Ecological Stoichiometric Characteristics And Soil Organic Carbon Pool Components Of Quercus Acutissima Plantation

In order to explore the response of ecological stoichiometry characteristics of Quercus acutissima plantation to forest age and the relationship between ecological stoichiometry characteristics and soil organic carbon pool components,Q.acutissima plantation at different forest ages(young forest 18a,middle-aged forest 30a,near-mature forest 45a,mature forest 67a)in Jurong City,Jiangsu Province,was selected as the research object.The contents of carbon,nitrogen and phosphorus in leaf,dry,fine root,leaf litter,soil and microbial biomass of Q.acutissima were measured,and their ecological stoichiometry ratios were calculated.The contents and turnover time of three components of soil organic carbon pool were measured and calculated by indoor constant temperature and humidity in laboratory.The conclusions are as follows:(1)With forest aging,soil organic carbon and total nitrogen content of Q.acutissima increased,while soil total phosphorus increased first and then decreased,and was at a low level(TP content was 0.42g·kg^-1).There was no significant difference in soil ecological stoichiometry among different forest ages.The average soil C:P ratio(80.09)was much higher than the national average(52.7).The ecological stoichiometric ratio of soil carbon,nitrogen and phosphorus generally increased with the increase of soil depth,and the differences among different soil layers were obvious.The soil of Q.acutissima forest showed a lack of total phosphorus and low phosphorus availability.The stand growth was seriously restricted by phosphorus,and the mineralization rate of soil organic matter was slow.Although the growth of forest age could improve the total phosphorus content of soil,the total phosphorus content of soil was still at a low level.In the process of forest management,the supplement of soil phosphorus should be emphasized,and phosphorus fertilizer could be applied appropriately.(2)With forest aging,the contents of soil microbial biomass carbon,nitrogen,and phosphorus in Q.acutissima forest showed an overall increasing trend.The difference of soil microbial eco-chemical stoichiometry between forest ages was not significant(P>0.05),and forest age had little effect on soil microorganisms,especially biomass.The soil microbial biomass of Q.acutissima forest was regulated by soil nutrient content,and there was a significant ecological stoichiometry coupling relationship between them.Although the increase of forest age could promote the transformation of soil microorganisms into available phosphorus in soil,the soil of Q.acutissima forest was still restricted by phosphorus due to the lack of total phosphorus and the consumption of available phosphorus.(3)With forest aging,the contents of carbon,nitrogen and phosphorus in leaves,dry,fine roots and litter leaves of Q.acutissima plantation showed an increasing trend.At the same forest age stage,the contents of carbon,nitrogen and phosphorus in different organs and litter leaves of Q.acutissima varied greatly.The organic carbon content as follows:leaves>litter leaves>fine roots>dry.The total nitrogen showed as follows:leaves>litter leaves>fine roots>dry.The total phosphorus showed as follows:leaves>fine roots>dry>litter leaves.The leaves and litters of Quercus acutissima had significant ecological econometric coupling with soil and soil microorganisms.The contents of carbon,nitrogen and phosphorus in leaf and litter of Quercus acutissima forest could significantly affect the contents of carbon,nitrogen and phosphorus in soil and soil microbial biomass.The leaf N:P of middle-aged forest,near-mature forest and mature forest in the study area were 16.36,16.14 and 16.11,and the average N:P of litter was 28.15.The growth of Q.acutissima forest was limited by phosphorus,and the phosphorus content was maintained by increasing the reabsorption of phosphorus before leaf litter.(4)The soil organic carbon mineralization rate in forest age gradient was as follows:mature forest>near-mature forest>middle-aged forest>young forest,and decreased significantly with the increase of soil depth.The trend of cumulative mineralization of soil organic carbon was:mature forest>near mature forest>middle-aged forest>young forest.The cumulative mineralization of soil organic carbon decreased significantly with the increase of soil depth.The results of soil organic carbon pool fitting showed that the soil active organic carbon content ranged from 0.13 to 1.26g·kg^-1,and increased with the increase of forest age.The variation range of soil slow-acting organic carbon content was 6.28-18.54g·kg^-1,which increased first and then decreased with the increase of forest age.The soil inert organic carbon content ranged from 8.63to 25.09g·kg^-1,and increased with the aging of forest.(5)Soil organic carbon pool components were significantly correlated with forest age,soil layer,total nutrients,soil available nutrients,soil microbial biomass,and leaf and leaf litter total nutrients.Ecological stoichiometry characteristics of leaf,leaf litter,soil and soil microorganisms of Q.acutissima plantation in the study area are closely related,which reflects the mutual balance and restriction of nutrient dynamic changes of Q.acutissima plantation ecosystem as an organic whole.The soil organic carbon pool was expanded due to the increase of litter accumulation and the increase of soil microbial biomass.At the same time,due to the increase of plantation productivity,the consumption of active carbon and the increase of microbial activity,the stability was reduced.