Climate-driven changes on phytoplankton–zooplankton coupling and nutrient availability in high mountain lakes of Southern Europe

1. The effect of climate variability on phytoplankton and zooplankton dynamics and nutrient availability was studied in two high mountain fishless lakes (La Caldera and Río Seco) of contrasting morphology, hydrology and dissolved inorganic nitrogen : soluble reactive phosphate (DIN : SRP) ratios during 1986 and after a 10‐year‐long drought in 1996 and 1997. 2. Thaw was delayed and water temperatures were lower in both lakes in 1996 than in 1986 and 1997. However, the lake‐specific DIN : SRP ratio was maintained in the 3 years studied, reflecting its local control. 3. On other hand, the presumptive limiting nutrient in each lake, P in La Caldera and N in Río Seco, showed higher concentrations in 1996 versus 1986 and 1997. Significant positive correlations between temperature and chlorophyll a were found in both lakes in 1996 but these relationships were negative or not significant in 1986 and 1997. Zooplankton biomass showed lower values in 1996 than in 1986 or 1997. 4. These findings can be explained by a decoupling of the phytoplankton–zooplankton interaction because of a constraint on zooplankton growth by low temperatures in the coldest year studied. This observation furnishes evidence that regional climatic control on the phytoplankton–zooplankton link can modulate the overall demand for nutrients.     

Nitrate Metabolism in Alfalfa Root Nodules under Water Stress

Three-month-old plants (vegetative stage) of alfalfa (Medicagosaliva L cv. Aragon) were supplied for one week with 1.0dm³(uniformly distributed) nutrient solutions containing 0 or 20mol m^–3 . One week after initiation of treatment, the plants were subjected to drought by withholding water. Bacteroidsand cytosol of nodules were obtained at different stages ofstress, and used for enzyme assays and for determination of, and . Proteins of bacteroids were more stable than cytosolic proteinswith respect to the detrimental effects of water stress and. Protein contents of bacteroids and cytosol were inversely related to proteolytic activitiesagainst azocasein in both nodule fractions. Specific nitrate reductase activity (NRA) and nitrite reductaseactivity (NiRA) of bacteroids from -treated plants were inhibited by c. 70% and 45%, respectively, as leafwater potential (_w) declined from –0.5 MPa (control) to–1.8 MPa. At still lower _w both activities began to increase:NRA was doubled, whereas NiRA only returned to its control level.Cytosolic NRA was strongly inhibited by drought, but the correspondingNiRA remained constant. Ammonia concentration in bacteroids and nodule cytosol keptbasically constant, whereas accumulated in the cytosol at severe stress, due to the activationof bacteroid nitrate reductase. Results indicate that nitrate and nitrite reductases of thebacteroids and the nodule cytosol act in different form: assimilatory,the cytosolic enzymes; and dissimilatory, the enzymes of bacteroidsat low _w The possibility that assimilation of also occurs in bacteroids at control or mild waterstress conditions is suggested. Key words: Assimilatory and dissimilatory reduction, bacteroids, Medicago saliva, nodule cytosol, water stress     

A new species of the wild dragon tree, Dracaena (Dracaenaceae) from Gran Canaria and its taxonomic and biogeographic implications

The arborescent taxa of Dracaena which form the dragon tree group comprise five species found in Macaronesia, Morocco (D. draco), East Africa (D. ombet, D. schizantha), Arabia (D. serrulata) and the island of Socotra (D. cinnabari). A new species of dragon tree, Dracaena tamaranae A. Marrero, R. S. Almeida & M. Gonzalez-Martin, is described from Gran Canaria, Canary Islands. This new species differs from D. draco, the only other Dracaena species currently known in Macaronesia, in having a growth form and inflorescence type and leaves more similar to the East African and Arabian species of Dracaena. In contrast, D. draco appears to be related to D. cinnabari. In this paper, we also present a study of the taxonomy, habitat and ecology of all the species of the dragon tree group. These are found in thermo-sclerophyllous plant communities of tropical-subtropical regions which are rather xerophilous and have a rainfall range of 200–500 mm. Our study indicates two independent colonization events for Dracaena in Macaronesia. In addition, we suggest that the dragon tree group provides an example of two major biogeographical disjunctions between East and West Africa. We postulate that this group has a Tethyan origin, a hypothesis supported by fossil and palaeoclimatic data, and thus parallels the distribution and dispersal pattern of other taxonomic groups.     

Resistance to Water Transfer in Desert Shrubs Native to Death Valley, California

Differences in plant resistance to water flow, patterns of water transport through stems, and stomatal behavior were studied on three species native to the exceptionally hot and dry habitat of Death Valley, California (—, and Larrea divaricata). Dawn xylem water potentials in July for Atriplex were — 27.5 bar under natural conditions. Corresponding values for Tidestromia and Larrea were respectively — 8.0 bar and -32.0 bar (natural) and — 7.5 bar and — 18.0 bar (irrigated). Recovery of xylem water potential in covered field plants of an irrigated transplant garden reached a maximum value in July of — 9.5 bar in Atriplex, — 5.7 bar in Tidestromia and — 7.0 bar in Larrea. Resistance to free-energy transfer was used to study resistance to water transport through the plants. Under field conditions irrigated Atriplex plants gave a whole plant resistance of 20.70 × 10⁶ s cm^-1, as compared lo 18.37 × 10⁶ s cm^-1 for Larrea and 10.01 × 10⁶ s cm^-1 for Tidestromia. Plant resistance to water How computed by this method on Atriplex plants grown under laboratory conditions gave a value of 3.73 × 10⁶ s cm^-1 at 35C. Paths of water flow in field plants as investigated with injected acid fuchsin indicated a sectorial straight type vessel. The relationship between transpiration rates and xylem water potentials in Atriplex hymenelytra was linear between transpiration 1.28 μg cm^-2 s^-1 and 2.35 μg cm^-2 s^-1 at 35°C. These results indicate that according to the Van den Honert model for water transport, plant resistance to water flow remained rather constant at this temperature. In Atriplex grown under laboratory conditions there was an adjustment of plant resistance so change in water flux at 9.5°C and 25°C. When laboratory-grown plants of Atriplex and Tidestromia were subjected to water stress by withholding water. Tidestromia closed stomata and reduced transpiration rates at higher water potentials than in Atriplex. The ratio of vapor pressure gradients of leaf/air to leaf diffusion resistance was proportional lo transpiration rates. It is suggested that Atriplex hymenelytra is a species that combines strong regulation of water loss by stomata with low efficiency of the water transport system. These plants are unable to prevent depression of plant water potential as transpiration increases. On the other hand. Tidestromia oblongifolia has little stomatal regulation of transpiration and a highly efficient water transport system. These plants sustain very high rates of transpiration without significant decrease in plant water potential.     

Effects of experimental food provisioning on reproduction in the Jackdaw Corvus monedula, a semi-colonial species

Two Jackdaw Corvus monedula colonies were given supplementary food before and during breeding in 1983. Breeding density and cavity use were compared with those of the same colonies in previous years, when no food was provided. Predation rate and reproductive parameters were compared with those in the same colonies in previous years and with those of two control colonies, without experimental food. Jackdaws preferred safe cavities with small minimum nest-entrance dimensions and avoided those with a high risk of nest predation. In experimental (fed) colonies, however, there was a tendency to use all cavities, which resulted in an increased breeding density. No nests were preyed upon by Ravens Corvus corax in the experimental colonies because supplemental food favoured group defence by increasing colony size and by increasing the time the Jackdaws spent in the colony. Additional food advanced laying date, increased clutch size independently of laying date and increased fledging success. Supplementary food significantly increased fledging success in less than half of all experimental studies on birds. We suggest that the key to this problem is the species' breeding strategy, and we show that supplementary food significantly increased fledging success in brood-reduction strategist species but not in species which directly adjusted their clutch size.     

The impact of researcher disturbance on nest predation rates: a meta‐analysis

The effects of visits to nests by researchers interested in quantifying avian nesting success have received considerable attention, as researchers have long been concerned about the possible negative effects of their own activities on the resulting estimates. There is a widely held view that investigator disturbance has an overall negative effect on breeding success by increasing nest predation rates in the nests studied. However, to date no one has statistically assessed the empirical evidence for such a relationship. We undertook a meta‐analysis of published results to assess whether researcher activities increase nest predation in birds. We also assessed the variability in this effect in relation to the traits of the study species and the methodology used. These analyses used data from 18 experimental studies involving 25 species from six avian orders. Our results suggest that, contrary to the traditional view, researcher activities do not generally affect the incidence of nest predation. Moreover, this relationship appears inconsistent among avian orders and, surprisingly, nest survival of passerines increased weakly with researcher activities. We also found significant positive effects of researcher activity on nest survival for species breeding on coastal areas and for species nesting on the ground. The possible explanation for these differences among orders and guilds could be due to different nest predator communities. This new perspective on the effect of investigators could have important implications for bird management and conservation, as well as for other fields of study such as ecology and evolution, in which nest survival rates measured in the field are widely used to test and support a range of hypotheses.     

New biostratigraphical constraints for the Norian/Rhaetian boundary: data from Lagonegro Basin,Southern Apennines,Italy

Giordano, N., Rigo, M., Ciarapica G. & Bertinelli A. 2010: New biostratigraphical constraints for the Norian/Rhaetian boundary: data from Lagonegro Basin, Southern Apennines, Italy. Lethaia. 10.1111/j.1502‐3931.2010.00218.x. Four stratigraphic sections belonging to Lagonegro succession (Southern Apennines) at Mt S. Enoc, Pignola‐Abriola, Sasso di Castalda and Mt Volturino have been studied in detail under to provide a new micro‐palaeontological data set based on conodonts and radiolarians for the characterization of the Norian/Rhaetian interval. The studied sections represent the different settings of the Lagonegro Basin (from proximal to distal facies) and permit a detailed, integrated, biostratigraphy of the Calcari con Selce (cherty limestones) and Scisti Silicei formations (bedded cherts with radiolarians) to be drawn up. The upper portion of the Calcari con Selce Formation, exhibits intermediate characteristics between the Calcari con Selce and Scisti Silicei Formation, in particular the progressive decrease in carbonate content against an increase in shales and cherts. Within the four sections studied, the Norian/Rhaetian interval has been documented both with conodonts and radiolarians. Because of the continuity and the absence of condensed facies, it has been possible to recognize the morphocline between species Misikella hernsteini and Misikella posthernsteini, here represented by all the transitional forms characterized by common features between the two species, gathered in three evolutionary steps. Moreover, the morphocline between M. hernsteini and M. posthernsteini has been involved in the definition of the Norian/Rhaetian Boundary, recognizing thus the FAD of M. posthernsteini, one of the possible biomarkers proposed for the boundary. The rich, well‐preserved, radiolarian associations of Pignola‐Abriola, Sasso di Castalda and Mt Volturino permit the correlation of Tethyan and American conodont successions, highlighting the importance of the mostly coincident occurrences of M. posthernsteini and Epigondolella mosheri morphotype A, which correspond to the base of Proparvicingula moniliformis A. Z. and the disappearance of bivalve Monotis. These coincident bioevents are used here to define the base of the Rhaetian stage. □Biostratigraphy, conodonts, Lagonegro Basin, Late Triassic, Norian/Rhaetian boundary, radiolarians.     

Localized and non‐localized effects of arbuscular mycorrhizal symbiosis on accumulation of osmolytes and aquaporins and on antioxidant systems in maize plants subjected to total or partial root drying

The arbuscular mycorrhizal (AM) symbiosis alters host plant physiology under drought stress, but no information is available on whether or not the AM affects respond to drought locally or systemically. A split‐root system was used to obtain AM plants with total or only half root system colonized as well as to induce physiological drought affecting the whole plant or non‐physiological drought affecting only the half root system. We analysed the local and/or systemic nature of the AM effects on accumulation of osmoregulatory compounds and aquaporins and on antioxidant systems. Maize plants accumulated proline both, locally in roots affected by drought and systemically when the drought affected the whole root system, being the last effect ampler in AM plants. PIPs (plasma membrane intrinsic proteins) aquaporins were also differently regulated by drought in AM and non‐AM root compartments. When the drought affected only the AM root compartment, the rise of lipid peroxidation was restricted to such compartment. On the contrary, when the drought affected the non‐AM root fraction, the rise of lipid peroxidation was similar in both root compartments. Thus, the benefits of the AM symbiosis not only rely in a lower oxidative stress in the host plant, but it also restricts locally such oxidative stress.     

Secondary phytohaemagglutinin (PHA) swelling response is a good indicator of T‐cell‐mediated immunity in free‐living birds

The validity of using the phytohaemagglutinin (PHA) test to measure acquired immunity, one of the most widely used methods, is currently being debated due to new knowledge on the complex physiology of the process. As a greater secondary response to repeated challenges linked to increases of circulating lymphocyte levels would be indicative of a T‐cell‐mediated immune response, we performed for the first time an experiment under natural conditions with repeated PHA challenges in free‐living adult birds and chicks to shed light on this topic. We found significantly stronger secondary response to PHA injection independent of sex or age, while controlling for body condition, the second response being on average 90% larger than the first. Likewise, lymphocyte counts were significantly higher in the second PHA challenge, whereas no significant differences were found among untreated birds. Significant positive correlations between the PHA response and both lymphocyte counts and plasma protein levels (mainly albumin, globulin precursor) were recovered, whereas no significant differences were recovered in plasma protein levels between challenges. Our results are consistent with those from captive birds, supporting the validity of the PHA skin‐swelling test as an accurate gauge of acquired T‐cell‐mediated immunity in birds.