黄土高原水土保持林对土壤水分的影响

黄土高原植被恢复的限制因素主要是土壤水分,植被与土壤水分关系的研究对黄土高原植被恢复具有重要意义.2008年7月1日至2009年10月31日间采用EnviroSMART土壤水分定位监测系统以每30min监测1次的频度,对晋西黄土区刺槐人工林地、油松人工林地、次生林地的土壤水分变化进行了研究.研究得出:次生林地0-150 cm土层中平均蓄水量为331.95mm,刺槐人工林地为233.85 mm,有整地措施的油松人工林地为314.85mm,刺槐人工林比次生林多消耗的98.10mm土壤水分主要来源于80 cm以下土层.次生林主要消耗0-80 cm土层的水分,而人工林不但对0-80 cm土层水分的消耗量大于次生林,对深层土壤的消耗也较次生林大,这将有可能导致人工林地深层土壤的“干化”.在土壤水分减少期(11-1月)刺槐人工林土壤水分的日均损耗量为0.86mm、油松人工林为0.82 mm、次生林为0.84 mm.土壤水分缓慢恢复期(2-5月)刺槐人工林地土壤水分的恢复速度0.90mm/d,油松人工林地为0.53 mm/d、次生林地为0.79 mm/d.土壤水分剧烈变化期(5-10月)刺槐人工林地土壤水分含量的极差为95.71mm,油松人工林地为179.1mm,次生林地为72.03mm.在干旱少雨的黄土高原进行植被恢复时,应多采取封山育林等方式,依靠自然力量形成能够与当地土壤水资源相协调的次生林,是防止人工植被过度耗水形成“干化层”、保障水土保持植被持续发挥生态服务功能的关键.     

岷江上游两种生态系统降雨分配的比较

植被的降雨分配作用对理解生态系统的水文功能具有重要的意义。该文对四川岷江上游岷江冷杉(Abies faxoniana)针叶林和川滇高山栎(Quercus aquifolioides)灌丛两种生态系统的降雨分配及降雨截留的影响因素进行了研究,探讨了植被分配降雨及截留降雨的影响机制和影响因素。文中采用定位观测的方法研究降雨分配。针叶林中冠层降雨截留占33.33%,树干茎流占0.07%,穿透雨占66.60%;而灌丛的冠层截留降雨为24.95%,穿透雨为75.05%;针叶林地被物的蓄留水能力(1.746 mm)要大于灌丛地被物的持水能力(0.941 mm);针叶林土壤的容积含水率(39.66%)也要高于灌丛土壤的容积含水率(38.19%);两种生态系统中的穿透雨率与降雨量的关系均可用逻辑斯谛方程较好地模拟。文中还选取了降雨量、降雨强度、降雨持续时间、两次降雨的间隔时间和次降雨期间的气温等5种因子分析影响两种生态系统降雨截留的主要因素。根据截留降雨与上述5种因子的偏相关分析结果:针叶林冠层的降雨截留主要受降雨量、降雨持续时间和间隔时间的影响;灌丛的降雨截留主要受降雨量、气温与降雨持续时间的影响。文中从当地的降雨特征与两种生态系统微气候差异的角度分析了两种生态系统降雨分配及降雨截留影响因素差异的原因。     

A Protocol for Conducting Rainfall Simulation to Study Soil Runoff

Rainfall is a driving force for the transport of environmental contaminants from agricultural soils to surficial water bodies via surface runoff. The objective of this study was to characterize the effects of antecedent soil moisture content on the fate and transport of surface applied commercial urea, a common form of nitrogen (N) fertilizer, following a rainfall event that occurs within 24 hr after fertilizer application. Although urea is assumed to be readily hydrolyzed to ammonium and therefore not often available for transport, recent studies suggest that urea can be transported from agricultural soils to coastal waters where it is implicated in harmful algal blooms. A rainfall simulator was used to apply a consistent rate of uniform rainfall across packed soil boxes that had been prewetted to different soil moisture contents. By controlling rainfall and soil physical characteristics, the effects of antecedent soil moisture on urea loss were isolated. Wetter soils exhibited shorter time from rainfall initiation to runoff initiation, greater total volume of runoff, higher urea concentrations in runoff, and greater mass loadings of urea in runoff. These results also demonstrate the importance of controlling for antecedent soil moisture content in studies designed to isolate other variables, such as soil physical or chemical characteristics, slope, soil cover, management, or rainfall characteristics. Because rainfall simulators are designed to deliver raindrops of similar size and velocity as natural rainfall, studies conducted under a standardized protocol can yield valuable data that, in turn, can be used to develop models for predicting the fate and transport of pollutants in runoff.     

Tree Canopy Effects on Simulated Water Stress in Southern African Savannas

A coupled energy and water balance model is used to simulate the effects of large tree canopies on soil moisture and water stress across a series of sites spanning a regional moisture gradient in southern Africa. The model tracks evapotranspiration from five components of the land surface at each site—the tree canopy, the grass under and between tree canopies, and the bare soil under and between tree canopies. The soil moisture dynamics are simulated at daily time steps and driven by a stochastic model of storm arrivals and storm depth. Evapotranspiration is modeled using the Priestley-Taylor approach, with potential evapotranspiration scaled by soil moisture availability. The soil moisture under tree canopies is compared to the soil moisture between tree canopies, and differences in average annual soil moisture stress conditions are analyzed at each site. The spatial distribution of large trees has important consequences for small-scale soil moisture dynamics across the rainfall gradient. The results indicate that tree canopies serve to reduce soil moisture stress of under-canopy vegetation in the middle of the rainfall gradient. At the dry end of the rainfall gradient, the effect of tree canopies on soil moisture is dependent on the amount of rainfall received in a given growing season.     

模拟降雨对西双版纳热带次生林和橡胶林土壤呼吸的影响

降雨作为一个重要的环境因子,对土壤呼吸具有重要的影响。研究土壤呼吸与降雨的关系,对准确估算大气中的CO2含量具有重要意义。本研究通过人工模拟降雨事件,应用野外原位测定方法,测量了热带次生林和橡胶林土壤呼吸速率、地下5cm土壤温度和土壤含水量的变化,以探究热带两种主要植被类型的土壤呼吸、土壤温度、土壤含水量对旱季单次降雨事件的响应过程与规律。研究发现,在旱季连续一周没有降雨的情况下,人工模拟降雨事件使土壤呼吸在降雨后的2h内被迅速激发,次生林的土壤呼吸最大达到11.15 μmolCO2·m-2·s-1,是对照的近7倍;橡胶林的土壤呼吸最大达到了15.88 μmolCO2·m-2·s-1,是对照的近11倍。随后激发效应迅速降低,尤其是橡胶林,在人工模拟降雨6h后处理与对照间无显著差异。人工模拟降雨前两种林型的土壤含水量与对照相比均无显著性差异,人工模拟降雨后的2d内土壤含水量均显著高于对照;人工模拟降雨前后土壤温度与对照相比均无显著性差异。本研究结果支持了"Birch effect",2种主要热带林型在旱季时期,由于单次降雨事件激发而释放到大气中的CO2是降雨前的数倍。     

黄土丘陵区不同土地利用模式对深层土壤含水量的影响

对陕北米脂人工经济林、神木退耕还林和榆林榆阳区防风固沙林具有代表性植被类型0～20 m土壤剖面水分特征的差异进行了研究,分析黄土丘陵区不同土地利用模式对深层土壤剖面水分分布和储存特征的影响及生态环境效应.结果表明: 在0～20 m土层,不同位点具有代表性土地利用方式均影响土壤含水量的垂直分布;在整个剖面中,人工经济林土壤储水量有显著差异,为矮化枣树 ＞ 未矮化枣树,储水量相差587.9 mm;神木退耕还林和榆林榆阳区防风固沙林土壤剖面中土壤储水量无较大差异,在神木整个剖面中土壤储水量的大小为退化人工草地 ＞ 柠条林,储水量相差98.8 mm;在榆阳为荒草地 ＞ 樟子松,储水量相差7.5 mm.与未矮化枣树相比,人工经济林矮化枣树减少了对土壤水分的消耗,矮化枣树冠幅较小,降低了蒸腾作用,从而更加有利于土壤水分的可持续利用;人工柠条林和退化人工草地土壤水分含量无明显差异,这是因为退化人工草地过去为苜蓿地,根系分布深以及生物量大,对土壤深层水分利用较大所致;防风固沙林樟子松与荒草地整个剖面中的平均土壤含水量较低,土壤砂粒含量较高,土壤持水性差,土壤含水量随土壤深度的增加而增加,平均土壤含水量分别为3.4%和3.6%,且该地植物对深层土壤水分影响有限.综上,土壤剖面中土壤水分除了受土壤质地的控制,不同土地利用模式由于植物根系不同,对土壤水分也产生较大的影响.为此,选择合适的植物对于土壤深层水的保护和持续利用非常重要.     

Variation in vegetative water use in the savannas of the North Australian Tropical Transect

Abstract. The decline in tree density on sandy soils in savannas is highly correlated with declining mean annual rainfall along the North Australian Tropical Transect (NATT). We reanalyse various data on water use by individual trees and argue that a common relationship can be used to estimate annual water use by tree stands along the NATT from ca. 600 mm mean annual rainfall to at least 1600 mm. Where rainfall is less than 600 mm, trees of a given size use less water than at sites where rainfall is higher. We use these relationships to relate water use at the stand scale with mean annual rainfall along the NATT. From this we show that the empirical data imply that the minimum depth of sandy soil that needs to be exploited by trees declines with increasing aridity along the NATT from more than 5 m to less than 1 m. This finding is consistent with other observations and the pattern that with increasing aridity, an increasing proportion of rainfall coming from isolated storms rather than from periods of extended monsoon activity.     

准噶尔盆地两种荒漠群落土壤呼吸速率对人工降水的响应

通过野外定位观测准噶尔盆地荒漠植物群落(假木贼群落和盐穗木群落)在不同人工模拟降水强度下的土壤呼吸、土壤温度和湿度动态,探讨了荒漠群落土壤呼吸速率对降水后土壤增湿的响应.结果发现两种荒漠植物群落的土壤呼吸速率均出现了模拟降水后10min减小、随后逐渐增加、达到最大值后再次衰减的现象.降水处理的土壤呼吸速率最大值出现滞后于对照处理,且呼吸速率最大值及最大值后的递减速率普遍高于对照.降水后土壤呼吸速率变化受温度和土壤湿度共同影响,降水后10min土壤呼吸速率的减小与土壤湿度最大值同步,呼吸速率最大值出现时间与地表温度一致,在降水后180～300min.2类群落3种降水处理间的土壤呼吸速率在模拟降水后(0～450min时段)均未达到显著差异.假木贼群落以5mm降水处理的平均土壤呼吸速率最大,盐穗木群落则以2.5mm 处理最大.土壤呼吸速率对模拟降水的响应受降水量、降水前土壤湿润状况、土壤质地等多种因素影响.     

中国东部森林样带典型森林水源涵养功能

通过对我国东部森林样带四个森林生态系统定位研究站（长白山站、北京站、会同站和鼎湖山站）的九种森林类型水源涵养监测数据的分析,研究了水热梯度下不同森林生态系统水源涵养功能。结果表明：在生长季的5-10月份,各森林类型的水源涵养特性表现出较大差异。林冠截留率的大小依次为：阔叶红松林＞杉木林＞常绿阔叶林＞针阔混交林＞季风常绿阔叶林＞落叶阔叶混交林＞马尾松林＞落叶松林＞油松林,最高的长白山站阔叶红松林的截留率是最低的北京站油松林的2.2倍。森林降雨截留量与林外降雨量呈显著的正相关,林冠截留率与降雨量呈显著负相关。枯落物最大持水深（5-10月份）以北京站落叶阔叶林最大,为6.0mm;鼎湖山站的季风常绿阔叶林最小,为1.0mm。0-60cm土层蓄水量最大的是会同站的人工杉木林,为247mm;最小的是北京站的落叶松林,仅为45.5mm;林分总持水量依次为：杉木林＞阔叶红松林＞常绿阔叶林＞针阔混交林＞季风常绿阔叶林＞落叶阔叶混交林＞马尾松林＞落叶松林＞油松林。各林分总持水量主要集中在土壤层,占总比例的90%以上。     

A preliminary assessment of rain throughfall beneath Portulacaria afra canopy in subtropical thicket and its implications for soil carbon stocks

Subtropical thicket dominated by the leaf- and stem-succulent tree Potulacaria afra (spekboom) accumulates extraordinarily high amounts of soil organic carbon for a semi-arid ecosystem. This has been attributed to high leaf litter production of canopy trees — especially spekboom — and the relatively cool beneath-canopy temperatures, which reduces mineralization of organic matter. High rainfall interception by the dense thicket canopy may also contribute to reduced mineralization of soil organic carbon stocks via a reduced Birch effect (wet-dry cycles) and overall reduced moisture of organic matter. Here we provide preliminary data on one easily measurable component of canopy interception, namely throughfall, which is the amount of rain falling on the canopy that is not intercepted by the canopy or diverted as stemflow. For 23 rainfall events > 1 mm in the period Jan-Jun 2006, we measured 275 ± 21 mm gross rainfall at three spekboom thicket sites. Mean throughfall was 56.4% across all events and ≤ 20% for small (≤ 5 mm) events. These values are the lowest recorded in the literature. Throughfall in tropical and temperate forests ranges from 70 to 90%, Mediterranean woodland trees 70-80%, and Savanna trees 75-84%. The low rates of throughfall recorded in this study support the hypothesis that the extreme accumulation of soil organic carbon in thicket soils is partly due to interception of rainfall and concomitant constraints on soil microbial activity. The extraordinary high interception of rainfall by the spekboom thicket canopy warrants further research at the ecosystem level.     

Rooting depth,water availability,and vegetation cover along an aridity gradient in Patagonia

Above-and belowground biomass distribution, isotopic composition of soil and xylem water, and carbon isotope ratios were studied along an aridity gradient in Patagonia (44–45°S). Sites, ranging from those with Nothofagus forest with high annual rainfall (770 mm) to Nothofagus scrub (520 mm), Festuca (290 mm) and Stipa (160 mm) grasslands and into desert vegetation (125 mm), were chosen to test whether rooting depth compensates for low rainfall. Along this gradient, both mean above-and belowground biomass and leaf area index decreased, but average carbon isotope ratios of sun leaves remained constant (at-27), indicating no major differences in the ratio of assimilation to stomatal conductance at the time of leaf growth. The depth of the soil horizon that contained 90% of the root biomass was similar for forests and grasslands (about 0.80–0.50 m), but was shallower in the desert (0.30 m). In all habitats, roots reached water-saturated soils or ground water at 2–3 m depth. The depth profile of oxygen and hydrogen isotope ratios of soil water corresponded inversely to volumetric soil water contents and showed distinct patterns throughout the soil profile due to evaporation, water uptake and rainfall events of the past year. The isotope ratios of soil water indicated that high soil moisture at 2–3 m soil depth had originated from rainy periods earlier in the season or even from past rainy seasons. Hydrogen and oxygen isotope ratios of xylem water revealed that all plants used water from recent rain events in the topsoil and not from water-saturated soils at greater depth. However, this study cannot explain the vegetation zonation along the transect on the basis of water supply to the existing plant cover. Although water was accessible to roots in deeper soil layers in all habitats, as demonstrated by high soil moisture, earlier rain events were not fully utilized by the current plant cover during summer drought. The role of seedling establishment in determining species composition and vegetation type, and the indirect effect of seedling establishment on the use of water by fully developed plant cover, are discussed in relation to climate change and vegetation modelling.     

长白山阔叶红松林降雨截留量的估算

林冠截留降雨过程是森林流域水分循环的重要组成部分,以往的研究多为1次或多次降雨量与截留量的关系,很少考虑雨强和树木特征.文中利用林冠截留降雨半经验半理论模型,以雨强和叶面积指数为模型输入,林冠湿润程度为参数,结合Penman-Monteith公式,有效地模拟了长白山阔叶红松林次降雨的截留过程和2004年5～9月的林冠截留总量.结果表明,研究期间的林冠截留总量为39.96 mm,占降雨总量的10.2%,与实测资料吻合.根据模拟结果,探讨了不同时间尺度上截留量与降雨量之间的关系,随着时间尺度的增大,截留量与降雨量的相关关系趋于明显.     

中国主要森林生态系统水文功能的比较研究(英文)

 基于中国不同区域生态站的观测资料,着重从降雨截留（林冠截留、枯枝落叶层截持和土壤蓄水）、调节径流和蒸散等3个方面对我国主要森林生态系统的水文生态功能进行了比较研究。各生态系统林冠年截留量在134～626 mm间变动,由大到小排列为：热带山地雨林,亚热带西部山地常绿针叶林,热带半落叶季雨林,温带山地落叶与常绿针叶林,寒温带、温带山地常绿针叶林,亚热带竹林,亚热带、热带东部山地常绿针叶林,寒温带、温带山地落叶针叶林,温带、亚热带落叶阔叶林,亚热带山区常绿阔叶林,亚热带、热带西南山地常绿针叶林,南亚热带常绿阔叶林,亚热带山地常绿阔叶林。枯落物持水量可以达到自身干重的2～5倍,但也因林型而异。土壤非毛管持水量变动在36～142 mm之间,平均89 mm。常绿阔叶林的非毛管持水量通常高于100 mm,而寒温带/温带落叶阔叶林和常绿针叶林通常低于100 mm. 土壤的非毛管持水量通常占生态系统中截持水量的90%,其次是枯落物和林冠层。这说明,森林土壤在调节降雨截留中占有重要地位,其水文功能的大小取决于土壤结构和空隙度,而这些恰恰又受枯落物和森林植被特征的影响。森林皆伐后,一般地表径流会显著地增加,而适当抚育措施则对地表径流影响不大。流域径流受诸多因素的影响,包括植被、土壤、气候、地形、地貌以及人类影响导致的流域景观变化,比较研究表明森林变化对流域径流的影响尚未得到一致的规律性的结果。通过对比研究不同森林的蒸散变化,发现随降雨量的增加,森林蒸散量略有增加,而相对蒸散率却在下降,相对蒸散率在40%～90%间变动。     

陕北黄土区雨季后山地枣林土壤水分动态变化研究

选取陕北延川县齐家山红枣试验基地枣林地、苹果林地和撂荒草地为研究对象进行土壤水分动态变化研究，结果表明：①不同坡位、不同坡向和不同整地方式的枣林地土壤水分存在显著差异；其中，研究区下坡位土壤水分最高，为14.19%；阴坡土壤水分最高，为14.19%；水平阶整地枣林土壤水分显著高于原状坡。②研究区不同植被类型间土壤水分垂直变化趋势基本一致。枣林地土壤水分最高，为11.49%；不同植被类型0~100 cm土壤贮水量依次表现为枣林地（144.76 mm） > 苹果林地（124.19 mm） > 撂荒草地（72.20 mm）。③不同植被类型土壤贮水亏缺度存在差异。雨季前，0~20 cm土层亏缺度最小，平均亏缺度表现为撂荒草地 > 枣林 > 苹果林；雨季后，土壤水分亏缺度表现为撂荒草地 > 苹果 > 枣林，除枣林地外均高于雨季前土壤水分亏缺度。④雨季后，研究区3种植被类型0~20 cm土层土壤水分亏缺加剧；20~100 cm土层中，枣林土壤贮水补偿度为正值，土壤水分得到补偿，但最高仅为22.95%，枣林土壤水分仍处于亏缺状态并未完全恢复；苹果林地土壤贮水补偿度则为负值，表明土壤水分亏缺进一步加剧；撂荒草地土壤水分补偿度基本维持在0左右，土壤水分亏缺没有持续恶化。     

海南西部桉树人工林土壤水分变化特征及其对林龄的响应

在海南西部儋州林场选取空间相邻、自然环境相似、不同林龄与连栽代次的桉树林样地和椰树林对照样地,通过2010—2012年连续3a定点取样,研究桉树林土壤水分变化特征及其对林龄的响应,分析桉树林种植对林地土壤水分的影响。结果表明:(1)1—4月土壤含水量持续减少,5—6月波动较大,7—10月增加到年内极大值,11—12月降低,但处于年内较高水平。(2)短伐桉树林(二代5年桉树林、三代1年桉树林、三代4年桉树林)、20a桉树林以及10a椰树林5个样地的月均土壤含水量存在显著或极显著差异。二代5年桉树林与三代1年桉树林之间以及20a桉树林与10a椰树林之间的土壤含水量差异均不显著;其余各林地之间土壤含水量差异显著或极显著。(3)随着土壤深度增加,短伐桉树林与20a桉树林、10a椰树林之间的土壤含水量差异增大。表层0—30 cm短伐桉树林年均土壤含水量为6.08%,20a桉树林为7.53%,10a椰树林为6.93%;80 cm以下则分别为8.10%、11.72%和11.95%。与10a椰树林、20a桉树林相比,短伐桉树林对土壤深层水分有较大负面影响。(4)短伐桉树林、20a桉树林和10a椰树林土壤含水量的变异系数由表层到深层逐渐递减,其中林龄较大的短伐桉树林变异系数较大,且变异系数较大的土层也较深厚。与20a桉树林、10a椰树林相比,林龄较大的短伐桉树林对深层土壤水分的消耗较多。(5)连栽代次愈多,林龄越大,土壤含水量愈少;采伐之后1a桉树林的土壤含水量明显增加,有利于桉树后期生长。     

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。     

黄土高原苹果园土壤水分及水分生产力模拟

以长武地区为例,采用WinEPIC模型模拟1980—2018年间黄土高原旱作苹果园地深剖面土壤水分和水分生产力变化动态,以期为该区苹果产业的可持续发展提供科学依据。结果表明: 长武地区苹果园年均产量为26.37 t·hm^-2,年均蒸散量为673.66 mm,年均水分生产力为4.07 kg·m^-3,成龄果树水分胁迫天数主要受降雨量影响,果树生长后期年均胁迫天数为46.46 d,深层土壤含水量最早于9龄果树开始接近凋萎湿度。长武地区苹果整个生长周期内供水量是对果园产量影响最大的因素,深层土壤有效水含量降低是制约果树生长中后期产量提高的最主要因素,在降水不足的年份果树会利用更深层土壤水分。当深层土壤可利用水分较少时,过多的降水并未被果树利用,而是转化为浅层土壤水分蒸发。对于成龄果树在年供水量低于500 mm或高于700 mm时都会造成产量的下降。针对不同生长时期的果园,在不同的降雨年份应该调整果园水分管理策略,可以通过补充灌溉、拦蓄集聚雨水、覆盖、修剪枝条等管理措施,降低果树非生产性耗水及自身奢侈性耗水,延缓深层土壤干层的出现时间,在保证果树生长的同时避免水资源的浪费。     

北京山区干旱胁迫下侧柏叶片水分吸收策略

干旱与半干旱地区,水分是限制树木生长的重要影响因子。由于降水稀缺且分配不均,叶片吸收水分是此地区树木吸收和利用小量级降水和凝结水的主要方式。北京山区处于易旱少雨的生态脆弱地带,森林植被经常遭受干旱胁迫,所以对该地区的森林系统而言,叶片直接吸收利用截留的降雨是干旱时期树木获得水分的重要途径。基于野外对比控制试验和室内盆栽模拟试验,选取北京山区的主要造林树种侧柏为研究对象,进行利用天然降雨与模拟降雨试验,研究降雨前后侧柏叶片吸水特征,探究侧柏在干旱环境下如何通过叶片吸水缓解干旱胁迫。结果表明：当侧柏长期处于干旱胁迫状态时,叶片可以利用降雨,从中获益用来缓解树木的干旱胁迫状态;叶片的吸水能力与降雨强度呈正相关关系,与土壤含水率呈负相关关系;重度干旱下侧柏植株在降雨强度为15 mm/h时叶片吸水现象最明显,叶水势变化最大为(1.18±0.17) MPa,叶片含水率变化最大为(8.47±1.00)mg/cm~2;当土壤水率高于20.8%时,基本不发生叶片吸水现象。试验结果说明在干旱地区叶片吸水是树木除根系吸水外的重要水分来源方式,并且对干旱地区有效利用短缺水资源,减轻植物水分亏缺具有重要意义。     

几种常用造林树种冠层对降水动能分配及其生态效应分析

本文从理论上系统地论述了林冠如何调节到达林地的降水动能,推导了计算大气降水和穿透水动能的理论和方法。经由理论推导指出并非所有的森林都适合作为水土保持林,即由穿透水的水滴直径较大,而且不受大气降水强度的影响及穿透水常常不是以最大的稳定速度到达林地这两个规律来讨论森林冠层在水土保持功效方面所具有的地位,可以做为营造水土保持林的理论基础。     

鹤山丘陵草坡的水文特征及水量平衡

 在中国科学院鹤山丘陵综合开放实验站的草坡集水区对大气降水和径流进行了连续4年的观测,并于1994年对该集水区的蒸散进行了测定,结果表明：1)鹤山丘陵区年均降水量1761.37mm,大气降水有明显的干湿季之分,干季降水量占全年降水量的12.47％,湿季占87.53％。年均降水量中有62.24％可引起地表产流,即年均产流降水量1096.3mm。产流降水以中、小雨频度为大,但产流水量主要由大、暴雨供给。文中根据降雨量较大地区的降水、产流特征和规律,提出了产流降水和产流水量的概念。2)鹤山丘陵草坡集水区年总径流系数50.12％,地表径流系数17.33％。地表径流主要集中在湿季产生,与降水量呈二次抛物线型回归关系,与降水强度关系不大。3)1994年水量平衡各分量中,实际降水输入1841.55mm,年径流量970.28mm,径流系数52．69％,径流是系统的最大输出项;蒸散量851.56mm,意味着年降水收入中46.24％的水量以汽态形式返回了大气。蒸散的月变化呈双峰型,不同于降水的季节分配,径流的月变化则与降水同步。系统蓄水年变化量19.71mm,约占年降水量的1.07％,但其月变化却非常大,在一68～104mm之间。草坡集水区的水量平衡是一种收入对支出的补给和收支项目中可变性的动态平衡。4)鹤山丘陵草坡水热季节分配失衡、产流降水量和地表径流量大是这种退化生态系统恢复的3个限制因素;认为退化生态系统恢复过程中系统水量支出和蓄留方式的转变是退化生态系统的恢复机理之一。