| Riparian soils play a fundamental role in transmitting, storing, and reacting with natural and human-introduced materials, such as organic matter, nutrients, and fine particle concentrations, and thus produce dominant effect on the hydrologic, biological, and geochemical processes which drive the maintenance of ecosystem services. The middle and lower reaches of the Yellow River riparian zone as basin terrestrial ecosystems and aquatic ecosystems is connected to the sensitive and fragile area, is facing the degradation of vegetation area, and the soil erosion and a series of problems caused by the riparian zone structure changes and function. Carried through the research of pattern dynamics of riparian vegetation,investigated the spatial and temporal pattern of soil environmental factors in study area, and reveal the coupling relationship and scale influence between vegetation patterns and soil environment in different scales, can provide new ideas for the research on riparian ecosystem structure and function, to accelerate the degradation of riparian ecosystem restoration and reconstruction has an important guiding role.The research in typical area of the middle and lower reaches of the Yellow River riparian zone.By the scobination of field research, laboratory test and statistical analysis, studied the dynamics of vegetation pattern, soil environmental factors in the middle and lower reaches of the Yellow River riparian,and find out the relationship between vegetation patterns and soil environment at different scales.This investigation was carried out in May 2014 along the Yellow River. And soil sampling and vegetation survey were conducted in Populus tomentosa and Salix matsudana plantations field. The mixed soil samples were collected 5 times repeatedly in vertical 0-20 cm depth, then put into polyethylene zip bag after mixing. Riparian vegetation characteristics were visually estimated for each plot using scoring method.First, this paper has taken the remote sensing imagery of 2003 ? 2009 and 2015, on the basic of field investigation, the type of land coverage in study region are divided into: river, agricultural land, rural residential areas, forest land, grass land, flood plain, channel and pond land landscape type, a total of 8kinds. Combined with the vegetation spatial structure and dynamics in the area in recent 12 years and driving force factors( distance from road(Dis_road)?distance from the residential areas(Dis_jmq)?distance from ponds(Dis_pond)) to analysis the spatial distribution characteristics of vegetation, the dynamicperformance of vegetation pattern and the driving mechanism of the change of vegetation pattern in this area. Secondly, in the present study, the spatial distributions of riparian soil physicochemical properties and its response to environmental factors were analyzed by employing methods of field investigation,experimental analysis, and redundancy analysis(RDA) in the research. Determined the soil physical and chemical indexes of representative riparian zone, quantitatively reveal the extent and scale of soil changes in different vegetation types through statistical analysis and spatial variation analysis respectively. Finally,via the analysis of the vegetation community characteristics and soil characteristics, determined the factors affecting the soil properties of riparian zone; Based on principal component analysis, analysis the relationship between vegetation and soil quality at different scales. Here are the main results and conclusions:(1) The total area of grassland has increased, patch density, number of patches are and the total area have the same increasing trend in different years. The increased of aggregation index and proportion of like Adjacencies in the grassland and forest land, the concentration of the grassland and the patch of forest land was increased, and the distribution of the patches increased continuously. The total area of forest land was increased in different year, the number of patches was increased, but the density of patch decreased first and then increased, which showed that the fragmentation degree of forest land increased in2009-2015. The landscape shape index of forest land has increased. The patch density decreased rapidly.The number of patches and landscape shape index in grassland and forestland, the distance to the residential area and roads almost had an impact on grassland and forestland in each year. The total area and number of patches of grassland and forestland and distance to residential in each year have significant correlation. In 2015, the perimeter-area fractal dimension of grassland landscape pattern has a significant negative correlation with the distance to the road(p<0.05). The landscape shape index changes of grassland and forestland in each year and the distance of the road and community areas have significantly correlations(p<0.05, p<0.01), which significantly positive correlated with the distance to residential areas,and significantly negative correlated with the distance to road. The patch cohesion index of grassland and forestland and distance to pond had significantly negative correlations in 2003 and 2009, 2015respectively(P < 0.05), The patch cohesion index of forestland in 2015 and distance to community area has a significant positive correlation, which means that more closer to the pond, farther away from residentialareas, the landscape patches of spatial connectivity is better. The distance to the community area and proportion of like Adjacencies of forestland have significant positive correlation in all three periods, which showed that the rate of reduction of aggregation near to the distance from the residential area is faster than the distance up to the community area.(2) The results showed that the riparian soil particle was composed significantly of silt, and the content of soil silt was notably lower within the 3 km buffer zones than that outside the 3 km buffer zones.With the increase of riparian buffer, soil bulk density was increased at the first and then decreased at the end, whereas soil moisture showed opposite variation with increase of riparian buffer distances, namely,decreased initially and then increased. Changes in soil chemical properties showed that, soil total nitrogen(TN) content between Populus tomentosa and Salix matsudana plantations has no change, and then nitrate nitrogen(NO3+-N) content was increased because of the increase of riparian buffer distance. The distribution of TP and AP under different riparian buffer distance had obvious difference due to the effects of vegetation types and planting years of the Populus tomentosa and Salix matsudana plantations, and the lowest value was observed in the 1.5 km buffer zone. The content of TC and TOC in Populus simonii plantation were lower than that in the Salix matsudana plantation, and with the increase of riparian buffer distances, both the soil TC and TOC contents increased initially and then decreased. The result of correlation analysis indicated that TOC content in the study area was positively and significantly related to TN(P<0.01), NO3+-N(P<0.01), and NH4+-N(P<0.05) contents, respectively. However, insignificant relationship between NO3+-N and NH4+-N was observed due to the difference of planting years and the nitrogen fertilization amounts before establishment of plantations between the Populus tomentosa and Salix matsudana plantations. Both the TN and TOC contents were negatively and significantly related to the content of sand(P<0.01) while was positively and significantly related to the content of clay(P<0.01),indicating that high sand content can promote porosity and permeability of soil. In addition, the results of RDA indicated that the TOC and NH4+-N contents increased with increasing height and coverage of the arborous layer. Soil TP and NO3+-N contents increased with increasing vegetation DBH and coverage of the plantation. With the increase of elevation value, the content of soil NH4+-N presented an increasing trend, indicating that soil properties was significantly influenced by the effects of community structure and elevation value.(3) At the local scale, the fitting equation of soil quality and canopy cover is ya=0.467+0.067 x, Correlation coefficient is 0.319, R2=0.102,which was Significant difference(F=5.322,p=0.026). The equation showed that there was a linear relationship between the variation of soil quality factors and vegetation characteristics(canopy cover). The analysis to the characteristics of forest vegetation landscape pattern changes under different riparian buffer zones showed that, with distance of buffer increased, total area, number of plaque, plaque density and patch shape index of riparian vegetation landscape showed the trend of increased at first and decreased at the end and all reached to a maximum value in 1.5-3.0 km buffer, and number of patches increased rate was significantly faster than that of total area, indicated that forestland fragmentation was increased in this area, and higher than the other buffers. Patch shape index was consistent with number of plaques and plaque density consistent of the buffer area, although total area was increased significantly, but fragmentation is more serious, shape became more complex, the degree of disorder becomes larger.Perimeter-area fractal dimension showed the opposite trend, which was decreased first and increased after, Proportion of Like Adjacencies and aggregation index were reached maximum in 3.0-4.5 km buffer distance, Patch cohesion index have the highest value in 3.0-4.5 km buffer distance, the lowest value in 1.5-3.0 km buffer distance. The landscape shape index of forestland in the study area forest reached to a maximum value in1.5-3.0 km buffer distance, number of pleaques and density were the highest, indicated that forestland in this area is mainly affected by human interference under the orderly planning, have the most serious fragmentation. Proportion of like adjacencies and the aggregation index have a strong correlations, the trend of forest pattern in the buffer are basically the same. The proportion of like adjacencies and the aggregation index in the zone of 3.0-4.5 km buffer distance have reached for the maximum value, and the value of the1.5-3.0 km buffer distance is the minimum. Which means that the forest landscape types at 3.0-4.5 km buffer distance have higher degree of aggregation, and the distribution of patches is more concentrated, and the forest landscape types at 1.5-3.0 km buffer distance have lower degree of aggregation, so the distribution of patches are more dispersed, this results matched with the results of the number of plaques and patch density. And the value of patch cohesion index at 3.0-4.5 km buffer distance was the highest, which indicated that the space in this region were well interconnected, and the value of patch cohesion index at 1.5-3.0 kmbuffer distance was the lowest, the connectivity is significantly less than the other buffers, makes the patches in this area were relatively dispersed. On a large scale, vegetation patterns and soil quality has no significant correlation, indicating that on a larger spatial scale, with the expansion of the scale,influencing factors increased, loss process and quantity of soil nutrient are more complicated, soil property was not the the main factor for the determination of vegetation pattern, vegetation patterns and soil nutrients may be controlled by different environmental factors or interfere process. |
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