【作者】 刘文国；

【导师】 彭镇华；

【作者基本信息】 中国林业科学研究院 ， 森林培育， 2010， 博士

【摘要】 本论文以湖南岳阳滩地抑螺防病林生态系统为研究对象,从土壤-植被-大气系统的角度出发,在典型调查的基础上,运用涡度相关(Eddy covariance,EC)法、树干液流(Sapflow)法对生态系统水热,CO2通量变化及其与外部环境因子的响应关系进行研究,旨在了解滩地抑螺防病林林生态系统本身及环境因子关系的动态变化过程,计量其水热,CO2通量值；对抑螺防病林生态系统合理经营管理,充分发挥其综合生态效应有重要价值。主要得到以下结论：(1)湖南岳阳抑螺防病林生态系统,同一能量平衡组分在不同的季节具有相似的日均变化过程规律,基本上呈较规则的单峰型,但在不同的季节收入量差异明显。从全年尺度看,净辐射通量共计2630.50MJ/m2,潜热年通量约为2035.40MJ/m2,大约消耗77%的净辐射能,而显热年通量水平为439.71MJ/m2,占净辐射能16.71%,土壤热通量为-4.06MJ/m2,表现为土壤释放热量,植物体储能等部分大约占净辐射能的6.29%。30min的全年能量收支平衡闭合度约为79%,约有21%的能量不知去向,依然存在不闭合现象。(2)土壤水分具有显著的时空尺度变化特征,结合样地基本情况,在空间垂直方向将土壤划分为水分易变层(0～20 cm)、土壤水分利用层(20～100 cm)和土壤水分相对稳定层(100 cm以下)3个层次。在时间方向上可将测定时期样地抑螺防病林地的土壤水分按其特点和时间顺序划分为：土壤聚水期、退水期和稳水期3个时期。土壤含水量主要受3个典型因素(Vi,Ui)(i=1,2,3)影响,逐步回归分析结果显示不同深度的土壤水分受环境因子的影响有差异,总体来看土壤水分主要受到空气温度、水汽压亏缺、土壤温度、降雨和太阳辐射的影响。随着土壤深度的增大回归方程相关系数平方越来越小,说明外部环境因子对深层次土壤水分的影响越来越弱。(3)分别从单株尺度和林分尺度对植被蒸腾进行了评估测算。其中在单株尺度上,不同的生长时期,不同的天气条件下,不同的方向和高度,树干液流速率各有差异。晴天杨树液流速率日变化呈现规律的单峰曲线,表现为白天高,夜间低的昼夜节律变化趋势；阴天杨树液流速率日变化呈现无规律性,而且值较低。林分蒸腾量在季节上的变化过程与降雨分布时间紧密相关,日蒸腾量在生长季上呈多峰型分布,峰值多在前期有降雨的情况下出现。(4)抑螺防病林生态系统2009年各个季节的水汽通量大多都为正值,森林向大气释放水分,且夏季水汽通量值最大,春、秋季次之,冬季最小,全年蒸散量为928.175mm,占全年降水量的53.70%。生长季日蒸散量变化过程显示,日蒸散量在生长季呈多峰型分布,整个生长季蒸散总量达805.17mm,占全年蒸散量的86.75%。不同天气条件下,环境因子对水汽通量的影响是不同的,晴天条件下环境因子与水汽通量的相关度普遍高于阴天天气。逐步回归分析结果显示晴天影响水汽通量的主要是净辐射、水蒸汽压亏缺、风速、5cm土壤温度,而多云天气影响水汽通量的主要是净辐射、风速、5cm土壤温度。(5)CO2通量的季节变化特征就是夏季活跃,春、秋季次之,冬季最弱,不同季节差异明显。白天CO2通量的变化呈单峰型曲线,日出后,随着太阳辐射的增强,CO2通量由正转负,森林转变为CO2的吸收碳汇,最大值基本出现在正午时分,随着太阳辐射的减弱,在日落前,再次达到碳收支平衡,森林生态系统转变为CO2碳源。夜间,由于没有了植物的光合作用,为持续的呼吸释放过程。不同天气条件下(晴天和阴天)CO2通量的日变化有明显区别,晴天CO2通量值要明显高于多云天气,而且日变化更有规律。生长季NEE日总值为负值,表现为碳汇；非生长季NEE日总值基本为正值,表现为弱的碳源。2009年全年观测的NEE、Re和GEE分别为-890.12 gC/(m2·a), 807.82 gC/(m2·a)和-1697.95 gC/(m2·a)。(6)抑螺防病林生态系统水分利用效率受多种环境因子的影响。春、夏、秋、冬四个季节,以春季水分利用效率平均值最高,夏季和秋季白天水分利用效率相差不大,冬季最小。更多还原

【Abstract】 Eddy-Covariance (EC) and sap flow method are employed in this study to investigate the energy balance, water budget and CO2 flux from the aspect of soil-vegetation-atmospheric system. The study site is located in Junshan district of Yueyang city, Hunan province. The primary goal is to find out the changes of the ecosystem and environmental factors, calculate the value of water vapor flux, the heat flux and CO2 flux. These will provide the basic to scientific and reasonable management and give full play to the ecological effect of the snail control and schistosomiasis prevention forests ecosystem. Main results and conclusions are the following:The daily variation regularity of energy balance components in different seasons shows signal peak curve but the ratio of energy partitioning in different components are not same in different time scale. The annual net radiation was 2630.50 MJ/m2 in 2009. The latent heat flux was 77% of the net radiation. The sensible heat flux was 16.71% of the net radiation. The soil heat flux and others only took about 6.29% of net radiation. The soil heat flux is negative, which means soil releases heat. The energy closure level was high in 30min scale, but there still had 21% energy missed.Soil moisture has the feature of spatial and temporal scale, and the difference of soil water content in different soil layers is significant. According to the basic situation of the plot, it can be divided into three levels in vertical direction. It also can be divided into three stages in time scale:water collection stage, water-falling stage and water steady stage. Soil water content is influenced by three typical factors (Vi, Ui) (i=1,2,3). Stepwise regression analysis shows: there are differences in influencing factors of soil moisture in different depth. Generally speaking, soil moisture is mainly influenced by air temperature, vapor pressure deficit, soil temperature, rainfall precipitation and radiation. The square of coefficient in regression equation is becoming smaller and smaller with soil depth increasing. It is suggested that the influence of environmental factors on soil moisture in deep soil layer is getting smaller. Vegetation transpiration is estimated in the plant scale and the stand scale. In the plant scale, there are differences of sap flow velocity in different growth stages, different weather conditions, different directions and different height. In sunny days, diurnal variation of the sap flow velocity of Populus has regular single-peak curve, which is high in the daytime, but was low at night. In wet days, daily variations of Poplar sap flow velocity are irregular and the value is low. It was close correlation between rate quarterly variation and precipitation timely distribution. The changing process of transpiration closely related to the time distribution of rainfall. The daily transpiration in seasonal scale shows multi-peak distribution.Water vapor flux in this ecosystem was positive in almost all seasons in 2009, which showed the ecosystem was water sink. Water vapor flux in summer was higher than in spring and autumn, and the water vapor flux in winter is the lowest. The evapotranspiration was 928.175mm, which was 86.75% of evapotranspiration in 2009. The influence of environmental factors on Water vapor flux was different on sunny days and cloudy days. Stepwise regression analysis shows:the water vapor flux in sunny days was affected by net radiation, vapor pressure deficit, wind speed and soil temperature in 5cm, while in cloudy day is net radiation, wind speed and soil temperature in 5 cm.There were obvious differences of the feature of CO2 Flux in seasonal scale:CO2 Flux in summer was higher than in spring and autumn, while it was the lowest in winter. The changes of CO2 in the day time showed signal peak curve. After the sunrise, the value of CO2 flux changed from positive to negative, which means the forest is a carbon sink, while the forest turned into a carbon source before the sunset. Without the photosynthesis at night, the forest releases CO2 through respiration. There were differences in diurnal variation of CO2 flux on sunny day and on cloudy day. The value in sunny day was higher than in the cloudy day, and it was more regular. The value in day time was negative during the growing season, and the forest absorbs CO2, while it was positive during non-growing season, and the forest releases CO2. The value of NEE, Re and GEE in 2009 were-890.12 gC/(m2·a),807.82 gC/(m2·a)和-1697.95 gC/(m2·a) respectively. Water use efficiency of the snail control and schistosomiasis prevention forests ecosystem was affected by many ecological factors. Its average value in the spring was higher than in the summer and autumn, while it the was lowest in the winter.更多还原