Effects Of N And P Addition On Ecological Stoichiometry Of Different Forest Age In Metasequoia Glyptostroboides

The characteristics of plant eco-stoichiometry and nutrient cycling reflect the influence of changes in the external environment on the distribution of elements in the plant,the interaction between elements,and the dynamic balance between elements.At present,most of the studies on the eco-stoichiometric characteristics of plants are mostly found in the comparison of multiple species under the difference of natural environment And there are only few studies on the different development stages of a single species under the addition of external nutrients.Metasequoia glyptostroboides Hu et Cheng is one of the pioneer afforestation tree species in coastal protection forests in eastern China.The efficacy of Metasequoia in conserving water sources and improving soil properties is of great significance for the development of muddy coasts.Exploring the response of stoichiometric and nutrient cycling characteristics of different ages of Metasequoia glyptostroboides plantations to the addition of nitrogen and phosphorus has great guiding significance.for an in-depth understanding of the nutrient cycling mechanism of Metasequoia glyptostroboides plantations,to increase the value of Metasequoia glyptostroboides plantations,to develop their potential efficiently,and to promote the construction of coastal shelter forest speciesIn this study,6-year-old and 24-year-old Metasequoia glyptostroboides plantations with similar site conditions were selected in Dongtai Forest Farm of Dongtai City,which lies in the eastern coastal area of China closing to the Yellow Sea,for nitrogen and phosphorus addition experiments.The nitrogen addition gradient settings are NCK,0.8,2.4,4.0,4.8 mol·m-2;the phosphorus addition gradient settings are PCK,0.05,0.2,0.6,1.0 mol·m-2.By investigating the response of the growth rate,soil nutrients,stoichiometric characteristics of leaf and root,internal stability of stoichiometric,nutrient recovery rate of different ages of Metasequoia glyptostroboides to nitrogen and phosphorus additions,and the characteristics of nutrient limitation of Metasequoia plantations of different ages,the influence mechanism of nitrogen and phosphorus addition on the eco-stoichiometric characteristics and nutrient cycling characteristics of Metasequoia glyptostroboides is revealed.The main results show:(1)Nitrogen addition obviously promotes the growth of young Metasequoia but has little effect on the growth of adult Metasequoia.Phosphorus addition obviously promoted the growth of adult Metasequoia but has no significant effect on the growth of young Metasequoia.Continuous nitrogen application will reduce the growth rate of young Metasequoia glyptostroboides,while continuous application of large amounts of phosphorus will increase the growth rate of adult Metasequoia glyptostroboides.(2)Nitrogen addition increased contents of the soil carbon,nitrogen,and phosphorus and N: P of Soil in which young Metasequoia live,but decreased the carbon,nitrogen and N: P contents of Soil in which adult Metasequoia live;N: P,and the soil carbon content of adult Metasequoia glyptostroboides.(3)Nitrogen addition significantly increased the nitrogen content and N: P of the leaves and roots of young Metasequoia,but significantly reduced the phosphorus content of the leaves and roots of the young Metasequoia.The leaf phosphorus and root content of adult Metasequoia glyptostroboides increased and the nitrogen content and N: P did not change much.Phosphorus addition increased the nitrogen content and N: P of the leaves and roots of young Metasequoia glyptostroboides,with the phosphorus content of the leaves decreasing.The nitrogen content of the leaves and roots of adult Metasequoia glyptostroboides and the phosphorus content of the roots increased significantly,with the root N: P decreasing significantly.Leaf nutrient content is closely related to root nutrient content.There is a clear synergy between the response of leaf and root N and P nutrients to the addition of nitrogen and phosphorus.(4)With the addition of nitrogen and phosphorus,the stoichiometric stability coefficients HN of young Metasequoia leaves and roots are 7.58 and 5.62.HN:P are 12.20 and 13.16.HP does not exist.HN:P of young Metasequoia leaves is significantly lower than that of adult Metasequoia glyptostroboides.There was no significant difference in root system HN:P between different age Metasequoia.(5)The effect of nitrogen addition on nutrient nitrogen recovery of young and adult Metasequoia did not change significantly.Nitrogen addition significantly improved the nutrient nitrogen recovery rate of young Metasequoia glyptostroboides,but reduces the nutrient phosphorus recovery rate of young Metasequoia glyptostroboides in a certain extent.Phosphorus addition increased the recovery rate of nutrient nitrogen of young Metasequoia to a certain extent,and had no significant effect on the recovery rate of nutrient nitrogen of adult Metasequoia.Phosphorus addition significantly reduced the recovery rate of nutrient nitrogen in adult Mtasequoia,and had no effect on the recovery rate of nutrient nitrogen in young Mtasequoia Significantly affected.The recovery rate of nitrogen and phosphorus nutrients of young Metasequoia glyptostroboides is mainly affected by soil nutrient content and leaf life.The recovery rate of nitrogen and phosphorus nutrients of adult Metasequoia glyptostroboides is mainly affected by the ability of soil nutrients and their own element ratio regulation.(6)With the addition of nitrogen and phosphorus,the correlation between nutrient content of leaf and litter leaf,recovery efficiency of nutrient and soil nutrient content of Metasequoia glyptostroboides is significantly weaker than that of root nutrient content.The growth rate of young Metasequoia glyptostroboides is significantly positively correlated with the nitrogen content of soil and root system with the addition of nitrogen The growth rate of adult Metasequoia glyptostroboides is significantly positively correlated with the phosphorus content of roots with the addition of phosphorus addition There is a significant correlation between the nitrogen and phosphorus contents of young Metasequoia leaves and litter leaves and nitrogen contents of roots with the addition of phosphorus.The contents of nitrogen and phosphorus in leaves and litter leaves of adult Metasequoia glyptostroboides were significantly positively correlated with the contents of nitrogen and phosphorus in roots with the addition of phosphorus.The recovery rate of nutrient phosphorus in adult Metasequoia glyptostroboides is significantly positively correlated with contents of soil and root phosphorus.