【作者】 萨如拉；

【导师】 张秋良；

【作者基本信息】 内蒙古农业大学 ， 森林培育， 2010， 博士

【摘要】 额济纳绿洲是我国西北荒漠地带的重要生态屏障,胡杨(Populus euphratica)是支撑额济纳绿洲的建群乔木树种,在额济纳绿洲主要制约胡杨生存发展的因素就是“水”。本文针对胡杨的水分生理特征和胡杨林SPAC系统的水分循环机理进行了分析研究,希望通过揭示此机理能够为保护和恢复额济纳绿洲生态环境找到有效的方法并提供科学依据。主要结果如下:(1)额济纳天然胡杨的胸径、树高、材积等总生长进程可划分为3个阶段,即慢—快—慢,速生期在6–15年,速生点在第6年。胡杨胸径最优生长模型是吉田正男方程;树高最优生长模型方程是柯列尔方程;材积最优生长模型方程是混合型、其次为修正Weibull方程。根据标准样地调查结果将额济纳天然胡杨林划分为四种典型林型:即河漫滩地胡杨成过熟林、柽柳(Tamarix ramosissima)胡杨青壮林、沙枣(Elaeag nusangastifolia)柽柳胡杨幼林、荒漠化胡杨疏林。(2)对胡杨根系调查的结果是:胡杨根系的88.88%分布在40～100cm的土层中,距树干越近,根系分布越多,根系分布随距离的增加而减少;根系按不同直径级的总体分布特征是吸收根(d<2mm)约占总根长密度的92.21%,而输导根(d>2mm)仅占8.79%,这表明胡杨以庞大的吸收根系(d<2mm)从土壤中吸收生存所需要的水分,是胡杨抵御和适应极端干旱的一种表现。(3)天然胡杨林的单位叶面积指数比较高,为2.90m2/m2,因此光能利用效率较高。20年生的胡杨的总生物量为74.99t/hm2,年平均生产力为3.75t/hm2·a。(4)胡杨不同林型的土壤中沙粒含量普遍偏高,特别是粒径0.5～1.0㎜的粗沙含量大。在胡杨幼龄林深层土壤中含有粘粒。土壤含水率总的特点是:大约0～30㎝的表层有干沙层,土壤含水率几乎为零;在30～150㎝范围内,随土层深度的增加,土壤含水率逐渐增大,变化平缓,但在60～100cm深度内土壤含水率有明显的升高现象。各林型土壤含水率由高到低依次为河漫滩胡杨成过熟林>胡杨幼林>胡杨青壮林;土壤持水能力依次为河漫滩胡杨成过熟林>戈壁>胡杨青壮林;判断额济纳绿洲胡杨生长所利用的土壤有效含水率范围为1.18%～20.05%;测得的水饱和土壤的水压传导率Kfs的数值表明,当地土壤的入渗能力相当强。(5)胡杨光合、蒸腾速率日变化曲线可分为两类,即单峰型和双峰型,双峰型中出现了“午休”现象;不同年龄胡杨光合速率和水分利用效率季节变化均为7月>5月>9月;胡杨叶水势日变化规律是,黎明前后水势值最高,随着光照、气温的升高,空气相对湿度下降,叶水势开始下降,黎明时的水势由大到小为幼树>中树>老树,说明老树吸水能力最强,幼树最差;在生长季晴天,胡杨树干液流速率日变化呈单峰型曲线,不同径级胡杨不同季节变化规律是,大径级(60cm)和中径级(28cm)胡杨液流速率均5月>8月,而小径级(15cm)的8月>5月;对影响净光合速率(Pn)和蒸腾速率(E)和树干液流的主要因素气温(Ta)、叶温(Tl)、空气相对湿度(RH)、光合有效辐射(PAR)、气孔导度(Gs)、细胞间CO2浓度(Ci)、叶室水汽压亏缺(VPDL)、风速(WS)等进行多元线性回归分析后的结果是,与Pn的相关系数由大到小的顺序为PAR、Tl、RH、Ci、Ta、Gs。与E的相关系数由大到小的顺序为Gs、PAR、Tl、RH、Ta、VPDL。与树干液流的相关系数由大到小的顺序为E、PAR、WS、Tl、Pn、RH、Ci、Ta、Gs。(6)选择了适合的计算方法计算得出额济纳绿洲总的年用水量为3.1456亿m(3包括生产、生活、生态用水),计算得出绿洲可用水量为4.4155亿m3,所以,目前绿洲生态环境和生产生活用水基本能够得到满足。因此,每年黑河水来水量必须保证在3.2亿m3以上才可以确保绿洲生态不恶化,不会向着逆向进行演替。(7)土壤-胡杨-大气(SPAC系统)水势梯度在不同年龄胡杨中分别是土壤:老树:大气为1:94:2757;土壤:中树:大气为1:171:2757;土壤:小树:大气为1:140:2757。中龄胡杨的水势梯度最大,其次是小树,最小的是老树。说明中龄胡杨吸收水分最积极,能力也最强;幼龄胡杨虽然还比较幼嫩,但仍需要很多水分供给;老龄胡杨已经趋于衰退,新陈代谢慢,因此吸收水分的动力不足。更多还原

【Abstract】 Ejina Oasis is an important ecological shelter for the desert zone in Northwest China, Populus euphratica is the dominant tree species of supporting Ejina Oasis, while "water" is the major restraining factor for survival and development of Populus euphratica in Ejina Oasis. In this paper, water physiological characteristics and water circulation mechanism of SPAC system of Populus euphratica were analyzed. We hope to find effective ways and provide scientific basis for the protection and restoration of ecological environment of Ejina Oasis through revealing this mechanism. The main results are as follows:(1) The total growth process of DBH, height and volumn of natural Populus euphratica in Ejina can be divided into three stages,namely slow - fast - slow,fast-growing period is from the 6th to15th years,fast-growing piont is in the sixth year. The optimal DBH growth model of Populus euphratica is Masao Yoshida equation; the optimal height growth model is Rолясрequation; the optimal volumn growth model is mixed equation, the second best model is Weibull equation. According to the survey results of standard plot, the natural Populus euphratica forest in Ejina could be divided into four typical forest types: namely the flood plain mature and over-mature stand of Populus euphratica, young and strong stand of Tamarix ramosissima and Populus euphratica, young stand of Elaeag nusangastifolia,Tamarix ramosissima and Populus euphratica, desertificated open forest of Populus euphratica.(2) The findings for the root system of Populus euphratica are: 88.88% of the root system of Populus euphratica distributes in the soil layers of 40～100cm, the more the soil layers close to the trunk, the more roots distribute. Root distribution amount reduces along with the increase of the distance from the trunk; the overall distribution characteristic of the roots with different level of diameter is that assimilating roots(d<2mm)approximately take up 92.21% of the total root length density, and transporting roots(d>2mm)only take up 8.79%, which indicates that Populus euphratica absorb necessary water for survival using the huge assimilating root system(d<2mm)from the soil, it is a kind of resisting and adapting performance of Populus euphratica to extreme drought.(3) The unit leaf area index of natural Populus euphratica is quite high, which can be 2.90m2/m2, therefore, the energy utilization efficiency is relatively high. The total biomass of 20 years old Populus euphratica is 74.99t/hm2, its annual mean productivity could be 3.75t/hm2·a. (4) The soil sand grain contents of different forest types of Populus euphratica are generally on the high side, especially the content of coarse sand with 0.5 ~ 1.0 mm grain diameter is large. The deep soil in young forest of Populus euphratica contains clay particles. The general characteristics of soil moisture content is: the surface soil of 0~30 cm has dry sand bed, the soil moisture content is almost zero; in the range of 30~150 cm, the soil moisture content gradually increases, while varied gently along with the increase of soil depth, however, the phenomenon of obviously rise in the depth of 60~100cm could be observed. The soil moisture contents of various forest types, in the order from high to low, are: flood plain mature and over-mature forest of Populus euphratica > young stand of Populus euphratica > young and strong forest of Populus euphratica; the order of the water holding capacities of the soils are: flood plain mature and over-mature forest of Populus euphratica > Gobi> young and strong forest of Populus euphratica; the scope of effective soil moisture content for judging the growth of Populus euphratic in Ejina Oasis is between 1.18%～20.05%; the measured numerical value of hydrolic pressure conductivity Kfs of water saturated soil shows that the infiltration capacity of the local soil is quite strong.(5) The diurnal variation curves of photosynthetic rate and evaporation rate for Populus euphratic can be divided into two types, namely the single-peak type and the double-peak type, and midday depression phenomenon emerged in the double-peak type; The seasonal variations of photosynthetic rate and water utilization efficiency for Populus euphratic with different ages are both in the orders of July> May> September; The diurnal variation law of the leaf water potential for Populus euphratic is that the highest water potential value emerged at the approximate time of the dawn, it began to decrease along with the rising of light intensity and air temperature and the declining of relative air humidity, the order of the leaf water potential at the daybreak time was young trees>middle age trees>old trees, which indicates that the water absorbing capacity of the old trees is the strongest, that of the young trees is the weakest; The diurnal variations of sap flow velocity for the tree trunks of Populus euphratic appears to be a single-peak curve in the sunny days of the growing season, seasonal variation laws of sap flow velocity for Populus euphratic with different diameter levels are as follows: that of Populus euphratic with large (60cm) and middle (28cm) diameter levels are both in the order of May>August, that of Populus euphratic with small diameter level is in the order of August > May; A multivariate linear regression analysis was carried out for the major influencing factors of net photosynthetic rate (Pn), evaporation rate (E) and sap flow of the tree trunks, including air temperature (Ta), leaf temperature (Tl), relative air humidity (RH), photosynthetic active radiation (PAR), stomatal conductance (Gs), intercellular CO2 concentration (Ci), vapor pressure deficit of leaf (VPDL) and wind speed (WS), the result shows that the correlation coefficients between Pn, in the order from large to small, are PAR, Tl, RH, Ci, Ta, Gs; the correlation coefficients between E, in the order from large to small, are Gs, PAR, Tl, RH, Ta, VPDL; the correlation coefficients between the sap flow of the tree trunks, in the order from large to small, are E, PAR, WS, Tl, Pn, RH, Ci, Ta, Gs.(6) Through selecting a suitable calculating method, a conclusion was made that the total water consumption of Ejina Oasis was 314.56 million m3, which includes water consumption for production, survival and ecological purposes, the water availability of the Oasis was 441.55 million m3, therefore, the water for ecological, production and survival purposes of the Oasis could basically be satisfied at present. The annual water inflow of Heihe River has to be guaranteed over than 320 million m3, in that case, the ecological environment would not get worse and adverse succession could be prevented.(7) The water potential gradients of Soil-Populus euphratic-Atmosphere (SPAC system) in Populus euphratic with different ages are, respectively, in the system of soil-old tree-atmosphere, 1:94:2757; in that of soil-middle aged tree-atmosphere, 1:171:2757; in that of soil-young tree–atmosphere, 1:140:2757. The water potential gradient of the middle aged Populus euphratic is the maximum, the second is that of the young trees, the smallest is that of the old trees, which indicates that the middle aged Populus euphratic is the most active for absorbing water, and its absorbing capacity is the strongest; the young aged Populus euphratic, though relatively tender, still needs a lot of water supply; the old aged Populus euphratic, with slow metabolism, is tending towards recession, therefore, the power of absorbing water is inadequate.更多还原