| In this paper,the 40-year-old Mixed Cunninghamia lanceolate-Phoebe bournei forest,Pure Cunninghamia lanceolate forest and Pure Phoebe bournei forest in Jingzhu Forest farm in Lanshan County were taken as the research object.The nutrient contents of soil(0-10 cm,10-20 cm,20-30 cm)and plant samples(leaves,branches,absorbent roots and transport roots)in four quarters of each stand in January(winter),April(spring),July(summer)and October(autumn)were determined.The soil nutrient indexes included,SOC,TN,AN,TP,TK,TCa,TMg,Plant nutrient indexes included,TC,TN,TP,TK,T Ca,TMg.The seasonal variation rules of soil and plant nutrients in different stand types and the correlation between soil nutrients and nutrients in plant organs were discussed.The main research results are as follows:(1)The contents of nutrient elements in soil were different among different stand types.The contents of soil organic carbon in mixed Cunninghamia lanceolatePhoebe bournei forest,pure Cunninghamia lanceolate forest and pure Phoebe bournei forest were 42.58 g·kg-1,41.86 g·kg-1 and 43.12 g·kg-1,respectively.There was no significant difference in soil organic carbon and total nitrogen content.The total calcium content of the mixed forest was 156.48 mg·kg-1,which was significantly higher than that of other stands(P<0.05).Soil organic carbon,total nitrogen and total phosphorus all reached the maximum value in summer,but decreased to the lowest value in winter.The total calcium content of mixed Cunninghamia lanceolate and pure Cunninghamia lanceolate forests was the lowest in winter and the highest in autumn,while the total calcium content of pure Cunninghamia lanceolate and Phoebe bournei forests was the lowest in autumn and the highest in summer.Correlation analysis showed that stand type had no significant effect on soil organic carbon.There was significant correlation between total P and stand type,season and their interaction.There was a positive correlation between soil total calcium and total magnesium in three stand types.In general,the mixed forest increased the content of most soil nutrients.(2)There were differences in nutrient content of different stand types between Cunninghamia lanceolate and Phoebe bournei.Among the three stands,the contents of total carbon,total calcium and total magnesium in leaves of Cunninghamia lanceolate were higher than those of Phoebe bournei,but the contents of total nitrogen and total phosphorus were lower than those of Phoebe bournei.The highest total carbon in leaves of mixed Cunninghamia lanceolate-Phoebe bournei forest was 438.75 g·kg-1,while the highest total nitrogen in leaves of pure Phoebe bournei forest was 17.11 g·kg-1.Total carbon and nitrogen of pure Cunninghamia lanceolate forest were 430.49 g·kg-1 and 13.49 g·kg-1,respectively,which were higher than those of mixed Cunninghamia lanceolate-Phoebe bournei forest.Except leaves,the total nitrogen content of all organs in pure forest was lower than that in mixed Cunninghamia lanceolate-Phoebe bournei forest.The nutrient indices of the three stands showed seasonal changes,and the seasonal changes of different organs were different.In the mixed forest,total nitrogen of Cunninghamia lanceolate leaves was higher in spring and autumn,but lower in summer and winter,while total nitrogen of roots was the highest in summer and the lowest in winter.The content of total nitrogen in pure Cunninghamia lanceolate trees was the highest in summer and the lowest in autumn.The content of total phosphorus in the absorbed roots of pure Phoebe bournei forest was the highest in summer and the lowest in spring.There were differences in nutrient fluctuations in different organs,and the seasonal dynamic changes of nutrients in leaves and absorbing roots were significant.The total phosphorus content in leaves and branches ranged from 0.55 g·kg-1 to 1.31 g·kg-1 and 0.58 g·kg-1 to 1.01 g·kg-1 in four seasons.The content of total phosphorus in the leaves of Phoebe bournei ranged from 1,06 g·kg-1 to 1.78 g·kg-1,and the content of total phosphorus in the branches ranged from 0.63 g·kg-1 to 1.07 g,kg-1,and the seasonal fluctuation of nutrient in Cunninghamia lanceolata was greater than that in Phoebe bournei.The correlation analysis showed that there were different correlation levels of nutrients in different organs of Cunninghamia lanceolata and Phoebe bournei in different stands.The total carbon of Cunninghamia lanceolata in mixed forests was significantly positively correlated with total magnesium in branches and total carbon in transport roots(P<0.05),while it was significantly negatively correlated with total magnesium in absorbed roots(P<0.05).However,there was no significant correlation between total carbon of Cunninghamia lanceolate leaves and nutrients of all organs.There was a significant negative correlation between total carbon and total phosphorus(P<0.05)in the leaves of mixed forest and Phoebe bournei(P<0.05).There was a significant negative correlation between total nitrogen and total phosphorus in the absorbed roots of pure Phoebe bournei forest and total magnesium in the transported roots(P<0.01).(3)The stoichiometric characteristics of various organs of different stand types of Cunninghamia lanceolate and Phoebe bournei were different.Among the three kinds of stands,C:N of leaves and transport roots of Cunninghamia lanceolata mixed forest was significantly higher than that of pure Cunninghamia lanceolate forest,while C:P was significantly lower than that of pure Cunninghamia lanceolate forest.The N:P of all organs in mixed forest was significantly lower than that in pure forest.The stoichiometric characteristics of the organs of the three stand plants showed seasonal changes.The leaf C:N of Mixed Cunninghamia lanceolate-Phoebe bournei forest was the highest in winter and the lowest in autumn,while the leaf C:N of pure Cunninghamia lanceolate forest was the lowest in winter and the highest in summer.The leaf C:N was the highest in winter and the lowest in summer in the mixed forest and Phoebe bournei forest,while the leaf C:N was the highest in summer and the lowest in autumn in pure Phoebe bournei forest.Correlation analysis showed that stoichiometric characteristics of plant nutrients had different responses to stand,season and their interactions,and seasonal factors had more significant effects on nutrients.(4)The correlation analysis of soil and plant nutrients showed that soil organic carbon in mixed forest and pure forest of Cunninghamia lanceolate showed a significant positive correlation with total carbon and total nitrogen of Cunninghamia lanceolate leaves,while soil total potassium and total calcium showed a significant negative correlation with total potassium and total calcium of Cunninghamia lanceolate roots.The correlation between different organs and soil nutrients was different.The correlation between roots and leaves and soil nutrients was stronger,while the correlation between roots and leaves and branches was poor.The structural equation model showed that the coupling effect between different tree species and soil was different,and the tree species characteristics had a more significant effect on soil nutrients.Stand type changed the coupling relationship between the same plant and soil,but did not affect the coupling relationship between each organ of the plant itself. |
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