Carbon limits non-linear response of nitrous oxide (N2O) to increasing N inputs in a highly-weathered tropical soil in Sri Lanka

There is growing evidence for a positive non-linear response in N2O emissions where increasing N fertilizer rates critically exceed crop requirements from a range of cropping systems. However, the majority of these studies have been conducted in temperate regions, and it remains unclear if the non-linear response hypothesis can be transferred to tropical regions due to their inherently lower carbon (C) content and fertility. This study assessed the impact of different nitrogen (N) fertilizer application rates in combination with a carbon source (green-waste compost) on soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions and crop productivity from a maize-soybean rotation in tropical Sri Lanka. Low cation exchange capacity and extremely high rainfall promoted higher annual cumulative N2O emissions than reported from other cropping systems, ranging from 2.4–9.16 kg N2O-N ha−1 yr−1 for the different fertilizer rates (0 N, 100 N, 220 N, 300 N). The ΔN2O emitted for every additional kilogram of fertilizer N applied (i.e. the marginal N2O emission), declined from ∼24 g kg−1 for the first 0−100 kg N applied to 7 g kg−1 at 300 kg N. This resulted in declining Emission Factors with increasing N rate, as factors other than N limited denitrification. The addition of compost removed this limitation, resulting in constant ΔN2O production rates and Emission Factors with increasing N inputs, suggesting low C availability limited N2O production at high N rates. The study shows that the non-linear response hypothesis might not hold for highly weathered tropical soils, where C availability limits N2O emissions at high N inputs. While the use of compost can be a viable option to increase soil fertility in these highly weathered tropical soils, it needs to be balanced with reduced N fertilizer application rates to avoid elevated losses of N2O

Activity of cell wall-associated enzymes in ripening olive fruit

Enzymatically active cell wall isolaled from olive (Olea europaea) fruit was employed Hi investigate some hydrolytic enzymes bound to the cell wall and the changes in these during ripening. Seven glycosidases. β-glucosidase (EC 3.2.1.21) α-galactosidase (EC 3.2.1.22). β-galactosidase (EC 3.2.1.23). α-arabinosidase (EC 3.2.1.55), α-mannosidase (EC 3.2.1,24). β-xylosidase (EC 3.2.1.37) and β-N-acetylglucosamidase (EC 3.2.1.30). as well as Cx-cellulase (EC 3.2.1.4) and endo-polygalacturonase (EC 3.2.1.15). were identified in the cell wall preparation, at four stages of ripeness (mature green. changing colour, black and black-ripe). Activities of all these cell wall-associated enzymes fionicallv and covalently linked) were determined either by cell wall incubation with artificial substrate or after extraction from the cell wall with buffers of high salt concentration (Cx-cellulase). and were compared to those of forms solubilized from acetone powders with 500 nM citrate buffer (cytoplasmic and/or apoplastic plus ionically hound to cell wall) In general, the activities of low ionic strength buffer-soluble enzymes were found to be much higher than those of the bound enzymes. The bound enzymes are present in the fruit at the green colour stage, whereas the activities of the soluble enzymes only increased from the changing colour stage onwards. The tenacity of binding of enzymes to the wall was investigated by treating the walls with high salt and measuring residual activity. The nature of the ionic and covalent binding and the changes during ripening were also established for wall-hound glycosidase During ripening there was a marked change in the percentages of covalently- and tonically linked activities of β-glucosidase and β-galaclosidase: al the changing colour stages about 75–80% of the bound active in was present in high ionic strength buffer while al the black-ripe stage it was only 15–20. A possible role for these cell wall degradative enzymes in olive softening is discussed.Peer reviewe

Trehalose accumulation in rice plants confers high tolerance levels to different abiotic stresses

Trehalose is a nonreducing disaccharide of glucose that functions as a compatible solute in the stabilization of biological structures under abiotic stress in bacteria, fungi, and invertebrates. With the notable exception of the desiccation-tolerant “resurrection plants,” trehalose is not thought to accumulate to detectable levels in most plants. We report here the regulated overexpression of Escherichia coli trehalose biosynthetic genes (otsA and otsB) as a fusion gene for manipulating abiotic stress tolerance in rice. The fusion gene has the advantages of necessitating only a single transformation event and a higher net catalytic efficiency for trehalose formation. The expression of the transgene was under the control of either tissue-specific or stress-dependent promoters. Compared with nontransgenic rice, several independent transgenic lines exhibited sustained plant growth, less photo-oxidative damage, and more favorable mineral balance under salt, drought, and low-temperature stress conditions. Depending on growth conditions, the transgenic rice plants accumulate trehalose at levels 3–10 times that of the nontransgenic controls. The observation that peak trehalose levels remain well below 1 mg/g fresh weight indicates that the primary effect of trehalose is not as a compatible solute. Rather, increased trehalose accumulation correlates with higher soluble carbohydrate levels and an elevated capacity for photosynthesis under both stress and nonstress conditions, consistent with a suggested role in modulating sugar sensing and carbohydrate metabolism. These findings demonstrate the feasibility of engineering rice for increased tolerance of abiotic stress and enhanced productivity through tissue-specific or stress-dependent overproduction of trehalose

Armazenamento de melão 'Orange Flesh' minimamente processado sob atmosfera modificada Storage of 'Orange Flesh' mellons minimally processed and packaged under modified atmosphere

O aumento da demanda por produtos minimamente processados traz um grande desafio para a ciência e tecnologia de alimentos, considerando-se a escassez de informações sobre a manutenção da qualidade desses produtos. O armazenamento desses em condições adequadas é um ponto fundamental para o sucesso dessa tecnologia. Objetivou-se com este trabalho avaliar o efeito da atmosfera modificada ativa na conservação do melão tipo Orange Flesh minimamente processado. Os frutos, após o processamento, foram embalados sob atmosfera modificada (AM Passiva- Controle, AM Ativa com 5% de CO2 e 5% de O2 e AM Ativa com 10% de CO2 e 2% de O2), armazenados em câmara fria (6 ± 1 ºC e UR 85 ± 5%) durante 8 dias e as amostras retiradas para análises de pH, sólidos solúveis totais (SST), acidez total titulável (ATT), açúcares solúveis totais (AST), firmeza, pectina total (PT), pectina solúvel (PS), e as enzimas pectinametilesterase (PME) e poligalacturonase (PG) a cada 2 dias de armazenamento. A atmosfera modificada ativa pouco influenciou no comportamento das variáveis pH, acidez total titulável (ATT), firmeza e pectina total com relação á atmosfera modificada passiva. No entanto, menor solubilização de pectinas foi detectada nas amostras armazenadas sob atmosfera com 10% de CO2 e 2% de O2. Não foram detectadas atividades das enzimas pectinametilesterase e poligalacturonase nos tratamentos analisados.<br>The increase of the demand for products minimally processed brings a great challenge for the food science and technology, considering the shortage of information about the maintenance of the quality of those products. The storage of those products in appropriate conditions is a fundamental point for the success of such technology. The objective of this work was to evaluate the effect of the active modified atmosphere on the quality and conservation of the 'Orange Flesh' melons processed minimally. The fruits, after the processing, were wrapped under modified atmosphere (Passive MA - Control, Active MA- with 5% of CO2 and 5% of O2 and Active MA with 10% of CO2 and 2% of O2), stored in a cold chamber (6 ± 1 ºC and 85 ± 5% RH) during 8 days and sampled for analyses of pH, total soluble solids, tritable acidity, total soluble sugars, firmness, total pectin, soluble pectin and pectinametylesterase and polygalacturonase activities every 2 days of storage. The variables firmness, total acidity and total pectin were not affected by the active modified atmosphere. However, smaller solubilization of pectins were detected in melons under atmosphere with 10% of CO2 and 2% of O2. Enzymatic activity was not detected in fruits from all treatments