【作者】 张婕；

【导师】 张志强；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2019， 硕士

【摘要】 杨树作为北方常用的人工造林树种之一,在用材林、生态林和景观林造林中被广泛应用,关于其蒸腾耗水问题也备受关注。本文以北京市顺义共青林场杨树为研究对象,利用TDP热探针法和带状径向生长仪对生长季杨树树干液流和树干径向变化进行连续测定,分析了不同天气状况、时间尺度树干日间和夜间液流速率特征以及和环境因子的相关关系,研究了树干径向变化特征及与气象、土壤水分等环境因子的关系,结果表明:(1)小胸径的样树对于周围环境变化响应更快速。典型晴天不同胸径杨树日变化基本为单峰曲线,液流峰值为0.0067g/Crm12.s,晴天的液流峰值约为阴天的1.3倍。典型雨天,各胸径的样树的树干液流日变化规律不太明显,但夜间液流较为活跃。(2)杨树生长季存在明显夜间液流,且夜间液流前半夜较后半夜明显活跃。各月夜间累积液流量占整日累积液流量的比例为5月>9月>6月>7月>8月,其中5月最高达8.5%,其次是9月份为8.4%,平均贡献率为7.2%,生长季初期和末期夜间液流占整日蒸腾的比例要大于生长季中期。(3)在一定范围内,胸径树高冠幅越大的样木,夜间液流通量越大。降雨较少的月份夜间液流与环境因子的相关性较高,此时夜间液流一部分用于补水一部分用于蒸腾,而在降雨量较大的月份夜间液流更多的是用于夜间补水,补水量取决于土壤含水率决定的所需的补水能力和日蒸腾强度造成的树体水分亏缺程度。夜间蒸腾显著存在于前半夜。(4)气象因子对树干液流的影响为太阳辐射>饱和水汽压差>空气温度>空气相对湿度>风速,太阳辐射对树干液流的直接作用最大,饱和水汽压差对液流速率的间接作用最大。在一定的范围内,林分日蒸腾量随着太阳辐射的增加而增加,但土壤含水量较低的情况下,林分蒸腾保持在较低的水平。在一定范围内,随着饱和水汽压差的增大,林分蒸腾量也变大,当饱和水汽压差超过一定值时,林分蒸腾反而受到抑制。(5)杨树茎干生长表现出明显的日变化,主要分为收缩期、膨胀期和生长阶段。杨树茎干在生长季表现出曲折增长的特点。样木的日间收缩量从5月到11月份先增加后减少,最大值在6月份为272.24μm。日均膨胀量在生长季初期到末期逐渐减小,树干的夜间膨胀量在生长季初期为159.43～203.47μm,夜间膨胀量在生长季末期为30.09～36.79μm,小胸径的树木比大胸径样树树干径向变化幅度更大。(6)杨树树干径向日间收缩量与与太阳辐射强度、饱和水汽压差、日间平均气温、最高气温为显著正相关,与空气相对湿度和土壤含水量呈显著负相关,树干日间的径向收缩取决于树木蒸腾耗水引起的失水量的大小。树干径向夜间膨胀量与夜间的平均温度、最低温度、最高温度、饱和水汽压差、降雨量、夜间液流通量为正相关,而与夜间空气相对湿度呈负相关,夜间液流通量一定程度上可以解释树干夜间膨胀量的变化。树干直径累积生长过程和幂函数y=axb的拟合结果最好,通过运用主成分分析和偏相关分析,表明日最低温度、太阳辐射和饱和水汽压差是影响树干径向生长的主要气象因子,并建立了线性回归模型。更多还原

【Abstract】 As one of the commonly used afforestation tree species in the north,Populus euramericana is widely used in timber forests,ecological forests and landscape forests.It is also concerned about its transpira?tion and water consumption.In this paper,the poplar tree in Shunyi Gonglin Forest Farm of Beijing was taken as the research object.The TDP thermal probe method and the strip radial growth instrument were used to continuously measure the sap flow and trunk radial variation of poplar trees in the growing sea-son,and analyzed different weather conditions.The relationship between daytime and nighttime flow rate characteristics of time-scale trunks and their relationship with environmental factors,the relation-ship between radial variation of trunks and environmental factors such as meteorology and soil moisture was studied.The results show that:(1)The small breast diameter sample tree responds more quickly to changes in the surrounding environment.On a typical sunny day,the daily variation of poplars with dif-ferent breast diameter is basically a single-peak curve.The peak value of the sap flow is 0.0067g/cm2· s,and the peak value of the sap flow on sunny days is about 1.3 times that of the cloudy day.On a typical rainy day,the daily variation of the sap flow of different breast diameter sample trees are not obvious,but the sap flow at night is more active.(2)There was obvious nighttime sap flow during the growing season of poplar,and it was significantly active in the middle of the night before midnight.The ratio of nighttime sap flow to total transpiration is May>September>June>July>August,with May reaching a maximum of 8.5%,followed by September at 8.4%,and the average contribution rate is 7.2%,the pro-portion of nighttime transpiration in the early and late growth seasons is greater than that in the middle of the growing season.(3)Within a certain range,the larger the crown of the breast diameter tree,the greater sap flow rate at night.At night,there is a high correlation between the sap flow and the envi-ronmental factors in the month when the rainfall is less.At this time,part of the night flow is used for hydration for a part of transpiration,while in the month of heavy rainfall,the sap flow is more for stem water recharge.The amount of water recharge depends on the required water replenishment capacity determined by the soil moisture content and the degree of tree water deficit caused by the daily transpi-ration intensity.Nighttime transpiration existed in the first half of the night.(4)The influence of mete?orological factors on sap flow is solar radiation>saturated water vapor pressure deficit>air tempera-ture>air relative humidity>wind speed,solar radiation has the direct effect on sap flow,and saturated water vapor pressure difference has the greatest indirect effect on sap flow rate.Within a certain range,the daily transpiration of the stand increases with the increase of solar radiation,but in the case of low soil water content,the stand transpiration remains at a lower level of saturated water vapor pressure dif-ference for transpiration activities.Within a certain range,with the increase of saturated water vapor pressure difference,the transpiration of stand stands also increases.When the saturated water vapor pressure difference exceeds a certain value,t:he stand transpiration is inhibited.(5)The stem growth of poplar showed obvious diurnal changes,which were mainly divided into systolic,expansion and growth stages.Poplar stems exhibit a tortuous growth during the growing season.The amount of daytime con-traction of the wood increased from May to November,and the maximum value is 272.24μm.The av-erage daily expansion decreased gradually from the early to the end of the growing season.The nighttime expansion of the trunk was 159.43～203.47μm at the beginning of the growing season,and the nighttime expansion was 30.09～36.79μm at the end of the growing season.The diameter of the small breast diameter tree was larger than that of the large breast diameter tree.(6)The radial diurnal contrac-tion of poplar trunks was significantly positively correlated with solar radiation intensity,saturated wa-ter vapor pressure difference,daily average temperature and maximum temperature,and negatively correlated with air relative humidity and soil water content.The radial contraction between the two de-pends on the amount of water loss caused by the transpiration of the trees.The radial nighttime expan-sion of the trunk is positively correlated with the nighttime average temperature,the lowest temperature,the highest temperature,the saturated water vapor pressure difference,the rainfall,and the nighttime liquid flux,but negatively correlated with the nighttime relative humidity,and the nighttime liquid flux is a certain degree.It can explain the change in the amount of radial expansion of the trunk.The cumu-lative growth process of trunk diameter and the power function y= axd have the best fitting results.Prin-cipal component analysis and partial correlation analysis show that the daily minimum temperature,solar radiation and saturated vapor pressure difference are the main meteorological factors affecting the radial growth of the trunk.A linear regression model was established.更多还原