【作者】 吴瑞菊；

【导师】 王百田；

【作者基本信息】 北京林业大学 ， 生态环境工程， 2007， 硕士

【摘要】 2006年7月在山西方山,采用4年生盆栽苗木,设置4个水分梯度,应用Li-6200便携式光合测定系统和Wescor Psypro露点水势仪,对该区5种主要造林树种(臭椿、新疆杨、沙枣、白榆、核桃)叶片气体交换参数和叶水势进行了定时定位观测。研究了苗木净光合速率(Pn)、蒸腾速率(Tr)及叶水势(Wp)的日进程及其与土壤含水量(swc)之间的动态关系。分别确定了对Pn、Tr最有效的swc,无效的swc和保证Pn、Tr高水平的swc阈。通过综合分析气孔导度(Cs)、羧化效率(CE)、气孔限制值(Ls)、细胞间C02浓度(Ci)4个指标随土壤水分的变化来判断苗木Pn从气孔限制转向非气孔限制的swc临界值。在叶片瞬时水分利用效率(wue)和叶片日平均水分利用效率(WUE)两个水平上研究苗木在不同水分条件下对水资源的有效利用状况,进而选取既能保证高的同化能力,又能保证高效水分利用的swc区间作为适宜苗木生长的土壤水分范围。结论主要有:苗木光合、蒸腾对土壤水分的响应各树种苗木Pn和Tr与swc间关系密切,其关系均可用通式y=ax3+bx2+cx拟合(沙枣Tr-swc为对数关系)。其中y表示Pn或Tr,x表示swc,a、b、c为拟合系数。令dy/dx=0,分别得出各树种Pn或Tr最高时所对应的swc,即对Pn、Tr最有效的swc。将此土壤水分士2的范围作为Pn、Tr保持高水平的土壤水分阈。各树种Tr高水平土壤水分阈普遍高于其Pn高水平土壤水分阈,此高出部分的起点土壤水分,即Pn高水平土壤水分阈的上限,为各树种开始奢侈蒸腾的土壤水分临界值。令通式y=0,计算得出Pn、Tr为0时对对应的土壤水分临界值。苗木Pn下降的气孔和非气孔因素5个树种Pn下降的主要因子由气孔因素非气孔因素的土壤水分临界值都介于8%-10%之间。可见, (8-10)%是影响苗木生长的关键水分段,此时,苗木叶片气体交换对swc的变化非常敏感,Cs、CE普遍开始由缓慢下降转变为迅速下降,Ls开始减小,Ci迅速增大,苗木叶片光合机构开始受到伤害,叶肉细胞的同化能力开始受到影响。苗木Cs-swc,CE-swc关系探讨各苗木Cs与swc间关系密切。其中臭椿、新疆杨和白榆Cs-swc关系为二次曲线形式,表现了高水分下Cs受抑制的现象,而沙枣、核桃Cs随Swc的增加分别直线和以指数形式增加。各苗木CE-swc关系可用通式y=ax2+bx+c表示。苗木叶片日平均水分利用效率(WUE) WUE采用Pn日进程曲线与坐标轴围成的图形面积与Tr日进程曲线与坐标轴围成的图形面积之比来计算。苗木总平均WUE的计算,采用其4个水分梯度下Pn日进程曲线与坐标轴围成的图形像素之和与4水分梯度下Tr日进程曲线与坐标轴围成的图形像素之和的比来表示,是苗木多日内全天平均水分利用状况的综合表现。5个树种以WUE总平均排序为,新疆杨>臭椿>沙枣>白榆>核桃。其中新疆杨对水分的综合利用效率是核桃的2倍,白榆的1.75倍。苗木叶片瞬时水分利用效率(wue)随土壤水分变化规律臭椿、新疆杨、沙枣、白榆wue随swc变化的总趋势可用三次四项式模拟,其通式为:y=ax3+bx2+cx+c。核桃wue随swc的变化呈“S”型曲线。保持wue高水平的swc阈从高至低依次为:沙枣>白榆>新疆杨>核桃>臭椿。可见,核桃和臭椿能在低的swc下维持相对较高的wue。Wp-swc关系核桃Wp与swc相关性微弱,难以进行关系拟合。其余4树种Wp-swc关系可用二次或三次多项式拟合。4树种Wp随着水分胁迫的加剧而升高,表现了高水势延迟脱水的耐旱特性。苗木生长适宜的土壤水分及其凋萎的土壤湿度5种苗木生长的适宜水分阈由高到低分别为:沙枣(14.71-16.37)%>核桃(13.50-15.50)%>新疆杨(1 1.00-13.58)%>白榆(10.41-12.86)%>臭椿(10.29-12.37)%。可见,经济林类树种,沙枣和核桃对土壤水分要求高,臭椿和白榆在较干旱土壤条件下生长良好。以苗木凋萎湿度为标准,对苗木的抗旱性排序为:白榆>沙枣>臭椿>核桃>新疆杨。更多还原

【Abstract】 Fixed-position and fixed-time observations of 5 main afforestation species leaf gas change were made under natural condition, at 4 water levels, by using potted 4-year-old saplings, Li-6200 portable photosynthesis system and Wescor Psypro water potential, etc. in the semi-arid area of the Loess Plateau, Jul., 2006. Diurnal courses of physi-ecological parameters such as net photosynthetic rate （Pn）, transpiration rate （Tr）, leaf water potential （Wp） and their dynamic relations with soil water content （swc） were explored. The soil water thresholds on which Pn or Tr peaks or diminishes to zero and those certain swc ranges within which Pn or Tr maintains high levels were identified. The water threshold at which the dominant cause of restricted Pn changed from stomatal to non-stomatal limitations was detected by a combination analysis of the relations between swc and leaf stomatal conductance （Cs）, carboxylation efficiency （CE）, limiting value of stomata （Ls）, intercelluar CO₂ concentration （Ci）. Water use under different water conditions was studied both by instantaneous water use efficiency （wue） and by daily average water use efficiency （WUE）. Swc ranges where both assimilative capacity and water use efficiency can be maintained at high levels were chosen as the most suitable soil moisture range for sapling growth. The Wp values of the saplings undergone severe water deficit were revealed. The main conclusions drawn are as follows: The response of Pn, Tr to soil moisturePn and Tr of each species shows close relations with swc, which fit to the general equation, y= ax³+bx²+cx （Tr-swc relation of Elaegnus angustifolia is logarithmic）. Where, y denotes Pn or Tr; x denotes swc; a, b, c are fitting coefficients. Make dy/dx=0, the swc value, at which Pn or Tr peaks, also the swc which has the most efficiency on Pn or Tr, can be calculated. A ±2 neighborhood of this swc is considered as the swc range which maintains high Pn or Tr. Each species has higher Tr soil water range than its Pn soil water range. The starting point of this higher part, that is, the upper limit of Pn soil water range is the water threshold from which luxurious transpiration begins. Make y=0 to calculate the soil water threshold at which Pn, Tr becomes zero. Stomatal and non-stomatal factors restricting PnFor 5 studied species, the soil water threshold at which the dominant cause of restricted Pn changes from stomatal to non-stomatal limitations ranges between 8 and 10. This shows that 8-10 swc range is vital to sapling growth. Sapling leaf gas exchange is sensitive to a swc change within this range, where Cs, CE declination generally begins to accelerate, Ls starts to decrease while Ci soars, and damage occurs to the photosynthetic mechanism, mesophyll assimilative capacity is thus affected. Cs-swc, CE-swc explorationClose relation was found between Cs and swc of each species. Cs-swc relations of Ailanthus altissima,Populus bolleana and Ulmus pumila fit into quadratic curves, showing restrained Cs in high swc whileto Elaegnus angustifolia and Juglans regia, Cs continue increasing with higher swc. The relations couldbe expressed respectively by an exponential and a linear equation.Daily average leaf water use efficiency （WUE）WUE was calculated as the ratio of the irregular figure area enclosed by Pn diurnal course curve andcoordinate axes to that of the Tr diurnal course curve. Total average WUE was the sum area ratio of 4irregular figures formed by Pn or by Tr curves. It describes the integrated water use status of eachspecies under various water conditions during the observational days. According to the total averagevalues, the species could be queued as Populus bolleana > Ailanthus altissima > Elaegnus angustifolia> Ulmus pumila >Juglans regia. Total average WUE of Populus bolleana is 2 times as much as that ofJuglans regia and 1.5 times as of Ulmus pumila.The law of leaf water use efficiency change with soil moistureThe overall changing trend of Juglans regia wue to swc takes the shape of "S", while that of the other 4species can be expressed by a general equation, y = ax³ + bx² + ex + c. According to swc ranges withinwhich high wue is maintained, the order is Elaegnus angustifolia > Ulmus pumila > Populus bolleana >Juglans regia > Ailanthus altissima. This reveals that Juglans regia and Ailanthus altissima canmaintain comparatively higher level of wue under comparatively low swc.Wp-swc relationsNo proper equation fitted the Wp-swc relation of Juglans regia due to poor correlation. Wp-swcrelations of the other 4 species can be described by quadratic curves or cubic equations. Wp of these 4species raise as soil water deficit gets more and more severe, revealing a drought tolerance characteristicvia maintaining high Wp.Suitable soil moisture range for sapling growth and the wilting moistureThe suitable soil moisture ranges for subject saplings growth were found as: Juglans regia （15-17） >Elaegnus angustifolia （14.58-16.37） > Populus bolleana （13.58-15.5） > Ulmus pumila （11.86-14.41） >Ailanthus altissima （10.29-13.37）. This reveals that species of economic value, like Elaegnusangustifolia and Juglans regia have high demand on soil moisture, while Ailanthus altissima and Ulmuspumila grow well in slightly dry conditions. Cite permanent wilting moisture as the standard to appraisesaplings drought resistance ability, the order is: Ulmus pumila > Elaegnus angustifolia > Ailanthusaltissima > Juglans regia > Populus bolleana.更多还原