Nutrition‐ and sex‐dependent utilization of body resources in relation to reproduction in a scorpionfly

Reproduction often comes at a cost of a reduction in body functions. In order to enhance their reproductive output, some insect species degenerate their thoracic muscles, typically resulting in reduced flight ability. From a life‐history trade‐off perspective, we expect the importance of body resource utilization to be amplified both with increased reproductive expenditure and with increased resource limitation. In this study, we measured age‐related changes in thorax weight, as a measure of flight muscle size, during a major part of the adult lifespan in males and females of the scorpionfly Panorpa vulgaris. The aim of the study was twofold: first to investigate whether scorpionflies have the potential to degenerate their flight muscles; second, and more importantly, to determine whether the magnitude of flight muscle degeneration is a plastic response in relation to resource availability, and if it differs between the sexes. The results clearly demonstrate that food availability does influence investment in flight muscle development. The build‐up of the thoracic muscles was strongly influenced by nutrient availability. Furthermore, the age‐related decrease in thorax weight was significantly different for males and females. Only females showed a strong age‐dependent decrease in thorax weight, indicative of muscle degeneration, yet no difference between food treatments was detected. For males, there was no significant directional change in thorax weight. Nevertheless, with increasing age, the difference in thorax weight between food treatments increased significantly. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 199–207.     

Alfalfa Stem Tissues: Cell-wall Development and Lignification

Alfalfa stems contain a variety of tissues with different patternsof cell-wall development. Development of alfalfa cell wallswas investigated after histochemical staining and with polarizedlight using light microscopy and scanning electron microscopy.Samples of the seventh internode, from the base of stems grownon cut stems, were harvested at five defined stages of developmentfrom early internode elongation through to late maturity. Internodeseven was elongating up to the third sample harvest and internodediameter increased throughout the entire sampling period. Chlorenchyma,cambium, secondary phloem, primary xylem parenchyma and pithparenchyma stem tissues all had thin primary cell walls. Pithparenchyma underwent a small amount of cell-wall thickeningand lignification during maturation. Collenchyma and primaryphloem tissues developed partially thickened primary walls.In contrast to a recent report, the formation of a ring shaped,lignified portion of the primary wall in a number of cells inthe exterior part of the primary phloem was found to precedethe deposition of a thick, non-lignified secondary wall whichwas degradable by rumen microbes. In numerous xylem fibres fromthe fourth harvest date onwards, an additional highly degradablesecondary wall layer was deposited against a previously depositedlignified and undegradable secondary wall. The pattern of lignificationobserved in alfalfa stem tissues suggests that polymerizationof monolignols by peroxidases at the luminal border of the primarycell wall creates an impermeable zone which restricts lignificationof the middle lamella region of tissues with thick primary walls.Copyright1998 Annals of Botany Company Alfalfa,Medicago sativaL., stem tissue, cell wall, development, lignification, degradation.     

Plant diversity positively affects short‐term soil carbon storage in experimental grasslands

Increasing atmospheric CO₂ concentration and related climate change have stimulated much interest in the potential of soils to sequester carbon. In ‘The Jena Experiment’, a managed grassland experiment on a former agricultural field, we investigated the link between plant diversity and soil carbon storage. The biodiversity gradient ranged from one to 60 species belonging to four functional groups. Stratified soil samples were taken to 30 cm depth from 86 plots in 2002, 2004 and 2006, and organic carbon contents were determined. Soil organic carbon stocks in 0–30 cm decreased from 7.3 kg C m^?2 in 2002 to 6.9 kg C m^?2 in 2004, but had recovered to 7.8 kg C m^?2 by 2006. During the first 2 years, carbon storage was limited to the top 5 cm of soil while below 10 cm depth, carbon was lost probably as short‐term effect of the land use change. After 4 years, carbon stocks significantly increased within the top 20 cm. More importantly, carbon storage significantly increased with sown species richness (log‐transformed) in all depth segments and even carbon losses were significantly smaller with higher species richness. Although increasing species diversity increased root biomass production, statistical analyses revealed that species diversity per se was more important than biomass production for changes in soil carbon. Below 20 cm depth, the presence of one functional group, tall herbs, significantly reduced carbon losses in the beginning of the experiment. Our analysis indicates that plant species richness and certain plant functional traits accelerate the build‐up of new carbon pools within 4 years. Additionally, higher plant diversity mitigated soil carbon losses in deeper horizons. This suggests that higher biodiversity might lead to higher soil carbon sequestration in the long‐term and therefore the conservation of biodiversity might play a role in greenhouse gas mitigation.     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: I. RELATIONSHIP BETWEEN TUBER GROWTH RATE AND ENZYME ACTIVITIES OF THE STARCH METABOLISM

Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. Cooling (+8°C) of individualtubers decreased their growth rates and increased the growthrates of non-cooled tubers of the same plant. The carbohydrateconcentration in non-cooled and cooled tubers did not differsignificantly, but ¹⁴C-import from labelled photosynthate waslower in cooled than in non-cooled tubers. The markedly lowerconversion rate of ethanol-soluble ¹⁴C to starch in cooled,in comparison to non-cooled tubers, was not associated withsignificant differences in the in vitro activities of starchsynthase, ADPG-pyrophosphorylase and starch phosphorylase understandard assay conditions (+30°C). However, the Q₁₀-valuesof the enzymes differed in vitro in the temperature range between30°C and 8°C, leading to a marked decrease in the activityratio of ADPG-pyrophosphorylase/starch phosphorylase in cooledtubers. In tubers differing in growth rates without manipulation, 14d after tuber initiation significant positive correlations werefound between ¹⁴C-concentration of tuber tissue and the in vitroactivities of starch synthase and ADPG-pyrophosphorylase anda significant negative correlation between ¹⁴C-concentrationand starch phosphorylase. In contrast, in tubers which wereanalysed 5 d after initiation, there were only small differencesbetween tubers in growth rate, ¹⁴C import and the activity ratioADPG-pyrophosphorylase/starch phosphorylase. From various directand indirect evidence it is concluded that the growth rate ofindividual tubers, and thus the sink strength, is at least inpart controlled by the activity of starch synthesizing enzymes. Key words: Potato tuber, cooling, starch synthesizing enzymes     

Mandibular Gland Volatiles and Their Ontogenetic Patterns in Queen Honey Bees,Apis mellifera carnica

Extracts of mandibular glands taken from adult queens of the honey bee, Apis mellifera carnica, were analysed by gas chromatography-mass spectroscopy. More than 100 compounds could be identified among which oxygenated fatty acids with six, eight, 10 and 12 carbon atoms are particularly interesting since they show structural relationships to the queen substance, (E)-9-oxo-2-decenoic acid. Changes in the patterns of volatiles were followed up from emergence until the full dominant status of an egg-laying queen in a strong colony. Generally, the amount of volatiles per gland was found to increase with age. The final level of queen substance (9-ODA) content is reached at the postmating stage about 10 days after emergence. Ontogenetic patterns of concentrations were determined for those components regarded to predominantly contribute to the royal pheromone. Characteristic compositions of signals, possibly involved in the premating, mating and postmating dominance status of a honey bee queen are discussed. Copyright 1997 Elsevier Science Ltd. All rights reserved     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: II. RELATIONSHIP BETWEEN GROWTH RATE, CARBOHYDRATE CONCENTRATION AND 14C-PARTITIONING WITHIN TUBERS

Potato plants (Solanum tuberosum L.) were grown in water culturein a controlled environment. The growth rates of individualtubers were closely reflected by their ¹⁴C-content 20 h after¹⁴CO₂ had been applied to the aerial parts of the shoot for4 h. The ¹⁴C-content of the tuber (sink strength) was significantlycorrelated to the ¹⁴C-concentration of the tuber tissue (¹⁴Cg^–1 fr. wt.=sink activity). The sink activity, which differedbetween individual tubers by up to a factor of 10, was alsoclosely related to the conversion rates of ¹⁴C into the starchand the remainder as well as to the ¹⁴C-content in the ethanolsoluble fraction. This indicates the simultaneous use of photosynthatefor growth and storage in the growing tubers. No preferenceof photosynthate utilization for either of these processes couldbe detected in relation to the sink activity of the tubers.Tubers with high sink activity imported ¹⁴C-labelled photosynthateat higher rates although their tissue contained higher concentrationsof reducing sugars and sucrose than the tissue of tubers withlow sink activity. Despite the close relationship between sinkactivity and the rate of starch synthesis (¹⁴C-conversion intostarch), no significant correlation was found between sink activityand the actual starch concentration of the tissue. The applicationof zeatin riboside directly onto individual tubers increasedtheir growth rates in comparison to non-treated tubers of thesame plant. The results indicate the importance of both growthand storage processes for the regulation of sink activity inyoung potato tubers. Key words: Potato tuber, ¹⁴C-photosynthate partitioning, zeatin riboside application     

Allocation of Photosynthate to Individual Tubers of Solanum tuberosum L.: III. RELATIONSHIP BETWEEN GROWTH RATE OF INDIVIDUAL TUBERS, TUBER WEIGHT AND STOLON GROWTH PRIOR TO TUBER INITIATION

Potato plants (Solanum tuberosum L.) were grown in water culture.About 14 d after tuber initiation no significant differenceswere found between apical and basal tuber parts in ¹⁴C-uptakeand partitioning into various fractions from ¹⁴C-labelled photosynthate.Thus, the fresh weight of these tubers could be used as a parameterfor the sink size. The ¹⁴C-content per tuber (sink strength)20 h after ¹⁴CO₂-supply to the foliage was significantly correlatedwith the tuber fresh weight. No correlation was found betweenthe ¹⁴C-concentration of the tuber (sink activity; ct. min^–g^– fr. wt.) and tuber fresh weight. Consequently, tuberfresh weight (sink size) per se must have been a factor whichinfluenced sink strength. Stolon parameters characterizing theirgrowth prior to tuber initiation (e.g. stolon volume) and theircapacity for photosynthate transport (diameter, length) weremeasured at the time of tuber initiation. Significant correlationswere found between these stolon parameters and subsequent growthof individual tubers. Anatomical studies on the proportion ofvarious tissues in the cross sectional area of stolons supportthe idea of a negative relation between growth of individualtubers and transport resistance in the phloem of the stolons.It is concluded that in the initial phase of tuber growth, mainlyfactors outside of the tuber determine its growth rate. In laterstages of tuber growth, when the sink strength increases, thecompeting strength of individual tubers for photosynthate isdominated mainly by factors within the tuber itself, such astheir sink size and sink activity. Key words: Potato tuber, sink size, tuber initiation, transport resistance     

Effect of Root Zone Temperature and Shoot Demand on Uptake and Xylem Transport of Macronutrients in Maize (Zea mays L.)

The effect of shoot demand for nutrients on nutrient uptakeand translocation in the xylem exudate was studied in maizegrowing in nutrient solution at uniform shoot zone (24/2C,day/night), but different root zone temperatures (RZT: 12C,18C, 24C). The shoot base (apical shoot meristem and zoneof leaf extension) was either kept within or lifted above thecooling zone. In plants with their shoot base above the coolingzone (RZT: 12C and 18C) shoot growth was significantly increasedbut not root growth. Therefore, at suboptimal RZT shoot freshweight increment d^–1 g^–1 root fresh weight, whichwas taken as a parameter for the shoot demand for nutrientsper unit root, varied strongly depending on the temperatureof the shoot base (shoot base temperature, SBT). In short-term studies (2 h and 1 d after onset of temperaturetreatment) rates of nutrient (nitrogen, N; potassium, K; phosphorus,P; calcium, Ca) uptake or translocation in the xylem exudatewere markedly decreased at suboptimal RZT (12C, 18C), irrespectiveof the SBT. In long-term studies (3, 5, and 10 d after onsetof temperature treatment) uptake and translocation of K, N,and Ca, but not P, increased in plants at suboptimal RZT whenthe shoot demand was high (shoot base above the cooling zone)but decreased when the shoot demand was low (shoot base withinthe cooling zone). These results suggest, that the increase of translocation ratesof N, K, and Ca after long-term exposure to suboptimal RZT wasa consequence of a higher shoot demand per unit root fresh weightand not due to a direct temperature effect on the nutrient uptakesystem. Key words: Xylem exudate, nutrient translocation, root zone temperature, shoot demand, nutrient circulation     

Influence of the Form of Nitrogen Supply on Root Uptake and Translocation of Cations in the Xylem Exudate of Maize (Zea mays L)

Concentrations of inorganic cations are often lower in plantssupplied with NH₄⁺ as compared with NO₃^–. To examine whetherthis is attributable to impaired root uptake of cations or lowerinternal demand, the rates of uptake and translocation of K,Mg, and Ca were compared in maize plants (Zea mays L.) withdifferent growth-related nutrient demands. Plants were grownin nutrient solution with either 1·0 mol m^–3 NO₃^–or NH₄⁺ and the shoot growth rate per unit weight of roots wasmodified by varying the temperature of the shoot base (SBT)including the apical shoot meristem. The shoot growth rate per unit weight of roots, which was takenas the parameter for the nutrient demand imposed on the rootsystem, was markedly lower at 12°C than at 24°C SBT.As a consequence of the lower nutrient demand at 12°C SBT,uptake rates of NO₃^– and NH₄⁺ declined by more than 50%Compared with NO₃^– supply, NH₄⁺ nutrition depressed theconcentrations of K and particularly of Ca in the shoot, bothin plants with high and with low nutrient demand. This indicatesa control of cation concentration by internal demand ratherthan by uptake capacity of the roots. Translocation rates of K, Mg and Ca in the xylem exudate werelower in NH₄⁺- than in NO₃^–-fed plants. Net accumulationrates of Ca in the shoot were also decreased, whereas net accumulationrates of K in the shoot were even higher in NH₄⁺-fed plants.It is concluded that reduced cation concentrations in the xylemsap of plants supplied with NH₄⁺ are due to the lower demandof cations for charge balance. The lower K translocation tothe shoot is compensated by reduced retranslocation to the roots.For Ca, in contrast, decreased translocation rates in NH₄⁺-fedplants result in lower shoot concentration. Key words: Nitrogen form, cation nutrition, charge balance, xylem exudate, recirculation