For mechanical weeding, the uprooting force of whole seedlings and the shearing force of basal stems were measured in two grass weeds ( Setaria faberi and Echinochloa crus-galli var. crus-galli ) and two broad-leaved weeds ( Chenopodium album and Amaranthus patulus ), using balance-type equipment and a pair of scissors, respectively. Seedlings were grown in plastic pots. Uprooting and shearing experiments were carried out on the 11th, 16th, 21st, and 26th days after sowing. The uprooting force, the shearing force required to fracture the specimen, plant dry matter weight and cross-sectional area exponentially increased as seedlings grew, but the uprooting stress and shearing toughness maintained similar values after the 2nd sampling time, except for the 3rd and 4th sampling times in C. album . The increases in uprooting force and the shearing force required to fracture the specimen were supported by an expansion of the cross-sectional area of stems of the broad-leaved weeds or pseudostems of grass weeds. The higher values of uprooting stress and shearing toughness in C. album were related to an increased area of lignified organs in the basal stems. There was a significant correlation between uprooting and shearing forces. The shearing force was always higher than the uprooting force, so that most seedlings were uprooted and not fractured at the basal stems or pseudostems. The mean ratio of uprooting force to root dry matter weight after the 2nd sampling time suggested a high uprooting resistance at an extremely low amount of root dry matter weight. 相似文献
Two experiments were conducted to test the hypothesis that when using similar protein/amino acid diets and environment temperature conditions, the performance and carbon turnover in muscle and liver tissues, as measured by the incorporation of stable isotopes (13C/12C), must be different between fast-growing Cobb 500® and slow-growing Label Rouge broilers.
For both experiments (Cobb and Label Rouge), 21-d-old birds were distributed in a completely randomised, 3 × 3 factorial design; three environmental temperatures (cyclic heat stress ad libitum, 22°C ad libitum, and 22°C restricted) and three crude protein concentrations (189.1, 210 and 220 g/kg CP) were used.
The Cobb 500® had better performance with higher concentrations of crude protein. Cyclic heat stress (a temperature factor), negatively affected this genetic strain’s performance. For the Label Rouge birds, the crude protein concentrations in the diet presented inconsistent results and cyclic heat stress did not affect the performance.
The carbon turnover rate was affected in the Cobb 500® strain, with a high protein content reducing carbon turnover in the evaluated tissues (liver and muscles). Feed intake had a greater impact on carbon turnover rates than cyclic heat stress. The Label Rouge birds were not affected by the evaluated factors, suggesting that genetic improvement has a leading role on tissue carbon turnover.
There is a genetic influence on carbon turnover in the liver and muscle tissues of broiler chickens. In addition, genetically fast-growing broilers are more susceptible to variations in diet composition and environmental temperature than less rapidly growing animals.
Long-term fluctuations of chlorophyll a concentration, and abundance of herbivorous or omnivorous small copepods during the spawning season of the Japanese sardine, Sardinops melanosticta , were examined in relation to the types of Kuroshio meander. The purpose was to clarify the influence of the meander on the production of food organisms for the sardine larvae and their survival in the Pacific coastal region of central Japan. During an A-type meander of the Kuroshio, when the offshore and inshore movements of the Kuroshio path were small except at the beginning of the meander, the surface chlorophyll a concentration in the coastal region was lower than that during a non-A-type meander with frequent and prompt fluctuations of the Kuroshio path. The abundance of small copepods was also low during the A-type meander except in the subsequent spring just after the beginning of an A-type meander, but often high during the non-A-type meander. Prompt fluctuations of the Kuroshio path during the non-A-type meander probably cause local upwellings which stimulate primary and secondary production near the Kuroshio, and may enhance the survival of the sardine larvae. On the contrary, the quasi-stationary state of an A-type meander may be unfavourable for the production of phytoplankton and nauplii of herbivorous or omnivorous small copepods, and therefore the survival of the sardine larvae becomes poor. 相似文献