Effects Of Enclosure And Afforestation On The Carbon,Nitrogen And Phosphorus In Plant And Soil Of Desertified Grassland In Horqin Sandy Land

Horqin Sandy Land,located at the eastern end of the semi-arid farming-pastoral ecotone in northern China,was a grassland with many lakes and lush vegetation dominated by palatable grass species,along with sparsely scattered woody species.However,due to unreasonable human activities such as overgrazing and reclamation superimposed on the fragile ecological environment matrix,desertification developed rapidly and became one of the most serious areas in modern China.Artificial afforestation and enclosure are two effective measures for ecological restoration of desertification grassland,and the process and mechanism of their influence on vegetation and soil have always been the concern of scholars.In this paper,by understanding the effects of artificial afforestation and closure on the plant community characteristics and soil physical and chemical properties of desertification grassland,the stoichiometric response of plant-soil carbon（C）,nitrogen（N）and phosphorus（P）stoichiometry under different restoration measures was discussed.In order to provide science for the formulation of sustainable restoration measures and the evaluation of ecological restoration effect of degraded ecosystem in Horqin sandy land.The research results show that:（1）After afforestation and enclosure of desertified grassland,the species quantity characteristics and species diversity of shrubs and herbs were significantly improved.Compared with grazing plots,the number of species,biomass,total coverage,number of plants,average plant height,species richness index,Simpson dominance index and Shannon-Wiener diversity index of plant communities after afforestation and enclosure all increased significantly（P<0.05）,while Pielou evenness index decreased significantly after enclosure.Both artificial afforestation and enclosure have restored the growth of plant communities,and artificial afforestation has a more significant restoration effect on Gramineae and Leguminosae plants,and the plant community structure is stable after artificial afforestation.（2）After afforestation and enclosure of desertified grassland,the soil quality was significantly improved.According to the basic physical and chemical properties of soil,after afforestation,the soil bulk density and fine sand grain content in 0～10 cm soil layer and 10～30cm soil layer,clay grain content in 0～10 cm soil layer,alkali-hydrolyzable N（AN）content in10～30 cm soil layer increased significantly（P<0.05）.After enclosure,the soil bulk density,fine sand content 0～10 cm soil layer,clay content,electrical conductivity（EC）and AN content in 0～10 cm soil layer and 10～30 cm soil layer increased significantly.In terms of soil nutrient content,after afforestation and enclosure,soil organic C content was significantly 10.06 times and 7.20 times,total N content was significantly increased by 8.75 times and 6.25 times,and total P content was significantly increased by 3.56 times and 1.67 times.Compared with enclosure,the content of AN in afforestation is higher in enclosure than in afforestation,and the average contents of soil organic C and total N are higher in afforestation than in enclosure,and the total P is significantly higher in afforestation than in enclosure.After afforestation,the soil C,N and P have stronger retention capacity.（3）Afforestation and enclosure in desertified grassland have significant effects on the contents of C,N and P in plants.After afforestation and enclosure,the total C content in leaves,total N content in roots and root C∶N changed significantly:the total C content in leaves increased significantly from 369.32 g·kg^-1 to 443.18 g·kg^-1 and 460.36 g·kg^-1 respectively after afforestation and enclosure（P<0.05）;C∶N of plant roots increased significantly from 29.71to 42.56 and 40.19.After afforestation,the total N content in plant roots decreased significantly from 13.32 g·kg^-1 to 9.60 g·kg^-1.The total N content of leaves is less than the average of 30g·kg^-1 in the leaves of plants in arid desert areas,and the total P content is greater than the average of 1.74 g·kg^-1 in the leaves of plants in typical desert and desertification areas in northern China.The plants in the study area have relatively low total N content and high total P content.There is no significant difference between C∶N∶P of leaves and C∶P and N∶P of roots in grazing,afforestation and enclosure.（4）Soil stoichiometry changed significantly after afforestation and enclosure in desertified grassland.After afforestation and enclosure,C∶N increased by 56.37%and 16.16%respectively（P>0.05）,C∶P significantly increased by 139.24%and 195.70%respectively（P<0.05）,and N∶P decreased by 28.33%（P>0.05）and 61.37 respectively.Compared with enclosure,afforestation increases C∶N more,and enclosure increases C∶P and N∶P more.The decrease of N∶P after restoration indicates that there is a lack of N in the soil,and attention should be paid to the supply of N in the soil during the subsequent restoration.（5）Pearson analysis shows that plant leaves,roots and soil are all affected by vegetation characteristics and soil physical and chemical properties;Except for the significant positive correlation between total N in leaves and total P content（P<0.01）,there was no significant correlation between total C,total N and total P content in leaves and roots of other plants,and C∶N in leaves and roots of plants was mainly affected by total N,while C∶P and N∶P were mainly affected by total P content.According to RDA analysis,the contents of available P,Shannon-Wiener diversity index and alkali-hydrolyzable N account for the largest amount of eco-stoichiometry in plant leaves,plant roots and soil respectively.The main driving factor of plant leaf and soil eco-stoichiometry is soil factor,and the main driving factor of plant root eco-stoichiometry is vegetation factor.In conclusion,the plant community,basic physical and chemical properties of soil and plant-soil stoichiometry have been improved in different degrees after afforestation and enclosure measures have been taken in desertification grassland.Both restoration measures can improve the quality of soil,and at the same time,the N∶P of afforestation and enclosure are reduced,which indicates that the soil is short of N,and it is necessary to supplement N in the later stage of restoration to further promote the restoration of degraded grassland.