中国金色藻属四个新记录种的超微结构研究

金色藻属Chrysochromulina的种类是海洋浮游植物的重要组成成分。报道了该属在我国的4个新记录种,即盅鳞金色藻Chrysochromulina cymbium Leadbeater ＆ Manton、毛刺金色藻C hirta Manton、粗柱金色藻C,megacylindra Leadbeater和普氏金色藻C pringsheimii Parke ＆ Manton,并在电子显微镜下观察了细胞的超微结构。     

Ultrastructure of Haller's organ in the tick Amblyomma americanum (L.)

Summary Haller's organ on the tarsus of the tick Amblyomma americanum (L.) (Acarina: Ixodidae; nymphal stage) was studied by scanning and transmission electron microscopy. It consists of a distal bristle group, (the anterior pit), and a proximal capsule which encloses several sensilla. The seven sensilla of the anterior pit (A1–A7) are all thick-walled and multi-innervated (2–9 neurons), but at least three different types can be differentiated. Sensilla A1 and A2 possess large, plugged pores (>1000 Å) and are the only sensilla with branching dendrites. A3 and A5 are characterized by a spoke-wheel arrangement of the cuticle wall and very fine pores (100–200 Å) penetrating the spokes centrally; A4, A6, and A7 do not exhibit any pore system but a single opening at the bristle tip is assumed.The capsule contains seven thin-walled, blunt-tipped sensilla, and several non-sensory cuticular projections (pleomorphs). All of these sensilla possess large plugged pores in the cuticle wall and numerous dendritic branches of several neurons (3–5) in the lumen. Glandular openings were found inside the capsule; their significance is discussed.The fine structure of Haller's organ supports the functions postulated by Lees (1948), namely olfaction for the capsule and humidity reception (among others) for the anterior pit.This research was supported in part by the Office of Naval Research, and by NIH Training grant ES 00069. Paper no. 3459 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh.     

Ultrastructure of prostomial photoreceptors in four marine polychaete species (annelida)

The photoreceptors of four polychaete species were investigated by transmission electron microscopy: Eteone longa and Anaitides mucosa (Phyllodocidae), Scolelepis squamata (Spionidae), and Heteromastus filiformis (Capitellidae). Four different types of light-sensitive organs could be distinguished: 1) a simple, unpigmented rhabdomeric type; 2) a simple ocellus composed of a sensory and a pigmented cell; 3) complex eyes with a lens consisting of secretory granules; 4) a simple, unpigmented type with modified cilia. In spite of its simpler organization the fourth type is listed last, because its function as a photoreceptor seems dubious. The first type (unpigmented rhabdomeric receptor) occurs in all four species investigated. It is the only type of photoreceptor in Heteromastus. Additionally, the two phyllodocids Eteone and Anaitides possess another kind of receptor (type 4) in close proximity to the type 1 receptor. Simple ocelli (type 2) are found in Scolelepis. A pair of complex eyes (type 3) is present in both Eteone and Anaitides, but they show important differences in the two species. First, the eyes in Eteone exhibit ciliary rudiments within the sensory processes, but such rudiments are absent in the eyes of Anaitides. Secondly, the sensory cells in Anaitides possess pigment granules, whereas in Eteone they do not. Thirdly, the lens in Eteone is composed of secretion granules of equal electron density, whereas in Anaitides the lens granules show increased electron density centrally. Lens material appears to be secreted from a single corneal cell in Eteone, and from several corneal cells in Anaitides. In both species these corneal cells are located distally outside the lens.     

Relative influence of fisheries and climate on the demography of four albatross species

Worldwide ecosystems are modified by human activities and climate change. To be able to predict future changes, it is necessary to understand their respective role on population dynamics. Among the most threatened species are top predators because of their position in the food web. Albatross populations are potentially affected by both human activities, especially longline fisheries, and climatic fluctuations. Based on long‐term data (1985–2006), we conducted through a comparative approach a demographic analysis (adult survival and breeding success) on four albatross species breeding on the Indian Ocean sub‐Antarctic Islands to assess the relative impact of climate and fisheries during and outside the breeding season. The study revealed that adult survival of almost all species was not affected by climate, and therefore probably canalized against climatic variations, but was negatively affected by tuna longlining effort in three species. Breeding success was affected by climate, with contrasted effects between species, with Southern Oscillation Index having an impact on all species but one. Differences in demographic responses depended on the foraging zone and season. In order to predict population trajectories of seabirds such as albatrosses, our results show the importance of assessing the relative influence of fishing and climate impacts on demography.     

Ultrastructure of the tongue and anterior process of the sublingual plica in four species of venomous snakes

The general histology and ultrastructure of the tongue and anterior process of the sublingual plica of four Taiwanese venomous snakes, the Chinese cobra (Naja naja atra), banded krait (Bungarus multicinctus), Taiwan habu (Trimeresurus mucrosquamatus), and bamboo snake (Trimeresurus stejnegeri stejnegeri) are described. The tongue fork exhibits a mid-dorsal invagination that broadens gradually toward its base. No mid-ventral invagination is observed. The epithelial cells on both dorsal and ventral aspects of the tongue fork have large and small microfacets, micropores and microvilli. The cell size, distribution pattern of the large microfacets, and the number of small microfacets present on both sides of the fork are essentially the same within a species, but vary among species. The function of these ultrastructures on the cell surface might be for the capture of chemical substances. The large microfacets are raised areas of the cell membrane, each with a pale granule contained within. The chemical nature of the pale granule is not yet known. The small pores surrounding the large microfacets are shallow hollows left after the release of the pale granules from the microfacets. The basic histological pattern of the tongue fork of these species is similar, being composed of a mucosal layer outside and dense musculature inside. No taste buds are discernible. The anterior processes are concave-like expansions of the anteriormost portions of the sublingual plicae. The oblique folds and micropapillae of this organ might be helpful for receiving the chemicals collected on the tongue, when the tongue makes contact with the elevated processes. The elevated processes may penetrate the ducts of Jacobson's organs to effect the final transfer.     

The influence of rainfall on diet and reproduction in four African rodent species

Arvicanthis nitoticus was found, during two seasons of the study, to begin breeding some two to three months after the start of the rains; at this time weed seeds first appeared in the stomach contents. Breeding continued during the rains and into the early part of the dry season while weed seeds and cereals formed the major part of the diet. Breeding declined during the early part of the dry season, and fat was laid down while weed seeds and cereals were still present but less abundant in the diet. Later in the dry season, breeding ceased and the diet was switched dramatically, first to the leaves and stems of dicotyledonous plants then almost exclusively to grass, and fat deposits were rapidly utilized. Arvicanthis living in an area where cereals were artifically supplied bred almost continuously. Mastomys natalensis also bred when seeds and cereals were most plentiful, but, by ranging widely over open ground, often managed to continue to find these foods, and insects, during the dry season. Supplied cereals failed to produce a reproductive response in Mastomys –instead, unprecedented fat deposits developed. Unseasonal reproduction in this species was, however, observed in an unseasonal wheat crop. Rhabdomys pumilio bred when cereals were plentiful but was also found breeding when its diet was mainly clover–a crop that is noted for its high crude protein content. The herbivorous Otomys angoniensis bred throughout the year and was unaffected by supplied cereals. It seems clear that the food supply of grani-vorous species is dependent on rainfall, and that prolongation of the normal rainy season may generate excess food and cover, resulting in and extended breeding season and unusually large numbers of these rodents.     

Ultrastructure of the synganglion in the larval tickAmblyomma americanum (Ixodoidea: Ixodidae)

The synganglion in the larvalAmblyomma americanum consists of a ganglionic mass pierced by the oesophagus. The nervous tissue consisting of an outer cortex and an inner neuropile is surrounded by an external neurilemma. The cortex comprises perineurium glial cells and neurosecretory and non-neurosecretory neuronal cell bodies. The neuropile consists of nerve fibres ensheathed by glial cells. The entire ganglionic mass is enclosed within a sinus of the circulatory system. No investigations using electron microscopy appear to have been made on the synganglion in the tick larval stage.     

Comparison of differentially expressed genes in the salivary glands of male ticks,Amblyomma americanum and Dermacentor andersoni

Genes expressed differentially in the salivary glands of unfed and fed male ticks, Amblyomma americanum (L.), were identified, cloned and sequenced, and some were compared with those expressed in the salivary glands of Dermacentor andersoni. Total protein and RNA increased sixfold in the salivary glands of fed male A. americanum, while in fed male D. andersoni salivary glands, RNA increased approximately 3.5 times. Feeding D. andersoni in the presence of females increased total RNA by 25% over those fed in the absence of females. Complementary DNAs were synthesized from RNA obtained from unfed and fed ticks and amplified using RNA arbitrarily primed polymerase chain reaction (RAP-PCR) with three different primers in separate reactions. Differential display showed clear banding differences between the fed and the unfed ticks in A. americanum and D. andersoni. Sixty-one cDNA fragments that appeared to be from differentially expressed genes in A. americanum were isolated, cloned and sequenced. Hybridization reactions with labeled cDNA probes confirmed the differential expression of many of the genes in unfed and fed ticks' salivary glands; however, many of the bands contained more than one fragment and some of the fragments isolated from apparently differential bands were not specific. Sequences for 28 of the cDNA fragments (150-600 nucleotides in length) demonstrated similarity to genes in the databases, but nine of these were similar to sequences of unknown function. Some of the gene fragments identified may be important to tick feeding or tick salivary gland physiology, including a histamine-binding protein, an organic ion transporter, an apoptosis inhibitor, a cathepsin-B-like cysteine protease, proteins involved in gene regulation and several proteins involved in protein synthesis. Cross-hybridization of identified cDNAs from A. americanum with cDNA probes synthesized from D. andersoni total RNA did not show significant similarity between the two species.     

Ultrastructure and wear patterns of the ventral epidermis of four snake species (Squamata,Serpentes)

Snakes are limbless tetrapods highly specialized for sliding locomotion. This locomotion leads to the skin being exposed to friction loads, especially on the ventral body side, which leads to wear. It is presumed that snakes therefore have specific optimizations for minimizing abrasion. Scales from snakes with habitat, locomotor and/or behavior specializations have specific gradients in material properties that may be due to different epidermal architecture. To approach this issue we examined the skin of Lampropeltis getula californiae (terrestrial), Epicrates cenchria cenchria (generalist), Morelia viridis (arboreal), and Gongylophis colubrinus (burrowing) with a focus on (i) the ultrastructure of the ventral epidermis and (ii) the qualitative abrasion pattern of the ventral scales. Scanning and transmission electron microscopy revealed variations in the structure, thickness, layering, and material composition of the epidermis between the species. Furthermore, SEM and white light interferometer images of the scale surface showed that the abrasion patterns differed, even when the snakes were reared on the same substrate. These data support the idea that (i) a specific gradient in material properties may be due to a variation in epidermis architecture (thickness/ultrastructure) and (ii) this variation may be an optimization of material properties for specific ways of life.     

The influence of water level fluctuations on the growth of four emergent macrophyte species

The influence of the amplitude of cyclic water level fluctuations on the growth of four species of emergent macrophyte (Cyperus vaginatus, Phragmites australis, Triglochin procerum and Typha domingensis) was studied in a controlled, pond-based experiment. The amplitudes of water level fluctuations were static, ±15, ±30 and ±45 cm, each cycling over a forty-day period. In all treatments the water level fluctuated around an initial water depth of 60 cm. Within each amplitude treatment, plants were grown at three elevations with the sediment surface at 20, 40 or 60 cm. Only T. domingensis and P. australis showed a significant response to amplitude. Biomass of T. domingensis was similar in the static, ±15 and ±30 cm amplitude treatments but dropped by ca. 52% when grown in amplitudes of ±45 cm. In contrast, the largest biomass for P. australis occurred in the ±30 cm amplitude treatment suggesting this species prefers moderately fluctuating water levels. The response of P. australis to amplitude was contingent upon elevation with plants growing in the ±45 cm amplitude, low elevation treatment having particularly low biomasses. C. vaginatus biomass increased with increasing elevation but did not respond to amplitude while T. procerum did not respond to either amplitude or elevation likely due to the ability of the species to photosynthesise under water. The relative growth rate and the average emergent surface area were logarithmically related in C. vaginatus suggesting flooding of the photosynthetic canopy was limiting the ability of this species to acquire atmospheric carbon. No clear relationship was found for T. domingensis or P. australis indicating that a factor other than access to atmospheric carbon was restricting the growth of these species.     

Synanthropic birds influence the distribution of Borrelia species: analysis of Ixodes ricinus ticks feeding on passerine birds

Ixodes ricinus ticks collected from 835 birds and from vegetation in the Czech Republic were analyzed. Host-seeking ticks (n = 427) were infected predominantly by Borrelia afzelii (25%). Ticks (n = 1,012) from songbirds (Passeriformes) were infected commonly by Borrelia garinii (12.1%) and Borrelia valaisiana (13.4%). Juveniles of synanthropic birds, Eurasian blackbirds (Turdus merula) and song thrushes (Turdus philomelos), were major reservoir hosts of B. garinii.     

4个观赏竹种的光合特性及其影响因子分析

本研究以白纹阴阳竹( Hibanobambusa tranquillans f. shiroshima H. Okamura )、鼓节竹( Bambusa tul doides‘Swolleninternode')、花秆早竹( Phyllostachys violascens f. viridisulcata P. X. Zhang et W. X. Huang)和美丽箬竹(Indocalamus decorus Q. H. Dai)4个观赏竹种为供试材料,分析了各竹种的光响应和CO2响应曲线及参数、光合和气体交换参数以及相关环境因子的日变化规律,并通过相关性分析、逐步多元回归分析和通径分析探讨了影响4个竹种叶片净光合速率( Pn)的主要因子。测定结果表明：随光合有效辐射强度( PAR)或胞间CO2浓度( Ci)的提高,各竹种叶片的Pn值均逐渐增大,但增幅有一定差异;各竹种的光响应和CO2响应参数均有较大差异,其中,白纹阴阳竹叶片的表观量子产量( AQY)最低,CO2饱和点( CSP)和CO2补偿点( CCP)也较低,其他参数均最高;而花秆早竹叶片的AQY和CCP值均最高,而其他参数总体上均最低。4个竹种的光合及气体交换参数日变化曲线均有一定差异;美丽箬竹叶片Pn值日变化曲线呈“双峰型”;白纹阴阳竹、鼓节竹和花秆早竹叶片的Pn值日变化曲线均呈“单峰型”,峰值分别出现在14：00、10：00和12：00;总体上看,4个竹种叶片的气孔导度( Gs)、Ci、蒸腾速率( Tr)和水分利用效率( WUE)总体上具有相似的日变化趋势。分析结果表明：按照总影响效应由高至低进行排序,对白纹阴阳竹叶片Pn值的主要影响因子为PAR、Tr、大气CO2浓度( Ca)、Ci,对鼓节竹叶片Pn值的主要影响因子为PAR、Tr、Ca、Gs,对花秆早竹叶片Pn值的主要影响因子为PAR、Tr、Gs、气温( Ta)、Ci,对美丽箬竹叶片Pn值的主要影响因子为PAR、空气相对湿度( RH)、Ta、Ca、Tr、Gs。综合分析结果显示：4个竹种中,白纹阴阳竹光合能力最强,但对弱光的适应和利用能力较弱,CO2同化能力强且适应范围广;鼓节竹和美丽箬竹对光和CO2的利用能力和适应范围均居中;花秆早竹光合能力和CO2同化能力最差,但对弱光的适应和利用能力较强,CO2适应范围较窄。     

Ultrastructure of spermiogenesis and spermatozoa of four Oriopsis species (Sabellinae, Sabellidae, Polychaeta)

The ultrastructure of sperm from four species of Oriopsis is described. Males of Oriopsis bicoloris produce sperm with an elongate nucleus divided into four rods, connected proximally, and four long mitochondria lying along the nucleus. The axoneme runs in the middle of the nuclear and mitochondria1 rods. Oriopsis brevicollaris males have sperm with an elongate nucleus and long midpiece comprised of four mitochondria wrapped around the axoneme. Males of O. mobilis have sperm with an elongate nucleus and long midpiece similar to that of O. brevicollaris , although the midpiece is much longer. Oriopsis dentata males havc sperm with a flattened head, similar to those of mammals, though the midpiece is simple and the axoneme free. The variability of reproductive mechanisms within the Polychaeta is discussed with reference to the elucidation of the function of various sperm morphologies. The implications for the taxonomy and systematics of Oriopsis , and the Sabellidae as a whole, are also discussed. It is concluded that Oriopsis is not monophyletic and examination of reproductive structures in other small sabellids is required. Study on reproduction in the type species, O. armandi , is needed to establish the reproductive method of Oriopsis and so allow revision of this genus.     

The influence of season on adenine nucleotide concentrations and energy charge in four marsh plant species

Unilateral pulse ultraviolet irradiation caused positively phototropic coiling (> 180°) and curvature (≤ 180°) in the growth zone of dark-grown broom sorghum ( Sorghum bicolor Moench, cv. Acme Broomcorn and Sekishokuzairai Fukuyama) first internodes. Coiling was induced by irradiation at 257 to 302 nm, and proceeded to develop almost linearly during 72 h or more involving new tissue produced after irradiation. Curvature, caused at 308 to 413 nm and by red light, developed rapidly during the first several hours then slowly to cease by about 24 h, and did not surpass 120° even at the optimum photon fluences. Action spectra were higher towards shorter wavelengths, having a shoulder at about 287 nm, and could not separate the two photoresponses. The curvature was partially but markedly suppressed by far-red following the ultraviolet irradiation, whereas the coiling was not affected. Possible involvement of a specific UV-B photoreceptor and phytochrome in curvature and of a UV-C photoreceptor in coiling is discussed.     

Ultrastructure and phylogenetic relationships of the unicellular green algae Ignatius tetrasporus and Pseudocharacium americanum (Chlorophyta)

The phylogenetic relationships of two unicellular green algae, Ignatius tetrasporus Bold et MacEntee and Pseudocharacium americanum Lee et Bold were investigated by ultrastructural and molecular methods. The zoospores from both species were covered neither by scales nor cell walls. The flagellar apparatus of the zoospores commonly included these features: the upper basal bodies were displaced counterclockwise in half to two‐thirds of the basal body diameter and did not overlap with each other; the lower basal bodies were directly opposed or slightly displaced clockwise; the distal fiber had gently sigmoid central striations; terminal caps were absent from the ends of the basal bodies; a V‐shaped proximal sheath extended from the upper basal bodies; a posterior fiber lay between the opposite lower basal bodies; and the coarsely striated band linked the sinister rootlet to the lower basal body. The suite of these features was not identical to that of any other quadriflagellate swimming cells, but some features including the lower basal body orientation, the striated distal fiber, and the coarsely striated fiber resemble those of the several organisms of the Siphonocladales sensu Floyd and O’Kelly. Phylogenetic analysis using 18S rDNA sequence data revealed that I. tetrasporus and P. americanum formed a monophyletic clade within the clade of Ulvophyceae sensu López‐Bautista and Chapman, but was not nested within any of the orders of the class that were examined.     

Ultrastructure and protein uptake of the embryonic trophotaeniae of four species of goodeid fishes (Teleostei: Atheriniformes)

Embryos of most species within the viviparous teleost family Goodeidae develop characteristics perianal processes that are considered to be derivatives of the embryonic hindgut. These processes, termed trophotaeniae, are covered with an epithelium that is continuous with the absorptive epithelium lining the hindgut. Gestation is intraovarian, and trophotaeniae mediate the uptake of maternally provided nutrients into the embryo from the ovarian fluid. Ultrastructural examination of the trophotaeniae of four goodeid species reveals substantial diversity in the organization of the epithelium within the family. The trophotaeniae of Alloophorus robustus, Zoogoneticus quitzeoensis, and Ilyodon furcidens have morphological features associated with the endocytosis of macromolecules and can be shown to endocytose the exogenous protein tracer horseradish peroxidase (HRP) rapidly. The trophotaenial epithelia of these species differ from one another with respect to other morphological features such as cell height, organization of the brush border, and the complexity of the intercellular spaces. The trophotaeniae of Goodea atripinnis lack an endocytotic apparatus and do not endocytose HRP. However, the overall organization of G. atripinnis trophotaenial cells suggests a function as a transporting epithelium. The cells have a dense brush border, numerous mitochondria, and many mitochondria that are enveloped by lamellar sheets of intracellular membrane. Post-fixation with osmium and potassium ferrocyanide reveals a marked difference in the complexity of the subepithelial connective tissue. Alloophorus robustus and Z. quitzeoensis exhibit an extremely electron-dense ground substance containing many acellular components. Goodea atripinnis exhibits an electron-lucid ground substance with few acellular components. © 1994 Wiley-Liss, Inc.     

Disrupting the Amblyomma americanum (L.) CD147 receptor homolog prevents ticks from feeding to repletion and blocks spontaneous detachment of ticks from their host

The CD147 receptor is a cell-surface glycoprotein in the IgG family that plays pivotal roles in intercellular interactions involved with numerous physiological and pathological processes such as extracellular matrix remodeling. We previously found an Amblyomma americanum (Aam) tick CD147 receptor homolog among genes that were up regulated in response to tick feeding stimuli. This study characterizes an AamCD147 receptor protein that is 72–83% conserved in other tick species and possess characteristic CD147 receptor sequence features: an extracellular (EC) region containing two IgG domains, a transmembrane and the cytoplasmic domains. Likewise, the AamCD147 EC domain folds into secondary structures that are consistent to the human homolog: an amino-terminus β-barrel that is linked to 2-carboxy-terminus β-sheets with consensus disulfide bonds conserved in each of the 2 domains. CD147 receptor signaling and regulatory mechanisms are putatively conserved in ticks as revealed by in silico analysis that show presence in the tick genome of CD147 receptor signaling protein homologs, cyclophilin (CyP) A and B, and chaperones that transport it to the plasma membrane, caveolin-1 and CyP60. The AamCD147 receptor has a dichotomous expression pattern of where it is up regulated in response to feeding in the salivary gland but remains constant at the midgut and ovary levels suggesting that it may regulate different functions in different tick organs. We speculate that biological functions of the AamCD147 receptor are essential to tick feeding success as revealed by RNAi-mediated silencing that caused ticks to obtain smaller blood meals, of which ～69% were below threshold to trigger spontaneous detachment of ticks from the host. These ticks showed unusual cuticle tenderness and assumed a reddish coloration, a phenomenon that has been attributed to tick midgut damage allowing red blood cells to leak into tick hemolymph. On the basis of the CD147 receptor being linked to tissue growth regulation in mammals, we speculate that silencing of the AamCD147 receptor blocked progression of the tick intermolt growth, a process that precedes tick engorgement and their spontaneous detachment of from the host to end feeding. The results are discussed in context of advances in tick molecular physiology.     

The influence of eclosion timing on winter survival and triacylglycerol accumulation in four temperate species of Drosophila

Abstract. Diapause incidence, winter survival and triacylglycerol content were studied in temperate species of Drosophila by outdoor rearing in Sapporo (a cool-temperate region), northern Japan. In strains of D.subauraria and D.triauraria (cool-temperate species) from northern Japan, diapause was induced in adults having eclosed after early September, but in those having eclosed after mid October in strains of D.rufa and D.lutescens (warm-temperate species) from southern Japan. A subtropical strain of D.triauraria did not enter diapause. In the strains of cool-temperate species from northern Japan, about 70% survived until spring when eclosed in mid autumn, whereas when eclosed earlier and later flies had a lower ability to overwinter. The warm-temperate species and a subtropical strain of D.triauraria also survived longer when eclosed in mid autumn than when eclosed later, but they were unable to survive until spring. The triacylglycerol content was higher in the cool-temperate species from northern Japan than in the warm-temperate species and a subtropical strain of D.trauraria. In each species the triacylglycerol content of adults was higher when they eclosed in early and mid than in late autumn. It is assumed that triacylglycerol plays an important role in overwintering of these Drosophila species and the low triacylglycerol level is the primary cause of the low overwintering capacity of individuals eclosing in late autumn.     

毛乌素沙地4种植物叶水势变化及其影响因素分析

对毛乌素沙地旱柳( Salix matsudana Koidz.)、小叶杨( Populus simonii Carr.)、北沙柳( Salix psammophila C. Wang et Chang Y. Yang)和沙蒿(Artemisia desertorum Spreng.)4种植物叶水势的月变化和日变化规律以及不同冠层叶水势的差异进行了研究,并分析了4种植物叶水势与气候因子及树干液流速度的相关性。结果表明：在5月份至8月份,旱柳、小叶杨和北沙柳清晨(5：00)的叶水势波动不明显;但3种植物正午(13：00)的叶水势有一定差异,其中旱柳和小叶杨正午的叶水势差异不明显,而北沙柳7月份和8月份的叶水势则明显小于其5月份和6月份;总体上看,各月份3种植物正午的叶水势均明显小于清晨叶水势。供试4种植物的叶水势日变化曲线均以“单峰型”为主,最高值出现在5：00至6：00,最低值出现在12：00至16：00;日间北沙柳的平均叶水势最低,而其他3种植物的平均叶水势差异不明显,5月份和8月份,北沙柳的平均叶水势分别为-11.9和-17.1 MPa,而旱柳、小叶杨和沙蒿的平均叶水势分别为-6.2和-7.1、-7.7和-7.3、-6.8和-8.4 MPa;但夜间4种植物的平均叶水势无明显变化。4种植物日间均表现出树冠下层叶水势高、上层叶水势低的趋势,而夜间则树冠上层和下层的叶水势几乎一致。相关性分析结果表明：4种植物的叶水势与气温、净辐射量以及树干液流速度负相关、与空气相对湿度正相关,其中,不同月份4种植物的叶水势与净辐射量和树干液流速度均极显著相关(P<0.01)。研究结果显示：毛乌素沙地不同植物叶水势的变化因种类、季节、气候条件的不同而异,但总体上看净辐射量是影响4种植物叶水势变化的最主要气象因子。