Altered physiological function,not structure,drives increased radiation-use efficiency of soybean grown at elevated CO<Subscript>2</Subscript>

Previous studies of elevated carbon dioxide concentration ([CO₂]) on crop canopies have found that radiation-use efficiency is increased more than radiation-interception efficiency. It is assumed that increased radiation-use efficiency is due to changes in leaf-level physiology; however, canopy structure can affect radiation-use efficiency if leaves are displayed in a manner that optimizes their physiological capacity, even though the canopy intercepts the same amount of light. In order to determine the contributions of physiology and canopy structure to radiation-use and radiation-interception efficiency, this study relates leaf-level physiology and leaf display to photosynthetic rate of the outer canopy. We used a new imaging approach that delivers three-dimensional maps of the outer canopy during the growing season. The 3D data were used to model leaf orientation and mean photosynthetic electron transport of the outer canopy to show that leaf orientation changes did not contribute to increased radiation-use; i.e. leaves of the outer canopy showed similar diurnal leaf movements and leaf orientation in both treatments. Elevated [CO₂] resulted in an increased maximum electron transport rate (ETR_max) of light reactions of photosynthesis. Modeling of canopy light interception showed that stimulated leaf-level electron transport at elevated [CO₂], and not alterations in leaf orientation, was associated with stimulated radiation-use efficiency and biomass production in elevated [CO₂]. This study provides proof of concept of methodology to quantify structure–function relationships in combination, allowing a quantitative estimate of the contribution of both effects to canopy energy conversion under elevated [CO₂].     

Noisy-threshold control of cell death

Background  

Cellular responses to death-promoting stimuli typically proceed through a differentiated multistage process, involving a lag phase, extensive death, and potential adaptation. Deregulation of this chain of events is at the root of many diseases. Improper adaptation is particularly important because it allows cell sub-populations to survive even in the continuous presence of death conditions, which results, among others, in the eventual failure of many targeted anticancer therapies.     

Abundance of introduced species at home predicts abundance away in herbaceous communities

Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites - grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.     

High sero-prevalence of caseous lymphadenitis identified in slaughterhouse samples as a consequence of deficiencies in sheep farm management in the state of Minas Gerais, Brazil

Background

Multiple congenital ocular anomalies (MCOA) syndrome is a hereditary congenital eye defect that was first described in Silver colored Rocky Mountain horses. The mutation causing this disease is located within a defined chromosomal interval, which also contains the gene and mutation that is associated with the Silver coat color (PMEL17, exon 11). Horses that are homozygous for the disease-causing allele have multiple defects (MCOA-phenotype), whilst the heterozygous horses predominantly have cysts of the iris, ciliary body or retina (Cyst-phenotype). It has been argued that these ocular defects are caused by a recent mutation that is restricted to horses that are related to the Rocky Mountain Horse breed. For that reason we have examined another horse breed, the Icelandic horse, which is historically quite divergent from Rocky Mountain horses.

Results

We examined 24 Icelandic horses and established that the MCOA syndrome is present in this breed. Four of these horses were categorised as having the MCOA-phenotype and were genotyped as being homozygous for the PMEL17 mutation. The most common clinical signs included megaloglobus, iris stromal hypoplasia, abnormal pectinate ligaments, iridociliary cysts occasionally extending into the peripheral retina and cataracts. The cysts and pectinate ligament abnormalities were observed in the temporal quadrant of the eyes. Fourteen horses were heterozygous for the PMEL17 mutation and were characterized as having the Cyst-phenotype with cysts and occasionally curvilinear streaks in the peripheral retina. Three additional horses were genotyped as PMEL17 heterozygotes, but in these horses we were unable to detect cysts or other forms of anomalies. One eye of a severely vision-impaired 18 month-old stallion, homozygous for the PMEL17 mutation was examined by light microscopy. Redundant duplication of non-pigmented ciliary body epithelium, sometimes forming cysts bulging into the posterior chamber and localized areas of atrophy in the peripheral retina were seen.

Conclusions

The MCOA syndrome is segregating with the PMEL17 mutation in the Icelandic Horse population. This needs to be taken into consideration in breeding decisions and highlights the fact that MCOA syndrome is present in a breed that are more ancient and not closely related to the Rocky Mountain Horse breed.     

Global food insecurity. treatment of major food crops with elevated carbon dioxide or ozone under large-scale fully open-air conditions suggests recent models may have overestimated future yields

Predictions of yield for the globe's major grain and legume arable crops suggest that, with a moderate temperature increase, production may increase in the temperate zone, but decline in the tropics. In total, global food supply may show little change. This security comes from inclusion of the direct effect of rising carbon dioxide (CO2) concentration, [CO2], which significantly stimulates yield by decreasing photorespiration in C3 crops and transpiration in all crops. Evidence for a large response to [CO2] is largely based on studies made within chambers at small scales, which would be considered unacceptable for standard agronomic trials of new cultivars or agrochemicals. Yet, predictions of the globe's future food security are based on such inadequate information. Free-Air Concentration Enrichment (FACE) technology now allows investigation of the effects of rising [CO2] and ozone on field crops under fully open-air conditions at an agronomic scale. Experiments with rice, wheat, maize and soybean show smaller increases in yield than anticipated from studies in chambers. Experiments with increased ozone show large yield losses (20%), which are not accounted for in projections of global food security. These findings suggest that current projections of global food security are overoptimistic. The fertilization effect of CO2 is less than that used in many models, while rising ozone will cause large yield losses in the Northern Hemisphere. Unfortunately, FACE studies have been limited in geographical extent and interactive effects of CO2, ozone and temperature have yet to be studied. Without more extensive study of the effects of these changes at an agronomic scale in the open air, our ever-more sophisticated models will continue to have feet of clay.     

Photosynthesis, productivity, and yield of maize are not affected by open-air elevation of CO2 concentration in the absence of drought

While increasing temperatures and altered soil moisture arising from climate change in the next 50 years are projected to decrease yield of food crops, elevated CO2 concentration ([CO2]) is predicted to enhance yield and offset these detrimental factors. However, C4 photosynthesis is usually saturated at current [CO2] and theoretically should not be stimulated under elevated [CO2]. Nevertheless, some controlled environment studies have reported direct stimulation of C4 photosynthesis and productivity, as well as physiological acclimation, under elevated [CO2]. To test if these effects occur in the open air and within the Corn Belt, maize (Zea mays) was grown in ambient [CO2] (376 micromol mol(-1)) and elevated [CO2] (550 micromol mol(-1)) using Free-Air Concentration Enrichment technology. The 2004 season had ideal growing conditions in which the crop did not experience water stress. In the absence of water stress, growth at elevated [CO2] did not stimulate photosynthesis, biomass, or yield. Nor was there any CO2 effect on the activity of key photosynthetic enzymes, or metabolic markers of carbon and nitrogen status. Stomatal conductance was lower (-34%) and soil moisture was higher (up to 31%), consistent with reduced crop water use. The results provide unique field evidence that photosynthesis and production of maize may be unaffected by rising [CO2] in the absence of drought. This suggests that rising [CO2] may not provide the full dividend to North American maize production anticipated in projections of future global food supply.     

Monitoring microbial predator-prey interactions: an experimental study using fatty acid biomarker and compound-specific stable isotope techniques

Naturally occurring microbial communities are complex, withautotrophs and heterotrophs often similarly sized and impossibleto separate by conventional size fractionation approaches. However,if it was possible to identify specific compounds that are characteristicof particular groups of microbes and determine the stable isotopecomposition of these biomarkers, the requirement for size fractionationcould potentially be negated. This work considered the usefulnessof such an approach by analysis of a simple laboratory predator–preysystem comprising Nanochloropsis oculata, an autotrophic flagellateprey and Oxyrrhis marina, a heterotrophic flagellate predator.In growth-grazing experiments the fatty acids 20:5(n–3)and 22:6(n–3) were used as biomarkers for N. oculata andO. marina respectively. Interpretation of ¹³C values of thesepredator and prey fatty acid biomarkers was not straightforwardsince although isotopic signature of the O. marina biomarkerwas consistently enriched compared to that of its N. oculataprey, the magnitude of enrichment in ¹³C increased with ageof culture (1.0–5.4 %). Given the variability we observedin our experimental cultures, it will be difficult to applythis approach to complex field situations without a comprehensiveunderstanding of the factors determining the ¹³C values of specificbiomarker molecules.     

Will photosynthesis of maize (Zea mays) in the US Corn Belt increase in future [CO2] rich atmospheres? An analysis of diurnal courses of CO2 uptake under free‐air concentration enrichment (FACE)

The C₄ grass Zea mays (maize or corn) is the third most important food crop globally in terms of production and demand is predicted to increase 45% from 1997 to 2020. However, the effects of rising [CO₂] upon C₄ plants, and Z. mays specifically, are not sufficiently understood to allow accurate predictions of future crop production. A rainfed, field experiment utilizing free‐air concentration enrichment (FACE) technology in the primary area of global corn production (US Corn Belt) was undertaken to determine the effects of elevated [CO₂] on corn. FACE technology allows experimental treatments to be imposed upon a complete soil–plant–atmosphere continuum with none of the effects of experimental enclosures on plant microclimate. Crop performance was compared at ambient [CO₂] (354 μ mol mol^?1) and the elevated [CO₂] (549 μmol mol^?1) predicted for 2050. Previous laboratory studies suggest that under favorable growing conditions C₄ photosynthesis is not typically enhanced by elevated [CO₂]. However, stomatal conductance and transpiration are decreased, which can indirectly increase photosynthesis in dry climates. Given the deep soils and relatively high rainfall of the US Corn Belt, it was predicted that photosynthesis would not be enhanced by elevated [CO₂]. The diurnal course of gas exchange of upper canopy leaves was measured in situ across the growing season of 2002. Contrary to the prediction, growth at elevated [CO₂] significantly increased leaf photosynthetic CO₂ uptake rate (A) by up to 41%, and 10% on average. Greater A was associated with greater intercellular [CO₂], lower stomatal conductance and lower transpiration. Summer rainfall during 2002 was very close to the 50‐year average for this site, indicating that the year was not atypical or a drought year. The results call for a reassessment of the established view that C₄ photosynthesis is insensitive to elevated [CO₂] under favorable growing conditions and that the production potential of corn in the US Corn Belt will not be affected by the global rise in [CO₂].