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21.
Plant density and size — two factors that represent plant survival and growth — are key determinants of yield but have rarely been analysed explicitly in the context of biodiversity–productivity relationships. Here, we derive equations to partition the net, complementarity and selection effects of biodiversity into additive components that reflect diversity-induced changes in plant density and size. Applications of the new method to empirical datasets reveal contrasting ways in which plant density and size regulate yield in species mixtures. In an annual plant diversity experiment, overyielding is largely explained by selection effects associated with increased size of highly productive plant species. In a tree diversity experiment, the cause of overyielding shifts from enhanced growth in tree size to reduced mortality by complementary use of canopy space during stand development. These results highlight the capability of the new method to resolve crucial, yet understudied, demographic links between biodiversity and productivity. 相似文献
22.
Abstract. Previous research has indicated that patch structure at small spatial scales (<100m2) in tallgrass prairies was defined by a diverse array of infrequent species because dominant species occurred in all samples at this scale. Also, patch structure was not significantly different from that derived from random species associations. Based on these results, we hypothesized that remo val of a dominant species would have no effect on patch structure in these prairies. We tested this hypothesis by removing a dominant grass, Schizachyrium scoparium (Poaceae), from half of each of four 10 m × 10 m study blocks, and comparing differences in patch structure between control and removal halves before and after removal. The minimum resolution in our study was 1 m2. Patches of similar species composition were defined by cluster analysis of presence/absence data and cover data. Patch sizes ranged from 1 to 34 m2. Following the removal of S. scoparium there was an overall increase in the number of species in the removal half of each block compared to pre-treatment levels. However, the number of patch types and number of spatially mapped groups, based on presence/absence or cover data, did not change between control and removal plots after the removal of S. scoparium. This supports the hypothesis that removal of a large, dominant species would have no effect on patch structure at this scale of resolution in these prairies. Thus, patch structure, as defined here, is an emergent property in these grasslands that is not predictable from changes in species composition. This property of stochastic patch structure results from interactions of processes operating at scales both larger and smaller than our scale of resolution. Stochastic models may provide a reasonable approach to modelling small-scale patch dynamics in tallgrass prairie communities. 相似文献
23.
随着对城市人居环境质量高度关注,城市生态学越来越受到重视。城市生态系统长期观测研究站(简称城市生态站),作为能够跟踪和研究城市生态系统长期变化规律的一种研究手段,在国内外得到了较快发展。在分析国内外城市生态站的研究经验和实践过程基础上,提出了城市生态站的科学目标、研究内容和主要工作,特别就城市生态站的观测工作、模拟实验工作和社会服务的基本框架和工作内容进行了论述,可以作为城市生态站建设的设计思路。为我国新建和完善城市生态站工作提供重要指导作用。 相似文献
24.
杂交试验是一项费时费钱的工作,因此在进行试验之前如能进行严密的设计,给出试验所需的样本大小是十分必要的,统计学中常见的估计样本容理的公式不宜应用于杂交试验,本文分两种情况给出了杂交试验中样本容量的估计公式,据此估计出的样本容量安排杂交试验,可在满足试验者要求的条件下,使试验的总成本最低或使试畜的总头数最少。 相似文献
25.
Measuring Success: Evaluating the Restoration of a Grassy Eucalypt Woodland on the Cumberland Plain, Sydney, Australia 总被引:10,自引:0,他引:10
Abstract We compared the floristic composition and structure of restoration areas of eucalypt woodland with untreated pasture (control) and remnant vegetation (reference) in western Sydney. The restored areas comprised over 1,000 ha of abandoned pasture, which had been treated to reduce weeds and planted with seedlings of 26 native plant species raised from seed obtained locally from remnant vegetation. Plantings were carried out 0–9 years ago. Floristic composition was measured in quadrats using frequency scores and cover abundance. As far as possible treatments and restoration ages were replicated across sites. Ordination and analyses of similarity failed to distinguish the composition of restored vegetation from that of untreated pasture, which were both significantly different from that of remnant vegetation. There was a weak compositional trend with age of restored vegetation, but this was not in the direction of increasing resemblance to remnant vegetation. There was some evidence for convergence in structural features of restored with remnant vegetation, but this was at least partly attributed to plant growth. Subject to constraints imposed by the sampling design, environmental factors, and spatial variation were discounted as explanations for the results. The results therefore suggest either failure of restoration treatments or a restoration trajectory that is too slow to detect within 10 years of establishment. Our conclusions agree with those of similar studies in other ecosystems and support: (1) the need to monitor restoration projects against ecological criteria with rigorous sampling designs and analytical methods, (2) further development of restoration methods, and (3) regulatory approaches that seek to prevent damage to ecosystems rather than those predicated on replacing losses with reconstructed ecosystems. 相似文献
26.
Dominique de Moulins 《Vegetation History and Archaeobotany》1996,5(1-2):153-156
Results of experimental retrieval of plant remains (both charred modern and fossil) from three sediment types (clay, gravel
and sandy loam) carried out by environmental archaeologists from the Ancient Monuments Laboratory and the Central Archaeology
Service, English Heritage, are reported. For each sediment type, six different treatments were carried out using three flotation
machines of the Siraf type, two other machines in use in two archaeological units and one experimental machine. The results
show that there is invariably considerable discrepancy between the amount of plant material present and that recovered, that
the Serif-type machine is among the best currently available and that pretreatment of particular mineral soils may improve
recovery of plant macrofossil material. 相似文献
27.
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29.
Experiments on plants are often carried out in growth chambers or greenhouses which necessitate the use of an artificial rooting
environment, though this is seldom characterized in detail. Measurements were made to compare the rooting environment in large
boxes (0.25 m3) with that in small pots (0.19, 0.55 and 1.90 dm3) in naturally lit chambers.
Diurnal temperature fluctuations of 14.6, 11.6 and 7.7°C occurred in the post compared with only 1.9°C in the boxes. Soil
drying to a matric potential of-50 kPa was approximately 25 times faster in the pots. The mean heights of 2 year old Sitka
spruce (Picea sitchensis (Bong.) Carr.) seedlings grown throughout their second growing season in the three sizes of pots were 38, 62 and 92% of the
mean height of those grown in the boxes. Soil solution nutrient concentrations in the boxes were considerably increased by
soil drying, an aspect which seems to have received little attention in experiments involving artificially imposed drought.
An alternative system of constraining the roots of individual plants within nylon fabric bags, embedded in larger volumes
of soil, to facilitate harvesting of complete root systems is described. The importance of the rooting environment in determining
the outcome of physiological experiments is also briefly discussed. 相似文献
30.
Systematic studies were undertaken on the Caloglossa continua ( Okamura) King et Puttock complex from Japan, Singapore, and Australia, based on morphology and reproductive compatibility. Specimens from Japan had two to six cell rows derived from a nodal axial cell, at the margin opposite the branch, whereas those from Australia possessed only a single cell row. Specimens from Singapore formed one to four cell rows per nodal axial cell and always contained at least one single cell row on any one thallus. These differences were maintained in cultured materials over a range of temperatures or salinities. Type material of C. continua had the same morphology as the Japanese specimens in this study. Carpospores discharged from the Japanese isolate germinated at 10°C, whereas those from Singapore and Australia died at this temperature. In hybridization experiments, the Japanese entity was completely nonfertile with both the Singaporean and Australian isolates. Many pseudocystocarps were produced in the crossing between the male from Australia and the female from Singapore, although the reciprocal combination did not produce any such structures. On the basis of the discontinuous morphology coupled with the complete reproductive isolation, the entities from Singapore and Australia are described here as C. monosticha sp. nov. The entities with multiple cell rows likely expanded their geographic range from tropical regions, where the majority of Caloglossa species are now distributed, to high-latitude regions, and such an expansion would be associated with acquiring low-temperature tolerance . 相似文献