苹果树冠层空气温差变化及其与环境因子的关系

于2002—2005年,采用红外测温仪观测得到苹果树主要生长季节冠层温度数据,结合同步观测得到冠层净辐射(Rn)、风速(V)、空气温度(Ta)和湿度(RH)等冠层微气象要素数据及0～80cm土壤含水量(SW),分析苹果树冠层-空气温差(△T)变化规律及其与环境因子的关系.结果表明:苹果树主要生长季节(萌芽期—果实迅速膨大期)晴天△T日变化呈多峰曲线分布,△T最高值都出现在12:00—13:00左右;阴天△T日变化呈多峰曲线分布,但△T绝对值明显低于晴天日.2003年和2004年晴天日14:00△T与Rn、V、RH及SW具有较好的复相关关系:ΔT=7.159-0.002Rn-0.061V-0.7RH-46.0SW(r=-0.825),与Rn、RH、V及SW的偏相关系数分别为0.125、-0.078、-0.036和-0.874,逐步回归方程式为ΔT=5.317-43.1SW,说明土壤水分对△T的影响程度相对最大.经2002年和2005年观测数据验证,△T观测值与计算值吻合关系较好,二者线性相关系数可达0.9083.这说明采用晴天日14:00时刻数据分析△T的影响机制,预测土壤水分含量具有很好的可行性.     

塔里木荒漠优势树种气体交换特性与环境因子的关系研究

在自然条件下对塔里木荒漠区优势树种--胡杨、灰叶胡杨的气体交换特性及其与环境因子的关系进行研究.结果表明:(1)在6～9月生长季,胡杨和灰叶胡杨的净光合速率(Pn)、蒸腾速率(Tr,除8月)日进程均为单峰曲线,胞间CO2浓度(GI)呈"V"字型曲线,Pn的峰值出现在12:00,Tr峰值明显滞后于Pn.生长季内胡杨各月份的Pn、水分利用率(WUE)、光能利用率(LUE)均高于灰叶胡杨,而Tr低于灰叶胡杨,气孔导度(Gs)相近.(2)气体交换与环境因子的统计分析表明,光量子通量密度(PPFD)是决定胡杨和灰叶胡杨Pn和Tr的主要环境因子,其次为气温(Tair).(3)灰叶胡杨对PPFD、Tair,、空气相对湿度(RH)的敏感性强于胡杨,通过高蒸腾耗水、低WUE来减轻高温干旱的伤害;胡杨通过主动调节Gs来控制蒸腾失水、提高光合效率,以较高的WUE和LUE适应日益干旱的荒漠环境,表现出较强的生态适应性.     

永定河沿河沙地杨树人工林蒸腾耗水特征及其环境响应

杨树是我国北方最常见的人工造林树种之一。一直以来在干旱、半干旱地区,速生杨树用材林和生态防护林的耗水问题备受关注。研究不同生长发育阶段杨树人工林蒸腾耗水及其对各环境因子的响应对于实现杨树人工林可持续经营具有重要价值。采用树干液流法结合微气象观测系统和土壤水分观测,在2010—2011年对位于北京南郊大兴林场、林龄为13a的杨树人工林林分蒸腾耗水和环境因子进行了同步观测,以期能够探究该林分的蒸腾耗水及其对环境因子的响应。结果表明,树干液流密度(Js)日变化呈明显的单峰曲线,单株样木耗水量随着胸径的增加而增大。在半小时尺度上,单株树木Js与浄辐射(Rn)、饱和水气压差(VPD)存在时滞,这种时滞现象随土壤水分条件不同而变化。林分蒸腾耗水总量在2010和2011年生长季内分别为113.7 mm和174.8 mm,占同期降雨的30.2%和36.9%,与该杨树人工林前期研究相比,随着林龄的增长2010—2011年的蒸腾量呈减小趋势。日尺度上,该人工林蒸腾耗水与净辐射(Rn)、饱和水汽压差(VPD)和土壤体积含水率(SWC)显著相关,在不同土壤水分条件下Rn与林分蒸腾的相关关系发生变化,而VPD过高会对林分蒸腾产生抑制。林分月蒸腾和年总蒸腾主要取决于同期降雨量,因此,降雨年际差异较大时,蒸腾的年际变化也相应较大。     

新疆阿克苏干旱区富士苹果树干液流动态变化研究

选择新疆阿克苏干旱区富士苹果为研究对象,利用TDP茎流计连续测定苹果树干液流,并用自动气象站同步记录环境因子变化,探讨环境因子对树干液流的影响。结果显示:液流速率连日的变化过程是一个最大值不同的正弦曲线,夜间液流速率降低,白天液流速率上升;晴天液流速率呈明显的单峰曲线,阴天液流速率表现为多峰或双峰曲线,不论是晴天还是阴天,苹果在夜间仍然有微弱的活动,这种现象可能与新疆阿克苏地区的地理位置和气候有关;在苹果主要生长季内,树干液流速率(Fs)与大气温度(Ta)、太阳辐射(Rn)、相对湿度(RH)有较好的复相关关系(R2=0.93*),且影响苹果树液流速率Fs的最主要气象因子为大气温度Ta;苹果生长季内耗水总量为4 059.64L,并以7月耗水量最大(765.34L),占耗水总量的18.85%。研究表明,TDP径流计能够精确测定生长季内苹果茎干的液流速率与耗水量,且在干旱区影响苹果茎干液流变化的主要环境因子依次是大气温度、太阳辐射、相对湿度。     

山茱萸人工林蒸腾速率混沌及分形特征

利用热扩散液流法测算了华北山地山茱萸人工林的蒸腾,采用相空间重建法,分析了林木蒸腾速率混沌及分形特征.结果表明:林木蒸腾过程是一种混沌运动,具有分形性质;2005年与2006年主要生长季节期间,延滞时间(τ)为10 min时,蒸腾速率(Tr)的分形维数(D)分别是1.054和1.041,二阶Renyi熵(K2)分别为0.0082和0.0086,此时嵌入维数(m)均为10,平均预报时长(T)分别约为122.0和116.3 min,描述其变化过程所需独立变量至少为2个,上限值为10个;尽管2005年和2006年主要生长季节Tr在数量上或外表变化规律上存在差异性(如:总蒸腾量相差25.6%),但在相同.r条件下,D和K2在2005年与2006年差异均极小,故本质特征或内在规律性不存在差异.     

沙地杨树人工林生理生态特性

自然条件下(5~10月份),利用Li-6400便携式光合作用测定系统对北京大兴地区集约栽培欧美107杨(Populus×euramericanacv.“74/76”)生理生态特性进行研究,探讨叶片在水分胁迫状态下光合作用、呼吸作用和蒸腾作用动态规律,并揭示其主要影响机理。实验结果表明叶片净光合速率(Pn)日变化均为单峰曲线,且Pn日平均值从春季到秋季呈下降趋势。从整个生长季来看,光合有效辐射PAR(r=0·815)和气孔导度Gs(r=0·805)与Pn的相关性显著,通过每月相关性分析,5、8月份影响Pn的主导因子为PAR和Gs,6、7月份影响Pn的主导因子为Gs,9、10月份影响Pn的主要因素为PAR。根据Fsrquhar和Sharkey提出的气孔限制和非气孔限制判断方法对Pn日变化进行分析,5月份8:00Pn达到峰值后由于气孔导度降低引起Pn下降,16:00以后由于非气孔因素PAR的降低,使得Pn继续降低;6、7月份8:00以后Pn降低限制因素同5月份一样由气孔导度降低引起,但是14:00左右,由于植物体内水分严重亏缺,叶片气孔不能正常开启使得叶片Pn、R和Tr均不能正常进行,8~10月份Pn降低主要受PAR限制。叶片呼吸速率(R)的主要影响因子为温度,且R的日变化和季节变化与大气温度(Ta)变化趋势基本一致,一天中清晨、傍晚Ta和R均为低点,14:00左右Ta和R都达到最大值,同样在季节变化中R和Ta在6、7月份最高,10月份最低。蒸腾速率(Tr)日变化全为单峰曲线,其最大值出现在12:00~14:00左右,Tr变化与许多环境因子和生理因子都具有密切的相关性,就整个生长季来说,PAR是其最主要的影响因子,然而叶片气孔限制值(LS)、Gs、叶片大气水汽压差(VpdL)、Ta等生理生态因素在不同月份分别起着极其重要的作用。     

不同林分内茶树光合特性及其影响因子和小气候因子分析

对板栗-银杏-茶(Castanea mollissima-Ginkgo biloba-Camellia sinensis)和板栗-茶(Castanea mollissima-Camellia sinensis)复合林分和纯茶(Camellia sinensis)林分内3个小气候因子[包括光合有效辐射强度(PAR)、空气温度(Ta)和空气相对湿度(RH)]和茶树光合特性[包括净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)和蒸腾速率(Tr)]的差异进行了比较,并采用多元回归分析探讨了影响茶树Pn的主要生理生态因子.结果表明:在不同测定时期3种林分内PAR、Ta和RH差异较大;同一时期纯茶林分内的PAR和Ta基本都高于2种复合林分,但纯茶林分内的RH总体上均低于2种复合林分;与纯茶林分相比,板栗和银杏与茶树复合种植有助于调节林分内的PAR、Ta和RH.2种复合林分内茶树的生长均受到板栗或银杏阴蔽的影响,纯茶林分中茶树的Pn最高,与板栗-银杏-茶复合林分内茶树的Pn有显著差异;而纯茶林分中茶树的Gs总体上高于复合林分、Ci与复合林分间差异不显著,且3种林分中茶树的Tr总体上也无显著差异.多元回归分析结果表明:在6个生理生态因子(Gs、Ci、Tr、PAR、Ta 和RH)中,Tr对3种林分内茶树的Pn影响最大,其次是Ta,其他因子在各种林分内的影响程度不同.研究结果表明:茶树复合种植可调节林分内的水热状况,改善茶树生长环境,值得在现有茶园中进行推广和应用.     

疏叶骆驼刺和多枝柽柳不同时期光合特性日变化及其与环境因子的关系

在自然条件下,利用Li-6400光合仪测定疏叶骆驼刺(Alhagi sparsifolia Shap.)和多枝柽柳(Tamarix ramosissima Ledeb.)7~9月份的气体交换参数,分析2种植物净光合速率(Pn)与环境因子——光合有效辐射(PAR)、空气温度(Ta)、大气CO2浓度(Ca)、相对湿度(RH)之间的关系,以明确影响其光合作用的主导环境因子,为恢复和重建过渡带植被提供理论依据。结果显示:(1)疏叶骆驼刺不同时期Pn的日变化均为单峰曲线,多枝柽柳7、8月份的Pn日变化为单峰曲线,9月份为双峰曲线,且疏叶骆驼刺Pn的平均值(7.08μmol·m-2·s-1)高于多枝柽柳(5.54μmol·m-2·s-1)。(2)2种植物7~9月份的蒸腾速率(Tr)日变化均为单峰曲线,且疏叶骆驼刺Tr的平均值(5.46mmol·m-2·s-1)高于多枝柽柳(4.40mmol·m-2·s-1);疏叶骆驼刺和多枝柽柳的胞间CO2浓度(Ci)的日变化趋势均呈"倒钟型"曲线,与Pn日变化趋势相反。(3)2种植物7~9月份的WUE日变化进程与各自的Pn日变化规律基本一致,多枝柽柳的WUE日均值(1.21 mmol·mol-1)明显高于疏叶骆驼刺(0.97mmol·mol-1)。(4)偏相关分析显示,骆驼刺和柽柳的Pn与PAR呈显著正相关关系,而与RH呈显著负相关关系;回归分析显示,骆驼刺和柽柳Pn日变化的变异分别有35.6%和42.4%是由环境因子的日变化造成的;通径分析显示,各环境因子对Pn都具有显著的影响,其大小顺序分别为:TaRHPARCa(骆驼刺)和PARCaTaRH(柽柳),且骆驼刺在7~9月份内PAR均为决策变量,RH为限制变量(除7月份外);而柽柳在8、9月份内PAR均是决策变量,RH、Ca是限制变量。研究表明,疏叶骆驼刺属于高光合高蒸腾低水分利用效率型,多枝柽柳属于低蒸腾低光合高水分利用效率型;7月份骆驼刺和柽柳Pn的下降主要是由于气孔限制引起,而8、9月份主要是由非气孔因素限制所致;PAR和RH是影响骆驼刺和柽柳最重要的环境因子,其次是Ca,而Ta在不同时期的影响程度不同;疏叶骆驼刺和多枝柽柳与环境协同进化过程中产生了一定的生态适应性,但柽柳的WUE明显高于骆驼刺,推测柽柳的抗旱能力强于骆驼刺。     

彰武松、樟子松光合生产与蒸腾耗水特性

本文采用Li-6400光合测定系统对性成熟(18a)阶段彰武松(Pinus densiflora var.zhangwuensis)和樟子松(Pinus sylvestris var.mongolica)光合及蒸腾指标不同季节日变化进行了测定,并采用切枝蒸腾法对两个树种叶片气孔蒸腾和角质层蒸腾进行对比测定,评价了气孔开闭敏感性,探讨了两个树种光合生产与蒸腾耗水特性。结果表明：在同样生境条件下,彰武松比樟子松有较大的光合速率(Pn)和较小的蒸腾速率(Tr)。在5月和7月,彰武松的Pn和Tr日变化呈现明显双峰型,其Pn和Tr“午休”现象均主要受气孔限制;在10月呈单峰型。樟子松的Pn和Tr日变化在整个生长季均呈单峰型,而且,彰武松日光合量(DAP)均高于樟子松,是樟子松的163.4%(5月)、211.1%(7月)和183.6%(10月)。光响应曲线参数表明：在不同月份,彰武松最大光合速率(Pmax)均大于樟子松,且光饱和点(LSP)较高,光补偿点(LCP)较低。在任意被测时刻,彰武松气孔导度(Gs)和Tr都小于樟子松。彰武松具有较小气孔和角质层蒸腾速度,并且在同样干旱条件下,彰武松气孔下陷,其气孔的开闭反应更加敏感。彰武松水分利用效率(WUE)较高,约是樟子松的2.29倍。这些结果暗示,彰武松以其高的光合速率和低的蒸腾耗水特性,提高水分利用效率,以其敏感的气孔开闭机制和旱生叶片结构进而实现在干旱半干旱地区的速生特性。     

不同径级的西伯利亚红松树干液流及蒸腾耗水特征的差异

基于热扩散技术,采用TDP法连续监测了新疆喀纳斯国家自然保护区内不同径级西伯利亚红松的树干液流,分析其在生长季内(6~9月)的液流变化及蒸腾耗水特性,为阐明喀纳斯保护区优势树种水分循环机理,以及理解区域尺度上森林生态系统水分循环及其过程应对未来气候变化的响应机制提供依据。结果显示:(1)不同径级西伯利亚红松在晴、阴、雨3种天气条件下的树干液流日动态变化均呈昼高夜低的多峰型曲线,但变化频率和变化幅度差异明显,日最大液流值的排序为晴天阴天雨天。(2)树干液流的发生较光合有效辐射的变化存在明显的滞后效应,不同径级西伯利亚红松的最大液流峰值滞后时间在30~207min。(3)西伯利亚红松的月平均树干液流的大小顺序为7月8月9月6月,且相同径级树干阳生面的液流速率均大于阴生面。(4)西伯利亚红松全株的蒸腾耗水量为7月份的最大,其值占整个生长季的61.8%;且大径级阳生面的蒸腾耗水总量(6 716.79g)和阴生面蒸腾耗水总量(4 649.08g)分别是相应小径级阳生面和阴生面的2.00和2.45倍。(5)气温、空气相对湿度和光合有效辐射是影响西伯利亚树干液流的主要因素,同时0~5cm和20~30cm土壤温度对其影响也较大。研究表明,西伯利亚红松在生长过程中,大径级树干的液流和蒸腾耗水量大于小径级,主要发生部位为树干的阳生面,且在7月份的变化最明显。     

Specialized 16SrX phytoplasmas induce diverse morphological and physiological changes in their respective fruit crops

The host-pathogen combinations—Malus domestica (apple)/`Candidatus Phytoplasma mali´, Prunus persica (peach)/`Ca. P. prunorum´ and Pyrus communis (pear)/`Ca. P. pyri´ show different courses of diseases although the phytoplasma strains belong to the same 16SrX group. While infected apple trees can survive for decades, peach and pear trees die within weeks to few years. To this date, neither morphological nor physiological differences caused by phytoplasmas have been studied in these host plants. In this study, phytoplasma-induced morphological changes of the vascular system as well as physiological changes of the phloem sap and leaf phytohormones were analysed and compared with non-infected plants. Unlike peach and pear, infected apple trees showed substantial reductions in leaf and vascular area, affecting phloem mass flow. In contrast, in infected pear mass flow and physicochemical characteristics of phloem sap increased. Additionally, an increased callose deposition was detected in pear and peach leaves but not in apple trees in response to phytoplasma infection. The phytohormone levels in pear were not affected by an infection, while in apple and peach trees concentrations of defence- and stress-related phytohormones were increased. Compared with peach and pear trees, data from apple suggest that the long-lasting morphological adaptations in the vascular system, which likely cause reduced sap flow, triggers the ability of apple trees to survive phytoplasma infection. Some phytohormone-mediated defences might support the tolerance.     

马占相思夜间树干液流的分配及其对整树蒸腾估算的影响

采用Granier热消散探针测定了马占相思(Acacia mangium)的树干液流,结合Li-6400光合测定系统测定的夜间叶片气孔导度和蒸腾,将夜间液流区分为夜间树干水分补充和叶片气孔蒸腾。叶片的蒸腾作用微弱,因此,夜间液流主要用于补充贮水部位的水分亏缺。马占相思夜间水分补充量年内和年际的变化不明显,树形特征的差异是解释夜间水分补充量变化的重要因子,夜间水分补充量对于整树蒸腾量的贡献因季节和树木径级的不同而有明显变化,但对整树总蒸腾量计算造成的误差可以忽略。     

树木胸径大小对树干液流变化格局的偏度和时滞效应

通过分析具不同水力结构的马占相思、荷木和粉单竹液流变化格局的偏度和时滞,探讨液流的空间分布特征及对冠层蒸腾的影响。结果表明:荷木的液流格局偏度和时滞随树木胸径的增加呈减小的趋势,但马占相思由于冠层开阔和林分分化程度高而规律不明显,粉单竹液流偏度随胸径减少,由于冠幅较小,接受的光照较均匀,个体间的时滞差异不明显,但时滞值比胸径近似的荷木小。树干水分传输过程中存在液流再分配的现象,边材的导水效率可能是影响时滞的重要原因。冠层蒸腾的空间异质性与树木储存水有关,大树储存水较多,冠层蒸腾的异质性小;小树储存水较少,液流被优先分配到光照充足的东南方位,导致冠层蒸腾较高的异质性。旱季受土壤水分的限制,大树储存水对蒸腾的贡献大于湿季,而小树蒸腾由于受到储水容量的制约,储存水对蒸腾的贡献小于湿季。冠层接受光照的迟或早以及辐射量的大小是引起蒸腾时间变化格局和树干不同方位液流格局差异的重要原因,但液流的横向交换弱化了这种现象,往往是个体间的差异掩盖了方位的差异。湿季较小胸径的树木比偏值(枝下高与胸高处液流偏度的比值)大于旱季,而较大胸径的树木比偏值恰好相反,总体而言,比偏值随着胸径的增加而逐渐下降。     

Estimating transpiration from 6-year-old Eucalyptus grandis trees: development of a canopy conductance model and comparison with independent sap flux measurements

Daily patterns of stomatal conductance (g_s), xylem pressure potential (P) and canopy microclimatic variables were recorded on 11 sample days as part of a one-year study of the water use of Eucalyptus grandis Hill ex Maiden in the eastern Transvaal, South Africa. Measured g_s was found to be largely controlled by quantum flux density (Q) and ambient vapour pressure deficit (D). Canopy conductance (g_c) was determined for hourly intervals using g_s measurements and leaf areas in four different canopy levels. A simple model was constructed to allow the prediction of g_c and transpiration from Q, D and season of year. The model was used to estimate transpiration rates from 10 trees in a later study of similarly-aged E. grandis trees, in which sap flow in each tree was measured using the heat pulse velocity (HPV) technique. Five of the trees were monitored on a summer day and five on a winter day. Correspondence between HPV sap flow and modelled transpiration was good for the summertime comparisons, but measured winter-time sap flow rates were underestimated by the model, especially under conditions of high sap flow. The discrepancy is believed to result from having insufficient data from the conductance study to describe the response of g_s to relatively high D in winter. Marked variation in transpiration per unit leaf area indicates that a relatively large number of trees must be sampled for the HPV technique to be used to obtain a mean rate for an entire stand in winter.     

Water savings in mature deciduous forest trees under elevated CO2

Stomatal conductance of plants exposed to elevated CO₂ is often reduced. Whether this leads to water savings in tall forest‐trees under future CO₂ concentrations is largely unknown but could have significant implications for climate and hydrology. We used three different sets of measurements (sap flow, soil moisture and canopy temperature) to quantify potential water savings under elevated CO₂ in a ca. 35 m tall, ca. 100 years old mixed deciduous forest. Part of the forest canopy was exposed to 540 ppm CO₂ during daylight hours using free air CO₂ enrichment (FACE) and the Swiss Canopy Crane (SCC). Across species and a wide range of weather conditions, sap flow was reduced by 14% in trees subjected to elevated CO₂, yielding ca. 10% reduction in evapotranspiration. This signal is likely to diminish as atmospheric feedback through reduced moistening of the air comes into play at landscape scale. Vapour pressure deficit (VPD)‐sap flow response curves show that the CO₂ effect is greatest at low VPD, and that sap flow saturation tends to occur at lower VPD in CO₂‐treated trees. Matching stomatal response data, the CO₂ effect was largely produced by Carpinus and Fagus, with Quercus contributing little. In line with these findings, soil moisture at 10 cm depth decreased at a slower rate under high‐CO₂ trees than under control trees during rainless periods, with a reversal of this trend during prolonged drought when CO₂‐treated trees take advantage from initial water savings. High‐resolution thermal images taken at different heights above the forest canopy did detect reduced water loss through altered energy balance only at <5 m distance (0.44 K leaf warming of CO₂‐treated Fagus trees). Short discontinuations of CO₂ supply during morning hours had no measurable canopy temperature effects, most likely because the stomatal effects were small compared with the aerodynamic constraints in these dense, broad‐leaved canopies. Hence, on a seasonal basis, these data suggest a <10% reduction in water consumption in this type of forest when the atmosphere reaches 540% ppm CO₂.     

Granier树干液流测定系统在马占相思的水分利用研究中的应用

介绍了Granier热消散探针在树干液流测定中的工作原理,并利用该系统长期监测广东鹤山马占相思林14株样树的液流密度,分析了树木个体内和个体之间液流密度的差异、整树和林段水分利用的量化特征.由于树木边材结构以及周围微环境的差别,树木内和个体间的液流密度差异非常明显,变异系数的平均值分别为15.51%-37.26%、37.46%-50.73%.尽管液流密度的差异较大,但同一株树木不同方位的液流密度之间却呈现明显的线性相关（p＜0.0001）,这是重要的特征值,使得只需测定某一方位的液流密度经尺度外推计算整树和林段蒸腾成为可能.树木液流对环境因子响应的变化规律取决于所参照的时间尺度,日变化主要受光辐射、水汽压差等气候因子的控制,而土壤水份对液流的季节变化影响较大.形态特征明显影响树木的液流,高大树木由于边材较厚、树干粗壮和冠幅较宽而承载较多的辐射能量,因而水分蒸腾较高.对树木液流密度在径向和方位上进行适当的整合,可较准确地计算整树和林段蒸腾.由液流估测的马占相思整树和林段蒸腾的结果显示,该群落的水分利用在时间和空间上均有明显的分化.     

Gibberellin-like Substances in the Transpiration Stream of Apple and Pear Trees

Gibberellin-like substances have been detected in sap exudingfrom decapitated apple and pear trees and also in the xylemsap sucked from stems of apple. The quantity of gibberellinin the sap appears sufficient to produce important effects onshoot development, and this result is discussed in relationto rootstock effects of fruit trees.     

基于树干液流及涡动相关技术的葡萄冠层蒸腾及蒸散发特征研究

针对西北干旱区绿洲经济作物葡萄树冠层蒸腾及蒸散发特征的相关问题,在甘肃省敦煌市南湖绿洲开展无核白葡萄树液流速率及蒸散发观测试验,采用基于热平衡原理的包裹式茎流计,详细分析了典型生长季7—9月份葡萄树蒸腾耗水规律,使用"单位叶面积上的平均液流速率SF×叶面积指数LAI"的方法,实现了从单株到林分冠层蒸腾的尺度扩展,并通过与涡动相关技术所测蒸散发数据对比,详细研究了葡萄地冠层蒸腾及蒸散发规律。结果表明:典型生长季中葡萄树液流速率日变化为单峰型曲线,日均耗水量从2.76 kg到10 kg不等,胸径越大的葡萄树日均耗水量越大;冠层蒸腾及蒸散发日变化曲线亦为单峰型,白天8:00—12:00与17:00—20:00期间,葡萄冠层蒸腾与蒸散发曲线均比较吻合,该时间段葡萄地蒸散发绝大部分来源于葡萄冠层蒸腾,而12:00—17:00之间由于午后太阳辐射强烈土壤蒸发量增加,葡萄蒸散发大于冠层蒸腾;典型生长季3个月中,葡萄冠层蒸腾量的变化范围在1.88—8.12 mm/d之间,日均冠层蒸腾量为6.12 mm/d,蒸散发在1.74 mm/d至10.78 mm/d之间,日均蒸散发量为7.13 mm/d;日均土壤蒸发量约为1.01 mm/d,只占总蒸散发量的14.2%,日均冠层蒸腾占日均蒸散发的比重达到85.8%,说明该生长阶段冠层蒸散发以作物蒸腾为主。     

Nighttime sap flow of Acacia mangium and its implications for nighttime transpiration and stem water storage

Aims Nighttime sap flow of trees may indicate transpiration and/or recharge of stem water storage at night. This paper deals with the water use of Acacia mangium at night in the hilly lands of subtropical South China. Our primary goal was to reveal and understand the nature of nighttime sap flow and its functional significance.Methods Granier's thermal dissipation method was used to determine the nighttime sap flux of A. mangium. Gas exchange system was used to estimate nighttime leaf transpiration and stomatal conductance of studied trees.Important findings Nighttime sap flow was substantial and showed seasonal variation similar to the patterns of daytime sap flow in A. mangium. Mean nighttime sap flow was higher in the less precipitation year of 2004 (1122.4 mm) than in the more precipitation year of 2005 (1342.5 mm) since more daytime transpiration and low soil water availability in the relatively dry 2004 can be the cause of more nighttime sap flow. Although vapor pressure deficit and air temperature were significantly correlated with nighttime sap flow, they could only explain a small fraction of the variance in nighttime sap flow. The total accumulated water loss (E L) by transpiration of canopy leaves was only ~2.6–8.5% of the total nighttime sap flow (E t) during the nights of July 17–18 and 18–19, 2006. Therefore, it is likely that the nighttime sap flow was mainly used for refilling water in the trunk. The stem diameter at breast height, basal area and sapwood area explained much more variance of nighttime water recharge than environmental factors and other tree form features, such as tree height, stem length below the branch, and canopy size. The contribution of nighttime water recharge to the total transpiration ranged from 14.7 to 30.3% depending on different DBH class and was considerably higher in the dry season compared to the wet season.     

Evaluation of the heat pulse velocity technique for measurement of sap flow in rainforest and eucalypt forest species of south-eastern Australia

Sap flow in the stems of two cut saplings each of Eucalyptus maculata (a canopy eucalypt forest tree), Doryphora sassafras and Ceratopetalum apetalum (both canopy rainforest trees of south-eastern coastal Australia) was measured by the heat pulse velocity technique and compared with water uptake from a potometer. Scanning electron micrographs of wounding caused by implantation of temperature sensor and heater probes into the sapwood showed that wounding was similar in rainforest and eucalypt species and was elliptical in shape. A circular wound has been implicitly assumed in previous studies. Accurate measurements of sapling water use were obtained using the smaller transverse wound dimension rather than the larger longitudinal dimension because maximum disruption of sap flow through the xylem vessels occurred in the transverse plane. Accurate measurements of sap flux were obtained above a minimum threshold sap velocity. These velocities were 15·7,10·9 and 9·4 cm h^?1 for E. maculata, C. apetalum and D. sassafras, respectively. Below the threshold sap velocity, however, sap flow could not be accurately calculated from measurements of heat pulse velocity. The minimum threshold sap velocity appeared to be determined by probe construction and xylem anatomy. Despite the elliptical wounding and inaccurate measurement of sap flow below the threshold sap velocity, total sap flow over the experimental period for two saplings of each species was within 7% of water use measured by the potometer.