Study On Carbon,nitrogen And Phosphorus Stoichiometry Of Chinese Fir Plantations In China

Ecological stoichiometry is an important theory to explore the interaction between biology and environment in ecological process,which is mainly applied to study the balance of multiple chemical elements,and can be served as a link between different levels of individuals,populations,communities and ecosystems.This theory would provide a new approach for revealing the relationships of nutrient balance and its patterns with environmental factors in Chinese fir plantations.Therefore,in this study,in main Chinese fir production areas,the vegetation-soil-litter continuum was took as research objects of different distribution areas and different site conditions(site index I:18?II:16?III:14),to clarify the conditions of nutrient levels and plant growth limitation in different components of Chiese fir plantations,and to reveal the changing patterns of stoichiometric characteristics along geographical and climatic gradients,which would provide basic theory for the establishment of scientific management measures.The main results are:1.We complied data on leaf N and P concentrations,N:P ratio,stand age,climate,and geographical location,and analyzed the correlations among these variables.The results showed that for all of the age groups considered,the average concentrations of the leaf N and P concentrations and the N:P ratio were 11.94 mg g^-1,1.04 mg g^-1,12.93.Significant differences were found in leaf P concentration and N:P ratio between five age groups,while the differences in leaf N concentration between the groups was not significant.Linear fitting results indicated that the leaf P concentration decreased,and leaf N:P ratio increased with the increase of the MAT(mean annual temperature)and soil N concentration.Redundancy analysis revealed that the first axis,with an explantatory quality of 0.350,indicated that the MAT,soil N concentration and stand age had a good relationship with the elaf P concentration and N:P ratio,while the second axis,with an explantory quantity of 0.058,indicated that the leaf N concentration was less affected by the environemntal factors.2.In a field experiment,we collected soil,leaf litter,and leaf samples of Chinese fir from19 sites across subtropical China to determine the spatial variations in leaf litter carbon(C),nitrogen(N),and phosphorus(P)stoiciometry,and their controlling factors.The results showed that:(1)The range of soil C:N,C:P,and N:P ratios were 7.32?18.27,20.15?230.48,and2.11?15.05,with mean value of 13.22,83.50,and 6.05,respectively.Well-constrained correlations were found for SOC and N,and N and P.Soil TN and TP contents increased with increasing altitude,whereas soil C:N:P ratios decreased.Soil TP content decreased,and C:P ratio increased with increasing mean annual temperature(MAT)and annual total solar radiation(ATSR).Soil C:N:P ratios increased with increased meam annual precipitation(MAP)and annual evaporation(AE).(2)Mean leaf litter C,N and P concentrations were 458.32 mg g^-1,8.87 mg g^-1,and 0.46mg g-1,respectively.The C:N,C:P,and N:P ratios were 52.93,1049.84,and 19.84,respectively.Leaf litter N and P concentrations were positively correlated with each other,while no significant relationships were found between leaf litter C and N concentrations,as well as C and P concentrations.Leaf litter stoichiometry showed linear or non-linear relationships with the geographical,climatic and soil chemical variables.Hierarchical partitioning(HP)analysis showed the geographical and climatic variables contributed the majority of explanations for leaf litter C and N concentrations,and N:P ratio.Variation of leaf litter P concentration was mainly regulated by soil chemical variables.(3)Mean leaf C concentration,C:N and C:P ratios were relatively high,while those of leaf N and P concentrations were relatively low in comparison to the mean values obtained from global and national studies.Leaf N:P ratio with the mean of 11.49 was significantly lower than14,indicating the growth of Chinese fir was limited by N.The mean CRE,NRE and PRE were5.46%,33.05%and 61.59%,respectively.Leaf C concentration and CRE increased along latitude,and the changes were mainly driven by mean annual temperature(MAT).Leaf P concentration and PRE increased,and C:P and N:P ratios decreased along altitude,and the changes were mainly driven by soil P concentration.Stand age significantly affected the leaf N and P concentrations,and C:N and C:P ratios.CRE and PRE were also influenced by the corresponding element concentration in leaves.3.By the data integration of soil,leaf litter,and leaf N and P stoichiometry,three pieces of evidence that induced N-limitation for the growth of Chinese fir were proposed from an ecological perspective.The results showed that:Firstly,leaf N:P ratio with the mean of 11.49was significantly lower than 14,which suggested and evidenced that the growth of Chinese fir was limited by N.Next,leaf N concentration was less affected by the environmental variables,showing low variability.Leaf P concentration and N:P ratio were significantly affected by soil P concentration(SP),mean annual temperature(MAT)and altitude(ALT),and both of them showed high variability.Thirdly,the P resorption efficiency(PRE)was significantly higher than N resorption efficiency(NRE).Leaf N:P ratio decreased with the increasing PRE and|NRE-PRE|.4.We explored the effects of site condition on tree stoichiometry at stand level.The results showed that significant trend was displayed along the site indexes for root C,N concentrations and C:N ratios,and marginally significant trend was for branch N,P concentrations,and C:N and C:P ratios.No significant trend was found for leaf stoichiometry,and all tree N:P ratios showed no significant differences among site indexes.Soil stoichiometry significantly affected the leaf stoichiometry and nutrient resorption,exhibiting the stoichiometric flexibility to some extent.In summary,the plant growth is limited by N at rapid growth stage,as a result,adding N fertilizer appropriately should be applied to promote tree growth and further advance the plantation productivity.At a regional scale,the plant-soil-litter continuum stoichiometry is regulated by geographical and climatic factors to varying degrees.Stoichiometric flexibility may be an important way for palnts to self-regulate,and helps plants maintain their normal life activities under different site conditions.