In order to develop a sound biotechnique for monitoring water quality that builds on the previous experiments carried out in our laboratory, a specific D. magna clone C 1242 was used to study the effects of pollutant...In order to develop a sound biotechnique for monitoring water quality that builds on the previous experiments carried out in our laboratory, a specific D. magna clone C 1242 was used to study the effects of pollutants on phototactic behavior. In all experiments, the animals showed a stable and repeatable phototactic index approximated 0.2 in the presence and 0.4 in the absence of fish kairomones, which decreased significantly in response to pollutants. There existed no pollutant×fish kairomone interaction, indicating the changes in phototactic behavior of animals imposed by pollutants were independent of the presence of fish kairomones. The detection limits for changes in phototactic behavior of D. magna clone C 1242 are 0.04 mg/L for copper, 0.02 mg/L for cadmium, and 0.80 mg/L for PCP, respectively, quite lower than LC 50(48 h). The changes in phototactic behavior in presence to pollutants occurred quickly(3 h) compared to the period over whole acute toxicity tests. Therefore, D. magna clone C 1242 could be potentially used to monitor water quality. Moreover, the phototactic behavior did not decrease further in the pollutant mixtures employed in our experiments compared to individual pollutants, except in the Cd-PCP treatment. This fact suggests that the formation of water quality criteria must be based upon pollutant mixture tests.展开更多
In the present experiment, wheat seedlings (Trticucum aestivum L.) were grown on a purple soil withvarious fertilizer treatments in order to investigate the responses of nitrogen and related eusyme activitiesin the rh...In the present experiment, wheat seedlings (Trticucum aestivum L.) were grown on a purple soil withvarious fertilizer treatments in order to investigate the responses of nitrogen and related eusyme activitiesin the rhizosphere. The results revealed the increments of both organic matter and total N in the soil withthe proximity to the growing roots, especially in the treatment of supplying pig manure in combination withchemical fertilizer, suggesting that they could come from root and microorganism exudation which could beintensified by inorganic-organic fertilization, being of benefit to improving the physical and biological envi-ronment in the rhizosphere of wheat. Much more inorganic N was observed in the fertilized soils surroundingwheat roots than in the CK treatment, indicating the improvement of crop N supply in the rhisosphere ofwheat by fertilization.The activities of invertase, urease and protease in the root zone were greatly enhanced as compared tothose in the other parts of soils except that the urease activities were similar in the rhizo8phere and nonrhi-zosphere of the CK and pig manure treatments, indicating that invertase and protease could be produced bygrowing roots and rhizosphere microorganisms, in contrast to urease which could be stimulated by urea. Also,significant increment of these three enzyme activities in the rhizosphere of wheat by fertilizatioll, especially byapplication of chemical fertilizer combined with pig manurel suggested that fertilization not only acceleratedthe renewal of organic matter but also enhanced bioavailability of organic N in that soil zone. This couldbe the reason why the total amount of inorganic N available for plants was increased more obviously in therhizosphere of wheat of the fertilization treatments than in that of the CK treatment.展开更多
A greenhouse pot experiment was conducted with hybrid rice (Ocyza Sativa L.) in order to stndy Nstatus and utilization in the rhizosphere of rice. The experiment was composed of three treatments: withoutN, ￣(15)NH_(4...A greenhouse pot experiment was conducted with hybrid rice (Ocyza Sativa L.) in order to stndy Nstatus and utilization in the rhizosphere of rice. The experiment was composed of three treatments: withoutN, ￣(15)NH_(4-) N and ￣(15) NO_(3-) N. Plant roots were separated from the soil by a nylon cloth, and 1 mm incrementsof soil, moving laterally away from the roots, were taken and analyzed for various N froms. The labelled Nin the plants ranged from 67.51% to 69.24% of the total amount of N absorbed by the rice seedlings withthe labelled fertilizer N treatments. This shows that the N in the plants came mainly from the fertilizers.However, the N absorbed by the rice seedlings accounted for less than 35% of the total amount of the Ndepletion in the soil near the rice roots, indicating an important N loss in the rhizosphere of rice. The soilredox potential (all treatments) and the concentration of the labelled NO_3-N (the labelled NH_(4-_)N treatmentonly) decreased as the distance from the rice roots increased in the rhizosphere of rice. In contrast, theconcentration of the labelled NH_(4-) N increased a.s the distance increased in the same soil zone. These resultssuggested that nitrification occurred in the soil around the rice roots. Therefore, the reason for the N lossin the rhizosphere of rice might be the NO_3 movement into the reductive non-rhizosphere soil (submerged)where denitrification can take place.展开更多
文摘In order to develop a sound biotechnique for monitoring water quality that builds on the previous experiments carried out in our laboratory, a specific D. magna clone C 1242 was used to study the effects of pollutants on phototactic behavior. In all experiments, the animals showed a stable and repeatable phototactic index approximated 0.2 in the presence and 0.4 in the absence of fish kairomones, which decreased significantly in response to pollutants. There existed no pollutant×fish kairomone interaction, indicating the changes in phototactic behavior of animals imposed by pollutants were independent of the presence of fish kairomones. The detection limits for changes in phototactic behavior of D. magna clone C 1242 are 0.04 mg/L for copper, 0.02 mg/L for cadmium, and 0.80 mg/L for PCP, respectively, quite lower than LC 50(48 h). The changes in phototactic behavior in presence to pollutants occurred quickly(3 h) compared to the period over whole acute toxicity tests. Therefore, D. magna clone C 1242 could be potentially used to monitor water quality. Moreover, the phototactic behavior did not decrease further in the pollutant mixtures employed in our experiments compared to individual pollutants, except in the Cd-PCP treatment. This fact suggests that the formation of water quality criteria must be based upon pollutant mixture tests.
文摘In the present experiment, wheat seedlings (Trticucum aestivum L.) were grown on a purple soil withvarious fertilizer treatments in order to investigate the responses of nitrogen and related eusyme activitiesin the rhizosphere. The results revealed the increments of both organic matter and total N in the soil withthe proximity to the growing roots, especially in the treatment of supplying pig manure in combination withchemical fertilizer, suggesting that they could come from root and microorganism exudation which could beintensified by inorganic-organic fertilization, being of benefit to improving the physical and biological envi-ronment in the rhizosphere of wheat. Much more inorganic N was observed in the fertilized soils surroundingwheat roots than in the CK treatment, indicating the improvement of crop N supply in the rhisosphere ofwheat by fertilization.The activities of invertase, urease and protease in the root zone were greatly enhanced as compared tothose in the other parts of soils except that the urease activities were similar in the rhizo8phere and nonrhi-zosphere of the CK and pig manure treatments, indicating that invertase and protease could be produced bygrowing roots and rhizosphere microorganisms, in contrast to urease which could be stimulated by urea. Also,significant increment of these three enzyme activities in the rhizosphere of wheat by fertilizatioll, especially byapplication of chemical fertilizer combined with pig manurel suggested that fertilization not only acceleratedthe renewal of organic matter but also enhanced bioavailability of organic N in that soil zone. This couldbe the reason why the total amount of inorganic N available for plants was increased more obviously in therhizosphere of wheat of the fertilization treatments than in that of the CK treatment.
文摘A greenhouse pot experiment was conducted with hybrid rice (Ocyza Sativa L.) in order to stndy Nstatus and utilization in the rhizosphere of rice. The experiment was composed of three treatments: withoutN, ￣(15)NH_(4-) N and ￣(15) NO_(3-) N. Plant roots were separated from the soil by a nylon cloth, and 1 mm incrementsof soil, moving laterally away from the roots, were taken and analyzed for various N froms. The labelled Nin the plants ranged from 67.51% to 69.24% of the total amount of N absorbed by the rice seedlings withthe labelled fertilizer N treatments. This shows that the N in the plants came mainly from the fertilizers.However, the N absorbed by the rice seedlings accounted for less than 35% of the total amount of the Ndepletion in the soil near the rice roots, indicating an important N loss in the rhizosphere of rice. The soilredox potential (all treatments) and the concentration of the labelled NO_3-N (the labelled NH_(4-_)N treatmentonly) decreased as the distance from the rice roots increased in the rhizosphere of rice. In contrast, theconcentration of the labelled NH_(4-) N increased a.s the distance increased in the same soil zone. These resultssuggested that nitrification occurred in the soil around the rice roots. Therefore, the reason for the N lossin the rhizosphere of rice might be the NO_3 movement into the reductive non-rhizosphere soil (submerged)where denitrification can take place.
