| Chinese fir is an important fast-growing afforestation tree species in South China.Poyang Lake watershed is the main producing area of Chinese fir,the area and volume of Chinese fir account for 31.3%and 35.5%of the arbor forest in the watershed respectively.It plays an important role in the construction of regional ecological barrier and the strategic reserve of wood production.Due to long-term continuous planting and unreasonable management,soil fertility decline and productivity decline in Chinese fir forest,soil and forest nutrient status and productivity maintenance and stability have attracted more and more attention.In recent years,eco-Chemometrics has been widely used to study the supply relationship of terrestrial ecosystem elements and has been used as an important indicator to evaluate the structure,function and stability of ecological system.In order to systematically understand the nutrient characteristics of Chinese fir forest in Poyang Lake watershed,98 Chinese fir forest plots with an area of 800 m2were set up in different regions,different stand types and different forest ages of Poyang Lake watershed.The contents and reserves of C,N and P in vegetation layer(tree layer,shrub layer and herb layer),soil layer(0?10,10?20,20?30,30?50,50?100 cm five soil layers)and litter layer(semi-decomposed and undecomposed)were investigated,measured and estimated.The stoichiometry and differentiation characteristics of C,N and P in plant-litter-soil of Chinese fir forest in Poyang Lake watershed were analyzed.The main results are as follows:(1)Soil C,N and P content and stoichiometric ratio of Chinese fir forest in Poyang Lake watershed had obvious regional characteristics.Soil C content ranged from 12.92g·kg-1to 36.06 g·kg-1,while soil N and P content ranged from 1.24 g·kg-1to 1.93 g·kg-1and from 0.32 g·kg-1to 0.46 g·kg-1,respectively.Soil C,N and P content were relatively higher in northeastern Jiangxi and lower in central Jiangxi.Soil C:N ranged from10.18 to19.79,while C:P and N:P ranged from 43.73 to 118.26 and from3.18 to5.67,respectively.Soil C:N and C:P in northeastern and southern of Jiangxi was significantly higher than other areas,while soil N:P in northwestern and northeastern of Jiangxi was significantly higher than that in central and southern of Jiangxi(p<0.05).Soil C,N and P storage in the four regions ranged from16.71 t·hm-2to 60.71 t·hm-2,from1.61 t·hm-2to 3.09 t·hm-2and from 0.72 t·hm-2to 0.89 t·hm-2,respectively.Soil C and N storage distribution also had significant regional differences,but soil P storage regional differences were not obvious.According to the regional characteristics of soil nutrient and stoichiometric ratio,corresponding forest management measures can be formulated for Chinese fir forests in different regions to improve the management efficiency of Chinese fir forests and promote the increase of wood yield.(2)There was no significant difference in soil C,N and P content and stoichiometric ratio between pure Chinese fir forest and broad-leaved mixed forest,but it showed obvious vertical distribution.Soil C and N content in different forest types showed a decreasing trend with the increase of soil depth,while the variation of soil P content was not obvious.Soil C:P and N:P decreased with the increase of soil depth.The soil C,N and P storage of different forest types showed heterogeneity with the increase of soil depth.In the management of Chinese fir forest,we should consider the influence of soil depth on survey sampling and Chinese fir forest management,and formulate scientific and reasonable management measures.(3)Soil C content of Chinese fir forest of different ages ranged from 15.64 g·kg-1to22.11 g·kg-1while soil N and P content ranged from 1.17 g·kg-1to 1.62 g·kg-1and from0.33 g·kg-1to 0.59 g·kg-1respectively,which showed different changes with the increase of forest age.Soil C content of over-mature forest was lower,but soil P content was higher,and soil N content of near-mature forest was the lowest.Soil C:N?C:P and N:P in Chinese fir forest of different ages ranged from 15.79 to 21.39,from2.57-79.90 and from 3.22 to5.35.Soil C:N of near-mature forest was significantly higher than that of young,middle-aged and mature forests;soil C:P and N:P of over-mature forests was significantly lower than other forests.Soil C:N of near-mature forest was significantly higher than that of young,middle-aged and mature forests;while soil C:P and N:P of over-mature forests was significantly lower than other forests.Soil C,N and P storage of different forest types ranged from 23.08 t·hm-2to 36.88 t·hm-2,from1.78 t·hm-2to 2.64 t·hm-2and from 0.67t·hm-2to 1.34 t·hm-2.Overmature forest had higher soil N and P storage,while soil C storge was lower.It can be seen that there are significant differences in the ecological functions of soil C fixation and the demand for N and P in different forest ages of Chinese fir forest.In order to improve the C fixation function of Chinese fir forest,timely cutting should be carried out to maintain the age of Chinese fir forest below overmature forest.(4)Stand types had significant effects on C,N and P content and stoichiometric ratio of Chinese fir forest.N content in tree layer of pure Chinese fir forest was significantly higher than that of mixed forest,and C content in tree layer of mixed forest was higher than that of pure forest.N content in shrub layer of mixed forest was significantly higher than that of pure forest,while P content was significantly lower than that of pure forest.N content in herb layer of mixed forest was significantly higher than that of pure forest.In pure forest and mixed forest,the contents of C and P in tree layer were significantly correlated with the contents of N.The C:N in shrub layer of pure forest was significantly higher than that of mixed forest,C:P and N:P in mixed forest were significantly higher than that of pure forest.The herb layer C:N of pure forest was significantly higher than that of mixed forest,and the C:P and N:P of mixed forest were higher than those of pure forest.It can be seen that the mixing of other tree species affects the nutrient absorption of Chinese fir in tree layer,shrub layer and herb layer,but the effect of mixing on Chinese fir forest is uncertain.(5)Forest age had significant effects on the contents of C,N and P in tree layer of Chinese fir forest.C content was the smallest in the branches of the near-mature forest,and the largest in the leaves and roots;The N content of branches and leaves was the highest in the near-mature forest period,while that of roots and stems was the highest in the over-mature forest period.The content of C,N and P in different components of Chinese fir forest showed that the content of C,N and P in leaves was the largest and that in roots was the smallest.With the increase of forest age,the average P content in tree layer increased first and then decreased,and the middle-aged forest was the largest.The biomass changes of different components at different stand ages were basically the same as that of C storage.With the increase of stand age,the C storage in leaves increased first and then decreased,and the branches,stems and roots showed an increasing trend.(6)The C,N and P content and stoichiometric ratios in shrub layer of Chinese fir forest varied significantly in different organs.The average contents of C,N and P in the shrub layer of Chinese fir forest at different stand ages were as follows:leaf>branch>root,and the average content of C showed a decreasing trend with the increase of stand age.Shrub layer C:N and C:P average:root>branch>leaf,N:P:leaf>root>branch.(7)Different stand types had significant effects on the litter C,N and P contents and stoichiometric ratios of C.lanceolata forest.The C content of non-decomposed and semi-decomposed litter in pure Chinese fir forest was significantly higher than that in mixed forest,and the N content was significantly lower than that in mixed forest,resulting in the C:N ratio of non-decomposed and semi-decomposed litter in mixed forest was significantly lower than that in pure Chinese fir forest,indicating that the litter in mixed forest had a high decomposition rate.The stoichiometric ratios of C:N and C:P in the litter uncalcined layer of C.lanceolata forest were the lowest in the middle-aged forest and the highest in the near-mature forest.With the increase of forest age,litterfall and C,N,P storage in undecomposed and semi-decomposed layers increased first and then decreased,and the increase reached the maximum in middle age forest.In summary,in the Poyang watershed the C,N and P content and stoichiometry of soil and plants of Chinese fir forest had significant regional variations and obvious regional characteristics.Soil C,N and P content were higher in Northeast Jiangxi and lower in central Jiangxi;There was no significant difference between pure Chinese fir forest and mixed Chinese fir and broad-leaved forest,but it showed obvious vertical distribution;With the increase of forest age,the C,N and P content showed different change laws.Stand types had significant effects on the content and stoichiometric ratio of C,N and P of arbor,shrub and grass of Chinese fir forest;the age of Chinese fir forest had a significant effect on the contents of C,N and P in the tree layer.In future management strategy should be based on different regions,different stand types and different ages of Chinese fir forest.The content of C,N and P and their stoichiometric ratios in different soil layers also have obvious regularities which should be considered in the management and the evaluation of the ecosystem function of Chinese fir forest to obtain scientific data for management and ecosystem function evaluation of Chinese fir forest,based on which sustainable management of Chinese fir forest could be better obtained. |
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