Reaponse of Soil Quality to Natural Vegetation Restoration Processes in the Ziwuling Area on the Loess Plateau
|School||Northwest University of Science and Technology|
|Course||Soil and Water Conservation and Desertification Combating|
|Keywords||natural vegetation restoration vegetation succession soil quality evaluation index Ziwuling area|
Resaerch on interaction between natural vegetation restoration and soil quality may provide important scitifical value for ecological rehabilitation and evaluation of environmental effect. The multiples methods of historical information collection, field investigation, germination experiment of soil seed bank and indoor analysis were used to study soil quality response to natural vegetation succession in the Ziwuling area of Loess Plateau. Characteristics of natural vegetation restoration and the contribution of soil seed bank to aboveground vegetation were investigated; the the response of soil physical, chemical and microbiological characteristic to vegetation natrural succession were analyzed. Based anlysis of soil properties, the key indices of soil quality were selected. And then, the evaluation index system of soil quality during natural vegetation restoration was built and the effect of environmental factors on vegetation succession had been studied. The main research conclusions are as follows:(1) Characteristic of natural vegetation restoration process: the succession process of natural vegetation restoration in Ziwuling area experienced as Artemisia scoparia community(1-5a)→Lmperata cylindrical community(5-10a)→Leymus scalinus+ Phragmites Trin. Community(10-15a)→Bothriochloa ischaemum+ Carex lanceolata community(15-20a)→Hippophae rhamnnnides- Periploca sepium community(20-30a)+ Sophora viciifolia- Cotoneaster multiflorus community(30-50a)→Acer ginnala community (50-60a). After that, due to influences of landform and soil water moisture, the vegetation succession experienced Betula platyphylla- Populus davidianna community(60-100a) to Quercus liaotungensis climax community(100-150a) on the the slope with good water conditionl, which complated positive succession process on the research area; but on the sunny slope with poor water condition, the vegetation succession envolved into the landform-soil climax community of Biota orientalis(60-80a). Results showed that the number of species in standing vegetation was 2.4 times than that in soil seed bank and the similarity index between standing vegetation and soil seed bank changed from 0.071 to 0.296. The diversity index change of herbage and shrub during vegetation restoration is expressed as parabola function, and the changing trend of diversity index in soil seed bank was the same as that in standing vegetation. Significant positive correlation was found between diversity index and restoration year.(2) Response of soil physical characteristic to vegetation restoration: soil porosity, field capacity and soil aggregate stability improved with an increase of vegetation restoration year. The fractal dimension (D) of soil aggregate decreased with increasing restoration years, and significant negative correlation between >0.2mm water-stable aggregate content and soil mean weight diameter (MWD) were found. In slow wetting (SW) treatment of the Le Bissonnais (LB) method, parts of big aggregates slaked into small water-stable aggregates through disintegration function,which weakened with an increase of vegetation restoration year. It showed that the stability of soil aggregate was enhanced during vegetation seccession.(3) Response of soil chemical characteristic to vegetation restoration: the content of soil organic matter (SOM), total N, and alkaline N increased as the vegetation restoration year increased, which showed obviously the trend of surface-accumulation (0-5 cm>5-10 cm>10-20 cm). Under the same life form of vegetation, the content of SOM, total N, and alkaline N increased with year. During the vegetation succession, the content of SOM, total N, and alkaline N fluctuated when the community changed from herbage to shrub or from shrub to abor. The content of soil available P fluctuated during vegetation succession, which was the highest in Acer ginnala forest whose restoration year was 60a. Soil C/N changed from 8.47 to 12.80.(4) Response of soil microbial characteristic to vegetation restoration: alk. phosphatase, invertase, and urease activity increased with the increasing of restoration year. In Betula platyphylla forest land whose restoration year was 75a,all enzyme activities were lower than those than other lands. Compared with bare land, MBC, MBN, and MBP increased. The order of MBC, MBN, and MBP on soil profile were 0-5 cm>5-10 cm>10-20 cm. The magnitudes of bacteria, actinomycete and fungi amount in soil were 106, 102 and 105. Fungi was relative sensitive, and the amount of actinomycete kept stable. There were no significant differences in distribution of microbial quotient in different restoration years and soil profiles. The correlation between each two indices among soil enzyme activity(invertase, alkaline phosphatase, catalase activity), mirobial biomass(the amount of bacteria and fungi), MBC, MBN, MBP, and soil chemical indices was very significant or significant.(5) Sil quality evaluation: Principal component analysis and factor analysis were used for soil quality evaluation. Eight indicators of soil bulk density, MWD, SOM, available P, alkaline phosphatase, catalase activity, fungi, MBC, microbial respiratory quotient were selected to use soil quality assessment during vegetation restoration in the Ziwuling area. Among them, SOM, fungi and microbial respiratory quotient were key indicators during vegetation restoration. Soil quality index (SQI) increased as the restoration year increased, which had significant correlation to restoration year in 0-5 cm profile. According the restoration period, soil quality evolvement could be divided into three stages: initial stage of vegetation restoration (1-20 a), when vegetation succession from herbage community to climax community of Bothriochloa ischaemum, SQI changed from 0.2420 to 0.3452, and soil quality was in the stage of slow accumulation; mid-term of vegetation restoration (20-60 a), when vegetation succession from herbage community to shrub community and some kinds of tress invaded, SQI changed from 0.4968-0.4970, soil quality was in the relative-stable stage ; later period of vegetation restoration (60-150 a), vegetation succession from arbor community to climax community of Quercus liaotungensis, SQI changed from 0.5613-0.7672, and soil quality was in the stage of slow increasing.(6) Interaction between vegetation and environmental factors: Canonical correspondence analysis (CCA) and Partial Canonical Correspondence Analysis (PCCA) were used to analyze the relationship between vegetation and environmental factors. According the effect of environmental factors to vegetation species, the sequences was landform>soil quality>soil seed bank>vegetation restoration year, landform and soil quality were the principal variables that affected vegetation restoration. Soil MWD, content of SOM, and alkaline N, alkaline phosphatase and urease activity were main soil quality factors, which strong affected the change of vegetation species.