How are nitrogen availability,fine‐root mass,and nitrogen uptake related empirically? Implications for models and theory

Understanding the effects of global change in terrestrial communities requires an understanding of how limiting resources interact with plant traits to affect productivity. Here, we focus on nitrogen and ask whether plant community nitrogen uptake rate is determined (a) by nitrogen availability alone or (b) by the product of nitrogen availability and fine‐root mass. Surprisingly, this is not empirically resolved. We performed controlled microcosm experiments and reanalyzed published pot experiments and field data to determine the relationship between community‐level nitrogen uptake rate, nitrogen availability, and fine‐root mass for 46 unique combinations of species, nitrogen levels, and growing conditions. We found that plant community nitrogen uptake rate was unaffected by fine‐root mass in 63% of cases and saturated with fine‐root mass in 29% of cases (92% in total). In contrast, plant community nitrogen uptake rate was clearly affected by nitrogen availability. The results support the idea that although plants may over‐proliferate fine roots for individual‐level competition, it comes without an increase in community‐level nitrogen uptake. The results have implications for the mechanisms included in coupled carbon‐nitrogen terrestrial biosphere models (CN‐TBMs) and are consistent with CN‐TBMs that operate above the individual scale and omit fine‐root mass in equations of nitrogen uptake rate but inconsistent with the majority of CN‐TBMs, which operate above the individual scale and include fine‐root mass in equations of nitrogen uptake rate. For the much smaller number of CN‐TBMs that explicitly model individual‐based belowground competition for nitrogen, the results suggest that the relative (not absolute) fine‐root mass of competing individuals should be included in the equations that determine individual‐level nitrogen uptake rates. By providing empirical data to support the assumptions used in CN‐TBMs, we put their global climate change predictions on firmer ground.     

The growth response of plants to elevated CO2 under non-optimal environmental conditions

Under benign environmental conditions, plant growth is generally stimulated by elevated atmospheric CO₂ concentrations. When environmental conditions become sub- or supra-optimal for growth, changes in the biomass enhancement ratio (BER; total plant biomass at elevated CO₂ divided by plant biomass at the current CO₂ level) may occur. We analysed literature sources that studied CO₂2environment interactions on the growth of herbaceous species and tree seedlings during the vegetative phase. For each experiment we calculated the difference in BER for plants that were grown under 'optimal' and 'non-optimal' conditions. Assuming that interactions would be most apparent if the environmental stress strongly diminished growth, we scaled the difference in the BER values by the growth reduction due to the stress factor. In our compilation we found a large variability in CO₂2environment interactions between experiments. To test the impact of experimental design, we simulated a range of analyses with a plant-to-plant variation in size common in experimental plant populations, in combination with a number of replicates generally used in CO₂2environment studies. A similar variation in results was found as in the compilation of real experiments, showing the strong impact of stochasticity. We therefore caution against strong inferences derived from single experiments and suggest rather a reliance on average interactions across a range of experiments. Averaged over the literature data available, low soil nutrient supply or sub-optimal temperatures were found to reduce the proportional growth stimulation of elevated CO₂. In contrast, BER increased when plants were grown at low water supply, albeit relatively modestly. Reduced irradiance or high salinity caused BER to increase in some cases and decrease in others, resulting in an average interaction with elevated CO₂ that was not significant. Under high ozone concentrations, the relative growth enhancement by elevated CO₂ was strongly increased, to the extent that high CO₂ even compensated in an absolute way for the harmful effect of ozone on growth. No systematic difference in response was found between herbaceous and woody species for any of the environmental variables considered.     

Multi-domain network infrastructure based on P4 programmable devices for Digital Data Marketplaces

Cluster Computing - There are many organizations interested in sharing data with others, and they can do this only if a multi-domain secure platform is available. Such platforms, often referred to...     

Orbital signatures in a late Miocene dinoflagellate record from Crete (Greece)

A high-resolution palynological study of the cyclically bedded Faneromeni section (upper Tortonian-lower Messinian) on Crete (Greece) is presented. This study aims to recognize orbitally-driven variations in the palynological record and to validate the age model based on the astronomical calibration of the sedimentary cycles. Four palynology-based environmental proxies were utilised using interpretations of fossil dinoflagellate associations based on modern ecological characteristics. Cross-spectral analysis between the proxy records and astronomical target curve, the 65°N summer insolation, yielded in most cases significant spectral power and coherence in the precession and/or obliquity frequency bands. Precession-controlled variations in the proxy records are related to lithology and indicate that maxima in continental input and minima in sea surface salinity coincide with sapropel formation. The influence of obliquity is most clearly reflected in the index of continental versus marine palynomorphs (S-D). The absence of a distinct time lag relative to obliquity indicates that the 41-kyr component in continental input is controlled by oscillations in regional Mediterranean climate rather than by glacial cyclicity. Phase relations in the different astronomical frequency bands of the spectrum, as compared with the Mediterranean Pliocene, essentially confirm the validity of the Miocene astronomical time scale. Finally, a major non-cyclic change in the palynological assemblage at 6.68 Ma indicates enhanced salinity and decreased river discharge. This shift coincides with a significant drop in sedimentation rate informally termed the “Early Messinian Sediment starvation Event”.     

Plasticity as a plastic response: how submergence-induced leaf elongation in Rumex palustris depends on light and nutrient availability in its early life stage

Plants may experience different environmental cues throughout their development which interact in determining their phenotype. This paper tests the hypothesis that environmental conditions experienced early during ontogeny affect the phenotypic response to subsequent environmental cues. This hypothesis was tested by exposing different accessions of Rumex palustris to different light and nutrient conditions, followed by subsequent complete submergence. Final leaf length and submergence-induced plasticity were affected by the environmental conditions experienced at early developmental stages. In developmentally older leaves, submergence-induced elongation was lower in plants previously subjected to high-light conditions. Submergence-induced elongation of developmentally younger leaves, however, was larger when pregrown in high light. High-light and low-nutrient conditions led to an increase of nonstructural carbohydrates in the plants. There was a positive correlation between submergence-induced leaf elongation and carbohydrate concentration and content in roots and shoots, but not with root and shoot biomass before submergence. These results show that conditions experienced by young plants modulate the responses to subsequent environmental conditions, in both magnitude and direction. Internal resource status interacts with cues perceived at different developmental stages in determining plastic responses to the environment.     

Localization of HLA on the short arm of chromosome 6

Summary A detailed marker gene study in a large Dutch kindred segregating for a reciprocal translocation between the chromosomes 6 and 20, t(6;20) (p21;p13), revealed a close linkage between the HLA genes and the breakpoint on the short arm of 6. During this study an apparent peak lod score of 2.9 was obtained at a recombination value of 0.05 for a linkage between HLA and the breakpoint, indicating that the chromosomal region, carrying the HLA genes, is situated near the breakpoint in band 6p21 close to the transition to 6p22.     

Efficacy and safety of a new vaginal contraceptive antimicrobial formulation containing high molecular weight poly(sodium 4-styrenesulfonate)

Host cell infection by sexually transmitted disease (STD)-causing microbes and fertilization by spermatozoa may have some mechanisms in common. If so, certain noncytotoxic agents could inhibit the functional activity of both organisms. High molecular mass poly(sodium 4-styrenesulfonate) (T-PSS) may be one of these compounds. T-PSS alone (1 mg/ml) or in a gel (2% or 5% T-PSS) completely prevented conception in the rabbit. Contraception was not due to sperm cytotoxicity or to an effect on sperm migration. However, T-PSS inhibited sperm hyaluronidase (IC(50) = 5.3 microg/ml) and acrosin (IC(50) = 0.3 microg/ml) and caused the loss of acrosomes from spermatozoa (85% maximal loss by 0.5 microg/ml). T-PSS (5% in gel) also reduced sperm penetration into bovine cervical mucus (73% inhibition by 1 mg gel/ml). T-PSS (5% in gel) inhibited human immunodeficiency virus (HIV; IC(50)= 16 microg gel/ml) and herpes simplex viruses (HSV-1 and HSV-2; IC(50) = 1.3 and 1.0 microg gel/ml, respectively). The drug showed high efficacy against a number of clinical isolates and laboratory strains. T-PSS (5% in gel) also inhibited Neisseria gonorrhea (IC(50) < 1.0 gel/ml) and Chlamydia trachomatis (IC(50) = 1.2 microg gel/ml) but had no effect on lactobacilli. These results imply that T-PSS is an effective functional inhibitor of both spermatozoa and certain STD-causing microbes. The noncytotoxic nature should make T-PSS safe for vaginal use. T-PSS was nonmutagenic in vitro and possessed an acute oral toxicity of >5 g/kg (rat). Gel with 10% T-PSS did not irritate the skin or penile mucosa (rabbit) and caused no dermal sensitization (guinea pig). Vaginal administration of the 5% T-PSS gel to the rabbit for 14 consecutive days caused no systemic toxicity and only mild (acceptable) vaginal irritation. T-PSS in gel form is worthy of clinical evaluation as a vaginal contraceptive HIV/STD preventative.     

The relationships of wood-, gas- and water fractions of tree stems to performance and life history variation in tropical trees

Background and Aims

The volume of tree stems is made up of three components: solid wood, gas and water. These components have important consequences for the construction costs, strength and stability of trees. Here, the importance of stem components for sapling growth and survival in the field was investigated, and then these stem components were related to two important life history axes of variation: the light requirements for regeneration and the adult stature of the species.

Methods

Stem fractions of wood, gas and water were determined for saplings and adults of respectively 30 and 58 Bolivian tropical moist-forest species. Sapling height growth and survival were monitored for 2 years in the field as indicators of sapling performance.

Key Results

Sapling stems consisted of 26 % wood (range 7–36 % for species), 59 % water (range 49–88 %), and 15 % gas (range 0–38 %) per unit volume. The wood fraction was the only determinant of sapling performance and was correlated with increased survival and decreased growth rate across species. The wood fraction decreased with light requirements of the species, probably because a high wood fraction protects shade-tolerant species against pathogens and falling debris. The gas fraction increased with the light requirements and adult stature of the species; probably as an aid in realizing a rapid height growth and accessing the canopy in the case of light-demanding species, and for rapidly attaining stability and a large reproductive size in the case of tall species. The water fraction was not correlated with the life history variation of tree species, probably because it leads to increased stem loading and decreased stability.

Conclusions

The wood fraction might partially explain the growth–survival trade-off that has been found across tropical tree species. The wood and gas fractions are closely related to the regeneration light requirements of the species. Tall species have a high gas fraction, probably not only because gas is a cheap filler, but also because it might lead to an increased stability of these tall trees.Key words: Adult stature, biomechanics, Bolivia, shade tolerance, second moment of area, tropical rain forest, wood density, wood specific gravity     

Ethylene insensitivity results in down-regulation of rubisco expression and photosynthetic capacity in tobacco

Little is known about the effect of hormones on the photosynthetic process. Therefore, we studied Rubisco content and expression along with gas exchange parameters in transgenic tobacco (Nicotiana tabacum) plants that are not able to sense ethylene. We also tested for a possible interaction between ethylene insensitivity, abscisic acid (ABA), and sugar feedback on photosynthesis. We measured Rubisco content in seedlings grown in agar with or without added sugar and fluridone, and Rubisco expression in hydroponically grown vegetative plants grown at low and high CO(2). Furthermore, we analyzed gas exchange and the photosynthetic machinery of transformants and wild-type plants grown under standard conditions. In the presence of exogenous glucose (Glc), agar-grown seedlings of the ethylene-insensitive genotype had lower amounts of Rubisco per unit leaf area than the wild type. No differences in Rubisco content were found between ethylene-insensitive and wild-type seedlings treated with fluridone, suggesting that inhibition of ABA production nullified the effect of Glc application. When larger, vegetative plants were grown at different atmospheric CO(2) concentrations, a negative correlation was found between Glc concentration in the leaves and Rubisco gene expression, with stronger repression by high Glc concentrations in ethylene-insensitive plants. Ethylene insensitivity resulted in plants with comparable fractions of nitrogen invested in light harvesting, but lower amounts in electron transport and Rubisco. Consequently, photosynthetic capacity of the insensitive genotype was clearly lower compared with the wild type. We conclude that the inability to perceive ethylene results in increased sensitivity to Glc, which may be mediated by a higher ABA concentration. This increased sensitivity to endogenous Glc has negative consequences for Rubisco content and photosynthetic capacity of these plants.     

Construction costs, chemical composition and payback time of high- and low-irradiance leaves

The effect of irradiance on leaf construction costs, chemical composition, and on the payback time of leaves was investigated. To enable more generalized conclusions, three different systems were studied: top and the most-shaded leaves of 10 adult tree species in a European mixed forest, top leaves of sub-dominant trees of two evergreen species growing in small gaps or below the canopy in an Amazonian rainforest, and plants of six herbaceous and four woody species grown hydroponically at low or high irradiance in growth cabinets. Daily photon irradiance varied 3-6-fold between low- and high-light leaves. Specific leaf area (SLA) was 30-130% higher at low light. Construction costs, on the other hand, were 1-5% lower for low-irradiance leaves, mainly because low-irradiance leaves had lower concentrations of soluble phenolics. Photosynthetic capacity and respiration, expressed per unit leaf mass, were hardly different for the low- and high-light leaves. Estimates of payback times of the high-irradiance leaves ranged from 2-4 d in the growth cabinets, to 15-20 d for the adult tree species in the European forest. Low-irradiance leaves had payback times that were 2-3 times larger, ranging from 4 d in the growth cabinets to 20-80 d at the most shaded part of the canopy of the mixed forest. In all cases, estimated payback times were less than half the life span of the leaves, suggesting that even at time-integrated irradiances lower than 5% of the total seasonal value, investment in leaves is still fruitful from a carbon-economy point of view. A sensitivity analysis showed that increased SLA of low-irradiance leaves was the main factor constraining payback times. Acclimation in the other five factors determining payback time, namely construction costs, photosynthetic capacity per unit leaf mass, respiration per unit leaf mass, apparent quantum yield, and curvature of the photosynthetic light-response-curve, were unimportant when the observed variation in each factor was examined.