Nylon Screen Research Articles

Nutrient Leaching from Corn Residues under Simulated Rainfall

AbstractCrop residues left on the soil surface after harvest are effective in reducing erosion; however, when subjected to rainfall‐leaching, the residues are a significant source of soluble nutrients to agricultural runoff. Nutrient leaching from crop residues as a function of rainfall intensity, and residue loading rate, was studied in a series of laboratory experiments under controlled conditions. Using a multiple‐intensity rainfall simulator corn (Zea mays L.) stover placed on a nylon screen at an equivalent field loading rate of 10 t ha−1, was subjected to simulated rainfall at intensities of 6, 12, 25, 51, and 99 mm h−1. In another series of experiments, simulated rainfall was applied at 25 mm h−1 to four stover loading rates of 5, 7, 10, and 15 t ha−1. In both experiments, leachate was sampled as a function of time and analyzed for PO4‐P, NH4‐N, NO3‐N, and total organic carbon (TOC). Nutrient concentrations and losses were generally greater at the lower rainfall intensities and higher stover loading rates. In each study, nutrient concentrations decreased hyperbolically with either time or cumulative leachate volume. For all loading rates and rainfall intensities, nutrient amounts (kg ha−1) leached from the stover followed the order C ≫N = P; however, the amounts of N as (NH4‐N + NO3‐N) or C leached were ≤1.5% of total nutrient in residue compared with 2.8 to 6.0% of total nutrient in residue for P. Stover exposed to field conditions over time showed leaching kinetics similar to freshly collected residues.

Nest Predation on Woodland Songbirds: When Is Nest Predation Density Dependent?

Nest predation. if density dependent, may structure avian communities by selecting for nest-site characteristics that dilute the predators' perception of nest density (e.g., by increasing the number and types of potential nest sites) thereby reducing losses to predators. We tested for density dependent nest predation at a site dominated by predation from raccoons, Procyon lotor. and blue jays. Cyanocitta cristata. We used cohorts of 20 artificial ground nests placed on experimental grids at four densities (1.7, 7, 65, and 167 nests/ha). Predation was density dependent for one of two temporal replicates. In a second experiment, we tested for density dependent predation on both ground and shrub nests using more realistic nest densities (3.5 and 8.9 nests/ha) and excluding avian and small mammal predators by placing nylon screening over the nests. Predation was density dependent on artificial ground nests and density independent on shrub nests. Finally, we analyzed predation on natural shrub nests separating out avian (i.e., jays) and large mammalian predation based on disturbance to the depredated nest. In each of three years there was no evidence for density dependent predation. An outbreak of periodic cicadas in the first experiment and the maturation of a large mulberry crop during the second experiment demonstrated the importance of the distribution and abundance of alternative foods on the response of predators toward heterogeneity in nest abundance.

Earthworm and soil moisture effects on the productivity and structure of grassland communities

The objectives of this study were (1) to evaluate the effect of earthworm activity on aboveground plant biomass production of native calcareous grassland communities in NW-Switzerland and (2) to determine which plant functional types (graminoids, non-legume forbs and legumes) are most responsive as indicators of potential effects on plant community structure. Earthworm activity was manipulated in the field by creating three earthworm densities (low: 37, ambient: 114, high: 169 worms m −2) and two soil moisture conditions (ambient and 280 mm yr −1 additional rain) in 30 1×1 m 2 trenched plots (to a depth of 45 cm with nylon screening). Earthworm density was censused and readjusted in the spring and autumn of 1996 and again in the spring of 1997 using the Octet electro-sampling method. Earthworm activity, measured as cumulative surface cast production, was significantly different among worm density treatments (low worm density: 591±49, ambient: 991±87, high: 1469±120 g cast d.m. m −2 yr −1), P<0.001. Cast production increased with increasing worm density, however increased soil moisture, which was significantly higher in plots receiving additional rain, did not affect worm activity at any worm density level. Surprisingly, earthworm activity had no effect on the aboveground biomass production of the plant community or of any plant functional type; however additional rain stimulated aboveground biomass production of graminoids (+30%, P=0.006) and Carex spp. (+200%, P=0.020). The lack of a stimulatory effect of increased earthworm activity on plant biomass production indicates that apparent earthworm-induced increases in plant nutrient availability were insufficient to promote the growth of the perennial plant species in these native grasslands. Our results, taken together with those from earlier studies in these grasslands, suggest that the effects of earthworm activity on plant community structure occur slowly where they relieve soil constraints on plant growth.

The compositional heterogeneity of particulate organic matter from the surface ocean: an investigation using flow cytometry and DT-MS

In this study the morphological and chemical heterogeneity of particulate organic matter (POM) in the surface ocean was investigated by the application of flow cytometry, direct temperature-resolved mass spectrometry (DT-MS), and multivariate statistics. In order to obtain a diverse collection of surface-ocean POM samples, POM was collected from a station in Great Harbor, Woods Hole, MA, U.S.A. (on a monthly basis) and on transects across the Mid-Atlantic Bight (in March 1996). Small-particle (<53 μm) POM was separated from large-particle (>53 μm) POM by filtration through a nylon screen. Aliquots of the small-particle POM were then further separated, via flow cytometric sorting, into phytoplankton and detrital pools. Broad-band molecular-level characteristics of these POM subclasses were obtained through DT-MS (16 eV, EI +) and were explored via principal component and discriminant analyses. For both the Woods Hole (WHTS) and the Mid-Atlantic Bight (MAB) data sets, the statistical treatments separated POM samples primarily according to their class and subclass distinctions; therefore, this paper focuses on the molecular-level differences among large-particle and small-particle POM, phytoplankton and detritus. Small-particle POM is found to be more enriched in protein, phytosterols, diglycerides and chlorophyll than large-particle POM, which is more enriched in pentose polysaccharide fragments, C 16:0 fatty acid, and cholesterol. At the WHTS site, large-particle POM is also enriched in chitin and appears to contain a significant grazer biomass component. In the MAB, the corresponding POM fraction appears more phytodetrital. Phytoplankton particles are enriched in protein, chlorophyll and lipids relative to detritus. Detritus is enriched in selected polysaccharides and appears to be composed of phytodetritus and/or fecal material.

Decomposition and nutrient release from C3 and C4 plant litters in a natural grassland

The rate of litter loss, and the release of N, P, K, Ca during litter decomposition of two C 4 plants ( Dichanthium ischaemum L. and Chrysopogon gryllus L.) and one C 3 plant ( Festuca ovina H.) were studied for 24 months. This was achieved by placing leaf and culm litter in nylon screen bags close to the soil surface, sampling every three months to mease the changes in litter weight and chemical composition during the experimental period. Litter decomposition was faster during the first 12 months for both leaves and culms of all species. The order was D. ischaemum > F. ovina > C. gryllus . The mean rate litter loss for the 12 and 24 month period was similar for leaf and culm litter. Nitrogen accumulation was observed during the entire experimental period for all species. Phosphorus release had occurred during the experimental period in the decreasing order: C. gryllus > D. ischaemum > F. ovina . Potassium release was observed after 12 and 24 months in the decreasing order D. ischaemum > C. gryllus > F. ovina , while calcium was accumulating. The decomposition rates were similar for C 4 and C 3 plants and their contribution to nutrient cycling depended on the release of the various elements during decomposition.

Efficacy of Spinosad and Standards for Control of Large Black Cutworm Larvae, 1997

Abstract The study was located on bentgrass range 1 north at the Ohio State Turfgrass Research and Education Center, Columbus, OH. Treatments were applied on 4 Sep to plots 4 X 6 ft arranged in a RCB, replicated 4 times. Liquid treatments were applied using a CO2 sprayer calibrated to deliver 2.0 gal/1000ft2. No immediate post-treatment irrigation was applied. The 100% creeping bentgrass range was mowed at 0.5 inch, had no thatch and was irrigated daily with 0.25 inch of water. On 5 Sep two 8-inch stainless steel cylinders were driven into the turf, about 2 hr after the last spraying to allow for complete drying of all treatments. Each cylinder was infested with six 5th- and 6th-instar BCW (1.0 to 1.25 inch) and covered with nylon screen. On 9 Sep (5 DAT), the covers were removed and each cylinder was flooded with a soapy water mix (15 ml Joy dishwashing detergent in 1.0 ga water) to flush out any live BCW. It was discovered that many of the larvae had pupated, so the turf cover was removed and the live pupae were added to the counts.

Efficacy of Spinosad and Standards for Control of Small Black Cutworm Larvae, 1997

Abstract The study was located on bentgrass range 1 north at the Ohio State Turfgrass Research and Education Center, Columbus, OH. Treatments were applied on 19 Aug to plots 4 X 6 ft arranged in a RCB, replicated 4 times. Liquid treatments were applied using a CO2 sprayer calibrated to deliver 2.0 gal/1000ft2. No immediate posttreatment irrigation was applied. The 100% creeping bentgrass range was mowed at 0.5 inch, had no thatch and was irrigated daily with 0.25 inch of water between (05:00 and 06:00). On 19 Aug, one 8-inch stainless steel cylinder was driven into the turf, about 2 hr after the last spraying to allow for complete drying of all treatments. Each cylinder was infested with eight 3rd- and 4th-instar BCW (0.375 to 0.5 inch) and covered with nylon screen. On 22 Aug (3 DAT) the covers were removed and each cylinder was flooded with a soapy water mix (15 ml Joy dishwashing detergent in 1.0 gal water) to flush out any live BCW.

Studies on the attractional effect of root exudates on hyphal growth of an arbuscular mycorrhizal fungus in a soil compartment-membrane system

The effects of tomato and bean rhizospheres on hyphal spreading of the arbuscular mycorrhizal (AM) fungus Glomus mosseae were studied using a soil compartment system in combination with hydrophobic polytetrafluorethylene (PTFE) membranes. Both the nylon screen and the PTFE membrane were freely permeable to hyphae but not to roots. Furthermore, the hydrophobic PTFE membrane seemed to be a barrier to the flux of soil solutions containing root exudates. The results show that water soluble exudates of tomato and bean roots greatly stimulate hyphal growth in the soil compartment system used. Moreover, water soluble root exudates of bean exert a clear attractional effect on AM hyphal growth.

Direct evidence on participation of root hairs in phosphorus ( 32 P) uptake from soil

Root hairs substantially extend root surface for ion uptake. Although many reports suggest a relationship between root hairs and phosphorus (P) uptake of plants, the role of root hairs in phosphorus uptake from soils is still debated. We measured uptake of phosphorus from soil directly via root hairs. Root hairs only were allowed to penetrate through a tightly stretched nylon screen (53 µm) glued to the bottom of a PVC tube. The penetrating root hairs grew for 2 and 4 days in soil labelled with radioisotope phosphorus (P) tracer 32P (185 kBq g-1 dry soil) filled in another PVC tube. Transparent plastic rings of thickness ranging from 0.25 mm to 2.0 mm were inserted between the two PVC tubes. This provided slit width for microscopic observations in situ, which confirmed that only root hairs were growing into the 32P labelled soil. In some cases no rings were inserted (slit width = 0) where both root hairs and root surface were in contact with the labelled soil (total 32P uptake). The uptake of32 P from soil via the root hairs only was quantified by measuring activity of 32P in the plant shoot (32P uptake only via root hairs). The results showed that when 70 percent of the root hairs grew into the labelled soil, they contributed to 63 percent of the total P uptake. With decreasing number of root hairs growing into the 32P labelled soil, the quantity of 32P in the plant shoot decreased. In this study, P uptake via root hairs was measured in a soil-based system, where root hairs were the only pathway of 32P from soil to the plant shoot. Therefore, this study provides a strong evidence on the substantial participation of root hairs in uptake of phosphorus from soil.

Head and Heart: Neuropsychological Reaction and Arterial Line Filtration during Cardiopulmonary Bypass

As part of a prospective study of neuropsychologic reactions after cardiopulmonary bypass and their relation to arterial line filters, 44 patients who underwent elective cardiac operations were randomized into two groups. Group A had a 40-micron nylon screen filter in the arterial line. No arterial filter was used in group B. Neuropsychological examinations of all patients were conducted before and at a mean of 8 days after the operation on a double blind basis by a single trained psychologist. The tests included the Wechsler Memory Scale, the trail-making test, the Hamilton Anxiety Rating Scale, and the Hamilton Rating Scale for Depression. The 2 groups were otherwise similar with respect to preoperative neurologic and intellectual status, anesthetic methods, duration of operation, operative procedures performed, and the time spent in the intensive care unit. Surprisingly, there was a highly significant improvement in all four test scores after surgery. There were no statistically significant differences in the test scores between the two groups but considerable inter-patient performance variability was noted. The arterial line filter did not appear to have an effect on test scores. Routine use of an arterial filter remains questionable.

Effect of potassium nutrition of rice on rhizosphere redox status

With four soils differing in K supplying power and with four rice cultivars (Oryza sativa L.) differing in K uptake kinetic parameters, the relationship between K fertilizer application and soil redox status in rhizosphere and; the distribution of ferrous iron and other toxic substances on the root surface and in the rhizosphere; and the effect of K supply on uptake of reduced iron by rice plants have been studied. The results show that K application on K-deficient soils reduced the content of active reducing substances and ferrous iron in the soil, raised the soil redox potential in the rhizosphere, increased the Eh value of rice roots and lowered the content of iron in the rice plants. These effects of K varied with different rice cultivars. When no K fertilizer was applied, active reducing substances and ferrous iron in rhizosphere soils were decreased more by the rice cultivars absorbing K strongly (e.g. Shanyou 64) than by cultivars absorbing K weakly (e.g. Zhongguo 91). Therefore, the diminution of the toxic substances by K application in the weakly K-absorbing cultivars was more significant. The observation of a rhizobox separated by a nylon screen showed that appreciably more iron oxides, compared with the control, were deposited at or adjacent to the root surfaces of the rice plant supplied with K fertilizer, fully demonstrating the relationship between K nutrition and the total oxidizing power of rice plants. According to the distribution of active reducing substances and ferrous iron, the oxidizing range of the rice root extended in K application treatment a few centimeters away from the root plane. K application to rice affected the soil redox status in rhizosphere in many ways. The main effect was an increase of the oxidizing power of the rice root. As a result, the value of soil Eh was increased, the contents of active reducing substances and ferrous iron were lowered, as well as the number of oxygen consuming microorganisms.

Enhanced biodegradation of diesel fuel through the addition of particulate organic carbon and inorganic nutrients in coastal marine waters.

Diesel fuel pollution in coastal waters, resulting from recreational boating and commercial shipping operations, is common and can adversely affect marine biota. The purpose of this study was to examine the effect of additions of particulate organic carbon (POC) in the form of naturally-occurring marsh grass (Spartina alterniflora), inorganic nutrients (nitrogen and phosphorus), inert particles, and dissolved organic carbon (DOC) on diesel fuel biodegradation and to attempt to formulate an effective bioremedial treatment for small diesel fuel spills in marine waters. Various combinations of treatments were added to water samples from a coastal marina to stimulate diesel fuel biodegradation. Diesel fuel was added in concentrations approximating those found in a spill and biodegradation of straight chain aliphatic constituents was estimated by measuring mineralization of 14C hexadecane added to diesel fuel. All treatments that included POC showed stimulation of biodegradation. However, the addition of inert particles (glass fiber filters and nylon screening) caused no stimulation of biodegradation. The addition of nitrogen and phosphorus alone did not result in stimulation of biodegradation, but nitrogen and Spartina (although not phosphorus and Spartina) did result in stimulation above that of Spartina alone. Maximum biodegradation rates were obtained by the addition of the Spartina POC, ammonium, and phosphate. The addition of mannitol, a labile DOC source with POC and phosphate resulted in a decrease in diesel fuel biodegradation as compared to POC and phosphate alone. The seasonal pattern of diesel fuel biodegradation showed a maximum in the summer and a minimum in the winter. Therefore, of the treatments tested, the most effective for bioremediation of diesel fuel in marine waters is the addition of POC, nitrogen, and phosphorus.

Root and Shoot Growth of Eucalyptus in Response to Container Configuration and Copper Carbonate

After 7 months Modifying container design by changing the height : width ratio of containers or coating the interior surface of containers with copper compounds are among the various strategies used to prevent potbound root systems. Root growth was stimulated when plants with a naturally deep root system were grown in containers with a 7.9 height : width ratio, while growth of plants with a shallow root system was severely restricted in those containers (Biran and Eliassaf, 1980). The growth of deep-rooted woody plants also increased when these plants were grown in deeper containers with a height : width ratio of 3.0 vs. shallow containers with a height : width ratio of 0.4 (Keever et al., 1985). Copper compounds applied to the inside of containers or flats inhibits root growth, resulting in a more fibrous root system with a better root distribution within the container (Arnold and Struve, 1989). Studies on various species found increased and decreased growth responses for plants in copper-treated vs. nontreated containers (Arnold and Struve, 1989; Beeson and Newton, 1992; Furuta et al., 1972). Our objectives were to determine whether shoot and root growth of a vigorously growing species, Eucalyptus citriodora Hook., would be better in tall vs. regular-shaped containers with the same volume and whether coating the inside of the container with CuCO3 would reduce root circling and improve root and shoot growth. Eucalyptus citriodora liners were transplanted on 15 Aug. into plastic 3.7-liter containers of regular (standard no. 1) or tall configuration. Regular containers were 16.0 cm in diameter and 17.5 cm tall; the dimensions of the tall ones were 10.0 and 40.0 cm, respectively. The height : width ratio of regular and tall containers were 1.1 and 3.8, respectively. All containers were filled with 3.0 liters of Univ. of California Mix no. 2 (Baker, 1985). Tall containers were manufactured from polyvinyl chloride pipe cut to the specified height. Nylon screen was fastened to the bottom of the pipe and taped around the outside of the pipe.

Calibrating the pesticide capture efficiency of passive dosimeters

A system has been devised for determining the absolute capture efficiency of passive dosimeters. The system is composed of three components: a wind tunnel, a tracer atomizer, and a capture efficiency test device (CETD). The CETD consists of a series of cylinders separated by nylon screens to intercept and capture the spray containing a tracer. The decline in tracer at the screens was used to determine the tracer incident on the first screen. This in turn was used to estimate the tracer incident on a test dosimeter of washed muslin. The capture efficiency of the dosimeter was expressed as the ratio of tracer captured to tracer incident on the dosimeter. The capture efficiency of the test dosimeter using the CETD was found to be independent of the time of exposure and quantity of tracer captured. The approach presented is novel in that the method for documenting capture efficiency does not require prior knowledge of the spray concentration. Elimination of this requirement allows the use of the device in a much larger array of test situations (e.g. field and greenhouse studies) than has been previously possible. Furthermore, the conceptual model can easily be modified to allow for capture efficiency measurements from a range of structures and materials such as plants or whole leaves, as well as insects and non-target animal species. The CETD is simple and portable and could be used to calibrate dosimeters in a variety of field situations.

Nylon netting technique for the study of the three dimensional growth of Rhizoctonia solani in soil

A technique for estimating the three-dimensional growth of Rhizoctonia solani in soil by measurement of growth of Rhizoctonia on intersecting vertical and horizontal planes of nylon netting or nylon cloth is described. The three-dimensional system was compared to a two-dimensional soil sandwich technique using either Millipore filter membranes, or nylon netting. The techniques are also compared to a three-dimensional, pellet soil-sampler technique. There was better adherence of hyphae to the nylon netting (1.7 mm dia pores) than to the Millipore membrane (0.45 μm dia holes) or the Nybolt 21-T nylon screen printing material (32 μm dia holes). The two-dimensional and three-dimensional nylon netting technique resulted in a far more sensitive measure of hyphal growth in soil than the pellet soil-sampler technique. The use of nylon netting to measure growth of hyphae of R. solani in soil would be most appropriate in disturbed soil with the choice of two-dimensional or three-dimensional measurements depending on the aims of the experiment.

Isolation of leukocytes infiltrating the islets of Langerhans of diabetes-prone mice for flow cytometric analysis

A simple method was developed for flow cytometric immunofluorescence analysis of cells infiltrating the islets of Langerhans in diabetes-prone rodents. Pancreases were submitted to collagenase P digestion and, in order to minimize collagenase action on leukocytes, islets were isolated before digestion was completed, that is, when exocrine tissue still remained around the islets. Islets, maintained in medium supplemented with sodium azide to prevent modulation of surface markers, were then pressed through a metal sieve and the cell suspension filtered through two different nylon screens. Cells were washed before immunofluorescence staining. Comparative phenotyping of spleen cells submitted to a similar treatment showed that, provided the collagenase P batch was screened, this procedure did not alter leukocyte surface markers and allowed multicolor analysis of the islet infiltrating cells.

A stereotypic, transplantable liver tissue-culture system.

A method of coculturing adult rat hepatic parenchymal cells (PC) and stromal cells in a three-dimensional framework of nylon filtration screens or biodegradable polymer meshes was developed in our laboratory. Rat liver stroma, which includes vascular and bile duct endothelial cells, fat-storing cells, fibroblasts, and Kupffer cells, were isolated by gradient centrifugation after in situ liver perfusion and expanded in monolayer culture prior to seeding onto nylon screens or bioresorbable polyglycolic acid (PGA) polymers oriented into a felt-like construct. A second inoculum of freshly isolated PC was applied after the stromal cells became established. Histological analyses revealed that PC proliferation occurred until all available space for expansion within the template was exhausted. These cells retained their rounded morphology, and after 4-5 wk 7-9 "layers" of PC filled the 140-microns deep template. Dioxin-inducible cytochrome P450 activity was detected for up to 58 d in culture, and albumin, fibrinogen, transferrin, and soluble fibronectin were detected in the medium by enzyme-linked immunosorbent assay (ELISA) for 48 d in vitro. Immunohistochemical analysis of sections through the cultures confirmed the presence of these proteins as well as cytokeratin at the cellular level; the extracellular matrix stained for both collagen type III and laminin. Long-term PC proliferation and function were enhanced by the presence of stromal cells as well as by a meshwork template whose geometry allows the interaction of PC with stroma and matrix on several different planes. To permit transplantation, cocultures of hepatic PC and stromal cells were established on PGA felt constructs instead of nylon screens. After approximately 24 d in vitro, these constructs were grafted into sites in the mesentery, omentum, and subcutaneous tissues of adult Long-Evans rats. The growth of hepatocytes after 30 d in situ was evident by histological analysis; grafts of cocultures regenerated a liver-like architecture consisting of sinusoids and putative biliary structures. In addition, PC at these extrahepatic graft sites were positive for albumin, transferrin, and fibrinogen synthesis by immunohistochemistry. Graft survival was enhanced when recipients were subjected to approximately 40% hepatectomy. Hepatic PC:stromal cell cocultures may prove useful in the restoration of liver function either by direct transplantation using PGA or similar templates, or as extracorporeal devices, using nylon screens.

The role of micro-arthropods in the defacement of sawn lumberby sapstain and mould fungi

Fungal sap stain, mould, and basidiomycete defacement of boards sawn from the sapwood of freshly felled logs of Corsican pine (Pinusnigra var. maritima (Aiton) Melville) was assessed during a 14-week field trial at a sawmill in southern England. The boards were placed in nonstickered stacks to reduce moisture loss, and stacks were constructed in a nest arrangement to allow experimental untreated board samples to be positioned centrally in each stack. The experimental samples were placed in plastic tanks, and the open tank faces were left either uncovered or were covered with a fine-mesh nylon screen to prevent entry of micro-arthropods. All the experimental samples were sterilized by γ-radiation prior to the tanks being installed into the board stacks. The outer casing boards, which surrounded the experimental tanks in each stack, were dip treated with a fungicide, a broad-spectrum insecticide-acaricide, a combination of the fungicide and the insecticide-acaricide, or water, which served as a control. After 8 and 14 weeks of exposure, casing boards were inspected for fungal infestation. The experimental sample boards removed from the centre of the stacks at the 8-week inspection were also assessed for fungal infestation. Boards that were accessible to arthropods (i.e., in open tanks surrounded by non-insecticide-treated boards) suffered severe sap stain. Experimental boards protected from arthropods by a mesh screen and (or) casing timbers treated with the insecticide chemical had minimal sap stain. In contrast, colonization by moulds was not reduced when either physical or chemical barriers were in place, suggesting that mould spores were mainly transmitted by air currents. Micro-arthropods were clearly implicated as primary agents of sap-stain transmission on green sawn lumber. They may also graze the moulds and therefore limit the intensity of defacement by these fungi.

Stereotypic culture systems for liver and bone marrow: Evidence for the development of functional tissue in vitro and following implantation in vivo

Stromal cell-associated liver cell and bone marrow (BM) culture on three-dimensional nylon screen or polyglycolic acid (PGA) felt templates conveys certain functional advantages to the parenchyma of these tissues. Hepatic parenchymal cells (PC) manifest long-term ( approximately 2 month) expression of liver-specific activities including cytochrome P450 enzyme activity and the synthesis of albumin, fibrinogen, transferrin, and other proteins. PC also undergo proliferation in association with stromal cells that were pre-established on these templates. PC mitoses are directly proportional to available space within the template for their expansion indication that geometric or sterotypic parameters influence the growth of these cells in vitro. BM cultured on a similar template exhibits long-term multilineage hematopoietic expression and limited expansion of progenitor cell numbers. Progenitor cell concentration within the cultures can be substantially enhanced if these cells are liberated from co-culture and reseeded onto a template containing fresh stromal cells. BM and liver cel cultures established on felt composed of bioresorbable PGA filaments was grafted into various sites in rats. Liver co-cultures generated sinusoids and other liver-like structures in situ; active hematopoietic blasts were observed at sites of BM co-culture grafts. Biodegradable polymer constructs may prove useful for certain clinical applications as vehicles for the delivery of tissues that were engineered in culture.

Phosphorus depletion in the rhizosphere as influenced by soil moisture

To study the influence of soil moisture on phosphorus (P) depletion in the rhizosphere, maize (Zea mays cv. Trak) was pre-grown in vermiculite filled-PVC tubes for 9 days and then the plants with the tubes were transplanted into soil columns maintained at two soil moisture levels (θ) of 0.14 and 0.20 cm3 cm−3 for 10 days. The soil columns were separated at 1 cm depth by a nylon screen of 53 μm inner mesh size, into 1 cm soil layer above and 3 cm soil column below screen. A root mat developed over the screen, but root hairs only could penetrate it. Regardless of the soil moisture level in the columns, and adequate and equal water and nutrients supply was maintained via wicks from an external nutrient solution to the plant roots in vermiculite. After 10 days, the soil columns were separated from the root mats, quickly frozen in liquid nitrogen and sliced into thin layers (0.2mm) using a refrigerated microtome to give soil samples at defined distances from the root mats for analyses. Lower soil moisture (θ=0.14) resulted in narrower and steeper depletion profile of 0.5 M NaHCO3 extractable P (NaHCO3-Pi) as compared to higher soil moisture (θ=0.20). Depletion of P in soil solution in the immediate vicinity of root mats did not differ much but the extension of the depletion zones was 0.10 cm at θ=0.14 and 0.20 cm at θ=0.20. The depletion up to 0.05cm with θ=0.14 and up to 0.07 cm with θ=0.20 was uniform, and may be attributed to the depletion in the root hair zone. Beyond the root hair zones, the theory of diffusion and mass flow was able to explain the observed differences in shape and extent of the P depletion profiles at the two soil moisture levels.