六盘山北侧叠叠沟小流域土壤物理性质空间变异的研究

2005年6-10月,在宁夏六盘山北侧叠叠沟小流域的不同坡面设置了93个调查样点,研究了土壤物理性质随土层深度、坡向、坡位及植被类型的变化.结果表明:(1)随土深增加,土壤密度和石砾含量逐渐增大,而土壤总孔隙度、毛管孔隙度、非毛管孔隙度、土壤饱和持水量、毛管持水量和田间持水量却逐渐减小,但非毛管孔隙度在100 cm以下土层时因石砾含量加大却随土深增加而增大;(2)各项土壤水文物理性质基本上均是阴坡优于半阴半阳坡和阳坡,半阴半阳坡与阳坡差别不大;(3)随着坡位下降,土壤厚度、土壤密度、石砾含量、非毛管孔隙度逐渐增大,总孔隙度和毛管孔隙度逐渐减小,各种持水量指标基本上也是程度不同地减小,但上坡的持水量指标大于阴坡坡顶;(4)4种植被类型0～30 cm土层的土壤密度为天然灌丛＜天然草地＜乔木林地＜退耕地;石砾含量为退耕地最低,其它3种植被类型差别不大;总孔隙度、毛管孔隙度、饱和持水量、毛管持水量和田间持水量均是天然灌丛＞天然草地＞乔木林地＞退耕地;非毛管孔隙度则是退耕地＞乔木林地＞天然灌丛＞天然草地.其次,还建立了土壤物理性质与海拔、坡向、坡度、坡位、土壤深度、地表植被覆盖度等之间的回归方程.     

Plant water relations and edaphoclimatic conditions affecting acorn production in a holm oak (<Emphasis Type="Italic">Quercus ilex</Emphasis> L. ssp. <Emphasis Type="Italic">ballota</Emphasis>) open woodland

Acorn production patterns and the annual evolution of water relations parameters of Quercus ilex ssp. ballota (Desf.) Samp. in a dehesa (an open woodland forest) subject to various soil treatments (ploughing, ploughing + sowing, control) were studied in southwest Spain from June 2006 to December 2008. The effects of soil water holding capacity and effective soil depth on soil and plant water status and acorn production were also investigated. Water parameters showed significant differences between the ploughing treatment and the control, and there were also significant temporal differences. Xylem water potential ranged from −3.4 ± 0.1 to −0.7 ± 0.2 MPa, and cuticular transpiration was 62.4–192.9 mmol H₂O kg⁻¹ s⁻¹. Acorn production did not differ significantly according to soil treatment, and showed large intra-specific variability. Individual values ranged from 0 to 1,220 g m⁻² (fresh weight). Positive relationships were found between xylem water potential, cuticular transpiration and relative water content measured at midsummer, and acorn production during the three studied years. These results suggest that climatic conditions and soil water availability have a strong influence on plant water status, and therefore on acorn development during summer. The results also reflect the ability of this species to adapt to the Mediterranean climate by preserving water during dry periods, which to a large extent can be attributed to stomatal closure at high relative water content levels, and low cuticular transpiration during these periods.     

地形因子对思茅松人工林土壤有机碳储量的影响

[目的]以思茅松人工中龄林为研究对象,探讨不同坡向、坡度和坡位对思茅松人工林SOC储量的影响,为精确评估思茅松人工林碳储量提供科学依据。[方法]对不同坡向、坡度和坡位不同土壤层次的SOC含量、全氮、土壤密度、C:N和SOC储量进行T检验和单因素方差分析,对不同土层的SOC储量和全氮、土壤密度、C:N之间进行Pearson相关分析。[结果]思茅松人工中龄林,SOC含量、全氮和C:N随着土层加深而减少,土壤密度随着土层加深而增加。不同的坡向和坡度显著影响SOC储量大小,阳坡的SOC储量要显著高于阴坡,坡度为20 30°的SOC储量要显著低于10 20°和0 10°,坡位对SOC储量大小无显著影响。在0 100 cm土层中,随着土层深度的增加,不同立地条件的思茅松人工中龄林的SOC储量呈减小趋势,不同坡向、坡位和坡度0 20 cm土层SOC储量均显著高于其它土层。坡向和坡度显著影响0 20 cm土层的SOC储量(P0.05);坡位对各层SOC储量均无显著影响(P0.05)。0 20 cm土层中SOC储量和土壤密度呈极显著负相关,和坡向、坡度呈显著负相关关系;除2040 cm土层外,其它土层的SOC储量与全氮之间呈极显著正相关;SOC储量和坡位与C:N在任一土层均无显著相关关系。[结论]立地条件差异影响SOC储量的大小与分布,尤其是坡向和坡度的不同会造成思茅松人工中龄林SOC储量的差异。     

Sand-fixing effects of Caragana microphylla shrub in Horqin sandy land, North China

In the semi-arid Horqin sandy land of north China, Caragana microphylla, a leguminous shrub, is the dominant plant species and is widely used in vegetation reestablishment programs to stabilize shifting sand. The sand-fixing effects of 6-and 11-year-old C. microphylla plantations were studied. The results showed that: 1) the wind velocity and sand transport rate in the plantation were less than those in dunes; 2) the air temperature in the plantation was lower than those in dunes. Relative humidity was higher and the soil temperature was lower, which benefits plant growth; 3) the physical and chemical characteristics of soil were improved to some extent over age. The porosity and percentage of tiny sand (diameter 0.05–0.1 mm) and clay particle (diameter < 0.05 mm) increased, bulk density in surface soil decreased, and saturated water-holding capacity improved. Organic C, total N, available N and available K content increased gradually, and soil fertility was enhanced. __________ Translated from Journal of Soil and Water Conservation, 2007, 21(1): 84–87 [译自: 水土保持学报]     

喀斯特断陷盆地不同植被恢复模式土壤水分动态变化

[目的]以喀斯特断陷盆地小流域中典型植被恢复模式,即桉树(Eucalyptus maideni)林、冲天柏(Cupressus duclouxiana)林、马尾松(Pinus massoniana)林以及天然次生灌丛、高盖度车桑子(Dodonaea viscosa)灌丛和低盖度车桑子灌丛为研究对象,探究断陷盆地不同植被恢复模式土壤水分时空变异规律,为该地区植被生态恢复工作提供参考。[方法]利用自动气象观测系统和土壤水分传感器同步监测2016年5月—2017年4月期间小流域降雨量与各林地土壤水分,采用变异系数与克里金插值分析方法,对6种植被恢复模式林地的土壤水分时空异质性以及持续干旱条件下土壤水分衰减特征进行研究。[结果]表明:(1)同一植被类型不同土层雨季和旱季土壤体积含水量垂直变化趋势相同,且雨季土壤水分含量显著高于旱季(P0.05),均为中等变异(Cv:12.88%28.66%)。(2)同一乔木林雨季和旱季的土壤活跃层与次活跃层垂直分布不同,但同一灌丛雨季和旱季分布相同。(3)6种植被恢复模式土壤体积含水量均在降雨量较充足的8—9月达到最大值,其变化范围介于26.25%44.08%之间,在降雨量明显不足的3—4月达到最小值,土壤体积含水量介于9.48%17.47%之间。(4)3种乔木林0 30 cm土层、3种灌丛0 10 cm土层充分降雨后约10 d土壤水分恢复为降雨前1 d水平,低盖度和高盖度车桑子灌丛10 30 cm土层土壤水分降雨后15 d恢复为降雨前1 d水平,并且接近植物萎蔫系数。[结论]不同植被恢复模式间雨季、旱季和月均土壤体积含水量均表现为桉树林天然次生灌丛冲天柏林马尾松林高盖度车桑子灌丛低盖度车桑子灌丛。喀斯特断陷盆地季节性干旱和临时性干旱问题严峻,乔木林和灌丛经充足降雨,达到田间持水量后,在连续放晴天气下林地土壤水分可供植物10 15 d的消耗。     

闽楠天然次生林自然更新的影响因子研究

[目的]分析闽楠天然次生林自然更新与环境因子之间的关系,为其科学经营及保护提供参考依据。[方法]以江西省吉安市闽楠天然次生林为研究对象,通过标准地调查获取数据,运用多元数量化模型I建立闽楠幼树幼苗重要值与环境因子的关系模型,采用单因素方差分析单个环境因子对闽楠幼树幼苗更新的影响。[结果]研究表明:密度(闽楠下种母树株数、郁闭度、株数密度)、坡位、腐殖质层厚度、坡向、林下植被盖度、凋落物层厚度是影响闽楠天然次生林自然更新的主要因素,偏相关系数在0.325 7 0.715 7之间,t检验结果为极显著或显著;模型复相关系数为0.966,F检验结果为极显著(F=30.96~(**))。[结论]闽楠下种母树株数对其幼树幼苗的更新起着最主要的作用,而郁闭度与株数密度过高或过低、凋落物层越厚、腐殖质层越薄、林下植被盖度越大均不利于其自然更新,同时,半阴坡、下坡位条件下的闽楠幼树幼苗的更新好于其它坡向与坡位。为促进闽楠幼树幼苗的自然更新,林分中闽楠下种母树应保留200株·hm~(-2)以上,以及对郁闭度、林下植被盖度及凋落物层厚度等实施相应的调控措施。     

Spatial pattern of a plant community in a wetland ecosystem in a semi-arid region in northwestern China

The spatial distribution characteristics of plant communities in a wetland-dry grassland ecosystem in arid and semi-arid regions in northwestern China and the main factors affecting the distribution pattern were studied. The Siertan wetland in the Haba Lake Nature Reserve was the study area. Four transect lines, each about 1 km long, were set up in the growing season along the biotope gradient in four directions: east, northeast, west and northwest. Attributes measured include frequency of occurrence, height, density, coverage, biomass and environmental soil factors. The data were analyzed using a two-way indicative species analysis (TWINSPAN), detrended correspondence analysis (DCA) and Spearman correlation coefficients. On this basis, the vegetation in the Siertan wetland was classified into three types and 14 associations. The first vegetation type was halophytic marsh vegetation, mainly distributed in the wetland zone. This type largely contains halophyte and hygric plants and its representative association is Phragmites communis + Kalidium foliatum. The second type was meadow vegetation, distributed in the ecotone. The meadow vegetation species are mainly mesophytic and their representative association is Nitraria tangutorum + Pennisetum flaccidum. The third vegetation type is grassland vegetation, which mainly consists of mesophytic and xerophytes, distributed in the arid grassland zone. The representative association of the third vegetation type is the association of Anaeurolepidium secalium + Saussurea runcinata. Correlation analysis between the axes of DCA and environmental soil factors shows that soil moisture content, organic matter, soil salt content and total nitrogen are the main environmental factors affecting the pattern of vegetation distribution along the biotope gradients from wetland to arid grassland. Other factors affecting the vegetation are microtopography and grazing pressure. Additionally, we have reported modifications and improvements to the importance value methodology. __________ Translated from Journal of Beijing Forestry University, 2008, 30(1): 6–13 [译自: 北京林业大学学报]     

Soil desiccation for Loess soils on natural and regrown areas

In the Loess Plateau, soil desiccation has become a serious problem for forest and grass vegetation. Soil desiccation leads to the formation of a dried soil layer (DSL). This paper presents the results of research carried out in the central part of the Loess Plateau. The objective of the research was to produce a statistically supported set of indicators for evaluating soil desiccation of forestlands, to present a heuristic idea for soil desiccation and to supply scientific support for replacing farmland with forest or grass in the Loess Plateau and other regions of China. Here, we suggest that more attention should be paid to soil desiccation and its effects on the ecosystem of the region in the future. The results showed that natural Quercus liaotungensis forestlands (NQF) retained more water content than regrown Robinnia pseudoscacia forestlands (RRF). Significant DSLs were formed in the RRF but not in the NQF. A possible reason for no formation of DSL in NQF could be due to the presence of an arbor–shrub–herb stand structure and large humus and litter accumulation, which increased the natural forest's (NF) adaptability to the environmental conditions. Soil water content in the north-facing slope was significantly larger than in the south-facing slope. DSLs formed in the 0–500 cm layer of the south-facing slope. When slope gradient was greater than 25°, soil water content deceased sharply and showed significant difference compared with 9°, 15° and 20° (P < 0.05). So, we conclude that plant species, aspect and slope angle could be the predicators for the formation of DSLs. The analysis on soil physical properties of 0–60 cm layer indicated that plant species, aspect and slope angle also have significant effects on bulk density, porosity, plant-available capacity, and hydraulic conductivity, especially in the 0–20 and 20–40 cm layers. In the NQF and RRF with north-facing slope, soil physical properties were improved.     

Plant community characteristics and their relationships with climate in the Hexi Corridor region of northwestern China

Species, coverage, density, appearance, important values and above ground biomass of desert plant communities in the Hexi Corridor region in northwestern China were investigated. Data on the meteorological factors at the investigation sites were collected. Their relationships were statistically analyzed. The results show that the composition of plant species and total density in the Hexi Corridor region are positively correlated with elevation and longitude, but negatively with latitude. The relation decreases from the southeast to the northwest in this region. In the desert regions with an accumulated temperature of >10°C greater than 3200°C, the shrubs, including semi-shrubs, occupy dominant positions in the communities. Their importance values reach 100. When the accumulated temperature is about 3000°C, the communities are often in some type of transition, either with herbage being the dominant species, with some semishrubs or shrubs as companion species, or the dominant species being semi-shrubs with some perennial herbage as companion species. In desert communities with an annual precipitation of over 110 mm, the main life forms of plants are semi-shrubs or perennial herbs. When precipitation is less than 110 mm, the main life forms of the vegetation are dwarf shrub or annual herbs. In the extreme arid regions with annual precipitation of around 50 mm in the northwestern part of the Hexi Corridor, barely some annual herbage come to life during the rainy season. Desert ecosystems consist of sparse vegetation with small biomass. They change with climate factors and are especially sensitive to precipitation, which is particularly important for their conservation. __________ Translated from Acta Botanica Boreali-Occidentalia Sinica, 2007, 27(5): 859–863 [译自: 西北植物学报]     

Characteristics of soil water consumption of typical shrubs (Caragana microphylla) and trees (Pinus sylvestris) in the Horqin Sandy Land area, China

Reforestation is one of the most effective ways to reduce the impacts of desertification. Caragana microphylla Lam. and Pinus sylvestris var. mongolica Litrin have been widely used to stabilize shifting sands in the Horqin sandy land area since the 1980s. However, soil water depletion has been of major concern in C. microphylla and P. ongolica plantations and in many places current soil moisture cannot meet the demand of growing plants. To determine the water budget of C. microphylla and P. mongolica plantations, we studied the effect of plantations on soil moisture and assessed the evapotranspiration in plantations of both species. Investigations were conducted at a fenced plot at Wulanaodu (42°29′N, 119°30′E, 479 m a. s. l), located at the western edge of the Horqin Sandy Land area in Inner Mongolia, northern China. Five year old C. microphylla and seven year old P. mongolica plants were selected from the plantations and transplanted to iron boxes (400 cm×200 cm×120 cm) which can drain extra water. Plant spacing of 1 m×1 m was applied to P. mongolica, and two plant spacings of 1 m×1 m and 1 m×2 m to C. microphylla. The transplanted plants grew for two years in the boxes. Soil moisture from soil surface to a depth 80 cm were measured at 20 cm intervals in boxes every 10 d (2004) or 3 d (2005) during the growing season with a TDR water meter. The evapotranspiration was estimated from a mathematical formula and the characteristics of soil water consumption and evapotranspiration of these two plantations were analyzed. The soil water of P. mongolica was more than that of C. microphylla at the same 1 m×1m spacing. The soil water of C. microphylla with the 1 m×2 m spacing was more than that of the 1 m×1 m spacing. The evapotranspiration ranged from high to low as follows: C. microphylla (1 m×1 m), C. microphylla (1 m×2 m) and P. mongolica (1 m×1 m) during the growing seasons. The evapotranspiration of individual plants ranging from high to low was C. microphylla (1 m×2 m), C. microphylla (1 m×1 m), and P. mongolica (1 m×1 m) during the growing season. C. microphylla grown for five year consumed more water than P. mongolica grown for seven years at the same spacing. __________ Translated from Acta Ecological Sinica, 2008, 28(5): 1981–1990 [译自: 生态学报]     

不同立地条件对飞播成苗的影响

以商洛市飞播林地为对象,通过调查、分析,研究了植被盖度、土壤类型和坡向对飞播造林成苗效果的影响,结果表明,不同植被盖度、土壤类型和坡向分别都会对飞播成苗面积比例和成苗地幼苗密度造成影响,植被盖度0.3～0.7,沙壤土和阴坡地的飞播造林成苗效果最好,它们二者在植被盖度为0.3～0.7时,分别是28.28%和2175株·hm-2,在沙壤土分别是32.6%和2631株·hm-2,阴坡地分别是38.5%和2 424株·hm-2;为取得最好的飞播效果,应选择一定的植被盖度范围、土壤类型和坡向。     

Effect of freezing-thawing on nitrogen mineralization in vegetation soils of four landscape zones of Changbai Mountain

• Introduction   

We studied the effect of freezing-thawing on nitrogen (N) mineralization of four vegetation soils from typical vegetation zones of Changbai Mountain with a laboratory incubation experiment. The soils were treated with two levels of soil water content, representing the low and high soil water contents found during late autumn and early spring in Changbai Mountain, respectively, and underwent cycling of freezing at −5 or −25°C and thawing at 5°C up to 15 times.     

Division of afforestation site type in the watershed of Wangjiagou, West Shanxi through GIS

Using quantification theory I, an analysis of the relation of soil water and qualitative factors, such as, slope degree, slope aspect, slope position, and soil in Wangjiagou watershed area has been done. The study aims to quantify the factors influencing soil water, the descending order of the factors being the slope aspect, soil, slope degree, and slope position, thereby scientifically facilitating division of afforestation site types and afforestation site products digitally on geographical information system (GIS). __________ Translated from Journal of Northwest Forestry University, 2006, 21(3): 184–188 [译自: 西北林学院学报, 2006, 21(3): 184–188]     

Understory plant diversity assessment of <Emphasis Type="Italic">Eucalyptus</Emphasis> plantations over three vegetation types in Yunnan,China

Biodiversity in managed plantations has become an important issue for long-term sustainability of ecosystems. The environmental effects of plantations comprised of fast-growing introduced trees have been vigorously debated. On one hand, monocultures have been said to exhaust resources, resulting in decreased biodiversity. Conversely, it has been stated that monocultures may favor regeneration of undergrowth plants from surrounding forests, increasing biodiversity. In order to clarify the effects of planting Eucalyptus trees on species composition, diversity, and functional type of understory vegetation in Yunnan province, a field trial was implemented to compare Eucalyptus plantations (EPs) with two other local current vegetation types (secondary evergreen forests (SEs), and abandoned farmlands (AFs)). Each vegetation type was sampled in each of three elevational ranges (low = 1,000–1,400 meters above sea level (masl), medium = 1,400–1,800 masl, and high = 1,800–2,200 masl). Sample sites within each elevational range had similar environmental characteristics (slope, aspect, etc.). Thus, we sampled three vegetation types at each of three sites at each of three elevations for a total of 27 plots. We calculated relative abundance and importance value of species and diversity indexes to evaluate differences among local current vegetation types and elevational ranges, employing multivariate ordination analyses and other methods such as Analyses of Variance (ANOVA) and Indicator Species Analysis. We found that fast growing introduced Eucalyptus plantations led to reduced plant diversity in the study area, and that rare or threatened species were recorded almost exclusively in the SE plots, being essentially absent from the EP and AF plots. The understory plant diversity did not correlate with the altitude gradient significantly. Eucalyptus plantations (EPs) have a simpler community structure than that of either secondary evergreen forests (SEs; similar to natural state) or abandoned farmlands (AFs). No variable significantly explained variation of the understory shrub layer, but soil moisture-holding capacity and overstory coverage were significant in explaining variation of the understory herb layer, suggesting that the study of soil physical properties is necessary for better understanding of their importance in Eucalyptus plantations and other local current vegetation types.     

A weeding-duration model for <Emphasis Type="Italic">Larix kaempferi</Emphasis> plantations in Hokkaido,northern Japan

In this study, a weeding-duration model for Larix kaempferi plantations was developed that employs a generalized linear model. The number of years that weeding is necessary is the response variable, and elevation, slope, maximum snow depth, annual precipitation, geological type, soil type, site index, slope aspect, and vegetation type are explanatory variables. Among the explanatory variables, geological type, soil type, slope aspect, and vegetation type are categorical data. We assumed a Poisson distribution for the response variable. The link function was log. Among the models that could be developed from these variables, we chose the model with the smallest Akaike’s information criterion (AIC). The weeding-duration model can be written as follows: years that weeding is necessary = Exp (−0.0172833 × site index + 0.0014053 × maximum snow depth (cm) + 1.7417731). The results of this study imply that weeding of Larix kaempferi plantations is needed for more years as the maximum snow depth increases and fewer years as the site index increases. This model is useful for cost–benefit analyses of afforestation or reforestation with Larix kaempferi.     

Factors affecting distribution of microbiotic crusts in the grain-for-green land of the loess region, northern Shaanxi, China

A field survey was conducted in the grain-forgreen land of the loess region, northern Shaanxi, China, from July to August of 2005 to provide a scientific evaluation of the grain-for-green project, including its soil and water conservation and other ecological benefits for the region. The distribution of microbiotic crusts were studied, while human disturbance, aspect, topography, vegetation structure and other factors affecting it were obtained from the analysis of survey data from 78 sample plots. Results show that crust coverage is larger on less-disturbed plots than on highly-disturbed ones, on north-facing plots than on south-facing ones and on gully-slopes than on ridge-slopes. Coverage increases with herbal coverage and trees can provide better conditions for distribution of crusts than shrubs. Therefore, crust coverage is larger in herb-dominated plots than in tree-dominated ones and crusts in shrub-dominated plots are smaller. However, we made no progress in our study on deciding how slope degrees and herb species affect the distribution of crusts. We believe that more studies are necessary for a further exploration of the relationship between them. __________ Translated from Journal of Beijing Forestry University, 2007, 29(1): 102–107 [译自: 北京林业大学学报]     

Effects of water stress on water use efficiency and water balance components of <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis> and <Emphasis Type="Italic">Caragana intermedia</Emphasis> in the soil–plant–atmosphere continuum

Hippophae rhamnoides (Sea buckthorn) and Caragana intermedia (Intermediate peashrub), which are nitrogen-fixing and perennial temperate shrubs, are extensively used in the agroforestry systems in the loess areas of China. In this study, artificially controlled water gradient experiments were carried out with both shrubs, based on four levels of water supply (normal precipitation, slight drought, drought, and extreme drought). The results showed significant impacts of drought on net photosynthesis rate, biomass accumulation, and biomass allocation in both species. Water use efficiency (WUE) varied with different species, scales, and water stress intensities. WUE at the leaf scale (WUEi) was highest under moderate water stress, while the WUE at the community scale (WUEb) decreased with increasing water stress. We observed alteration in the diel and seasonal transpiration of both species in response to water stress. The night-time transpiration accounted for a small but significant proportion of the water balance, and its importance tended to increase with increasing drought. Both species experienced water deficits under all treatments. Soil moisture of H. rhamnoides declined more severely than that of C. intermedia. The ratio of transpiration to evapotranspiration (T/ET) ranged from 50 to 80% for both species in the growing season. The T/ET and WUEi of H. rhamnoides were comparatively smaller under severe water stress but increased under moist conditions. Our data suggest that H. rhamnoides uses water resources more efficiently under favorable water conditions, and C. intermedia shows competitive advantages under drought conditions. Moreover, possible strategies to maintain water balance in the water-limited agroforestry systems are discussed.     

沙丘不同部位中间锦鸡儿人工林土壤养分特性及植物群落特征

以青海共和盆地沙丘上12年生的中间锦鸡儿人工林为研究对象,并以流动沙丘为对照,探讨在沙丘上建立中间锦鸡儿人工林后,沙丘部位对土壤养分含量以及植物群落的影响。在中间锦鸡儿人工林内沙丘的迎风坡中部、坡顶、背风坡中部和流动沙丘采集土壤样品,深度为0 5,5 10,10 20和20 50 cm。结果表明:与流动沙丘相比,沙丘3个部位中间锦鸡儿人工林0 20 cm的有机质、0 50 cm的全氮和全磷含量得到显著提高。迎风坡中间锦鸡儿人工林0 5 cm深度的土壤有机质和全氮、0 20 cm深度的全磷含量显著高于坡顶和背风坡。在沙丘上建立中间锦鸡儿人工林后,草本植物种类、数量和植被盖度增加,迎风坡草本植物盖度明显高于坡顶和背风坡。     

Factors affecting transpiration of Pinus tabulaeformis in a semi-arid region of the Loess Plateau

The effects of soil water and meteorological factors affecting transpiration of Pinus tabulaeformis were studied under different levels of soil water content to offer a scientific basis for increasing efforts in afforestation survival and management of soil water in forested land. Under artificial control methods for soil water and potting experiments, the transpiration rate (T _r) of P. tabulaeformis and environmental factors were measured using a portable steady porometer (Li-1600) and a speedy weight method (BP-3400) during a representative fine day in the growing season of 2004. The results indicated that the diurnal course of T _r and R _st of P. tabulaeformis displayed a double-peaked curve and a “W” curve under different levels of soil water content. Given a representative fine day, the T _r could be represented as a cubic relation with soil water content (SWC). The SWC which caused maximum T _r values of P. tabulaeformis was 17.7%, 19.8%, and 17.5% in July, August and October respectively. T _r was affected not only by physiological characteristics, but also by SWC and meteorological factors. T _r was significantly correlated with meteorological factors when the soil water was sufficient, but this correlation would decrease under conditions of serious water stress. Under such stress conditions, air temperature was the primary factor to affect T _r in July and August and photosynthetically active radiation (PAR) was the primary factor in October. When soil water is sufficient, the main factors affecting T _r were relative humidity (RH), air temperature (T _a) and leaf temperature (T _l) in July, August and October respectively. __________ Translated from Science of Soil and Water Conservation, 2007, 5(1): 49–54 [译自: 中国水土保持科学]     

Transpiration and canopy conductance of Caragana korshinskii trees in response to soil moisture in sand land of China

Caragana korshinskii is widely used in vegetation reestablishment programs to stabilize the shifting of sand on the Loess Plateau. This sand shifting of sand exerts pressure on the limited soil water and vice versa. However, detailed transpiration and sap flow studies that focus on water use in these stands remain limited. The hourly sap flows, along with successive soil water balance and meteorological measurements, on three trees were measured using the thermal heat balance method during the growing season period. Results showed that the midday sap flow and stand transpiration were significantly lower during the stress period (from May to July) compared with those at the beginning of August concurrently with high soil water content. The heat balance measurements underestimated the transpiration obtained from the soil water balance method. When the tree conductance was fitted with climatic variables and soil water content, the canopy conductance increased exponentially with above-canopy radiation, whereas it decreased logarithmically with decreasing vapor pressure deficit. In the absence of water stress, the tree conductance was unchanged when the relative extractable water remained above 0.4, whereas the conductance decreased linearly after the wilting point. The model was generally well fitted to the measured transpiration data in terms of the response during the dry and rainy seasons, thus demonstrating the feasibility of developing a quantity schedule for C. korshinskii transpiration on the Loess Plateau in the presence of a soil water stress.