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161.
162.
In order to address the question of how elevated CO2 concentration (EC) will affect the water relations and leaf anatomy of tropical species, plants of Jatropha gossypifolia L. and Alternanthera crucis (Moq.) Bondingh were grown in five EC open top chambers (677 mol mol–1) and five ambient CO2 concentration (AC) open top chambers (454 mol mol–1) with seasonal drought. No effect of EC was found on morning xylem water potential, leaf osmotic potential, and pressure potential of plants of J. gossypifolia. In A. crucis EC caused a significant increase in morning xylem water potential of watered plants, a decrease in osmotic potential, and an increase of 24–79 % in pressure potential of moderately droughted plants. This ameliorated the effects of drought. Stomatal characteristics of both leaf surfaces of J. gossypifolia and A. crucis showed time-dependent, but not [CO2]-dependent changes. In J. gossypifolia the thickness of whole leaf, palisade parenchyma, and spongy parenchyma, and the proportion of whole leaf thickness contributed by these parenchymata decreased significantly in response to EC. In A. crucis EC caused an increase in thickness of whole leaf, bundle sheath, and mesophyll, while the proportion of leaf cross-section comprised by the parenchymata remained unchanged. These effects disappeared with time under treatment, suggesting that acclimation of the leaf anatomy to the chambers and to EC took place in the successive flushes of leaves produced during the experiment. 相似文献
163.
Impact of rising tropospheric ozone on potato: effects on photosynthesis, growth, productivity and yield quality 总被引:4,自引:0,他引:4
In view of its importance for human nutrition, the European Commission funded a collaborative research programme (1998–99) to evaluate the impact of future increases in atmospheric ozone (O3 ) and carbon dioxide (CO2 ) concentrations on yield and tuber quality in potato ( Solanum tuberosum L.). This was the first large-scale open-top chamber project to provide field-based data spanning a wide range of European climatic conditions and ozone concentrations for a widely used cultivar, cv. Bintje. Intensive measurements of physiological and developmental effects were made throughout crop growth to improve the mechanistic understanding of the processes involved. Analysis of the experimental results and modelling work based on the extensive database revealed that the increasing tropospheric O3 concentrations predicted under future climatic scenarios in Europe are likely to reduce tuber yield in potato. However, season-long exposure to elevated O3 had both beneficial and detrimental effects on tuber quality. Most of the significant physiological and growth effects occurred during the later stages of crop development, when elevated O3 reduced photosynthesis and promoted senescence. The observed changes in the quality and nutritional attributes of tubers, such as decreased content of reducing sugars and increased nitrogen concentrations, may be attributable to reduced carbohydrate allocation. 相似文献
164.
《Experimental parasitology》1998,90(3):270-276
Breijo, M., Spinelli, P., Sim, R.B., and Ferreira, A. M. 1998.Echinococcus granulosus:An intraperitoneal diffusion chamber model of secondary infection in mice.Experimental Parasitology90, 270–276. The present work describes a new experimental model of secondary infection which allows, through the recovery of the parasite together with its localin vivoenvironment, examination of the local nonadaptive immune response of the infected host and the differentiation of the parasite from protoscoleces to cysts. In this model we administered protoscoleces within silicone diffusion chambers, previously implanted into the peritoneal cavities of mice. The process of designing the model involved, first, determination of the optimal time postimplantation to infect the mice and, second, evaluation of the parasite's ability to establish infection within the chambers. The optimal time for infection was considered to be after the inflammation caused by implantation of the chambers had subsided. Our results showed that by day 20 postsurgery, three parameters used as indications of inflammation (complement C3, serum amyloid P protein, and polymorphonuclear cells in the peritoneum and in the chamber contents) had reverted to their normal levels. In our study of parasite differentiation, we found that 2–3% of the total number of parasites inoculated into the chambers were recovered as viable cysts after 100 days. Throughout the infection period, the population of parasites recovered was heterogeneous; certain parasite morphologies that have not been described previously were observed. In conclusion, the use of intraperitoneal diffusion chambers offers a potential tool for investigating thein vivodifferentiation process of secondary cysts ofEchinococcus granulosusin mice and the early local interactions between host and parasite during this process. 相似文献
165.
Xylem water transport: is the available evidence consistent with the cohesion theory? 总被引:9,自引:2,他引:7
U. ZIMMERMANN F. C. MEINZER R. BENKERT J.J. ZHU H. SCHNEIDER G. GOLDSTEIN E. KUCHENBROD A. HAASE 《Plant, cell & environment》1994,17(11):1169-1181
Since its introduction in the late 19th century, the so-called cohesion theory has become widely accepted as explaining the mechanism of the ascent of sap. According to the cohesion theory, the minimum standing vertical xylem tension gradient should be 0·01 MPa m−1. When transpiration is occurring, frictional resistances are expected to make this gradient considerably steeper. The results of numerous pressure chamber measurements reported in the literature are generally regarded as corroborating the cohesion theory. Nevertheless, several reports of pressure chamber measurements in tall trees appear to be incompatible with predictions of the cohesion theory. Furthermore, the pressure chamber is an indirect method for inferring xylem pressure, which, until recently, has not been validated by comparison against a direct method. The xylem pressure probe provides a means of testing the validity of the pressure chamber and other indirect techniques for estimating xylem pressure. We discuss here the results of concurrent measurements made with the pressure chamber and the xylem pressure probe, particularly recent measurements made at the top of a tall tropical tree during the rainy season. These measurements indicate that the pressure chamber often substantially overestimates the tension previously existing in the xylem, especially in the partially dehydrated tissue of droughted plants. We also discuss other evidence obtained from classical and recent approaches for studying water transport. We conclude that the available evidence derived from a wide range of independent approaches warrants a critical reappraisal of tension-driven water transport as the exclusive mechanism of long-distance water transport in plants. 相似文献
166.
Christian Stiegler Franziska Koebsch Ashehad Ashween Ali Tania June Edzo Veldkamp Marife D. Corre Joost Koks Aiyen Tjoa Alexander Knohl 《Global Change Biology Bioenergy》2023,15(10):1221-1239
The rapidly growing areal extent of oil palm (Elaeis guineensis Jacq.) plantations and their high fertilizer input raises concerns about their role as substantial N2O sources. In this study, we present the first eddy covariance (EC) measurements of ecosystem-scale N2O fluxes in an oil palm plantation and combine them with vented soil chamber measurements of point-scale soil N2O fluxes. Based on EC measurements during the period August 2017 to April 2019, the studied oil palm plantation in the tropical lowlands of Jambi Province (Sumatra, Indonesia) is a high source of N2O, with average emission of 0.32 ± 0.003 g N2O-N m−2 year−1 (149.85 ± 1.40 g CO2-equivalent m−2 year−1). Compared to the EC-based N2O flux, average chamber-based soil N2O fluxes (0.16 ± 0.047 g N2O-N m−2 year−1, 74.93 ± 23.41 g CO2-equivalent m−2 year−1) are significantly (~49%, p < 0.05) lower, suggesting that important N2O pathways are not covered by the chamber measurements. Conventional chamber-based N2O emission estimates from oil palm up-scaled to ecosystem level might therefore be substantially underestimated. We show that the dynamic gas exchange of the oil palm canopy with the atmosphere and the oil palms' response to meteorological and soil conditions may play an important but yet widely unexplored role in the N2O budget of oil palm plantations. Diel pattern of N2O fluxes showed strong causal relationships with photosynthesis-related variables, i.e. latent heat flux, incoming photosynthetically active radiation and gross primary productivity during day time, and ecosystem respiration and soil temperature during night time. At longer time scales (>2 days), soil temperature and water-filled pore space gained importance on N2O flux variation. These results suggest a plant-mediated N2O transport, providing important input for modelling approaches and strategies to mitigate the negative impact of N2O emissions from oil palm cultivation through appropriate site selection and management. 相似文献
167.
168.
The noncalcified inner branchiostegal cuticle, which lines the branchial chamber, was examined histologically and ultrastructurally over the molt cycle in the blue crab, Callinectes sapidus. In intermolt crabs (stage C4) the epithelium underlying the inner cuticle is cuboidal and has abundant intercellular spaces and a prominent basement membrane. Apolysis occurs at stage D0 and dissolution of the cuticle is accompanied by the formation of numerous lysosomes in the epithelium. During stage D1, cells increase in height, apical mitochondria become more abundant, and the cuticle continues to be resorbed. An epicuticle is formed in early D2, arising from a fusion of small subunits apparently attached to short apical microvilli. Cuticle deposition continues through D2 and is complete by stage D3. By the time cuticle deposition is complete, the epithelium has become extremely columnar and cells are filled with bundles of microtubules. In stage D4, an amorphous electron‐dense core appears in the microtubule‐filled cells, which are attached to the cuticle at their apical end and anchored to their basement membrane at the basal surface. These microtubule‐filled cells persist through ecdysis, stage E, but during stage A1 the cores disappear and some organelles begin to reappear in the cytoplasm. By stage A2, the cells return to the cuboidal morphology seen in intermolt and remain so throughout the remainder of the molt cycle. This new pattern of cuticle deposition resembles that observed in the gills of crustaceans in that the cuticle is uncalcified and there is no postecdysial cuticle formation. However, instead of apolysis being delayed until just before ecdysis, the inner cuticle is formed during the first half of premolt, allowing the epithelial cells time to differentiate into a morphology that provides tensile strength for the stress of ecdysis. These new observations demonstrate that cuticle formation can follow very diverse structural and temporal patterns. In order to integrate and coordinate these diverse patterns, it is suggested that a suite of feedback mechanisms must be present. J. Morphol. 240:267–281, 1999. © 1999 Wiley‐Liss, Inc. 相似文献
169.
Dirk Nehring Peter Adamietz Norbert M. Meenen Ralf Pörtner 《Biotechnology Techniques》1999,13(10):701-706
Chondrocyte pellets were cultivated in a perfused flow chamber and supplied with medium by a constant flow rate from a conditioning vessel. In this conditioning vessel the medium was aerated and used medium was exchanged semi-continuously. The higher amount of DNA and glycosaminoglycane (GAG) in these pellets compared to control cultures under stationary conditions showed a positive effect of the reactor system, compared to standard culture conditions. A diffusion reaction model was applied to calculate the oxygen uptake of the cell pellet and to describe the oxygen profile within the pellet. The model included diffusion within the cell pellet and oxygen uptake of the cells. Calculated data were compared to experimental data obtained by tissue engineered chondrocyte cell pellets. Model calculations agreed rather well with experimental data. 相似文献
170.
Regina Lindborg Matti Ermold Lenka Kuglerov Roland Jansson Keith W. Larson Ann Milbau Sara A. O. Cousins 《Ecology and evolution》2021,11(22):16228
Global warming affects plant fitness through changes in functional traits and thereby ecosystem function. Wetlands are declining worldwide, and hence, ecosystem functions linked to wetlands are threatened. We use Caltha palustris “a common wetland plant” to study whether warming affects growth and reproduction differently depending on origin of source population, potentially affecting phenotypic response to local climate. We conducted a 2‐year in situ temperature manipulation experiment using clone pairs of C. palustris in four regions, along a 1300‐km latitudinal gradient of Sweden. Open‐top chambers were used to passively increase temperature, paired with controls. Growth and reproductive traits were measured from 320 plants (four regions × five sites × two treatments × eight plants) over two consecutive seasons to assess the effect of warming over time. We found that warming increased plant height, leaf area, number of leaves, and roots. High‐latitude populations responded more strongly to warming than low‐latitude populations, especially by increasing leaf area. Warming increased number of flowers in general, but only in the second year, while number of fruits increased in low‐latitude populations the first year. Prolonged warming leads to an increase in both number of leaves and flowers over time. While reproduction shows varying and regional responses to warming, impacts on plant growth, especially in high‐latitude populations, have more profound effects. Such effects could lead to changes in plant community composition with increased abundance of fast‐growing plants with larger leaves and more clones, affecting plant competition and ecological functions such as decomposition and nutrient retention. Effects of warming were highly context dependent; thus, we encourage further use of warming experiments to predict changes in growth, reproduction, and community composition across wetland types and climate gradients targeting different plant forms. 相似文献