Nitrogen Utilization Strategies Of Dominant Species From Primary Succession Along Hailuogou Glacier,Mt.Gongga

Nitrogen(N)is the mineral nutrient required in the greatest amount,and plant N utilization is a key component of the N cycle in terrestrial ecosystems.The ability of plants to adapt to environmental N sources determines its ability to adapt to environmental changes,which in turn affects community vegetation composition and ecosystem processes.Nitrogen use strategies such as N preference,allocation trade-offs and photosynthetic nitrogen use efficiency(PNUE)are important characteristics of plant nutrient utilization,physiological characteristics and survival strategies.Studying plant N utilization strategies during primary succession can deepen our understanding of plant N nutrient acquisition and utilization of plant N nutrients,and further understand the mechanisms of species coexistence,competition,and community construction during primary succession.In this study,focus on dominant species-soil at the early-,middle-and late-stages of primary succession on the Hailuogou Glacier foreland,Mt.Gongga,China: The proportional contributions of different N form and plants N preference were calculated by using the natural abundance of N isotopes(?15N value)of dominant species and soil,to study the N acquisition strategy of dominant species at different succession stages;leaf N allocation of different components of dominant species in different succession stages were measured,to verify the tradeoffs for N allocation to photosynthesis versus cell walls of dominant species;analyzed the changes in PNUE and the relationships between these leaf functional traits.Integrating plant N acquisition,leaf nitrogen allocation and use reveals N utilization strategies of dominant species during primary succession.The main findings are as follows:1.The contributions of soil NH4+(f NH4+)and NO3-(f NO3-)to N source were significantly different of dominant species at different succession stage(p < 0.05),dominant species preferred NO3-at early-and middle-succession stage,f NO3-were 83.50% and 63.34%,respectively.Dominant species preferred NH4+ at late succession stage,and f NH4+ was 87.05%.Along with succession,the content of soil dissolved organic N gradually increased,and its contribution increased to 19.33% of dominant species.2.Along with succession,leaf N allocation proportion of photosynthetic system(PP)of dominant species was significantly higher in the middle stage than the earlyand the late-stage(p < 0.05),there was no significant difference between the early-and the late-succession stage(p > 0.05).Leaf N allocation proportion of cell wall(Pcell wall)of dominant species was significantly different among different stages(p < 0.01),and the pattern was the late stage > the early stage > the middle stage.Correlation analysis indicated that there was a trade-off between PP and Pcell wall of dominant species during primary succession.3.There were significant differences in PNUE of dominant species at different succession stages(p <0.05),the pattern was the middle stage > the late stage > the early stage.Correlation analysis showed that there was a significant correlation between leaf functional traits of dominant species,i.e.specific leaf area,Pp and leaf construction cost have significant correlations with PNUE.PNUE is a comprehensive value affected by multiple factors.The N acquisition preference of dominant species was affected by many factors during primary succession,which is manifested in that dominant species preferred NO3-at early-and middle-succession stages,and dominant species preferred NH4+ at late succession stage.At early stage,owing to the prodigal use,the higher N and P of the early N-fixing species did not translate into higher photosynthetic capacity and PNUE;At middle stage,the exploitative strategies,manifested in higher PNUE,and quickreturn energy economics with lower construction cost and shorter payback time,helped broad-leaved forests win fast.At late stage,climax coniferous species achieved even higher photosynthetic P use efficiency and longer leaf life span helped them win steady.The change of dominant plant nitrogen utilization strategy during the primary succession may represent an important driving mechanism for the primary succession in glacier foreland.