【作者】 李熙波；

【导师】 杨玉盛；

【作者基本信息】 福建师范大学 ， 自然地理学， 2012， 博士

【摘要】 城市绿地随城市化迅速扩大在改善城市生态环境的同时具有可观的碳汇效益。目前,我国已主动承诺大幅降低碳排放强度,但我国传统森林碳汇的提升难度正逐渐加大,如能准确评估城市绿地的固碳能力,则对我国缓解减排压力、实现减排承诺都非常有意义。本研究通过在城市化进程迅速的中国沿海省会城市——福州市内的闽江公园内(26003’N，119°15’E)选择临近分布的番石榴(Psidium guajava)、南洋杉(Araucaria cunninghamii)和黄花槐(Sophora xanthantha)片林以及各自毗邻的沟叶结缕草草坪(Zoysia matrella)为研究对象,采用样方清查法与碳平衡法,估算了各绿地的碳汇效益,并针对当前城市绿地碳循环研究的薄弱环节——地下碳过程开展了系统的研究,探讨了土壤关键碳通量——土壤呼吸和地下凋落物碳归还的调控机制,以及二者在两种城市绿地覆被下的差异,并进一步探讨城市绿地土壤有机碳的形成机制。这对客观评价城市绿地的碳源汇功能,揭示其碳汇机制,以及完善我国碳预算都具有重要意义。研究结果表明：片林植被碳库要明显高于比邻草坪,同时也具有更高的生态系统总碳库。与临近的片林相比,草坪土壤呼吸速率均表现出高值更高,低值更低的特点,草坪生态系统的土壤呼吸及其组分具有更高的Q1o值,表明草坪土壤呼吸对末来环境因子变化的响应更为敏感。片林地上凋落物动态呈现为双峰模式,峰值分别出现在春季4-5月份和夏末秋初的8-9月份。草坪的修剪分别在5月和10月,各草坪全年地上草屑总量(4.1-4.8t.C.hm-2.a-1)要高于片林全年地上凋落物总量(2.5-4.0t·C.hm-2.a-1)。各片林之间地下凋落物归还峰值出现的月份各不相同。相对而言,各草坪根系的死亡动态之间比较接近,基本上从4月份起根系死亡量开始逐渐增加,于秋季10月份达到最大值。片林全年根系碳归还量在4.2-7.2t·C·hm-2.a-1之间与各自毗邻草坪(5.8-7.0t·C·hm-2·a-1)并无显著差异(P>0.05)。各绿地中,黄花槐凋落物的分解速率最快,分解系数为3.54。各草坪凋落物的分解速率次之,并且彼此较为接近在2.90-2.98之间。南洋杉与番石榴的最小分别为1.09和1.22。野外同位素实测数据表明,在建植10a的草坪表层0-20cm土壤中,源自于草坪植物的SOC占42%,在整个培养过程中,5%(CL)和10%(CH)草屑添加量处理的C02的累计排放量(分别为2.94mg C·g-1soil和3.61mg C·g-1soil)显著高于对照(CK,1.2mg C·g-1soil,P<0.05)。其中C4-CO2为CL和CH累计排放C02的主要组成,分别占累积排放的64.5%和80.2%。此外,草屑添加处理还可显著提高培养土壤微生物生物量、土壤的潜在可矿化碳量SOC分解系数。这些结果表明C4相对于土壤原有的C3对于微生物代谢而言具有更高的底物可利用性,能刺激微生物生物量增加,同时提高土壤SOC潜在可矿化碳量,有助于SOC的形成。全年片林净初级生产力(NPP,10.3-14.0t.C.hm-2·a-1)与草坪NPP(11.8-13.1t·C·hm-2·a-1)相当,但片林的净生态系统生产力(NEP,4.20-6.47t.C·hm-2·a-1)明显高于草坪(1.8-3.4t·C.hm-2·a-1)。片林与草坪NEP的流向差异体现在：片林的植被碳库累积速率均高于毗邻草坪,而土壤碳库累积速率相对较低。造成这种差异的原因除了有片林和草坪植物自身碳分配的差异外,二者人为管理措施的不同也是原因之一。此外,片林人为移出地上凋落物的不同去向将给其碳汇估算带来一定的不确定性,而草坪土壤碳汇存在时间期限,建植4年和8年的草坪土壤固碳速率分别可达1.4t·C·hm-2·a-1和1.3t·C.hm-2.a-1,但建植10年的草坪土壤固碳速率就迅速降低自0.4t.C.hm-2.a-1。上述数据和研究结果表明,尽管草坪具有更高的土壤固碳速率,但城市片林比草坪具有更高的生态系统碳汇。因此在城市绿化中,从碳汇效益角度考虑,应尽量优先考虑种植片林,并采用合理的管理措施避免片林碳汇流失。更多还原

【Abstract】 Urban green space expanding rapidly due to urbanization could improve urban environment and has considerable carbon (C) sequestered ability. Recently, Chinese government has committed to dramatically reduce CO2emissions intensity. However, increasing C sick of traditional forest has been more difficult. Therefore, accurate assessing the C sink of urban green space will be meaningful for China to relieve the pressure in reducing emission of CO2and to be helpful for fulfilling Chinese obligations towards the Kyoto Protocol.This study was conducted at the Minjiang Park in Fu’zhou City, the capital city of Fujian province (26°03’N,119°15’E) and one of the fastest urbanized inshore city in southeast China. In this study, ecosystem C sequestration in three urban forests and lawns were quantified by inventory method and C budget method. Below ground C allocation and soil organic C (SOC) formation mechanism were also investigated. This study is not only essential for objective evaluating C sink of urban green spaces, but also helpful for perfecting C budget of China.The result showed that three urban forests had higher vegetation and ecosystem C storage than abut lawns. Lawns have relative higher seasonal maximum of soil respiration rate and lower minimum than each close-by urban forest. Moreover, the Q10values of soil respiration and its components in lawns were also higher each close-by urban forest. These results suggest soil respiration in lawns will be more sensitive to future climate change. Seasonal dynamics of liiterfall in urban forests showed binomial patterns with the first peak occurring from April to May and the second peak occurring during August and September. Lawn mowing conducted in May and October. Annual clipping residue of lawns (4.1-4.8t·C·hm-2·a-1) were higher than the annual aboveground litterfall in urban forests (2.5-4.0t·C·hm-2·a-1). The peak values of belowground litterfall in urban forests were not appeared in same month, while those in lawns usually appeared in October. There was no significant difference in annual belowground litterfall between each urban green space (P>0.05). Litter decomposition rate (k) of yellow flower of pagodatree (k=3.54) was fastest among these urban green spaces. Lawns came next with k values from2.90to2.98. The k values of araucaria and guava were lowest (1.09and1.22, respectively).Field C isotope analysis indicated, lawn-derived C contributed42.0%soil organic C (SOC) under10years old lawn. Indoor simulative experiment showed that during incubation experiment, cumulative CO2emissions of5%(CL) and10%(CH) clipping addition treatments (2.94mg C·g-1soil and3.61mg C·g-1soil, respectively) were significantly higher than that of control (CK,0%clipping addition). The cumulative CO2emissions in CL and CH consisted chiefly of C4-CO2which accounted for64.5%and80.2%, respectively, of cumulative CO2emissions in CL and CH. Moreover, clipping addition could obviously increase soil microbial biomass, potential mineralizable C and SOC decomposition rate. These results indicate C4was easier than C3for microbe utilizing and could enhance both microbial biomass and potential mineralizable C, therefore improve C4-SOC formation.Annual net primary productivity (NPP) in urban forests (10.3-14.0t·C·hm-2·a-1) and lawns (11.8-13.1t·C·hm-2·a-1) were similar. However, urban forests had higher net ecosystem productivity (NEP,4.20-6.47t·C·hm-2·a-1) than that of lawns (1.8-3.4t·C·hm-2·a-1). There are different NEP distribution between urban forests and lawns. Urban forest has higher vegetation C accumulation rate and lower soil C accumulation rate than lawn. This discrepancy may partly due to the different C allocation strategy in arboreal and herbaceous species. On the other hand, the discrepancy was also likely attribute to different managements in these two types of green spaces. Moreover, various destinies of aboveground litterfall removed from urban forests add the uncertainty of there C budget. SOC accumulations in lawns are time limited. SOC accumulate rate in 4-years-old and8-years-old lawns were1.4and1.3t·C·hm-2·a-1, respectively. However, the rate in8-years-old lawn rapidly dropped to0.4t·C·hm-2·a-1.In conclusion, above results suggest that although urban lawns have faster SOC accumulate rate, urban forests have larger ecosystem C sick than lawns. Therefore, urban forest deserves to give priority in urban green space construction, and suitable managements should be adopted to avoid C loss.更多还原