Postglacial-period and Recent Invasions Shape the Population Genetics of Botryllid Ascidians along European Atlantic Coasts

The colonial urochordate Botryllus schlosseri is a sedentary species of Mediterranean origin that became cosmopolitan, probably because of postglacial-period dispersal and human-mediated invasions of colonies attached to ship hulls. Here we studied microsatellite allele diversity of Atlantic coast populations from an area ranging from European regions south of the last glacial front to regions that had been permanently ice-covered. Gene diversity levels varied dramatically among populations residing in areas subject to different glacial conditions. Five populations from the Iberian Peninsula, in an area south of the last glacial front, as well as two populations from presumed refugia in Brittany, expressed high gene diversity values (expected heterozygosity [He]: 0.76–0.80; average number of alleles per locus [A]: 7.25–8.75). Two populations inhabiting areas that experienced permafrost conditions (Helgoland Island, Germany, and Plymouth, England) had intermediate values (He: 0.40–0.42; A: 3.0–4.0), whereas the Auchenmalg, Scotland, population, from an area previously covered by ice, showed a remarkably low value (He: 0.17; A: 1.75). Therefore, most European populations of B. schlosseri mirrored the movement of the ice front in the last ice age. A second population from the area that was covered by permanent ice (Lossiemouth, Scotland), however, had a high He of 0.61 and an intermediate A of 3.67. Results were compared with recent invasions (populations less than 200 years old) in the United States and New Zealand that had a higher degree of genetic variation than the European native populations established thousands of years ago. Given the overall dearth of studies on this subject, we suggest that in contemporary established Botryllus populations, gene diversity is affected by ecological factors, some of which can be traced directly to the last ice age. Other parameters of gene diversity are influenced by selection pressure, which might be more intense in northern regions.     

Nutrient stress and performance of invasive Hieracium lepidulum and co-occurring species in New Zealand

Many studies have highlighted the relationship between nutrient fluctuations and enrichment in the process of plant invasion. However, invasion may be also associated with conditions of plant stress, either nutrient depletion or toxicity, in the environment. In this study, we investigate the possible role of nutrient stress in the invasion of Hieracium lepidulum (Stenstroem) Omang, in South Island, New Zealand. We do this by comparing several performance attributes, and their plasticity, for H. lepidulum and a number of co-occurring species, across a series of nutrient depletion and toxicity tests. H. lepidulum had intermediate yields, high root:shoot ratios and high tissue nutrient contents at control nutrient concentrations. H. lepidulum differed in edaphic tolerance from all but Chionochloa flavescens var. brevis, in being insensitive to nutrient dilutions other than nitrogen. The significance of performance in terms of edaphic tolerance and adaptations are discussed. Intermediate yields at control nutrient levels suggest that H. lepidulum should not be competitive compared to high yielding species including Agrostis stolonifera and Poa cita, but should be competitive with lower yielding Coprosma rugosa and C. flavescens var. brevis. Conversely, significant yield decreases under nitrogen limitation stress suggests that H. lepidulum will not likely occupy very nutrient poor sites. H. lepidulum, along with C. flavescens var. brevis, were found to be tolerant of ammonium as an alternative source of nitrogen, while other species were not. These data suggest that H. lepidulum and C. flavescens var. brevis would be relatively tolerant of the stresses associated with acidic soils compared to the other species, but not to stresses associated with absolute shortage of nitrogen. Combined results point to the likely occurrence of H. lepidulum at sites of intermediate fertility. The possible roles of ammonium stress and disturbance reliance in further defining H. lepidulum ecology is discussed.     

Ecophysiological traits associated with drought in Mediterranean tree seedlings: individual responses versus interspecific trends in eleven species

Species differ regarding their drought tolerance and individuals of a given species can modify their morphology and physiology in response to drought. However, since evolutionary and ecological selective pressures differ, individual and interspecific responses to drought might not match. We determined summer survival and a number of ecophysiological variables in two factorial experiments with seedlings of eleven tree species present in Mediterranean ecosystems, grown under slowly imposed water stress and control conditions. Plants experiencing drought exhibited reduced growth, low specific leaf area, chlorophyll content, and photosynthetic rate when compared to the controls, and species-specific drought tolerance was associated with an analogous set of trait values. However, while species with high leaf area ratio and shoot-root ratio exhibited greater drought tolerance, drought induced the reversed response within species. Contrary to expectations, water use efficiency was lower in drought-tolerant species and decreased in water-stressed individuals compared to the control plants. There was a distinctive phylogenetic signal in the functional grouping of species, with oaks, pines, and other genera being clearly different from each other in their drought tolerance and in their functional responses to drought. However, all relationships between ecophysiological variables and drought tolerance were significant after accounting for phylogenetic effects, with the exception of the relationship between drought tolerance and photochemical efficiency. Our results show that drought tolerance is not achieved by a single combination of trait values, and that even though evolutionary processes and individual responses tend to render similar results in terms of functional traits associated with drought, they do not necessarily match.     

Respiration and photosynthesis of bladders and leaves of aquatic utricularia species

In aquatic species of carnivorous utricularia, about 10 - 50 % of the total biomass consists of bladders. Utricularia bladders are physiologically very active organs though their chlorophyll content may greatly be reduced. To specify energetic costs of carnivory, respiration (RD) and net photosynthetic rate (PN) were compared in bladders and leaves or shoot segments of six aquatic utricularia species with differentiated (U. ochroleuca, U. intermedia, U. floridana) or non-differentiated shoots (U. vulgaris, U. australis, U. bremii) under optimum conditions (20 degrees C, [CO (2)] 0.20 mM, 400 micromol m (-2) s (-1) PAR). RD of bladders of six utricularia species (5.1 - 8.6 mmol kg (-1)(FW) h (-1)) was 75 - 200 % greater, than that in leaves in carnivorous or photosynthetic shoots (1.7 - 6.1 mmol kg (-1)(FW) h (-1)). Within individual species, this difference was statistically significant at P < 0.002 - 0.01. However, PN in photosynthetic leaves/shoots (40 - 117 mmol kg (-1)(FW) h (-1)) exceeded that in bladders (5.2 - 14.7 mmol kg (-1)(FW) h (-1)) 7 - 10 times. RD of empty bladders of U. ochroleuca was exactly the same as that in bladders containing prey. Though utricularia bladders are essential for uptake of growth limiting mineral nutrients N and P from prey as the main benefit of carnivory, the current results support previous work showing that bladder function requires greater metabolic (maintenance) cost and very low photosynthetic efficiency (great RD : PN ratio).     

Nutrient limitation and stoichiometry of carnivorous plants

The cost-benefit model for the evolution of carnivorous plants posits a trade-off between photosynthetic costs associated with carnivorous structures and photosynthetic benefits accrued through additional nutrient acquisition. The model predicts that carnivory is expected to evolve if its marginal benefits exceed its marginal costs. Further, the model predicts that when nutrients are scarce but neither light nor water is limiting, carnivorous plants should have an energetic advantage in competition with non-carnivorous plants. Since the publication of the cost-benefit model over 20 years ago, marginal photosynthetic costs of carnivory have been demonstrated but marginal photosynthetic benefits have not. A review of published data and results of ongoing research show that nitrogen, phosphorus, and potassium often (co-)limit growth of carnivorous plants and that photosynthetic nutrient use efficiency is 20 - 50 % of that of non-carnivorous plants. Assessments of stoichiometric relationships among limiting nutrients, scaling of leaf mass with photosynthesis and nutrient content, and photosynthetic nutrient use efficiency all suggest that carnivorous plants are at an energetic disadvantage relative to non-carnivorous plants in similar habitats. Overall, current data support some of the predictions of the cost-benefit model, fail to support others, and still others remain untested and merit future research. Rather than being an optimal solution to an adaptive problem, botanical carnivory may represent a set of limited responses constrained by both phylogenetic history and environmental stress.     

The role of antioxidant enzymes in photoprotection

The enzymatic component of the antioxidant system is discussed as one of the defensive mechanisms providing protection against excessive light absorption in plants. We present an analysis of attempts to improve stress tolerance by means of the creation of transgenic plants with elevated antioxidant enzyme activities and conclude that the effect of such transgenic manipulation strongly depends on the manner in which the stress is imposed. The following factors may diminish the differences in photosynthetic performance between transgenic plants and wild type under field conditions: effective functioning of the thermal dissipation mechanisms providing a primary line of defense against excessive light, long-term adjustments of the antioxidant system and other photoprotective mechanisms, the relatively low level of control over electron transport exerted by the Water–Water cycle, especially under warm conditions, and a decrease in the content of the transgenic product during leaf aging.     

A 50 Hz sinusoidal magnetic field does not damage MG-63 three-dimensional tumor spheroids but induces changes in their invasive properties

The possibility that a sinusoidal 50 Hz magnetic field with a magnetic flux density of 1 mT can damage MG-63 osteosarcoma spheroids and induce variations in the invasive properties of these three-dimensional model systems after 2 days of exposure was investigated. Specifically, possible damage induced by these fields was examined by determining changes in spheroid surface morphology (light microscopy), growth (spheroid diameter and protein content determination), lactate dehydrogenase release, and reduced glutathione amount. Possible changes in the invasive properties were studied by invasion chambers. The results show no induction of cell damage by ELF fields while invasion chamber assays demonstrate a significant increase in the invasive potential of exposed spheroids. In order to determine if the fibronectin or hyaluronan receptors are involved, Western blot analysis was conducted on these two proteins. No significant variations were observed in either receptor in MG-63 multicellular tumor spheroids.     

中国西南纵向岭谷区外来入侵植物对生物多样性的影响

论述中国西南纵向岭谷区外来入侵植物对生物多样性的影响。中国西南纵向岭谷区是我国生物多样性保护的关键地区。目前,该区域已成为外来植物入侵的重灾区,外来入侵植物种类多达70余种,其中,紫茎泽兰Ageratina adenophora（Eupatoriumadenophorum）、飞机草Chromolaena odorata（Eupatorium odoratum）和肿柄菊Tithonia diversifolia等在该区域危害严重,该区域的生态系统的结构与功能遭受破坏,本地物种面临灭绝,农、林、牧生产乃至区域的生态安全受到威胁。该区域的外来入侵植物的危害居全国之冠。研究该区域的外来入侵植物,揭示其危害规律,遏制其危害速度,最终清除该区域的外来入侵植物,恢复该区域的生态平衡,具有十分重要的现实意义和科学价值。文中详细论述了外来入侵植物对植物物种多样性、植物群落多样性、生态系统多样性、农牧业及林业的影响,最后指出消除和控制外来入侵植物的途径。     

Morpho-anatomical and physiological leaf traits of two alpine herbs, Podophyllum hexandrum and Rheum emodi in the Western Himalaya under different irradiances

Morpho-anatomical leaf traits and photosynthetic activity of two alpine herbs, Podophyllum hexandrum (shade-tolerant) and Rheum emodi (light-requiring), were studied under field (PAR>2 000 μmol m⁻² s⁻¹) and greenhouse (PAR 500 μmol m⁻² s⁻¹) conditions. Mesophyll thickness, surface area of mesophyll cells facing intercellular spaces (S_mes), surface area of chloroplasts facing intercellular spaces (S_c), intercellular spaces of mesophyll cells (porosity), photon-saturated rate of photosynthesis per unit leaf area (P _Nmax), and ribulose-1,5-bisphosphate carboxylase/oxygenase activity decreased in the greenhouse with respect to the field and the decreases were significantly higher in R. emodi than in P. hexandrum. P. hexandrum had lower intercellular CO₂ concentration than R. emodi under both irradiances. The differences in acclimation of the two alpine herbs to low irradiance were due to their highly unlikely changes in leaf morphology, anatomy, and P _Nmax which indicated that the difference in radiant energy requirement related to leaf acclimation had greater impact under low than high irradiance.