Jose Antonio Pascual

Changes in the microbial activity of an arid soil amended with urban organic wastes

Abstract Changes produced in the biological characteristics of an arid soil by the addition of various urban wastes (municipal solid waste, sewage sludge and compost) at different doses, were evaluated during a 360-day incubation experiment. The addition of organic materials to the soil increased the values of biomass carbon, basal respiration, biomass C/total organic C ratio and metabolic quotient (qCO2), indicating the activation of soil microorganisms. These biological parameters showed a decreasing tendency with time. Nevertheless, their values in amended soils were higher than in control soil, which clearly indicates the improvement of soil biological quality brought about by the organic amendment. This favorable effect on soil biological activity was more noticeable with the addition of fresh wastes (municipal solid waste or sewage sludge) than with compost. In turn, this effect was more permanent when the soil was amended with municipal solid waste than when it was amended with sewage sludge.

Enzymatic activities in an arid soil amended with urban organic wastes : Laboratory experiment

This work studied the changes in soil oxidoreductase and hydrolase activities during 360 days of incubation of an arid soil amended with different amounts of organic materials (fresh and composted urban organic wastes). The enzymatic activities were stimulated by such amendments. The soil receiving sewage sludge showed the highest overall activity. The different enzymatic activities rose after amendment then decreased rapidly with time; 360 days after organic amendment, the soil receiving the highest dose showed significantly higher enzymatic activity than the unamended soil. The soil amended with compost showed lower, though more stable, overall enzymatic activity than the soils amended with fresh wastes (municipal solid waste and sewage sludge). The soil receiving organic material to raise its organic matter content by 0.5% did not generally show significant differences from the unamended soil, while the differences produced in the soils receiving organic material to raise their organic matter content by 1.5% were still significant 360 days after amendment.

16S rDNA analysis reveals low microbial diversity in community level physiological profile assays

The metabolic diversity of microbial communities is fundamental for the multiple soil functions mediated by microorganisms. Community level physiological profiles (CLPPs) based on sole C source oxidation have been used as a fast and reproducible tool to study soil microbial functional diversity because the utilisation of available carbon is the key factor governing microbial growth in soil. Our aim was to assess the phylogenetic affiliation of the microorganisms responsible for C consumption after inoculating Biolog plates. For this purpose, two semi-arid Mediterranean forest soils with significantly different patterns of C consumption and microbial community structure were used. Following the inoculation of the Biolog plates, suspensions from seven wells were sampled after 1, 2 and 7 d of incubation. DNA was extracted and the microbial communities analysed by polymerase chain reaction followed by denaturing gradient gel electrophoresis (PCR-DGGE) and sequencing of excised bands. Despite major differences in the microbial communities of the soils studied, their DGGE banding patterns after incubation were similar for all the analysed C source suspensions. Microorganisms belonging to beta-Proteobacteria (Ralstonia sp. and Burkholderia sp.) and alpha-Proteobacteria (Rhizobium sp.) were dominant. These opportunists had a competitive advantage under the conditions at which the CLPPs were analysed. This study reveals that significantly different CLPP patterns can be generated on the basis of only 3-4 genera, as reflected by PCR-DGGE analysis. Also for this reason, CLPPs based on incubations of soil suspensions should just be used as a screening method and always be accompanied by other techniques for community analysis.

Evaluation of urban wastes for agricultural use

Abstract Three different groups of municipal wastes: The organic fraction of municipal solid wastes, sewage sludges, and composts of these materials were characterized in order to evaluate their suitability as fertilizers. The parameters determined were: pH, contents of N, P, K, total organic C, water-soluble C, extractable C, pH 2-soluble C, pH 2-precipitated C, heavy metals, and organic phytotoxic substances as well as microbiological activity (respiration). The physiological effect of these wastes on seed germination was also studied. Sewage sludges showed the highest N and P contents while NO3 - content was higher in composts. The fresh wastes exhibited a higher organic matter content than composts but the organic matter of the latter was most stable and humified. Aqueous extracts of the fresh products (municipal solid wastes and sewage sludges) inhibited the germination of Lepidium sativum seeds.

Stimulation of barley growth and nutrient absorption by humic substances originating from various organic materials

Abstract We compared the effect of humic substances extracted from municipal wastes (sewage sludge and a compost) and those extracted from more humified materials (leonardite, peat and a commercial humic acid) on plant growth and nutrient absorption during hydroponic cultivation. The results showed that doses representing less than 10 mg C l −1 favoured plant growth, while higher doses sometimes inhibited it. Humic substances favoured the development of the aerial part rather than the root. The effects of both groups of humic substances were similar both as regards plant growth and nutrient absorption. The absorption of macronutrients (nitrogen, phosphorus and potassium) was significantly affected by the addition of humic substances, but differed for each nutrient. Nitrogen absorption, for example, was stimulated by the lowest doses, such stimulation decreased as the dose increased, while the opposite was true for phosphorus. The absorption of micronutrients was favoured by the lowest doses while doses above 10 mg C l −1 inhibited it, which was probably one of the causes of the depressed growth observed with the highest doses.

Transference of heavy metals from a calcareous soil amended with sewage-sludge compost to barley plants

Barley plants were cultivated in a calcareous soil (pH 8.77) amended, at different rates, with sewage-sludge composts containing different heavy-metal contents and the transference of these heavy metals to the plant was studied. The addition to the soil of contaminated compost (mainly in Cd) at a high rate led to a decrease in grain yield but did not affect straw yield. Cadmium and Zn were easily absorbed by barley plants, increasing their concentration with respect to the control in plants grown in the soil amended with compost containing high amounts of these metals. However, Ni and particularly Cu were retained by organic matter and were not transferred to plants. Regardless of the compost heavy-metal contents, plants grown in amended soils showed higher N and P contents than control plants. The concentrations of Cd and Zn in soils were positively correlated with Cd and Zn contents in the plants, while no correlation was found between the concentrations of Cu or Ni in soil and plant. After cultivation, amended soils showed a better nutritional state than control soil (higher N-NO3− and total- and available-P than the control).

Persistence of immobilised and total urease and phosphatase activities in a soil amended with organic wastes

This paper reports on the persistence of total and immobilised enzyme activities (urease and phosphatase) in a soil amended with organic wastes containing high levels of total-urease and phosphatase activity. Fresh organic materials showed the highest values for both total-enzymatic activities. The addition of organic waste to soil increased both total-enzymatic activities in the soil, which, after 360 days, showed values above those of the control. Immobilised enzymes were also higher in the fresh wastes than in the soil with compost, while the specific enzymatic activity levels (enzymatic activity per unit of carbon) were similar. The immobilised urease activity was greater in the amended soil than in the control. At the beginning of the incubation period, the immobilised urease activity was significantly higher in the soil amended with fresh organic wastes than with compost. However, this activity decreased with incubation, whilst the compost-immobilised urease activity increased with time. The effect of organic amendment on immobilised phosphatase activity was similar to that shown by immobilised urease but less pronounced. The persistence of both enzymes was significantly higher in the soil amended with compost than in that amended with fresh materials.

Biochemical and chemical-structural characterization of different organic materials used as manures

A chemical, chemical-physical and biochemical comparison was made between two municipal wastes of differing degrees of maturity (one fresh and the other composted) and a variety of organic materials (manure, leonardite and commercial HA). The chemical analysis revealed the different degrees of stability of the organic matter of the different materials. The enzymatic activities determined (urease, phosphatase, protease-BAA and β-glucosidase) reflected the distinct nature of the organic materials studied, high values corresponding to little evolved organic matter and low values to stabilized organic matter. Pyrolysis-gas chromatography was shown to be a suitable technique for characterizing organic materials, those most liable to mineralization being both municipal wastes and the manure. Although composting stabilizes the organic matter, the structural-chemical composition of the compost was more similar to that of the fresh materials than to that of the more evolved materials.

Deciphering the hormonal signalling network behind the systemic resistance induced by Trichoderma harzianum in tomato.

Root colonization by selected Trichoderma isolates can activate in the plant a systemic defense response that is effective against a broad-spectrum of plant pathogens. Diverse plant hormones play pivotal roles in the regulation of the defense signaling network that leads to the induction of systemic resistance triggered by beneficial organisms [induced systemic resistance (ISR)]. Among them, jasmonic acid (JA) and ethylene (ET) signaling pathways are generally essential for ISR. However, Trichoderma ISR (TISR) is believed to involve a wider variety of signaling routes, interconnected in a complex network of cross-communicating hormone pathways. Using tomato as a model, an integrative analysis of the main mechanisms involved in the systemic resistance induced by Trichoderma harzianum against the necrotrophic leaf pathogen Botrytis cinerea was performed. Root colonization by T. harzianum rendered the leaves more resistant to B. cinerea independently of major effects on plant nutrition. The analysis of disease development in shoots of tomato mutant lines impaired in the synthesis of the key defense-related hormones JA, ET, salicylic acid (SA), and abscisic acid (ABA), and the peptide prosystemin (PS) evidenced the requirement of intact JA, SA, and ABA signaling pathways for a functional TISR. Expression analysis of several hormone-related marker genes point to the role of priming for enhanced JA-dependent defense responses upon pathogen infection. Together, our results indicate that although TISR induced in tomato against necrotrophs is mainly based on boosted JA-dependent responses, the pathways regulated by the plant hormones SA- and ABA are also required for successful TISR development.

Citrus compost and its water extract for cultivation of melon plants in greenhouse nurseries. Evaluation of nutriactive and biocontrol effects.

Two different types of citrus composts, and their water extracts, were tested with regard to their utilisations as partial substitutes for peat in growing media for melon seedlings in greenhouse nurseries. Both compost showed higher plant growth than peat. Compost composed by citrus waste and green residue (C2) showed greater plant growth than compost obtained from the same organic matrices mentioned above further the addition of sludge obtained from citrus industry (C1). Compost C2 showed a greater auxinic effect than C1 and it was the only one that showed cytokinic effect. Both composts also demonstrated a biocontrol effect against Fusarium oxysporum for melon plants: the effects were also higher in C2 than in C1. Higher number of isolated fungi was active against F. oxysporum in compost C2, than compost C1. No different bacterial biocontrol efficacy was observed between both composts. The water extracts of both composts gave lower plant yields than their solid matrices, their relative effects being similar to those of the solid composts (C2 extract gave higher plant yields than the extract from C1). The biocontrol effects of compost water extracts followed the same trend.