Carbon in Amazon forests: unexpected seasonal fluxes and disturbance-induced losses

The net ecosystem exchange of carbon dioxide was measured by eddy covariance methods for 3 years in two old-growth forest sites near Santarém, Brazil. Carbon was lost in the wet season and gained in the dry season, which was opposite to the seasonal cycles of both tree growth and model predictions. The 3-year average carbon loss was 1.3 (confidence interval: 0.0 to 2.0) megagrams of carbon per hectare per year. Biometric observations confirmed the net loss but imply that it is a transient effect of recent disturbance superimposed on long-term balance. Given that episodic disturbances are characteristic of old-growth forests, it is likely that carbon sequestration is lower than has been inferred from recent eddy covariance studies at undisturbed sites.     

Soil pH on mobility of imazaquin in oxisols with positive balance of charges

The influence of soil pH on the leaching potential of the ionizable herbicide imazaquin was assessed on the profile of two highly weathered soils having a net positive charge in the B horizon, in contrast to a soil having a net negative charge in the whole profile, using packed soil column experiments. Imazaquin leached to a large extent and faster at Kd values lower than 1.0 L kg(-1), a much more lenient limit than usually proposed for pesticides in the literature (Kd < 5.0 L kg(-1)). The amount of imazaquin leached increased with soil pH. As the soil pH increased, the percentage of imazaquin in the anionic forms, the negative surface potential of the soils, as well as imazaquin water solubility also increased, thus reducing sorption because of repulsive electrostatic forces (hydrophilic interactions). For all surface samples (0-0.2 m), imazaquin did not leach at soil pH values lower than pKa (3.8) and more than 80% of the applied amount was leached at pH values higher than 5.5. For subsurface samples from the acric soils, imazaquin only began to leach at soil pH values > zero point of salt effects (ZPSE > 5.7). In conclusion, the use of surface K(oc) values to predict the amount of imazaquin leached within soil profiles having a positive balance of charges may greatly overestimate its actual leaching potential.     

Productivity and nutritional value of BRS capiaçu grass (Pennisetum purpureum) managed at four regrowth ages in a semiarid region

Tropical Animal Health and Production - The objective of this study was to evaluate the productivity, productive efficiency, and nutritional value of the elephant grass cultivar BRS capiaçu...     

Live and frozen Artemia nauplii for catfish Lophiosilurus alexandri (Steindachner, 1876) larvae in different salinities

Tropical Animal Health and Production - The objective of the study was to verify the combination of live and frozen Artemia nauplii, in different salinized water, and its influence in growth and...     

Acetosolv delignification of marabou (<Emphasis Type="Italic">Dichrostachys cinerea</Emphasis>) wood with and without acid prehydrolysis

The chemical composition of marabou(Dichrostachys cinerea) wood and its treatment with acetic acid were investigated.Two different treatment approaches,direct acetosolv and combined acid prehydrolysis/acetosolv,were evaluated.The effects of acetic acid concentration(50%,70% and 90%) and temperature(normal boiling temperature and 121°C) on yield of solids,solubilization of lignin and hemicelluloses and recovery of cellulose were evaluated for both treatments.High solubilization of marabou components was observed in the direct acetosolv treatment at 121°C,especially at the highest acetic acid concentration,where around 84.8% of lignin and 78% of hemicelluloses were removed.When the material was subjected to acid prehydrolysis prior to acetosolv treatment,lignin solubilization was improved,especially at low acetic acid concentrations.Above 80% of the solubilized lignin was recovered from the liquors in the direct acetosolv treatment,but the recovery was lower in the combined treatment.Cellulose was well preserved in all the treatment schemes.     

Structural characterization of Peruvian carrot (Arracacia xanthorrhiza) starch and the effect of annealing on its semicrystalline structure

Structural characteristics of native and annealed Peruvian carrot (Arracacia xanthorrhiza) starches were determined and compared to those of cassava and potato starches. Peruvian carrot starch presented round and irregular shaped granules, low amylose content and B-type X-ray pattern. Amylopectin of this starch contained a large proportion of long (DP > 37) and short (DP 6-12) branched chains. These last ones may contribute to its low gelatinization temperature. After annealing, the gelatinization temperatures of all starches increased, but the ΔH and the crystallinity increased only in Peruvian carrot and potato starches. The annealing process promoted a higher exposure of Peruvian carrot amylose molecules, which were more quickly attacked by enzymes, whereas amylopectin molecules became more resistant to hydrolysis. Peruvian carrot starch had structural characteristics that differed from those of cassava and potato starches. Annealing affected the semicrystalline structure of this starch, enhancing its crystallinity, mainly due to a better interaction between amylopectin chains.     

Seasonal Variation of n-Alkanes and Polycyclic Aromatic Hydrocarbon Concentrations in PM10 Samples Collected at Urban Sites of São Paulo State, Brazil

Two campaigns were conducted in 2003 and 2004 at sites of different characteristics in São Paulo State. Atmospheric samples were collected twice a month during a 1-year campaign (an extensive campaign) from April 2003 to May 2004 at São Paulo City (SPA) site. The results showed that the pollutant concentrations were controlled not only by local source emissions but also through pollutant transport, both of which were dictated by the prevailing meteorological conditions. Chrysene, benzo(e)pyrene, and benzo(b)fluoranthene were the major compounds found, and diagnostic ratios indicated the multiplicity of sources: industrial, vehicular emission, and atmospheric transport. Intensive campaign (from July 15 to 30, 2003) samples showed higher cancer risk than those collected in the extensive campaign. Samples collected at the urban site (SPA) presented comparable values of PM₁₀ to the urban site influenced by sugarcane burning (Araraquara, ARQ). On the other hand, PAH average concentrations were higher at SPA than at other sites. In both campaigns, the highest value for dry atmospheric deposition flux was found in autumn and winter. Individually, BPe presented the highest deposition flux followed by BbF in the intensive campaign. It seems that during those periods, the dry deposition was the main airborne PAH removal mechanism. Diagnostic ratios suggested also vehicular emissions at the sites and photochemical reactions influencing in the atmospheric particulate matter composition. SPA and PRB samples presented higher cancer risk than ARQ in the intensive campaign.     

Comprehensive prediction of plant cytoplasmic and apoplastic effectors underlying Erwinia psidii pathogenicity

Erwinia psidii (Eps) is the causal agent of emerging diseases of eucalypt and guava; however, the mechanisms underlying its pathogenicity are not fully understood. Here, we predicted factors involved in the ability of Eps to cause disease on its host plants. For that, the genomes of four Eps strains exhibiting different virulence on eucalypt were sequenced, and hrp/hrc genes coding for the type III secretion system (T3SS), effectors injected into the plant cell cytoplasm through the T3SS (T3SEs) and their plant subcellular localizations, as well as proteins deployed to the host apoplast, were predicted. It was found that Eps possesses a complete hrp/hrc gene cluster based on comparison with Erwinia amylovora. A total of 18 T3SEs were predicted, 11 of which were shared among all strains, none were exclusive to any strain and seven were absent in at least one strain. No sequence variation among strains was found for five T3SE candidates whereas extensive variation was found for six, suggesting the latter may be determinants of virulence differences. The T3SE candidates are predicted to target the plant cell nucleus, cytoplasm, mitochondrion, chloroplast and peroxisome. The predicted apoplastic effector repertoire common to all four strains was over-represented in proteins of unknown functions or predicted to possess enzymatic activities, among which the most abundant were oxidoreductases and peptidases. Proteins with lytic transglycosylase activity were predicted in strain-specific apoplastic effector repertoires. These results provide an important framework for future research aimed at uncovering the factors underlying Eps pathogenicity.