Impact of moisture and UV degradation on Beauveria bassiana (Balsamo) Vuillemin conidial viability in turfgrass

Beauveria bassiana conidial viability in turfgrass was evaluated using a two-component nucleic acid stain and fluorescence microscopy. Turfgrass samples along with the top 5 cm of soil were used for conidial extraction and viability evaluation on 1, 2, 3, 7, 14 and 21 days after treatment. There were no differences in conidial viability between two Orthoptera strains, 3622 and 5977, and both strains were able to persist in a sandy loam soil for up to three weeks after application. High and low irrigation levels were applied to each of the two strains and results show that higher irrigation (5.1 cm/week) maintains conidial viability better than a low irrigation level (2.5 cm/week). Mean conidial viability was approximately 8–12% greater in plots with the high irrigation regime. Rather than significantly increase soil moisture levels, it is hypothesized that the greater amount of irrigation helps to move the conidia deeper into the thatch layer and soil profile, an area that provides protection from damaging surface temperatures and UV exposure. Rainfall that occurred during the beginning of the 2005 test minimized the irrigation effect, and the irrigation treatment differences were more pronounced after 48 h. Four different UV protectants were evaluated for an impact on conidial viability of strain 3622. Two protectants, an optical brightener and magnesium silicate clay, when added to an emulsifiable oil formulation, significantly increased conidial viability on all evaluation dates. The clay particles act as a sunlight blocker while the optical brightener absorbs UV light. The combined protection from the oil and the additive increased conidial viability by approximately 10% on all evaluation dates. Results from this study provide insight into ways to increase entomopathogenic fungal viability under field conditions.     

Assessment of germination and carnivorous activities of a nematode-trapping fungus Arthrobotrys dactyloides in fungistatic and fungicidal soil environment

Carnivorism is the ability of nematode-trapping fungi to trap and digest the nematodes by sophisticated devices called traps. Delivery of nematode-trapping fungi in soil for bio-control of pest nematodes often fails or gives inconsistent results. Possible reasons for failure could be the effect of soil fungistasis on germination of nematode-trapping fungi in soil environment, use of avirulent species and sensitivity of these fungi to fungicidal residues in soil. Exploitation of nematode-trapping fungi for nematode control demands that it be compatible with fungicides applied in soil or crops and proliferate in soil. This investigation represents is one of the first to evaluate the effect of fungicides on the nematode-trapping fungus Arthrobotrys dactyloides. A. dactyloides showed in vitro carnivorous potential against Meloidogyne incognita, Meloidogyne javanica, Meloidogyne graminicola, Helicotylenchus dihystera and Heterodera cajani. Conidia of A. dactyloides exposed to agricultural soils showed poor germination but formed conidial traps, which captured and killed the soil nematodes. Conidial traps, which trapped the nematodes, grew well in all soils after killing and nutrient absorption from nematode body. Soil amended with 20 mg ai kg⁻¹ of carbendazim and thiram, 30 mg ai kg⁻¹ of mancozeb, 50 mg ai kg⁻¹ of captan, and 100 mg ai kg⁻¹ of carboxin completely checked the conidial trap formation and nematode capturing. 30, 50 and 100 mg ai kg⁻¹ of metalaxyl adversely affected the conidial trap formation and nematode capturing in soil. Propiconazole inhibited 15.2% conidial trap formation up to 50 mg ai kg⁻¹ but caused 93.3% inhibition of conidial traps formation and complete inhibition of nematode capturing at 100 mg ai kg⁻¹. Sulphur, triademefon, and tricyclazole showed least toxic effect on conidial trap formation and nematode capturing activities of A. dactyloides in soil up to 100 mg ai kg⁻¹.     

Variation of soil nutrients and particle size under different vegetation types in the Yellow River Delta

The Yellow River Delta wetland, located at the southern coast of Bohai Gulf, provides important ecosystem services such as flood control, water purification, biodiversity conservation, nutrient removal and carbon sequestration, shoreline stabilization, tourism attraction and wetland products maintains in the Yellow River Delta. This study assessed how agricultural activities in a reclamation wetland changed soil pH, soil electric conductivity, soil nutrient and soil particle size as compared to natural vegetation by using a combination of field experiments and lab analysis. The vegetation type included adjacent alfalfa field (Medicago sativa), cotton field (Gossypium spp.), Chinese tamarisk shrub (Tamarix chinensis), and reed marsh (Phragmites sage). The results indicated that the soil pH was higher (pH > 8) in alfalfa field and cotton field, and alfalfa field and reed marsh had significant function in reducing soil salt content, soil electric conductivity of alfalfa field at 0–30 cm were 140.38 ± 14.36, 114.48 ± 14.36, 125.30 ± 11.37 μs/cm. The effect of different vegetation types on soil nutrient was significant (P < 0.05). Soil organic matter at 0–10 cm in Chinese tamarisk shrub and reed marsh was 21.66 ± 3.82 g/kg and 16.51 ± 4.60 g/kg, which was higher than that of alfalfa field (10.47 ± 2.36 g/kg) and cotton field (9.82 ± 1.27 g/kg), but soil total nitrogen content in alfalfa field was the highest, which is significantly higher than that of cotton field, Chinese tamarisk shrub and reed marsh(P < 0.05), the content of soil total nitrogen at 0–10 cm and 10–20 cm was 7.67 ± 0.38 g/kg and 5.97 ± 0.51 g/kg, respectively, while the content of available P and available K was reversed. The difference of soil particle size between layers was not significant (P > 0.05), the sand content of Chinese tamarisk shrub soils in 0–10 cm was the highest, the next was alfalfa field and cotton field, and the content of silt and clay in reed marsh was higher than the others. The correlation and significant degree between soil particle size and soil nutrient was related with vegetation types, and soil organic matter was significantly positively correlated with soil silt and clay content on the alfalfa field. The results demonstrated that wetland cultivation was one of the most important factors influencing on the nutrient fate and reserves in soil, which could lead to rapid nutrient release and slow restoration through abandon cultivation. Consequently, compared with cotton field, alfalfa field is more favorable to sustainable management of wetland cultivation in the Yellow River Delta. It should be considered in wetland restoration projects planning.     

Growth and root distribution of Vallisneria natans in heterogeneous sediment environments

Plant growth, biomass allocation and root distribution were investigated in the submerged macrophyte Vallisneria natans growing in heterogeneous sediments. Experimentally heterogeneous sediment environments were constructed by randomly placing 4 cm of clay or sandy loam into the top (0–4 cm) or bottom (4–8 cm) layer within an experimental tray, providing two homogeneous and two heterogeneous treatments. Biomass accumulation was significantly affected by the experimental treatments: higher in the homogeneous sediment of clay (32 mg per plant) and the two heterogeneous treatments (about 27 mg per plant), but lower in the homogeneous sediment of sandy loam (15 mg per plant). Root: shoot ratio was also different among the four treatments. Compared with the treatments of clay in the top layer, plants allocated more biomass to roots at the treatments of sandy loam in the top layer. Heterogeneous sediments significantly affected root distribution pattern. Compared with the treatments of sandy loam in the bottom layer, root number (7–8 versus 13–14) and total root length (3.6–4.0 cm versus 29.5–40.0 cm) in the bottom layer were significantly higher in the treatments with clay in the bottom layer. These results indicate that both sediment structure and nutrient availability influence growth and root system distribution of V. natans.     

Capacities of soil water reservoirs and their better regression models by combining “merged groups PCA” in Chongqing,China

Soil water resource, together with the surface and sub-surface water resource, is essential to the regional water balance and world water cycle. A total of 90 soil samples were collected from 30 different soil profiles of dry fields throughout Chongqing, China randomly to show how soil could be a crucial part of water resources by discussing their five types of calculated soil water reservoir capacities, namely the total soil water reservoir capacity (mm) (TC), soil water storage capacity (mm) (SC), unavailable soil water reservoir capacity (mm) (UC), available soil water reservoir capacity (mm) (AC), and soil dead water storage capacity (mm) (DC) in certain layer, respectively. Overall, the total soil water reservoir capacity in 0–40 cm was about 209 mm, of which 70 mm belonged to available soil water reservoir capacity. Not all the five types of soil water reservoir capacities had significant correlations between each other. Soil structure, especially the size and quantity of soil pore was mainly determined by soil particle composition (clay, silt, and sand content). The more sand and less clay led to the more soil macropores, which provided room for soil water. Thus, clay, silt, and sand content jointly produced profound influence on soil water reservoir capacities. Nevertheless, specific water capacity and topographic factors displayed weak correlations to soil water reservoir capacities, which required further research works. Ultimately, the better regression models were achieved by multiple regression analysis coupled with “merged groups PCA” than by multiple regression analysis with “all variables PCA”. UC, SC, TC and DC could be well simulated (mostly R² > 0.70; P < 0.05) through normal multiple regression analysis using original variables as well as multiple regression analysis with “merged groups PCA”. Only regression models of TC and DC were highly significant (mostly R² > 0.70; P < 0.05) through “all variables PCA” method. And there were poor coefficients of determination (R²) for AC (mostly R² < 0.40; P < 0.05) by all the three regression methods.     

Assessment of soil salinization risks under irrigation with brackish water in semiarid Tunisia

The salinity problem is becoming increasingly widespread in arid countries. In semiarid Tunisia about 50% of the irrigated land is considered as highly sensitive to salinization. To avoid the risk of salinization, it is important to control the soil salinity and keep it below plant salinity tolerance thresholds. The objective of the present study was to provide farmers and rural development offices with a tool and methodology for predicting, monitoring of soil salinity for a better agronomical strategy. The experiments were carried out in the highly complex and heterogeneous semiarid Kalâat Landalous irrigated district of Tunisia. The field and laboratory measurements of soil and water properties were conducted in 1989 and 2006 at different observation scales (2900 ha, 1400 ha, 5200 m long transect, and soil profiles). Seventeen years of reclamation of a saline and waterlogged soil led to the reduction of average electrical conductivity of the soil saturated paste extract (ECe), measured at 5 soil depths (from 0 to 2 m) below the plant salt tolerance threshold and the dilution of groundwater salinity from 18.3 to 6.6 dS m⁻¹. The variation in soil salt storage (ΔMss = Mss₂₀₀₆ − Mss₁₉₈₉) in the vadose zone was negative, equal to about −145 × 10³ ton (≈−50 ton ha⁻¹). During the same period, the salt balance (Siw–Sdw) estimated from the input dissolved salt brought by irrigation water (Siw) and output salts exported by the drainage network (Sdw) was equal to −685 × 10⁶ kg and the Sdw was 945 × 10⁶ kg. Under irrigation and efficient drainage, the soil salinization could be considered as a reversible process. At the transect scale, the high clay content and the exchangeable sodium percentage was negatively correlated to saturated hydraulic conductivity. The textural stratification, observed at soil profile scale, favors accumulation of salt in the soil. Based on the findings related to the multiscale assessment of soil salinity and groundwater properties, soil salinization factors were identified and a soil salinization risk map (SRU) was elaborated. The shallow groundwater constitutes the main risk of soil salinization. This map can be used by both land planners and farmers to make appropriate decisions related to crop production, and soil and water management.     

Germination characteristics of the grass weed Digitaria nuda (Schumach.)

The effect of various pre-treatments and their interaction with temperature on cumulative percentage and the rate of germination were evaluated for Digitaria nuda. Stored and fresh seeds were pre-treated with either 0.02 M KNO₃, soaked in water for 24 h (priming), sterilized with 0.5% NaOCl or heat treated at 60 °C. Seeds were germinated at constant temperatures of 25 and 30 °C and fluctuating temperature regimes of 25/10 and 30/15 °C. The effect of pre-chilling on germination of stored and fresh seed was evaluated at 30/15 °C, and seed emergence in two soil types at different burial depths (0, 0.5, 1, 2, 3, 4, 5 and 6 cm) was also determined. The pre-treatment of stored seed with KNO₃ resulted in the highest germination percentage (100%), whereas the pre-treatment of fresh seed with water for 24 h gave the best germination (99%), at constant temperatures of 25 and 30 °C. Pre-chilling of seed increased germination by more than 30%. Emergence from clay loam soil was greater compared with the emergence from sandy loam soil. Total seedling emergence decreased exponentially with increasing burial depths with only 5% of seed germinating from a burial depth of 6 cm. Results from this study showed that germination requirements are species specific and knowledge of factors influencing germination and emergence of grass weed seed can assist in predicting flushes in emergence allowing producers to implement control practices more effectively.     

Evaluation of integrating topographic wetness index with backscattering coefficient of TerraSAR-X image for soil moisture estimation in a mountainous region

The estimation of soil moisture by using the backscattering coefficient of radar in a mountainous region is a challenging task due to the complex topography, which impacts the distribution of soil moisture and changes the backscattering coefficient. Complicated terrain can disturb empirical moisture estimation models, thereby, the resulting estimates of soil moisture are very unlikely reliable. This article proposed an innovative way of integration of the topographic wetness index (TWI) and the backscattering coefficient of soil obtained from the TerraSAR-X image, which improves the accuracy of measurement of the soil moisture. The standard estimation error and the coefficient of determination from the model were used to evaluate the performance of TWI. Our results show that the standard estimation error was decreased from: (1) 4.0% to 3.3% cm³ cm⁻³ at a depth of 5 cm and (2) 4.5% to 3.9% cm³ cm⁻³ at a depth of 10 cm. The most reliable estimation was observed at a depth of 5 cm, when it was compared with those of 0–5 cm, 10 cm and 15 cm. The TWI from the digital elevation model (DEM) is useful as a constraint condition for modeling work. This article concludes that the integration of the backscattering coefficient of soil with TWI can significantly reduce the uncertainty in the estimation of soil moisture in a mountainous region.     

Response of Potamogeton crispus root characteristics to sediment heterogeneity

Plant growth, biomass allocation, root distribution and plant nutrient content were investigated in the submerged macrophyte Potamogeton crispus growing in heterogeneous sediments. Three experimental sediments heterogeneous in nutrient content and phosphorus release capacity were used: sandy loam with low nutrient content (A), clay with intermediate nutrient content (B), and clay with high nutrient content (C). Biomass accumulation was significantly affected by the sediment type, and was highest in clay C (1.23 mg per plant dry weight) but lowest in sandy loam (0.69 mg per plant dry weight). The root:shoot ratios in treatments A, B and C were 0.30, 0.14 and 0.09, respectively. P. crispus allocated more biomass to roots in sandy loam compared with the other sediments. The average root numbers in sediments A, B and C were 16, 19 and 20, respectively, and the total root lengths in sediments A, B and C were 238.84, 200.36 and 187.21 cm, respectively. Almost 90% of the root biomass was distributed in the 0–15 cm depth in sediments B and C, compared with 64.53% in sediment A. The rank order of plant nitrogen and phosphorus concentrations in the sediment types was C > B > A. These results indicate that both sediment structure and nutrient availability influence the growth and distribution of the root system of P. crispus.     

Effect of fire on soil nutrients and under storey vegetation in Chir pine forest in Garhwal Himalaya,India

The study was carried out in the Pinus roxburghii Sargent (Chir pine) forest in the sub-tropical region of Garhwal Himalaya to assess the effect of fire on soil nutrient status at different altitudes (700 m, 800 m and 1000 m), soil depths (0–20 cm, 20–40 cm and 40–60 cm) and on under storey vegetation. The soil nutrients and under storey vegetation were assessed before fire (pre-fire) and after fire (post-fire). The results of the study indicate that fire plays an important role in soil nutrient status and under storey vegetation. The nutrients (soil organic carbon, nitrogen, phosphorus and potassium), decreased in post-fire assessment and with increasing altitudes, and soil depths, compared to pre-fire assessment. The under storey vegetation diminished after fire in all forest sites. The study concludes that in Chir pine forest, fire plays a role in reducing soil nutrients along the altitudinal gradient, soil depths and under storey vegetation. Thus, these nutrients can be saved through some management practices e.g. by early controlled burning and by educating local villagers about the negative impacts of severe wild fires on soil and vegetation.     

Variability of soil carbon sequestration capability and microbial activity of different types of salt marsh soils at Chongming Dongtan

Variations in the soil carbon sequestration capability of different types of salt marsh soils at Chongming Dongtan and its influencing factors were studied by analyzing the soil organic carbon (SOC) content, organic matter input and microbial activities. The results indicated that the total SOC content at Area A (southeast of Dongtan, sandy soil with Phragmites communis) was only 46.11% of that of Area B (northeast of Dongtan, clay soil with mixed P. communis and Spartina alterniflora) (P = 0.000 < 0.05), but their organic matter input per year was almost identical. These findings implied that Area B had a lower output of SOC. The microbial biomass at Area A was 3.83 times greater than that at Area B (P = 0.049 < 0.05); the soil catalase and invertase activities at Area A, which were related to carbon metabolism, were 60.31% (P = 0.006 < 0.05) and 34.33% (P = 0.021 < 0.05) higher than at Area B, respectively; and the soil respiration at Area A was also higher than at Area B. These findings implied that the microbial activities at Area A were greater than those at Area B, and therefore the carbon metabolism was rapid, resulting in increased SOC output at Area A. Increased water content and salinity in the clay soil at Area B may inhibit the microbial activities, thereby reducing the decomposition of the organic matter and enhancing carbon sequestration. In addition, some artificial measures for controlling spread of S. alterniflora at Area B (mowing/digging and tillage (M + D); mowing/digging and tillage/waterlogging (M + D + W)) were found to generally improve the microbial activity of soil, thereby increasing SOC output. However, when the two different physical controlling modes were compared, the SOC and microbial activities of the soil subjected to the M + D + W treatment were relatively high and low, respectively, due to waterlogging restraining the microbial metabolism. These findings indicated that the difference in microbial activities was the important factor leading to variability in the SOC sequestration capability between Areas A and B. Additionally, with the exception of soil texture and vegetation types, environmental conditions and artificial turbulence also influenced microbial activities of soil, and hence SOC output and organic carbon sequestration capability.     

Preservation of Agaricus subrufescens strains at low temperature by using cultures on sorghum grains

BackgroundOne of the main problems for the preservation of genetics resources of Agaricus subrufescens is to maintain the viability of the strains because the mycelium is very sensitive to cooling and therefore it ages rapidly.AimsEvaluate the viability of A. subrufescens strains stored as cultures on sorghum grain (spawn) at different temperatures.MethodsEighteen strains of A. subrufescens and three strains of Agaricus bisporus were studied. Spawn's viability was evaluated under the following conditions: (1) control at 25 °C (C), (2) cooling to 4 °C (R) and (3) freezing in liquid nitrogen at ?196 °C (LN). Samples were recovered from week 4 every 2 weeks until week 12 and week 24 in C and R, whereas in LN samples were recovered at 4, 12 and 24 weeks. Viability was evaluated in 50 seeds, by strain and condition, recovering the mycelium in Petri dishes with potato dextrose agar medium (PDA). Mycelium growth was also evaluated on PDA after 14 days of recovery.ResultsMost strains showed 100% viability and they were recovered usually in 1 day. In LN the viability ranged between 84 and 100% depending on the strain, but in some cases recovery took more than 10 days. Mycelial growth decreased gradually over time and although the results show significant differences between treatments C and R, the decline is associated with ageing of the mycelium rather than the treatment itself.ConclusionsCulture on sorghum grain and storage at low temperature is an interesting way to preserve genetic resources of A. subrufescens.     

Long-term tillage effects on soil organic carbon and dissolved organic carbon in a purple paddy soil of Southwest China

The impact of conservation tillage practices on soil carbon has been of great interest in recent years. Conservation tillage might have the potential to enhance soil carbon accumulation and alter the depth distribution of soil carbon compared to conventional tillage based systems. Changes in the soil organic carbon (SOC) as influenced by tillage, are more noticeable under long-term rather than short-term tillage practices. The objective of this study was to determine the impacts of long-term tillage on SOC and dissolved organic carbon (DOC) status after 19 years of four tillage treatments in a Hydragric Anthrosol. In this experiment four tillage systems included conventional tillage with rotation of rice and winter fallow system (CTF), conventional tillage with rotation of rice and rape system (CTR), no-till and ridge culture with rotation of rice and rape system (NT) and tillage and ridge culture with rotation of rice and rape system (TR). Soils were sampled in the spring of 2009 and sectioned into 0–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm depth, respectively.Tillage effect on SOC was observed, and SOC concentrations were much larger under NT than the other three tillage methods in all soil depths from 0 to 60 cm. The mean SOC concentration at 0–60 cm soil depth followed the sequence: NT (22.74 g kg^?1) > CTF (14.57 g kg^?1) > TR (13.10 g kg^?1) > CTR (11.92 g kg^?1). SOC concentrations under NT were significantly higher than TR and CTR (P < 0.01), and higher than CTF treatment (P < 0.05). The SOC storage was calculated on equivalent soil mass basis. Results showed that the highest SOC storage at 0–60 cm depth presented in NT, which was 158.52 Mg C ha^?1, followed by CTF (106.74 Mg C ha^?1), TR (93.11 Mg C ha^?1) and CTR (88.60 Mg C ha^?1). Compared with conventional tillage (CTF), the total SOC storage in NT increased by 48.51%, but decreased by 16.99% and 12.77% under CTR and TR treatments, respectively. The effect of tillage on DOC was significant at 0–10 cm soil layer, and DOC concentration was much higher under CTF than the other three treatments (P < 0.01). Throughout 0–60 cm soil depth, DOC concentrations were 32.92, 32.63, 26.79 and 22.10 mg kg^?1 under NT, CTF, CTR and TR, and the differences among the four treatments were not significant (P > 0.05). In conclusion, NT increased SOC concentration and storage compared to conventional tillage operation but not for DOC.     

Changes in soil microbial community under willow coppice: The effect of irrigation with secondary-treated municipal wastewater

The effect of secondary-treated wastewater irrigation of a short-rotation willow coppice on soil microbial parameters was evaluated twice in 3 years using microbiological and biochemical properties. The soil metabolically active microbial biomass, basal respiration, N-mineralization, potential nitrification, alkaline and acid phosphatase and dehydrogenase activities were measured. The microbial community metabolic profile was determined with Biolog EcoPlates and bacterial community structure was assessed using denaturing gradient gel electrophoresis. After 2 years, a significant increase had occurred in soil microbial biomass, respiration and nitrogen mineralization activity both in the irrigated and in the non-treated plots. Wastewater irrigation increased the soil potassium concentration and enhanced the activity of alkaline phosphatase. Plant growth and irrigation affected the nitrogen mineralization activity—the increase was twice as high in the control plots as in the irrigated plots after 2 years. Potential nitrification, acid phosphatase activity and microbial community metabolic activity did not differ significantly (P > 0.05) between the control and the irrigated plots during the study. The comparison of soil profiles indicated that the observed increases in the soil microbiological parameters were allocated to the upper 10 cm. The establishment of willow plants on the fields affected the microbial community structure, with an increased diversity and higher similarity among the planted plots after 2 years. From our results we conclude that the willow coppice affected the soil bacterial community structure and had a positive effect on soil biological activity. Irrigation with pre-treated wastewater affected soil chemical and biochemical properties.     

Environmental driving factors affecting plant biomass in natural grassland in the Loess Plateau,China

Plant biomass is a key parameter for estimating terrestrial ecosystem carbon (C) stocks, which varies greatly as a result of specific environmental conditions. Here, we tested environmental driving factors affecting plant biomass in natural grassland in the Loess Plateau, China. We found that above-ground biomass (AGB) and below-ground biomass (BGB) had a similar change trend in the order of Stipa bungeana > Leymus secalinus > Artemisia sacrorum > Artemisia scoparia, whereas shoot ratio (R/S) displayed an opposite change trend. There was a significantly positive linear relationship between the AGB and BGB, regardless of plant species (p < 0.05). Furthermore, more than 50% of the AGB were found in 20–50 cm of plant height in Compositae plants (A. sacrorum, A. scoparia), whereas over 60% of the AGB were found in 20–80 cm of plant height in Gramineae plants (S. bungeana, L. secalinus). For each plant species, more than 75% of the BGB was distributed in 0–10 cm soil depth, and 20% was distributed in 10–20 cm soil depth, while less than 5% was distributed in 20–40 cm soil depth. Further, AGB and BGB were highly affected by environmental driving factors (soil properties, plant traits, topographic properties), which were identified by the structural equation model (SEM) and the generalized additive models (GAMs). In addition, AGB was directly affected by plant traits, and BGB was directly affected by soil properties, and soil properties associated with plant traits that affected AGB and BGB through interactive effects were 9.12% and 3.59%, respectively. However, topographic properties had a weak influence on ABG and BGB (as revealed by the lowest total pathway effect). Besides, soil organic carbon (SOC), soil microbial biomass carbon (MBC), and plant height had a higher relative contribution to AGB and BGB. Our results indicate that environmental driving factors affect plant biomass in natural grassland in the Loess Plateau.     

Production of a collagenase from Candida albicans URM3622

Culture conditions (pH, time, temperature, inoculum size, orbital agitation speed and substrate concentration) for an extracellular collagenase produced by Candida albicans URM3622 were studied using three experimental designs (one 2⁶⁻² fractionary factorial and two 2³ full factorial). The analysis of the 2⁶⁻² fractionary design data indicated that agitation speed and substrate concentration had the most significant effect on collagenase production. Based on these results, two successive 2³ full factorial design experiments were run in which the effects of substrate concentration, orbital agitation speed and pH were further studied. These two sets of experiments showed that all variables chosen were significant for the enzyme production, with the maximum collagenolytic activity of 6.8 ± 0.4 U achieved at pH 7.0 with an orbital agitation speed of 160 rpm and 2% substrate concentration. Maximum collagenolytic activity was observed at pH 8.2 and 45 °C. The collagenase was stable within a pH range of 7.2–8.2 and over a temperature range of 28–45 °C. These results clearly indicate that C. albicans URM3622 is a potential resource for collagenase production and could be of interest for pharmaceutical, cosmetic and food industry.     

Phosphorus reduction from agricultural runoff in a pilot-scale surface-flow constructed wetland

Excess P in surface waters in Quebec is the primary cause of water quality deterioration and the majority of it is coming from agricultural land as non-point source pollution. The objective of this study was to compare how two substrates, a sandy clay loam and a sand soil, influenced P retention in a surface-flow constructed wetland (CW). A secondary objective was to determine if the hydraulic residence time of the wetland differed between soil types. Measurements were taken at a pilot-scale CW site between July 5 and October 1, 2007. Three cylindrical tank replicates filled with sandy clay loam soil, and three with a sandy soil were planted with cattails (Typha latifolia L.) and reed canary grass (Phalaris arundinaceae L.). The tanks were flooded continuously with an artificial agricultural runoff solution containing 0.3 mg L^?1 dissolved reactive P. The six treatment tanks retained 0.9–1.6 g P m^?2, which corresponded to an average removal efficiency of 41%; there was no significant difference in the P retention by the two soil types. A bromide tracer test revealed a mean hydraulic retention time of 2.2 days for all tanks; however, the active volume of the sand tanks was greater. This investigation suggests that a sandy soil may be less prone to reducing conditions in a surface-flow CW and therefore maintain its role as a P sink for longer than the sandy clay loam.     

Effects of yak dung patch dropped in cold season on soil and pasture on the Qinghai-Tibetan Plateau

To clarify how dung patches from grazing yaks affect soil and pasture in the alpine meadow of Qinghai-Tibetan Plateau, yak dung was collected, mixed and redistributed in a cold grazing season. The soil physical and chemical properties and forage growth were then monitored under the yak dung patch, and 10 cm and 50 cm from the edge of yak dung patches. The result has shown that yak dung significantly improved soil moisture, total organic matter, and soil available N and P under or close to the dung patches. The forage production at 10 cm from the dung patch (303 g/m²) was significantly higher than that at 50 cm from the dung patch (control) (284 g/m²) in the second year, while the production was similar to the control in the first and the third year. The process of yak dung decomposition was slow and yak dung remains were observed 3 years after the drop. The dung patches also formed a strong ‘shell’, very difficult for plant underneath to penetrate and grow. Therefore, almost all plants under yak dung patches died, leading to decline in forage yield in the first, second, and the third year. In practice in the Qinghai-Tibetan Plateau regions, yak dung is often collected as fuel by the local farmers. Removing yak dung from alpine meadow may on one hand lead to losses in soil nutrients, but on the other hand reduces some of the negative effects, e.g. the reduction of forage yield under yak dung patches.     

Validation of cell density and viability assays using Cedex automated cell counter

A method using Cedex automatic cell counter (Innovatis) to determine the cell density and viability of a whole cell-based immunotherapy product has been developed and validated for the assay performance characteristics including specificity, accuracy, precision, linearity, range, and robustness. Instrument-to-instrument variation due to intrinsic differences in handmade flow cells was also evaluated. For cell density, Cedex demonstrated acceptable specificity, accuracy and precision for cell densities ranging from 3.13 × 10⁵ to approximately 1.0 × 10⁷ cells/mL, with intermediate precision of about 5% relative standard deviation (RSD). However, a marked difference was observed between the two instruments studied and they therefore could not be used interchangeably without additional calibration procedures that went beyond the manufacturer's recommendation. For viability, mixing known numbers of non-viable cells with highly viable cells allowed evaluation of the specificity, accuracy and linearity of the viability determination. Acceptable levels of accuracy (95.3–106.4% recovery) and precision (RSD < 5%) were demonstrated for the viability range from 50 to 100%. The instrument-to-instrument difference was less than 4.6%. The assays for both cell density and viability were sufficiently robust for assay parameters. However, the effect of certain parameters was cell line-dependent, suggesting that Cedex performance should be verified for each cell line of interest.