Direct and indirect effects of climate on decomposition in native ecosystems from central Argentina

Abstract Climate affects litter decomposition directly through temperature and moisture, determining the ecosystem potential decomposition, and indirectly through its effect on plant community composition and litter quality, determining litter potential decomposition. It would be expected that both the direct and indirect effects of climate on decomposition act in the same direction along gradients of actual evapotranspiration (AET). However, studies from semiarid ecosystems challenge this idea, suggesting that the climatic conditions that favour decomposition activity, and the consequent ecosystem potential decomposition, do not necessarily lead to litter being easier to decompose. We explored the decomposition patterns of four arid to subhumid native ecosystems with different AET in central‐western Argentina and we analysed if ecosystem potential decomposition (climatic direct effect), nutrient availability and leaf litter potential decomposition (climatic indirect effect) all increased with AET. In general, the direct effect of climate (AET) on decomposition (i.e. ecosystem potential decomposition), showed a similar pattern to nutrient availability in soils (higher for xerophytic and mountain woodlands and lower for the other ecosystems), but different from the pattern of leaf litter potential decomposition. However, the range of variation in the ecosystem potential decomposition was much higher than the range of variation in litter potential decomposition, indicating that the direct effect of climate on decomposition was far stronger than the indirect effect through litter quality. Our results provide additional experimental evidence supporting the direct control of climate over decomposition, and therefore nutrient cycling. For the ecosystems considered, those with the highest AET are the ecosystems with the highest potential decomposition. But what is more interesting is that our results suggest that the indirect control of climate over decomposition through vegetation characteristics and decomposability does not follow the same trend as the direct effect of climate. This finding has important implications in the prediction of the effects of climate change on semiarid ecosystems.     

Effect of some heterocyclic herbicides on CO2 assimilation by spinach chloroplasts

We have studied the inhibitory effect of heterocyclic herbicides simazine, paraquat, pyrazon and amitrole on photosynthetic CO₂ fixation and on the level of intermediates of the CO₂ assimilation cycle in isolated spinach (Spinacia oleracea) chloroplasts, as well as their in vitro activities on ribulose-1,5-bisphosphate carboxylase and fructose-1,6-bisphosphatase. The half inhibitory concentrations (I₅₀) of CO₂ assimilation were about 1 μM for simazine and paraquat, and 10 μM for pyrazon. Amitrole, with an I₅₀ 100 μM, gave only a weak inhibition. In the presence of simazine or pyrazon the triose-phosphates/phosphoglycerate ratio diminished because of a decrease of the triose-phosphates percentage from 47% to 19%, which means an inhibition of the phosphoglycerate reduction step by a low NADPH synthesis. However, there was not a parallel increase of phosphoglycerate, because of collateral pathways leading to phospho-enolpyruvate, amino acids and other non-identified compounds. Paraquat did not give such a decreased ratio, which could be explained as an inhibition of some step of the Calvin cycle later than triose-phosphates by the H₂O₂ formed in a Mehler reaction. Amitrole did not show any effect on the pattern of intermediates. Simazine and pyrazon at 10 μM concentration promote a 20–30% activation of ribulose-1,5-bisphosphate carboxylase activity, whereas paraquat, pyrazon and simazine showed an I₅₀ about 100 μM for the inhibition of the photosynthetic fructose-1,6-bisphosphatase.     

Order Parameters of a Transmembrane Helix in a Fluid Bilayer: Case Study of a WALP Peptide

A new solid-state NMR-based strategy is established for the precise and efficient analysis of orientation and dynamics of transmembrane peptides in fluid bilayers. For this purpose, several dynamically averaged anisotropic constraints, including ¹³C and ¹⁵N chemical shift anisotropies and ¹³C-¹⁵N dipolar couplings, were determined from two different triple-isotope-labeled WALP23 peptides (²H, ¹³C, and ¹⁵N) and combined with previously published quadrupolar splittings of the same peptide. Chemical shift anisotropy tensor orientations were determined with quantum chemistry. The complete set of experimental constraints was analyzed using a generalized, four-parameter dynamic model of the peptide motion, including tilt and rotation angle and two associated order parameters. A tilt angle of 21° was determined for WALP23 in dimyristoylphosphatidylcholine, which is much larger than the tilt angle of 5.5° previously determined from ²H NMR experiments. This approach provided a realistic value for the tilt angle of WALP23 peptide in the presence of hydrophobic mismatch, and can be applied to any transmembrane helical peptide. The influence of the experimental data set on the solution space is discussed, as are potential sources of error.     

The Most Likely Time and Place of Introduction of BTV8 into Belgian Ruminants

Background

In northern Europe, bluetongue (BT) caused by the BT virus (BTV), serotype 8, was first notified in August 2006 and numerous ruminant herds were affected in 2007 and 2008. However, the origin and the time and place of the original introduction have not yet been determined.

Methods and Principal Findings

Four retrospective epidemiological surveys have been performed to enable determination of the initial spatiotemporal occurrence of this emerging disease in southern Belgium: investigations of the first recorded outbreaks near to the disease epicenter; a large anonymous, random postal survey of cattle herds and sheep flocks; a random historical milk tank survey of samples tested with an indirect ELISA and a follow-up survey of non-specific health indicators. The original introduction of BTV into the region probably occurred during spring 2006 near to the National Park of Hautes Fagnes and Eifel when Culicoides become active.

Conclusions/Significance

The determination of the most likely time and place of introduction of BTV8 into a country is of paramount importance to enhance awareness and understanding and, to improve modeling of vector-borne emerging infectious diseases.     

Tomato yellow leaf curl viruses: ménage à trois between the virus complex,the plant and the whitefly vector

Tomato yellow leaf curl disease (TYLCD) is one of the most devastating viral diseases affecting tomato crops in tropical, subtropical and temperate regions of the world. Here, we focus on the interactions through recombination between the different begomovirus species causing TYLCD, provide an overview of the interactions with the cellular genes involved in viral replication, and highlight recent progress on the relationships between these viruses and their vector, the whitefly Bemisia tabaci. Taxonomy: The tomato yellow leaf curl virus‐like viruses (TYLCVs) are a complex of begomoviruses (family Geminiviridae, genus Begomovirus) including 10 accepted species: Tomato yellow leaf curl Axarquia virus (TYLCAxV), Tomato yellow leaf curl China virus (TYLCCNV), Tomato yellow leaf curl Guangdong virus (TYLCGuV), Tomato yellow leaf curl Indonesia virus (TYLCIDV), Tomato yellow leaf curl Kanchanaburi virus (TYLVKaV), Tomato yellow leaf curl Malaga virus (TYLCMalV), Tomato yellow leaf curl Mali virus (TYLCMLV), Tomato yellow leaf curl Sardinia virus (TYLCSV), Tomato yellow leaf curl Thailand virus (TYLCTHV), Tomato yellow leaf curl Vietnam virus (TYLCVNV) and Tomato yellow leaf curl virus(TYLCV). We follow the species demarcation criteria of the International Committee on Taxonomy of Viruses (ICTV), the most important of which is an 89% nucleotide identity threshold between full‐length DNA‐A component nucleotide sequences for begomovirus species. Strains of a species are defined by a 93% nucleotide identity threshold. Host range: The primary host of TYLCVs is tomato (Solanum lycopersicum), but they can also naturally infect other crops [common bean (Phaseolus vulgaris), sweet pepper (Capsicum annuum), chilli pepper (C. chinense) and tobacco (Nicotiana tabacum)], a number of ornamentals [petunia (Petunia×hybrida) and lisianthus (Eustoma grandiflora)], as well as common weeds (Solanum nigrum and Datura stramonium). TYLCVs also infect the experimental host Nicotiana benthamiana. Disease symptoms: Infected tomato plants are stunted or dwarfed, with leaflets rolled upwards and inwards; young leaves are slightly chlorotic; in recently infected plants, fruits might not be produced or, if produced, are small and unmarketable. In common bean, some TYLCVs produce the bean leaf crumple disease, with thickening, epinasty, crumpling, blade reduction and upward curling of leaves, as well as abnormal shoot proliferation and internode reduction; the very small leaves result in a bushy appearance.     

Solution state NMR structure and dynamics of KpOmpA, a 210 residue transmembrane domain possessing a high potential for immunological applications

The three-dimensional structure of the outer membrane protein A from Klebsiella pneumoniae transmembrane domain was determined by NMR. This protein induces specific humoral and cytotoxic responses, and is a potent carrier protein. This is one of the largest integral membrane proteins (210 residues) for which nearly complete resonance assignment, including side chains, has been achieved so far. The methodology rested on the use of 900 MHz 3D and 4D TROSY experiments recorded on a uniformly ¹⁵N,¹³C,²H-labeled sample and on a perdeuterated methyl protonated sample. The structure was refined from 920 experimental constraints, giving an ensemble of 20 best structures with an r.m.s. deviation of 0.54 Å for the main chain atoms in the core eight-stranded β-barrel. The protein dynamics was assessed, in a residue-specific manner, by ¹H-¹⁵N NOEs (pico- to nanosecond timescale), exchange broadening (millisecond to second) and ¹H-²H chemical exchange (hour-weeks).     

Contrasting functional trait syndromes underlay woody alien success in the same ecosystem

We performed a comprehensive comparative study of functional traits in coexisting alien and native woody species in order to examine the strategies related to resource use and dispersion underlying alien success in mountain Chaco woodlands of central Argentina. Our approach integrated seemingly contrasting pieces of evidence in the region. We specifically assessed whether (i) the ‘functional acquisitive trend’ previously observed along a broad environmental gradient accounts for woody alien naturalization when considering a single mesic ecosystem; or (ii) more than one trait syndrome is important among alien species, which would be more in line with the context‐dependent nature of biological invasions at a local scale. Fifteen vegetative and regenerative traits were measured on the most common 14 native and 11 alien woody species. We compared the attributes of (i) native and alien species and (ii) between native species and two contrasting groups of alien species identified in the previous analysis. The overall trait comparison (i) showed that, in terms of vegetative attributes, woody alien species tend to be on average more acquisitive than native species. However, (ii) two contrasting syndromes were revealed among alien species: a group of seven deciduous species with acquisitive attributes; and a group of four evergreen species showing markedly more conservative attributes than the first group. The functional attributes of ‘conservative aliens’ completely overlapped with the range observed for native species, except for an exclusive dispersal phenology and a stronger tendency to clonal spread. Acquisitive aliens, in turn, proved to be beyond the range of attributes of native species, at the acquisitive extreme, as they did in previous comparisons. Despite their importance, general trends in plant functional attributes across regions and ecosystems can sometimes obscure trends at more local scales that are nevertheless important for the understanding and management of particular systems. Our study concurs with previous general trends when looking at the overall comparison between native and alien species, but unveils contrasting functional strategies among alien species when examining their attributes more closely, even within the same ecosystem.     

The use of temperature gradient tunnels for studying the combined effect of CO2, temperature and water availability in N2 fixing alfalfa plants

Atmospheric CO₂ concentration and temperature are increasing as a consequence of human activity. Periods of low water availability are expected to increase in Mediterranean ecosystems. Temperature gradient tunnels were used to provide near to ambient conditions and conditions simulating predicted increases in CO₂ and temperature for an alfalfa crop. The performance, construction, and running costs of the tunnels are reported and discussed. Two levels of water supply were included in the treatments. Plants were grown in large, 13 L pots, keeping a fixed soil volumetric water content and with nodule fixation as the only nitrogen source for the plant. Regardless of water regime, the effect of elevated CO₂ on plant growth was temperature dependent. Dry matter was enhanced when elevated CO₂ and temperature were combined. Plant yield improvement was partly a result of increased photosynthetic rates. There were no effects on plant N concentration. Decreased specific nodule activity might suggest that lack of differences in plant N were a consequence of reduced nodule enzyme activity.     

Increasing importance of small phytoplankton in a warmer ocean

The macroecological relationships among marine phytoplankton total cell density, community size structure and temperature have lacked a theoretical explanation. The tiniest members of this planktonic group comprise cyanobacteria and eukaryotic algae smaller than 2 μm in diameter, collectively known as picophytoplankton. We combine here two ecological rules, the temperature–size relationship with the allometric size‐scaling of population abundance to explain a remarkably consistent pattern of increasing picophytoplankton biomass with temperature over the ?0.6 to 22 °C range in a merged dataset obtained in the eastern and western temperate North Atlantic Ocean across a diverse range of environmental conditions. Our results show that temperature alone was able to explain 73% of the variance in the relative contribution of small cells to total phytoplankton biomass regardless of differences in trophic status or inorganic nutrient loading. Our analysis predicts a gradual shift toward smaller primary producers in a warmer ocean. Because the fate of photosynthesized organic carbon largely depends on phytoplankton size, we anticipate future alterations in the functioning of oceanic ecosystems.