Effects Of C,N And P Stoichiometry On Community Biomass Of Typical Stands In The Qinling Mountains

Carbon?C?,nitrogen?N?and phosphorous?P?are the most basic nutrient elements in plants,and their stoichiometric ratio in the plants reflects nutrient restriction pattern in the ecosystem to a certain extent.Stand age is one of the most important factors that influence the carbon pool dynamics of forest ecosystems.In order to investigate the effects of C,N and P stoichiometry on stands biomass in the Qinling Mountains,a total of 28 permanent sample plots were chosen in Tongtian River National Forest Park and Jialing River Source National Forest Park in Feng County,Baoji city,and natural forest of 4 different-age groups were used as the research object in Pinus armandi and Quercus aliena var.Acuteserrata.On the basis of stand investigation,combining with the analysis of indoor samples,we systematacially analyzed the C,N,P stoichiometry of tree leaves,litter and soil,the biomass and carbon storage of each stand,the relationship between the stoichiometry and biomass and the content and distribution of the metal elements in the soil in P.armandi and Q.aliena var.Acuteserrata with different ages.We further understood not only the effects of tree species and ages on the stoichiometry of tree leaves,litter and soil as well as the limitation of N and P nutrients,but also the effects of stoichiometry in each component on the stands biomass.The main results were as following:1.This study indicated that the biomass of P.armandi stands was 136.69—172.47 t·hm^-2 and the biomass of Q.aliena var.Acuteserrata stands was 117.42—387.53 t·hm^-2;the biomass in both stands was increased with the increase of the forest age,and the growth rate of Q.aliena var.Acuteserrata stands was greater than that of the P.armandi stands.The total carbon storage was 145.01—191.38 t·hm^-2 in P.armandi stands and was 155.95—268.11 t·hm^-2 in Q.aliena var.Acuteserrata stands.The carbon storage in the vegetation layer of P.armandi was about 41.4%-48.1%of the total carbon storage of the community,and the litter layer was 6.1%—9.1%,and the soil layer accounts for 43.6%—52.5%.The carbon storage in the vegetation layer of Q.aliena var.Acuteserrata was about 36.9%-68.8%of the total carbon storage of the community,and the litter layer was 4.5%—5.1%,and the soil layer accounts for 26.7%—57.9%.2.The C,N and P contents were the highest in tree leaves and the lowest in soil in each age group of two forests.The C content in P.armandi leaves was higher than that in Q.aliena var.Acuteserrata leaves,while N and P contents were lower.Tree species had extremely significant effects on the stoichiometric characteristics of plant leaves,C content,N content,C:N and C:P of litters and P content and N:P in the soil.Stand age significantly affected C content of leaves and litters.Also,it had extremely significant effect on P content,C:P ratio and N:P ratio in the soil.The N:P ratio ranged from 7.47 to 12.5,and the nitrogen played the dominant role in normal growth of plants.3.The soil Pb content of the two forest stands in the study area was higher than the soil background value in Shaanxi province and in China,but the Zn content was lower than the soil background value in Shaanxi province and in China.The soil Pb content in P.armandi forest was lower than that in Q.aliena var.acuteserrata forest,and in both of the two forests the soil Pb content was the lowest in young forest.In0-40 cm soil layer,the content of Zn and Pb were basically columnar distribution,which would not change greatly with the depth of soil layer.4.There was no relationship between the amount as well as the ratio of various elements and the biomass.There was an extremely significantly positive correlation between the content of N in litter and the biomass;and significantly positive correlation between the N:P ratio and the biomass.The C:P ratio in surface soil was extremely significantly negatively correlated with the biomass;and the N:P value in surface soil was significantly negatively correlated with the biomass.The soil Pb content in 0-10 cm was significantly positively correlated with the P content in surface soil,and significantly negatively correlated with the C:P ratio and the N:P.There was a significantly positive correlation between the soil Pb content in10-20 cm and the P content in soil.The Zn content in 0-10 cm was significantly negatively correlated with the C:P ratio in soil.The soil Zn content in 10-20 cm was extremely significantly positively correlated with the C content and the N content,and significantly positively correlated with the soil P content.