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61.
Julián Pérez-Flores Alejandra Arias Pérez Yesenia Primo Suárez Vinicio Calderón Bolaina Asunción López Quiroga 《Agroforestry Systems》2018,92(2):365-374
Cacao agroforestry systems (cacao-AFS) produce abundant litter. After decomposing, litter releases nutrients into the soil. The aim of this research was to estimate litter production and its nutrient content in 35- and 55-year-old cacao-AFS. The research was conducted in three cacao-AFS of each age, in Cardenas, Tabasco, México. Four traps per cacao-AFS were used to collect litter. Litter was collected every 15 days for one year. It was then fractioned into cacao leaves, shade tree leaves, petioles, branches and stems, and cacao flowers and fruits. To determine nutrient content of litter, samples were composited by age of cacao-AFS and by season of the year. Then chemical analysis was done in triplicate. Data were subjected to analysis of variance, orthogonal contrasts, and Student t and Duncan tests. Cacao-AFS produce litter all year. Thirty-five-year-old cacao-AFS produced more litter than 55-year-old cacao-AFS (2042 vs 1570 kg DM ha?1 year?1). Except for the shade tree leaf fraction (559.5 vs 642 kg DM ha?1), 35-year-old cacao-AFS were superior to 55-year-old cacao-AFS in all the other litter fractions. Cacao leaf fraction was the main source of litter in cacao-AFS of both ages. Neither age of cacao-AFS nor the season of the year affected N, K, Zn or S content in litter. Orthogonal contrasts indicated statistical differences between ages of cacao-AFS for P, Ca, and Fe content in litter. Both N–P–K–Ca–Mg contents in litter of 35-year-old cacao-AFS (1.2–0.4–1.2–1.7–0.4%) and in litter of 55-year-old cacao-AFS (1.1–0.6–1.2–1.4–0.4%) are enough to recover the nutrients extracted by the cacao crop. 相似文献
62.
Disturbances favour plant invasions because they provide a pulse of resources for seedling establishment and growth. However, little attention has been paid to the importance of the different disturbance regimes in the extent of invasion. In this paper we asked to what extent invasion depends on spatial and temporal patterns of disturbance. By using the spatially explicit model Fateland, we simulated how Cortaderia selloana, a large-wind dispersed perennial grass invading Mediterranean grasslands, responds to different medium-term (up to 55 years) disturbance regimes. The different scenarios combine disturbance frequency, extent of disturbance and temporal and spatial disturbance variability, and they roughly mimic real situations of habitat management and disturbances in cultural landscapes.The model predicted that the proportion of invaded area would increase with disturbance frequency. The extent of the disturbance overcame the importance of frequency. Aggregated disturbances randomly distributed in space had a more positive effect on invasion than scattered disturbances at repeatedly fixed locations. Whether the disturbances regularly occurred in time or were irregularly distributed did not influence the percentage of invaded landscape. Our simulation analysis unambiguously supports the hypothesis that disturbances are essential for the persistence and expansion of Cortaderia sellona. The high amount of seed rain from a few individuals (e.g., gardens) make this species very sensitive to landscape changes produced by different disturbance patterns (e.g., land abandonment, habitat management or rubbish dumping). Our results can contribute to redirect land management options. 相似文献
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Morris WE Venzano AJ Craig MI Diodati JA Funes D Elizondo A Mercado E Capellino F Delgado F Blanco-Viera J 《The Canadian veterinary journal. La revue veterinaire canadienne》2010,51(8):877-880
This study reports 3 cases of spontaneous papillomavirus infection in 1-week-old calves. Thickening of the omasum and abomasum wall, with acute inflammation, necrosis, ulceration, and neoplastic changes were seen in 1 calf. In the other 2, small papillomas were observed in the omasal mucosa, exhibiting proliferation of the parakeratinized epithelium. Papillomavirus antigens were detected by immunohistochemistry and virus-like particles were seen through electron microscopy. 相似文献
66.
Fire severity as a key factor in post-fire regeneration of Pinus pinaster (Ait.) in Central Portugal
Context
Mediterranean pine woodlands are strongly affected by wildfires; however, there are knowledge gaps in the role of fire severity on Pinus pinaster Ait. regeneration.Objectives
The principal questions were: (a) does post-fire regeneration of Maritime Pine differ where canopies were consumed to a low vs. high degree and (b) which factors, besides fire severity, could explain these differences.Methods
Pine recruitment was monitored from 2 to 36?months after a summer wildfire in 18 25?m2 plots, equally divided over two fire severity classes based on crown consumption. Besides the degree of crown consumption, three quantitative fire severity indices as well as post-fire site conditions, seed input and understory vegetation recovery were measured.Results
Pine seedling densities were consistently higher in the plots with low than high crown consumption but due to marked spatial variability, they were only significantly different at two out of the eight sampling occasions. This variability could be explained by a quantitative index based on the diameter of twigs, as well as by seed input and post-fire site conditions (ash and litter cover).Conclusion
Fire severity was found to strongly affect the pine recruitment following wildfire, using both a qualitative visual severity index and a quantitative, more labour-intensive one. 相似文献67.
Reif JS Mazzoil MS McCulloch SD Varela RA Goldstein JD Fair PA Bossart GD 《Journal of the American Veterinary Medical Association》2006,228(1):104-108
OBJECTIVE: To determine the prevalence of lobomycosis, a mycotic infection of dolphins and humans caused by a yeastlike organism (Lacazia loboi), among dolphins in the Indian River Lagoon in Florida. DESIGN: Cross-sectional study. ANIMALS: 146 Atlantic bottlenose dolphins. PROCEDURE: Comprehensive health assessments of bottlenose dolphins in the Indian River Lagoon of Florida (n = 75) and in estuarine waters near Charleston, SC (71), were conducted during 2003 and 2004. Bottlenose dolphins were captured, examined, and released. Skin lesions were photographed and then biopsied. Tissue sections were stained with H&E and Gomori methenamine silver stains for identification of L. loboi. RESULTS: 9 of 30 (30%) dolphins captured in the southern portion of the Indian River Lagoon had lobomycosis, whereas none of the 45 dolphins captured in the northern portion of the lagoon or of the 71 dolphins captured near Charleston, SC, did. Affected dolphins had low serum alkaline phosphatase activities and high acute-phase protein concentrations. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that lobomycosis may be occurring in epidemic proportions among dolphins in the Indian River Lagoon. Localization of the disease to the southern portion of the lagoon, an area characterized by freshwater intrusion and lower salinity, suggests that exposure to environmental stressors may be contributing to the high prevalence of the disease, but specific factors are unknown. Because only dolphins and humans are naturally susceptible to infection, dolphins may represent a sentinel species for an emerging infectious disease. 相似文献
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69.
Evan Siemann Juli A. Carrillo Christopher A. Gabler Roy Zipp William E. Rogers 《Forest Ecology and Management》2009
The foraging activities of nonindigenous feral hogs (Sus scrofa) create widespread, conspicuous soil disturbances. Hogs may impact forest regeneration dynamics through both direct effects, such as consumption of seeds, or indirectly via changes in disturbance frequency or intensity. Because they incorporate litter and live plant material into the soil, hogs may also influence ground cover and soil nutrient concentrations. We investigated the impacts of exotic feral hogs in a mixed pine-hardwood forest in the Big Thicket National Preserve (Texas, USA) where they are abundant. We established sixteen 10 m × 10 m plots and fenced eight of them to exclude feral hogs for 7 years. Excluding hogs increased the diversity of woody plants in the understory. Large seeded (>250 mg) species known to be preferred forage of feral hogs all responded positively to hog exclusion, thus consumption of Carya (hickory nuts), Quercus (acorns), and Nyssa seeds (tupelo) by hogs may be causing this pattern. The only exotic woody species, Sapium sebiferum (Chinese tallow tree), was more than twice as abundant with hogs present, perhaps as a response to increased disturbance. Hogs increased the amount of bare soil by decreasing the amounts of plant cover and surface litter. Plots with hogs present had lower soil C:N, possibly due to accelerated rates of nitrogen mineralization. These results demonstrate that hogs may influence future overstory composition and reduce tree diversity in this forest. Management of hogs may be desirable in this and other forests where large-seeded species are an important component of the ecosystem. Further, by accelerating litter breakdown and elevating nitrogen in the soil, hogs have the potential to impact local vegetation composition via nitrogen inputs as well. 相似文献
70.
海豚组织中多氯联苯(PCBs)气相色谱测定的改良方法研究 总被引:4,自引:0,他引:4
研究和建立了一种测定海豚体内不同组织中多氯联苯(PCBs)前处理的改良方法,即将海豚组织分为低脂样品和高脂样品,分别经萃取、净化、浓缩等处理后,用Agilent6890N型气相色谱仪、63Ni放射源ECD检测器测定,采用保留时间定性和峰面积外标法定量。结果显示,加标回收率为75.8%~119.2%,精密度为5.6%~11.2%,方法检出限为0.126~0.642ng.g-1,说明该方法的准确性、可重复性符合海洋生物体痕量有机污染物分析要求。海豚组织样品的实际测定结果表明,该方法适合海豚体内PCBs含量的分析测定。 相似文献