| Robinia pseudoacacia plantation is one of the major soil and water conservation forests in Loess Plateau,but a great scale of soil drying and forest degradation in Robinia pseudoacacia plantations have made a threat to the benefits of vegetation construction and recovery in Loess Plateau.Selecting typical Robinia pseudoacacia plantations across different vegetation zones and of different forest ages in loess plateau as the research objects,this study illustrated the characteristics of C,N,P contents and C:N:P ecological stoichiometry in soil and microbial biomass of Robinia pseudoacacia plantations.We also analyzed the impact of the environmental factors and forest age on them.At the same time,combining with leaf litter-green leaves-twigs-roots of Robinia pseudoacacia,links between above-and below-ground ecological stoichiometry of Robinia pseudoacacia plantations have been revealed.The aims were to promote the understanding of overall ecological characteristics and functions of Robinia pseudoacacia plantations in Loess Plateau,and to provide data support and theoretical basis for the vegetation construction and recovery in Loess Plateau.The results showed that:1)C,N,P contents in soil and microbial biomass of Robinia pseudoacacia plantations on Loess Plateau show a pattern of regional differentiation.As a whole,Contents of soil organic C within 0~20 cm soil layer varies between 2.02~15.27 g·kg-1,soil total N contents varies between 0.24~1.59 g·kg-1,soil total P contents varies between0.24~1.59 g·kg-1,soil available N contents varies between 5.03~36.78 mg·kg-1,soil available P contents varies between 0.77~16.29 mg·kg-1,soil microbial biomass C varies between 84.75~391.71 mg·kg-1,and soil microbial biomass N varies between 5.88~120.66mg·kg-1,showing that the mean nutrients contents in Robinia pseudoacacia plantations within Loess Plateau are lower than the mean value of the corresponding nutrients.2)As the plants grew,soil properties have been improved with certain features due to the growth of plants.In the Robinia pseudoacacia plantations,with the growth of Robiniapseudoacacia,soil organic C and total N contents increase gradually,soil total P and available N and P change irregularly,and soil microbial biomass C,N and P contents show a rising trend.However,soil organic matter accummulation and microbial biomass have no significant increase during the former several years' growth of Robinia pseudoacacia.They begin to make apparent improvents at the mature stage,and appear to decrease in amounts or in increase rates in over-matured forest.3)Allocation of C,N and P differs among different parts and among different growth stages of Robinia pseudoacacia,which drives corresponding changes of C:N:P ratios in different organs.The C:N:P stoichiometric characteristics in different organs also exhibit the growth and strateges of Robinia pseudoacacia to the environment.Since elements concentrations in plants are affected by many factors,there are limits to predict the plant nutrients limitation through the value of foliar N:P ratio or through the stoichiometric correlations between different plant organs and between plant and soil.4)Values of C:N:P ratios in soil and soil microbial biomass of Robinia pseudoacacia plantations across the Loess Plateau are lower than the global level,which are present with an average value of 8.8 for soil C:N,1.2 for soil N:P,10.3 for soil C:P and 5.2 for soil microbial biomass C:N.Environmental factors have little impact on soil C:N ratio,but exert significant influences on soil N:P and C:P ratios as well as soil microbial biomass C:N ratio.And although forest age nearly show no influence on C:N ratios of the soil and soil microbe,it impact on C:P and N:P ratios of them.Variations in C:N:P ratios of plant-soil-soil microbial biomass correspond to each other.There was no consistent temporal pattern in soil and soil microbial biomass C:N:P stoichiometry along the successional stages. |
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