Layer Of Residues Research Articles

The effect of crop residue layers on evapotranspiration, growth and yield of irrigated sugarcane†

A layer of harvest residues from the previous crop can reduce wasteful evaporation from the soil surface and thereby increase the efficiency of use of limited water resources for agricultural production. The practice of harvesting sugarcane green and leaving crop residues in the field, as opposed to burning the residue, has been re-adopted in many sugarcane industries worldwide. However, a better understanding of the dynamic impacts of residue layers on various aspects of the cropping system is required to (1) enable the formulation of sets of best management practices for specific production scenarios, and (2) promote the use of residue layers in areas where it is desirable and has not been adopted, such as irrigated sugarcane production in South Africa. The objective of this study, therefore, was to quantify the effect of 2 different types of residue layers on crop growth, cane yield and evapotranspiration of fully irrigated sugarcane. A layer of cane tops and dead leaves (Trash) and a layer of green tops (Tops) were applied to the soil surface of sugarcane crops (plant crop and first ratoon crop of variety N14) grown on lysimeters at Pongola, South Africa. Observations of crop growth (stalk population, stalk height, canopy cover), cane yield and evapotranspiration for these treatments were compared to that of a bare soil treatment. The data were also used to derive values of crop evaporation coefficients for different development phases and these were compared to FAO56 recommendations. Initial stalk population in the plant crop and radiation capture in the plant and ratoon crop were affected negatively by crop residue layers, but without significantly reducing final stalk population and cane yield. Peak stalk population occurred later in crops grown in residue layers, but peak and final stalk populations were unaffected. Evapotranspiration was reduced by both residue layers, mainly due to a slower developing canopy (reduced transpiration) and reduced evaporation from the soil, during the pre-canopy phases. Increased drainage was observed under residue layers, emphasising the importance of accurate irrigation scheduling to avoid water logging. The FAO56 methodology for calculating crop evaporation coefficient values for the initial, development and late season phases are supported by the results obtained here. Crop evaporation coefficient values were significantly reduced by residue layers. It is important that irrigation scheduling practices be adjusted to realise the potential water savings of sugarcane production systems that make use of residue layers. This study provides the information required to do that. The information could also be used to improve the ability of the crop models to accurately simulate crop growth and evapotranspiration in a residue layer cropping system.Keywords: water use, irrigation, stalk population, canopy development, lysimeter, crop evaporation coefficient, trash blanket

Structure of the human M2 muscarinic acetylcholine receptor bound to an antagonist

The parasympathetic limb of the autonomic nervous system regulates the activity of multiple organ systems. Muscarinic receptors are G protein coupled receptors (GPCRs) that mediate the response to acetylcholine released from parasympathetic nerves.1–5 Their role in the unconscious regulation of organ and central nervous system function makes them potential therapeutic targets for a broad spectrum of diseases. The M2 muscarinic acetylcholine receptor (M2 receptor) is essential for the physiologic control of cardiovascular function through activation of G protein-coupled inwardly-rectifying potassium channels, and is of particular interest because of its extensive pharmacological characterization with both orthosteric and allosteric ligands. Here we report the structure of antagonist-bound M2 receptor, the first human acetylcholine receptor to be characterized structurally. The antagonist QNB binds in the middle of a long aqueous channel extending approximately two-thirds through the membrane. The orthosteric binding pocket is formed by amino acids that are identical in all 5 muscarinic receptor subtypes, and shares structural homology with other functionally unrelated acetylcholine binding proteins from different species. A layer of tyrosine residues forms an aromatic cap restricting dissociation of the bound ligand. A binding site for allosteric ligands has been mapped to residues at the entrance to the binding pocket near this aromatic cap. The M2 receptor structure provides insights into the challenges of developing subtype-selective ligands for muscarinic receptors and their propensity for allosteric regulation.

Synthesis and thermal degradation characterization of novel poly(phosphazene-aryl amides)

New fully aromatic poly(phosphazene-aryl amides) were prepared by polycondensation reaction of our synthe- sized aromatic diamine: 1,1,3,5-tetraphenoxy-4,6-bis(4-aminophenoxy)oligocyclotriphosphazene (monomer 1) with terephthaloyl dichloride. Their chemical structure and composition were characterized by elemental analysis, 1 H and 31 P NMR (Nuclear Magnetic Resonance), and FT-IR (Fourier transform infrared) spectroscopy, whereas their thermal degradation properties were determined by DSC (Differential Scanning Calorimetry) and TGA (Thermal Gravimertic Analysis) techniques. The solid residues of all samples were analysed by FT-IR and SEM (Scanning Electron Microscopy). Compared to conventional PPTA (poly(p-phenylene terephthamide)), PPAA (poly(phosphazene-aryl amide)) shows excel- lent thermal stability and solubility in polar protic solvents. All poly(phosphazene-aryl amides) show two thermal degrada- tion in the temperature range 150-600°C. The monomer 1, due to its structure, shows the first maximum rate of thermal decomposition temperature around 150-350°C, which may be due to the decomposition of the P-O-C bone. Morphology of the solid residues by Scanning Electron Microscope exhibit that the granular of the solid residues gradual disappearance with the increase of monomer 1 content. The surface layer of PPAA solid residues has been grumous, for the syneresis of P-O-P took place.

Detection of allosteric signal transmission by information-theoretic analysis of protein dynamics.

Allostery offers a highly specific way to modulate protein function. Therefore, understanding this mechanism is of increasing interest for protein science and drug discovery. However, allosteric signal transmission is difficult to detect experimentally and to model because it is often mediated by local structural changes propagating along multiple pathways. To address this, we developed a method to identify communication pathways by an information-theoretical analysis of molecular dynamics simulations. Signal propagation was described as information exchange through a network of correlated local motions, modeled as transitions between canonical states of protein fragments. The method was used to describe allostery in two-component regulatory systems. In particular, the transmission from the allosteric site to the signaling surface of the receiver domain NtrC was shown to be mediated by a layer of hub residues. The location of hubs preferentially connected to the allosteric site was found in close agreement with key residues experimentally identified as involved in the signal transmission. The comparison with the networks of the homologues CheY and FixJ highlighted similarities in their dynamics. In particular, we showed that a preorganized network of fragment connections between the allosteric and functional sites exists already in the inactive state of all three proteins.—Pandini, A., Fornili, A., Fraternali, F., Kleinjung, J. Detection of allosteric signal transmission by information-theoretic analysis of protein dynamics.

A de novo peptide hexamer with a mutable channel

The design of new proteins that expand the repertoire of natural protein structures represents a formidable challenge. Success in this area would increase understanding of protein structure, and present new scaffolds that could be exploited in biotechnology and synthetic biology. Here we describe the design, characterisation and X-ray crystal structure of a new coiled-coil protein. The de novo sequence forms a stand-alone, parallel, 6-helix bundle with a channel running through it. Although lined exclusively by hydrophobic leucine and isoleucine side chains, the 6 Å channel is permeable to water. One layer of leucine residues within the channel is mutable accepting polar aspartic acid (Asp) and histidine (His) side chains, and leading to subdivision and organization of solvent within the lumen. Moreover, these mutants can be combined to form a stable and unique (Asp-His)3 heterohexamer. These new structures provide a basis for engineering de novo proteins with new functions.

Aplicação do método de Polarização Induzida em área de disposição de resíduos sólidos no município de Caçapava do Sul - RS

A geofisica e um metodo eficaz para investigacao de areas impactadas pelos mais diversos tipos de contaminantes, principalmente em locais de disposicao de residuos solidos domiciliares e tambem utilizada na caracterizacao de contrastes de propriedades fisicas em presenca de substâncias poluentes. Este trabalho utilizou o metodo de Polarizacao Induzida numa area de disposicao de residuos solidos desativada, localizada no municipio de Cacapava do Sul - RS. O aterro esta assentado sobre rochas metamorficas fraturadas, pertencentes ao Complexo Metamorfico Vacacai (Neoproterozoico). Foram realizadas 8 linhas de caminhamento eletrico, com espacamento de 5 m entre eletrodos e 10 niveis de investigacao, alem de 83 medidas de direcao e sentido de fraturas. O resultado geofisico permite caracterizar a camada de residuos por baixos valores de cargabilidade. Anomalias verticais abaixo da camada de residuos sao interpretadas como zonas de fratura com possivel acumulo de chorume, caracterizadas por baixos valores de cargabilidade.

Evidence of the Participation of Remote Residues in the Catalytic Activity of Co-Type Nitrile Hydratase from Pseudomonas putida

Active sites may be regarded as layers of residues, whereby the residues that interact directly with substrate also interact with residues in a second shell and these in turn interact with residues in a third shell. These residues in the second and third layers may have distinct roles in maintaining the essential chemical properties of the first-shell catalytic residues, particularly their spatial arrangement relative to the substrate binding pocket, and their electrostatic and dynamic properties. The extent to which these remote residues participate in catalysis and precisely how they affect first-shell residues remains unexplored. To improve our understanding of the roles of second- and third-shell residues in catalysis, we used THEMATICS to identify residues in the second and third shells of the Co-type nitrile hydratase from Pseudomonas putida (ppNHase) that may be important for catalysis. Five of these predicted residues, and three additional, conserved residues that were not predicted, have been conservatively mutated, and their effects have been studied both kinetically and structurally. The eight residues have no direct contact with the active site metal ion or bound substrate. These results demonstrate that three of the predicted second-shell residues (α-Asp164, β-Glu56, and β-His147) and one predicted third-shell residue (β-His71) have significant effects on the catalytic efficiency of the enzyme. One of the predicted residues (α-Glu168) and the three residues not predicted (α-Arg170, α-Tyr171, and β-Tyr215) do not have any significant effects on the catalytic efficiency of the enzyme.

Relationship between the Crystal Structure and Morphology of Carboxylic Acid Polymorphs. Predicted and Experimental Morphologies

Polymorphs of carboxylic acids crystallize from solvent evaporation experiments as crystals with needle or plate morphology. Experimentally, it has been observed that the crystallization solvent does not sensibly modify the crystal morphology of a given polymorph. Hence, a theoretical study of the morphology of these polymorphs was conducted to relate the crystal structures with their macroscopic crystal shapes. Methodologies with an increasing degree of complexity were used, and the best results were obtained from those calculations considering the attachment energy (Eatthkl) released on attachment of a new dhkl layer to a growing crystal surface. The experimental habits of the polymorphs of carboxylic acids are reproduced well by the morphology simulations, so the observed crystal shapes can be rationalized in terms of the intermolecular interactions between the growth units. In the crystal structures of the C, B, and E polymorphs, layers of pure CH3 residues produce weak van der Waals interactions resu...

Effects of forest slash and burn on the distribution of trace elements in floodplain sediments and mountain soils of the Subandean Amazon, Peru

Forest clearing through slash and burn to open up agricultural land is an ongoing process in large parts of the Amazon Basin. This activity severely affects the structure and balance of the natural ecosystem, and also has the potential to cause substantial changes in landscape geochemistry. The latter is the topic of this study, with special attention on translocation of potentially toxic trace elements from deforested areas to downstream aquatic and terrestrial systems. Sampling of floodplain sediments and mountain soils (Inceptisols on redbed lithologies) was carried out in two adjacent Subandean river basins, with deforestation extents of ca. 1/3 and 2/3 of the basin areas. Several toxic and potentially toxic metals (e.g., Hg, Cd, Pb, Cu and Ni) and other major and minor elements showed concentration peaks at certain depths in the alluvial deposits of both basins. These peaks were associated with organic matter, and occurred just below layers of combustion residues originating from burning of in situ biomass. Downward migration of particles originating in the combustion residues is suggested to be the direct mechanisms of the metal enrichments. Further evidence of an in situ origin of the metal peaks in the sediments was provided by the geochemical composition of soils located upstream of the floodplains. Disturbed soils (i.e. soils of pasture, coffee plantations, secondary forest and recently swidden fields) were found to be similar to soils under natural forest. Moreover, trace element concentrations in floodplain deposits were similar in the two drainage basins despite the large difference in exploitation degree. Thus, no evidence was found of large scale (basin-wide) increases in trace-metal leaching or translocation as a result of the extensive deforestation and agricultural land-use that has been practiced in the Amazonian highland jungle over more than 100 a.

Molecular characterization and glomalin production of arbuscular mycorrhizal fungi colonizing a heavy metal polluted ash disposal island, downtown Venice

In this work the arbuscular mycorrhizal (AM) fungal communities colonizing a polluted ash dump island, downtown Venice, were studied by using a multimodal approach. The island, Sacca San Biagio, was covered with a thick layer of municipal solid waste residues produced by an incinerator operating from 1973, to 1984. Such residues contained high levels of heavy metals (Cu, Pb and Zn). We characterized the AMF communities present in soils on Sacca San Biagio island by using molecular methods. Nine AM fungal sequence types were detected in the roots of three plant species, representative of the dominant flora, by using partial SSU ribosomal RNA genes. The most abundant sequence types corresponded to Glomus intraradices/ Glomus fasciculatum, and to Glo18, a sequence detected so far only in planta. Two sequences were new to science. Glomalin-related soil protein (GRSP), extracted from rhizosphere soil of dominant plant species, ranged from 1.6 to 2.3 mg g −1. The occurrence of an active AM fungal community able to live in such harsh environment was evinced by the correlation between mycorrhizal colonization and GRSP content.

Role of the β-Subunit Arginine/Lysine Finger in Integrin Heterodimer Formation and Function

Formation of the integrin alphabeta heterodimer is essential for cell surface expression and function. At the core of the alphabeta interface is a conserved Arg/Lys "finger" from the beta-subunit that inserts into a cup-like "cage" formed of two layers of aromatic residues in the alpha-subunit. We evaluated the role of this residue in heterodimer formation in an alphaA-lacking and an alphaA-containing integrin alphaVbeta3 and alphaMbeta2 (CD11b/CD18), respectively. Arg261 of beta3 was mutated to Ala or Glu; the corresponding Lys252 of beta2 was mutated to Ala, Arg, Glu, Asp, or Phe; and the effects on heterodimer formation in each integrin examined by ELISA and immunoprecipitation in HEK 293 cells cotransfected with plasmids encoding the alpha- and beta-subunits. The Arg261Glu (but not Arg261Ala) substitution significantly impaired cell surface expression and heterodimer formation of alphaVbeta3. Although Lys252Arg, and to a lesser extent Lys252Ala, were well tolerated, each of the remaining substitutions markedly reduced cell surface expression and heterodimer formation of CD11b/CD18. Lys252Arg and Lys252Ala integrin heterodimers displayed a significant increase in binding to the physiologic ligand iC3b. These data demonstrate an important role of the Arg/Lys finger in formation of a stable integrin heterodimer, and suggest that subtle changes at this residue affect the activation state of the integrin.

Three isoforms of complement properdin factor P in trout: Cloning, expression, gene organization and constrained modeling

Properdin is a plasma glycoprotein and the only known naturally occurring positive regulator of the complement system, stabilizing the alternative pathway convertase (C3bBb). In order to elucidate the molecular evolution of properdin factor P (pfc), here we report the cloning and characterization of three gene isoforms of properdin in rainbow trout (Oncorhynchus mykiss). The predicted polypeptide sequences of trout properdins pfc1, pfc2 and pfc3 (447, 449 and 447 amino acids, respectively) share 78-90% identity to each other, showing the highest identity score (47%) with their zebrafish ortholog protein. The overall identity with human, mouse and xenopus properdin polypeptides is 44%, 42% and 45%, respectively. The 'domain' architecture of trout properdins resembles that of the mammalian counterpart proteins, composed of six thrombospondin repeat type 1 domains (TSR-1-TSR-6). TSR domains of the three trout properdin isoforms seem to adopt the folding pattern of human thrombospondin 1 TSP-1 domains, where each TSP-1 domain forms an antiparallel three-stranded structure that consists of alternative stacked layers of Trp and Arg residues from respective strands capped by disulfide bonds on each end. The trout pfc2 and pfc3 genes are arranged in nine and ten exons, respectively, which span approximately 3.5kb of the genome. In contrast to the expression profile of the properdin gene in mammals, liver is the main source of the trout properdin mRNA transcripts. In a phylogenetic analysis, trout pfc1, pfc2 and pfc3 genes are clustered with their orthologs from other teleost species. This is the first report of three separate genes coding for properdin factor P in a vertebrate species.

Characterization of protein resistant, grafted methacrylate polymer layers bearing oligo(ethylene glycol) and phosphorylcholine side chains by neutron reflectometry

Neutron reflectometry was used to investigate the structures of end-tethered protein resistant polymer layers based on poly(oligo(ethylene glycol) methyl ether methacrylate) [poly(OEGMA)] and poly(2-methacryloyloxyethyl phosphorylcholine) [poly(MPC)]. Layers having different graft densities were studied in both the dry and wet states. A stretched parabolic model was used to fit the neutron data, resulting in a one-dimensional scattering length density profile of the polymer volume fraction normal to the film. Measured in D(2)O, the cutoff thicknesses of OEGMA and MPC layers at high graft density (0.39 chainsnm(2) for OEGMA and 0.30 chainsnm(2) for MPC) and a chain length of 200 repeat units were 450 and 470 A, respectively, close to their contour length of 500 A, suggesting that the grafts become highly hydrated when exposed to water. It was also found that at similar graft density and chain length, the volume fraction profiles of poly(OEGMA) and poly(MPC) layers are similar, in line with the authors' previous results showing that these surfaces have similar protein resistance [W. Feng et al., BioInterphases 1, 50 (2006)]. The possible correlation of protein resistance to water content as indicated by the average number of water molecules per ethylene oxide (N(w,EO)) or phosphorylcholine (N(w,PC)) moiety was investigated. N(w,EO) and N(w,PC), estimated from the volume fraction data, increased with decreasing graft density, and when compared to the reported number of water molecules in the hydration layers of EO and PC residues, led to the conclusion that water content slightly greater than the water of hydration resulted in protein resistant surfaces, whereas water content either less than or greatly in excess of the water of hydration resulted in layers of reduced protein resistance.

RETRACTED: Local Encoding of Computationally Designed Enzyme Activity

One aim of computational protein design is to introduce novel enzyme activity into proteins of known structure by predicting mutations that stabilize transition states. Previously, we showed that it is possible to introduce triose phosphate isomerase activity into the ribose-binding protein of Escherichia coli by constructing 17 mutations in the first two layers of residues that surround the wild-type ligand-binding site. Here, we report that these mutations can be "transplanted" into a homologous ribose-binding protein, isolated from the hyperthermophilic bacterium Thermoanaerobacter tengcongensis, with retention of catalytic activity, substrate affinity, and reaction pH dependence. The observed 10(5)-10(6)-fold rate enhancement corresponds to 70% of the maximally known transition-state binding energy. The wild-type sequences in these two homologues are almost perfectly conserved in the vicinity of their ribose-binding sites, but diverge significantly at increasing distance from these sites. The results demonstrate that the computationally designed mutations are sufficient to encode the observed enzyme activity, that all the observed activity is encoded locally within the layer of residues directly in contact with the substrate and that, in this case, at least 70% of transition state stabilization energy can be achieved using straightforward considerations of stereochemical complementarity between enzyme and reactants.

Long-term deactivation of Pt/alumina catalyst by organosilicons in the total oxidation of hydrocarbons

The deactivation of a supported platinum catalyst by long-term exposure to hexamethyldisiloxane was investigated. Ethyl acetate containing several tenfold excess of organosilicon relative to the real application was fed to the reactor. Three sets of catalyst and the blank support were aged for 350, 650, and 1000 h. The ex situ activity measurements on the aged pellets showed that all samples were deactivated as they were exposed to hexamethyldisiloxane. Silicon species were found at the surfaces of both the catalyst and the blank support. The quantitative analysis of silicon loading showed a linear profile versus poison exposure time and axial position in the bed. The radial silicon distribution in an individual pellet revealed an eggshell distribution of silicon residues, which is an indication of a diffusion-limited mechanism of silicon deposition. The deactivation was attributed to deposition of thin layer of silicon residues, which blocks the surface sites.

Identifying and manipulating structural determinates linking catalytic specificities in terpene synthases

Terpene synthases are a mechanistically intriguing family of enzymes that catalyze complex, multistep reactions that are capable of generating hundreds of structurally diverse hydrocarbon and oxygenated scaffolds of biological and commercial importance. Interestingly, distantly related terpene synthases from fungi to plants all contain an invariant three-dimensional fold, and molecular comparisons of their active sites indicate that they are enriched with relatively inert amino acid residues that do not react directly with the reaction intermediates. Therefore, catalytic specificity appears to rely on the contour and dynamics of the active site created by the positioning of amino acid backbones and side chains on this catalytic surface and by supporting layers of residues surrounding the synthase active site cavity. Despite the high degree of structural relatedness among terpene synthases, previous studies suggest that no clear relationship between phylogenic organization and catalytic specificities is easily deciphered. We now report on the reciprocal interconversion of catalytic specificities between two distinct yet evolutionarily related terpene synthases based on the systematic identification and mutational replacement of variable residues within and surrounding the active site. Furthermore, we uncover previously undocumented biosynthetic activity during the interconversion, activity that could have been present in a common ancestor of these two highly related synthases. These results provide a simplified means for mapping structural features that are responsible for functional attributes and a strategy for identifying residues that differentiate divergent biosynthetic properties in phylogenetically related terpene synthases.

Modulating Protein Structure with Fluorous Amino Acids: Increased Stability and Native-like Structure Conferred on a 4-Helix Bundle Protein by Hexafluoroleucine

There has recently been much interest in exploiting the unusual properties associated with fluorocarbons to modulate the physicochemical properties of proteins. Here we present a detailed investigation into the effect on structure and stability of systematically repacking the hydrophobic core of a model protein with the extensively fluorinated (fluorous) amino acid l-5,5,5,5',5',5'-hexafluoroleucine (hFLeu). The starting point was a 27-residue peptide, alpha(4)-H, that adopts an antiparallel 4-alpha-helix bundle structure, and in which the hydrophobic core comprises six layers of leucine residues introduced at the "a" and "d" positions of the canonical heptad repeat. A series of peptides were synthesized in which the central two (alpha(4)-F(2))(,) four (alpha(4)-F(4)), or all six layers (alpha(4)-F(6)) of the core were substituted hFLeu. The free energy of unfolding increases by 0.3 (kcal/mol)/hFLeu on repacking the central two layers and by an additional 0.12 (kcal/mol)/hFLeu on repacking additional layers, so that alpha(4)-F(6) is approximately 25% more stable than the nonfluorinated protein alpha(4)-H. One-dimensional proton, two-dimensional (1)H-(15)N HSQC, and (19)F NMR spectroscopies were used to examine the effect of fluorination on the conformational dynamics of the peptide. Unexpectedly, increasing the degree of fluorination also appears to result in peptides that possess a more structured backbone and less fluid hydrophobic core. The latter only occurs in alpha(4)-F(4) and alpha(4)-F(6), suggesting that crowding of the hFLeu residues may restrict the amplitude and/or time scales for rotation of the side chains.

Effects of composted swine manure on weed seedbank

Deep-bedded hoop structures where pigs are raised on a thick layer of crop residues represent a promising swine production system that allows recycling of farm waste products. A field study was conducted to evaluate the impact of swine compost on weed seedbank abundance, seed persistence, and seedling emergence. Experiments were conducted from 1998 to 2001 in a chisel plow corn–soybean–winter wheat rotation. In the fall of 1998, and before compost application, weed seedbank abundance, species composition, and viability were characterized. Annual weed seed inputs attributed to compost were assessed between 1998 and 2000 and seedbanks were characterized again in the fall of 2001. Giant foxtail, common lambsquarters, common waterhemp, and Pennsylvania smartweed comprised 99.5 and 80.7% of seeds detected in the seedbank and compost, respectively. Between 1 � 1 and 169 � 48 weed seeds m � 2 of soil surface

Efeito da cobertura de resíduos de culturas na evaporação direta da água do solo

The influence of corn, bean and wheat crops residues used as soil surface mulching to control the water evaporation demands, for two soils textural classes, was analyzed in the present work. The treatments consisted of three layers of crop residues, corresponding to 0, 50 and 100% of dry matter produced by irrigated cropping systems, and three water evaporative demands of 3, 6 and 8mm d-1, for two soil textural classes, silty sand and heavy loamy soils, with 84% of sand and 76% of clay, respectively. The experiment was carried out in laboratory, with the soil sample conditioned in a 45-cm high and 20-cm nominal diameter PVC pipes columns. The water evaporation rate from the bare soil column presented different behavior for the three water evaporation demands tested. For water evaporative demand of approximately 3mm d-1, the treatments with corn and wheat crops residues, which represented mulching layer of 50 and 100% of dry matter, the water evaporation rate reached only the first evaporation stage. For treatment with 50% of dry matter with residues produced by bean crop, the evaporation stage moved beyond the first evaporation stage. Finally, for mulching with 100% of bean crop dry matter, the rate of soil water evaporation was influenced by the evaporative demand tested. The relationship among evaporation rate for treatment with 100% of dry matter and the water evaporative demands of 7,0, 5,0 and 2,5mm d-1 were 46, 41 and 47%, respectively

Activity and role of the enchytraeid worm Cognettia sphagnetorum (Vejd.) (Oligochaeta: Enchytraeidae) in organic and mineral forest soil

Summary Site preparation following clear felling of coniferous forest creates a mosaic of different kinds of habitats for soil decomposers, ranging from bare mineral soil to thick layers of organic soil and felling residues. To study whether the impact of enchytraeids on nutrient mineralisation processes is different in residues, organic layer, and mineral soil, a microcosm experiment was conducted in the laboratory. Microcosms contained mineral soil (sand) alone or with soil organic layer (humus and F-layer materials) and spruce needles, either separately or together. Enchytraeids (Cognettia sphagnetorum) were introduced to the half of the microcosms. Numbers of enchytraeids, their gut content, and soil pH and mineral nitrogen were determined twice, 8 and 13 weeks from the start. Population increase of C. sphagnetorum was found only in the soil organic layer. In the mineral soil, enchytraeids ingested sand grains together with bacteria and protozoans. In the organic soil enchytraeid intestines were filled with dark coloured humus material in which plant fragments, fungal hyphae and bacterial colonies were recognized. Enchytraeids significantly increased the amount of NH 4 -N in the bare mineral soil. When a soil organic layer was present on the mineral soil, enchytraeids decreased NH 4 -N in the presence of needles but had no effect when needles were absent. Enchytraieds did not affect the pH of the mineral soil, but they slightly increased that of the soil organic layer. The results of this experiment revealed that C. sphagnetorum is able to maintain its population and its functional importance also in resource poor mineral soil. Its effect on nitrogen dynamics appears to be dependent on environmental conditions, resource quality and development of a population, i.e. acceleration, no effect and inhibition of nitrogen mineralisation are all possible.