不同耕作方式对宁南旱地土壤团聚体的影响

在宁南旱区对试验耕地定位实行连年传统翻耕(CT)、隔年免耕—深松(NT→ST)及深松—免耕(ST→NT)三种不同处理。用干筛法和湿筛法对连续3年处理后土壤团聚体的变化进行测定,分析结果表明,干筛法中NT→ST处理在0~40 cm土层中0.25 mm的机械稳定性团聚体比处理前和CT处理分别高33.11%、29.51%;ST→NT处理在0~40 cm土层中0.25 mm机械稳定性团聚体含量比处理前和CT处理分别高40.51%、36.91%。湿筛法中NT→ST处理在0~30 cm土层中0.25 mm的水稳性团聚体含量比处理前高7.33%,NT→ST处理在0~10 cm土层0.25 mm的水稳性团聚体比CT处理高1.47%,而在10~40 cm土层NT→ST处理和CT0.25 mm的水稳性团聚体含量差异不显著;ST→NT处理在0~40 cm土层中0.25 mm水稳性团聚体含量比处理前和CT处理分别高10.75%、10.12%。分析结果同时说明,采用深松—免耕(ST→NT)轮耕方式更有利于土壤团聚体含量和稳定性的增加。     

Use of Onion (Allium cepa) and Garlic (Allium sativum) Wastes for the Prevention of Fungal Disease (Saprolegnia parasitica) on Eggs of Rainbow Trout (Oncorhynchus mykiss)

This study was designed to prevent fungal disease (Saprolegnia parasitica) that occurs on rainbow trout eggs (Oncorhynchus mykiss) by using wastes of onion (Allium cepa) and garlic (Allium sativum) plants. For this purpose, fertilized rainbow trout eggs were exposed to garlic skin, garlic stem and onion skin aqueous methanolic extracts by bathing in concentrations of 0.4, 0.8, 1.6 and 3.2 g/L, whereas the control group was left untreated. The larvae in all groups were monitored until they become free-swimming larvae, the number of eggs died due to fungus was recorded, and the data obtained from experimental groups and control group were compared. As a result, it was determined that onion skin had no effect on the number of eggs that died due to fungus (p > .05), while garlic skin and garlic stem extracts significantly reduced the number of fungal infestations without affecting the number of live larvae or the embryological development of the eggs (p < .05). In light of these data, we conclude that garlic skin (0.4, 0.8, and 1.6 g/L) and garlic stem (0.8 and 1.6 g/L) aqueous methanolic extracts are effective at preventing Saprolegnia parasitica infestation on rainbow trout eggs and may be used in aquaculture.     

Seasonal and long‐term changes in fishing depth of Lake Constance whitefish

Abstract The ecosystem of Lake Constance in central Europe has undergone profound modifications over the last six decades. Seasonal and inter‐annual changes in the vertical distribution patterns of whitefish were examined and related to changes in biotic and abiotic gradients. Between 1958 and 2007, the average fishing depth in late summer and autumn was related to two factors influencing food supply of whitefish – lake productivity and standing stock biomass. In years with low food supply, whitefish were harvested from greater depths, where temperatures were up to 4 °C lower. The whitefish’s distribution towards colder water might be a bioenergetic optimisation behaviour whereby fish reduce metabolic losses at lower temperatures, or it may result from a reassessment of habitat preference under conditions of limited food supply, according to the ideal free distribution theory.