On the 13C/12C isotopic signal of day and night respiration at the mesocosm level

While there is currently intense effort to examine the ¹³C signal of CO₂ evolved in the dark, less is known on the isotope composition of day‐respired CO₂. This lack of knowledge stems from technical difficulties to measure the pure respiratory isotopic signal: day respiration is mixed up with photorespiration, and there is no obvious way to separate photosynthetic fractionation (pure c_i/c_a effect) from respiratory effect (production of CO₂ with a different δ¹³C value from that of net‐fixed CO₂) at the ecosystem level. Here, we took advantage of new simple equations, and applied them to sunflower canopies grown under low and high [CO₂]. We show that whole mesocosm‐respired CO₂ is slightly ¹³C depleted in the light at the mesocosm level (by 0.2–0.8‰), while it is slightly ¹³C enriched in darkness (by 1.5–3.2‰). The turnover of the respiratory carbon pool after labelling appears similar in the light and in the dark, and accordingly, a hierarchical clustering analysis shows a close correlation between the ¹³C abundance in day‐ and night‐evolved CO₂. We conclude that the carbon source for respiration is similar in the dark and in the light, but the metabolic pathways associated with CO₂ production may change, thereby explaining the different ¹²C/¹³C respiratory fractionations in the light and in the dark.     

The Measurement of Stomatal Responses to Stimuli in Leaves and Leaf Discs

A comparison has been made of stomatal responses in intact leaves,leaf discs supplied with water via their cut edges and leafdiscs floating on water. Xanthium pennsylvanicum leaf discswatered via their cut edges appeared to be more turgid thanintact leaves; this considerably slowed down the rate of stomatalopening but it slightly increased the final steady-state stomatalopening. When the water potential of such leaf discs was loweredby pre-treatment with mannitol solutions rates of stomatal openingincreased whereas maximum steady-state openings decreased. In tobacco leaf discs floating on water the stomata in contactwith water were wider open than those in contact with normalair and they did not respond to treatment with carbon dioxide-freeair. The rate of photosynthesis was severely reduced in tobaccoleaf discs floating with the lower epidermis on water, mostprobably owing to the slow rate of diffusion of carbon dioxidein water. By floating such discs on osmotica the degree of stomatalopening was increased, however, a response to treatment withcarbon dioxide-free air was still not measurable. It is postulatedthat, on account of the relative unavailability of carbon dioxidefrom the water, the carbon dioxide concentration in the substomatalcavities of the lower surface is abnormally low, irrespectiveof whether ordinary air or carbon dioxide-free air is availableto the upper surface. A comparison between porometer readings and measurements ofsiliconerubber impressions of stomatal pores taken from insidethe porometer cup confirmed that the silicone-rubber impressionmethod of assessing stomatal responses to stimuli has severelimitations, especially at small stomatal apertures.     

Ancient DNA reveals traces of Iberian Neolithic and Bronze Age lineages in modern Iberian horses

Multiple geographical regions have been proposed for the domestication of Equus caballus . It has been suggested, based on zooarchaeological and genetic analyses that wild horses from the Iberian Peninsula were involved in the process, and the overrepresentation of mitochondrial D1 cluster in modern Iberian horses supports this suggestion. To test this hypothesis, we analysed mitochondrial DNA from 22 ancient Iberian horse remains belonging to the Neolithic, the Bronze Age and the Middle Ages, against previously published sequences. Only the medieval Iberian sequence appeared in the D1 group. Neolithic and Bronze Age sequences grouped in other clusters, one of which (Lusitano group C) is exclusively represented by modern horses of Iberian origin. Moreover, Bronze Age Iberian sequences displayed the lowest nucleotide diversity values when compared with modern horses, ancient wild horses and other ancient domesticates using nonparametric bootstrapping analyses. We conclude that the excessive clustering of Bronze Age horses in the Lusitano group C, the observed nucleotide diversity and the local continuity from wild Neolithic Iberian to modern Iberian horses, could be explained by the use of local wild mares during an early Iberian domestication or restocking event, whereas the D1 group probably was introduced into Iberia in later historical times.     

Identification and characterization of 17 microsatellite primers for the tick,Ixodes ricinus,using enriched genomic libraries

Ixodes ricinus is the main vector for important infectious diseases in both humans and in animals. Microsatellite loci were isolated from a dinucleotide‐enriched library made from I. ricinus sampled in Norway. Seventeen polymorphic microsatellites were further characterized among 24 individuals sampled from an island in the Oslofjord region. The number of observed alleles ranged from two to 17 and the observed heterozygosities between 0.10 and 0.83. Analysis of family materials gives evidence of non‐Mendelian inheritance of several of the characterized loci, among which most could be explained by presence of null alleles.     

New microsatellite resources for groupers (Serranidae)

We characterized nine microsatellite loci and identified an additional 60 genomic regions containing microsatellites in the red hind grouper, Epinephelus guttatus. The nine loci were highly polymorphic, and primers designed from red hind genomic DNA produced a strong amplification product in a test panel of 16 other groupers in the genera Epinephelus and Mycteroperca collected from across the world. Most of the amplified regions were homologous to the red hind locus and a well‐defined microsatellite repeat was generally evident. The nine loci, together with the 60 uncharacterized microsatellite‐containing regions, provide a powerful tool for ecological and evolutionary studies in groupers.     

Effects of Drought on Partitioning of Nitrogen in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the translocation and partitioningof nitrogen on the seventh day after anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. A 9-d drought treatment was imposed just after anthesisand this coincided with the period of endosperm cell divisionin the grains. Warigal, which had a higher grain yield thanCondor under drought, absorbed up to 15-times more nitrogenand translocated 1.5-fold more nitrogen to the shoot via thexylem. In both varieties, nitrogen redistributed from vegetativeorgans accounted for more than 60 per cent in control and 70per cent in droughted plants of the nitrogen needed for eargrowth. The net loss of nitrogen increased by 4-3 per cent inthe leaves, but decreased by 60 per cent in the stem under drought.Stem and roots appeared to play an important role in the nitrogeneconomy of droughted plants: less nitrogen was translocateddirectly to the grains from the senescing leaves and 40–60per cent more nitrogen was translocated to the roots. Nearlyall the nitrogen reaching the roots in the phloem was reloadedinto the xylem stream and translocated back to the shoot. Thetransfer of nitrogen through the stem was reduced under droughtand this resulted in a constant C:N ratio of the grains whichmay be important in the regulation of endosperm cell division. Triticum aestivum L., wheat, drought, nitrogen, senescence, translocation     

Time series analysis of climate‐related factors and their impact on a red‐listed noble crayfish population in northern Sweden

1. Global climate change is predicted to raise water temperatures and alter flow regimes in northern river systems. Climate‐related factors might have profound impacts on survival, reproduction and distribution of freshwater species such as red‐listed noble crayfish (Astacus astacus) in its northern limit of distribution. 2. In this study, noble crayfish capture data over 27 years from the River Ljungan, Sweden, were examined. Time series of catch per unit effort (CPUE) were analysed in relation to the North Atlantic Oscillation (NAO) index, regional weather factors and water flow. CPUE was assumed to reflect differences in population size. Two models were constructed to explore the relative impact of different climate factors and density dependence on variability of catch sizes. 3. The most parsimonious model for CPUE time series, explaining 72% of the variance in CPUE, included density‐dependent population dynamics of the crayfish and climate or weather factors. The specific effect from density dependence in the model was 37%, while climate/weather factors contributed with 35% of the variation. The most important climate/weather factors are variations in NAO index and water flow. Temperature did not improve the model fit to capture data. 4. The best model was evaluated using independent data sets that gave correlations between model predictions and data ranging from 0.44 to 0.53. The density dependence shows a time lag of 1 year, while climate variables show time lags from 2 to 6 years in relation to CPUE, indicating effects on different cohorts of the crayfish population. 5. Both density dependence and climatic factors play a significant role in population fluctuations of noble crayfish. A 6‐year time lag for NAO index is puzzling but indicates that some as yet unidentified factors related to NAO might act on the juvenile stages of the population. Water flow shows a 2‐year lag to the CPUE, and high flow in the river may affect adult survival. The reasons for fluctuation of crayfish catches in response to climate need to be identified, and fishing quotas should consider the different cohort sizes because of variation in environment. Reintroduction programmes for crayfish need to consider effects of climate change when designing management strategies.