Study On The Stoichiometric Characteristics Of Soil-Plant Ecosystem In Robinia Pseudoacacia Forest On The Loess Plateau

Since conversion of cropland to forest and grassland project carried out,the Loess Plateau had built a large number of artificial vegetation,which,to a certain extent,curbed the deterioration of the ecological environment.However,with the increase in age,the internal environment and soil properties of forest ecosystem would change,which influenced pattern of the nutrient distribution.Therefore,to study chemical characteristics of soil-plant ecosystem in Robinia pseudoacacia forest land,and to analysis the relationship between nutrient content and ecological characteristics of leaf-root-soil ecosystem,were very important to study mechanism of carbon and nitrogen nutrient cycling.The main conclusions are as follows: 1.The content of soil moisture decreased gradually with the growth period of Robiniapseudoacacia.Soil saturated hydraulic conductivity gradually increased with theincrease of mean age.They were all greatly affected by soil depth.There was nosignificant effect of locust number and soil depth on bulk density.With the extension of the growth period,the average soil water content of 0-200 cm in Robinia pseudoacacia forest decreased gradually.In the same month,there was no significant difference between 10 and 15 years,so did between 25 and 40 years.And Compared with10 years,40 years,were reduced by 16.70%,34.01%,22.70%,25.39%.The content of soil moisture decreased gradually in March,May,August and October between 0 and 200 cm.The soil saturated hydraulic conductivity gradually increased with the increasing age,between 0 and 50 cm,comparing with10 years,40 years,were increased by 59.56%,and gradually reduced with the increase of soil depth.2.With the increase of locust age,the nutrient content of soil increased between 0 and200 cm,which was affected by different depths of soil.With the growth of forest age,the content of soil nutrient increased,meanwhile the contents of organic C,total N,available P and N were decreased and then increased,rather than total P and K increased gradually.Compared with organic C,total N,total P,total K of 10 years,forest,the forest growth of 40 years,were increased in 30.56%,26.95%,5.56%,23.02%.Because of "accumulation effect on surface" of soil nutrient,the content of soil nutrient was higher on surface,and had decreasing trend with the increase of the soil depth.Soil nutrients except total potassium were less.3?With the increase of age,the ratios of C: N,C: P and N: P in soil were decreasedfirstly and then increased,while the ratios of C: P and N: P decreased with theincrease of soil depth.The stoichiometric ratio in this region was overall small.With the increase of age,the ratios of C: N,C: P and N: P were decreased firstly and then increased,which showed that with the growth of Robinia pseudoacacia,the accumulation rate of carbon,nitrogen and phosphorus in soil were faster firstly and then slower.From the ratio of C: N greater than C: P greater than N: P,we can inferred that accumulation rate of C was greater than N and P.4?With change of age,the contents of C,N,P and their stoichiometry in Robiniapseudoacacia changed obviously,rather than the effects of C,N,P andstoichiometry on the number of roots were not significant.The content of organic carbon in leaves decreases with the growth of Robinia pseudoacacia age,total nitrogen and total phosphorus content decreased first and then increased with the length of 40 years of locust growth,leaf nutrient was 10 years reduced by 12.22%,20.42%,30.77%.With growth,the carbon sequestration capacity of locust decreased gradually,N,the accumulation rate of P element decreases first and then increases with the growth of C: N with the ratio of Robinia pseudoacacia.Leaf limit fluctuated,leaf C: P ratio first increased with age growth decreased,N: P than Robinia pseudoacacia leaves increases gradually with age 40 years,10 years was the measurement of leaves were increased by 13.46%,9.28%,14.02%.Growth rate of Robinia pseudoacacia with age increased,and the area was under the restriction of P.4 years in the 0-200 cm soil layer of Robinia pseudoacacia root of organic carbon,total nitrogen,total phosphorus,C: N and C: P ratio decreased with increasing years showed a fluctuating trend,with a mean root N: P ratio limit increases.5?With the growth of the locust,the ratio of C,N,P distributions in the blade-root-soilhad different change trend.The stoichiometric ratios of soil and leaves had nosignificant correlation,rather than stoichiometric ratio of root had certain relationwith soil and leaf.For the organ of plant and soil,the distribution of C,N,P in root and soil decreased,which showed that the soil nutrients are in continuous improvement with the growth of the tree.For roots and leaves,the distribution of C was relatively stable,rather than the distribution ratio of N and P decreased firstly and then increased,which it first enrich to root before enriching leaf.Measurement of leaves and soil chemical ratio had no significant correlation,however root stoichiometry had certain relation with soil and leaf,showing that plant absorbing nutrient from the soil was closely related with the root,and internal nutrient contents of root and leaf were closely related,in a dynamic balance.