| Due to human disturbance and unreasonable resources development and utilization,the original ecological protection function of arid river valley in the upper reaches of the Minjiang River and the ability to conserve water resources have reduced,the soil and water loss was quite serious,degradation of ecosystem is serious and the ecological environment is extremely fragile.Under the background of the implementation of a series of ecological environment construction projects based on vegetation construction in ecologically fragile areas,the selection of suitable vegetation restoration patterns is particularly necessary and urgent.Therefore,this study is aimed at the needs of ecological environment construction in the upper reaches of the Minjiang River and the scientific issues of soil erosion research.Based on the field investigation,the mountain forest-dry valley interlaced zone is taken as the research object,soil physical and chemical properties,soil organic carbon dynamics,water conservation function and soil conservation function under different vegetation restoration patterns were studied,obtaining a vegetation restoration model suitable for mountain forests-arid valleys and fragile zones in order to provide a theoretical basis for the restoration and reconstruction of degraded ecosystems in mountain forests and arid valleys.The main findings are as follows:(1)The soil water content of different vegetation restoration patterns was the highest in July and the lowest in April.The average soil bulk density was in the order of grassland(G),Minjiang cypress-pinus tabulaeformis(MP),Locust forest(LF),natural secondary forest(NSF),Minjiang cypress(M),Seabuckthorn and Berberis wilsonii Hemsl(S).The patterns of NSF,M and G were dominated by coarse silt and physical clay,which accounted for 79.97%,72.96%and 70.64%,respectively.Sand grains and physical clay dominated the pattern of S accounting for 46.53%and27.7%,respectively.The patterns of LF and MP are mainly sand grains and coarse silt,accounting for 75.33%and 70.7%respectively.The dispersion degree of soil particles is low,the deflection is larger,the peak state value is higher,and the imbalance degree of particle distribution is different in the pattern of G and LF.In addition to the G and LF pattern,the remaining vegetation restoration patterns meet the soil inhomogeneity coefficient(Cu)>5,and the curvature coefficient(Cs)in the range of 1-3,belong to the well-equipped soil.The soil organic matter content,total nitrogen content and effective phosphorus content were the highest in the pattern of S,respectively,47.53 g kg-1,4.94 g kg-1 and 8.19 mg kg-1,followed by NSF pattern.The NSF pattern has the highest available potassium,while the pattern of LF and G is lower.The particle size of>2 mm is mainly in soil non-waterstable aggregate for the different vegetation restoration patterns,accounting for about 60%of all the aggregates.The particle sizes of>2 mm and<0.25 mm were mainly in soil waterstable aggregate for NSF pattern,and the particle size of<0.25 mm was mainly for the other vegetation restoration patterns.The average aggregate contents of<0.25 mm particle size were more than 50%in different soil layers,and the average aggregate contents of<0.25 mm particle size was up to 89%for the LF pattern.For the NSF pattern,the preservation probability of soil aggregates in the particle size of>0.25 mm was the highest,and the stability index was also the highest.For the M pattern,the preservation probability of soil aggregates in the particle size of>0.25 mm and the stability index was also the lowest.(2)The content of soil organic carbon,soil labile organic carbon(LOC),soil organic carbon density of LOC,soil organic carbon density,soil inactive organic carbon(NLOC)and soil organic carbon density of NLOC were the highest in the pattern of S,while the indexes of LF and G patterns were lower.Compared with the 0-10cm soil layer,the content of LOC in the 10-20cm soil layer and the 20-40cm soil layer decreased by 31.40%and 32.08%respectively,and the content of NLOC decreased by 29.89%and 45.31%respectively,and the soil organic carbon density increased by 71.34%and 195.29%respectively.Soil organic carbon density of S pattern and NSF pattern was higher than the average level of the forest type in China(44-264t C hm-2),and the other vegetation recovery patterns were lower than this value.The results showed that the soil carbon sink potential of the different vegetation restoration pattern is greater in the study area.The efficiency ratios of the labile organic carbon in different vegetation restoration patterns was as following:S>NSF>G>M>LF>MP,and the overall level was low and the average value was only 0.26.The carbon pool management index ranged from 48.31 to 251.56for the different vegetation restoration patterns,and was as following:S>NSF>M>MP>G>LF.The content of light fraction organic carbon(LFOC),The particulate organic content(POC)and soil readily oxidizable organic carbon(ROC)content were higher in the patterns of S and NSF,and the pattern of LF was lower.Each component of soil organic carbon could better characterize the soil condition of different vegetation restoration patterns in the study area.(3)Under different rainfall conditions,both the through-fall quantity and through-fall ratio showed as follows:M>S>MP>LF>NSF.The stemflows were higher for the patterns of M and S,and with the increase of rainfall,the stemflow of arbor dominated vegetation was more sensitive than that of shrub and mixed forest.The range of rainfall interception were from1.331mm to 3.824mm for the different vegetation restoration patterns,and the interception accounted for 25.49%-26.62%of the total rainfall.The interception rates of NSF were the highest(50.32%,37.31%and25.49%,respectively),and the interception ratio of M were the lowest(26.61%,17.51%and 10.35%,respectively).Under different vegetation restoration patterns,the litter stock of the litter was in the order of NSF>LF>MP>M>S>G.Under different vegetation restoration patterns,the proportion of semidercomposed litter layer in the existing total was greater than that of undecomposed litter layer,which were more than 60%,among which the pattern of M was the highest,accounting for 79.89%,and the pattern of NSF was the lowest,accounting for 60.66%.The maximum water holding capacity of litter in LF and NSF pattern was 53.25 t hm-2 and 53.22 t hm-2,respectively,followed by that in MP pattern,and the maximum water holding capacity of litter in G was the least.The semi-decomposed litter layer of different vegetation restoration patterns had a higher water holding capacity than that of the undecomposed litter layer,and the relationship between water holding capacity and time of soaking showed mutiple relevance such as logarithmic,power function,linear and exponential function.The relationship between water absorption rate and time of soaking for the undecomposed layer and semi-decomposed layer of litters showed power functions under different vegetation restoration patterns.Soil available moisture storage capacity showed the order of S>NSF>MP>G>LF>M under different vegetation restoration patterns.The soil permeability was strong for the patterns of S and NSF.The soil infiltration process can be fitted by Kostiakov formula for all vegetation restoration patterns.(4)By entropy-weighing method,from the point of view of inorganic silt-clays,organic colloid,water-stable aggregates and soil organic matter,evaluation indicators system of the soil anti-erodibility was established based on 11 indexes such as the<0.05 mm soil particles content,<0.002 mm soil particles content,soil structural index,soil aggregation condition,soil aggregation degree,soil dispersion rate,waterstable aggregate content of>0.25 mm particle size,waterstable aggregate content of>0.5 mm particle size,damage rate of soil structure,average weight diameter and soil organic matter content in a mountain forest-arid valley area.The results showed that the soil anti-erodibility of three patterns(NSF,M,S)was the better for all vegetation restoration patterns.Soil anti-erodibility of NSF was 1.48 times and1.39 times of patterns of LF and G respectively.Soil chemical properties were sensitive to soil anti-erodibility in the study area.Index of soil anti-scourability increased with the extension of scour time under different vegetation restoration patterns.Index of soil anti-scourability was the highest(5.477)for the pattern of NSF,followed by M pattern,and the index of soil anti-scourability of G pattern was the lowest.Index of soil anti-scourability was not only related to soil particle characteristics,but also has significant or extremely significant positive correlation with soil organic matter content and soil active organic carbon content under different vegetation restoration patterns.The surface runoff and sediment yield of G pattern was the highest and the surface runoff and sediment yield of NSF pattern was the lowest,and the pattern of G was significantly higher than the other vegetation restoration patterns.(5)Evaluation indicators system of soil ecological function was established based on 26 indexes such as the litter stock of the litter,the maximum water holding capacity of litter,litter decomposition intensity,soil organic matter content,soil total nitrogen,soil available phosphorus,soil available potassium,soil bulk density,capillary porosity,soil structural index,soil aggregation degree,soil dispersion rate,stability index,Cu,Cs,fractal dimension of non-waterstable aggregate,soil initial infiltration rate,soil steady infiltration rate,fractal dimension of waterstable aggregate,soil structural index,damage rate of soil structure,the index of soil anti-scourability,LOC,NLOC,POC,ROC and carbon management index.By the combined methods of entropy-weighing and technique for order preference by similarity to an ideal solution,the results of soil ecological function evaluation were obtained by integrating relative approximation degree and proximity degree under different vegetation restoration patterns.The order from good to bad as follows:NSF,M,S,MP,LF and G for all vegetation restoration patterns.Based on the results of sensitivity and stability analysis,it was determined that the patterns of NSF,M,S were suitable for vegetation restoration in mountainous forest-arid valley ecotone. |
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