【作者】 阎光宇；

【导师】 林光辉； 高亚辉；

【作者基本信息】 厦门大学 ， 水生生物学， 2012， 博士

【摘要】 湿地能量交换和蒸散是影响湿地各生态过程和功能的重要因素,其影响湿地水热平衡、养分循环、碳累积以及植被生产力。滨海湿地生态系统位于陆地与海洋的交汇处,易受潮汐周期性的影响。由于潮汐可能作为一个能量源或汇,其带来的横向通量会影响湿地生态系统的能量分配和能量收支,进而影响到滨海湿地生态系统结构和功能。红树林是滨海湿地主要的湿地类型,也是蓝碳碳汇的主要贡献者,其能量交换及水汽通量(蒸散)已经成为滨海湿地生态学研究的重要科学问题。本论文以中国福建亚热带红树林生态系统为研究对象,结合涡度相关技术(Eddy covariance, EC)和树干茎流法(Sap flow)对亚热带红树林生态系统的能量平衡、蒸散及红树植物蒸腾(水分利用)进行了系统研究,分析了能量平衡各分量的分配特征、能量闭合水平以及影响能量闭合和能量分配的因素；研究红树林生态系统蒸散的变化特征及其影响因素。此外,还分别从生态系统和植物个体水平上对比分析了红树植物水分利用的特征及其对环境因子的响应等,并揭示了滨海湿地特有环境因子-潮汐对滨海湿地生态系统的能量平衡、蒸散及红树植物蒸腾的调节机理。主要结果与结论如下：1.2009-2011年红树林生态系统半小时尺度和日尺度Rn-G (Rn:净辐射；G：土壤热通量)和LE+HS (LE:潜热通量；Hs：显热通量)的线性回归相关指数分别为0.63-0.69和0.67-0.79,表明利用用涡度相关法可以准确评估生态系统的能量分配和蒸散水平。通过对2009-2011年亚热带红树林能量各组分季节变化和分配的研究发现：生态系统能量平衡各组分在年内的变化过程主要受季节气候的变化,在不同时间尺度上,该生态系统能量平衡各分量分配比例不同。冬季,显热占主导地位,其他季节潜热占主导地位。总体看来,两个站点的能量主要分配给潜热通量(38.15%)和显热通量次之(28.56%),而土壤热通量最小(<0.1%)。2.通过不同生态系统对比研究中发现,红树林滨海湿地生态系统潜热通量占净辐射比例(LE/Rn)与其他湿地生态系统接近,但是远远低于陆地生态系统(农田、阔叶林生态系统等)。而较低的LE/Rn及能量不闭合可能与潮汐影响有关。潮汐是影响滨海湿地生态系统能量闭合和能量分配的重要因子。冬季潮汐活动降低波文比值,并显著降低了生态系统能量闭合度；夏季则相反,导致生态系统的波文比显著增大,并在一定程度上提高了能量闭合度。红树林生态系统较低的普利斯特里-泰勒系数(LE/LEeq比率)(小于0.8)及较低的冠层表面导度(5-9mm s-1),以及冬季和夏季下午较低的解耦合系数值都说明：在受到淹水和高盐度严重胁迫下,红树林生态系统蒸散主要受到生物调节,即气孔和饱和水汽压差(VPD)控制。3.蒸散红树林生态系统蒸散(ET)发具有规律的日变化进程和季节动态。夏季大于春秋两季,冬季最小。2009-2011年全年总蒸发量分别为945.54mm、886.49mm、1062.00mm。环境因子在很大程度上制约着蒸散的变化,其中以净辐射和饱和水汽压差对蒸散影响最大。潮汐活动也是影响生态系统的蒸散的主要环境因子。夏秋季,潮汐活动降低ET;冬春季,潮汐活动使ET增大。分别利用Priestley-Taylor (PT)模型和Penman-Monteith (PM)模型来模拟亚热带红树林生态系统的蒸散,都能得到较好的拟合结果。4.蒸散,红树植物树干茎流密度(SFD)随PAR和VPD的变化呈现明显的昼夜动态和季节动态,表现为典型的单峰型曲线。不同径级的秋茄和白骨壤的SFD范围分别为15.37-38.21g m-2s-1和21.26-73.15gm-2s-,说明红树植物的SFD处于较高的水平。然而,不论从个体水平上还是生态系统水平上,红树植物水分利用都十分保守。秋茄和白骨壤的最大日蒸腾量小于分别为0.31-5.43kg d-1和2.01-10.61k d-1。外推得到秋茄和白骨壤林段总蒸腾量分别为85.56mm和129.51mm,红树植物的蒸腾量约占生态系统蒸散(915.50mm)的23%。5.不同季节,环境因子对树干茎流、日蒸腾量(F)和蒸散的响应程度不同。夏季,与树干茎流相关性较高(R2>0.4)的因子是光合有效辐射(PAR)、饱和水汽压差(VPD)和风速；冬季主要影响因子变为PAR、VPD和气温(Ta)。对于F,除了以上因子外,空气相对湿度也是影响F的主要的环境因子。其中,PAR和VPD是影响红树植物蒸腾的最主要因子(R2>0.7)。而对于ET,除了PAR之外,其他因子与ET的相关性都较弱(R2<0.4)。由此说明,PAR是反映红树林生态系统蒸散的重要环境参数。6.蒸散红树植物的冠层气孔导度随着VPD的增加而降低,随PAR的增加而呈线性增加,并且随VPD的增加,气孔导度对PAR的敏感性逐渐下降。虽然冠层表面导度也随VPD的增加而降低,随PAR的增加而增加,但是相关指数较低。说明冠层表面导度对环境因子的敏感性较低。7.成熟红树植物的蒸腾和生态系统的蒸散对周期性潮汐活动的响应不同。其中,潮汐浸淹对白骨壤的蒸腾影响最大(SFD降低7.5%,日蒸腾量降低了16.83%),秋茄次之(SFD降低5.8%,日蒸腾量降低了12.35%),蒸散最少(降低了4.5%和10.26%)。同时,周期性潮汐淹水也在一定程度上使树林生态系统的初级生态系生产力(GEP),净生态系统交换(NEE)和生态系统呼吸(ER)分别降低了6.56%,6.84%和12.08%。以上结果表明：由于独特的地理位置,红树林受到潮汐带来淹水和盐度的胁迫,因此红树植物水分利用十分保守,其蒸腾作用主要受到植物生理的调控,而潮汐活动显著改变了红树林生态系统的水热平衡及植物水分利用。为进一步揭示红树植物生态系统高水分利用效率及高生产力的原因机理奠定基础。对于研究湿地生态系统CO2净交换、水汽通量及二者之间的关系,深刻认识与理解湿地生态系统物质循环与能量交换特点、把握湿地碳循环过程及其驱动机制具有重要意义。更多还原

【Abstract】 Energy exchange and evapotranspiration (ET) between land surface and the atmosphere is among the most important processes in any ecosystem since it can significantly affect temperature, water transport, plant growth and many other ecosystem processes. Understanding the magnitude and changes of various energy fluxes as well as related regulatory mechanisms is critical for quantifying ecosystem functions and their responses to climate change. Located between the interface of land and sea (intertidal zone), estuarine wetland ecosystems is affected by the periodic tidal flooding, where tidal activities and upstream hydrology can play vital roles in regulating the magnitude and dynamics of the energy budget through horizontal transportation of mass and energy, and then affect the ecological processes and functions of estuarine wetlands,. Despite of the importance roles mangrove forests playing in regulating matter exchange in the coastal zones, there are still limited studies on the energy balance and ET in mangrove ecosystems. In this dissertation study, energy balance, ET variations and water use of mangrove trees of subtropical mangrove ecosystems in Yunxiao (23°55’N,117°23’E) of Fujian province, China were investigated by combining eddy covariance technique and tree sap flow methods. The characteristics of energy distribution of energy balance components, energy closure level, ET variation, water use of mangrove trees as well as their response to environmental factors were all discussed, including tidal influence on energy balance, ET and water use of mangroves. The purpose of this research is to understand the characteristics of energy flux, water vapor flux and water consumption by transpiration of the mangrove forests and lay the foundation for further researches on environmental mechanism, especial the tidal regulation in coastal zone. Main results and conclusions are listed below.1. The results of energy closure in the past three years (2009-2011) as indicated as the correlation index of liner regression between Rn-G (Rn:net radiation, G:soil heat flux) and LE+HS(LE:latent heat, Hs:sensible heat) were0.63-0.69and0.67-0.79, indicating that the flux data quality was reliable and suitable for the ecosystem energy partitioning studies. Daily flux of net radiation (Rn), latent heat flux (LE), sensible heat flux (Hs), and soil heat flux (G) had remarkable seasonal variation. Seasonal energy flux was controlled by the seasonal change. The sensible heat was greater than latent heat and the bowen ratio was larger than1during winter season. The latent heat dominated the energy flux and had greater energy flux than sensible heat and the bowen ratio reduced to0.4-0.6from spring to autumn. Overall, the latent heat showed the higher ratio (38.15%) in net radiation than that of the sensible heat (28.56%), whilst the ratio of soil heat was neglectable (<0.1%). The latent heat was almost equal to sensible heat under flooding and high salinity stress.2. When comparing the energy partitioning in different ecosystem, the LE/Rn was closed to that of wetland ecosystems, but was much lower than that of terrestrial ecosystems including agriculture ecosystem, broad-leave forest ecosystem and so on. This indicated that mangrove forest in subtropical zone was water conservative. In addition, tidal activity was also the important factor influencing energy closure and energy partitioning. Tidal activity can significantly reduced the bowen ratio and energy closure in winter, whereas it would dramatically increased the bowen ratio, and at the same time enhanced the energy closure to some extent in summer. The low value of LE/LEeq all year and low Ω value in winter and summer after indicated the stomata and VPD mostly controlled ET in any hydraulic or salinity stress condition specifically during dry season. And the low canopy surface conductivity (gc-e) showed that transpiration might be reduced though stomatal closure under sever water stress, and the reduced stomatal conductivity can limited energy partitioning to latent heat.3. ET variation had regular diurnal process, and presented obvious seasonal dynamic with the seasonal change. Compared with the other terrestrial ecosystems using eddy covariance system, it had more water consumption in summer with the mean daily value of3.4mm d-1and the whole year ET value of838-1062mm during2009-2011. Both the Priestly-Taylor and Penman-Monteith models could perform well to ET for mangrove ecosystems. It was also seen that the environment factor could markedly effected ET. Net radiation and VPD were key factors to affect ET. In addition, tidal activity also adjusted the ET, which was reduced in summer and autumn, while was enhanced in winter and spring.4. Variations of sap flow density (SFD) following closely the variation in PAR and VPD showed regular single-peak curve. The peak value of SFD of Kandelia obovata and Avicennia marina of different diameter was15.37-38.21g m-2s-1and21.26-73.15g m-2s-1, respectively. Compare with the other species, sap flowwas fairly high in the outer xylem of mangroves in our sites. Maximum daily water use for Kandelia obovata and Avicennia marina was ranged from0.31-5.43kg d-1,2.01-10.61kg d-1. Further extrapolated to the whole stand transpiration (Es), Es was85.56mm for Kandelia obovata, and129.51mm for Avicennia marina during observation period (201006-201105), respectively. The percentage of Es/ET in four seasons in our sites was at the range of16-26%with mean value of23%, clearly indicating that the individual mangrove tree water use followed leaf-level mechanisms in being conservative.5. Different environmental factors had different influences on sap flow (SFD), daily water use (F) and ET in different season. Photosynthetically active radiation (PAR), vapor pressure deficit (VPD) and windspeed (v) were key factors to affect SFD in summer. While PAR, VPD and Tα were key factors to affect SFD in winter. For daily water use, relative humility was also the key factor beside of PAR and VPD. Among those factors, PAR and VPD were major factors affecting mangrove transpiration. However, except for PAR, the dependence of ET on environmental factors was weaker.6. The gc-t decreased with VPD increasing, increased linearly with PAR increasing. And with the increased level of VPD, the sensitivity of gc-t to PAR decreased gradually. Like gc-t, the gc-e also decreased with VPD increasing, and increased linearly with PAR increasing. Compared with gc-t, its correlation coefficient was lower, indicating the lower sensitivity of gc-e to environmental factors.7. Periodic flooding reduced ET and stand transpiration (Es) in mature trees of K. obovata and A. marina in our study. The mean daily water use was reduced by16.83%for A. marina trees,12.35%for K. obovata and10.26%for daily ET, respectively. Meanwhile, ecosystem GEP, NEE and ER were reduced by6.56%,6.84%, and12.08%under tidal flooding.The above results suggest that, due to the unique geographical location, the mangrove plants are water conservative under tidal flooding and salinity stress in subtropical zone, so their transpiration are mainly regulated by plant physiological processes. Moreover, tidal activities exerte significant impact on the water heat balance of mangrove ecosystems and the water use patterns of mangrove forests. This study lays the foundation for further study of mechanism of high water efficiency and high productivity about mangrove ecosystem. Furthermore, this will be of great importance in studing of the relationship of ecosystem CO2exchange and water vapor flux, understanding of the characteristics of material cycle and energy exchange, grasping the carbon cycle and its driving mechanism in wetland.更多还原