| In this study,we chose three different vegetation types which was restored to forest in the Loess Hilly Region of Northern Shaanxi.Through field vegetation surveyed and statistical of species composition,species diversity analyzed,at the same time,measured the content of C,N,and P in soil-leaf-litter.In order to investigate the correlations among soil-leaf-litter C,N and P contents and their ecological stoichiometric characteristics under different rainfallfactors,and clarify the dynamic process of function between soil and different artificial vegetation communities in Loess Hilly Region.Discussed the major factors affecting the nutrient content and the stoichiometric characteristics of plants and soils on a large scale,which will provide theoretical guidance for the future restoration and reconstruction of vegetation in the loess hilly regions,also reasonable allocation of vegetation patterns,and promote the further acceleration of the ecological restoration of the Loess Plateau.The main conclusions are as follows:?1?The vegetation types,diversity and distribution pattern showed significant differences under different rainfall gradients,but the canopy density of different plants showed different.The degree of canopy closure in different rainfall gradients was Fuxian?FX?>Yan'an?YA?>Mizhi?MZ?;shrubs in Yan'an were significantly higher than those in Mizhi and Fuxian by1.62 and 1.03 times,respectively;Herbs in Fuxian County were significantly higher than Mizhi and Yan'an respectively.0.56,0.45 times,but there is no significant difference between Mizhi and Yan'an?2?From the differences in vegetation composition in different regions,it is known that Average annual rainfall significantly affects the vegetation types.Fuxian County has rich natural hydrothermal than Yan'an and Mizhi,so that the water of soil in Fuxian County is largest among three counties.Whereas that the grass in Fuxian has best growth.ranged between 1.6-9.1 g·kg-1,1.0-12.5 g·kg-1,2.6-8.0 g·kg-1;N??????0.3-0.7 g·kg-1,0.4-0.8g·kg-1,0.3-1.0 g·kg-1;P????????0.4-0.6 g·kg-1,0.3-0.6 g·kg-1,0.3-0.6 g·kg-1.Soil C:N,C:P,N:P values as a whole showed that Fuxian County was significantly higher than Yan'an and Mizhi.The nutrient contents of soil C,N and P showed a significant increase with the increase of average annual precipitation,but there was no significant difference between Mizhi and Yanan.?3?With the increase of average annual precipitation,the change ranges of arbor,shr-ub and herb leaf C in three regions were 417.76-449.68g·kg-1,427.78-480.07g·kg-1,and435.16-474.21g·kg-1;The ranges of N was 18.18-31g·kg-1,14.68-31.04g·kg-1,and9.52-16.42g·kg-1,respectively.The variation ranges of P were 2.02-2.06g·kg-1,1.52-2.51g·kg-1 and 1.86-2.76g·kg-1.There was no significant difference in arbor leaves P among different rainfall gradients,but in shrubs and abandoned lands,Yan'an was significantly higher than Mizhi,and Mizhi was significantly higher than Fuxian.Leaf C:N values were significantly higher in Mizhi than Yan'an and Fuxian in different vegetation types;C:P values ranked Yanan<Mizhi<Fuxian in shrubs and herbs,compared to Mizhi and Yan'an The main nutrient element limiting the growth of vegetation in Fuxian County maybe P.The growth of vegetation in the Mizhi area is maybe mainly limited by N;in the Yan'an area,maybe it is limited by N and P elements commonly.?4?The nutrient contents of C,N and P and their stoichiometric characteristics of pla nt litter showed different patterns of change among different regions.The changes of t ree,shrub and herb litter C in three regions were 349.24-418.14g·kg-1,352.05-423.38g·kg-1,and 354.25-436.83g·kg-1,respectively;the content of N were 11.46-18.46g·kg-1,10.61-17.18g·kg-1,and 6.15-14.16g·kg-1,respectively;P ranged from 1.73-1.96 g·kg-1,1.04-2.16g·kg-1,1.49-1.92g·kg-1,respectively.The total content of litter C and N was sig nificantly higher in Fuxian than in Yan'an and Mizhi,while P was higher in Yan'an t han in Mizhi and Fuxian.?5?According to the correlation analysis of leaf,litter,soil,carbon,nitrogen and phosphorus content,and ecological stoichiometry ratio,there was a significant correlation among the contents of soil,leaf,and litter C,N,and P.Among the nutrient ratios of C,N,and P in leaf,litter,and soil,only soil C:P showed significant correlation with leaf and litter C:P ratio,in which soil C:P ratio and litter C:P ratio and N:P ratio showed a very significant positive correlation,and there was a significant positive correlation between leaf C:P ratio and N:P ratio. |
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