Poorly crystalline iron and aluminium oxides contribute to the carbon saturation and sorption of dissolved organic carbon in the soil

Soil carbon (C) saturation implies an upper limit to a soil's capacity to store C depending on the contents of silt + clay and poorly crystalline Fe and Al oxides. We hypothesized that the poorly crystalline Fe and Al oxides in silt + clay fraction increased the C saturation and thus reduced the capacity of the soil to sorb additional C input. To test the hypothesis, we studied the sorption of dissolved organic carbon (DOC) on silt + clay fractions (<53 µm) of highly weathered oxic soils, collected from three different land uses (i.e., improved pasture, cropping and forest). Soils with high carbon saturation desorbed 38% more C than soils with low C saturation upon addition of DOC, whereas adsorption of DOC was only observed at higher concentration (>15 g kg^?1). While high Al oxide concentration significantly increased both the saturation and desorption of DOC, the high Fe oxide concentration significantly increased the desorption of DOC, supporting the proposition that both oxides have influence on the DOC sorption in soil. Our findings provide a new insight into the chemical control of stabilization and destabilization of DOC in soil.     

黄金鲈与伊犁鲈杂交后代在气提泵循环水养殖系统中生长分析

研究通过黄金鲈(Perca flavescens)雌鱼与伊犁鲈(Perca schrenki)雄鱼进行杂交,以期加快鲈鱼的生长速度,推迟其性成熟和提高上市规格.为减少饲养环境条件和人为管理差异造成生长试验误差,研究采用试验鱼同池混养的方法进行生长比较.在气提泵循环水养殖系统中,经690 d的生长比较试验.结果表明:杂交鲈体重增长比黄金鲈快33.91%;杂交鲈的性腺发育被推迟或性腺发育不良;黄金鲈和杂交鲈的成活率分别为87.50%和82.08%,二者在成活率上无显著差异(P=0.29).杂交鲈适宜在高密度循环水养殖条件下生长,杂交优势较为显著,可以取代黄金鲈进行集约化养殖生产.     

Comparative ecologies of domestic and naturalised rainbow trout in northern Lake Huron

Northern Lake Huron (Ontario, Canada) supports the largest concentration of freshwater salmonid cage culture farms in Canada and receives inputs of domestic‐strain rainbow trout (Oncorhynchus mykiss) through escapement. We assessed the potential effects of these domestic fish on the naturalised rainbow trout of this ecosystem by comparing their respective ecologies. Mature adults were sampled from spawning tributaries, primarily in spring, and to a lesser extent in fall. Fish of domestic origin comprised ~80% of rainbow trout sampled from sites near cage culture facilities but <20% of rainbow trout sampled from more distant sites. Domestic adults in spawning condition (gametes free‐flowing) were present in the spawning tributaries in both spring and fall sampling seasons, whereas naturalised fish in spawning condition were only observed in the spring. Domestic adults were younger and smaller (in length), appeared to have shorter lifespan and had a higher male to female ratio compared with their naturalised counterparts. Growth rates (change in length with age) of naturalised and domestic females in the wild were similar, but domestic males grew more slowly than naturalised males. Domestic females also produced smaller eggs than naturalised females. Food web positions (inferred from δ¹³C and δ¹⁵N) of domestic and naturalised fish were very similar but varied more strongly with body size in the former. Domestic‐strain rainbow trout of cage culture origin can survive, grow and attempt to spawn in northern Lake Huron and have the potential to compete for food, mates and spawning habitat with naturalised rainbow trout.     

Pharyngeal neuromuscular dysfunction associated with bilateral guttural pouch tympany in a foal

A 2-month-old warmblood filly was presented for a 1-week history of a large, nonpainful, fluctuant swelling of the parotid and laryngeal area. Bilateral guttural pouch tympany was diagnosed. Surgical correction resolved the guttural pouch tympany; however, postoperative pharyngeal neuromuscular dysfunction developed.     

Factors associated with variation in Neospora caninum bulk-milk S/P ratios in initially bulk-milk negative testing Dutch dairy herds

We conducted a study on 81 initially bulk-milk ELISA negative dairy herds taken from a random sample of Dutch dairy herds to evaluate variation in bulk-milk S/P ratios and to study reasons for bulk-milk conversion. These herds were repeatedly (3-month intervals) tested between April 2004 and August 2005 and serostatus of all animals had previously been established as negative (N), low-positive (LP) or high-positive (HP). Of these herds, herd- and test-related factors associated with variation in sample over positive (S/P) ratios were analysed using a multivariable linear-mixed model with ‘herd’ as random effect. In addition, changes of animal serostatus in converting herds were described. S/P ratios were calculated as the optical density of the bulk-milk sample minus the optical density of the negative serum control divided by the difference in optical density between the positive and negative serum control.

Sixteen bulk-milk conversions in 12 dairy herds were seen with few indications of serological conversion in lactating cattle except for one herd in which recrudescence of infection appeared likely in nine cows. The effect of HP serostatus on bulk-milk S/P ratio was 2–3 times stronger compared with LP serostatus. In addition, bulk-milk S/P-ratio increased when the proportion of HP animals between 1 and 60 days in milk increased and decreased when the average milk-production level of the herd increased. Besides these herd-related factors, the use of different ELISA-testkits between test rounds had a significant effect on the S/P-ratio in bulk-milk samples.