【作者】 张燕；

【导师】 吴斌； 张志强；

【作者基本信息】 北京林业大学 ， 复合农林学， 2010， 博士

【摘要】 目前,在北方水资源短缺地区的生态建设中,杨树人工林生态系统水量平衡和耗水机理成为日益关注的问题。本文目的是定量分析北京大兴地区杨树人工林(黑杨派)生态系统能量平衡和水量平衡状况,并从水量平衡角度探讨北京大兴林场现有种植密度和规模杨树人工林的可持续发展问题。利用涡度相关、树干液流和微气象综合观测系统对其进行研究,综合分析2006至2009年的连续观测数据。能量闭合和能量分配结果如下：2006-2008年Rn-G(Rn,净辐射；G,土壤热通量)和LE+H(LE,潜热通量；H,显热通量)线性回归相关指数达0.84(半小时)和0.93(日尺度),结果表明该站点数据质量达到中上水平,该数据用于能量分配和水量分配研究具有科学依据。能量不闭合主要发生在夜间。摩擦风速、稳定度、降雨和叶面积指数影响能量闭合：摩擦风速增大和稳定度增加,能量平衡比例接近1；雨天能量不闭合程度比晴天高,随着日降雨量增大,能量平衡比例远离平衡状态；叶面积通过影响摩擦风速来间接影响能量平衡比例。2006-2009年生长季能量主要分配给潜热(LE／Rn：0.71-0.83),显热通量次之(H／Rn：0.2-0.29),分配给土壤热通量的能量最少(G／Rn：0-0.01)。在不同生态系统能量分配的对比研究中,发现人工杨树林LE／Rn与农田生态系统相差不大,远远高于其它林分系统,天然针叶林LE／Rn比天然阔叶林小。生长季和非生长季能量分配差异主要受叶面积指数和反照率的影响,在杨树同一生长期,饱和水汽压和土壤水分变化决定潜热和显热通量的变化。水量平衡研究结果表明,2006和2009年为干旱年份,年水量平衡处于赤字状态(降雨量PPT小于实际蒸发散AET),需要灌溉；2007和2008年的全年降雨量大于多年平均降雨量(569mm),属于湿润年份,降雨供水量基本满足杨树需水量。对于月尺度的水量平衡,每年生长季5月和6月都存在蒸发散量大于降雨的状况,需要抽取地下水进行灌溉,9月份和10月根据前期的降雨状况来判断是否需要灌溉。其次从年月尺度上量化该生态系统需水量与供水量的比例关系,同时对比分析不同站点的杨树林供水量(降雨)和需水量关系。研究发现半湿润、暖温带地区的沙地杨树人工林耗水很大,供需不平衡；在不同站点对比研究中,在相同降雨量下,大兴杨树人工林蒸发散量要远高于其它站点,主要是因为大兴年平均气温较高,同时还发现成熟杨树生态系统的蒸发散量大于降雨量。最后研究环境因素对水量平衡各组分的影响,气象因素中净辐射和饱和水汽压对蒸发散、蒸腾、土壤蒸发有着显著的影响。在不同站点水量供需对比研究中,发现降雨、地下水深度、温度是影响杨树生态系统水量平衡的重要因素。在影响因素分析基础上,对杨树人工林蒸发散量进行回归分析,建立经验公式。并同其它蒸发散计算方法进行对比分析,对不同计算方法模拟所得的蒸发散结果进行验证,为干旱缺水地区杨树人工林的水资源管理提供理论方法。总之,由于北京大兴水资源缺乏地区杨树人工林需水量很大,导致水量不平衡,会使现有种植密度和规模杨树人工林的可持续发展面临巨大挑战。如无论是干旱还是湿润年份,每年3-5月大部分时间存在水量供需矛盾,为了缓解矛盾,需要人工抽取地下水(水位,-16.5m,下降速率为0.71m year-1)进行灌溉,必然会加重地下水危机。因此,在水资源缺乏地区杨树人工林种植和管理应该充分考虑对当地环境水文效应和水资源造成的影响。更多还原

【Abstract】 Populus is extraordinarily popular in China which has greatest plantation area in the world, so recently hydrological circulation and effect of Populus plantation get more consideration. Our central objective was to study sustainability of Populus based on water balance in water crisis region, which located in the warm temperate and sub-humid climate zone.The energy balance is an important and objective method for estimation reliability of energy and materials exchange between ecosystem and atmosphere. This study analyses energy balance and energy components for Populus plantation using three years’data (2006-2008) measured by eddy covariance method. The results of energy closure and energy partition were following:The high energy closure caculated from half-hourly data or daily data indicated high data quality and reliability of energy partition. The energy imbalance mainly happened at night wihich induced to data uncertainty at daily and yearly scale. We found the energy bclosure was best in November and worst in April at monthly scale. Energy closure was related to the friction velocity and atmosphere stability. Energy closure got better and closed to 1.0 when friction velocity and atmosphere stability increased. Energy closure got worse during rainy days and was far away from 1.0 when rainfall quantity increased. Energy closure was indirectly influenced by LAI which was related with friction wind. The bowen ratio and albedo were reasonably determined when energy balance ratio closed to 1.0, which were two important parameters for energy partition. Daily flux of net radiation(Rn)、latent heat flux(LE)、sensible heat flux(H)、soil heat flux(G) had remarkably seasonal variation. Seasonal flux of Rn、LE、H、G was exposed to variation due to leaf area index and rainy days. LE dominated the energy flux and had greater energy flux than H after leaf expansion within at the end April and at the beginning of May. H was greater than LE during leafless period (November to April). Difference of energy partition in growing season and in dormant season was mainly controlled by leaf area index (LAI) and albedo. VPD and soil volume moisture (VWC) had influence on change of latent heat flux (LE) and sensible heat flux (H) during the short growth period of Populus. When contrasting the energy partition in different ecosystem, the LE/Rn of Populus plantation was much greater than that of ecosystem including natural or artificial forest ecosystem. Agriculture ecosystem had the highest LE/Rn. The LE/Rn of the coniferous forest was lower than that of broadleaf ecosystem.We found that seasonal evapotranspiration (AET) and transpiration (T) were exposed to the extremely fluctuation and variability due to the changes of seasonal precipitation and leaf area index (LAI) Populus plantation at Beijing Daxing site had more water consumption with a mean value 1.60±0.04 mm/day from 2006 to 2008, compared with those in the other sites using eddy covariance system. Populus transpiration of mean value 1.78±0.03 mm/day from 2006 to 2009 measured by sapflow probes was as great as those at the other sites. The annul water budget in 2006 and 2008 were deficit and profit in 2007 and 2009. The main supply of PPT and consumption of AET from 2006 to 2009 were 482 and 599,661 and 561,662 and 672,414 and 517mm, respectively. The dry period between March and June required irrigation drawing groundwater to balance drawback of monthly water budget. In comparision with the different sites, the main water supply and consumption of Populus plantation at Daxing site in sub-humid climate district need more water supply for growth than those at the other sites, where there was the same precipitation as Daxing site. The main reason was that multi-years mean temperature (12.2℃) with an increasing trend was higher than those at other sites. Populus plantation under the same plant area and stand age condition simultaneously needed more water for AET resulting from increasing temperature. The continuously increasing water use of Populus plantation conflicted with main water supplying (PPT). Irrigation which was helpful for increasing water supply in the system alleviated the contradiction between water supply and consumption. However the irrigation drawing groundwater aggravated the severity of water crisis due to low water table.We concluded that Populus plantations may not be sustainable in Beijing area due to water shortage including low groundwater recharge and water stress. The hydrological impact of Populus plantation should be taken into consideration involving with water resource management and wood production.更多还原