厦门地区露地栽培多肉植物的种类筛选及其园林应用研究

本文介绍适合厦门地区露地栽培的仙人掌等多肉植物种类及其园林应用情况,并结合多年的观察记录,对这类植物的适应性进行评估和讨论,就其发展前景作简要阐述。     

Towards a density measure for assessments of arid plant populations – examples from the southern Namib Desert

Plant species in arid environments are often widely spaced making population assessments difficult. In order to minimise observer bias we tested two repeatable simple methods during red data assessments in the southern Namib Desert. Both the transect‐based and the quadrat‐based method resulted in over‐estimates of the true population size. However, because of case of application, the transect method warrants further development.     

Water use efficiency of two succulents with contrasting CO2 fixation pathways

Two succulents with similar growth forms but different types of photosynthesis, Cotyledon orbiculata (crassulacean acid metabolism, CAM) and Othonna opima (C₃ pathway), were investigated with respect to the modulation of water use efficiency (WUE) during the transition from the rainy season to subsequent drought. Environmental conditions were simulated in a controlled-environment experiment on the basis of data collected in the habitat of the two species in the southern Namib desert. Experiments included one or more periods of hot bergwind, which frequently occurs in this region. When water was readily available, daily net CO₂ fixation was similar in the two species. This result confirms that the daily CO₂ fixation of CAM plants is as high as that of morphologically similar C₃ plants adapted to the same habitat. As expected, both species reduced CO₂ fixation and water loss through transpiration during simulated hot bergwind periods and their WUE values increased. However, after the second hot bergwind period, nearly identical WUEs were recorded: 41.0 and 40.0 mmol mol^?1 for C. orbiculata and O. opima, respectively. Therefore the statement that a CAM plant is a better ‘water saver’ than a C₃ plant does not necessarily hold for CAM and C₃ plants with similar growth forms growing under the same environmental conditions.     

CO2 exchange of CAM exhibiting succulents in the southern Namib desert in relation to microclimate and water stress

The responses of CO₂ exchange and overnight malate accumulation of leaf and stem succulent CAM-plants to water stress and the particular climatic conditions of fog and föhn in the southern Namib desert have been investigated. In most of the investigated CAM plants a long term water stress gradually attenuated any uptake of external CO₂ and led to CO₂ release throughout day and night. No CAM-idling was observed. Rainfall or irrigation immediately restored daytime CO₂ uptake while the recovery of the nocturnal CO₂ uptake was delayed. Dawn peak of photosynthesis was only found in well watered plants but was markedly reduced by the short term water stress of a föhn-storm. Morning fog with its higher diffuse light intensity compared with clear days increased photosynthetic CO₂ uptake considerably. Even in well watered plants nocturnal CO₂ uptake and malate accumulation were strongly affected by föhn indicating that the water vapour pressure deficit during the night determines the degree of acidification.     

Effects of invasion of fire‐free arid shrublands by a fire‐promoting invasive alien grass (Pennisetum setaceum) in South Africa

Arid shrublands in the Karoo (South Africa) seldom accumulate sufficient combustible fuel to support fire. However, as a result of invasion by an alien perennial grass (Pennisetum setaceum), they could become flammable. This paper reports on an experiment to assess the effects of fire following invasion by P. setaceum. We established 10 plots (5 × 10 m) separated by 2.5 m, and added grass fuel to five plots (5 and 10 tons ha^?1 to alternate halves of the plot) leaving the remaining five plots as interspersed controls. Plots with fuel added were burnt, and fire behaviour was measured during the burns. Rates of fire spread were generally low (0.01–0.07 m s^?1) and did not differ significantly between burn treatments. Mean fireline intensities were higher in the high compared with the low fuel treatments (894 and 427 kW m^?1, respectively). We recorded plant species and their cover before and after burning on each of the plots. After 15 months of follow‐up monitoring in the burn plots, only two species, the dwarf shrub (Tripteris sinuata) and the perennial herb (Gazania krebsiana) resprouted. Most individuals of other species were killed and did not reseed during the 15‐month study. The mass of added fuel load (high or low) did not influence vegetation recovery rates after fire. Should future invasions by P. setaceum lead to similar fuel loads in these shrublands, inevitable fires could change the vegetation and may favour spread of the flammable grass. Our results have important implications for predicting the effects of invasive alien plants (especially grasses) on fire‐free ecosystems elsewhere. The predicted impacts of fire may alter species composition, ultimately affecting core natural resources that support the Karoo economy.     

Turgoränderungen in Blasenzellen von Mesembryanthemaceen

Die epidermalen Blasenzellen von verschiedenen Mesembryanthemaceen Arten können bei mangelnder Wasserversorgung offenbar kurzfristig als Wasserspeicher für das photosynthetisch aktive Gewebe genutzt werden. Durch die bei der teilweisen Entleerung auftretende Abflachung der Blasenzellen werden bei Mesembryanthemum crystallinum die Abstände zwischen den Blasenzellen verringert, so daB die Flache, die fiir den Gasaustausch der Stomata mit der umgebenden Luft zur Verfiigung steht, 24 h nach Abbruch der Wasserversorgung auf 1/3, reduziert wird. Damit bilden die Blasenzellen beinahe eine “zweite Epidermis”, die bei Drosanthemum-Blättern durch eng aneinandergepreßte Blasenzellen erreicht wird und die die Wasserverluste durch Transpiration verringern könnte. Der Turgor in den Blasenzellen von Drosanthemum ändert sich am natürlichen Standort (südliche Namib) im Tagesverlauf: in der Morgendämmerung sinkt der Turgor urn 2 bar und steigt erst während der Nacht wieder an. Der Turgorabfall läuft parallel zu einer lichtbedingten Malatsynthese im grünen Gewebe, dessen osmotische Aktivität für den Wasserverlust der Blasenzellen verantwortlich sein könnte. Die absolute Höhe des Turgordruckes ist in den Blasenzellen der jüngsten Blätter 5 bis 10 mal größer als in den alteren Blattern.     

Successive cambia in Aizoaceae: products and process

The transverse and longitudinal sections of the stems and roots of 11 genera of Aizoaceae, representing a wide range of growth forms from hard fibrous stems to fibre‐free roots, were studied using light microscopy and scanning electron microscopy. In most of the genera, fibres are the first xylary product of each vascular cambium, followed by vessels in a parenchyma background. Variations on this pattern help to prove that fibres are produced by vascular cambia, except in Ruschia and Stayneria, in which both the lateral meristem and the vascular cambia produce fibres. Cylinders of conjunctive tissue parenchyma that alternate with the vascular cylinders are produced by the lateral meristem. The concept that the lateral meristem gives rise to the vascular cambia and secondary cortex is supported by photographic evidence. Radial divisions occur in the origin of the lateral meristem, and then again as vascular cambia arise from the lateral meristem; these radial divisions account for storeying in fibres and conjunctive tissue. Raylessness characterizes all Aizoaceae studied, with the exception of Tetragonia, which also differs from the remaining genera by having vasicentric axial parenchyma, a scattering of vessels amongst fibres, and the presence of druses instead of raphides. Several vascular cambia are typically formed per year. Several vascular cambia are active simultaneously in a given stem or root. Roots have fewer fibres and more abundant conjunctive tissue parenchyma than stems. Successive cambia result in an ideal dispersion of vascular tissue with respect to water and photosynthate storage and retrieval capabilities of the parenchyma, and to liana stem plans. The distribution and relative abundance of fibres, vessels, secondary phloem, and conjunctive tissue parenchyma relate primarily to habit and are not a good source of systematic data, with the probable exception of Tetragonia. The general pattern of lateral meristem and vascular cambial ontogeny is the same as in other families of the core Caryophyllales, although the patterns of the tissues produced are diverse. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 153 , 141–155.     

Othonna cerarioides (Asteraceae: Othonnineae), a new species from Namaqualand,South Africa

Othonna cerarioides Magoswana and J.C. Manning is described as a new species from Namaqualand, Northern Cape Province of South Africa. It is an erect shrub with rod-like stems and branches, bearing numerous spur-shoots with obovate-oblanceolate leaves clustered at the tips, and up to nine disciform capitula per spur-shoot. Othonna cerarioides is anomalous in the genus in that the style of some of the disc florets is bifid. Othonna is diagnosed within subtribe Othonnineae by female-sterile disc florets with simple (or very rarely minutely bifid) styles. The disc florets in the closely related genus Hertia are bisexual with well branched styles.     

A comparison in species distribution model performance of succulents using key species and subsets of environmental predictors

Identifying the environmental drivers of the global distribution of succulent plants using the Crassulacean acid metabolism pathway of photosynthesis has previously been investigated through ensemble‐modeling of species delimiting the realized niche of the natural succulent biome. An alternative approach, which may provide further insight into the fundamental niche of succulent plants in the absence of dispersal limitation, is to model the distribution of selected species that are globally widespread and have become naturalized far beyond their native habitats. This could be of interest, for example, in defining areas that may be suitable for cultivation of alternative crops resilient to future climate change. We therefore explored the performance of climate‐only species distribution models (SDMs) in predicting the drivers and distribution of two widespread CAM plants, Opuntia ficus‐indica and Euphorbia tirucalli. Using two different algorithms and five predictor sets, we created distribution models for these exemplar species and produced an updated map of global inter‐annual rainfall predictability. No single predictor set produced markedly more accurate models, with the basic bioclim‐only predictor set marginally out‐performing combinations with additional predictors. Minimum temperature of the coldest month was the single most important variable in determining spatial distribution, but additional predictors such as precipitation and inter‐annual precipitation variability were also important in explaining the differences in spatial predictions between SDMs. When compared against previous projections, an a posteriori approach correctly does not predict distributions in areas of ecophysiological tolerance yet known absence (e.g., due to biotic competition). An updated map of inter‐annual rainfall predictability has successfully identified regions known to be depauperate in succulent plants. High model performance metrics suggest that the majority of potentially suitable regions for these species are predicted by these models with a limited number of climate predictors, and there is no benefit in expanding model complexity and increasing the potential for overfitting.