【作者】 郭曼；

【导师】 郑粉莉； 安韶山；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2009， 博士

【摘要】 土壤质量对植被自然恢复过程响应的研究对生态建设与环境效应评价有重要的科学价值。本论文针对黄土丘陵区退耕还林(草)工程环境效应评价的迫切需求,以黄土丘陵区典型草原带宁夏固原地区云雾山和森林草原过渡带延安燕沟流域为研究区,采用野外调查、室内土壤种子库萌发试验和土壤分析相结合的方法,研究了黄土丘陵区自然恢复过程中植被演替规律、土壤种子库特征及贡献,分析了土壤物理性质、化学性质、酶活性和微生物学性质的动态变化;基于相关分析、敏感性分析及主成分分析,筛选土壤质量的评价指标;运用综合指数法定量评价土壤质量对植被自然恢复过程的响应程度,以期为黄土丘陵区进行快速生态建设提供理论依据。主要结论如下:1)提出了植被自然恢复过程中土壤样品的采集深度:通过LSD分析了各土壤质量因子在土壤剖面土层之间的差异,表现为0~5cm>5~10cm>10~20cm,土层之间的差异程度随着植被恢复年限的增加而增强。表层(0~5cm)土壤性质对植被恢复的响应最为敏感,表层以下土层(5~10cm和10~20cm)土壤性质对植被恢复的响应敏感程度降低;结合主成分分析,发现0~5cm土层土壤可基本涵盖0-20cm土层95%以上的信息量,建议研究土壤质量对植被恢复过程的响应时应采集表层0-5cm土层土壤进行分析。既可以表现出土壤质量对植被恢复过程响应的敏感程度,又可以减少采样的工作量。2)阐明了自然恢复过程中植被演替规律:黄土丘陵区草原带植被群落演替以猪毛蒿与虫实等为主的一年生草本开始,逐步演替为多年生草本群落,最后形成以长芒草与大针茅为优势种的顶级群落;物种多样性呈波动性上升趋势,植被演替到后期,物种趋于多样化,群落达到稳定状态;土壤种子库密度为3542.5粒/m2,主要优势种为野艾蒿和鹅观草;地上植被物种数是土壤种子库的1.14倍,地面植被与土壤种子库的物种组成相似性系数变化于0.167~0.276之间。森林草原过渡带自然恢复过程中植被由一年生草本群落至多年生草本群落,进而演替到灌木群落,最终到达顶级乔木群落(杜梨林),物种多样性明显增加,植被演替到后期,灌木和乔木占据主要生态位,群落稳定性增强;土壤种子库密度为5889.29粒/m2,以野艾蒿和狗尾巴草为优势种,地上植被物种数是土壤种子库的1.69倍;地上植被与土壤种子库的物种相似性系数变化于0.235~0.421之间,黄土丘陵区土壤种子库对地面植被演替的贡献较少。3)分析了土壤团聚体对植被自然恢复过程的响应:采用Le Bissonnais(LB)法测定土壤水稳性团聚体含量,发现黄土丘陵区土壤团聚体破坏机制主要是土壤孔隙中的气泡爆破产生的消散作用。与传统方式湿筛法(Yoder)相比较,>0.5 mm团聚体含量和MWD均表现为FW <WS<SW<Yoder,LB法3种湿润处理中,LB法FW与SW处理与传统Yoder法具有高度可比性;植被自然恢复过程中土壤水稳性团聚体表现为由小团粒向大团粒方向转化,土壤结构稳定性增加,抗蚀性增强。草原带植被自然恢复75a期间,>0.5mm团聚体由45.71%增加到88.92%,MWD由1.08mm增加到2.98mm;森林草原经过100a的自然恢复,>0.5mm团聚体由21.03%增加到80.89%,MWD由0.49mm增加到2.66mm。4)研究了土壤化学性质和生物学性质对植被自然恢复过程的响应:草原带土壤有机碳密度、氮密度、碱解氮含量、酶活性、呼吸速率,微生物量碳、氮在植被恢复0a~23a期间变化幅度较大,植被恢复23a~75a期间趋于平缓;土壤速效磷含量则呈先下降后趋于平缓的趋势;土壤C/N比变化范围为9.11~10.44;森林草原过渡带土壤有机碳密度、氮密度、碱解氮、酶活性、呼吸速率,微生物量碳、氮在植被恢复0~29a期间增加幅度较大,植被恢复29a~55a期间,呈下降趋势,植被恢复55a~100a期间再次增加;土壤速效磷含量呈现先下降后上升的趋势;土壤C/N比变化范围为8.70～11.79。5)筛选了土壤质量评价指标:基于相关性分析、敏感性分析及主成分分析,筛选土壤有机碳密度、MWD、氮密度、土壤脲酶、碱性磷酸酶、微生物量碳、微生物量氮和呼吸熵等8个指标来作为黄土丘陵区植被自然恢复过程中土壤质量评价指标体系。对比分析了基于筛选的8个土壤质量评价指标与基于测定的20个土壤质量因子计算的土壤质量综合指数(SQI),二者随植被恢复年限变化的趋势一致,验证了所选取的8个土壤质量评价指标体系具有较强的代表性和实用性。6)评价了土壤质量对植被自然恢复过程的响应:黄土丘陵区草原带植被自然恢复过程中,土壤质量变化可分为2个阶段,第一阶段是土壤质量快速增长阶段,发生在植被恢复0a~23a期间,SQI变化范围为0.052~0.742,土壤质量由较低水平向中等水平转化;第二阶段是土壤质量平稳变化阶段,发生在植被恢复23a~75a期间,SQI变化范围为0.615～0.722,土壤质量处于中等水平;森林草原过渡带植被恢复自然过程中,土壤质量变化可分为3个阶段,第一阶段是土壤质量显著上升阶段,发生在植被恢复0a~29a期间,SQI从0.107增加到0.454,土壤质量由低水平向较低水平转化;第二阶段是土壤质量下降趋势,发生在植被恢复29a~55a期间,此阶段由于草本群落退出优势地位,灌木的侵入使地表覆盖度减少,植物对土壤养分和水分的消耗大于积累,SQI由0.454降至0.242,土壤质量处于较低水平;第三阶段是土壤质量再次上升阶段,发生在植被恢复55a~100a期间,SQI由0.242增加到最大值0.823,土壤质量由较低水平向高水平方向转化。更多还原

【Abstract】 The effect of vegetation natural restoration on soil quality is an important issue of environmental effect assessment on“the Grain for Green Project”. This doctoral dissertation took two research areas of the typical grassland zone (Guyuan, Ningxia province) and the transition area from grassland to forest zone (Yangou catchment, shaanxi province) as research sites to study soil quality responses to vegetation natural restoration. According to research methods of the field investigation, experiments of soil seed bank germination, soil property analysis, and statistic analysis, we studied the characteristics of vegetation succession and soil seed bank in the process of vegetation natural restoration; analyzed the response of soil physical, chemical, enzyme activity, microbiological properties to vegetation natural restoration processes; selected soil quality assessment indicators based on correlation analysis, sensitivity analysis, and principal component analysis; and also quantitatively evaluated response of soil quality to vegetation natural restoration processes through soil synthetical index method. The main results are as follows:1) Soil sampling depths during vegetation natural restoration was proposed. LSD analysis showed that there were significant differences of soil quality factors among 0-5, 5-10, and 10-20 cm layers of soil profile, the order was 0-5 cm>5-10 cm>10-20 cm. It showed that the differences between the soil layers increased with the increase of vegetation restoration years. The response of soil properties in the top layer (0-5cm) to vegetation restoration was the most sensitive, the sensitivity of other two layers (5-10cm and 10-20cm) decreased, compared to the top layer. Based on the principal component analysis, the soil property information in top layer could cover more than 95% of the information in the 0-20 cm soil layer. Hence, 0-5 cm soil layer could be best the soil layer to study the response of soil quality to vegetation natural restoration, this sample method could show sensitivity of response of soil quality to vegetation natural restoration and reduced sampling workload.2) Vegetation succession during natural restoration was clarified. At the grassland zone, plant community began with annual herb community mainly composed of Artemisia scoparia and Corispermum hyssopifolium, then succeeded to perennial herb community, at last formed climax community mainly composed of Stipa bungeana and Stipa grandis. Species diversity was volatility increased with the increase of restoration years. At the last succession stage, the dominant species tended to diversification, plant community was stable state. Density of soil seed bank was 3542.5 seeds/m2, main dominant species were Artemisia lavandulaefolia and Roegneria kamojii; the species of above-ground vegetation was 1.14 times than of soil seed bank; while the relative coefficient of species composition between above-ground plants and seed bank was varied from 0.167 to 0.276. At the transition area from grassland to forest zone, the process of vegetation succession began with annual herb community, succession followed shrub community, and lastly became tree community (Pyrus betulaefolia). With the increase of vegetation natural restoration years, species diversity increased distinctly, shrub and tree community occupied the dominant ecological niche at the last period of vegetation succession, plant community was stability. Density of soil seed bank was 5889.29 seeds/m2, main dominant species were Artemisia lavandulaefolia and Setaria viridis, the species of aboveground vegetation were 1.69 times than of soil seed bank; the relative coefficient of species composition between ground plants and soil seed bank was varied between 0.235 and 0.421. It explained that contribution of soil seed bank to species composition of above-ground was relatively small in the loessial hilly-gully region.3) Response of soil structure to vegetation natural restoration process was analyzed. Using Le Bissonnais (LB) methods, we measured soil water-stable aggregate content during vegetation natural restoration in the loessial hilly-gully region. It showed that the primary broken mechanism of soil aggregate was dissipation by“air explosion”in the soil. Comparing with the traditional method (Yoder Method), >0.5 mm aggregate content and MWD all showed FW<WS<SW<Yoder. In the 3 treatments of LB methods, the treatments of FW and SW had high comparability with traditional method (Yoder Method). During the process of vegetation natural restoration, soil water-stable aggregates transformed from micro-aggregate to macro-aggregate, with the increasing of soil structure stability, and enhanced soil corrosion resistance. At the grassland zone, during 75 years vegetation natural restoration, >0.5 mm aggregate content increased from 45.71% to 88.92%, MWD increased from 1.08 mm to 2.98 mm; at transition area from grassland to forest zone, during 100a vegetation natural restoration, >0.5 mm aggregate content increased from 21.03% to 80.89%, MWD increased from 0.49 mm to 2.66 mm.4) Response of soil chemical properties and biological properties to vegetation natural restoration process was researched. At the grassland zone, soil organic carbon density, nitrogen density, soil alkaline nitrogen, soil enzyme activity, soil respiration rate, soil microbial biomass C and soil microbial biomass N increased greatly within vegetation restoration of 23 years, then tended steady from 23a to 75a of vegetation restoration. Soil available phosphorus content decreased first and tended steady later. Soil C/N varied from 9.11 to 10.44. At the transition area from grassland to forest zone, soil chemical properties and biological properties increased greatly within vegetation restoration of 29 years, decreased from 29a to 55a of vegetation restoration, went up again from 55a to 100a of vegetation restoration; Soil available phosphorus content decreased first and increased later. Soil C/N change from 8.70 to 11.79.5) Soil quality indicators were selected. Based on correlation analysis, sensitivity analysis and principal component analysis, we chose MWD, soil organic carbon density, nitrogen density, soil urease, soil alkaline phosphatase, soil microbial biomass C, soil microbial biomass N and microbial respiration quotient as soil quality evaluation index during vegetation natural restoration in the loessial hilly-gully region. Contrasting analysis two way of SQI calculation which based on the 8 soil quality indexes and the 20 soil quality factors, we found that both of them had same change trend with vegetation restoration year. It tested and verified that the 8 soil quality evaluation indexes were highly representative and practicability.6) Response of soil quality to vegetation natural restoration process was assessed. At the grassland zone, during vegetation natural restoration, the change of soil quality had two stages, the first stage was rapidly growing stage of soil quality, which occurred within vegetation restoration of 23 years, SQI was from 0.052 to 0.742, soil quality transformed from the low level to the middle level; the second stage was slowly changing stage of soil quality, which occurred from 23a to 75a of vegetation restoration, SQI was from 0.615 to 0.722, soil quality was in middle level. At the transition area from grassland to forest zone, during vegetation natural restoration, the change of soil quality included three stages, the first stage was increasing significantly stage of soil quality, which occurred within vegetation restoration of 29 years, SQI increased from 0.107 to 0.454, soil quality transformed from low level to relatively lower level; the second stage was decreasing stage of soil quality, which occurred from 29a to 55a of vegetation restoration, during this period, the herbosa community exited dominant position, and then the shrub community invaded reducing vegetation coverage, and soil nutrient and moisture were consumed more than accumulated by plant, SQI decreased from 0.242 to 0.454, soil quality was in the lower level; the third stage was increasing stage of soil quality again, which occurred from 55a to 100a of vegetation restoration, SQI increased from 0.242 to 0.823, soil quality transformed from the relatively lower level to the high level.更多还原