Phosphorus is an important element for larch (\%Larix gmelinii\% Rupr.)root development.P-availability in rhizosphere is close with root exudates or excretions,e.g.,organic acid exudation,proton excretion.These materi...Phosphorus is an important element for larch (\%Larix gmelinii\% Rupr.)root development.P-availability in rhizosphere is close with root exudates or excretions,e.g.,organic acid exudation,proton excretion.These materials from roots will affect pH value of rhizosphere.The aim of this paper were to study on pH changes at different P-stress conditions,and to test on the relation between available P and pH in rhizosphere.This work was carried out under pot experiment and field soil smaple analysis.Larch seedlings,1 and 2-year-old,were planted into sand pots.Nutrient solution with different P contents (0,0.035,0.071 and 0.142g·L -1 respectively) were supplied everyday.There were 2 replicates for 1-year-old seedlings,5 replicates for 2-year-old seedlings at ecch P-level treatment.After 1-year-old seedlings growing for 40 days and 2-year-old seedlings growing for 90 days,seedlings were taken out and used to visualize acidification by means of an agar plate technique.The result showed that pH of rhizosphere decreased from 6.40 to 4.73～4.84 in 1-year-old seedlings and to 5.30～5.50 in 2-year-old after 36h incubation.Average pH decreased were 1.56～1.67 for 1-year-old seedlings,and 0.90～1.10 for 2-year-old seedlings.There was not significant,for pH variations in rhizosphere,among four kind treatments.The pH change was not affected by P-level.The result of soil sample analysis,from 12-year-old,21-year-old,and 40-year-old pure larch stands respectively,indicated that the pH changes in rhizosphere is 0.11,0.04,and 0.09,respectively,lower than that in the non-rhizosphere,acidification is not significant,While the available P in the rhizosphere is 18.1%,86.5% and 23.4%,higher than that in the non-rhizosphere in three stands.The correlation between pH variations and available P was not remarkable at this analysis.This means that there was no relationship between the available P and pH change of rhizosphere in larch root system.展开更多
Time, cost and quality are the three main targets to be controled in project management. However, the control and management of time and cost risk are usually carried out respectively, which will bring such problems a...Time, cost and quality are the three main targets to be controled in project management. However, the control and management of time and cost risk are usually carried out respectively, which will bring such problems as the delay of schedule by reason of the impracticability of cash flow, the money difficulties caused by delay of schedule and so on. In order to control and manage the time and cost risk effectively and simultaneously, a time & cost risk control model based on schedule programme was established with the use of the quantitativemodels of BCWS, BCWP and ACWP in this paper. Subsequently, the analysis of variance for the whole project and the single activity was introduced on the basis of BCWS, BCWP and ACWP so that the project can be controlled and managed effectively. Furthermore, an example given behind in detail expressly illustrated that the model set up above was practicableto project management. However, the method of optimizing the cash flow based on time and cost risk to obtain BCWS should be considered properlyand carefully with respect to the different circumstances of the project, and an efficient and adequate interval report system should be set up on the site of the project.展开更多
Plants show different growth responses to N sources supplied with either NH4^＋ or NO3^-. The uptake of different N sources also affects the rhizosphere pH and therefore the bioavallability of soil phosphorus, particu...Plants show different growth responses to N sources supplied with either NH4^＋ or NO3^-. The uptake of different N sources also affects the rhizosphere pH and therefore the bioavallability of soil phosphorus, particularly in alkaline soils. The plant growth, P uptake, and P availability in the rhizosphere of oat （Arena nuda L.） grown in hydroponics and in soil culture were investigated under supply with sole NH4^＋-N, sole NO3-N, or a combination. Sole NO^- -fed oat plants accumulated more biomass than sole NH4^＋ -fed ones. The highest biomass accumulation was observed when N was supplied with both NH^＋ -N and NO3^- -N. Growth of the plant root increased with the proportion of NO3^- in the cultural medium. Better root growth and higher root/shoot ratio were consistently observed in NO3^- fed plants. However, root vigor was the highest when N was supplied with NO3^- ＋NH4^＋. NH4^＋ supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO4 added as P source. No P deficiency was observed, and plant P concentrations were generally above 2 g kg^-1. P uptake was increased when N was supplied partly or solely as NO3^--N, similarly as biomass accumulation. The results suggested that oat was an NO3-preferring plant, and NO3^- -N was essential for plant growth and the maintenance of root absorption capacity. N supply with NH4^＋ -N did not improve P nutrition, which was most likely due to the absence of P deficiency.展开更多
文摘Phosphorus is an important element for larch (\%Larix gmelinii\% Rupr.)root development.P-availability in rhizosphere is close with root exudates or excretions,e.g.,organic acid exudation,proton excretion.These materials from roots will affect pH value of rhizosphere.The aim of this paper were to study on pH changes at different P-stress conditions,and to test on the relation between available P and pH in rhizosphere.This work was carried out under pot experiment and field soil smaple analysis.Larch seedlings,1 and 2-year-old,were planted into sand pots.Nutrient solution with different P contents (0,0.035,0.071 and 0.142g·L -1 respectively) were supplied everyday.There were 2 replicates for 1-year-old seedlings,5 replicates for 2-year-old seedlings at ecch P-level treatment.After 1-year-old seedlings growing for 40 days and 2-year-old seedlings growing for 90 days,seedlings were taken out and used to visualize acidification by means of an agar plate technique.The result showed that pH of rhizosphere decreased from 6.40 to 4.73～4.84 in 1-year-old seedlings and to 5.30～5.50 in 2-year-old after 36h incubation.Average pH decreased were 1.56～1.67 for 1-year-old seedlings,and 0.90～1.10 for 2-year-old seedlings.There was not significant,for pH variations in rhizosphere,among four kind treatments.The pH change was not affected by P-level.The result of soil sample analysis,from 12-year-old,21-year-old,and 40-year-old pure larch stands respectively,indicated that the pH changes in rhizosphere is 0.11,0.04,and 0.09,respectively,lower than that in the non-rhizosphere,acidification is not significant,While the available P in the rhizosphere is 18.1%,86.5% and 23.4%,higher than that in the non-rhizosphere in three stands.The correlation between pH variations and available P was not remarkable at this analysis.This means that there was no relationship between the available P and pH change of rhizosphere in larch root system.
文摘Time, cost and quality are the three main targets to be controled in project management. However, the control and management of time and cost risk are usually carried out respectively, which will bring such problems as the delay of schedule by reason of the impracticability of cash flow, the money difficulties caused by delay of schedule and so on. In order to control and manage the time and cost risk effectively and simultaneously, a time & cost risk control model based on schedule programme was established with the use of the quantitativemodels of BCWS, BCWP and ACWP in this paper. Subsequently, the analysis of variance for the whole project and the single activity was introduced on the basis of BCWS, BCWP and ACWP so that the project can be controlled and managed effectively. Furthermore, an example given behind in detail expressly illustrated that the model set up above was practicableto project management. However, the method of optimizing the cash flow based on time and cost risk to obtain BCWS should be considered properlyand carefully with respect to the different circumstances of the project, and an efficient and adequate interval report system should be set up on the site of the project.
基金Project supported by the National Natural Science Foundation Council of China (No.30660086)the Natural Science Foundation of Inner Mongolia of China (No.200607010302)+2 种基金Hong Kong Research Grants Council (No.2465/05M)Hong Kong University Grants Committee (No.AOE/B-07/99)Hong Kong Baptist University Matching Research Fund.
文摘Plants show different growth responses to N sources supplied with either NH4^＋ or NO3^-. The uptake of different N sources also affects the rhizosphere pH and therefore the bioavallability of soil phosphorus, particularly in alkaline soils. The plant growth, P uptake, and P availability in the rhizosphere of oat （Arena nuda L.） grown in hydroponics and in soil culture were investigated under supply with sole NH4^＋-N, sole NO3-N, or a combination. Sole NO^- -fed oat plants accumulated more biomass than sole NH4^＋ -fed ones. The highest biomass accumulation was observed when N was supplied with both NH^＋ -N and NO3^- -N. Growth of the plant root increased with the proportion of NO3^- in the cultural medium. Better root growth and higher root/shoot ratio were consistently observed in NO3^- fed plants. However, root vigor was the highest when N was supplied with NO3^- ＋NH4^＋. NH4^＋ supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO4 added as P source. No P deficiency was observed, and plant P concentrations were generally above 2 g kg^-1. P uptake was increased when N was supplied partly or solely as NO3^--N, similarly as biomass accumulation. The results suggested that oat was an NO3-preferring plant, and NO3^- -N was essential for plant growth and the maintenance of root absorption capacity. N supply with NH4^＋ -N did not improve P nutrition, which was most likely due to the absence of P deficiency.
