【作者】 陈卉；

【导师】 林光辉； 高亚辉；

【作者基本信息】 厦门大学 ， 水生生物学， 2013， 博士

【摘要】 红树林是全球净初级生产力最高的生态系统之一,也是全球蓝碳的主要贡献者之一。碳循环研究是阐明红树林碳汇潜力及调控机制的前提,但目前亟缺乏红树林生态系统碳固定及其去向的系统研究,特别是对于亚热带地区的红树林。本研究结合传统调查、野外定位观测和控制实验,利用涡度协方差技术和稳定同位素技术探讨了亚热带地区(云霄和高桥)红树林的碳固定、掉落物分解及其同化过程,并着重分析了极端天气如台风活动对红树林生态系统碳交换过程的影响及生物入侵背景下红树林湿地的掉落物分解与同化过程。主要结果与结论分述如下：(1)云霄和高桥的亚热带红树林均具有很高的生物量和年掉落物产量。云霄(2008年8月)和高桥(2009年10月)红树林的生物量分别为82.17-118.74和85.04-161.08Ton ha-1,其中枝和直根的比例最高,根冠比的变化范围为0.35-1.47；2009-2012年云霄和高桥红树林的平均年掉落物产量分别为848.44和728.62g m-2,表现出明显的季节动态和年际动态,其中叶掉落物比例最高；温度、降雨量、风速是影响红树林掉落物量的主要气候因子。(2)生态系统碳通量研究结果表明,云霄和高桥红树林全年都表现为较强的碳汇：2009-2012年云霄和高桥红树林生态系统平均固定了683和721g C m-2yr-1,两地的年总生态系统生产力(GEP)差异较小(分别为1871和1763g C m-2yr-1),但云霄红树林的年生态系统呼吸量(RE)显著高于高桥的(分别为1287和1096g C m-2yr-1),两个站点RE/GEP比分别为0.69和0.63。光照、云量、空气饱和蒸气压差(VPD)和温度共同调控白天红树林生态系统的NEE：云霄和高桥红树林都在中等云量(晴空指数kt值分别为0.3-0.6和0.4-0.6)时达到最大NEE。传统方法(掉落物法)估算得到的净初级生产力远高于碳通量观测结果,可能是因为传统研究低估了掉落物量在净初级生产力中所占的比例,这意味着对掉落物产量及其去向的研究将变得更为重要。(3)2009至2011年期间登陆的23个台风活动对红树林碳水通量影响的综合分析表明：台风的风速、持续时间、登陆距离是调控红树林生态系统碳水循环的最重要台风特征。频繁强台风带来的强降水和大风会使红树林形成大量的掉落物,也会在短期内起到降温的效果。在强台风登陆之后,生态系统最大NEE均显著降低,而且白天生态系统暗呼吸Rd也显著降低；除了2010年10月登陆的13级台风Megi,其他台风登陆后光量子效率α均显著增大。高VPD和高温都会抑制白天红树林的NEE,但VPD和温度对红树林NEE的调控作用与台风强度和登陆时间相关。台风登陆前后NEE的变化方向及大小主要受到GEP和RE的共同调控：在2010年7月12级台风Conson-Chanthu和2010年9月10级台风Namtheum-Fanapi登陆后,红树林生态系统NEE的日总量分别下降了26%和57%,但台风Megi登陆后红树林NEE反而增加了140%。这些改变在台风过后几周内就得到恢复,说明红树林生态系统碳交换过程对台风干扰呈现出较强的生态弹性。(4)红树林生境内乡土红树植物秋茄(Kandelia obvata)的凋落叶片比入侵植物互花米草(Spartina alterniflora)凋落叶片分解得更快(分解常数和半分解期分别为0.021、0.012d-1和34、59d),但在盐沼生境中二者分解速度没有显著差异(分解常数和半分解期分别为0.016、0.014d-1和43、50d)；互花米草凋落叶的淋溶速率显著高于秋茄的(0.14和0.09g d-1)；秋茄和互花米草凋落叶的分解模式一致,都在分解初期(28天)快速减少后变缓直到平稳；分解过程中凋落叶的总氮剩余量保持下降趋势,C/N比与其氮含量呈显著负相关关系；秋茄和互花米草凋落叶的δ13C值随分解都变得更负(分别下降1‰和1.5‰),且这种趋势在盐沼生境中表现得更明显。这意味着互花米草入侵并未显著改变红树林湿地的掉落物分解过程。(5)乡土红树林生境内多毛类混合利用了红树植物凋落叶等食物,但在互花米草入侵后多毛类主要以互花米草为食。野外控制实验结果表明：入侵植物互花米草凋落叶对乡土红树林生境内多毛类的食物来源影响最大,但这种影响会随分解过程而减弱。在添加乡土红树植物秋茄凋落叶后,多毛类δ13C值的变化较小且平稳,但在添加外来互花米草凋落叶后多毛类的δ13C值在分解初期(28天)快速增加达到最大值,之后又降低回初始水平。互花米草和秋茄掉落物之间主要营养成分的不同以及它们在分解过程中的差异可能是造成底栖动物多毛类对外来种和乡土植物掉落物选择利用的主要原因。更多还原

【Abstract】 Mangrove ecosystems are among the most productive natural ecosystems in the world, and global mangrove wetland is one of major contributors to earth’s blue carbon sink. Systematic study of mangrove carbon cycle will improve our understanding of the regulatory mechanisms of mangrove carbon sink, and prediction of their responses to global change. However, there are limited studies on mangrove carbon sequestration and sink strength, especially for subtropical mangrove ecosystems. In this study, eddy covariance technique was used to quantify mangrove carbon sequestration and their determining factors in Yunxiao, Zhangzhou and Gaoqiao, Zhanjiang, China; then traditional survey, field control experiment and stable isotope technique were applied jointly to investigate litter decomposition and their consumption processes. The main findings and conclusions from this study were summarzied as follows:(1) The total biomass was82.17-118.74Ton ha-1for the mangrove forests in Yunxiao (August2008) and85.04-161.08Ton ha-1for the mangrove forests in Gaoqiao (October2009), respectively, with branch and taproot having the highest proportions. Below ground biomass were mainly distributed in a depth of0-30cm, and their below to above-ground ratios ranged from0.35-1.47. Mean annual litter production was843.20-1011.51and964.98g m"2for the Yunxiao and Gaoqiao mangrove forests from2009to2012, with the leaf litter having the highest proportion. Litter production showed obvious seasonal and inter-annual variation, attributed to the changes in temperature, rainfall and wind conditions.(2) During the last four years (2009-2012), the net ecosystem CO2exchange (NEE) was687and721g C m-2yr-1for Yunxiao and Gaoqiao mangrove forests, respectively. The mean annual gross ecosystem productivity (GEP) was1871and1763g C m-2yr-1, respectively for Yunxiao and Gaoqiao mangrove forests during the same period, with corresponding mean annual total ecosystem respiration (RE) of1287and1096g C m-2yr-1and RE/GEP of0.69and0.63, respectively. Solar irradiance, cloud, vapor pressure deficit (VPD) and temperature co-regulated daytime NEE. Both Yunxiao and Gaoqiao mangrove ecosystems reached their maximum NEE under moderate cloudiness (clearness index of0.3-0.6and0.4-0.6). Net primary productivity (NPP) estimated by traditional survey (litter fall method) was much higher than that from eddy flux measurements, likely due to the underestimation of litter proportion in NPP by the traditional survey method, which underscored the importance of research on litter fall for understanding mangrove carbon cycle processes.(3) Frequent typhoons with strong wind and intensive rainfall caused defoliation and local cooling effect during typhoon season. Results from our synthesis of23typhoons during2009-2011demonstrated that wind speed, duration and distance of typhoon from mangrove ecosystem were the most important factors controlling the mangrove ecosystem carbon and water fluxes. In2010, the maximum NEE was slightly decreased following typhoon. Except for category13typhoon Megi (October2010), the apparent quantum yield was significantly greater than that before typhoon. Daytime RE also exhibited significant decrease after typhoon landfalls, particularly following typhoon Megi. Daily total NEE values were decreased by26%and57%following category12typhoon Conson-Chanthu (July2010) and category10typhoon Namtheum-Fanapi (September2010), respectively, while they were significantly increased by140%following typhoon Megi. These changes were quickly reversed within a few weeks right after the typhoon events indicating that mangrove ecosystems have strong resilience to the frequent typhoon disturbances.(4) The leaf litter of Kandelia obvata decomposed faster than that of Spartina alterniflora at the mangrove decomposition site, with a decay constant and half life time of0.021,0.012d-1and34,59d for K. obvata and S. alterniflora, respectively. However, there was no significant difference between species at the salt marsh decomposition site. The leaf litter of S. alterniflora leached faster than that of K. obvata with a leaching rate of0.14,0.09g d-1, respectively. The dry mass loss rates were similar for the leaf litter of both plant species and both decomposition site, degrading rapidly in the first28days, then following by a slower, steady decrease for the remaining period of the experiment. Total nitrogen content of leaf litter decreased during the decomposition, and the C/N ratio was negatively correlated with nitrogen content for the decomposed leaf litter. The δ13C values of decomposing leaf litter decreased during decomposition, about1%o for K. obvata and1.5%o for S. alterniflora).(5) Polychaetes depended on mangrove leaf litter, microphytobenthos and particular organic matter for their foods at the mangrove site, but mainly used S. alterniflora leaf litter at the salt marsh site. The preliminary results from a field control experiment showed that the δ13C values of polychaetes were affected significantly by added leaf litter during decomposition. After adding exotic S. alterniflora leaf litter, polychaetes at the mangrove site had larger enrichment in813C values than that at the salt marsh site. Mangrove polychaetes assimilated more carbon from exotic S. alterniflora leaf litter than from native mangrove leaf litter. However, the significant carbon consumption only occurred within the half-life time (<2months) of exotic S. alterniflora leaf litter indicating significant impact of Spartina invasion on the food sources of local polychaetes. Decomposition rate and nutrient content might contribute to the selective utilization of litter from exotic S. alterniflora and native mangroves by the polychaetes in the mangrove wetlands.更多还原