Fine Root Morphological Characteristics And Ecological Stoichiometry In Mature Chinese Fir Plantations Along An Elevation Gradient In Dabie Mountains

In order to reveal the adaptation strategies of plants to environmental changes,the mature Chinese fir(Cunninghamia lanceolata)plantations along an elevation gradient(750,850,1000,1150 m a.s.l.)were selected in Tianma National Nature Reserve in Anhui Province.Their fine roots at different layers(0-10,10-20 and 20-30 cm)were sampled to determine the biomass,characteristic parameters and ecological stoichiometry.The main results are as follows.1.The biomass and characteristic parametersFine root biomass,length density,specific root length,surface area density and volume density at 0-30 cm soil depth initially decreased and then increased with the increase in elevation.The fine root biomass peaked at 750 m,and the other indices showed the maximum values at 1150 m.Fine root biomass,length density,surface area density,and volume density decreased with soil depth at each elevation,while specific root length initially decreased and then increased.With the measured elevation range,the fine root biomass and morphological index values were the lowest at 850 m.At each elevation,fine roots with diameter of 0-1.0 mm made the greatest contribution to total fine root length,total fine root surface area,and total fine root volume at each soil layer.There was a positive significant correlation between fine root biomass and length density,specific root length and surface area density.However,fine root biomass and specific root length were negatively correlated.2.Fine root carbon(C),nitrogen(N),phosphorus(P)contents and stable C and N isotopesThe average contents of C,N and P in fine roots of Chinese fir plantations were 329.70 g/kg,10.30 g/kg and 0.70 g/kg,respectively.The average values of fine rootδ15N and δ13C were-1.23‰,-26.97‰,respectively.The C,P and N contents of fine root at 0-30 cm soil depth initially increased and then decreased with the increase in elevation,while δ15N and δ13C initially decreased and then increased.The contents of C and δ13C in the fine roots decreased firstly and then increased with the increase in soil depth along the elevation gradient,while N and P content decreased,and δ15N increased.A week correlation between fine root δ15N and C content was observed,as was similar in relation between δ13C and C contents.3.Fine root C,N and P stoichiometryThe average C/N,N/P and C/P ratios of fine roots in Chinese fir plantations were 32.58,14.94 and 488.09,respectively.With the increase of elevation gradient,the C/N,N/P and C/P ratios of fine roots decreased first,then increased and finally decreased.With the increase of soil depth,the C/N ratio of fine roots showed an increasing trend,and the N/P ratio of fine roots decreased first and then increased.Fine root P content was positively significantly correlated with C and N contents.To a certain extent,the contents of C and N in fine roots were affected by fine root P content.Within the measured elevation range,the growth of Chinese fir plantation might be limited by N and P.Fine root N and P contents,C/N and C/P ratios were closely correlated to fine root biomass,length density,surface area density,and volume density,while the C content and N/P ratio were weakly correlated to fine root traits.There was no significant correlation between the stoichiometry and the fine root length.4.Relationship between main functional traits of fine roots and soil physicochemical propertiesIn the 0-10 cm,10-20 cm soil layers,soil moisture content decreased first and then increased with the increase of elevation.However,soil bulk density and pH increased first and then decreased.In the 20-30 cm soil layer,the soil moisture content decreased first and then increased with the elevation increase.The soil bulk density increased first,then decreased and finally increased.The soil pH increased first and then decreased.Soil moisture was the main factor controlling fine root biomass and its configuration.Soil bulk density was only positively correlated with fine root biomass and surface area density,while negatively correlated with other indicators.There was a significant negative correlation between soil pH and fine root biomass and root length density.The correlation between soil pH and fine root nutrients and their stoichiometric ratios was not significant.