Direct Observation of the Photodegradation of Anthracene and Pyrene Adsorbed onto Mangrove Leaves

An established synchronous fluorimetry method was used for in situ investigation of the photodegradation of pyrene (PYR) and anthracene (ANT) adsorbed onto fresh leaves of the seedlings of two mangrove species, Aegiceras corniculatum (L.) Blanco (Ac) and Kandelia obovata (Ko) in multicomponent mixtures (mixture of the ANT and PYR). Experimental results indicated that photodegradation was the main transformation pathway for both ANT and PYR in multicomponent mixtures. The amount of the PAHs volatilizing from the leaf surfaces and entering the inner leaf tissues was negligible. Over a certain period of irradiation time, the photodegradation of both PYR and ANT adsorbed onto the leaves of Ac and Ko followed first-order kinetics, with faster rates being observed on Ac leaves. In addition, the photodegradation rate of PYR on the leaves of the mangrove species in multicomponent mixtures was much slower than that of adsorbed ANT. Compared with the PAHs adsorbed as single component, the photodegradation rate of ANT adsorbed in multicomponent mixtures was slower, while that of PYR was faster. Moreover, the photodegradation of PYR and ANT dissolved in water in multicomponent mixtures was investigated for comparison. The photodegradation rate on leaves was much slower than in water. Therefore, the physical-chemical properties of the substrate may strongly influence the photodegradation rate of adsorbed PAHs.     

The growth of Kandelia candel seedlings in mangrove habitats of the Zhangjiang estuary in Fujian, China

Propagules of Kandelia candel collected from the Zhangjiang estuary were planted in mangrove habitats along the intertidal gradient. The rooting rates of K. candel propagules varied spatially. The lowest rate occurred in Avicennia marina forest (69.7%). The rates were higher in K. candel forest (90.0%), at the fringe of the mangrove forest (89.3%) and on the bare tidal flat outside the mangrove forest (82.7%). After one year, the survival rates of seedlings planted under A. marina forest, K. candel forest, at the fringe of the mangrove forest, and on the bare tidal flat were 13.7%, 54.7%, 76.0%, and 34.7%, respectively. Among the surviving K. candel seedlings, those at the fringe of the mangrove forest and on the bare tidal flat had greater height, stem diameter, leaf number, leaf area, and biomass than those under A. marina and K. candel forests. These results demonstrated that establishment and growth of K. candel seedlings occurred successfully at the fringe of the mangrove forest, but were the worst under A. marina forest. The performance of K. candel seedlings was independent of physico-chemical characters of sediment. However, interspecies competition, propagule predation by insects and crabs, and the incident light had significant effects on seedling survival and growth.     

Transposition of the maize autonomous element Activator in transgenic Nicotiana plumbaginifolia plants

The maize autonomous transposable element Ac was introduced into haploid Nicotiana plumbaginifolia via Agrobacterium tumefaciens transformation of leaf disks. All the regenerated transformants (R0) were diploid and either homozygous or heterozygous for the hygromycin resistance gene used to select primary transformants. The Ac excision frequency was determined using the phenotypic assay of restoration of neomycin phosphotransferase activity and expression of kanamycin resistance among progeny seedlings. Some of the R0 plants segregated kanamycin-resistant seedlings in selfed progeny at a high frequency (34 to 100%) and contained one or more transposed Ac elements. In the primary transformants Ac transposition probably occurred during plant regeneration or early development. Other R0 transformants segregated kanamycin-resistant plants at a low frequency (≤ 4%). Two transformants of this latter class, containing a unique unexcised Ac element, were chosen for further study in the expectation that their kanamycin resistant progeny would result from independent germinal transposition events. Southern blot analysis of 32 kanamycin-resistant plants (R1 or R2), selected after respectively one or two selfings of these primary transformants, showed that 27 had a transposed Ac at a new location and 5 did not have any Ac element. Transposed Ac copy number varied from one to six and almost all transposition events were independent. Southern analysis of the R2 and R3 progeny of these kanamycin-resistant plants showed that Ac continued to transpose during four generations, and its activity increased with its copy number. The frequency of Ac transposition, from different loci, remained low (≤ 7%) from R0 to R3 generations when only one Ac copy was present. The strategy of choosing R0 plants that undergo a low frequency of germinal excision will provide a means to avoid screening non-independent transpositions and increase the efficiency of transposon tagging.     

东灵山不同林型五角枫叶性状异速生长关系随发育阶段的变化

分析植物叶片性状种内水平的异速生长关系有助于加深理解生长发育过程中叶片的资源利用模式.分析了东灵山3个主要林型(白桦林、胡桃楸林、辽东栎林)中五角枫成树、幼树、幼苗的叶面积、叶体积、叶含水量与叶干重之间的异速生长关系.结果表明:成树叶面积增长速度小于叶干重的增长速度,幼树、幼苗叶面积与叶干重保持同速增长;成树、幼树叶干重与叶体积保持同速增长,幼苗叶体积的增长速度超过了干重的增长速度;成树叶含水量的增长速度小于叶干重的增长速度,幼树、幼苗两性状间保持等速增长.叶含水量与叶干重的异速生长指数在不同的林型间有显著差异,白桦林叶含水量的增长速度小于叶干重的增长速度,其余两个林型均为等速增长趋势.这些结果揭示了不同发育阶段五角枫资源利用方式的转变.随叶干重的增加,成树将更多的叶生物量投资于同化和支持结构;幼树则保持对光合面积和光合同化结构的稳步投资;而幼苗主要投资于叶面积的增大.叶含水量与叶干重的异速曲线在不同林型间的差异说明叶片代谢活性相较于其他叶性状可塑性更高.     

干旱胁迫下外源脱落酸和硅对沙枣幼苗叶片水势及保护酶活性的影响

以一年生沙枣幼苗为材料,研究了外源脱落酸和外源硅在干旱（T2:SRWC=35%~40%,处理时间30 d）胁迫下沙枣幼苗叶片相对含水量、叶片水势、质膜相对透性、丙二醛(MDA)含量、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性的影响。结果表明：沙枣幼苗T2干旱处理时,与对照(ck)相比其叶片相对含水量和水势均极显著降低,质膜相对透性有所增大,沙枣幼苗被受到了一定程度的伤害。同时,向T2干旱处理的幼苗使用外源脱落酸(ABA)后,可以极显著提高其叶片相对含水量和过氧化氢酶活性,极显著降低叶片质膜相对透性和丙二醛含量,叶片水势也有所降低,这说明使用外源脱落酸能够减轻干旱胁迫对沙枣幼苗的伤害。同时,向T2干旱处理的幼苗使用外源硅(Si)时,与未使用外源硅的T2相比其叶片相对含水量和超氧化物歧化酶(SOD)活性极显著上升,叶片水势也有下降趋势,这说明使用外源硅在一定程度上能够缓解干旱胁迫对沙枣幼苗的伤害。     

Seedling survivorship,growth, and response to disturbance in Belizean mangal

Species zonation patterns across tidal gradients in mangrove forests are formed by successful seedling establishment and maintained by replacement of adults by conspecific seedlings. These two processes rarely have been examined experimentally in neotropical mangal. We studied survivorship and growth of seedlings of two species of mangrove, Rhizophora mangle L. and Avicennia germinans (L.) Steam, across a tidal gradient in Belize, Central America. Propagules of each species were planted in common gardens at tidal elevations corresponding to lowest low water (LLW), mean water (MW), and highest high water (HHW). Sixty-nine percent of Rhizophora seedlings planted at MW and 56% of those planted at LLW survived 1 year. Forty-seven percent of MW Avicennia seedlings also survived 1 year. No individuals of either species survived at HHW, and neither did any LLW Avicennia seedlings. Among the surviving Rhizophora seedlings, LLW seedlings grew more rapidly in terms of height, diameter, leaf production, and biomass than did MW seedlings. Insect herbivory was twice as high on MW seedlings as on LLW Rhizophora seedlings. We also examined the response of established Rhizophora seedlings to experimental removal of the adult Rhizophora canopy. Seedlings in canopy removal areas had higher survivorship, grew twice as fast, produced more leaves, and had less than half the herbivory of seedlings growing beneath an intact canopy. These results provide insights into underlying causes and maintenance of zonation in Caribbean mangrove forests.     

2010年冬季寒冷天气对闽江口3种红树植物幼苗的影响

2010年10月8日-2011年2月26日,跟踪监测了闽江河口互花米草治理试验区人工种植的秋茄(Kandelia candel)、无瓣海桑(Sonneratia apetala)和拉关木(Leguncalaria racemosa)1年生幼苗叶片相溶性物质含量以及活性氧代谢等生理生化指标.结果表明:可溶性糖和脯氨酸含量均随气温的逐步降低而增加,秋茄可溶性糖含量最高,拉关木脯氨酸含量最高;整个监测期无瓣海桑和拉关木幼苗叶片超氧阴离子(O2)产生速率显著高于秋茄(P＜0.01),而超氧化物歧化酶(SOD)和过氧化物酶(POD)活性显著低于秋茄(P＜0.01);3种植物叶片丙二醛(MDA)含量及电解质渗透率均随着气温的降低而增加,其中无瓣海桑和拉关木MDA含量及电解质渗透率与日最低气温为显著和极显著的负相关关系.2010年冬季持续寒冷天气对闽江河口湿地1年生土著种秋茄幼苗无破坏,对引进种无瓣海桑和拉关木造成了严重的低温胁迫并使幼苗基本全部死亡.     

Photosynthesis of plant régénérants. Specificity ofin vitro conditions and plantlet response

Regenerants from tobacco(Nicotiana tabacum L. cv. White Burley) leaf segments cultivatedin vitro in vessels with solid agar medium under usual conditions (plantlets) grew under very low irradiance (I = 40 μxmol m?2 s?1), very high relative humidity (more than 90%) and decreased CO₂ concentration (c_a) during light period. In comparison with seedlings of a similar number of leaves and similar total leaf area grown in sand and nutrient solution, the plantlets had lower dry mass of shoots and roots per plant and thinner leaves almost without trichomes and epicuticular waxes. Due to a low transpiration rate under high relative humidity the water potential of plantlet leaves was higher than that of seedling leaves and the difference in water potential between leaves and medium was lowei. The rate of water loss from leaves detached from plantlets was considerably faster than that from seedlings under the same conditions (I = 110 μrnol m^?2; s^?1, temperature 30 °C, relative humidity 50 %). Net photosynthetie rates (P_n) of leaves of plantlets and seedlings measured under saturating I, natural ca and the leaf temperature 20 °C were similar, nevertheless the shape of curves relating Pn to c» indicated some differences in photosynthetie parameters(e.g. saturation of Pn under lower ca> higher CO2 compensation concentration in plantlets than in seedlings). Similarly compensation and saturating I were lower in plantlets than in seedlings. The shape of transpiration curves as well as the expressive linear phases of P_N(ca) and P_N(I) curves of plantlet leaves indicated ineffective stomatal control of gas exchance. These results were confirmed by microscopic observations of stomatal movementsin situ     

Solvent Effect on the Photolysis of Riboflavin

The kinetics of photolysis of riboflavin (RF) in water (pH 7.0) and in organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol, ethyl acetate) has been studied using a multicomponent spectrometric method for the assay of RF and its major photoproducts, formylmethylflavin and lumichrome. The apparent first-order rate constants (k_obs) for the reaction range from 3.19 (ethyl acetate) to 4.61 × 10⁻³ min⁻¹ (water). The values of k_obs have been found to be a linear function of solvent dielectric constant implying the participation of a dipolar intermediate along the reaction pathway. The degradation of this intermediate is promoted by the polarity of the medium. This indicates a greater stabilization of the excited-triplet states of RF with an increase in solvent polarity to facilitate its reduction. The rate constants for the reaction show a linear relation with the solvent acceptor number indicating the degree of solute–solvent interaction in different solvents. It would depend on the electron-donating capacity of RF molecule in organic solvents. The values of k_obs are inversely proportional to the viscosity of the medium as a result of diffusion-controlled processes.KEY WORDS: dielectric constant, kinetics, photolysis, riboflavin, solvent effect, viscosity     

Growth responses of the mangrove Avicennia marina to salinity: development and function of shoot hydraulic systems require saline conditions

Background and Aims Halophytic eudicots are characterized by enhanced growth under saline conditions. This study combines physiological and anatomical analyses to identify processes underlying growth responses of the mangrove Avicennia marina to salinities ranging from fresh- to seawater conditions.Methods Following pre-exhaustion of cotyledonary reserves under optimal conditions (i.e. 50 % seawater), seedlings of A. marina were grown hydroponically in dilutions of seawater amended with nutrients. Whole-plant growth characteristics were analysed in relation to dry mass accumulation and its allocation to different plant parts. Gas exchange characteristics and stable carbon isotopic composition of leaves were measured to evaluate water use in relation to carbon gain. Stem and leaf hydraulic anatomy were measured in relation to plant water use and growth.Key Results Avicennia marina seedlings failed to grow in 0–5 % seawater, whereas maximal growth occurred in 50–75 % seawater. Relative growth rates were affected by changes in leaf area ratio (LAR) and net assimilation rate (NAR) along the salinity gradient, with NAR generally being more important. Gas exchange characteristics followed the same trends as plant growth, with assimilation rates and stomatal conductance being greatest in leaves grown in 50–75 % seawater. However, water use efficiency was maintained nearly constant across all salinities, consistent with carbon isotopic signatures. Anatomical studies revealed variation in rates of development and composition of hydraulic tissues that were consistent with salinity-dependent patterns in water use and growth, including a structural explanation for low stomatal conductance and growth under low salinity.Conclusions The results identified stem and leaf transport systems as central to understanding the integrated growth responses to variation in salinity from fresh- to seawater conditions. Avicennia marina was revealed as an obligate halophyte, requiring saline conditions for development of the transport systems needed to sustain water use and carbon gain.     

Effects of pretreated domestic wastewater supplies on leaf pigment content, photosynthesis rate and growth of mangrove trees: A field study from Mayotte Island, SW Indian Ocean

After 12 and 18 months of daily wastewater discharge into mangrove plots in Mayotte Island, SW Indian Ocean, leaf pigment content, photosynthesis rate and growth of Rhizophora mucronata and Ceriops tagal mangrove trees were evaluated and compared with similar individuals from control plots. Chlorophyll and carotenoid contents, measured using an HPLC analyser, were significantly higher in leaves of mangrove trees receiving wastewater discharges. Photosynthesis and transpiration rates, analysed using an LCi portable system, increased significantly for mangrove trees in impacted plots. Measurements of leaf areas, young branch length and propagule length showed significant increases in plots receiving wastewater. These results suggest a beneficial effect of domestic wastewater on R. mucronata and C. tagal mangrove tree functioning. Analyses and observations on mangrove ecosystems as a whole - taking into account water and sediment compartments, crab populations and nitrogen and phosphorus cycles - are nevertheless necessary for evaluation of bioremediation capacities of mangrove ecosystems.     

Effects of sea level rise on mangrove Avicennia population growth,colonization and establishment: Evidence from a field survey and greenhouse manipulation experiment

Mangroves will either face longer tidal inundation or retreat landwards in response to on-going accelerated sea level rise. However, little is known about the growth, regeneration or colonization of mangrove seedlings under the different tidal inundation regimes associated with accelerated sea level rise. In the present study, a field survey and a greenhouse mesocosm experiment were conducted to evaluate possible effects of accelerated sea level rise on colonization, establishment and seedling growth of a mangrove pioneer species, Avicennia marina. Avicennia populations at different elevations of the intertidal zone on Xiamen Island in Fujian Province, China showed distinctive patterns in both seedling density and plant age. The seedlings at lower elevations had less annual biomass accumulation and population productivity, but higher shoot to root ratios, suggesting that elevation has positive effects on seedling growth. The greenhouse mesocosm experiment with 1-year-old A. marina seedlings utilized five inundation periods (0, 2, 4, 6 and 12 h in a semidiurnal tidal cycle) and two inundation depths (root immersion and canopy immersion). Both inundation period and depth exerted significant and negative effects on biomass accumulation, photosynthetic rate, leaf electron transportation and water use efficiency. However, the negative effects of canopy immersion were more profound than root immersion. Canopy immersion exacerbated the effects of prolonged inundation, with no seedlings surviving under canopy immersion at the 12-hour treatment. These results suggest that at lower elevations with higher sea level, canopy immersion will have greater negative effects on seedling colonization, establishment and early growth of A. marina. This finding is instrumental in predicting the future dynamics of mangrove forests under increasing sea levels.     

红树林湿地相手蟹科动物摄食生态研究进展

相手蟹科物种是红树林湿地的主要底栖动物类群,在生态系统中起着重要的作用。我国大陆地区目前已记录的相手蟹科物种数量为12种,低于其它红树林地区(国内常用的采样方法会造成螃蟹物种数量和密度的低估),其中褶痕相手蟹(Sesarma plicata)、无齿相手蟹(S.deaani)和双齿相手蟹(S.bidens)等是常见种。红树植物叶片是相手蟹科动物的主要食物来源,相手蟹科动物通过地表摄食和洞穴贮存的形为消耗了大量的红树植物凋落叶,使这些凋落叶的有机质和营养元素得以保留在生态系统内,在凋落叶的周转和物质归还方面起到重要的作用。它们同时也摄食红树植物的繁殖体并且对不同物种的繁殖体具有摄食偏好,这可能对一些红树物种的植被更新能力和红树植被群落结构产生影响。相手蟹科动物对不同物种和不同状态的红树叶片也存在摄食偏好,通常对腐烂的叶片摄食偏好较强;螃蟹的摄食偏好与叶片的营养成份、粗纤维和单宁含量以及C/N比等性质有关;但在恶劣的野外环境下,螃蟹则会表现出随机性摄食。目前关于相手蟹科动物生态学作用的认识仍不充分,例如它们的种群大小和对凋落物的转化作用等,有待于进一步研究。     

The influence of seasonality in estimating mangrove leaf chlorophyll-a content from hyperspectral data

Mangrove photosynthetic activity and, consequently, physiological stress can be monitored indirectly using leaf chlorophyll-a (Chla) measurements. Recent studies have demonstrated the feasibility of mangrove leaf Chla content estimation from in situ hyperspectral vegetation indices (VI) but no such research has been conducted using data collected from contrasting seasons (i.e. dry and rainy). In this study, mangrove leaves were collected in a sub-tropical forest of the Mexican Pacific for Chla content determination and in situ hyperspectral measurements (450–1,000 nm). Specifically, we tested 35 VI to estimate Chla content based on a leaf sample of 360 collected from the same trees during both the dry and rainy seasons. The forest examined contained three species of mangrove (Rhizophora mangle, Avicennia germinans and Laguncularia racemosa) exhibiting various conditions of health (dwarf condition, tall and healthy). A principal component analysis, followed by linear regression analyses, were conducted in order to identify those VI that best predict mangrove leaf Chla content during the two seasons. The results indicate that VI derived from hyperspectral measurements collected during the dry season are better at estimating leaf Chla content than those collected during the rainy season. Among the 35 VI, the Vog1 (R₇₄₀/R₇₂₀) index was found to be the best predictor of mangrove leaf Chla content, resulting in R ² values of 0.80 and 0.68 for the dry and rainy season respectively. These results would suggest that for identifying variation in mangrove forest stress (i.e. health) in sub-tropical regions, hyperspectral measurements should be carried out during the dry season.     

Barnacle fouling impedes the gaseous exchange and food production of the mangroves <Emphasis Type="Italic">Kandelia obovata</Emphasis>, a dominant mangrove species in Hong Kong and Taiwan

Barnacle fouling has shown to impede gas exchange ability of mangroves. Fouled mangrove plants may therefore obtain less carbon dioxide and water for photosynthesis, resulting in reduced food and chloroplasts production, but such hypothesis remains untested. The objective of the present study compared the stomata density (essential for obtaining carbon dioxide and water molecules) and leaf chlorophyll concentration (essential for photosynthesis) of fouled and non-fouled (control) of seedlings, juveniles and adults of the mangroves Kandelia obovata, in Hong Kong and Taiwan. The seedlings and juveniles of the dominant mangrove plant species, Kandelia obovata, in Hong Kong and Taiwan had a higher density of stomata but a lower chlorophyll concentration in the leaves, when the trunks and twigs were fouled by the barnacle Fistulobalanus albicostatus. Fouled K. obovata appears to develop more stomata in the leaves to compensate the blocking effect of the lenticel from barnacle fouling. As fouling impacts the gaseous exchange ability of mangroves, fouled plants could obtain less carbon dioxide and water for photosynthesis, resulting in reduced food and chloroplasts production. Fouled adult plants, however, had variable responses in leaf chlorophyll concentrations among the study sites, suggesting adults were more tolerant of barnacle fouling. The present study reveals seedling and juvenile mangrove plants are very susceptible to barnacle fouling, which impedes the gaseous exchange mechanism and food production, which can subsequently result in reduced growth, fitness and survival. Handling editor: P. Viaroli     

Effects of Salinity Fluctuation on Photosynthetic Gas Exchange and Plant Growth of The Red Mangrove (Rhizophora mangle L.)

The red mangrove (Rhizophora mangle L.) in southern Floridaoccurs frequently in two distinct growth forms, tall and scrubplants, with the scrub form usually found in coastal inlandareas having a higher fluctuation of soil water salinity. Inthe present study, effects of constant and fluctuating salinitieson leaf gas exchange and plant growth of red mangrove seedlingswere investigated under greenhouse conditions. Both constantand fluctuating salinity treatments significantly affected leafgas exchange and plant growth of red mangrove seedlings. Seedlingssubjected to the fluctuating salinity with the mean of both100 and 250 mol m^–3 NaCl showed significantly lower photosynthesisand plant growth than those subjected to the corresponding constantsalinity with the same mean. The photosynthetic and growth ratesof the seedlings under these fluctuating treatments were aslow as, or even lower than those expected if they were growingunder the high constant salinity of their respective fluctuationtreatments. Seedlings subjected to the fluctuating salinitywith the mean of 500 mol m^–3 NaCl, however, demonstratedslightly higher CO₂ assimilation rate and stomatal conductance,but the same plant growth rates as those under the constant500 mol m^–3 NaCl treatment. These results suggest that,in general, fluctuating salinity has significant negative effectson photosynthesis and plant growth relative to constant salinitywith the same mean. If this finding can be applicable to fieldsituations, the low photosynthesis and plant growth observedpreviously in several scrub mangrove forests probably can beattributed in part to the salinity fluctuation of soil waterin these mangrove forests. Key words: Fluctuating salinity, photosynthesis, growth, growth forms, mangroves     

Leaf and flower formation in shoot tips of mangrove trees in Pernambuco, Brazil

Leaves are major components of mangrove productivity, but data on leaf dynamics are scarce. We marked the shoot tips of three species in four sites of a riverine mangrove and monitored leaf formation, senescence and abscission and flower formation. The leaf area and biomass in the mangrove were estimated using phytosociological data. Leaf size and formation were similar among the four sites. The tips of Rhizophora mangle had more leaf scars (41), more leaves present (9.7), a faster leaf formation rate (one every 26 days) and a shorter life span (8.4 months) than those of Avicennia schaueriana (10, 8.1, 48 days and 13.1 months, respectively) and Laguncularia racemosa, except for the shorter life span (15, 6.6, 31 days and 6.8 months, respectively). The proportion of tips that flowered was higher in L. racemosa (13 %) and in R. mangle (11 %) than in A. schaueriana (2 %). The largest biomass of the average R. mangle leaf (0.75 vs. 0.53 and 0.37 g leaf^?1, of L. racemosa and A. schaueriana, respectively) and the highest plant density of this species (2,590 vs. 694 and 202 plant ha^?1, respectively) resulted in it having the greatest leaf productivity (10.6 Mg ha^?1 year^?1 compared to 2.4 Mg ha^?1 year^?1 for L. racemosa and 0.3 Mg ha^?1 year^?1 for A. schaueriana). The total leaf production is higher in this mangrove than most of those reported for other mangroves in the world.     

盐沼草—白骨壤混种减轻污损动物危害的生物防治效果研究

广西北仑河口区新造高程约220 cm 的潮间带裸滩,移植白骨壤与茳芏、沟叶结缕草、芦苇和南水葱四种盐沼草进行混种,研究盐沼草-红树混种减轻污损动物对人工红树林危害的生物防治效果。结果表明：沟叶结缕草和茳芏可快速生长和扩展,缓流、促淤能力高于长势较差的南水葱和芦苇。在盐沼和白骨壤上发现19种污损动物,其中潮间藤壶、白条地藤壶、黑口滨螺和粗糙滨螺为优势种。茳芏和沟叶结缕草受污损程度较南水葱和芦苇轻。四种盐沼草受污损程度均低于白骨壤。白骨壤＋茳芏、白骨壤＋沟叶结缕草混种均可有效减轻污损动物对白骨壤苗木危害,这两类树-草混种处理区苗木的高度、叶数、枝数、枝下高和存活率等指标均较其他处理区好。初步判断“盐沼草-红树林协同生态修复体系”对于营造人工红树林有较高应用价值。     

Water relations of the upper and lower surfaces of maize leaves

The objective of this study was to determine if the two surfaces of a leaf had different, or the same, water potentials. Maize (Zea mays L. cv. Cargill 805) was the test plant. During an 11 day period, the water potentials of the upper and lower surfaces of the maize leaves were measured daily with anin situ thermocouple psychrometer under growth-room conditions. Plants were grown in pots with a well-watered, commercial greenhouse soil. Stomatal resistance also was measured. The water potential of the upper surface was less negative (more wet) than that of the lower surface. The overall average of the water potential of the upper and lower surfaces was ?1.48 and ?2.07 MPa, respectively. The stomatal resistance of the upper surface was greater than that of the lower surface. The average stomatal resistance during the experiment was 780 and 600 s m^?1 for the upper and lower surfaces, respectively. Since the upper and lower surfaces were not at the same water potential, the results indicated that the parallel-resistance equation, used to combine resistances on the two surfaces of a leaf, was not strictly valid when applied to the maize leaves, as the law assumes equal potentials on the two surfaces.