）At the physiological level,larch at successional tops had high levels of SLA and nutrient traits（N and Mn）,while larch at the restored state showed low levels of SLA,high LDMC and P.At the metabolic level,larch at successional tops showed decreased levels of sucrose and sugar alcohols,and increased levels of organic acids and amino acids,while larch at the restored state showed decreased levels of starch,amino acids and organic acids,and increased levels of sugar alcohols and flavonoids.Meanwhile,the key enzymatic activities of metabolic pathways sucrose synthase and isocitrate lyase were up-regulated in larch at successional tops,andα-amylase and phenylalanine deaminase were up-regulated in larch at the restored state.Thus,different patterns of carbon allocation were observed in larch between successional tops and recovery states.Thus,long-term natural succession and short-term artificial intervention lead to a shift in the carbon and nitrogen allocation pattern of larch,which is closely related to the regulatory mechanisms of functional traits and enzyme activities.Different resource allocation strategies facilitated the growth and recovery of larch under different restoration pathways.