丘陵赤红壤蒸散量的变化特征及计算模型

分析了南亚热带丘陵赤红壤区蒸散量的动态变化特征．结果表明,蒸散量存在年际变化和显著的季节性变化,月蒸散量最大值是最小值的10．80-15．41倍,湿季期(3-9月),蒸散量约占年蒸散总量的77％,旱季期(10月一次年2月),蒸散量约占年蒸散总量的23％．揭示了南亚热带丘陵赤红壤区年降雨总量、3-9月的降雨量足以满足蒸散的需求,而10月一次年2月的降雨量不足以满足蒸散的需求,蒸散将消耗土壤水库贮水的规律．以修正的彭曼公式为基础,建立了南亚热带丘陵赤红壤区蒸散量的计算模型．通过试验实测值与模型计算值的比较,证明计算模型的可靠性程度是非常满意的.     

晋西北小叶杨林水分生态的研究

１９９３年生长季（５～１０月）小叶杨的平均蒸腾强度为０．０７６８ｇ·ｇ－１·ｈ－１。蒸腾强度日进程呈现早、晚低,中午高的单峰曲线。并与光照、气温和用对湿度间均具有二次抛物线关系。蒸腾强度季节变化与土壤含水量、光照、气温和相对湿度间的关系则均不明显。小叶杨在生长季的蒸腾耗水量为４０．７ｍｍ,其林分总蒸散量为２９６．１ｍｍ,各占同期降水量２３４．８ｍｍ的１７．３％和１２６％。在生长季降水量仅为多年同期平均量５９．７％的情况下,林地土壤水分收支亏缺量达１０７．６ｍｍ。     

杉木人工林蒸散规律的研究及乱流扩散法应用的探讨

 本文根据乱流扩散法原理,利用实验集水区连续6年实测数据,对杉木人工林蒸散规律进行了探讨。结果表明：杉木人工林年平均蒸散量875.45mm,占年降雨量的82.2%。其中,林冠蒸散量781.77mm,林地93.68mm,分别为总蒸散量的89.3%和10.7%。与水量平衡法的结果比较,为水量平衡法的101.2%。在研究蒸散规律的同时,对乱流扩散法的应用及参数的估算也进行了较详细的分析。     

鼎湖山顶级森林生态系统水文要素时空规律

运用连续7a(1993～1999)的水文观测资料,对南亚热带顶级生态系统鼎湖山季风常绿阔叶林集水区水文要素时空规律进行分析,得到如下一些主要结论：(1)鼎湖山多年平均降水量为1910mm,湿季降水量占年降水量80％,干季仅占20％。6月份的降水量最大,1月份最小。(2)季风常绿阔叶林冠层截留率为31．8％,湿季的截留量占全年截留量的66．7％,截留量最大值和最小值所在的月份分别为7和1月份。各月的截留率差异很大,截留量大的月份,截留率较低;截留量小的月份,截留率较高。(3)季风常绿阔叶林集水区多年平均总径流量953．0mm,总径流系数49．9％,其中地表径流量为252．3mm,地表径流系数13．2％;地表径流与降水量之间存在二次抛物线型回归关系,与降水强度的关系不大,这说明季风常绿阔叶林的产流形式是是蓄满产流。(4)季风常绿阔叶林多年平均蒸散948．2mm,占同期降水量的49．7％;蒸散力1031．4mm,年蒸散系数为0．92,蒸散月变化规律较降水量的月变化规律有所滞后。(5)系统贮水量的月变化很大,2～8月份,系统处于蓄水阶段;9月份至翌年1月份,系统处于失水阶段。蓄水和失水的最大值分别出现在湿季和干季的第一个月,即4月份和10月份。(6)集水区多年平均水量总输入2129．9mm,实际输入1910mm(降水量),其中219．9mm的水量输入是由系统贮水量变化而产生。支出的总水量2129．9mm,实际支出1901．3mm(径流和蒸散量),其中228．6mm的水量支出是由系统贮水量变化引起的。     

黄土塬区麦田蒸散特征

利用大型称重式蒸渗仪研究了黄土塬区冬小麦不同时段单元（生育期、月、日、时）的蒸散特征,并分析了叶面积指数、土壤含水量和气温、降水等因子对蒸散的影响.结果表明,在试验年份,各生育期内冬小麦的日蒸散量:孕穗 抽穗期﹥开花期﹥起身期﹥拔节期﹥灌浆期﹥返青期﹥成熟期﹥越冬期;生长前期蒸散受温度影响较大,中期受叶面积指数影响较大,后期土壤水分成为蒸散的限制因子,灌浆期内冬小麦日均蒸散量因受土壤水分亏缺影响而显著下降,日均蒸散量从孕穗 抽穗期的625 mm·d^-1 减小到灌浆期的2.66 mm·d^-1;月蒸散以4～6月最高,3个月蒸散量占试验期间总蒸散量的80％以上;麦田逐日蒸散变化曲线上的波动峰值反映了受降水作用土壤水分状况改善条件下的蒸散特征;时蒸散过程在总体遵循周期性的前提下表现出随天气而改变的现象.     

奈曼地区灌溉麦田蒸散量及作物系数的确定

利用大型蒸渗仪测定了奈曼地区春小麦(Triticum aestivum L.)全生育期的蒸散量,并引用FAO Penman-Monteith等5种方法计算了相应时期的参考作物蒸散量,比较了FAO Penman-Monteith公式与其它4种方法间的关系,最后运用作物蒸散量和参考作物蒸散量计算了春小麦的作物系数．结果表明,春小麦苗期每周日平均蒸散量小于3mm·d^-1,随着叶面积系数增大,日平均蒸散量达到最大值6．49mm·d^-1(抽穗开花期),最终下降至1．94mm·d^-1(灌浆成熟期);根据试验年份的降雨分布情况,该地区的自然降水不能满足春小麦对水分需求,小麦苗期、拔节期和抽穗开花期水分亏缺比较严重,是田间水分管理的关键时期;与FAO Penman-Monteith公式的计算结果相比较,用Penman公式和FAO-24 Blaney-Criddle公式估算奈曼地区参考作物蒸散量误差较小;奈曼地区春小麦苗期、营养期、生殖期、成熟期4个生长阶段的作物系数分别为0．45、0．90、1．1l和0．52,其中成熟期的作物系数值与FAO-24给出的小麦作物系数值差异较大．     

古尔班通古特沙漠南缘梭梭(Haloxylon ammodendron)群落能量平衡及蒸散特征

梭梭是北方荒漠区重要的固沙植物,具有较强的荒漠环境适应能力。研究梭梭群落能量及蒸散变化对科学管理水资源、保护与建设生态植被等有重大意义。基于波文比自动观测系统在古尔班通古特沙漠南缘丘间地实时连续测定的2018年气象和能量数据,运用波文比-能量平衡法对梭梭群落能量平衡和蒸散特征进行了分析。结果表明:梭梭生长季(4—10月)太阳净辐射和土壤热通量的日变化呈单峰状分布,净辐射通量最高值出现在13:30左右,土壤热通量最大值出现时间比净辐射推迟2 h,波文比在梭梭生长旺盛期全天变化稳定,萌发期和枯落期白天变化较小,夜间波动较大,湍流通量以显热通量为主;在晴天和阴雨天条件下,梭梭生长旺盛期的日蒸散量均明显大于萌发期和枯落期,且日蒸散量在旺盛期呈双峰型,萌发期和枯落期呈单峰型;2018年梭梭生长季蒸散量为279.67 mm,日均蒸散强度1.31 mm/d,梭梭群落的蒸散受到气象、自身生长特性以及土壤水分的影响,4月蒸散强度开始逐渐增大,由于多阴雨天气导致6月的蒸散强度有所降低,7月达到最大,9—10月水分、温度等条件缺乏,梭梭生理活动微弱,蒸散强度急剧减小。     

辽河三角洲湿地生长季蒸散量时空格局及影响因素

蒸散是湿地系统水分损失的重要途径之一,有效量化湿地蒸散量并对其时空格局进行研究具有重要意义。本文以Landsat数据和气象观测数据为基础,利用SEBAL模型估算辽河三角洲湿地1985—2017年共8期植被生长季的蒸散量,并分析其时空格局和影响因素。结果表明:(1)反演得到的蒸散量平均相对误差为9.01%,估测值与实测值相关系数为0.61,基本满足湿地蒸散研究需求;(2)研究区多年日蒸散量均值和相对变化率整体呈双峰态势,极小值出现在2005年,极大值出现在1989年和2014年;(3)日蒸散量具有水陆交界处最低、西部较低、中东部和南部高的趋势,具有显著的空间分异特征;(4)不同土地利用/覆被类型的蒸散量大小依次为:水体区湿地植被区非湿地植被区非植被区(除水体外),多年不同土地利用/覆被类型的蒸散量变化也呈双峰态势,日总蒸散量变化与土地利用转型有关,土地利用/覆被是导致湿地蒸散时空分异的重要因素;(5)平均蒸散量与太阳辐射、气温、风速、相对湿度四个气象因子加权值显著相关,相关系数为0.69,两者年际波动趋势基本一致,蒸散量变化与气象条件变动联系密切。     

基于改进SW模型的千烟洲人工林蒸散组分拆分及其特征

蒸散组分拆分是准确评估陆地生态系统生产力以及估算水分利用效率的重要基础。利用改进后的Shuttleworth-Wallace模型,将蒸散拆分为植被蒸腾、土壤蒸发和冠层截留蒸发,并采用Monte Carlo随机参数化方案对模型参数进行优化。将模型与千烟洲亚热带人工针叶林站点的2011年涡度相关及小气候观测资料结合,对千烟洲人工林蒸散及其组分进行模拟。研究结果表明:半小时尺度上蒸散量模拟值与实测值的一致性在晴天和雨天都较高。半小时尺度上全年蒸散模拟值与实测值的决定系数、均方根误差和平均偏差为0.73、1.55 mmol m~(-2)s~(-1)和0.21 mmol m~(-2)s~(-1)。蒸散是该生态系统水分输出的最主要贡献项,占全年降水的80%。在蒸散中,植被蒸腾约占总蒸散量的85%,可推测2011年千烟洲人工林生态系统有较高的水分利用效率。该生态系统的蒸腾量季节变化明显,主要受饱和水汽压差和气温两种环境因素以及植被的叶面积指数影响且与三者均呈正相关;土壤蒸发约占总蒸散量的5%,季节变化平缓;模拟的冠层截留蒸发量约占总蒸散量的10%,季节变化大,与降水量呈正相关,与暴雨频次呈负相关,说明冠层无法有效截留强降水。该模型参数较少、时间分辨率高且可以有效模拟蒸散及其组分特征,是陆地生态系统水分循环过程研究有力的模型工具。     

宁夏六盘山人工林和天然林生长季的蒸散特征

为了系统地认识森林生态系统结构对蒸散特征的影响,2009年5-10月,应用热扩散技术和传统水文学方法,对六盘山香水河小流域华北落叶松人工林和华山松天然林的蒸散及分量进行对比研究.结果表明: 华北落叶松人工林生长季总蒸散量为518.2 mm,是同期降雨量的104.6%,远高于天然林蒸散量420.5 mm.两种林分总蒸散量在其垂直层次上的分配比例相近,表现为冠层蒸腾量>草本+土壤层蒸散量>灌木蒸腾量,但林分各组成分量占总蒸散量的比例明显不同.其中,人工林冠层月均截留量和蒸腾量为19.6和25.2 mm,分别是天然林的1.2和1.9倍;人工林灌木层月均蒸腾量为 4.4 mm,占天然林的23.4%;人工林草本+土壤层月均蒸散量为37.1 mm,是天然林的1.8倍.采用Penman-Monteith方程对林分的实测蒸散量进行对比检验,两种方法对林分蒸散量的估计值基本接近.
     

基于茎干直径微变化制定苹果灌溉制度

茎干直径的动态微变化是研究植物体水分和生长状况的重要指标。利用测树器监测西北旱区盛果期苹果树茎干直径微变化规律,根据监测记录获得茎干直径日最大值(MXTD)、茎干直径日最大收缩量(MDS)数据,并探讨茎干直径微变化规律及其对环境因素的响应,为茎干直径微变化用于指导精确灌溉提供科学依据。实验结果表明,晴天或多云天气下,苹果树茎干直径在每天的7:00或8:00时刻达到一天最大值,在16:00左右达到一天的最小值,茎干直径年增长量与果实产量成反比例关系。整个生育期MXTD呈先快速增加后平稳的变化特征。2010年MDS与茎干水势(φstem)呈显著负相关关系(r2=0.76***,n=14),这表明MDS可以反映苹果树的水势状况。生育后期的MDS对环境因素响应比生育前期敏感,全生育期MDS与气象因素的决定系数大小顺序为日最大水汽压差(VPDmax)日最高温度(Tmax)净辐射(Rn)。茎干直径微变化规律可以反映西北旱区盛果期果树的水分状况,可以为果园灌溉制度的确定提供科学依据。     

The effect of two growth forms of Norway spruce on stand development and radiation interception: a model analysis

Summary Development of tree and canopy structure, and interception of photosynthetically active radiation (PAR) were studied in two model stands of Norway spruce consisting of trees with rapid versus slow site capture. The tree models were derived using Burger's (1953) sample tree material, from which two subpopulations of dominant trees were selected using the rate of horizontal site capture of the tree crowns as the criterion of division. The development of stand structure and interception of PAR were simulated in the two model canopies. The simulation period covered the period from tree age 15–80 years. The average development of the trees in the two subpopulations proved to be very different. The rapidly expanding trees were characterized by low mean within-crown needle area density and a long crown. The slowly expanding trees were smaller but had a higher mean within-crown needle area density. Up to approximately 40 years of age the stand of rapidly expanding trees contained more leaf area and intercepted more radiation than the stand of slowly expanding trees, when canopy cover was held constant. After 40 years of age this relationship was reversed due to the subsequent decline of leaf area in the stand of rapidly expanding trees and the increase in leaf area in the stand of slowly expanding trees. The biological relevancy and silvicultural implications of the simulated patterns of tree and stand development are discussed.     

Variation in competition in eucalypt forests: the importance of standardization in pattern analysis

Abstract. Contrasting views have been put forward that competition intensity should either increase with community standing crop or remain constant. Testing these hypotheses with long-lived plants in natural communities is possible using pattern analysis, involving statistical summaries of the relationships between the total size and distance of nearest neighbors. This approach, however, may produce a spurious negative correlation between competition intensity and standing crop in cases where individual size increases with standing crop. A method for overcoming this problem using data standardization is illustrated using data from 15 stands in a variety of forest types (subalpine woodland, dry forest, warm wet forest, cool wet forest, and near-rainforest) in southeastern Australia. Standing crop, estimated from stand volume, and water availability, estimated from evapotranspiration, varied significantly among forest types. Total size and nearest neighbor distance was measured for 50 pairs of trees in three stands of each forest type. The sum of nearest neighbor sizes increased significantly with interneighbor distance in all forest types, indicating that competition contributed to pattern at all levels of standing crop. The slopes of the regression equations describing these relationships varied significantly among forest types and with evapotranspiration, suggesting that competition intensity varied. This result, however, was shown to be the product of a significant positive correlation between individual size and standing crop. Once this correlation was removed by using standardized measures of tree size, there was no evidence for variation in competition intensity among forest types or with evapotranspiration.     

Evapotranspiration measurements in Eriophorum vaginatum tussock tundra in Alaska

Evapotranspiration was measured periodically from late June through mid-August 1978 in Eriophorum vaginiatum tussock tundra near Eagle Creek, Alaska. The average evapotranspiration rates from tussock and intertussock areas were 0.8 mm d⁻¹ and 1.3 mm d⁻¹, respectively. Potential evaporation was calculated according to the Penman equation using microclimate data collected at the same time actual evapotranspiration was measured. Actual evapotranspiration was 0.56 ± 0.06 ( X ± SE, N = 10) of the potential evaporation from moss and 0.43 ± 0.08 ( X ± SE, N = 10) of the potential evaporation from E. vaginatum tussocks. Seventy three percent of the variability in the ratio of actual evapotranspiration to potential evaporation from tussocks was accounted for by linear regression on net radiation. Eighty nine percent of the variability in the same ratio for mosses was explained by linear regression on the vapor pressure deficit of the air and net radiation.     

Diurnal patterns of canopy photosynthesis,evapotranspiration and water use efficiency in chickpea (Cicer arietinum L.) under field conditions

Diurnal changes in net photosynthetic rate (PN), evapotranspiration rate (ET) and water use efficiency (WUE=PN/ET) of field grown chickpea (Cicer arietinum) L. cv. H-355 were studied from the vegetative phase through maturirty at Haryana Agricultural University Farm, Hissar, India. The maximum photosynthetic rate (PN max) increased from the initial vegetative phase to pod formation and declined at a rapid rate from pod filling to maturity. The response of PN to photosynthetic photon flux density (PPFD) (400–700 nm) was temperature-dependent during the day, i.e. on cool days the PN rates were lower for certain quanta of PPFD during the first half than during the second half of day, and vice versa on warm days. ET was affected both by crop cover and evaporative demand up to flowering, but thereafter it was independent of crop cover and followed the course of evaporative demand. ET was related to air temperature during the day while PN was related to PPFD. There was a lag of two to three hours between PN_max (around noon) and ET_max (around 2 p.m.). WUE increased from the vegetative stage through flowering but decreased thereafter to maturity.Abbreviations DAS days after planting - ET evapotranspiration - LAI leaf area index - PAR photosynthetically active radiation (in figures) is equivalent to PPFD (see below) - PN net photosynthetic rate - PPFD photosynthetic photon flux density - WUE water use efficiency (= PN/ET)     

Groundwater Capture Using Hybrid Poplar Trees: Evaluation of a System in Ogden,Utah

A phytoremediation system was installed in 1996 in Ogden, Utah, with the objective of controlling groundwater containing petroleum hydrocarbons. Hybrid poplar trees were deeply and densely planted in rows oriented perpendicular to the direction of groundwater flow, and the stand was never irrigated. Piezometers were installed to measure water table elevation and contaminant levels upgradient, within, and down-gradient of the trees. In 1998, an analysis of the root structure of a representative tree indicated that roots had extended down to the saturated zone, approximately 6 ft below ground surface. The rate of water use by the stand during 1998 was estimated from reference evapotranspiration (ET_o), leaf area, and a water use multiplication factor ($tH) specific to poplar trees. Sap velocity data were collected to measure actual water use by the stand in late summer of 1998. Estimated and measured values compared favorably, with measured values averaging 2.8 gallons day^-1 tree^-1 (1.7 mm day^-1 tree^-1). Water use by the stand in 1999 averaged an estimated 445 gallons day^-1 (6.9 mm day^-1 for the stand). Although the trees transpired a volume of water equivalent to a 10-ft thickness of the saturated zone, water table elevation data collected in 1999 did not indicate a depression in the water table.     

Vegetative and reproductive responses,oil yield and composition from olive trees (Olea europaea) under contrasting water availability during the dry winter‐spring period in central Argentina

In Argentina, the climatic pattern of the olive production areas is characterised by a marked water deficit during winter and spring months. A field experiment was carried out to evaluate the effect of water availability during the pre‐flowering–flowering period on vegetative, reproductive and yield responses of olive trees grown in central Argentina. From the end of autumn to mid‐spring, four irrigation treatments were imposed to olive trees (Olea europaea, cv. Arbequina and Manzanilla) at 0, 25, 50 and 75% estimated crop evapotranspiration (ETc). Also, a control treatment was kept at 100% ETc for the entire year. For the first crop year evaluated, water deficit applied at early June, approximately 4 months prior to bloom, reduced the vegetative shoot growth and delayed the flowering time, resulting in shortening of the fruit maturation period and, ultimately, decreased fructification. Trees irrigated with high (75% of ETc) and full (100% of ETc) winter‐spring water supply presented significantly higher values of flower density, fruit density and final fruit yield which resulted in water productivity (kg fruits mm^?1 of irrigation/ha) enhancements of about 500% (cv. Arbequina) and 330% (cv. Manzanilla) with respect to those obtained from the corresponding unirrigated treatments. Differences between treatments in oil content and composition were primarily attributed to variations in fruit maturity. Differences in fatty acid composition were stronger in cv. Arbequina where a gradual increase in oleic acid content was registered in parallel to the increase in irrigation water supply. From a practical stand point, results obtained from most of the analysed parameters were quite similar for both T75 and T100 treatments. Thus, the possible convenience of irrigation at T75% ETc should be considered since it may warrant profitable olive production while saving a considerably quantity of irrigation water in the olive production area in central Argentina.     

Pollen-limited reproduction in blue oak: implications for wind pollination in fragmented populations

Human activities are fragmenting forests and woodlands worldwide, but the impact of reduced tree population densities on pollen transfer in wind-pollinated trees is poorly understood. In a 4-year study, we evaluated relationships among stand density, pollen availability, and seed production in a thinned and fragmented population of blue oak (Quercus douglasii). Geographic coordinates were established and flowering interval determined for 100 contiguous trees. The number of neighboring trees within 60 m that released pollen during each tree's flowering period was calculated and relationships with acorn production explored using multiple regression. We evaluated the effects of female flower production, average temperature, and relative humidity during the pollination period, and number of pollen-producing neighbors on individual trees' acorn production. All factors except temperature were significant in at least one of the years of our study, but the combination of factors influencing acorn production varied among years. In 1996, a year of large acorn crop size, acorn production was significantly positively associated with number of neighboring pollen producers and density of female flowers. In 1997, 1998, and 1999, many trees produced few or no acorns, and significant associations between number of pollen-producing neighbors and acorn production were only apparent among moderately to highly reproductive trees. Acorn production by these reproductive trees in 1997 was significantly positively associated with number of neighboring pollen producers and significantly negatively associated with average relative humidity during the pollination period. In 1998, no analysis was possible, because too few trees produced a moderate to large acorn crop. Only density of female flowers was significantly associated with acorn production of moderately to highly reproductive trees in 1999. The effect of spatial scale was also investigated by conducting analyses with pollen producers counted in radii ranging from 30 m to 80 m. The association between number of pollen-producing neighbors and acorn production was strongest when neighborhood sizes of 60 m or larger were considered. Our results suggest that fragmentation and thinning of blue oak woodlands may reduce pollen availability and limit reproduction in this wind-pollinated species.     

Heat balance components and evapotranspiration from a sedge-grass marsh

Daily course of heat balance components (sensible heat, latent heat of evaporation and ground heat fluxes) and evapotranspiration were computed from meterological data recorded in a sedge-grass marsh in South Bohemia, Czechoslovakia. Bowen-ratio method and tank measurements were used, and several comparisons made with parallel aerodynamic measurements. Two simplified empirical formulae for calculating evapotranspiration are suggested: one based on net radiation, the other based on net radiation and on the difference between the mean relative air humidities at the upper and lower levels of the boundary layer above the stand. The seasonal courses and totals of heat-balance components and evapotranspiration obtained in three years (1977 to 1979) are compared and discussed.