Relationship between plant phosphorus status and the kinetics of arsenate influx in clones ofdeschampsia cespitosa (L.) beauv. that differ in their tolerance to arsenate

Uptake kinetics of arsenate were determined in arsenate tolerant and non-tolerant clones of the grassDeschampsia cespitosa under differing root phosphorus status to investigate the mechanism controlling the suppression of arsenate influx observed in tolerant clones. Influx was always lower in tolerants compared to non-tolerants. Short term influx of arsenate by the high affinity uptake system in both tolerant clones was relatively insensitive to root phosphorus status. This was in contrast to the literature where the regulation of the phosphate (arsenate) uptake system is normally much more responsive to plant phosphorus status. The low affinity uptake system in both tolerant and non-tolerant clones, unlike the high affinity uptake system, was more closely regulated by root phosphate status and was repressed to a much greater degree under increasing root phosphorus levels than the high affinity system.     

Effects of calcium and phosphate on the corpuscles of Stannius of the teleost fish,Oreochromis mossambicus

Summary Removal of the corpuscles of Stannius (CS) in Oreochromis mossambicus leads to hypercalcemia and hypophosphatemia. The effects on CS size and ultrastructure of different calcium and phosphate concentrations of the ambient water and of the food were investigated. A six-fold increase of the calcium concentration of the water leads to a four-fold increase in CS volume; this is mainly caused by an increase in the size and number of the type-1 cells. The effect of external calcium is most probably mediated by the calcium concentration of the blood plasma. Plasma ionic calcium may be the relevant factor. Changes in the calcium concentration of the food had no effect on the CS. Similarly, hyperphosphatemia or hypophosphatemia induced by high phosphate concentrations of the water or the food, or by a phosphate-deficient diet, had no noticeable effect on the CS. The results support the hypothesis that the type-1 cells produce the hypocalcemic factor of the CS. There is no evidence for the production by the CS of an endocrine factor involved in the control of phosphate metabolism.     

Water relations of indigenous versus exotic tree species,growing at the same site in a tropical montane forest in southern Ethiopia

The objective of the study was to compare the water relations of two indigenous [Podocarpus falcatus (Thunb.) Endl., Croton macrostachys Hochst. ex. Del.] and two exotic tree species (Eucalyptus globulus Labille., Cupressus lusitanica Miller) growing in the same location in the montane Munessa State Forest, southern Ethiopia. Stem flow was measured with Granier type thermal dissipation probes. Sap flux, normalized per unit sapwood area, and the total sapwood areas of the particular trees were used to estimate daily transpiration. Maximum daily transpiration values (60 kg water) were recorded for Croton when at full foliage. After shedding most of its leaves in the dry season transpiration was reduced to 8 kg per day. Eucalyptus had the next highest transpiration (55 kg), in this case at the peak of the dry season. It transpired 4–5 times more than Podocarpus and Cupressus trees of similar size. Maximum stem flux density was tree-size dependent only in Croton. Diurnal patterns of stem flux indicated that Croton, Eucalyptus and Podocarpus, in contrast to Cupressus, responded more directly to light than to atmospheric water pressure deficit. At high VPD (>1.0 kPa) stem flux reached a plateau in Croton and Podocarpus indicating stomatal limitation. Per unit leaf area Croton had the highest and Podocarpus and Cupressus the lowest daily transpiration rates. In summary, the pioneer tree Croton had the lowest and Podocarpus the highest water use efficiency. The contribution of the study to the understanding of the role of each tree species in the hydrology of the natural forest and the plantations is discussed.     

Experimental growth responses to groundwater level variation and competition in five British wetland plant species

New experimental evidence from controlledglasshouse studies was used to testprevious empirical field observations aboutthe interactions of hydrological dynamicswith individual plant species in wetlandhabitats. Manipulation of water levels, andthe presence/ absence of competitorspecies, produced significant morphologicalresponses (e.g. resource allocation toabove- and below-ground structures; plantheight; leaf size; tiller production) inmature individuals of five freshwaterwetland plant species characteristic ofBritish northern poor-fen habitats. Theseresponses provide evidence for potentialadvantages in survival and ability tospread vegetatively. The data also providenew insight into factors controlling thedistribution of wetland plants alonggradients of water table level, in thepresence or absence of competing species.Although there were variations betweenspecies, the effects of competition were,in general, less than those attributable tohydrological regime.     

The prevalence of non-indigenous species in southern California embayments and their effects on benthic macroinvertebrate communities

The prevalence of non-indigenous species (NIS) in southern California embayments was assessed from 123 Van Veen grab samples collected in nine bays and harbors during the summer of 1998. NIS occurred in all but two samples. They accounted for only 4.3% of the 633 taxa but contributed 27.5% of the abundance. There was no significant difference in the proportion of NIS abundance among ports harboring large vessels, small boat marinas, and areas where boats were not moored. Three species accounted for 92% of the NIS abundance: a spionid polychaete worm Pseudopolydora paucibranchiata, a mytilid bivalve Musculista senhousia, and a semelid bivalve Theora ubrica. The NIS did not appear to have a negative impact at the overall community level since NIS abundance was positively correlated with the abundance and richness of other species. This may be due to biogenic structures built by P. paucibranchiata and M. senhousia that enhance the abundances of other macrofauna.     

Mechanical behavior of a new biphasic calcium phosphate bone graft

The aim of this study was to create a new porous calcium phosphate implant for use as a synthetic bone graft substitute. Porous bioceramic was fabricated using a foam-casting method. By using polyurethane foam and a slurry containing hydroxyapatite-dicalcium phosphate powder, water, and additives, a highly porous structure (66 ± 5%) was created. The porous specimens possess an elastic modulus of 330 ± 32 MPa and a compressive strength of 10.3 ± 1.7 MPa. The X-ray diffraction patterns show hydroxyapatite and beta-pyrophosphate phases after sintering. A rabbit model was developed to evaluate the compressive strength and elastic modulus of cancellous bone defects treated with these porous synthetic implants. The compressive mechanical properties became weaker until the second month post implantation. After the second month, these properties increased slightly and remained higher than control values. New bone formed on the outside surface and on the macropore walls of the specimens, as osteoids and osteoclasts were evident two months postoperatively. Considering these properties, these synthetic porous calcium phosphate implants could be applicable as cancellous bone substitutes.     

无瓣海桑与乡土红树植物混交对林地大型底栖动物的影响

选择广东省雷州市附城镇和珠海市淇澳岛沿海1年生无瓣海桑人工林,分别在林下混种乡土红树植物红海榄或木榄幼苗,对混交林和无瓣海桑纯林林地大型底栖动物群落进行比较,探讨无瓣海桑与乡土红树植物混交对林地大型底栖动物的影响。结果显示,混交林和无瓣海桑纯林之间大型底栖动物群落的优势种存在差异;相似性分析检验(One-Way ANOSIM)、等级聚类和非参数多变量标序结果均表明1年无瓣海桑+红海榄混交林、1年无瓣海桑+木榄混交林和1年无瓣海桑纯林之间大型底栖动物群落结构差异显著。研究还发现在无瓣海桑人工林林下混交红海榄或木榄这两种乡土红树植物,可提高林地底栖动物的生物量和物种多样性。BIOENV分析说明大型底栖动物分布与红海榄或木榄这两种混交的乡土树种的凋落物量密切相关,这进一步证实了混交乡土红树植物对林地底栖动物多样性和分布的影响。两个研究地实验结果均显示,在无瓣海桑林下种植木榄的效果要优于红海榄,表现在木榄的平均苗高、凋落物量、凋落物量占群落凋落物总量百分比和幼苗成活率均高于红海榄,其对提高林地大型底栖动物生物量和物种多样性的效果也明显优于红海榄。     

Microhabitat use by rodent species in a central Brazilian cerrado

We analysed microhabitat use by the rodents Calomys tener, Necromys lasiurus and Thalpomys lasiotis and the factors that may influence their abundances in “murundu” grasslands (open fields with termite mounds) at Aguas Emendadas Ecological Station, Planaltina, Federal District, Brazil. Two grids with 100 sampling points were established and traps were placed at each intersection of the grid, where five microhabitat variables were also measured. Rodents were trapped from June through October 2008. Microhabitat explained 21% of the variation in community structure, with grass density and the number of termite mounds explaining most of the variation. Necromys lasiurus was most often captured in areas with dense grasses, whereas T. lasiotis and C. tener were most often in areas less dense with grasses.     

草甘膦对入侵植物加拿大一枝黄花和伴生植物白茅光合特性的影响

入侵植物加拿大一枝黄花(Solidago canadensis)给许多地区带来了较大危害,目前常采用化学防除法进行防除,但除草剂防治入侵植物的同时难免会影响土著植物的生长。为探讨草甘膦对入侵植物与本地植物光合特性的影响,以加拿大一枝黄花及其伴生种白茅(Imperata cylindrica)为研究对象,采用盆栽控制试验方法,研究不同浓度草甘膦处理21后单种、混种加拿大一枝黄花和白茅的生长特征及光响应过程。结果表明:1)草甘膦显著抑制两种植物的生长。随处理浓度升高,加拿大一枝黄花的株高增长量不断减小、叶片枯萎率不断增加;白茅的分蘖死亡率、叶片枯萎率不断升高。白茅对草甘膦较敏感,0.6mL/L浓度下白茅先失绿,1.2mL/L下其分蘖死亡率、叶片枯萎率均超50%;1.8mL/L下加拿大一枝黄花叶片枯萎率超50%。施药后与单种相比,混种加拿大一枝黄花株高增长略快、叶片枯萎率略低,混种白茅分蘖死亡率及叶片枯萎率均较低,但单、混种之间差异不显著。种间关系显著影响白茅的分蘖数。2)随处理浓度递增,加拿大一枝黄花和白茅叶片净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)均不断降低,白茅下降更快。两个物种胞间CO_2浓度(C_i)的变化不同,随着浓度升高,单种加拿大一枝黄花C_i先下降而后上升,而混种时的C_i则不断下降;单、混种白茅C_i均上升。3)草甘膦显著影响加拿大一枝黄花和白茅最大净光合速率(P_(nmax))、光饱和点(LSP)和光补偿点(LCP);对两个物种暗呼吸速率(R_d)的影响不显著,对加拿大一枝黄花表观量子效率(AQY)的影响同样不显著,但显著影响白茅AQY。种植方式显著影响两个物种P_(nmax)、LSP以及白茅R_d和AQY。0.6mL/L草甘膦对混种加拿大一枝黄花和白茅P_(nmax)的影响要大于对单种植株的影响,随处理浓度上升,对不同种植方式下两种植物P_(nmax)的影响趋近。与本地种白茅相比,入侵植物加拿大一枝黄花具有更高的光合速率和生长速率;草甘膦显著降低两个物种的生长和光合作用,白茅对草甘膦处理更敏感。     

Rapid, landscape scale responses in riparian tundra vegetation to exclusion of small and large mammalian herbivores

Productive tundra plant communities composed of a variety of fast growing herbaceous and woody plants are likely to attract mammalian herbivores. Such vegetation is likely to respond to different-sized herbivores more rapidly than currently acknowledged from the tundra. Accentuated by currently changing populations of arctic mammals there is a need to understand impacts of different-sized herbivores on the dynamics of productive tundra plant communities. Here we assess the differential effects of ungulate (reindeer) and small rodent herbivores (voles and lemmings) on high productive tundra vegetation. A spatially extensive exclosure experiment was run for three years on river sediment plains along two river catchments in low-arctic Norway. The river catchments were similar in species pools but differed in species abundance composition of both plants and vertebrate herbivores. Biomass of forbs, deciduous shrubs and silica-poor grasses increased by 40–50% in response to release from herbivory, whereas biomass of silica-rich grasses decreased by 50–75%. Hence both additive and compensatory effects of small rodents and reindeer exclusion caused these significant changes in abundance composition of the plant communities. Changes were also rapid, evident after only one growing season, and are among the fastest and strongest ever documented in Arctic vegetation. The rate of changes indicates a tight link between the dynamics of productive tundra vegetation and both small and large herbivores. Responses were however not spatially consistent, being highly different between the catchments. We conclude that despite similar species pools, variation in plant species abundance and herbivore species dynamics give different prerequisites for change.     

The influence of harvester and Messor capensis nest-mounds on the productivity and distribution of some plant species in the southern Karoo,South Africa

Nest-mounds of the harvester ant Messor capensis occur on and around nutrient-rich patches, along minor drainage lines in nutrient-rich soils, and on the plains, generally in nutrient-poor soils. Nest-site selection is related to the presence of suitable deep soils, the presence of stones and the distance from the nearest neighbouring nest. Two plant species, Galenia fruticosa and Pteronia pallens, were significantly associated with Messor capensis nest-mounds, both in numbers of mounds occupied and in numbers of individuals. A third species, Drosanthemum montaguense, was also more common in numbers of individuals, while a fourth species, Rhinephyllum macradenium was negatively associated with these mounds. The analysis of species guilds by soil type shows that significantly more species of nutrient-rich soils are present on M. capensis nest-mounds. Also, significantly more taller, woody species occurred on nest-mounds than in inter-mound spaces. Two species, Pteronia pallens and Osteospermum sinuatum, growing on ant nest-mounds had significantly longer inter-nodes than the same species growing off mounds. However, two other species, Pteronia cf. empetrifolia and Galenia fruticosa showed no difference in inter-node lengths between plants growing on and off mounds. Six of the nine species of plants sampled on ant nest-mounds had significantly higher seed production than plants of the same species growing in inter-mound spaces. The other three species showed a tendency towards more seeds per plant on ant nest-mounds. The proportions of live and dead plants on mounds differed between species. Only Ruschia spinosa showed a significant difference between the numbers of dead plants in the population on and off mounds, with more dead plants occurring on mounds. Significantly more seeds set on individuals of Pteronia pallens growing on ant nest-mounds than those growing off nest-mounds, but no such difference occurred in P. cf. empetrifolia. There was no significant difference in the proportion of seeds parasitized by the tephritid fly Desmella anceps for individuals of P. pallens and P. cf. empetrifolia growing on and off mounds.     

Accumulation of selenium by different plant species grown under increasing sodium and calcium chloride salinity

High levels of naturally occurring selenium (Se) are often found in conjunction with different forms of salinity in central California. Plants considered for use in phytoremediation of high Se levels must therefore be salt tolerant. Selenium accumulation was evaluated for the following species under increasing salt (NaCl and CaCl) conditions:Brassica napus L. (canola),Hibiscus cannibinus L. (kenaf),Festuca arundinacea L. (tall fescue), andLotus tenuis L. (birdsfoot trefoil). The experimental design was a complete randomized block with four salt treatments of <1, 5, 10, and 20 dS m^-1, four plant species, three blocks, and six replicates per treatment. Ninety days after growing in the respective salt treated soil with a Se concentration of 2 mg Se kg^-1 soil, added as Na₂SeO₄, all plant species were completely harvested. Among the species tested, shoot and root dry matter yield of kenaf was most significantly (p<0.001) affected by the highest salt treatment and tall fescue and canola were the least affected species. Generally there was a decrease in tissue accumulation of Se with increasing salt levels, except that low levels of salinity stimulated Se accumulation in canola. Canola leaf and root tissue accumulated the highest concentrations of Se (315 and 80 mg Se kg^-1 DM) and tall fescue the least (35 and 7 mg Se kg^-1 DM). Total soil Se concentrations all harvest were significantly (p<0.05) lower for all species at all salt treatments. Removal of Se from soil was greatest by canola followed by birdsfoot trefoil, kenaf and tall fescue. Among the four species, canola was the best candidate for removing Se under the tested salinity conditions. Kenaf may be effective because of its large biomass production, while tall fescue and birdsfoot trefoil may be effective because they can be repeatedly clipped as perennial crops.     

The potential use of identification of skeletal remains for the early detection of Ammotragus: an exotic ungulate species in Southern Spain

The main aim of our work was to evaluate osteometry as a complementary tool for the early detection of Ammotragus lervia, an exotic ungulate, which currently shows an expanding trend in southeastern Spain. For this purpose, 142 metacarpi and 123 metatarsi from seven Iberian ungulate species were determined by means of a classification function. In a general way, this function works, but regarding related species (those very similar from a morphometrical view), correct determination was reached in only 44.4–90% of the cases. However, in these cases, we can use auxiliary criteria like sexually dimorphic traits, and reach 100% correct identification of bones.     

Soil calcium and plant disease in serpentine ecosystems: a test of the pathogen refuge hypothesis

Ecologists have long sought mechanistic explanations for the patterns of plant distribution and endemism associated with serpentine soils. We conducted the first empirical test of the serpentine pathogen refuge hypothesis, which posits that the low levels of calcium found in serpentine soils provide associated plants with a refuge from attack by pathogens. We measured the range of soil calcium concentrations experienced by 16 wild population of California dwarf flax (Hesperolinon californicum) and experimentally recreated part of this range in the greenhouse by soaking serpentine soils in calcium chloride solutions of varying molarity. When flax plants grown in these soils were inoculated with spores of the rust fungus Melampsora lini we found a significant negative relationship between infection rates and soil calcium concentrations. This result refutes the pathogen refuge hypothesis and suggests that serpentine plants, by virtue of their association with low calcium soils, may be highly vulnerable to attack by pathogens. This interaction between plant nutrition and disease may in part explain demographic patterns associated with serpentine plant populations and suggests scenarios for the evolution of life history traits and the distribution of genetic resistance to infection in serpentine plant communities.     

Potential use in phytoremediation of three plant species growing on contaminated mine-tailing soils in Sardinia

We have analyzed the relationship between total Zn, Pb and Cu concentrations in the soil and the capacity of three plant species to accumulate these elements in their leaves. The study was carried out in a highly contaminated area at Sulcis-Iglesiente (SW-Sardinia, Italy). We took samples of the leaves of Dittrichia viscosa, Cistus salviifolius and Euphorbia pithyusa subsp. cupanii and samples of the soil beneath each of them at depths of 0-30 and 30-60 cm, both in contaminated mine tailings and surrounding areas. Due to the anthropic origin of the soil materials the results varied considerably. Bioavailability of trace elements was mainly related to the calcium-carbonate content and the crystalline and amorphous forms of iron in the soil. The concentration of Zn in the leaves of the three plant species studied was highest, followed by Pb and finally Cu. The leaves of Dittrichia viscosa contained the highest concentrations of trace elements and this species may be considered as being a “phytoextractor” in soils where the trace-element concentrations are not too high. Euphorbia pithyusa subsp. cupanii had low trace-element concentrations in its leaves despite growing in highly contaminated soils, and so might be used as a “phytostabilizer”. Although Cistus salviifolius does not grow in the most contaminated soils, could be considered as a contamination indicator up to a given level.     

Relative host plant species use by the lantana biological control agent Aconophora compressa (Membracidae) across its native and introduced ranges

Aconophora compressa Walker (Hemiptera: Membracidae) was released in 1995 against the weed lantana in Australia, and is now found on multiple host plant species. The intensity and regularity at which A. compressa uses different host species was quantified in its introduced Australian range and also its native Mexican range. In Australia, host plants fell into three statistically defined categories, as indicated by the relative rates and intensities at which they were used in the field. Fiddlewood (Citharexylum spinosum L.: Verbenaceae) was used much more regularly and at higher densities than any other host sampled, and alone made up the first group. The second group, lantana (Lantana camara L.: Verbenaceae; pink variety) and geisha girl (Duranta erecta L.: Verbenaceae), were used less regularly and at much lower densities than fiddlewood. The third group, Sheena’s gold (another variety of D. erecta), jacaranda (Jacaranda mimosifolia D. Don: Bignoniaceae) and myoporum (Myoporum acuminatum R. Br.: Myoporaceae), were used infrequently and at even lower densities. In Mexico, the insect was found at relatively low densities on all hosts relative to those in Australia. Densities were highest on L. urticifolia, D. erecta and Tecoma stans (L.) Juss. ex Kunth (Bignoniaceae), which were used at similar rates to one another. It was found also on a few other verbenaceous and non-verbenaceous host species but at even lower densities. The relative rate at which Citharexylum spp. and L. urticifolia were used could not be assessed in Mexico because A. compressa was found on only one plant of each species in areas where these host species co-occurred. The low rate at which A. compressa occurred on fiddlewood in Mexico is likely to be an artefact of the short-term nature of the surveys or differences in the suites of Citharexylum and Lantana species available there. These results provide further incentive to insist on structured and quantified surveys of non-target host use in the native range of potential biological control agents prior to host testing studies in quarantine.     

The relationship between phosphate status and photosynthesis in leaves

Spinach (Spinacia oleracea L.) and barley (Hordeum vulgare L.) were grown in hydroponic culture with varying levels of orthophosphate (Pi). When leaves were fed with 20 mmol·l^–1 Pi at low CO₂ concentrations, a temporary increase of CO₂ uptake was observed in Pi-deficient leaves but not in those from plants grown at 1 mmol·l^–1 Pi. At high concentrations of CO₂ (at 21% or 2% O₂) the Pi-induced stimulation of CO₂ uptake was pronounced in the Pi-deficient leaves. The contents of phosphorylated metabolites in the leaves decreased as a result of Pi deficiency but were restored by Pi feeding. These results demonstrate that there is an appreciable capacity for rapid Pi uptake by leaf mesophyll cells and show that the effects of long-term phosphate deficiency on photosynthesis may be reversed (at least temporarily) within minutes by feeding with Pi.Abbreviation Pi orthophosphate     

The accumulation and assimilation of dimethylselenide by four plant species

Plants of Agrostis tenuis Sibth., Hordeum vulgare L., Lycopersicon esculentum Mill. and Raphanus sativus L. were grown hydroponically in sealed systems and fumigated with 8 g m^-3 [⁷⁵Se]-dimethylselenide. The accumulation of ⁷⁵Se was measured and the shoot tissues were extracted to examine the products of the ⁷⁵Se assimilation. Characteristic differences were observed between species in the accumulation of ⁷⁵Se and the transport from shoots to roots. High-voltage electrophoresis and chromatography of extracts made with 80% aqueous ethanol revealed the presence of inorganic selenite as an assimilation product as well as the selenium analogues of glutathione and methionine. Extensive incorporation of ⁷⁵Se into protein-bound selenomethionine was observed in all plant species.Abbreviation DMSe dimethylselenide     

The dnaJ gene as a novel phylogenetic marker for identification of Vibrio species

The utility of the dnaJ gene for identifying Vibrio species was investigated by analyzing dnaJ sequences of 57 type strains and 22 clinical strains and comparing sequence homologies with those of the 16S rDNA gene and other housekeeping genes (recA, rpoA, hsp60). Among the 57 Vibrio species, the mean sequence similarity of the dnaJ gene (77.9%) was significantly less than that of the 16S rDNA gene (97.2%), indicating a high discriminatory power of the dnaJ gene. Most Vibrio species were, therefore, differentiated well by dnaJ sequence analysis. Compared to other housekeeping genes, the dnaJ gene showed better resolution than recA or rpoA for differentiating Vibrio coralliilyticus from Vibrio neptunius and Vibrio harveyi from Vibrio rotiferianus. Among the clinical strains, all 22 human pathogenic strains, including an atypical strain, were correctly identified by the dnaJ sequence. Our findings suggest that analysis of the dnaJ gene sequence can be used as a new tool for the identification of Vibrio species.     

Screening for antiproliferative activity of six southern Brazilian species of Hypericum

The crude methanolic extracts of six species of Hypericum growing in southern Brazil (Hypericum caprifoliatum Cham. & Schlecht., H. carinatum Griseb., H. connatum Lam., H. myrianthum Cham. & Schlecht., H. polyanthemum Klotzsch ex Reichardt and H. ternum A. St. Hil.) were screened for their antiproliferative activity against two cell lines (HT-29 human colon carcinoma cells and H-460 non-small cell lung carcinoma). The most active crude extracts were those from H. caprifoliatum, H. myrianthum and, to a lesser extent, from H. connatum. All plants were submitted to fractionation with solvents in increasing polarity and re-assayed for the two cell lines used previously, as well as U-373 human malignant glioma cells. The most active fractions were the hexane fractions obtained from H. caprifoliatum, H. myrianthum and H. ternum.