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排序方式: 共有84条查询结果,搜索用时 15 毫秒
1.
Estelle Arbellay Markus Stoffel Elaine K. Sutherland Kevin T. Smith Donald A. Falk 《Annals of botany》2014,114(5):973-980
Background and Aims
Resin ducts (RDs) are features present in most conifer species as defence structures against pests and pathogens; however, little is known about RD expression in trees following fire injury. This study investigates changes in RD size and density in fire scars of Douglas fir (Pseudotsuga menziesii) and western larch (Larix occidentalis) as a means to evaluate the ecophysiological significance of traumatic resinosis for tree defence and survival.Methods
Transverse and tangential microsections were prepared for light microscopy and image analysis in order to analyse axial and radial RDs, respectively. Epithelial cells of RDs and fusiform rays associated with radial RDs were also examined. RDs were compared between normal xylem and wound xylem at four different section heights along the fire-injured stem.Key Results
Following fire injury, P. menziesii axial RDs narrowed by 38–43 % in the first year after injury, and the magnitude of this change increased with stem height. Larix occidentalis axial RDs widened by 46–50 % in the second year after injury. Radial RDs were of equivalent size in P. menziesii, but widened by 162–214 % in L. occidentalis. Fusiform rays were larger following fire injury, by 4–14 % in P. menziesii and by 23–38 % in L. occidentalis. Furthermore, axial RD density increased in both species due to the formation of tangential rows of traumatic RDs, especially in the first and second years after injury. However, radial RD density did not change significantly.Conclusions
These results highlight traumatic resinosis as a species-specific response. Pseudotsuga menziesii produce RDs of equivalent or reduced size, whereas L. occidentalis produce wider RDs in both the axial and radial duct system, thereby increasing resin biosynthesis and accumulation within the whole tree. Larix occidentalis thus appears to allocate more energy to defence than P. menziesii. 相似文献2.
A mild bleaching event was observed among Pocillopora spp. in the southern Gulf of California in the spring of 2006. Uniform bleaching occurred in numerous colonies on the upper
portions of their branches. Most (∼90%) colonies that exhibited bleaching contained a species of endosymbiotic dinoflagellate,
Symbiodinium C1b-c, which differed from the Symbiodinium D1 found inhabiting most unbleached colonies. Analysis of chlorophyll fluorescence, indicated a decline in photosystem II
photochemical activity, especially among colonies populated with C1b-c. By early August, most affected colonies had recovered
their normal pigmentation and fluorescence values were once again high for all colonies. No mortality was observed among tagged
bleached colonies nor did symbiont species composition change during recovery. This unusual episode of bleaching did not appear
to be a response to thermal stress, but may have been triggered by high levels of solar radiation during a period of unseasonally
high water clarity in the early spring. 相似文献
3.
豆科植物在中国草原生态系统中的地位及其生理生态研究 总被引:11,自引:0,他引:11
豆科(Leguminosae)植物在改良土壤肥力、保持水土、提供多种经济产品方面功能显著,但我国干旱、半干旱草原区草场的退化使豆科植物资源受到严重破坏,有的面临灭绝的危险.本文明确了豆科植物在草原生态系统中的重要性,并综述了其光合、固氮等重要生理过程的研究进展,总结出自然生态系统中豆科植物的高光合机理和环境胁迫对固氮特性的影响,同时指出在豆科植物的适生机制和固氮潜能的发挥等还有很大的研究前景,在生产实践中,播种豆科灌木和豆科牧草是解决大面积人工林、草场"氮缺乏"的有效措施. 相似文献
4.
Herman Hummel 《Helgoland Marine Research》2003,56(4):247-251
The genetic diversity, differentiation and performance of some dominant invertebrates in the marine coastal zone of Europe
are reviewed in order to discuss the use of the metapopulation concept in the marine coastal realm. A consistently high genetic
diversity of the species studied (mussels of the Mytilus edulis complex, Baltic clams Macoma balthica and lugworms Arenicola marina), a low differentiation and an almost uniform ecophysiological performance (determined by growth, maximum length, level reserve
constituents or stress resistance) all along the coast of Europe do not support the use of the metapopulation concept.
Electronic Publication 相似文献
5.
The major factors thought to control the distribution of associations on the sea cliffs in Britain are discussed in relation to the zonation of cliff vegetation, and some experiments to investigate the effects of these factors are described.The seeds of the maritime cliff species are able to germinate in higher salinities than those of closely related inland species.Relative growth rates of maritime cliff species indicate stimulation at low salinities over non-saline conditions, and less reduction in growth at higher salinities than those of closely related inland species.Increasing salinity reduces both photosynthesis and dark respiration in Lavatera arborea. Mesophyll and stomatal resistances are increased while transpiration is reduced.The distribution of ions within Lavatera arborea grown at different salinities indicates differential accumulation between young leaves, old leaves and roots.Nomenclature follows Clapham, Tutin & Warburg (1962). 相似文献
6.
7.
Summary Juvenile plants ofPlantago lanceolata andP. major ssp.major were grown in a flowing solution system at 7.5 mM or 9.5 M NO3. The parameters investigated were: RGR, shoot weight percentage, leaf length, length of main root axis, shoot concentrations of major ions and organic N, and the specific uptake rate for NO3. At 9.5 M NO3 growth ofP. major was not hampered, whereas shoot growth and leaf length ofP. lanceolata were reduced. The NO3 concentration ofP. lanceolata decreased more than that ofP. major. The different performances of the species at 9.5 M NO3 were associated with different specific uptake rates. In both treatments the root system ofP. major was shorter than that ofP. lanceolata. P. lanceolata accumulated more NO3 in the leaves. The performance of thePlantago species is discussed in relation to the availability of nutrients in their habitats.Grassland Species Research Group. Publication no. 37. 相似文献
8.
Summary The production of nitrate in an old established dune grassland soil and its uptake by plants was studied by comparing amounts of mineral nitrogen and numbers of nitrifying bacteria in the rhizosphere on the one hand, and on the other accumulated nitrate and levels of nitrate reductase (NaR) of individual plants of three Plantago species,i. e., P. major, P. lanceolata andP. coronopus. For these three Plantago species andP. media basal levels of NaR in the absence of nitrate were determined in plants grown in culture solutions. The basal NaR levels ofP. major andP. media (species occurring on nutrient-rich soils) were significantly higher than those ofP. lanceolata andP. coronopus (species found on nutrient-poor soils). NaR activity increased in the presence of nitrate and was suppressed by ammonium.From the numbers of nitrifying bacteria in the rhizosphere and NaR activity in the leaves it was concluded that nitrate was produced in the root environments of the three Plantago species and that the compound was taken up by the plants. NaR activities and numbers of nitrifying bacteria were higher for individuals ofP. major than for those ofP. lanceolata andP. coronopus. No correlation was found between the ammonium levels and the numbers of nitrifying bacteria in the soil, and no indications of inhibition of nitrifying bacteria in the rhizosphere were obtained. For individuals ofP. lanceolata a correlation was found between the numbers of nitrifying bacteria in the soil and NaR activity in the leaves. The results are discussed in relation to the ecological habitats of the three species.Grassland Species Research Group Publication No.38. 相似文献
9.
A rapid method for screening antifungal compounds and performing ecophysiological studies with filamentous fungi has been developed by the use of specific semi-solid media and spectrophotometric/turbidimetric measurements using the Bioscreen C with 2×100 microtitre well plates. The medium composition and preparation, inoculum size, medium volumes, and incubation parameters for measuring initial germination and growth dynamics have been optimised. These have been applied to assess the effectiveness of 18 concentrations of propyl propane thiosulfinate (PTS) against Aspergillus flavus in YES medium under different environmental regimes. Minimum inhibitory concentrations (MIC), and non-inhibitory concentration (NIC) values, and a newly developed MIC(50), have been calculated for the efficacy of these concentrations of PTS under four different environmental conditions (0.995 and 0.95 water activity (a(w)); 20 and 25°C) over 7d periods with automated measurements every 20 min. Data were modelled using the Lambert-Pearson Model, a mathematical modelling approach previously used for bacterial inhibition. Results have been compared with traditional growth rate data and Lethal Dose(50) (LD(50)) values. This approach could have major implications for rapid screening assays for growth and secondary metabolite production by filamentous organisms and has major advantages in terms of time reduction, culture medium volumes required, measurement and the ability to integrate and model key parameters for comparing efficacy. 相似文献
10.
L. T. Ellis A. K. Asthana P. Srivastava I. Omar K. K. Rawat V. Sahu 《Journal of bryology》2013,35(1):47-63
AbstractBryophyte biomass and diversity vary strongly with altitude in the tropics. Low abundance and low species numbers in lowland rain forests are most likely due to reduced diurnal activity times combined with high nocturnal respiration rates at high temperatures. This may exclude many montane species from the warm lowlands. However, an alternative hypothesis explains the observed pattern, namely a limited desiccation tolerance of montane species, precipitation being more concentrated but less frequent in most lowland forests compared to montane cloud forests. To test this hypothesis, we studied the desiccation tolerance of four montane and four lowland bryophyte species. The effects of prolonged drought were quantified with chlorophyll fluorescence (Fv/Fm) and the extent of electrolyte leakage. Both montane and lowland species survived dry periods of ≧80 days, which far exceeds the duration of dry periods in the wet lowland tropics. We can thus exclude intolerance to long dry spells as an explaination for the absence of the tested montane species in the lowlands. We should continue to focus on other mechanisms to explain the altitudinal gradient of bryophyte abundance and diversity in the tropics, in order to understand this pattern, as well as to predict future trends under climatic warming. 相似文献