【作者】 莫彬；

【导师】 曹建华；

【作者基本信息】 广西师范大学 ， 生态学， 2007， 硕士

【摘要】 了解不同土地利用方式下土壤活性有机碳的大小和动态变化,对调节土壤养分流、维持土壤内在的生产力以及深入研究土壤碳循环的机理高度相关。基于它活跃的性质和重要作用,研究土壤活性有机碳组分对土地利用变化的响应规律成为当前土壤碳和养分循环方面的一个热点。岩溶地区同样属于生态环境脆弱区,却没有引起足够的重视,研究程度比较薄弱,由于石灰土的富钙、偏碱性,而且含有高浓度CO2的土壤环境是岩溶发育最为活跃的部位,土壤碳的动态变化与循环特征受到高钙环境胁迫的影响,碳转移有其自身的规律,因此,通过分析土壤碳库中对土地利用方式变化最为敏感、变化最为活跃的土壤活性有机碳主要组分(溶解有机碳DOC、微生物量碳MBC)的动态变化与环境因子、土壤呼吸、土壤营养元素之间的变化关系,可以为进一步研究和评价岩溶地区土地利用变化对土壤有机碳和土壤质量的影响提供基础数据。研究结果表明:(1)土壤DOC的动态变化受到植被、土壤温、湿度,土壤理化性质等多种因素的制约,这些因子之间相互作用,对DOC的产生有着较为复杂的影响,回归分析结果表明,在耕地中,土壤有机碳、土壤温度和土壤pH对土壤DOC的贡献率极大,而对于林地和草地的回归分析结果则显示土壤温度对土壤DOC的影响最为显著,不同土地利用方式下土壤活性有机碳对环境因子的响应也各不相同,这表明土壤溶解有机碳受众多因素的制约而呈现出一种动态平衡关系,进一步的机理仍需要进行深入研究。(2)不同的土地利用方式下上覆植被类型不同,其凋落物数量、质量及分解行为不同,有机质的输入量及质量也不相同,从而形成不同的土壤溶解有机碳含量差异,土壤有机碳的大小也存在较大差别。从全年平均值来看,林地土壤溶解有机碳分别比草地和耕地高25%、48%;从3月到8月,三者均随气温的上升呈增加的趋势,林地和耕地在8月均达到最大值,而草地则在10月达到最大值;林地和草地土壤微生物量碳分别高于耕地81%和45%,林地和草地在10月达到最大值。不同的土地利用方式导致土壤活性有机碳的差异较大,这说明岩溶生态系统中土地利用方式对土壤碳库的大小有较大影响。(3)林地的溶蚀能力在全年的各阶段均高于草地和黄豆地,这与林地有较好的保水能力和较低的pH值有关。土下50 cm处的溶蚀量也高于20 cm处,不同土地利用方式在春季的土下溶蚀量明显高于夏、秋、冬两季,这与自然保护区内全年降雨量几乎全部集中在4、5、6三月,而在全年的其它月份,降雨量明显减少而蒸发量增大有关。(4)从DOC占土壤总有机碳的比例来看,其大小顺序为:草地>洼地农田>坡耕地>林地。土壤溶液中DOC浓度和组成存在明显的空间变异性。4种不同土地利用方式下DOC占SOC的比例在土壤剖面中大体上呈先下降后上升的趋势,这与DOC随下渗水的迁移有关。方差分析结果表明,不同利用方式下土壤溶解有机碳含量产生明显的剖面分布差异。土层差异和土地利用方式对土壤溶解有机碳的影响均达到显著水平,林地各土层溶解有机碳含量较其它几种利用方式高,但从溶解有机碳占总有机碳的比例来看,草地在各个层位上均比其它土地利用方式为高,其中,林地的比例则最小,这表明土地利用方式不仅对土壤溶解有机碳含量的剖面分布产生影响,而且对溶解有机碳的组成和结构也有较大影响。(5)在土下20 cm和50 cm处,草地全氮含量均显著高于林地和黄豆地,而林地与黄豆地的全氮含量则相差不大。草地与林地和黄豆地的含氮量差异显著,而林地与黄豆地之间差异不显著。在土下20 cm处,全氮含量高的草地其碱解氮的含量却低于黄豆地和林地,除了在11月到次年的3月林地的碱解氮含量高于黄豆地外,全年的其余时间内黄豆的碱解氮含量均为最高。林地也在8月达到最高值,而草地最高值则出现在6月。土下50 cm处,不同土地利用方式下土壤碱解氮的含量变化趋势与土下20 cm处变化不大,峰值出现的月份相同。林地、耕地与草地土壤碱解氮的含量差异达显著水平,林地与耕地之间差异不显著。相关分析表明,黄豆地溶解有机碳含量与土壤碱解氮显著正相关,草地则呈正相关,而林地则呈现负相关关系。因此,土壤溶解有机碳对碱解氮的释放与活化作用较为复杂,可能与DOC的组成和结构有关。(6)在土下20 cm处,林地土壤全磷的含量较草地和黄豆地高。从全年来看,林地的全磷含量在全年的各月份均保持比较稳定,波动不大。黄豆地从3月到8月全磷含量一直呈上升趋势,8月到11月则下降,到了冬季则有缓慢上升,这可能与黄豆的生长季节有关。方差分析表明,林地与草地、黄豆地差异显著,草地与黄豆之间差异不显著。在土下50 cm处,三种土地利用方式的变化均不大。土下20 cm处土壤有效磷的含量明显高于土下50 cm处,但其月际动态变化均很相似,在春季呈上升趋势而在夏秋两季则略有下降,在冬季又有所上升。相关分析表明:土壤溶解有机碳与有效磷含量均为显著正相关,这说明溶解有机碳对有效磷有较好的活化作用。(7)黄豆地的全钾含量较高,而林地与草地全钾含量相差不大。这与每年黄豆地在每年春季施用草木灰有关。土下20 cm处土壤全钾含量明显高于土下50 cm处,林地与草地全钾含量相差不大。黄豆地在3月到8月其全钾含量呈上升趋势,从8月到次年三月则一直在降低。而林地则与此相反。土下20 cm处黄豆地、林地和草地的土壤速效钾的含量相差不大,且20 cm与50 cm处的变化趋势相同。相关分析表明:黄豆地、草地和林地中土壤钾的含量与土壤有效钾含量呈正相关。(8)全钙、全镁含量在各种土地利用方式下的全年的变化波动均不大,且在土下50 cm处的全钙含量均略高于土下20 cm处,这与当地全年的降雨量大,土壤中的Ca受到强烈的淋溶、淋洗,土壤中的Ca易向下层迁移有关。全镁含量在土下20 cm和50 cm处相差不大。林地和草地的全钙含量明显高于黄豆地,这说明随着土地利用方式由农地向草地和林地的转变,地表覆被不断增加,土壤酸性增强,促进了Ca的溶解。(9)石漠化地土壤与原始林地相比,土壤全N、P、K分别下降了78%、75%和47%,土壤速效N、P、K也分别下降了83%、78%和46%。值得注意的是,坡耕地土壤的化学性质与原始林地相比,各指标也有非常明显的下降,土壤质量接近于石漠化土壤,土质劣化现象比较严重,有机质、全N、P、K和速效N、P、K分别下降了348%、52%、53%、37%、60%、57%和30%。由此可见,在由林地、草地向坡耕地的转变过程中,随着植物种群的数量与种类不断下降,生物富集养分作用也在不断减弱,土壤质量不断退化。土壤主要营养元素的含量变化与土壤有机质的变化方向趋于一致,表明土壤有机质的大量淋失直接导致了土壤养分含量的降低。在我国西南岩溶地区,碳酸盐岩化学溶蚀强烈,残留物极少,成土十分缓慢,土层浅薄,母岩风化对土壤养分物质的补充极其微弱,因此,生物的富集作用对于土壤的形成、肥力的积累、补充和土壤结构的改善就有着重要的意义,一旦生物小循环被破坏,整个系统即处于无补充的完全输出状态,造成土壤肥力的丧失。(10)在石漠化的演替进程中,土壤有机质、氮、磷、钾、微生物量和腐殖质品质均有不同程度的下降,土壤质量的变化与石漠化的发展阶段具有方向一致性和阶段同步性的特点。运用聚类分析方法对岩溶石漠化进程中各演替阶段的土壤质量指标进行了较为全面的分析,并从中筛选出石漠化进程土壤质量退化的预警性指标。土壤微生物量碳、有机质、胡敏酸/富里酸的比值、速效氮、胡敏酸、全磷、微生物量氮、溶解有机碳、全钾、速效磷和速效钾在一定程度上可以较为准确地反映石漠化演替进程中土壤质量退化的特征,在建立石漠化的监测和预警体系时可以作为土壤质量退化方面的主要预警指标之一。更多还原

【Abstract】 Soil active organic carbon (SAC) refers to the fractions of organic carbons that are easy to move and to be oxidized and mineralized, and they are quite available to plants and soil microorganisms. Soil dissolved organic carbon (DOC) and microbial biomass carbon (MBC) are considered to be the useful indicators of SAC. Soil active organic carbon is involved in all biological and biochemical processes in soil, the minor change of SAC can be detected before the content of total organic carbon (TOC) in soil has changed, although it accounts for small fraction of TOC. The types of vegetation influence the size and quality of soil organic matter. Over the last several centuries, extensive areas of native vegetation of karst areas in Maolan, Guizhou Province have been converted to croplands and grasslands. The impacts of these land use changes on soil organic carbon (SOC) are unclear. In order to assess the impacts of land use changes on active soil organic carbon, we compared the DOC, MBC concentrations in adjacent plots of native forest, cropland, grassland with the same elevation, exposure and soil type. The results showed that the mean forest DOC were higher than that of grassland and cropland 25%, 48% respectively. From May to August, they all increased with the increase of temperature. The forest and cropland DOC reached the highest value in August while the grassland reached the peak value in October. The forest MBC was higher than that of grassland and cropland 81%, 45% respectively. Land use changes play an important role in the changes of DOC and MBC in soils. The relationship between active soil organic carbon and environmental factors is complicated which still needs to be further studied.The soil dissolved organic carbon plays an important role in the karst ecosystem. DOC is involved in all biological and biochemical processes in soil, the minor change of DOC can be detected before the content of total organic carbon(TOC) in soil has changed, although it accounts for small fraction of TOC. The types of vegetation influence the size and quality of soil dissolved organic carbon. The profile distribution of soil DOC under different land use patterns as affected by human practice is necessary for assessing the alteration of soil quality. 4 types of land use (forestry field, the grassland field, the depression field, the hillside maize field), which are widely distributed in karst area of Guizhou Province, southwest of China, were selected to investigate profile distribution of DOC. In each pedon at 0-75cm depth, soil samples were collected from 4-5layers. The results showed that the profile distribution of DOC was different under different land use patterns, indicating the significant effect of land use patterns on DOC.DOC in the forest field were higher than that of in the grassland field, the depression field and the hillside maize field. The soils under grassland field contained a larger proportion of DOC to organic carbon. The results obtained could potentially provide theoretic support for understanding the effects of land use change on soil DOC and establishment of sustainable land use patterns.We also compared the contents of major nutrient elements of soil under different land use patterns and the relationship with DOC. The results showed that under three land use patterns, different nutrient elements such as N,P,K have different evolve trends during the year studied. The contents of nutrient elements beneath 20cm of the soil always higher than that of beneath 50cm of the soil.And according to the analysis of the variation of pH, the contents and the composition of organic matter major nutrients(N,P,K) and the microbial biomass of the soils ,we found that the soil quality degenerated quickly with the development of karst rocky desertification. The method of hierarchical cluster analysis were used to evaluate the early warning indicators of soil quality degeneration in the process of karst rocky desertification.更多还原