Biocidal treatment of soil is used to remove or inhibit soil microbial activity, and thus provides insight into the relationship between soil biology and soil processes. Chemical (soil pH, phosphodiesterase, protease) and biological (substrate induced respiration) characteristics of three contrasting soils from tropical savanna ecosystems in north Queensland, Australia were measured in field fresh samples and following autoclaving (121 °C/103 kPa for 30 min on two consecutive days). Autoclaving treatment killed the active soil microbial biomass and significantly decreased protease activity (90%) in all three soils. Phosphodiesterase activity in kaolinitic soils also significantly decreased by 78% and 92%. However, autoclave treatment of smectitic soil only decreased phosphodiesterase activity by 4% only. This study demonstrates phosphodiesterase can remain stable in extreme conditions. This might be a characteristic vital to the cycling of phosphorus in shrink–swell clays in Australian tropical savanna ecosystems. 相似文献
The objective of this study was to evaluate acute endocrine effects as well as histological changes in testicular parenchyma induced by the contraceptive compound RTI‐4587‐073(l). Six miniature stallions were used in this experiment. The treatment group (n = 3) received one oral dose of 12.5 mg/kg of RTI‐4587‐073(l), and the control group (n = 3) received placebo only. The stallions' baseline parameters (semen, testicular dimensions, endocrine values) were collected and recorded for 5 weeks before treatment and for 6 weeks after treatment. Multiple blood samples were collected for endocrine analysis. Testicular biopsies were obtained before treatment, 1 day after treatment and every other week after treatment. Ultrasound exams were performed to monitor the dimensions of the stallions' testes. All stallions were castrated 6 weeks after treatment. Sperm numbers, motility and percentage of morphologically normal sperm decreased (p < 0.05), while the number of immature germ cells increased in ejaculates from treated animals (p < 0.05). Serum concentrations of inhibin and follicle‐stimulating hormone did not change. Testosterone concentrations initially transiently decreased (p < 0.05) after administration of RTI‐4587‐073(l), and increased several days later (p < 0.05). Testicular content of testosterone and estradiol 17‐β was lower in treated stallions than in control stallions on Day 1 after treatment (p < 0.05). Severe disorganization of the seminiferous tubules, significant loss of immature germ cells and complete depletion of elongated spermatids were observed in testicular biopsies obtained from treated stallions 1 day, 2 and 4 weeks after treatment. These changes were still present in the testicular samples taken from treated stallions after castration. The results of this study confirmed that RTI‐4587‐073(l) has antispermatogenic effects in stallions. Furthermore, we concluded that this compound causes acute sloughing of immature germ cells from the seminiferous tubules. RTI‐4587‐073(l) has significant but transient effects on Leydig cell function in stallions. 相似文献
Seagrasses are submerged marine plants that have been declining globally at increasing rates. Natural resource managers rely on monitoring programs to detect and understand changes in these ecosystems. Technological advancements are allowing for the development of patch-level seagrass maps, which can be used to explore seagrass meadow spatial patterns.
Objectives
Our research questions involved comparing lacunarity, a measure of landscape configuration, for seagrass to assess cross-site differences in areal coverage and spatial patterns through time. We also discussed how lacunarity could help natural resource managers with monitoring program development and restoration decisions and evaluation.
Methods
We assessed lacunarity of seagrass meadows for various box sizes (0.0001 ha to 400.4 ha) around Cat Island and Ship Island, Mississippi (USA). For Cat Island, we used seagrass data from 2011 to 2014. For Ship Island, we used seagrass data for seven dates between 1963 and 2014.
Results
Cat Island, which had more continuous seagrass meadows, had lower lacunarity (i.e., denser coverage) compared to Ship Island, which had patchier seagrass beds. For Ship Island, we found a signal of disturbance and path toward recovery from Hurricane Camille in 1969. Finally, we highlighted how lacunarity curves could be used as one of multiple considerations for designing monitoring programs, which are commonly used for seagrass monitoring.
Conclusions
Lacunarity can help quantify spatial pattern dynamics, but more importantly, it can assist with natural resource management by defining fragmentation and potential scales for monitoring. This approach could be applied to other environments, especially other coastal ecosystems.
Soil samples collected from a peach orchard near a well containing 1 pg kg?1 1,2-dibromo-3chloropropane (DBCP) (contaminated) and from a peach orchard with a well containing 0.1 pg kg?1 DBCP (uncontaminated) contained less than 0.1 gg kg?1 and 0.5 μg kg?1 DBCP residue, respectively. Soil profiles did not explain the presence of DBCP in the contaminated well. However, a possible spill of DBCP approximately 30 m from the contaminated well may have contaminated the well water. Soil samples taken at the site of the possible spill contained high concentrations of DBCP in the upper meter and at 6.1 m where the water table was encountered. The data indicate that the water contamination resulted from this spill of DBCP and not from normal agricultural use. 相似文献
Several isoflavonoid phytoalexins produced by soybeans are known to be estrogenic, with potential beneficial health effects in humans. Increased production of phytoalexins by the soybean plant will facilitate research efforts in this area. In this study, phytoalexin induction and accumulation in soybean cotyledon tissue was observed using four species of Aspergillus: A. sojae, A. oryzae, A. niger, and A. flavus. All four Aspergillus species tested elicited phytoalexin accumulation in living soybean cotyledons. Results from a time course study indicated that maximum concentrations of the phytoalexin glyceollin, 955 microg/g fresh weight (fw), occurred at day 3 in soybean cotyledon tissue inoculated with A. sojae. Other Aspergillus species caused an accumulation of glyceollin at significantly lower levels. A maximum concentration of coumestrol of 27.2 microg/g fw was obtained from soybean cotyledons inoculated with A. niger. Soybean phytoalexins induced by food-grade A. sojae and A. oryzae allowed the collection of higher concentrations of phytoalexins for further examination in several in vitro and in vivo biological studies conducted to determine potential estrogenic activities. 相似文献
Studies were conducted to determine changes in organic matter and microbial biomass carbon in comparison with structural stability at the surface soil (0–5 cm) of a Charlottetown fine sandy loam, an Orthic Podzol, at three tillage and grassland sites situated in Prince Edward Island. The tillage experiments, established for 3–5 years, included comparisons of mouldboard ploughing, direct drilling, shallow tillage, and chisel ploughing. Two indices of soil structural stability were used: mean weight diameter (MWD) and aggregation index (AI). The latter index assigns a weight factor to aggregate size ranges based on their value for plant germination and root growth.Direct drilling and reduced tillage increased the level of soil organic carbon by 10–17%, relative to mouldboard ploughing. Organic carbon was more enriched in 1–2 mm and 4.75–9.00 mm macroaggregates, especially the former, compared with whole soil. The MWD of aggregates after wet sieving was 33% and 55%, relative to the grassland sites, for mouldboard ploughing and direct drilling, respectively. On these soils of similar mineralogy and particle size, a close linear relationship (r=0.942) was observed between organic carbon (r=0.947) and nitrogen (r=0.923). The AI was significantly correlated to both organic carbon and microbial biomass carbon using power regression. In contrast to MWD, the AI under direct drilling and reduced tillage, associated with an organic carbon level of 2.5%, approximated the AI under grass. Overall, the study showed that minimum tillage systems in humid climates can improve structural stability at the soil surface of fine sandy loams over a relatively short time frame. 相似文献
This article presents and illustrates an approach to designing and analyzing studies involving mixtures/combinations of drugs
or chemicals along fixed-ratio rays of the drugs or chemicals for generalized linear models. When interest can be restricted
to a specific ray, we consider fixed-ratio ray designs to reduce the amount of experimental effort. When a ray design is used,
we have shown that the hypothesis of additivity can be rejected when higher order polynomial terms are required in the total
dose-response model. Thus, it is important that we have precise parameter estimates for these higher order polynomial terms
in the linear predictor. We have developed methodology for finding a Ds-optimal design based on this subset of the terms in the linear predictor. 相似文献