A field trial was conducted investigating the single season growth response of 1+0 313 PSB Engelmann spruce (Picea engelmannii Parry ex Engelm.) and lodgepole pine (Pinus contorta Dougl. ex Loud.) seedlings planted into two different soil thermal regimes at three high-elevation locations spanning 200 km in the Engelmann Spruce-Subalpine Fir (ESSF) biogeoclimatic zone in the Cariboo Mountains of central British Columbia. Temperature treatments represented the extremes of soil temperature commonly found in high-elevation clear-cuts. A warm soil treatment (clear day, mid-afternoon soil temperature in mid-summer of 18 to 25 °C at –10 cm) consisting of a bare mineral soil hummock (average dimensions of 100 cm × 100 cm × 40 cm) was contrasted with a cool soil treatment (clear day, mid-afternoon soil temperature in mid-summer of 10 to 13 °C at –10 cm) comprised of organic forest floor overlying mineral soil. By the end of the growing season, seedlings of both species planted into the warm treatment generally exhibited greater root, stem, foliage, and total seedling biomass than cool treatment seedlings. Measurements of root growth at 30, 60, and 90 days after planting showed that total root number and total root length were consistently greater for warm treatment seedlings than for cool treatment seedlings. Root growth was greater from the bottom rather than from the side of the root plug for all seedlings. These results suggest that the effect of low soil temperatures on outplanted styroblock conifer seedlings is pronounced and may be limiting growth performance in high-elevation plantations in British Columbia. We recommend silvicultural treatments that secure natural regeneration, ensure that warmer microsites are always planted, and utilize seedling stocktypes able to make rapid lateral root growth into warmer surface organic horizons. 相似文献
Gross and histologic postmortem studies were performed on the hind feet of feedlot cattle that had, or were free from, lesions of toe tip necrosis. The hind feet of feedlot cattle were collected by 3 veterinary feedlot practices in southern Alberta, Canada. Three studies of these feet were conducted: i) prediction of disease based on the presence or absence of apical white line separation, ii) gross assessment of the distribution and severity of lesions within affected claws, and iii) microscopic evaluation of the distal phalanx and surrounding soft tissues of affected claws. Prediction of toe tip necrosis based on the presence of apical white line separation was statistically significant (P < 0.0001). This, combined with a pattern of lesions indicative of an ascending infection of the distal phalanx and the absence of other lesions, suggests that the pathogenesis involves bacterial infection originating from the most distal aspect of the toe, at the apical white line. 相似文献
The onset and progression of Salmonella infections was investigated in commercial turkey flocks from placement at 1 d old until slaughter in “brood and move” systems using a longitudinal observational approach based on faeces and environmental sampling with subsequent culture of Salmonella.
Persistent Salmonella Newport contamination was found within rearing houses and on their external concrete aprons after cleaning and disinfection between crops of heavily shedding young birds.
Salmonella shedding was often detected by 5 d of age and the frequency of positive samples peaked at 14–35 d. Thereafter Salmonella isolations declined, especially in the later (fattening) stages. Samples were still Salmonella-positive at low prevalence in half of the intensively sampled houses at slaughter age.
A number of management interventions to combat Salmonella infection of flocks, including sourcing policy, competitive exclusion cultures and cleaning and disinfection, were inadequate to prevent flock infection, although improved disinfection on one unit was associated with a delay in the onset of flock infection.
A sterilized, but undecomposed, organic by-product of municipal waste processing was incubated in sandy soils to compare C and N mineralization with mature municipal waste compost. Waste products were added to two soils at rates of 17.9, 35.8, 71.6, and dry weight and incubated at for 90 d. Every 30 d, nitrate and ammonium concentrations were analyzed and C mineralization was measured as total CO2-C evolved and added total organic C. Carbon mineralization of the undecomposed waste decreased over time, was directly related to application rate and soil nutrient status, and was significantly higher than C mineralization of the compost, in which C evolution was relatively unaffected across time, soils, and application rates. Carbon mineralization, measured as percentage C added by the wastes, also indicated no differences between composted waste treatments. However, mineralization as a percentage of C added in the undecomposed waste treatments was inversely related to application rate in the more productive soil, and no rate differences were observed in the highly degraded soil. Total inorganic N concentrations were much higher in the compost- and un-amended soils than in undecomposed waste treatments. Significant N immobilization occurred in all undecomposed waste treatments. Because C mineralization of the undecomposed waste was dependant on soil nutrient status and led to significant immobilization of N, this material appears to be best suited for highly degraded soils low in organic matter where restoration of vegetation adapted to nutrient poor soils is desired. 相似文献
OBJECTIVE: The risk factors for fractures are incompletely understood. An outstanding question concerns the optimal amount of dietary calcium needed to minimise the risk of fracture. DESIGN: We examined the associations of dietary calcium and other nutrients with self-reported fracture risk in a prospective cohort study. Nutrient intakes were estimated using a semi-quantitative food-frequency questionnaire administered at recruitment. SETTING: The UK. Participants: A total of 26 749 women and 7947 men aged 20-89 years. RESULTS: Over an average of 5.2 years of follow-up, 1555 women and 343 men reported one or more fractures, 72% of these resulting from a fall. Among women, fracture risk was higher at lower calcium intakes, with a relative risk of 1.75 (95% confidence interval (CI) 1.33-2.29) among women with a calcium intake of < 525 mg day- 1 compared with women with a calcium intake of at least 1200 mg day- 1 (test for linear trend, P < 0.001). The association of dietary calcium with fracture risk was stronger among women aged under 50 years at recruitment than among women aged 50 and above. Dietary calcium intake was not associated with fracture risk in men. Fracture risk was not related to the dietary intake of any other nutrient examined. CONCLUSION: In this population, women with a low dietary calcium intake had an increased risk of bone fracture, and this association was more marked among younger women than among older women. 相似文献
The source–sink ratio during grain filling is a critical factor that affects crop yield in wheat, and the main objective of this study was to determine the source–sink relations at both the canopy scale and the individual culm level under two nitrogen (N) levels at the post-jointing stage. Nine widely-used cultivars were chosen for analyzing source–sink relations in southwestern China; and three typical cultivars of different plant types were subjected to artificial manipulation of the grain-filling source–sink ratio to supplement crop growth measurements. A field experiment was conducted over two consecutive seasons under two N rates (N+, 150 kg ha–1; N–, 60 kg ha–1), and three manipulations were imposed after anthesis: control (Ct), removal of flag and penultimate leaves (Lr) and removal of spikelets on one side of each spike (Sr). The results showed that the single grain weights in the three cultivars were significantly decreased by Lr and increased by Sr, which demonstrated that wheat grain yield potential seems more source-limited than sink-limited during grain filling, but the source–sink balance was obviously changed by climatic variations and N deficient environments. Grain yield was highly associated with sink capacity (SICA), grain number, biomass, SPAD values, and leaf area index during grain filling, indicating a higher degree of source limitation with an increase in sink capacity. Therefore, source limitation should be taken into account by breeders when SICA is increased, especially under non-limiting conditions. Chuanmai 104, a half-compact type with a mid-sized spike and a long narrow upper leaf, showed relatively better performance in source–sink relations. Since this cultivar showed the characteristics of a lower reduction in grain weight after Lr, a larger increase after Sr, and a lower reduction in post-anthesis dry matter accumulation, then the greater current photosynthesis during grain filling contributed to the grain after source and sink manipulation. 相似文献
Chromium (Cr) is an essential mineral element and has been used in pig diets to improve growth performance, insulin sensitivity, immune response and carcase traits and to reduce heat or other stress responses. The aims of thiss study were to determine the impact of nano-sized chromium tripicolinate (nCrPic) on growth performance, feed efficiency and carcase characteristics of finisher gilts during the summer period. A total of 60 finisher Large White x Landrace gilts were stratified on initial weight and then within strata randomly allocated into two treatment groups in three replicates during mid-summer for 28 days. All pigs were housed in individual pens and had ad libitum access to feed and water. Pigs were fed either a control finisher diet (wheat-based diet containing 13.8 MJ digestible energy (DE) per kilogram and 0.56 g available lysine/MJ DE) or a control diet containing 400 ppb Cr as nCrPic. Dietary nCrPic supplementation increased feed intake by 6 % over the entire study (P?=?0.05). In particular, dietary nCrPic increased average daily feed intake (ADFI) by 8 % (P?=?0.02) during the final 2 weeks of the study. Moreover, dietary nCrPic tended to improve average daily feed (ADFI) over the entire study (P?=?0.09). However, there were no significant effects of nCrPic on feed conversion ratio (FCR), final weight, hot standard carcase weight (HCWT), P2 depth or dressing percentage. Plasma cortisol was decreased by 25 % (P?=?0.06) by dietary nCrPic supplementation. However, there were no effects of nCrPic on plasma glucose, insulin and nonesterified fatty acids (NEFA), might because of the higher feed intake. In conclusion, this study demonstrates that dietary nCrPic supplementation at 400 ppb can increase feed intake in finisher gilts during mid-summer, suggesting that nCrPic can ameliorate some of the negative effects of heat stress in pigs, possibly via decreased of circulating cortisol. 相似文献