| To comprehensively understand the stoichiometric characteristics of different plantation ecosystems within different vegetation belts,in this paper,the ecosystems of Robinia pseudoacacia and Pinus tabulaeformis plantation in Yichuan County,which belongs to forest belt and Ansai County,which belongs to forest steppe belt in the Loess hilly-gully region,northern Shaanxi,were studied.We compared and analyzed the carbon(C),nitrogen(N),and phosphorus(P)stoichiometries in the arbor(leaf,branch,trunk,root),litter,and soil of the deciduous broad-leaved tree species Robinia pseudoacacia and evergreen coniferous tree species Pinus tabuliformis plantations.The seasonal variation and interannual variation of the stoichiometric characteristics of each component were also studied.At the same time,the relationships of ecological stoichiometric characteristics among plant leaf,litter and soil were further explored,and the interaction effects among C,N,and P elements and nutrient cycling relationships were revealed,in order to enrich the research on the nutrient coupling cycle mechanism of the ecosystem in the Loess Plateau,and to provide theoretical basis for the rational plant planning and vegetation restoration of Robinia pseudoacacia and Pinus tabulaeformis plantations in the Loess Plateau.The main findings are as follows:1)There were significant differences in the C,N,and P concentrations and their ratios between the Robinia and Pinus plantation ecosystems.The C concentrations in arbor organs of Pinus were significantly higher than that of Robinia,but the concentrations of N and P were significantly lower than those of Robinia.In addition,the ratios of C:N and C:P in the components of Robinia were significantly lower than those in Pinus,while the N:P ratio was significantly greater than that in the components of Pinus,indicating that the growth of Robinia is mainly limited by P,and Pinus limited by N.For different vegetation zones,the C concentrations of Robinia and Pinus leaf,P concentrations of Robiniabranch,N concentrations of Pinus root and the C,N concentrations of Pinus litter in Yichuan were lower than those in Ansai,while only P concentrations in leaf and N concentrations in branch of Pinusin Yichuan were greater than those in Ansai,and elements of other organs did not show significant differences.The soil C and N concentrations decreased with increasing soil depth,but the P concentrations remained constant in both plantationsand there were certain differences in the elements and ratios between different tree species and different regions.The correlation analysis among leaves,litter,and soil stoichiometric characteristics of Robinia and Pinus plantation indicated that litters,as an important link between plant and soil nutrient cycling,make the leaves and litter,litter and soil elements show strong correlation.2)The seasonal variations of C,N and P concentrations and their ratios in the organs and litter of Robinia and Pinus were inconsistent.The stoichiometric characteristics of different tree species showed significant differences.For example,the C concentrations in the leaf of Robinia leaf remained at a relatively high level in June and then increased after a short decline.The N and P concentrations of the Robinia leaf always showed a downward trend and reached the lowest value in October.The C concentrations in the leaf of Pinus were maintained at a stable level in the early growth season and increased significantly after August,while the N and P concentrations showed a trend of decreasing first and then increasing.The stoichiometric characteristics of the nutrient elements of plant components under different vegetation belts showed similar seasonal variations.The seasonal variations of C,N,and P concentrations and their ratios in the soil layers of Robinia and Pinus in Yichuan County and Ansai County were also different.Although the seasonal changes of C,N,and P concentrations and their ratios in most soil layers were not significant,their seasonal trends are more obvious,especially in the surface of soil the seasonal changes showing significant volatility.The soil nutrient concentrations and its ratios under different vegetation belts showed different patterns of change.In addition,analysis of the variability of plant leaves in Yichuan County and Ansai County indicated that tree species are the major sources of variation,and the sampling month and the interaction between the sampling month and the tree species also had a significant effect on the variation of N and P concentrations.The nutrient contents of plant leaves under different vegetation belts are also different,indicating that different vegetation belts are also one of the factors that affect the source of plant leaf variability.3)The C,N,and P concentrations of each component of Robinia and Pinus and their ratios showed different interannual variations.The C concentrationsin leaf,branch,and litter of Robinia and Pinus in Yichuan County and Ansai County decreased with the increase of the year.The N and P concentrations in each organ of Robinia and Pinus showed inconsistent variations with the increase of years.The ratios of C:N,C:P in leaves,branches,stems,and litters of Robinia in Yichuan County did not show significant interannual changes,while the C:N and C:P ratios increased with age in Pinus organs such as branch,trunk and root in Yichuan area.This shows that the nutrient variation between different tree species and between different organs varies.In addition,the soil C and N concentrations in Yichuan County and Ansai County did not show significant interannual changes in three years and only the soil surface C concentrations had a significant change.Soil P concentrations did not show a significant interannual change in Yichuan County,and soil P concentrations increases with the increase of the year in Ansai County.The ratio of soil C:N and C:P increased with the increase of year in Yichuan County,while the soil C:N,C:P,and N:P ratios in Ansai County showed a relatively stable trend and did not show significant interannual variety. |
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