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161.
Eragrostis pilosa (Linn.) P Beauv., a C4 grass native to east Africa, was grown at both ambient (350 μmol mol−1 and elevated (700 μmol mol−1 ) CO2 in either the presence or absence of the obligate, root hemi-parasite Striga hermonthica (Del.) Benth. Biomass of infected grasses was only 50% that of uninfected grasses at both CO2 concentrations, with stems and reproductive tissues of infected plants being most severely affected. By contrast, CO2 concentration had no effect on growth of E. pilosa , although rates of photosynthesis were enhanced by 30–40% at elevated CO2 . Infection with S. hermonthica did not affect either rates of photosynthesis or leaf areas of E. pilosa , but did bring about an increase in root:shoot ratio, leaf nitrogen and phosphorus concentration and a decline in leaf starch concentration at both ambient and elevated CO2 . Striga hermonthica had higher rates of photosynthesis and shoot concentrations of soluble sugars at elevated CO2 , but there was no difference in biomass relative to ambient grown plants. Both infection and growth at elevated CO2 resulted in an increase in the Δ13 C value of leaf tissue of E. pilosa , with the CO2 effect being greater. The proportion of host-derived carbon in parasite tissue, as determined from δ13 C values, was 27% and 39% in ambient and elevated CO2 grown plants, respectively. In conclusion, infection with S. hermonthica limited growth of E. pilosa , and this limitation was not removed or alleviated by growing the association at elevated CO2 . 相似文献
162.
Criconemoides ornatus at 500, 1,000, and 10,000 specimens per 15-cm pot containing 1,500 cc of soil was not pathogenic or parasitic on "Loveli'' peach. The number of nematodes recovered was always less than the inoculum. Inocula of 1,000 and 10,000 specimens were pathogenic to centipede grass, but the 500 inoculum level was not. The number of nematodes recovered from parasitized centipede grass was considerably higher than the inoculum. 相似文献
163.
164.
Caroline E. R. Lehmann Catherine L. Parr 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2016,371(1703)
Tropical grassy biomes (TGBs) are changing rapidly the world over through a coalescence of high rates of land-use change, global change and altered disturbance regimes that maintain the ecosystem structure and function of these biomes. Our theme issue brings together the latest research examining the characterization, complex ecology, drivers of change, and human use and ecosystem services of TGBs. Recent advances in ecology and evolution have facilitated a new perspective on these biomes. However, there continues to be controversies over their classification and state dynamics that demonstrate critical data and knowledge gaps in our quantitative understanding of these geographically dispersed regions. We highlight an urgent need to improve ecological understanding in order to effectively predict the sensitivity and resilience of TGBs under future scenarios of global change. With human reliance on TGBs increasing and their propensity for change, ecological and evolutionary understanding of these biomes is central to the dual goals of sustaining their ecological integrity and the diverse services these landscapes provide to millions of people.This article is part of the themed issue ‘Tropical grassy biomes: linking ecology, human use and conservation’. 相似文献
165.
The mesocotyl is an embryonic organ present in Poaceae that plays an important role in seedling emergence. The elongation of this first internode contributes decisively to the coleoptile reaching the soil surface. This study examines the process of mesocotyl elongation under controlled conditions in three caryopsis collection sites of Digitaria sanguinalis (L.) Scop. originating from Spain (Barcelona and Girona) and Argentina that may have two patterns of germination: radicular or coleoptilar. The frequencies of the two germination patterns varied significantly depending on the origin. Light inhibited the elongation of the mesocotyl drastically, resulting in maximum lengths of 3.5 mm, while in darkness the maximum length was 57 mm. The time-course evolution displayed under dark conditions was quite similar for all sites of origin and both germination patterns; the growth rate ranged from 0.23 to 0.30 mm h? 1. Within localities, caryopses with a coleoptilar pattern of germination showed a lower growth rate than those with a radicular one. 相似文献
166.
Calli were induced from mature caryopses of timothy grass (Phleum pratense L.) on MS medium (Murashige and Skoog 1962) supplemented with 500 mg·dm−3 casein hydrolysate and 5 mg·dm−3 2,4-D (2,4-dicholorophenoxyacetic acid) or 2 mg·dm−3 dicamba (3,6-dichloro-o-anisic acid). Twelve-week-old calli were passaged on media with reduced levels of auxins (2 mg·dm−3 2,4-D or 1 mg·dm−3 dicamba). Tissues induced on medium with 2,4-D were transferred on medium with 2,4-D and on medium with dicamba; parallely
calli initiated on medium with dicamba were passaged on medium with 2,4-D or dicamba. Calli from various media sequences were
used to establish cell suspension cultures in media containing 2 mg·dm−3 2,4-D or 1 mg·dm−3 dicamba. An assessment of regeneration ability of calli was made on MS medium containing 0.2 mg·dm−3 kinetin. Callus tissue induced and/or subcultured on any of the media with 2,4-D did not regenerate plants while dicamba
added to the media was the effective stimulator of regenerability. In the presence of 2,4-D calli and suspensions produced
a jelly-like extracellular matrix. In cell suspension this phenomenon was observed 4–5 days after each passage. The measurements
of electric potential of calli, growing on MS medium with kinetin were performed. Non-regenerating callus areas had an electric
potential close to 0 mV while parts of tissue with meristematic centres were characterized by lower values of electric potential. 相似文献
167.
Dinitrogen fixation in white clover (Trifolium repens L.) grown in pure stand and mixture with perennial ryegrass (Lolium
perenne L.) was determined in the field using 15N isotope dilution and harvest of the shoots. The apparent transfer of clover N to perennial ryegrass was simultaneously assessed.
The soil was labelled either by immobilizing 15N in organic matter prior to establishment of the sward or by using the conventional labelling procedure in which 15N fertilizer is added after sward establishment. Immobilization of 15N in the soil organic matter has not previously been used in studies of N2 fixation in grass/clover pastures. However, this approach was a successful means of labelling, since the 15N enrichment only declined at a very slow rate during the experiment. After the second production year only 10–16% of the
applied 15N was recovered in the harvested herbage. The two labelling methods gave, nonetheless, a similar estimate of the percentage
of clover N derived from N2 fixation. In pure stand clover, 75–94% of the N was derived from N2 fixation and in the mixture 85–97%. The dry matter yield of the clover in mixture as percentage of total dry matter yield
was relatively high and increased from 59% in the first to 65% in the second production year. The average daily N2 fixation rate in the mixture-grown clover varied from less than 0.5 kg N ha−1 day−1 in autumn to more than 2.6 kg N ha−1 day−1 in June. For clover in pure stand the average N2 fixation rate was greater and varied between 0.5 and 3.3 kg N ha−1 day−1, but with the same seasonal pattern as for clover in mixture. The amount of N fixed in the mixture was 23, 187 and 177 kg
N ha−1 in the seeding, first and second production year, respectively, whereas pure stand clover fixed 28, 262 and 211 kg N ha−1 in the three years. The apparent transfer of clover N to grass was negligible in the seeding year, but clover N deposited
in the rhizosphere or released by turnover of stolons, roots and nodules, contributed 19 and 28 kg N ha−1 to the grass in the first and second production year, respectively.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
168.
Whether an exotic species becomes integrated into a community or aggressively takes it over depends upon many interacting factors. Using contextual analyses, we combined genetic data about an invasive plant with information about the neighboring species, the community, and the environment to determine what factors enable a genotype or species to invade. We transplanted 50 individuals of each of three clones of the invasive grass Phalaris arundinacea, reed canary grass, into 150 random locations within a Vermont pasture. For each individual, we recorded clonal identity, neighbor identity, community indices (species richness and species diversity), and an environmental variable (soil moisture). The response variables were survivorship, above-ground biomass, below-ground biomass and the ratio of above- to below-ground biomass. Clonal identity affected both survivorship and below-ground biomass. The fastest tillering clone had poor survivorship but survivors produced a large amount of below-ground biomass, making this clone more likely to successfully overwinter. Neighbor species affected above- and below-ground biomass. Reed canary grass produced more above- and below-ground biomass when Anthoxanthum odoratum, a common pasture grass species, was abundant. Community attributes also influenced growth. Although we expected diverse plots to repel the invasion, plants in the more diverse plots had higher amounts of below-ground biomass. Finally, environmental effects also influenced growth. Reed canary grass produced more above-ground biomass in wetter plots, confirming that it does well under wet conditions. 相似文献
169.
草鱼出血病细胞培养灭活疫苗的研究:疫苗的稳定性及佐剂和加强免疫对草鱼免疫应答的影响 总被引:5,自引:0,他引:5
CFRV 疫苗具有较好的稳定性。4℃保存8个月,其免疫保护力仍为83.6%,草鱼免疫后的血清中和抗体效价为119.2±8.8(2),与保存开始时相比,没有显著的差别。28℃保存8d,其免疫原性也基本上保持在原来的水平。CFRV 疫苗在此两温度下的免疫有效期分别为8个月和8d。不完全弗氏佐剂对 CFRV 疫苗有明显的增效作用;用 CFRV 疫苗对草鱼进行加强免疫,可明显地增强草鱼对该疫苗的免疫应答,由此证明草鱼具有免疫回忆反应。
相似文献
170.