Search

The growth performance of individual plants in a population can be affected by the plant-plant interaction, which has been well recognized and is called neighborhood interference. Though mechanisms are still unclear, the variations in gas exchange parameters in relation to the neighborhood interference between individual plants are crucial for evaluating the effects of plant-plant interaction. CO 2 assimilation in leaves of teak under natural conditions of dry seasons and wet seasons as well as its response to variations in light flux density and CO 2 concentration in different neighborhood interferences were simultaneously measured with Li-6400 portable photosynthesis system in a 21-year-old tropical plantation forest in Jianfengling, Hainan Island, China. This article dealt with the change rule of neighborhood interference on tree characteristics of gas exchange and its dynamic response to light en-vironments of individual plants. Diurnal courses of photosynthesis of individual leaves were not affected by neighborhood interfer-ence, but net photosynthetic rates showed a negative relationship with the intensity of neighborhood interference. The ratio of daily average P n in weak, moderate, strong and heavy neighborhood interferences was 2.5:2.3:1.7:1.0, and the daily maximum P n in weak interference was 2.8 times that in heavy interference. Leaf transpiration and stomatal conductance decreased with the increasing of interference intensity. Characteristics of photosynthetic light response and CO 2 response changed with the neighborhood interference, and values of leaf gas exchange parameters including A sat , Q sat , α A , CE , V cmax and J max in weak interference were enhanced by 2.7, 1.3, 1.4, 2.7, 1.9 and 2.8 times, respectively, than those in heavy interference. But changes in those parameters partly depended on light environment and CO 2 concentration, and the influence of changes in light environment on weak interference individuals was sig-nificantly stronger than that on heavy interference. Beyond the growth CO 2 concentration, the influence resulting from changes in CO 2 concentration on heavy interference individuals was obviously stronger than that on weak interference. Neighborhood interference can be described as a major means of intraspecific competition of population in a plantation forest with uniform forest structure and consistent management. Carbon assimilation can be affected by the neighborhood interference, and result in divergence in growth performance. Indices of neighborhood interference can be used to evaluate the intraspecific competition, and based on this point, we can make maximum use of resources after stand structure has been well adjusted.

1. 1. Anterior kidney phagocytes from channel catfish (Ictalurus punctatus) exposed to 10 and 24°C from 1 day to 5 weeks were assayed for phagocytic ability and respiratory burst activity to Aeromonas hydrophila and Edwardsiella ictaluri. 2. 2. The results of this study indicated that phagocytosis in channel catfish remained partially functional at low temperature without adaptation, although partial suppression was observed. 3. 3. Adaptation to low temperature did lead to an improvement in the respiratory burst which would imply improved bacterial killing ability. 4. 4. Our study suggests that phagocytosis may play a significant role in preventing disease at low environmental temperature.

Channel catfish Ictalurus punctatus were subjected to a simulated handling (including bleeding) and transport stress. Using flow cytometry in conjunction with monoclonal antibodies to channel catfish B and T lymphocytes (minimal cross-reaction with thrombocytes) and neutrophils coupled with routine hematological methods, we demonstrated significant decreases in the percentage of B lymphocytes and increases in T lymphocytes and neutrophils of transported fish, yet there was no change in neutrophil phagocytic function. These data suggest that the length of the stressing event or the duration of exposure of the neutrophils to cortisol could determine if immune responses become suppressed. These data prompted us to expose channel catfish in vivo, and isolated neutrophils in vitro, to cortisol at various concentrations and for various time periods. Exposure of neutrophils to cortisol concentrations of 100 μg/dL for 2 h did not suppress phagocytosis; however, significant decreases in the percent phagoc...

The purpose of this study was to compare the phagocytosis of Aeromonas hydrophila, Edwardsiella ictuluri, Edwardsiella tarda and Micrococcus luteus by channel catfish neutrophils. Various aspects of opsonization effect and bactericidal ability of channel catfish neutrophils were investigated. Percent phagocytosis range from a low of 1% to a high of 91%. The highest percent phagocytosis and phagocytic indices routinely occurred with normal serum and were highest for M. luteus (91.78%, 55.25) and A. hydrophila (87.52%, 43.60). In all cases, the percent phagocytosis and phagocytic index was lowest in assays without serum. Channel catfish neutrophils displayed a bactericidal/static ability for each bacterium tested except E. tarda . Neutrophils exhibited a greater inhibitory capacity for A. hydrophila and M. luteus than for the other bacteria when in the presence of normal or inactivated catfish serum.

Z. Jaafar (&)Department of Biological Sciences, National University of Singapore,Singapore 117543, Singaporee-mail: jaafarz@si.eduPresent Address:Z. JaafarDivision of Fishes, National Museum of Natural History, SmithsonianInstitution, Washington, DC 20004, USAC. DexiangNational Parks Board, 1 Cluny Road, Singapore 259569, Singapore

1. Temperatures of 18 degrees C for acclimation or assay had minimal or no effect on channel catfish phagocyte function. Significant suppression was observed at 10 degrees C acclimation and assay temperature. 2. According to the results of a multiple acclimation/assay temperature combination study, the primary impact of temperature on phagocyte function was due to the assay temperature. 3. The only functional change caused by acclimation temperature was the possible adaptation of the respiratory burst. However, 10 degrees C acclimation did cause a decline in the number of lymphocytes in the anterior kidney but not the number of neutrophils. In a temperature-kinetic study, the suppressive effect of 10 degrees C assay temperature was confirmed. 4. Results of our study indicated that phagocytosis in channel catfish is temperature-mediated. However, phagocytes appeared to be more resistant to low temperature than lymphocytes, which implies the importance of phagocytosis in the defense mechanisms of channel catfish at low temperatures.