【作者】 盛浩；

【导师】 杨玉盛；

【作者基本信息】 福建师范大学 ， 自然地理学， 2010， 博士

【摘要】 土地利用/覆被变化(LUCC)是当前生物圈碳素循环的最主要人为驱动力之一。土壤碳库的储量约为大气碳库的2-3倍,土壤呼吸(土壤CO2排放过程)是土壤圈碳流入大气圈的主要形式。准确评价区域土地利用变化对土壤呼吸的影响,对于理解地下土壤代谢和区域碳收支的相互作用具有重要的意义。土壤呼吸由根际自养呼吸和土壤异养呼吸组成,精确分离土壤呼吸组分有助于准确理解和模拟陆地生态系统的地下碳平衡。本研究通过在我国亚热带闽北山区(福建建瓯市),选择本底条件基本一致、土地利用史清晰且具有代表性的土地利用方式序列：天然常绿阔叶林、次生常绿阔叶林、杉木(Cunninghamia lanceolata)人工林、木荷(Schima superba)人工林、柑橘园和坡耕地作为研究对象,采用“空间换时间”的方法,研究土地利用变化对土壤呼吸及其组分的影响,揭示我国亚热带山区地下生态过程对区域土地利用变化的响应,提高人们对山区碳排放的关注,为进一步认清土壤有机碳积累机制提供基础数据,也为精确制定国家温室气体排放清单和山区碳汇技术开发提供基础数据和技术支撑。通过对上述典型土地利用方式土壤呼吸连续3年的定位观测,结果表明：土壤呼吸具有明显的季节模式,季节动态主要与土壤温度变化一致。土地利用变化后,土壤呼吸的表观温度敏感性(Q1o值)从天然林的2.10升高到坡耕地的2.71,唯独改为柑橘园后Q1o值降到1.66。本区土地利用变化后,土壤呼吸平均下降48%,其中改为次生林下降32%,改为人工林下降46%-48%,改为柑橘园下降63%,改为坡耕地下降50%。本区土地利用变化后,土壤呼吸的下降主要与年凋落物输入量、活细根(直径<2 mm)生物量、表层土壤有机碳和轻组有机碳储量下降有关。这些指标又直接或间接的反映出土地利用变化后植物生产力的下降。上述结果表明,土地利用变化后,植物生产力下降引起的呼吸底物有效性(如土壤有机碳和养分)和土壤碳输入(如细根周转和凋落物)的减少是导致土壤呼吸下降的主要原因。本区天然林改为次生(人工)林,土壤CO2排放量的减幅(32%-48%)高出热带平均水平(29%),改为农业用地,土壤CO2排放量的减幅(50%-63%)高出全球平均水平(33%)。本区土地利用变化导致细根周转和土壤有机碳储量的降幅明显高出热带和全球平均水平,很可能是本区土地利用变化后土壤CO2排放的减幅高出热带和全球平均水平的关键因素。基于根排除法技术,分离了不同土地利用方式的土壤呼吸组分,一年的野外定位观测结果表明：根际呼吸和土壤异养呼吸具有明显的季节变化,两者的季节动态都受温度和光合作用的物候的共同影响。对任一土地覆盖而言,根际呼吸的表观Q1o值高于土壤异养呼吸的表观Q1o值,本区土地利用变化后,表观Q1o值有升高的趋势,仅改为柑橘园Q1o值下降。土地利用变化后,根际呼吸下降41%-91%,高于土壤异养呼吸的降幅(13%-43%),这也导致根际呼吸占总土壤呼吸的比例(RC)呈降低趋势。土地利用方式改变后,细根生物量大幅下降,是导致根际呼吸大幅下降的关键因素。土地利用变化后,土壤异养呼吸也显著下降,但天然林改为坡耕地后,土壤异养呼吸并未有显著差异。本区土地利用变化后,地上和地下输入(凋落物和细根周转)和土壤资源(地表枯枝落叶层、表层土壤有机碳和轻组有机碳储量)大幅下降,引起土壤微生物的底物供应减少,是导致土壤异养呼吸下降的主要原因。这些结果表明,土地利用变化后,土壤异养呼吸和根际呼吸对新近光合产物的输入具有类似的响应。此外,在强烈人为干扰的土地利用方式下,养分有效性的增加,也强烈影响着土壤异养呼吸的C02排放。上述数据和研究结论表明,加强亚热带山区天然林保护,促进地带性植被恢复,合理营造人工林,降低坡地农业的耕种强度,对于增强山地土壤碳吸存、维系山区植被和土壤较高的生产力,促进山区的可持续开发都具有重要意义。更多还原

【Abstract】 Land use/cover change (LUCC) is widely recognized as one of the most important driving forces of global carbon cycles. Tropical-subtropical soils contain at least one third of the global soil organic carbon storage and annual biosphere-atmosphere CO2 exchange. The tropical-subtropical soil respiration (Rs, soil CO2 efflux) is the major carbon flux from pedosphere into atmosphere. Assessing the impact of land-use changes on Rs is of vital significance to understand the interactions between belowground metabolism and regional carbon budgets. The Rs consisted overwhelmingly of those from root (autotrophic) and microbial (heterotrophic) components. Partitioning Rs into rhizospheric (RR) and heterotrophic (RH) components is essential for understanding and modelling belowground carbon balance.Using "space for time" method, the influence of land use/cover change (LUCC) from natural forest to secondary forest, plantations, orchard and sloping tillage on Rs and it components were evaluated in mid-subtropical mountainous area in South China. In this study, the monthly in situ Rs was examined between 09:00 and 12:00 hours over a 3-year period within the representative land-use sequence. Results showed that the RS exhibited a distinct seasonal pattern, and it was dominantly controlled by the soil temperature. After the land-use conversion, the apparent temperature sensitivity of Rs (Q10) was increased from 2.10 in natural forest to 2.71 in sloping tillage land except for an abnormal decrease to 1.66 in citrus orchard. Contrarily, the annual Rs was reduced by 32% following the conversion of natural forest to secondary forest,46-48% to plantations,63% to citrus orchard and 50% to sloping tillage land, with the average reduction of 48%. Such reduction of annual Rs could be explained by the decrease of topsoil organic carbon and light-fraction organic carbon storages, live biomass of fine root (<2 mm) and annual litter input, which indirectly/directly correlated with plant productivity. Our results suggest that substrate availability (e.g., soil organic carbon and nutrients) and soil carbon input (e.g., fine root turnover and litterfall) through plant productivity may drive the Rs both in natural and managed ecosystems following strong disturbance events.Besides, a root-exclusion approach was employed to partition Rs within a representative land-use sequence. Results showed that both RH and RR varied seasonally, and were predominately controlled by temperature as well as by the interaction between temperature and the phenology of photosynthate input. The apparent Q10 values of RR were totally higher than those of RH for various land covers, and both tended to increase following the land-use changes only except for an abnormal decrease in orchard. The contribution of RR to Rs decreased with the land-use changes resulted from the larger reduction of RR (41-91%) than RH (13-43%). The fine root biomass was remarkably declined following the land-use changes, which was considered to be the major driving force for the substantial decrease of RR. The RH also decreased with the land-use conversion, but levelled out in the sloping tillage. Both soil substrate supply from above-and underground-inputs (litterfall and fine root turnover) and from soil resources (litter layer mass, SOC and LFOC) were marked reduced, which could account for the decrease of RH after the land-use changes. Our results suggest that the RH and RR showed great potential to respond equally to substrate availability (e.g., recently photosynthate input and labile carbon) through plant productivity following the land-use changes. Besides, the RH may also be controlled by nutrient availability (e.g., soil inorganic nitrogen content) through chemical fertilizing in intensive human-disturbed land covers.更多还原