?¹³C And ?¹⁵N Traits Of Dominant Trees And Their Responses To Elevations In Lingshi Mountain Of Southeastern Coastal Zone

In July 2012,dominant tree investigation and soil survey and sampling were conducted according to the standard of terrestrial biota observation and analysis along 9 elevations in Lingshi Mountain of soutneastern Fujian coastal zone.The foliar element contents,chlorophyll contents,leaf area ?15N and ?13C values of dominant trees and soil ?15N and ?13C values,elements and carbon flux along various elevations were determined respectively by SPAD-502,CI-203 laser leaf platometer,MAT 253 Isotope Ratio Mass Spectrometer,Flash EA1112 HT Elemental Analyzer and LI-8100 soil carbon flux admeasuring apparatus,to analyze foliar traits of dominant trees along various elevations,investigate the distribution and difference of 815N and ?13C values among dominant trees and their response to the elevation,study the effects of foliar elements on ?15N and ?13C discrimination,and reveal the correlation between foliar and soil?15N and ?13C,between soil ?15N and ?13C and soil elements and carbon flux.The responses of foliar ?15N and ?13C traits of dominant trees and their responses to the environment were analyzed in terms of foliar and soil ?15N and ?13C and element contents in order to better understand the "environment-plant-environment" ecological mechanism and provide theoretical references for community distribution,ecosystem nutrient cycling,degraded ecosystem restoration and plant absorption of nitrogen deposition of main evergreen broad-leaf forests in mid-subtropical coastal regions.The results show that:1.The analysis of foliar element contents of dominant trees along multi elevations showed that C had highest concentration while Cu had lowest.Most elements of dominant arbor species showed insensitive responses to elevation,except Na.The elements of dominant shrub species presented various responses to the change of elevation.Based on the chlorophyll contents of dominant trees in multi elevations,there were significant differences between those of arbors and shrubs in elevations of 300 and 400 m,extremely significant differences among dominant arbors in the elevations from 300 to 700 m and among dominant shrubs in the elevations from 200 to 400 m.The leaf area of dominant trees decreased with elevations.The values of SLA of dominant arbor and shrub species were between 0.011?0.027,showing the adverse tendency with the elevations and there were significant difference between SLA values of arbor and shrub species at the same elevation.2.The foliar ?15N values of 63 samples in 26 dominant trees were from-6.0405‰ to 0.472‰,with the average of-3.1025‰.The foliar ?15N values significantly varied between different functional plants and the average ?15N value of arbors(-2.6538‰)was higher than that of shrubs(-3.3991‰).An obvious parabola curve was shown in the correlation between foliar ?15N values of dominant trees and elevations and the elevation of 400 m played an important part in foliar 815N discrimination.From the elevations of 100 m to 400 m,foliar ?15N values generally decreased with elevations while from the elevations of 400 m to 900 m,foliar ?15N values increased with elevations.Obvious variations in foliar ?15N values were shown among dominant trees in Lingshi Mountain due to species and elevations.3.In terms of the relation between foliar ?15N values and element contents of dominant trees,N and C/N of dominant arbor species had most significant effects on ?15N values,Ca and Mn had obvious correlations with ?15N values and C,K and Cu showed insignificant correlations with ?15N values.The ?15N values of dominant shrub species showed significant positive correlation with Ca,P and Mg while negative correlation with C/N.The correlation analysis of foliar ?15N values and element contents of 6 dominant arbor and shrub species at the elevations of 300 m and 400 m indicated that there were extremely significant correlations between ?15N and N,C/N,between N and C/N,between K and C,between Mg and C,Ca,between Mn and C,K and Ca,between Cu and Fe and there were significant correlations between?15N and P,between Ca and C,K,between Mn and Na,Mg,between Cu and C,K,between Zn and Ca,Mg and Mn.The close correlation between ?15N and N and C/N suggested the intensive effects of N availability on foliar ?15N values in various elevations.4.The foliar ?13C values of dominant trees were from-27.4265‰ to-35.984‰,among which over 95%were from-29‰?35‰ with the average of-32.4938‰.The average ?13C value of arbors(-31.6242‰)was higher than that of shrubs(-32.5807‰).An obvious parabola curve was shown in the correlation between foliar ?13C values of dominant trees and elevations and the elevation of 300 m played an important part in foliar ?13C discrimination.From the elevations of 100 m to 300 m,foliar ?13C values generally decreased with elevations while from the elevations of 300 m to 900 m,foliar ?13C values increased with elevations.The research of dominant trees occupied multi elevations indicated that the variation range of foliar ?13C values differed with elevations,owing to the differences of species and ecological niches.Compared with ?15N,?13C was more intensively affected by elevations.5.The dominant trees that occupied 4 or more elevations were chosen and correlation between foliar?13C values and element contents was analyzed.Foliar ?13C values of Castanopsis carlesll had parabola correlation with N and C/N in elevations from 300 m to 800 m;foliar ?13C values of Sloanea sinensis had parabola correlation with C,N,C/N,Fe and Mn in the elevations from 200 m to 700 m;foliar ?13C values of Cryptocarya chinensis had significant parabola correlation with N and C/N in multi elevations;foliar 813C values of Ardisia quinquegona had optimal parabola fitting with N and Mg and the foliar 813C values of Irenina pithecollobii and Psychotria rubra had curvilinear correlation with only a few elements6.The amplitude of variation in foliar ?15N was greater than that in ?13C of dominant trees along various elevations in Lingshi Mountain.The variation coefficient of foliar 815N of dominant trees was-0.2556,which showed great variation amplitude.as the maximum was 2.27 times larger than the minimum.The variation coefficient of foliar 813C of dominant trees was-0.0431 and there was only difference of 15%between the maximum and minimum.The foliar ?15N and ?13C values of dominant trees were uncorrelated but they both had parabola correlation with elevation.There was no obvious correlation between foliar ?15N and AMT and AMP while a significant negative correlation was found between foliar ?13C and AMT as well as between foliar 813C and AMP.7.The soil ?13C values of 0 cm?20 cm soil layers of various elevations were from-27.69‰ to-20.21%o with the average of-25.15%o and The soil ?15N values of 0 cm?20 cm soil layers of various elevations were from-0.5‰ to 5.56‰ with the average of 2.71‰.There were highly significant differences in soil?13C and ?15N values of various elevations,and soil 813C and 815N values were obviously positively correlated.There were insignificant differences in soil 813C and 815N values of different soil layers and obvious interaction between soil layer and elevation wasn't found.Soil ?13C had highly significant positive correlation with soil moisture and temperature and soil ?15N had significant positive correlation with soil moisture and temperature.The soil ?15N values(-0.5‰?5.56‰)were higher than foliar ?15N values(-6.0405‰?0.472‰)in various elevations.The same trend occurred in the relation between soil ?13C values(-25.57‰?20.21‰)and foliar ?13C values(-27.4265‰?35.984‰),and a significant positive correlation was found between soil and foliar ?13C values.