| Pinus Massoniana is widely distributed in the red soil region of southern China with its barren tolerance,drought resistance and slight acid preference.However,its habitat vulnerability is determined by human activities and natural conditions such as topography,climate and soil parent material,especially in the red soil hilly region where granite is developed.Besides,due to its unitary stand structure,lack of understory vegetation such as shrubs and herbs,and bare soil layer,the surface soil is constantly scoured by rainwater,which is extremely vulnerable to soil erosion,and becomes the forest type with the largest degraded area in the forest ecosystem in the southern region of China.Therefore,it is urgent to restore vegetation and improve soil and water conservation function of eroded-degraded Pinus massoniana forest in this region.Based on field investigation,positional observation and indoor analysis,this study used 7 vegatation restorations,included contour grass irrigation belt(T1),small hole sowing grass(T2),strip ditch sowing grass+replanting broad-leaved trees(T3),arbor-shrub-grass mixed(T4),fish scale pits(T5),full-slope grass-sowing(T6),closed management(T7),as well as untreated bare land(CK1),and severely eroded-degraded Pinus massoniana forest land with no untreatments(CK2).Through the combination of field investigation and indoor analysis,the community characteristics of vegetation growth,soil root system characteristics,litter water conservation characteristics,soil physicochemical properties,soil microbial community characteristics,soil permeability,soil anti-erodibility and anti-scourability,and runoff and sediment of different vegetation restorations in the sample plots from 2016 to 2021 were analyzed.Comprehensive evaluation of different vegetation restoration measures was carried out from three aspects of vegetation,soil and hydrology,and the vegetation restorations suitable for the typical severe erosion and degraded land in the south were screened out,in order to provide scientific theoretical basis for the restoration and reconstruction of eroded and degraded ecosystems.The main conclusions are as follows:(1)Different vegetation restorations significantly improved the vegetation community structure and vegetation growth characteristics.The vegetation coverage of each vegetation restoration has increased significantly from 2016 to 2021,reaching more than 90%in 2021.The vegetation coverage of T1,T2,T3,T4,T5,T6,T7 treatments were 56.92%,58.92%,60.04%,59.92%,57.92%,58.92%,57.58%higher than that of CK2,respectively.In addition,the increase of vegetation coverage of T3 and T4 was higher than that of other vegetation restorations,and the increase of vegetation coverage of CK2 was the lowest.The tree height,crown width,and diameter at breast height of trees and shrubs increased significantly under different vegetation restorations,and highest growth rate of tree and shrubs was T3.Different vegetation restorations of plant Shannon-Wiener diversity,richness and Pielou index in 2016-2021 were increased,and plant Shannon-Wiener diversity and richness index weres higher in T3,T4,T5,and T7,while the T1,T2,and T6 is were lower in richness index.The dominance index showed a downward trend on the whole.And the Simpson index generally decreased in all vegetation restorations.(2)Leaf functional traits and root traits were significantly improved by different vegetation restorations.The net photosynthetic rate,length,width,surface area,water content,and carbon(C),nitrogen(N),and phosphorus(P)contents in leaves of Pinus massoniana,Schima superba,and Dicranopteris dichotoma under different restorations were significantly increased,and their significantly higher than those of CK2.While the C:N,C:P ratio in leaves of Pinus massoniana,Schima superba,and Dicranopteris dichotoma and N:P ratios of Pinus massoniana were significantly decreased from 2016 to 2021.The leaf water content of Pinus massoniana,Schima superba,and Dicranopteris dichotoma was significantly positively correlated with the leaf length,width and surface area,and the functional properties of Pinus massoniana and Schima superba were limited by the N content in the leaves,and the functional properties of the leaves of Dicranopteris dichotoma were mainly affected by the P content.The soil root biomass,root length,root diameter,and root surface area under different vegetation restorations were significantly increased from 2016 to 2021,which were significantly higher than those in the CK1 and CK2.The C,N and P contents of roots in each vegetation restoration were significantly increased,which were significantly higher than those in the CK2,while the root C:N,C:P,and N:P ratios decreased significantly from 2016 to 2021.The C and C:N ratio of roots were the main factors affecting the functional properties of leaves of Pinus massoniana,Schima superba,and Dicranopteris dichotoma.The biomass,length,surface area,C,N and P contents in root were the highest in the T3 in 2021.(3)Different vegetation restoration measures significantly improved soil physicochemical properties.Soil water content,porosity,shear resistance strength,silt,clay and>0.25 mm water stable aggregates,soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),available phosphorus(AP),total potassium(TK)and available potassium(AK)contents and their nutrient storage were significantly increased under all vegetation restoration,which were significantly higher than those in CK1 and CK2.Soil bulk density,hardness,collapse coefficient,sand content,failure rate of aggregates>0.25 mm,and fractal dimension of aggregates decreased significantly,and were significantly lower than those of CK1 and CK2.There were significant or extremely significant correlations among soil physical and chemical properties.Soil organic carbon and total potassium content had positive effects on soil clay and silt,but had negative effects on soil sand.Soil fungi,bacteria,actinomycts,arbuscular mycorrhizal fungi(AMF),gram-positive bacteria(G~+),gram-negative bacteria(G~-),soil microbial biomass carbon and nitrogen contents in vegetation restoration were significantly increased from 2016 to 2021,which were significantly higher than those in CK1 and CK2,except that G~+was significantly lower than that in CK1 and CK2.The ratio of G~+:G~-in each vegetation restoration showed a decreasing trend from 2016 to 2021,and was significantly lower than that in CK1 and CK2.The redundancy analysis showed that vegetation cover and litter C content were the main factors influencing soil microbial community structure,explaining 44.19%and 47.82%of the total changes in soil microbial community structure,respectively.The G~+:G~-ratio was the key factor influencing changes in soil physical and chemical properties,explaining 55.81%and 42.61%of the changes in physical and chemical properties,respectively.(4)The different vegetation restoration measures significantly improved the water storage and soil retention functions.The thickness and storage volume of litter in each vegetation restoration significantly increased,and significantly improved the natural water holding capacity,maximum water holding capacity,maximum storage capacity and effective storage capacity of litter,which were significantly higher than those in the CK2,and the best effect of litter water retention function in each vegetation restoration measure was in the T3,followed by the T4.The initial infiltration rate,stable infiltration rate,average infiltration rate,soil anti-erodibility index and soil anti-scour coefficents all increased significantly,and were significantly higher than those in CK1 and CK2.The infiltration rate of each vegetation restoration measure decreases rapidly with the extension of infiltration time and then stabilizes after the 60th minute of infiltration,and the infiltration rate decreases with the deepening of the soil layer;Soil permeability and soil anti-erodibility and soil anti-scourability were mainly influenced by the soil root system,which explained 97.87%of the variation in soil permeability,and the oil anti-erodibility and soil anti-scourability were highly significantly correlated with the characteristics of the soil root system;The runoff and sediment yeild of each sample site were quadratic functions of rainfall,while the runoff and sediment yield of different vegetation restoration were significantly lower than those of the CK1 and CK2.The highest benefits in terms of runoff and sand reduction were found in T3,where the benefits in flow reduction and sediment reduction reached 88.77%and 99.81%respectively in 2021.(5)Based on 53 indexes of vegetation,soil and hydrological factors of of vegetation community characteristics,litter,root system characteristics of water conservation,soil physicochemical properties,soil microbial community characteristics,soil permeability,soil anti-erodibility and anti-scourability and slope efficiency characteristic of runoff and sediment reduction of 53 indicators,a comprehensive evaluation index system of soil and water conservation function of different vegetation restoration measures in eroded and degraded land was constructed.Using the combination of analytic hierarchy process and approaching ideal point method,the evaluation results of soil and water conservation function of different vegetation restorations were obtained,performing as T3>T4>T1>T5>T2>T7>T6>CK2.Therefore,the characteristics of vegetation-soil-hydrology changes of different vegetation restorations in eroded-degraded region from 2016 to 2021 were comprehensively studied,and a soil and water conservation function evaluation system for different vegetation restorations was constructed.The T3,T4,and T1 measures were screened out to be more suitable for the vegetation restoration of the eroded-degraded Pinus massoniana forest land in the red soil area,and provided a scientific theoretical basis for the ecological restoration and reconstruction of the eroded and degraded land. |
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