【作者】 韩磊；

【导师】 贺康宁；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2011， 博士

【摘要】 树木蒸腾耗水量的准确测算是防护林体系优化配置、造林树种选择以及造林密度等林业生态工程建设技术中最关键、最核心的问题。本文针对黄土半干旱区水土保持防护林体系建设中影响林分稳定的水分环境年际盈亏变化特点,2004年～2009年在山西省方山县北京林业大学径流林业试验地,以主要造林树种侧柏(Platycladus orientalis)、油松(Pinus tabulaeformis)、白榆(Ulmus pumila)和刺槐(Robinia pseudoacacia)为研究对象,以林地土壤水分动态、林木水分生理及其林下植被的生长过程为主要研究内容,通过对林木冠层蒸腾模拟,进行林地蒸散耗水系统研究,并得出以水量平衡为基础的耗水—林分密度关系。该研究可为最终确定与当地自然降水水分生产潜力相适应的适度生物量和覆盖度,客观科学评价半干旱地区林业生态建设的潜力及发展前景提供理论依据。主要研究结果如下：(1)研究地区(1945-2009)多年平均年降水量为503mm,年际间的降水变幅较大,其多水年和少水年的降水量可相差1-2倍。降水集中于盛夏,春末夏初降水偏少,年降水变率为20.01%,生长季(5～9月)降水变率为23.86%。(2)通过不同林分林下植被的生长状况调查及植被数量特征和生物多样性的分析,结果表明：无论是刺槐、白榆还是油松,高密度林分内林木的树高、胸径、冠幅等生长指标值,均比低密度林分内的低。密度过高的林分林内的水分供给已不能满足林木正常生长的需要,导致林木的生长滞缓,成为大片“小老树”；在密度较大的白榆林内,大量的树木出现的严重的枯梢现象,表明林内水分环境已严重恶化。(3)利用盆栽试验,用PSYPRO露点水势仪研究不同造林树种的叶水势、萎蔫系数与耗水指数,分析了各树种耐旱机理,结果表明各树种叶水势对环境因子的响应不尽相同,侧柏在干旱胁迫下存活的时间最长,萎蔫系数的大小为：白榆(4.58%)>油松(4.25%)>侧柏(4.08%)；而土壤水分利用效率的大小为：侧柏(80.57%)>油松(79.76%)>白榆(78.19%),说明在相同的土壤和水分条件下,侧柏、油松对干旱环境的适应自身调节能力更强。对林木水分生理对土壤含水量的响应进行分析,确定了林木生长适宜的土壤水分范围分别为侧柏：9.88%-13.21%；油松：10.14%-14.66%；白榆：10.78%～13.71%。(4)通过热扩散茎流计(TDP)技术对林木树干液流速率实时监测并计算得到冠层蒸腾速率(Ec),结果表明太阳辐射(Rs)、大气水分亏缺(VPD)是影响树冠蒸腾变化的主导环境要素,Ω系数描述了冠层与大气的耦联程度也表示叶或冠层蒸腾对气孔导度调节的敏感性,冠层蒸腾极大地受控于气孔导度(gc)。各环境因子与gc之间均呈显著相关,但受VPD和Rs影响更加显著,相关系数为VPD>Rs>Ta。(5)应用两种理论模型对林木冠层气孔导度和冠层蒸腾进行模拟和验证,建立了模型参数。方法一利用茎流计实测数据回算冠层气孔导度,根据Jarvis-type模型进行参数率定后模拟实测冠层气孔导度进而利用Penman-Monteith方程模拟侧柏、油松和白榆的冠层蒸腾,分别可以解释85%(侧柏)、90%(油松)、80%(白榆)的变量,其全天的整体相对误差分别为3.12%,4.42%和5.81%,取得了较好的结果。这比使用Li-1600稳态气孔计计算叶片气孔阻力之后进行尺度扩展进而模拟蒸腾的日变化过程具有更高的精度。而另外一种基于Jarvis-Stewart阶乘模型的半经验公式即直接利用基于环境变量的阶乘方程模拟冠层蒸腾从而避免了先通过回算Penman-Monteith方程得出冠层气孔导度这一过程,从结果看该方法同样表现出很好的拟合效果,但从理论角度分析,该方法忽略了湍流交换和能量平衡法则,计算所产生的误差不可估。(6)预测不同树种生长发育期的实际耗水量,研究实际蒸散量和潜在蒸散量,并对试验地降水资源的环境容量进行了分析。应用模型分析黄土半干旱区2009年生长季侧柏、油松与白榆的林木蒸腾耗水量分别为：侧柏156.95 mm,油松171.72 mm,白榆238.91 mm；林地实际蒸散量分别为侧柏林440.10 mm,油松林463.08 mm,白榆林527.92 mm；根据降水资源环境容量理论和水量平衡原理,计算得出降水资源环境容量分别为：坡面拍光处理集水造林,17年生侧柏林分的林木集水面积不小于3 m2,林分理论密度不大于3236株hm-2,白榆林分的林木集水面积不小于7 m2,林分理论密度不大于1382株hm-2；自然坡集水造林,油松林分的林木集水面积不小于6 m2,林分密度不大于1689株hm-2。更多还原

【Abstract】 Estimating plant water use is an important step in assessing the effects of increasing vegetation cultivation on the hydrological cycle especially in the semi-arid Loess Plateau of China. In this study, water movement monitoring in Soil-Plant and Plant-Atmosphere system combined with sap flow techniques provided a low-cost option to study the canopy physiological transpiration of main tree species-Platycladus orientalis, Pinus tabulaeformis, Ulmus pumila and Robinia pseudoacacia response to environmental factors on a continuous basis. This research was conducted atTuqiaogou watershed of Fangshan County in Shanxi province. With the guidance of SPAC theory, we analyzed the dynamic changes of precipitation resource in plot, the soil water in forest land, the physiological moisture characteristics of different trees and the content of undergrowth. After modeling the water transpired by tree canopy, we studied the stand evaportranspiration and water requirements of different trees, consequently the relationship between water consumption and forest density was concluded based on water balance theory. These studies could provide the scientific bases for assessment of water environment capacity and the potentiality of forest constructions in semi-arid region.The major findings and conclusions are as follows:(1) Dynamic analysis of precipitation in study site. The average annual precipitation (1945～2009) in study site is 503 mm, large amplitude between more and less yearly precipitation. Above 70% of precipitation concentrated in midsummer. Inter-annual variability of precipitation reached 20.01% and 23.86% in growth season.(2) Analysis of soil water under different forest land and characteristics of undergrowth diversity. As the planting density increase, the average height, DBH and canopy area will be decreased. A number of trees in Ulmus pumila has been a serious phenomenon of dieback, reflecting that dense forests consumes more water, with the result that catchment yield may decline and even soil desiccation occurred.(3) Analysis of the physiological moisture characteristics in different trees, such as leaf water potential, the wither index, soil water depleted index etc. Physiological characteristics of main tree species in Fangshan were discussed. The results show that the mechanisms of leaf water potential response to environmental variables are different, Platycladus orientalis survivals much longer time than others. The wither index reflected as follow:Ulmus pumila (4.58%)> Pinus tabulaeformis (4.25%)> Platycladus orientalis (4.08%); Soil water use efficiency ranked from high to low as Platycladus orientalis (80.57%)> Pinus tabulaeformis (79.76%)> Ulmus pumila (78.19%).(4) Analysis of the sap flow characters and canopy conductance & transpiration in main tree species.Canopy transpiration (Ec) calculated from sap flow monitoring of TDP technology, the results show that solar radiation (Rs) and vapor pressure deficit (VPD) is the dominant environmental factors for Ec. The dimensionless decoupling coefficient (Ω) showed transpiration of main tree species in this trial was strongly controlled by stomatal conductance, and the canopy was highly coupled to the atmosphere. Canopy conductance (gc) variation was to be strongly related to atmosphere vapor pressure deficit, solar radiation and weakly to air temperature.(5) Model established for predicting the canopy conductance and (or) canopy transpiration with two different methods. The first method was of sap flow based transpiration measurements to parameterize the Jarivis-type model of canopy conductance, and simulate the canopy transpiration using the Penman-Monteith equation. Cross validation shows that this model provided good predictions of canopy conductance and transpiration for Platycladus orientalis, Pinus tabulaeformis and Ulmus pumila, in which 85%,90%, and 80% of the variability was explained respectively. The average relative error of this modeled was found to be less than the traditional porometer method.Another method based on Jarvis-Stewart model express Ec as a function of its driving environmental variables, directly estimate the Ec rather than canopy conductance, was found suitable for predicting the canopy transpiration to variation in vapour pressure deficit, solar radiation and air temperature. However, these functional forms ignored law of turbulent exchange and energy balance, the resulting error was not correctly predicted.(6) Assessment of actual tree water consumption within growing season and analysis of actual & potential evaportranspiration to estimate water environment capacity in plot. The canopy transpiration of Platycladus orientalis, Pinus tabulaeformis, Ulmus pumila were separately 156.95 mm,171.72 mm and 238.91 mm during the growing season. Actually, evaportranspiration were separately 440.10 mm, 463.08 mm and 527.92 mm. And under the theory of water balance, water environment capacity were calculated as follow:the suitable stand density volume of Platycladus orientalis and Ulmus pumila on tamped slope should be less than 3236 plant hm-2 and 1382 plant hm-2 separately (the rational catchment area should be more than 3 m2 and 7 m-2every tree). The reasonable stand density volume of Pinus tabulaeformis on natural slope should be less than 1689 plant hm-2 with the rational catchment area should be more than 6 m2.更多还原